Power Quality Lecture Ppt 311b6t

Power Quality • The concept of powering, grounding and protecting electric equipment in a manner that is suitable to the operation of that equipment. • In other words......doing what it takes to keep the electric supply to equipment transparent or unnoticed.

Why is it a Concern? • Power quