Eee-viii-electrical Design Estimation And Costing 10ee81 -solution 4q526u

Electrical Design Estimation and Costing

10EE82

VTU Question Solution

Unit-1 1.Define the estimating and mention the purpose of estimating and costing.

(Jan-2016)

Estimating is an art of assessment of quantities of different items and cost thereof to plan the amount required for executing a work before actually carrying out the work. OR Estimating means to determine the quantities of various items required to execute a job and to assets the cost of execution. 2.Write a short note on comparative statement.

(Jan-2016)

Bidding goods and services is important for several reasons. The bidding process: • allows "comparison shopping" for the best pricing and service • allows for an informed and objective choice among potential suppliers • encourages competition among suppliers • provides a standard for comparing price, quality, and service • provides a list of qualified suppliers for future bids • provides access to University business for suppliers The bid process begins with the development of a set of specifications or objectives. The Contract (CA) in conjunction with the requester must define the requirements exactly. Colleagues, technical personnel, trade manuals, and suppliers may be consulted for assistance in developing specifications. The requirements are then communicated to the selected suppliers by a Request for Quotation (RFQ) or a Request for Proposal (RFP).

3.Briefly explain the modes of tendering.

(Jan-2016)

Prepare Reasonable Cost Estimates Project cost estimating is not an exact science; however, estimators are expected to prepare reasonable project cost estimates that represent the cost to complete the project. These costs include those required not only for the contractor to construct

Department of EEE, SJBIT

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the project but, also includes the costs for the purchase of right of way, mitigation of environmental issues and any other costs that will be incurred to complete the project. Project alternatives and their associated cost estimates must be thoroughly compiled by diligently using all of the available data, modifying that data with good judgment and using past cost estimating experience so that the cost estimates can be used with confidence. Coordination between the project planning cost estimates, the project design cost estimates, and the specifications and policies that will be in place during the construction of the project is required. Cost Estimates are Not Static Cost estimates, in a sense, are never completed. They are not static, but have to be reviewed continually to keep them current. The Project Manager (PM) is responsible for keeping the project cost estimate up-to-date throughout the project development process, reviewing all project cost estimates and ensuring that the current project cost estimates are entered into the Project Management data base and a hard copy is in the project file.

4. What is estimating and what are the importance of the estimating and costing(Jun -2015) Electrical estimating is a process used by electricians, construction managers and engineers to determine the amount and cost of electricity required for a specific location or process. There are two general methods of creating accurate electrical estimates: computer software or manual calculations. Both methods have value, benefits and risks. Original electrical estimating software options were quite clumsy to use, but recent enhancements have vastly improved this tool for electrical estimation. Electrical estimating computer software has increased in popularity as it has improved in quality and performance. This tool is designed for use by electricians, architects and electrical engineers. There are different versions available for residential, commercial or prototype development. An estimating technique is an approach to predicting cost or revenue. Using a consistent methodology is important to achieve reliable and comparable results. Firms may have specific policies their personnel have to follow when making estimates to ensure that the approach will be similar no matter who prepares the estimate. This can help reduce problems associated with variances in methodology, like an offer from one mechanic in a shop of a very low price for service while another indicates the cost of a job will be much higher. Department of EEE, SJBIT

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When preparing estimates, people can broadly divide them into detailed and approximate types. Approximate estimates offer a rough guess of the cost, based on similar projects, experience, and quick research. They can be helpful for getting a general idea of expenses before proceeding with a more detailed estimate. For people soliciting estimates, they can't be quoted as firm bids, but may provide a frame of reference. A homeowner looking for a new roof, for example, could ask for an approximate estimate from several contractors to learn more about the range of possible prices.

5.Explain the following:1)Electrical schedules 2)Catalogues 3)Purchase system 4)Market survey . (Jun -2015) Electrical Schedule: The electrical load schedule is an estimate of the instantaneous electrical loads operating in a facility, in of active, reactive and apparent power (measured in kW, kVAR and kVA respectively). The load schedule is usually categorised by switchboard or occasionally by subfacility / area.

Catalogues: The main objective of a catalogue is to promote the products and services offered by your company. A catalogue layout properly designed must show your company's products or services arranged neatly, so that they can be easily recognized; and, at the same time, it must look attractive to improve your sales. In addition, the catalogue layout must be strategically arranged in order to give more importance to certain items or to make the catalogue look more eyecatching. Finally, the visual coherence on which a company's corporate Image is ed must be kept. A catalogue may promote products within promotional packages or lithe known products; it may inform the audience about the new comfort and convenience of a service or it can simply contain small businesses' month offers. Market Survey and source selection: Market research is a continuous process for gathering data on product characteristics, suppliers' capabilities and the business practices that surround them—plus the analysis of that data to make acquisition decisions. This requires one to collect and analyze information about the market that subsequently can be used to determine whether the need can be met by products or services Department of EEE, SJBIT

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available in the commercial market; whether commercial practices regaiding customizing, modifying products or tailoring services are available to meet customer needs; what are the customary and conditions, including warranty, buyer financing, and discounts under which commercial sales are made; and whether the distribution and logistics capabilities of potential suppliers are sufficient to meet the needs of the government. Marret research information can be used to shape the acquisition strategy, to determine the type and content of the product description or statement of work, to develop the strategy, the and conditions included in the contract, and the evaluation factors used for source selection. Various locational difficulties are described: 1. Remoteness 2. Confined sites 3. Labor availability 4. Weather 5. Design considerations (related to location). 6. Vandalism and site security

6. List out guidelines for inviting tenders.

(Jan -2015)

Bidding goods and services is important for several reasons. The bidding process: • allows "comparison shopping" for the best pricing and service • allows for an informed and objective choice among potential suppliers • encourages competition among suppliers • provides a standard for comparing price, quality, and service • provides a list of qualified suppliers for future bids • provides access to University business for suppliers The bid process begins with the development of a set of specifications or objectives. The Contract (CA) in conjunction with the requester must define the requirements exactly. Colleagues, technical personnel, trade manuals, and suppliers may be consulted for


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assistance in developing specifications. The requirements are then communicated to the selected suppliers by a Request for Quotation (RFQ) or a Request for Proposal (RFP).

7. Write the necessity of estimating and costing.

(Jan-2015)

Electrical estimating is a process used by electricians, construction managers and engineers to determine the amount and cost of electricity required for a specific location or process. There are two general methods of creating accurate electrical estimates: computer software or manual calculations. Both methods have value, benefits and risks. Original electrical estimating software options were quite clumsy to use, but recent enhancements have vastly improved this tool for electrical estimation. Electrical estimating computer software has increased in popularity as it has improved in quality and performance. This tool is designed for use by electricians, architects and electrical engineers. There are different versions available for residential, commercial or prototype development. An estimating technique is an approach to predicting cost or revenue. Using a consistent methodology is important to achieve reliable and comparable results

8. Explain by giving examples for the following . i) Contingencies ii) Overhead charges iii) Profit

(June-2014)

Estimating the cost of labor for electrical construction can vary greatly from project to project, depending on the installation crew’s experience and the complexity of the project. Charging an hourly installation rate is common for electrical contractors until installation data (number of hours per installer for job completion) can be collected and projects can be estimated based on the amount of work. Electrical contractors are responsible for installing, repairing, and maintaining electrical systems in homes and commercial buildings. Due to the differences in skills and costs between home systems and commercial systems, most companies will focus solely on either residential or commercial work. Fortunately, the process of pricing an electrical job is similar no matter what


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type of building is involved. For those with a basic understanding of construction and electricity, it is fairly easy to price an electrical job and develop an appropriate estimate.

9. Explain activities of Purchase department.

(June-2014)

FUNCTION/ROLE OF A PURCHASING DEPARTMENT  

To buy at the right time, right price and right Ensuring the continuity of supply



Selection and evaluation of suppliers/vendors

 

Aware of long-term and short term effects Preserving and enhancing reputation of company



Aware of all supply options



Maintain stock level

MAJOR PURCHASING ACTIVITIES  

Obtaining and analyzing quotations of vendors/suppliers Interview representatives and correspondence



Deciding best buying and conditions

 

Negotiating and checking contracts Scheduling orders and following up



Work with finance department to obtain discount, matching invoices, receipt,



purchase journal entry,ing of invoices for payment and settlement of s Disposing of surpluses



Other activities like assisting with preparation of material expenditure/purchasing budget.

Unit – 2 1. Briefly explain the factors to be considered while deciding choice of wiring sys(Jan-2016) General rules for interior wiring: 1) No lighting circuit should contain more than 10 points of lights, fans and socket outlets or a total load of 800 W. Department of EEE, SJBIT

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2) Switches must always be placed on the live wires only. 3) Each circuit should be provided with a separate cut-out in the distribution boards for their live wires. 4) When the total load exceeds 800 W for lighting only, 3-ph supply is to be taken and the load is to be distributed equally among the three phases. 5) No power circuit should contain more than 3000 W load and in no case, more than two socket outlets are allowed in one power circuit. 6) The main switch board must be fixed within 15 cms from the meter board (MB) so that it is easily accessible to disconnect in case of emergency. 7) The meter board, main switch and distribution board are to be installed at a minimum height of 1.5 m from the floor. 8) All sub-circuits (lighting or power circuit) should have its own continuous earth wire (each sub-circuit is earthed separately). 9) The wall plug socket should be of 3-pin type and the third (big) terminal is always connected to the earth. Adequate numbers of socket outlets are to be provided at suitable places in all rooms so as to avoid use of long lengths of flexible cords. Only 3-pin, 5A socket outlets are to be used in all light and fan circuits and only 3-pin, 5A socket outlets are to be used in all power circuits. All socket outlets are to be mounted at a minimum height of 1.3 m above floor and are to be controlled by individual switches which are to be located immediately adjacent to it. For 5A socket outlets installed at a height of 25 cm above the floor, the switch may, if desired, be mounted at a height of 1.3 m above the floor level. Socket outlets accessible to children should be shuttered or interlocked type. No socket outlet of rating higher than 15 A is to be installed. Appliances requiring a current of more than 15 A shall be connected through a double pole switch of appropriate rating. Socket outlets are not to be located centrally behind the appliances connected to them. 10) The power (or heating) circuit must be drawn separately in AEH (All Electric Home)installations from the meter board itself. 11) When the total load exceeds 5 kVA, the installation must have an ELCB (Earth Leakage Circuit Breaker).


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12) All the metal parts like metal sheaths / conduits of wiring and metal casings of all consumer appliances (starter body, iron clad switches etc.) must be earthed properly to avoid danger due to electric shock. 13) The current rating of the conductor used should be corresponding to the connected load to ensure safety to the consumers. Also, all light conductors are to be insulated or otherwise safeguarded to avoid danger. 15) All incandescent lamps should have a minimum clearance of 2.5 m from the floor level and ceiling fan should have a minimum clearance of 2.75 m from the floor. 16) The height at which conduit runs on a wall (horizontal run) must be a minimum of 3 m from the floor. 17) A switch board which contains switches, sockets, regulators etc. is to be installed such that its bottom lies 1.25 m above the floor. 18) The distance between the ceiling and the horizontal run may vary from 0.25 m to 0.5 m and depends on the type of building. 19) No fuse or switch is provided on an earthed conductor. 20) Each circuit is to be protected from drawing excessive current (due to overload or insulation failure) by a fuse or automatic circuit breaker. 21) Every installation is to be properly protected near the point of entry of supply cables by a main switch and fuse unit. The main switch shall have two poles in case of single phase supply three poles in case of three phase supply. 22) Depending on the size of the kitchen, one or two 3-pin, 15 A socket outlets are to be provided to plug-in hot plates and other appliances. Dining rooms, living rooms and bed rooms, if required, are to be provided with at least one 3-pin, 15 A socket outlets in each. 23) Every circuit or apparatus is to be provided with a separate means of isolation such as a switch. 24) No additional load is to be connected to an existing installation without ensuring that the installation


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25) Lamp holders used in bath rooms are to be constructed or shrouded in insulating materials and fitted with protective shield and the earth continuity conductor shall not be less than 7/0.915 mm size. 26) The switch board and socket outlets should not be fixed at locations where there are chances of water entering even in traces. 27) Looping of neutral and phase wires may be done on any one of the brass connectors embedded in insulating material such as in junction box terminals or switch terminals or holder terminals, etc. 28) After completion of work, the installations are to be tested for insulation resistance, polarity of single pole switches, earth resistance and earth continuity before energization.

2.List out the general rules and guidelines for residential installation.

(Jun -2015)

1. Every installation is to be properly protected near the point of entry of supply cables by 2linked main switch and a fuse unit. 2. Conductor used is to be of such a size that it carry load current safely. 3. Every sub-circuit is to be connected to a distribution fuse board. 4. A switch board is to be installed so that its bottom lies 1.25mts above the floor. 5. All plugs & socket outlets are of 3-pin type 6. All incandescent lamps are to be hung at ht of 2.5mt above the floor 7. No fuse or switch is to be provided in earthed conductor 8. In any building , light, fan power wiring are to be kept separately. 9. Unless otherwise specified, the clearance between the bottom most point of the ceiling fan and the floor shall be not less than 2.4 m. the minimum clearance between the ceiling and the plane of the blade shall be not less than 30 cm. 10. Each 15 A socket outlet provided in building for the use of domestic appliances such as AC, water cooler etc. 11. Each socket outlet shall be controlled by a switch which shall preferably be located immediately adjacent thereto or combined therewith. 12. Ordinary socket outlet may be fixed at any convenient place at a height above 20 cm from the floor level. In a situation where the socket outlet is accessible to children, socket outlet which automatically gets screened by the withdrawal of plug is preferable. Department of EEE, SJBIT

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3.Estimating the quantity of materials required for writing a newly constructed building where plan is shown in fig Assume the details of the load All dimensions are in meters (Jun -2015)

KITCHEN

HALL

BATH

3 ROOM 3.(J VERANDAH un 4 4 201 5)(J Total Loadun = 4.5kW = 4.5 x1000W = 4500W 20% additional load = 4500 x (20/100) = 900W 201 Total Load = 4500W + 900W = 5400W 5)5

1.(Ju n201 3 5)(Ju n 2201 5)5

Total Current = I = P/V = 5400W /220V =24.5A Now select the size of cable for load current of 24.5A (from Table 1) which is 7/0.036 (28 Amperes) it means we can use 7/0.036 cable according table 1. Now check the selected (7/0.036) cable with temperature factor in Table 3, so the temperature factor is 0.94 (in table 3) at 40°C (104°F) and current carrying capacity of (7/0.036) is 28A, therefore, current carrying capacity of this cable at 40°C (104°F) would be Current rating for 40°C (104°F) = 28 x 0.94 = 26.32 Amp. Since the calculated value (26.32 Amp) at 40°C (104°F) is less than that of current carrying capacity of (7/0.036) cable which is 28A, therefore this size of cable (7/0.036) is also suitable with respect to temperature. Now find the voltage drop for 100feet for this (7/0.036) cable from Table 4 which is 7V, But in our case, the length of cable is 35 feet. Therefore, the voltage drop for 35feet cable would be Actual Voltage drop for 35feet = (7 x 35/100) x (24.5/28) = 2.1V And Allowable voltage drop = (2.5 x 220)/100 = 5.5V


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Here The Actual Voltage Drop (2.1V) is less than that of maximum allowable voltage drop of 5.5V. Therefore, the appropriate and most suitable cable size is (7/0.036) for that given load for Electrical Wiring Installation

4. What are the general rules to be followed for internal wiring.

(Jan-2015)

1. Every installation is to be properly protected near the point of entry of supply cables by 2linked main switch and a fuse unit. 2. Conductor used is to be of such a size that it carry load current safely. 3. Every sub-circuit is to be connected to a distribution fuse board. 4. A switch board is to be installed so that its bottom lies 1.25mts above the floor. 5. All plugs & socket outlets are of 3-pin type 6. All incandescent lamps are to be hung at ht of 2.5mt above the floor 7. No fuse or switch is to be provided in earthed conductor 8. In any building , light, fan power wiring are to be kept separately. 9. Unless otherwise specified, the clearance between the bottom most point of the ceiling fan and the floor shall be not less than 2.4 m. the minimum clearance between the ceiling and the plane of the blade shall be not less than 30 cm. 10. Each 15 A socket outlet provided in building for the use of domestic appliances such as AC, water cooler etc. 11. Each socket outlet shall be controlled by a switch which shall preferably be located immediately adjacent thereto or combined therewith. 12. Ordinary socket outlet may be fixed at any convenient place at a height above 20 cm from the floor level. In a situation where the socket outlet is accessible to children, socket outlet which automatically gets screened by the withdrawal of plug is preferable.

5. The fig shows the plan of a low income group government quarter. Draw the single line dia for lighting and heating circuits on the sketch. Calculate total load , length and size of the wire by taking safety factor equals to two.


(June-2014)

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Total load of Sub-Circuit 1 = (2 x 1000) + (4 x 80) + (2×120) = 2000W + 320W + 240W = 2560W Current for Sub-Circuit 1 = I = P/V = 2560/230 = 11.1A Total load of Sub-Circuit 2 = (6 x 80) + (5 x 100) + (4 x 800) = 480W + 500W + 3200W= 4180W Current for Sub-Circuit 2 = I = P/V = 4180/230 = 18.1A Therefore, Cable suggested for sub circuit 1 = 3/.029” (13Amp) or 1/1.38mm (13Amp) Cable suggested for Sub-Circuit 2 = 7/.029” (21Amp) or 7/0.85mm (24Amp) Total Current drawn by both Sub-Circuits = 11.1A + 18.1A = 29.27 So cable suggested for Main-Circuit = 7/.044” (34Amp) 0r 7/1.04mm (31Amp)

Unit – 3 1. List out the design consideration of electrical installation in commercial bldgs.(Jan-2016) Design consideration of Electrical Installation in Commercial building: i. Deciding the number of Sub-circuits: The total load in a commercial building is calculated taking into consideration the general lighting load,the motor load and other power loads. The total requirements are then tabulated and the number and size of sub-circuits are determined. The load on each light-fan sub-circuits shall be restricted to 800 watts or 10 outlets and the load on each power sub-circuit should be restricted to 3000 watts or 2 outlets. ii. Deciding the size of rating of switch boards and distribution boards: Sub circuits are fed from sub-distribution boards, which is turn are fed from main distribution boards and to which supply comes from the main switch board. The sub-distribution boards, maindistribution boards, sub-switch boards, and main switch boards are designed stage by stage considering the load at different levels. The distribution fuse boards shall be located as near Department of EEE, SJBIT

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as possible to the centre of the load they are intended to control. They shall be marked "Lighting" or "Power" as the case may be, and also marked with voltage and number of phases of the supply. (Refer IS: 732 - 1983) iii. Deciding the size of Cables: The size of cables or conductors feeding the different stages of supply connection can be found out by calculating the actual current value at each stage. For electricity distribution from a substation or main switch board to a number of subswitchboards, PVC insulated armored and PVC sheathed cable installed in under ground trenches should be made use of. iv. Deciding the size of conduits: The size of conduit is determined from the size of the cables and the number of cables to be drawn though it. The conduit size is stated in term of its outer diameter. v. Bus bar and bus bar chamber: Bus bar camber consists of bus bars which are strips of copper or aluminium. The incoming lines are connected to these distribution bus bars through the main switch fuse and the load circuits are supplied from the bus bar through the switch fuse units. In a bus-bar chamber these are fixed four of which three are for the three phases and the fourth for the neutral. The size of busbar chamber depend on (a) size and number of strips used, (b) number and rating of switches to be mounted on it. vi. Mounting arrangement of switchboards and distribution boards: Switchboards and distribution boards can be mounted on to the wall or on the floor. Any type of mounting frame can be made with suitable angle iron. The size of angle iron depends upon the weight and size of the switchboard or distribution board to be mounted on the frame.

2.Explain the determination of load calculation selection of size of service connection and nature of supply.

(Jun -2015)

Conduit wiring : •

Rigid non-metallic conduits are used for surface, recessed and concealed conduit wiring. Conductors of ac supply and dc supply shall be bunched in separate conduits. The numbers of insulated cables that may be drawn into the conduit are given in table. Maximum permissible number of 1.1 kV grade single core cables that may be drawn into


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rigid non metallic conduits Conduit shall be fixed by saddles secured to suitable wood plugs or other plugs with screws at an interval of not more than 60 cm. whenever necessary, bends or diversions may be achieved by bending the conduits or by employing normal bends, inspection bends, inspection boxes, elbows or similar fittings.

3. Fig Shows the plan of ground floor of school building .School building consists at ground floor ,1st floor and 2nd floor having same plan that of ground floor. Draw single line diagram for ground floor and calculate materials required for three floors.

10

7.( Ju n20 Class 15 )(J Room un 1 20 15 )5

d

7.( Ju n20 Class 15 )(J Room un 2 20 15 )5

7.( Ju n20 Class 15 )(J Room un -3 20 15 )5

7.( Ju n20 Staff 15 )(J room un 20 15 )5

d

d

d

1.(J un 201 5)(J un Wc201 1 5)5 Wc 2

(Jun -2015)

2

Wc 3 Wc 4

1.( (all dimensions are in meters) Ju n20 i.15 Number of Sub-circuits: )(J un Taking 8 points per circuit or 560 W per 20 No. of Sub-circuits in ground floor main 15 )5

age

circuit building = 45 / 8 = 6

No. of Sub-circuits in first floor main building = 44 / 8 = 2 No's 10 way single phase ICDB's are required for wiring the circuits in the two floors. No. of Sub-circuits in ground floor Auxillary building = 30 / 8 = 4 No. of Sub-circuits in first floor Auxillary building = 27 / 8 = 4 2 No's 10 way single phase ICDB's are required for wiring the circuits in the two floors. Then 1 no. 4 way single phase ICDB is required for wiring the 4 no's 15A power socket outlets. ii. Deciding the cable size: Department of EEE, SJBIT

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i. Total wattage of the scheme = 16900 watts = 16.9 kw, 3-phase 4 wire system of supply is choosen. Load current = 16900 23.5 3 415 L IA = = × 3 1/2 core 25 sq mm PVC insulated aluminium conductor cable or four core 7/2.24 mm aluminium conductor cable of current carrying capacity 42A can be used. (Higher size of cable is choosen taking into the future expansion of the building) ii. The distribution boards are located at different locations as shown in fig. 3.3 and 3.4. Cable has to be run from the main switch board to the different distribution boards in each area. a) Average load on DB.1 and DB.3 = 3960 watts. Load current = 3960 16.5 240 A = Single core 1/2.24 mm aluminium conductor cable of current carrying capacity 20A can be used for connecting MSB and DB's 1 and 3. b) Average load on DB.2 and DB.4 = 2640 watts. Load current = 2640 11.0 240 A = Single core 1/1.80 mm aluminium conductor cable of current carrying capacity 15A can be used for connecting MSB and DB's 2 and 4. c) Average load on DB.5 = 4000 watts. Load current = 4000 16.67 240 A = Single core 1/2.80 mm aluminium conductor cable of current carrying capacity 27A can be used for connecting MSB and DB.5. iii. a) Wiring of light, Fan and 5A Socket points from the distribution boards can be done by 1/1.40 mm single core aluminium conductor cable. b) Wiring of 15A power socket points from the DB.5 can be done by 1/1.80 mm single core aluminium conductor cable. iii. Deciding the switchboards and distribution boards:

The rating of switch boards & distribution boards are decided by knowing the load current, each level. 10 way, 6 way or 4 way. Single phase 15A per way ICDB's can control the different sub-circuits. The average load on DB's 1 & 3 draws a current of 15.5A, & the load on DB.5 draws a current of 17.4A. So 30A DP isolator can serve as incomers to these DB's. The avrage load & DB's 2 and 4 draws a current of 10.3A. So 15A DP isolator can serve as incomers. Since Department of EEE, SJBIT

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the total load current of the scheme is 23A, the main switch incoming is choosen as 60A TPN switch, also considering the future expansion of the building. 3 No's 30A DPIC switches and 2 no's 15A DPIC switches are provided for controlling the five DB's located at different places. 1 no 30A TPN switch is kept as spare for future expansion. The schematic or line diagram shown in fig. 3.5 w ill help in understanding this arrangement more clearly. iv. Bus bar and Bus bar chamber.

a. 25.4 mm x 3.18 mm AL strips are c for neutral bar considering the maximum current flowing through the bus bar is 60A. Length of 25.4 mm x 3.18 mm Al. Strips for phase bars 1 x 3 = 3m Length of 12.7 mm x 3.18 mm Al. Strips for phase bars 1 = 1m 4 no's 30A/15A/DPIC switches are to be fixed on to the top of the bus bar chamber and 1 no, 60A TPN, 1 no 30A TPN and 1 no. DPIC switches to the bottom of bus bar chamber. .3 m. The busbar chamber is made up of 16 SWG MS sheets. Total area of 16 SWG MS sheets required for the bus bar 2) Allowance for wastage and cutting 20% = 0.28 sq. m (m2) Total = 1.66 sq. m (m2) b. To keep the bus bars in fact inside the bus bar chamber, bakelite s of thickness 0.3 mm

Total area of 2 no's bakelite sheets for bus bar s.

Allowance for wastage = 0.02 sq. mm & cutting 20% Total = 0.14 sq. mm c. For inter connecting the switches of different ratings to the bus bars, different sizes of Al. strips/ wires can be used.

30A TPN/DP switch = No. 4 SWG aluminium wire.


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15A DP switch = No. 8 SWG aluminium wire.

(1 set for 30A TPN & 3 sets for 30A DP) = 3 m Length of n

4. List and explain the design considerations of electrical installation in commercial buildings

(Jan-2015)

Ans : Same as Unit-3 (1a)

5. fig shows the plan of ground floor of school building. School building consists of gnd floor, 1st floor, 2nd floor having same plan that of gnd floor. Draw single line dia for gnd floor & calculate material required for three floors.

(June-2014)

Load = 5.8kW = 5800W Voltage = 230V Current = I = P/V = 5800 / 230 = 25.2A 20% additional load current = (20/100) x 5.2A = 5A Total Load Current = 25.2A + 5A = 30.2A Now select the size of cable for load current of 30.2A (from Table 1) which is 7/1.04 (31 Amperes) it means we can use 7/0.036 cable according table 1 Now check the selected (7/1.04) cable with temperature factor in Table 3, so the temperature factor is 0.97 (in table 3) at 35°C (95°F) and current carrying capacity of (7/1.04) is 31A, therefore, current carrying capacity of this cable at 40°C (104°F) would be Current rating for 35°C (95°F) = 31 x 0.97 = 30 Amp. Since the calculated value (30 Amp) at 35°C (95°F) is less than that of current carrying capacity of (7/1.04) cable which is 31A, therefore this size of cable (7/1.04) is also suitable with respect to temperature.


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Now find the voltage drop for per ampere meter for this (7/1.04) cable from (Table 5) which is 7mV, But in our case, the length of cable is 35 meter. Therefore, the voltage drop for 35 meter cable would be: Actual Voltage drop for 35meter = = mV x I x L (7/1000) x 30×35 = 7.6V And Allowable voltage drop = (2.5 x 230)/100 = 5.75V Here the actual Voltage drop (7.35V) is greater than that of maximum allowable voltage drop of 5.75V. Therefore, this is not suitable size of cable for that given load. So we will select the next size of selected cable (7/1.04) which is 7/1.35 and find the voltage drop again. According to Table (5) the current rating of 7/1.35 is 40Amperes and the volte drop in per ampere meter is 4.1 mV (See table (5)). Therefore, the actual voltage drop for 35 meter cable would be Actual Voltage drop for 35meter = = mV x I x L (4.1/1000) x 40×35 = 7.35V = 5.74V This drop is less than that of maximum allowable voltage drop. So this is the most appropriate and suitable cable size.

Unit - 4 1.List out the points to be checked while carrying out inspection of wiring install(Jan-2016) Internal wiring should be inspected once a year and the following points should be checked while carrying out inspection of tho wiring installation. 1. Service Connections: In case of overhead line, check and ensure that: (i) The lines are terminated at a sufficient distance from the building. (ii) The danger notice exists to warn the staff. (iii) The fuse wire of correct rating is provided on the phase line. (iv) The lead-in wires are of size sufficient to carry the full- load current.


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(v) The lead-in pipe is properly earthed and bonded and pipe ends are provided with insulating bushes to protect the wires from mechanical damage. ln case of underground cable check up and ensure that (i) the cables are properly sealed and there is no leakage of cable oil (ii) there are earth connections to the cable armouring. 2. Main Switchboard: In case of main switchboard check and ensure that (i) The voltage available is correct. (i.e. within permissible limits of declared voltage.) (ii) The main switch is provided close to the point of commencement of supply. (iii) The fuse of correct size is provided on the live pole. (iv) The main switch is easily identified and is easily accessible so that in case of emergency the entire supply to the building can be switched off at once. (v) There is a clear working space all round the board (as mentioned in IE rule 51 i.e. 0.914 m). (vi) The phase and neutral wires are clearly marked for identification. (vii) Caution notice in Hindi or other local language is placed. 3. Miscellaneous: The points to be checked are : (i) No branch circuit feeds more than 10 points or 800 watt load. (ix) The leakage current is not more than 1/5,000 of maximum supply current. (iii) The insulation resistance between conductor and earth and between conductors is more than permissible value as per IE rule. (iv) The single pole switches are provided on the live conductor. (v) The electrical resistance from the point of connection with the earth electrode to any point on ECC in the complete installation is not more than one ohm. (vi) The metallic frames of all power equipment are earthed by two independent earth conductors. (vii) The metallic covering of iron clad switch, distribution board. submain distribution boards. GI pipe, conduit pipes enclosing VIR or PVC cables are properly earthed.

2. Mention the different types of tests conducted on wiring installations. Explain in detail testing of polarity. Department of EEE, SJBIT

(Jan-2016) Page 19


10EE82

Testing of Polarity of Single Pole Switches. It in necessary that single pole switches are placed in + ve side or live side so that by making switch off the lamp can be made quite dead. The reason of it is that if the switch in provided on neutral wire, then lamp holder or the fan as well as part of wiring will remain alive, even when the single pole switch is in open position which may easily lead to accidents. For example, a person who is replacing lamp even after opening the single pole switch is liable to get shock if he comes in with the line terminal of the lamp holder. As regard the function of a single pole switch, it is equally effective whether it is connected in live or neutral wire but from the safety point of view it is necessary that all single pole switches are provided on phase or outer wire, never on neutral wire. To ensure that all the switches are placed in phase or live conductors and not in neutral conductor, this test is performed. A convenient and quicker method of performing this test is by means of a small neon tube tester. While performing polarity test by means of a small neon tube tester, its one terminal is held in the hand and the other against the feed terminal of the switch; if the switch is correctly connected the neon lamp will glow. Pocket neon testing tubes for the purpose are available An alternative method is by means of a test lamp. In this method all the lamps are removed, main switch is put in ‘on’ position, main fuse is inserted, one end of test lamp is connected to earth and the other end is tapped by lead to each of each switch in turn. If the test lamp lights on one of the two s, it indicates that switch is on the live wire as shown in Fig. 5.2 (a) and if test lamp, does not give light on either of the switch, it indicates that the switch is on neutral wire, so must be connected correctly.

Polarity Test Testing of Earth Continuity Path. For safety all the metal pieces or coverings such as conduits, metal covers of switches etc. must be solidly connected to earth otherwise on the damage of insulation, the leakage current will start giving severe shock to the person touching it. Department of EEE, SJBIT

Page 20


10EE82

In case of conduit wiring there is a possibility of the conduit ts to become loose or to be separated resulting in high resistance in the earth path. For earth continuity test, main switch should be opened, main fuse withdrawn, all other switches in on position and lamps in their respective holders. One end of the earth continuity tester is connected to an independent earth and the other end is connected to the wiring say to a switch or conduit. The pointer will indicate the earth resistance, which should not exceed the value of one ohm. Higher than this value shows that conduit or switch has not been properly earthed.

3. Estimate the material required for single phase overhead service line of a house located 20 meters away from the pole. With following loads: Lighting load = 800 watts, Heating = 2 kW. Take factor of safety 2.

(Jan-2016)

4. Write short note on service lines.

(Jun -2015)

This describes various types of utility electrical services and supply voltages. The nominal system supply voltages listed below can vary by ±10% or more. Watt Node meter models are available in seven different versions that cover the full range of electrical services types and voltages. Meters and current transformers are designed for use on either 50 or 60 Hz systems. Classification of Different Services: Alternating current electric power distribution systems can be classified by the following properties: 

Frequency: 50 Hz or 60 Hz



Number of phases: single or three phase



Number of wires: 2, 3, or 4 (not counting the safety ground)



Neutral present: 

Wye connected systems have a neutral



Delta connected systems typically do not have a neutral



Voltage levels:



Low Voltage: 600 volts or less


Page 21


 

10EE82



Medium Voltage: 601 volts to about 34,500 volts



High Voltage: 46,000 volts and up

Line-to-line

voltages

are

typically

1.732

times

the

phase-to-neutral

voltages: In symmetrical three-phase electrical system, the phase-to-neutral voltages should be equal if the load is balanced.

5. Write the reason for excess recording of energy consumption by energy meter(Jan -2015) Meters can be manipulated to make them under-, effectively allowing power use without paying for it. This theft or fraud can be dangerous as well as dishonest. Power companies often install remote-reporting meters specifically to enable remote detection of tampering, and specifically to discover energy theft. The change to smart power meters is useful to stop energy theft. When tampering is detected, the normal tactic, legal in most areas of the USA, is to switch the subscriber to a "tampering" tariff charged at the meter's maximum designed current. At US$0.095/kWh, a standard residential 50 A meter causes a legally collectible charge of $5,000.00 per month. Meter readers are trained to spot signs of tampering, and with crude mechanical meters, the maximum rate may be charged each billing period until the tamper is removed, or the service is disconnected.


Page 22


10EE82

A common method of tampering on mechanical disk meters is to attach magnets to the outside of the meter. Strong magnets saturate the magnetic fields in the meter so that the motor portion of a mechanical meter does not operate. Lower power magnets can add to the drag resistance of the internal disk resistance magnets. Magnets can also saturate current transformers or power-supply transformers in electronic meters, though countermeasures are common. Rectified DC loads cause mechanical (but not electronic) meters to under-. DC current does not cause the coils to make eddy currents in the disk, so this causes reduced rotation and a lower bill. Some combinations of capacitive and inductive load can interact with the coils and mass of a rotor and cause reduced or reverse motion. All of these effects can be detected by the electric company, and many modern meters can detect or compensate for them. The owner of the meter normally secures the meter against tampering. Revenue meters' mechanisms and connections are sealed. Meters may also measure VAR-hours (the reflected load), neutral and DC currents (elevated by most electrical tampering), ambient magnetic fields, etc. Even simple mechanical meters can have mechanical flags that are dropped by magnetic tampering or large DC currents. Newer computerised meters usually have counter-measures against tampering. AMR (Automated Meter Reading) meters often have sensors that can report opening of the meter cover, magnetic anomalies, extra clock setting, glued buttons, inverted installation, reversed or switched phases etc. Some tampers by the meter, wholly or in part. Safe tampers of this type normally increase the neutral current at the meter. Most split-phase residential meters in the United States are unable to detect neutral currents. However, modern tamper-resistant meters can detect and bill it at standard rates.[34] Disconnecting a meter's neutral connector is unsafe because shorts can then through people or equipment rather than a metallic ground to the generator or earth. A phantom loop connection via an earth ground is often much higher resistance than the metallic neutral connector. Even if an earth ground is safe, metering at the substation can alert the Department of EEE, SJBIT

Page 23


10EE82

operator to tampering. Substations, inter-ties, and transformers normally have a high-accuracy meter for the area served. Power companies normally investigate discrepancies between the total billed and the total generated, in order to find and fix power distribution problems. These investigations are an effective method to discover tampering. Power thefts in the U.S. are often connected with indoor marijuana grow operations. Narcotics detectives

associate

abnormally

high

power

usage

with

the

lighting

such

operations

require.[35] Indoor marijuana growers aware of this are particularly motivated to steal electricity simply to conceal their usage of it.

6. Find the materials required for 1-

overhead service lines of a house located 10 meters

away from pole, with following loads :Lightning =300 watts, Heating= 2500 watts.Assume safety factor=2

(Jan -2015)

power supply and another for domestic supply. Assuming efficiency of motor 85% and power factor 0.8, we have full- load currents of motors as ( ) ( ) ( ) 1 2 34 0.75 1, 000 0.75 , 415 , 3 1.54 3 415 0.85 0.8 3.7 1, 000 3.7 , 415 , 3 7.57 3 415 0.85 0.8 5.5 1, 000 5.5 , 415 , 3 11.25 3 415 0.85 0.8 I I For kW V phase motor A I For kW V phase motor A I For kW V phase motor A × = Total full- load current for these motors = 1.54 + 1.54 + 7.57 + 11.25 = 21.9 A Hence cable from meter board to main board shall have a current carrying capacity 1.6 times of full- load current of the mot Hence 3-core, 1100 V grade PVC insulated, 16 mm2 aluminium conductor having current carrying capacity of 38 A shall be used from meter board to main board. The current rating of main switch in the starting current of one motor of highest rating plus full

1. Length of 31 mm exible conduit from meter board to main switch board and from main switch board to distribution board, including wastage = 1.0 m 2. Length of 25 mm exible conduit from HG conduit to motor terminals fan machine no. 4, including wastage = 1.0 m


Page 24


10EE82

3. Length of 19 mm exible conduit required for connecting motor switches to motor starters for all the four machines and HG conduit to motor terminals for machines no. 1, 7. Explain points to be checked while carrying out inspection of wiring installat(Jan-2015) Conductors configuration spacing and clearances, Span lengths 1) No conductor of an overhead line, including service lines, erected across a street shall at any part thereof be at a height less than(a) for low and medium voltage lines 5.8 metres (b) for high voltage lines

6.1 metres

(2) No conductor of an overhead line, including service, lines, erected along any street shall at any part thereof be at a height less than(a) for low and medium voltage lines 5.5 metres (b) for high voltage lines

5.8 metres

(3) No conductor of an overhead line including service lines, erected else- where than along or across any street shall be at a height less than(a) for low, medium and high voltage lines up to and including 11,000 volts, if bare ;4.6 metres (b) for low, medium and high voltage lines up to and including 11,000 volts, if insulated 4.0 (c) for high voltage lines above 11,000 volts

5.2 metres

(4) For extra-high voltage lines the clearance above ground shall not be less than 5.2 metres plus 0.3 metre for every 33,000 volts or part thereof by which the voltage of the line exceeds 33,000 volts:

PROVIDED that the minimum clearance along or across any street shall not be

less than 6.1 metres.

8. Write the reason for excess recording of energy consumption by energy mtr (June-2014) Meters can be manipulated to make them under-, effectively allowing power use without paying for it. This theft or fraud can be dangerous as well as dishonest.


Page 25


10EE82

Power companies often install remote-reporting meters specifically to enable remote detection of tampering, and specifically to discover energy theft. The change to smart power meters is useful to stop energy theft. When tampering is detected, the normal tactic, legal in most areas of the USA, is to switch the subscriber to a "tampering" tariff charged at the meter's maximum designed current. At US$0.095/kWh, a standard residential 50 A meter causes a legally collectible charge of $5,000.00 per month. Meter readers are trained to spot signs of tampering, and with crude mechanical meters, the maximum rate may be charged each billing period until the tamper is removed, or the service is disconnected. A common method of tampering on mechanical disk meters is to attach magnets to the outside of the meter. Strong magnets saturate the magnetic fields in the meter so that the motor portion of a mechanical meter does not operate. Lower power magnets can add to the drag resistance of the internal disk resistance magnets. Magnets can also saturate current transformers or power-supply transformers in electronic meters, though countermeasures are common. Rectified DC loads cause mechanical (but not electronic) meters to under-. DC current does not cause the coils to make eddy currents in the disk, so this causes reduced rotation and a lower bill. Some combinations of capacitive and inductive load can interact with the coils and mass of a rotor and cause reduced or reverse motion. All of these effects can be detected by the electric company, and many modern meters can detect or compensate for them. The owner of the meter normally secures the meter against tampering. Revenue meters' mechanisms and connections are sealed. Meters may also measure VAR-hours (the reflected load), neutral and DC currents (elevated by most electrical tampering), ambient magnetic fields, etc. Even simple mechanical meters can have mechanical flags that are dropped by magnetic tampering or large DC currents. Newer computerised meters usually have counter-measures against tampering. AMR (Automated Meter Reading) meters often have sensors that can report opening of the meter cover, magnetic


Page 26


10EE82

anomalies, extra clock setting, glued buttons, inverted installation, reversed or switched phases etc. Some tampers by the meter, wholly or in part. Safe tampers of this type normally increase the neutral current at the meter. Most split-phase residential meters in the United States are unable to detect neutral currents. However, modern tamper-resistant meters can detect and bill it at standard rates.[34] Disconnecting a meter's neutral connector is unsafe because shorts can then through people or equipment rather than a metallic ground to the generator or earth. A phantom loop connection via an earth ground is often much higher resistance than the metallic neutral connector. Even if an earth ground is safe, metering at the substation can alert the operator to tampering. Substations, inter-ties, and transformers normally have a high-accuracy meter for the area served. Power companies normally investigate discrepancies between the total billed and the total generated, in order to find and fix power distribution problems. These investigations are an effective method to discover tampering. Power thefts in the U.S. are often connected with indoor marijuana grow operations. Narcotics detectives

associate

abnormally

high

power

usage

with

the

lighting

such

operations

require.[35] Indoor marijuana growers aware of this are particularly motivated to steal electricity simply to conceal their usage of it.

9. find the material required for 1pase overhead service line of a house located 10 mts away from pole, with foll loads : Lighting = 300 Watts; factor=2.

Heating= 2500 Watts Assume safety (June-2014)

power supply and another for domestic supply. Assuming efficiency of motor 85% and power factor 0.8, we have full- load currents of motors as 1, 000 0.75 , 415 , 3 1.54 3 415 0.85 0.8 3.7 1, 000 3.7 , 415 , 3 7.57 3 415 0.85 0.8 5.5 1, 000 5.5 , 415 , 3 11.25 3 415 0.85 0.8 I I For kW V phase motor A I For kW V phase motor A I For kW V phase motor A × = − = = × × Total full-load current for these motors = 1.54 + 1.54 + 7.57 + 11.25 = 21.9 A


Page 27


10EE82

Hence cable from meter board to main board shall have a current carrying capacity 1.6 times of fullHence 3-core, 1100 V grade PVC insulated, 16 mm2 aluminium conductor having current carrying capacity of 38 A shall be used from meter board to main board. The current rating of main switch in the starting current of one motor of highest rating plus full load curr 1. Length of 31 mm exible conduit from meter board to main switch board and from main switch board to distribution board, including wastage = 1.0 m 2. Length of 25 mm exible conduit from HG conduit to motor terminals fan machine no. 4, including wastage = 1.0 m 3. Length of 19 mm exible conduit required for connecting motor switches to motor starters for all the four machines and HG conduit to motor terminals for machines no. 1,

Unit-5 1.

List out important consideration regarding motor installations.

(Jan-2016)

IMPORTANT CONSIDERATION REGARDING MOTOR INSTALLATION WIRING

These are as detailed below. 1. All equipment used in power wiring shall be of iron clad construction and wiring shall be of the armoured cable or conduit type (IE Rule 51). 2. Woodwork shall not be used for mounting of switchgear. 3. Looping of conductors and use of the ts shall not be done, 4. The length of exible conduit used for connections between the terminal boxes of motors andstarters, switches and motors shall not exceed 1.25 metres. 5. Every motor, regardless of its size shall be provided with a switch fuse placed near it. [IE Rule 50 clause (d)] 6. In addition to switch fuse all motors shall be provided with suitable means for starting and stopping (starters) placed at convenient places. The starters are used to limit the starting current to a desirable value. Direct-on-line starters, star-delta starters, auto transformer-starters (or rotor Department of EEE, SJBIT

Page 28


10EE82

resistance starters in case of slip-ring induction motor)are used for ac motors of rating up to 0.75 kW, above 0.75 kW and below 11 kW and above 11 kW respectively. 7. The conduit should preferably be laid in covered trenches to facilitate operator movement (safe). 8. Laying of cables must be in separate conduits for separate motors.

2.The Fig. shows the plan of workshop. One 15 HP, 3 phase, 415 y induction motor is installed. Show the key diagram and estimate quantity of material required.

(Jan-2016)

Assumptions made: 1. The motor and starter are to be procured through separate contract. 2. Motor disconnect switches and main switches are to be supplied by wiring contractor. 3. All the conduits are to be run exposed on walls. 4. The main switch, motor switch and starter shall be mounted at a height of 1.5 metres from ground level. 5. Two earth wires will be run side by side for earthing the motor, starter and switches. 6. The motor shall be installed on suitable foundation, 0.2 m above the floor level. 7. Motor efficiency 85% and power factor 0.8 (lagging). Full load current = Starting current = 1.5 times full-load current = 1.5 X 15.06 = 22.6A. Hence three-core PVC 1100V grade, 6 mm2 aluminium conductor cable of current carrying capacity 24 A may be used. The main switch and motor switch to be used will be 32 A. 415V TPIC switches. As from meter board to main board and main board to motor control board only one 3-core cable is to be run so a HG conduit of size 25mm will be run from meter board to main board and from main board to motor control board. From, motor starter to motor two 3-core cables carried so HG conduit of size 31 mm will be used. Flexible conduit of size 25 mm will be used for connecting motor switch and motor starter and of size 31 mm will be used for connecting heavy gauge conduit to motor. Length of 25mm HG Rigid Conduit Department of EEE, SJBIT

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10EE82

From meter board to main board = 0.3 m from main board to motor switch (mounted on control board) = 22.5 metres Total = 22.8 metres Wastage 10% = 2.3 metres Total = 25.1 metres = 25 metres (say) Length of 31 mm HG Conduit From motor starter to ground = 1.5 metres Below ground level = 0.2 metres Along ground up to foundation = 1.0 metres Up to top of motor foundation = 0.2 + 0.2 = 0.4 metre Total = 1.5 + 0.2 + 1.0 + 0.4 = 3.1 metres Wastage 10% = 0.31 metre Total = 3.1 + 0.31 = 3.41 = 3.5 metres (say) Length of 25 mm exible conduit required for connecting motor switch to motor starter= 0.25m Length of 31 mm exible conduit required for connecting heavy gauge conduit to motor = 1 metre Length of 3 core, 1100 V grade, 1/2.80 mm (6 mm2) aluminium conductor PVC cable (i) 1 Length from meter board to main board = 0.3 m (ii) 1 Length from main board to motor switch = 22.5 m (iii) l Length from motor switch to motor starter = 0.25 m (iv) 2 Lengths from motor starter to motor terminal box = 2 (3.2 + l) = 8.2 m Total Length= 31.25 m Wastage and for connections, 10 96 = 3.13 m Total = 34.38 = 36 metres (say) Length of Earth Wire According to IE rules, the motor frame, motor switch, motor starter,main switch are to be earthed by means of two separate and distinct connections. Hence two separate earth electrodes will be provided for earthing purpose. From the table for size for earth wire, for 10 HP motor 8 SWG GI wire will be required as earth wire. Length of earth wire required Department of EEE, SJBIT

Page 30


10EE82

= 2 (25 + 3.5 + 0.25 + l) = 59.5 metres = 60 metres (say) or 6 kg. SL

Description of Material With Full Specifications

Quantity

Rem

N

Required

a rks

O

Qu

Unit

ant ity 1

32A, 415V, TPIC rewirable type switch fuse unit

2

IC boards complete with locking arrangement 1

no

etc.

1

do

3.5

m

25

do

Heavy gauge (HG) 16 SWG conduit

1

do

i) 31 mm

0.2

do

ii) 25 mm

5

do

Flexible conduit

35

nos

i) 31 mm

2

do

ii) 25 mm

6

do

3 core, 1100 V, grade 6 mm2 aluminium 4

do

6

conductor PVC cable

25

do

7

Conduit bends

6

do

i) 31mm

2

3

4

5

2

nos

ii) 26 mm 8

Conduit Saddles i) 31 mm ii) 25 mm

9

Lock nuts i) 31 mm


Page 31


10EE82

ii) 25 mm 10

Flexible pipe coupling complete with locknuts i) 31 mm ii) 25 mm

11

Wooden bushings i) 31 mm ii) 25 mm

12

Teak wood gutties

13

8 SWG GI wire

14

Shock treatment chart

15

Iron screws 32 mm

16

Caution plates

17

GI thimbles with nuts and bolts

18

Earth wire clips

19

GI Plate 600 mm x 600 mm x 60 mm

20

GI pipe 19 mm diameter

21

GI pipe 12 mm diameter

22

8 SWG GI wire

23

CI Cover 30 cm x 30 cm

24

GI bolts nuts, check nuts with washers

25

Funnel with wire mesh

26

Charcoal

27

Salt

28

Soldering material Civil

Engineering

works

(Digging,

Finishing,

Foundation of motor, covering up, building up of CI frame, cement etc.)


Page 32


10EE82

3. Explain determination of input power, current to motors & rating of cables.(Jun -2015) Step 1: Data Gathering The first step is to collate the relevant information that is required to perform the sizing calculation. Typically, you will need to obtain the following data: Load Details The characteristics of the load that the cable will supply, which includes: 

Load type: motor or feeder



Three phase, single phase or DC



System / source voltage



Full load current (A) - or calculate this if the load is defined in of power (kW)



Full load power factor (pu)



Locked rotor or load starting current (A)



Starting power factor (pu)



Distance / length of cable run from source to load - this length should be as close as possible to the actual route of the cable and include enough contingency for vertical drops / rises and termination of the cable tails Cable Construction The basic characteristics of the cable's physical construction, which includes: 

Conductor material - normally copper or aluminium



Conductor shape - e.g. circular or shaped



Conductor type - e.g. stranded or solid



Conductor surface coating - e.g. plain (no coating), tinned, silver or nickel


Page 33

Electrical Design Estimation and Costing  

10EE82

Insulation type - e.g. PVC, XLPE, EPR Number of cores - single core or multicore (e.g. 2C, 3C or 4C) Installation Conditions How the cable will be installed, which includes:



Above ground or underground



Installation / arrangement - e.g. for underground cables, is it directly buried or buried in conduit? for above ground cables, is it installed on cable tray / ladder, against a wall, in air, etc.



Ambient or soil temperature of the installation site



Cable bunching, i.e. the number of cables that are bunched together



Cable spacing, i.e. whether cables are installed touching or spaced



Soil thermal resistivity (for underground cables)



Depth of laying (for underground cables)



For single core three-phase cables, are the cables installed in trefoil or laid flat? Step 2: Cable Selection Based on Current Rating Current flowing through a cable generates heat through the resistive losses in the conductors, dielectric losses through the insulation and resistive losses from current flowing through any cable screens / shields and armouring. The component parts that make up the cable (e.g. conductors, insulation, bedding, sheath, armour, etc) must be capable of withstanding the temperature rise and heat emanating from the cable. The current carrying capacity of a cable is the maximum current that can flow continuously through a cable without damaging the cable's insulation and other components (e.g. bedding, sheath, etc). It is sometimes also referred to as the continuous current rating or ampacity of a cable. Cables with larger conductor cross-sectional areas (i.e. more copper or aluminium) have lower resistive losses and are able to dissipate the heat better than smaller cables. Therefore a 16 mm2 cable will have a higher current carrying capacity than a 4mm2 cable.


Page 34


10EE82

Base Current Ratings

Table 1. Example of base current rating table (Excerpt from IEC 60364-5-52) International standards and manufacturers of cables will quote base current ratings of different types of cables in tables such as the one shown on the right. Each of these tables pertain to a specific type of cable construction (e.g. copper conductor, PVC insulated, 0.6/1kV voltage grade, etc) and a base set of installation conditions (e.g. ambient temperature, installation method, etc). It is important to note that the current ratings are only valid for the quoted types of cables and base installation conditions. In the absence of any guidance, the following reference based current ratings may be used

4. A 10 HP (metric), 415 v, 3 ,50Hz squirrel cage IM is to be installed in a flour mill, the plan of which is shown in fi Shows the wiring dia of the layout and estimate the quantity of materials required and its cost.

(Jun -2015)

We depend on electricity to light our homes, turn on our television sets, and even cook our meals. When the power goes out because of a storm, a short circuit, or another problem in the electrical circuit, understanding what the basic components of an electrical system is a must. Department of EEE, SJBIT

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10EE82

Your homes’ electricity starts with the electrical service connection. This is where the electric company connects their wires to your homes’ feeder wires that attach to the meter on your home or power pole. This is the device that measures the amount of electricity your home uses and determines the amount of money the electric company charges you on a monthly basis. From here your meter either feeds a disconnect switch or a main breaker or fuse . A typical home has a single phase service consisting of an “A” phase and a “B” phase, a neutral and a ground wire. Disconnect Switch A disconnect switch is mounted on the outside of your home close in proximity to the meter on the outside of your home or power pole. The advantage of having a disconnect switch is for safety. In the event of a fire or flash flood, you can shut the power off from the outside of your home verses having to enter a burning home or a flooded basement. The other instance is having a transfer switch in which you can switch between live power and a generator for backup power. Main Breaker A breaker consists of a main breaker that is sized according to your homes’ load needs. It is used to turn the power on and off to the entire electrical . Typically, homes have a 100 amp or a 200 amp service. A main breaker of 100 amps will only allow 100 amps to flow through it without tripping. In a tripped state, no current will flow throughout the . It is the interrupt between the service and the branch circuits of the . This main breaker protects the main service wires from damages that would occur given an overload. In that case, the wires would heat up and eventually could cause a fire.


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10EE82

Branch Circuit Breakers Breakers that feed lighting, outlets, central air conditioning and sub-s are considered branch circuits. These circuits can either be 120 volts or 240 volts. The 120 volt circuits require a single pole breaker, using only one phase of the electrical service. These circuits provide power to lighting, outlets and furnaces. The breakers are usually sized at 15 or 20 amps. In a 240 volt circuit, a two-pole breaker uses both phases of a circuit. Examples of 240 volt appliances would be an electric range, an electric stove or central air conditioning. These appliances don’t work unless both “A” and “B” phases are working. Most of these examples would require a two-pole 30 amp breaker. to size your breaker by the name plate rating on the device you are connecting to. Switches Switches are the devices that turn on and off lights and fans in your home. These switches come in many different styles and colors to suit your design needs. There are single-pole, three-way, four-way and dimmer switches. Their purpose is to alter the flow of current to your lights and fans in a home. Outlets Electrical outlets are used to plug portable devices into. Televisions, lights, computers, freezers, vacuums and toasters are all good examples of devices that can be plugged into an outlet. Outlets consist of a hot feed, a neutral and a ground. Some outlets are used especially for wet areas. Wiring Department of EEE, SJBIT

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10EE82

Your home’s wiring consists of romex, BX cable or wiring concealed in conduit. Romex is a brand name for a type of plastic insulated wire. The formal name is NM that means non-metallic sheath. This is suitable for use in dry, protected areas (inside stud walls, on the sides of joists, etc.), that are not subject to mechanical damage or excessive heat. Bx cable is known as armored cable. Wires are covered by aluminum or steel flexible sheath that is somewhat resistant to damage. Single strands of conductor wire are pulled through conduit that is the safest method for wiring for durability purposes. These different types of wiring carry electrical current from the to the device being fed. Wiring is sized according to the load demand required. Check the rated required load requirements marked on each device to determine the needed size wire to carry the needed load.

5. List any eight important considerations regarding motor installation wiring (Jan-2015) Same Ans as 1 of unit -5

6. A 10 HP (metric) , 415V, 3 Phase, 50 Hz induction motor is to be installed in a workshop, the plan of which is shown in below fig. show the layout of the wiring (key dia) & estimate the quantity of material required. The wiring is to be surface conduit. Assume efficiency of motor = 85% & powerfactor 0.8 lagging.

(June-2014)

Decide Number of Conductor and Layer of Conductor: 

If N: number of conductors [strands], d: Diameter of strands, ,X: number of layers.


Page 38

Electrical Design Estimation and Costing o

10EE82

Usually the relation between N&X take as followed. N= 3X2-3X+1



If N is given we can used the above relation get X, then we can get the total Diameter of cable as dT= (2X-1)d.



If Total Number of Conductor (N)=19 Than 19=3×2-3x+1. So Number of Layer (x)=3 o Than Diameter of Cable dT = (2x-1)d =5d



No conductor of an overhead line including service lines, erected else- where than along or across any street shall be at a height less than(a) for low, medium and high voltage lines up to and including 11,000 volts, if bare ;4.6 metres (b) for low, medium and high voltage lines up to and including 11,000 volts, if insulated 4.0



(c) for high voltage lines above 11,000 volts

5.2 metres

(4) For extra-high voltage lines the clearance above ground shall not be less than 5.2 metres plus 0.3 metre for every 33,000 volts or part thereof by which the voltage of the line exceeds 33,000 volts:

PROVIDED that the minimum clearance along or across

any street shall not be less than 6.1 metres. Voltage

Min. Ground Clearance

Fault Clear Time

400 KV

8.8 Meter

100 mille second

220 KV

8.0 Meter

120 mille second

132 KV

6.1 Meter

160 mille second

66 KV

5.1 Meter

300 mille second


Page 39


10EE82

Unit-6 1.List out the main components of overhead lines.

(Jan-2016)

The main components of an overhead line are enlisted, as below. 1. s: Poles or towers depending upon the working voltage and the region where these are used. The function of the line in obviously to the conductors so as to keep them at a suitable level above the ground. 2. Cross arms and Clamps: These are either of wood or steel angle section and are used on pole structures to the insulators and conductors. 3. Insulators: Pin, strain or suspension types, as the case may be, for ing the conductors and taking strain or suspending the conductors respectively. 4. Conductors: Copper, aluminium or ACSR or of any other composition depending upon the current to be carried and the span of the line. 5. Guys and Stays: Braces or cables are fastened to the pole at the termination or angle poles to resist lateral forces. 6. Lightning Arrestors is discharge excessive voltages built upon the line, to earth, due to lightning. 7. Fuses and Isolating Switches: to isolate different parts of the overhead system. 8. Continuous Earth Wire: is run on the top of the towers to protect the line against lightning discharges. 9. Vee-Guards are often provided below bare overhead lines running along or across public streets to make the line safe if it should break. 10 Guard Wires are provided above or below power lines while crossing telephone or telegraph lines. The guard wires and steel structures are solidly connected to earth. 11. Phase Plates in order to distinguish the various phases. 12. Bird Guards: A stick of ebonite with rounded top is xed near the insulator on the cross arm to prevent flash-over due to birds pecking on the conductors (on line with pin insulators).


Page 40


10EE82

13. Danger Plate: It ia provided on each pole, as a warning measure indicating the working voltage of the line and the word “danger”. It is provided at a height of 2.5 m from the ground. 14. Barbed Wire: Barbed wire in wrapped on a pole at a height of about 2.5 m from the ground for at least 1 metre. This prevents climbing by unauthorized persons. 15. Miscellaneous Items such as vibration dampers, top hampers, beads for jumpers etc.

2.. Estimate the quantity of material required for running 80 km, single circuit of 66 kv transmission line using four legged fabricated steel structures. The conductor used No.2 ACSR. Assume a span of 500 mts and every 10th tower is an anchor tower.

(Jan-2016)

Length of line = 1 km Average span = 120 m Number of spans = 1000 8 120 = (as 3 conductors run in 3-phase 11 kV line) metres = × × = 128 1000 Length of conductor × 1 km weighs 128 kg 128 3060 391.68 390 1000 kg say kg

3 . What are the requirements of the line s? Describe factors governing ht of pole? (Jun -2015) A transmission tower (electricity pylon in the United Kingdom and parts of Europe, and a hydro tower in certain provinces of Canada where power generation is mainly hydro-electric) is a tall structure, usually a steellattice tower, used to an overhead power line. They are used in high-voltage AC and DC systems, and come in a wide variety of shapes and sizes. Typical height ranges from 15 to 55 metres (49 to 180 ft),[1]though the tallest are the 370 m (1,214 ft) towers of a 2700-metre-long span of Zhoushan Island Overhead Powerline Tie. In addition to steel, other materials may be used, including concrete and wood.


Page 41


10EE82

There are four major categories of transmission towers:[1] suspension, terminal, tension, andtransposition. Some transmission towers combine these basic functions. Transmission towers and their overhead power lines are often considered to be a form of visual pollution. Methods to reduce the visual effect include undergrounding.

4. Estimate the quantity of materials required for adding 132KV bay at 132KV grid ss. (Jun -2015) The sub-station is connected with three substations or load viz. A (3.2 mw), B (3.2MW) and C (3.2MW) at 33KV and D (36MW) at 132 KV. The generated 16.2 KV is stepped up to 132 KV and is supplied to the 132KV sub-station through two double circuit transmission lines. After analyzing the requirements of the loads & SIL of transmission lines the whole arrangements are done in the following way: 2.1 Assumptions  The value of surge impedance of transmission lines under consideration = 325 Ω  Total load requirement = 3.2 MW + 3.2 MW + 3.2 MW + 36 MW  The distance between the substation & the neighboring generating station is 50km. The SIL of 132 KV line = (132KV) 2 /325 = 53.61 = 54 MW (approx) The SIL of 33 KV line = (33KV) 2 /325 = 3.35 = 3.5 MW (approx) Observing the total load demand, the input to the substation must be greater than the requirement. So one double circuit 132KV transmission lines (54 X 2 = 108 MW) only can satisfy this. The second double circuit tower is constructed keeping in mind the future load demand increase. The lines first supply the power to the 132KV bus A of the sub-station. As the distance between the substation and the generating station is only 50km, the SIL can increase to 1.2 times of the theoretical value. Hence the input of the substation can be as high as (108 X 1.2) MW i.e. almost 130 MW

5. Draw & explain typical ac electrical power supply system.


(Jan-2015)

Page 42


10EE82

An electric power system is a network of electrical components used to supply, transmit and use electric power. An example of an electric power system is the network that supplies a region's homes and industry with power - for sizable regions, this power system is known as the grid and can be broadly divided into the generators that supply the power, the transmission system that carries the power from the generating centres to the load centres and the distribution system that feeds the power to nearby homes and industries. Smaller power systems are also found in industry, hospitals, commercial buildings and homes. The majority of these systems rely upon three-phase AC power - the standard for large-scale power transmission and distribution across the modern world. Specialised power systems that do not always rely upon three-phase AC power are found in aircraft, electric rail systems, ocean liners and automobiles. Modern ac power systems usually consist of the (i) generating stations (ii) step up transformer stations (iii) transmission lines (iv)switching stations (v) step down transformer stations (vi) primary (high voltage) distribution lines or net-works (vii) service transformer banks (viii) secondary (low voltage)distribution lines. Essentially elements (ii), (iii), (iv) and (v) fall in the transmission system and distribution may or may not include all elements enumerated above; for example, some systems may have no primary transmission, some may not have secondary transmission and the others may not have transmission at all, being very small and so on. Generation voltages are 3.3, 6.6, 11 or 33 kv, most usual value adopted in practice is 11 kv. The primary transmission voltages are 110, 132, 220 or 400 kv depending upon the distance, the amount of power to be transmitted and the system stability. Secondary transmission voltage is normally of the order of 33 or 66 kv. The voltages for primary distribution are 1, 6.6 or 3.3 kv depending upon the requirements of the bulk consumers and for secondary distribution usable voltage is 400 volts.

6. Estimate quantity of materials required for adding 132KV bay at 132 KV grid substation.

(June-2014)

Ans is same for que 4 of unit -6


Page 43


10EE82

Unit-7&8 1. Write short note on guarding of over head lines.

(Jan-2016)

Overhead Line 

Pole Foundation hole should be drilled in the ground with the use of earth-augers. However, if earth-augers are not available a dog pit of the size I.2 x O.6 m should be made in the direction of the line.



The depth of the pit shall be in accordance-with the length of the pole to be planted in the ground as given in respective Indian Standards.

Tubular Pole 

Steel Tubular Poles, Rolled Steel Joists and Rails – A suitable pad of cement concrete, stone or steel shall be provided at the bottom of the pit, before the metallic pole is erected.



Where metal works are likely to get corroded ( points where the pole emerges out of the ground ), a cement concrete muff, 20 cm above and 20 cm below the ground with sloping top shall be provided.

RCC Pole 

RCC poles generally have larger cross-section than the PCC poles and, therefore, the base plates or muffing are usually not provided for these types of poles.



However, for PCC poles, a base plate ( 40 x 40 x 7 cm concrete block ) shall be provided. Cement concrete muff with sloping top may also be provided, 20 cm above and 20 cm below-the ground level, when the ground or local conditions call for the same.

H.V Line (120m To 160m Span)


Page 44

Electrical Design Estimation and Costing 

10EE82

The insulators should be attached to the poles directly with the help of ‘D’ type or other suitable clamps in case of vertical configuration of conductors or be attached to the cross arms with the help of pins in case of horizontal configuration



Pin insulator:; and recommended for use on straight runs and up to maximum of 10’ deviation.



The disc insulators are intended for use a pole positions having more than 30’ angle or for dead ending of I1 kV lines.



For lines having=, a bend of 10” to 30’, either double cross arms or disc insulators should be used for HT lines up to 11 kV. For low and medium voltage line, shackle insulators should be used



For Vertical configuration for Conductor erection:



Distance between Pole’s Top to Disc insulation=200mm.



Between Disc insulator to Disc Insulator=1000mm.



Between Disc insulator to Guy Wire=500mm.

2. Estimate the quantity of material required for 11 kV feeder running 1.5 km line using 9 mt RCC poles.The conductor used is ACSR of 611 x 2.59 mm with an average span of 120 mts.Assume every 8th pole is the Anchor pole. (DP structure).

(Jan-2016)

3. Explain the classification of substations.

(Jan-2016)

CLASSIFICATION OF SUBSTATlON The substations may be classified in numerous ways such as on the basis of (i) nature of duties (ii) service rendered (iii) operating voltage (iv) importance and (v) design. Classification of Substations on The Basis of Nature of Duties. The substations, on the basis of nature of duties, may be classified into the following three categories: 1. Step-Up or Primary Substations. Such substations are usually associated with generating stations. The generated voltage, which is usually low (11 or 33 kV), is stepped up to primary transmission voltage so that huge blocks of power can be transmitted over long distances to the load centres economically.


Page 45


10EE82

2. Primary Grid Substations. Such substations are located at suitable load centres along the primary transmission lines. In these substations, the primary transmission voltage is stepped down to different suitable secondary voltages. 'l‘he secondary transmission lines are carried over to the secondary substations situated at the load centres where the voltage is further stepped down to sub-transmission or primary distribution voltages. 3. Step-Down or Distribution Substations. Such substations are located at the load centres, where the sub-transmission/primary distribution voltage is stepped down to secondary distribution voltage (415/240 V). These are the substations which feed the consumers through distribution network and service lines. Classification of Substations on The Basis of Service Rendered. The substations, according to service rendered are: 1. Transformer Substations. Transformers are installed on such substations transform the power from one voltage level to another level as per needs. 2. Switching Substations. Such substations are meant for switching operation of power lines without transforming the voltage. At such substations different connections are made between various transmission lines. 3. Converting Substations. Such substations are meant for either converting ac to dc or vice versa or converting frequency from higher to lower or vice versa. Classification of Substations on The Basis of Operating Voltage. The substations, according to operating voltage, may be categorised as. 1. High Voltage Substations (HV Substations) involving voltages between 11 kV and 66 kV. 2. Extra High Voltage Substations (EHV Substations) involving voltages between 132 kV and 400 kV. 3. Ultra High Voltage Substations (UHV Substations) operating on voltage above 400 kV. Classification of Substations on The Basis of Importance. 1. Grid Substations. These are the substations from where bulk power is transmitted from one point to another point in the grid. These are important because any disturbance in these substations may cause the failure of the grid.


Page 46


10EE82

2. Town Substations. These substations step-down the voltages at 33/11 kV for further distribution in the towns and any failure in such substations results in the failure of supply for whole of the town. Classification of Substations on The Basis of Design. 1. Indoor Type Substations. In such substations the apparatus is installed within the substation building. Such substations are usually for a voltage up to 11 kV but can be erect/ad for the 33 kV and 66 kV when the surrounding atmosphere i* contaminated with impurities such as metal corroding gases and fumes, conductive dust etc. 2. Outdoor Substations. These substations are further subdivided into: (a) Pole Mounted Substations. Such substations are erected for distribution of power in localities. Single stout pole or H-pole and 4-pole structures with suitable platforms are employed for transformers of capacity up to 25 kVA, 125 kVA and above 125 kVA (but up to 250 kVA) respectively.

4. Draw and estimate material required for 66/11 KV substation with following details:i) Input line 66 KV 2 nos. ii) Transformer 66/11 KV 2 nos of 100 MVA. iii) 4 Nos. of 11 KV outgoing lines 2 on each transformer. Show the position of isolators or protective devices.


(Jan-2016)

Page 47


10EE82

Material Calculation: a) Equipment on primary side i.e., 66 kV: i) GOS, 800A, 66KV grade complete set with earth set: 1 set ii) GOS, 800A, 66KV grade without earth bus: 1 set iii) Transformer 6300 KVA, 66KV/11KV with oil immersed, forced air cooling with on load tap changer: 1 Set b) Equipment on secondary side i.e., 11 kV: i) 11KV class lighting arrestor’s plinth mounted: 6 No’s ii) GOS 400A, 11KV class: 4 set iii) Battery set with charger: 1 set iv) Auxiliary Transformer for station operator 50KVA, 11KV/440V: 1 Set v) Take of structure on 9 m, RCC pole, 11KV class, 4 sets vi) 300 MVA, 1250A switch gear with instrument transformer outdoor type 11KV class: 1 set c) Protecting devices and equipments:


Page 48


10EE82

i) Lightning arrestor’s 66KV class: 2 sets ii) Circuit breaker 66KV class: 1 set iii) PT’s 66KV/110KV: 1 set iv) CT’s 800A/5A, 400A/5A, 200A/5A: 3 No’s v) for relays and controls for transformer: 1 No. vi) for relays and controls for accumulator: 1 No vii) for relays and controls for line: 1 No d) Cable for power control: i) UG cable 11KV class 3 core for feeders 150mm²/240mm²: 300 m ii) UG cable, 11KV class single core 100mm² for banks: 175 m iii) Cable end and terminals 11KV class single core 1000mm² UG cable: 6 No’s

5. List the points to be considered at the time of erection of overhead lines.

(Jun -2015)

At crossings of overhead lines by other overhead lines, the two lines must be kept at the necessary safety distances between the lines and the ground. As a rule, the line with the lower voltage es under the line with higher voltage. Construction workers try to plan these crossings in such a way that their construction is as economical as possible. This is usually done by leaving unchanged the line that is crossed, if possible. Undercrossings of existing lines are often constructed in proximity to the line's pylons, since this can often be accomplished without raising the existing pylons and while keeping the necessary safety distances between the ground and the other line. In the course of undercrossings the pylon picture is frequently changed, and because of its small height it is preferable to create an arrangement with conductors in one level. Sometimes at such crossings there can be problems because of the maximum pylon height allowed for flight safety reasons. If it is not possible at a given location for the pylons of the upper line to be built at a necessary height, the line running below it will be rebuilt on smaller pylons or replaced with an underground cable. Department of EEE, SJBIT

Page 49


10EE82

A unique undercrossing of two powerlines can be found north of Kincardine at Scotland at 56°5'17"N 3°43'11"W. Here crosses the powerline Kincardine-Tealing two other lines. One of the two circuits of Kincardine-Tealing powerline crosses these lines on two small pylons and the other circuit via an underground cable.

6.A pole for an overhead 11KV-3phase , 50Hz line is to be earthed (pipe) & a stay is to be provided.Make a neat sketch showing how it should be done. Prepare a list of materials required

(Jun -2015)

7. Write a short note on conductor erection.

(Jun -2015)

Line s. The s used for transmission and distribution of electrical power must have the characteristics-high mechanical strength, light in weight, low initial as well as maintenance cost, longer life, good looking and easily accessible for painting and erection of line conductors. The line s are of various types including wood, steel, reinforced concrete poles and lattice steel towers. i. Wooden Poles. These are cheapest, easily available, providing insulating properties and therefore, are extensively used for distribution purposes, specially in rural areas, keeping the cost low. Their use is usually limited to low pressures (up to 22 kv) and for short spans (up to 60m). the wooden poles, well impregnated with creosote oil or any preservative compound, have life form 25 to 30 years. The disadvantage of such s is that these need periodical inspection because they tend to rot and their life is short. ii. Steel Poles. The steel poles are of three types (i) rail poles (ii) tubular poles and (ii) rolled steel joists. These poles possess greater mechanical strength and so permit use of longer spans (50-80 m) but cost is higher. The average life of steel poles is more than 40 years. iii. RCC Poles. These give good outlook, need no maintenance, have got insulating properties and resistance against chemical action, very strong and can be used for longer spans (80-200m) and have very long life. Since these poles are very heavy, therefore, transportation cost is heavy and require care in handling and erection. Department of EEE, SJBIT

Page 50


10EE82

iv. Lattic Steel Towers. These are mechanically stronger and have got longer life. Due to robust construction long spans (300 m and above) can be used and are much useful for crossing fields, valleys, railway lines, rivers etc. Even though these are two to four times costlier than wooden poles, yet for tall s and longer span these prove economical. These towers need periodical painting or galvanizing for protection against corrosion. Narrow-base lattice steel towers are used for transmission at 33 kv and broad-base lattice steel towers are used for transmission at 66 kv and above. Conductor materials Properties of Overhead Bare Conductors: Current Carrying Capacity 

Strength



Weight



Diameter



Corrosion Resistance



Creep Rate



Thermal Coefficient of Expansion



Fatigue Strength



Operating Temperature



Short Circuit Current/Temperature



Thermal Stability



Cost

Categories of Overhead Conductors: Homogeneous Conductors: 

Copper



AAC( All Aluminum Conductor)



AAAC (All Aluminum Alloy Conductor)



The core consists of a single strand identical to the outer strands. Since all the strands are the same diameter, one can show that the innermost layer always consists of 6 strands,


Page 51


10EE82

the second layer of 12 strands, etc., making conductors having 1, 7, 19, 37, 61, 91, or 128 strands. Non Homogeneous Conductors: 

ACAR (Aluminum Conductor Alloy Reinforced)



ACSR (Aluminum Conductor Steel Reinforced)



ACSS (Aluminum Conductor Steel ed)



AACSR (Aluminum Alloy Conductor Steel Reinforced.



the strands in the core may or may not be of the same diameter. In a 30/7



ACSR conductor the aluminum and steel strands are of the same diameter. In a 30/19



ACSR they are not. Within the core or within the outer layers, however, the number of strands always increases by 6 in each succeeding layer. Thus, in 26/7 ACSR, the number of layers in the inner layer of aluminum is 10 and in the outer layer 16

Categories of Overhead Conductors 

VR (Vibration Resistance)



Non-Specular



ACSR / SD



(Self Damping)

Choices of overhead depend upon: Power Delivery Requirements 

Current Carrying Capacity



Electrical Losses

Line Design Requirements 

Distances to be Spanned



Sag and Clearance Requirements

Environmental Considerations


Page 52


Ice and Wind Loading



Ambient Temperatures

10EE82

8. A pole for an overhead 11KV , 3-Ohase, 50Hz live is required to be earthed (pipe) & a stay is to be provided . Make a neat sketch showing how it should be done. Prepare a list of materials required.

(Jan -2015)

9. Write short notes on indoor ss? List advantages and disadvantages of outdoor ss over indoor ss.

(Jan -2015)

Air Insulated Substation (AIS) or Outdoor Substations have all switchgear equipment, busbars and other switchyard equipment installed outside open to atmosphere. In earlier days for any voltage ratings AIS or outdoor substation is employed. Indoor Substation type is only employed in places where high pollution or saline environment exists. Indoorsubstations are of two types



Substation with conventional switchgear equipment enclosed in big building. Size of switchyard is similar to AIS Substation.



Substation with SF6 enclosed modules (Gas Insulated Substation) in building which takes about 10% of the total AIS substation space

Because

of excellent

properties

of

SF6

gas

such

as

high

dielectric

strength,

high

electronegativity, for EHV substations more than 230kV now a days Indoor Gas Insulated Substations (GIS) are employed in place of AIS substations. However the cost of GIS indoor substation is higher compared to AIS substation but it has some benefits which includes high reliability, less space requirement and less maintenance. Some of the advantages and disadvantages

of

outdoor

switchyard

is

discussed

below.

Advantages of Outdoor Substation (AIS):


Page 53


10EE82

This type of substation arrangement is best suited for low voltage rating substations (step down substations) and for those substations where there is ample amount of space available for commissioning the equipment of the substation



The construction work required is comparatively less to indoor switch yard and the cost of switchgear installation is also low



In future the extension of the substation installation is easier



The time required for the erection of air insulated substation is less compared to indoor substation



All the equipment in AIS switch yard is within view and therefore the fault location is easier and related repairing work is also easy



There is practically no danger of the fault which appears at one point being propagated to another point for the substation installation because the equipment of the ading connections can be spaced liberally without any appreciable increase in the cost

Disadvantages of Air Insulated Substation (AIS): 

More space is required for outdoor substation when compared to indoor gas insulated substation (GIS)



Outdoor switch yards are more vulnerable to faults as it is located in outside atmosphere which has some influence from pollution, saline environment and other environmental factors. Deposition of saline particles on insulators can cause insulator failures. They are also vulnerable to direct lightning strikes and other external events such as heavy winds, rains and cyclones. Therefore reliability wise air insulated substation or outdoor substations are relatively low compared to indoor substation



Regular maintenance is required compared to indoor substations (Maintenance for Gas Insulated Substation is very minimal and reliability is very high) as they are exposed to outside environment


Page 54


10EE82

10. Estimate the quantity of material required for installation of 132/32KV ss with main & transfer bus scheme having 2 x 40MVA Transformers

(Jan -2015)

SL No

Equipments

Quantity

Unit

1 2 3 4 5 6 7 8 9 10 11 12 13 14 16 17 18 19 20 21 22

a). 132 kV b). 33 kV Line Isolators a). 132 kV b). 33 kV Bus Isolators a). 132 kV b). 33 kV Tendom Isolators 132 kV CTs a). 132 kV b). 33 kV a). 132 kV CVT b). 33 kV PT LA (Lightining Arrestors) a). 132 kV b). 33 kV Post Insulator Transformers a). 132/33 kV, 40 MVA b). 33/4 kV 250 kVA Control a). T/F control and relay b). B/C c). Double feeder d). Distance protection e). 33 kV tripple feeder U/F Relay Energy meter 0.2 acc. Cla(ABT) Control and Power Cable Structures DC equipments ( Protection & Conn) Bus Bar and Insulator S/S and Control Room Lighting Earthmat and Earthing Firefighting equipment Boundary wall, fencing, Control room building Store shed etc. Land (Subject to Actual)

11 2 10 8 15 4 12 33 9 6 12 12 92 2 1 2 1 1 2 3 1 1 LS Provision 60 1 1 (LS Provision)

nos do do do do do do do do do do do do do do do do do do do do do MT set


Page 55


11. Explain the classification of substations.

10EE82

(Jun-2014)

On the basis of design substations may be classified in to (a)Outdoor type i. Pole mounted (single stout pole/ H-type/ 4-pole structure employed for transformers of 25 kVA, 100 kVA and above 100 kVA) ii. Foundation mounted (For transformers above 250 kVA and voltage of 33 kV and above

(b) Indoor type (In this the substation apparatus are installed within the building) Outdoor substation :

When transformers are installed out door, certain clearances must be maintained. • Clearance between supplier’s and consumer’s structure should not be less than 333 meters. This is for maintaining the minimum sectional clearance of 206 m at 11 kV. • Supplier’s and consumer’s structure shall be braced together when the clearance between them is 5 m or less. • The ground clearance of the live parts of CTPT unit shall not be less than 3.7 m. • Phase to phase clearance at the AB switch shall be 915 mm • Phase to earth clearance at the AB switch shall be 610 mm. It is the clearance between the operating rode of the AB switch and the jumpers of 11 kV down conductors • The ed length of 11 kV jumpers shall be limited to 1.5 m for standard conductors and 2.44 m for solid conductors (No. 2 or No. 0 SWG copper). • Where there is a cable end box with open terminations, the clearance of the live pars to ground shall not be less than 305 m • The ground clearance of ht parts, usually 11 kV at the transformer bushings shall not be less than 2.75 m. Department of EEE, SJBIT

Page 56


10EE82

• The ground clearance of AB switch handle shall be between 1 and 1.2 m Indoor Substation :

Indoor substation of 11 kV/415 V are usually installed at industrial areas and other load areas like multistoried buildings, telephone exchange etc. Substation building is constructed for installing transformer, HT and LT etc. Room size should be sufficient, so as to give adequate clearance between wall and various equipments. Suitable ventilation for entry of fresh air at the bottom of transformer room and exit of hot air at top on opposite sides are necessary. The installation of transformer should that the cable boxes are on the sides and not facing the door. The OH line terminates on a DP structure outside the indoor substation. All protection accessories such as AB switch, LA and DO fuse are installed in the DP structure. CT PT unit is installed for connecting metering device. Supply to HT side of transformer is brought through UG cable. Both sides of the transformer are protected by suitable capacity CB. Adequate fire fitting equipment shall be provided at easily accessible positions. Danger notice board should be provided on the HV and MV equipments. 12. Draw and estimate materials required for 66/11KV substation, with foll details : i) Input lines-2, having 66KV ii)Output line-2,66Kv iii) Output line-0, 6 numbers,11KV


(Jun-2014)

Page 57


10EE82

Material calculation for lighting: As the lighting load is more than 800 watts, two circuits are used. First Circuit: Verandah, hall, bed room and kitchen = 780 watts. Second Circuit: Room, Inner Verandah, lavatory and bath = 325 watts. First Circuit: Load current = 780/230 = 3.39 A. Factor of safety = 2. Current to be observed in wire table = 3.39 x 2 = 6.78 A. Therefore 3/22 PVC or VIR Copper wire suitable. Second Circuit: Load current = 325/230 = 1.41 A. Factor of safety = 2. Current to be observed in wire table = 1.41 x 2 = 2.82 A. Therefore 1/18 PVC or VIR copper wire is suitable. Length of Casing and Capping


Page 58

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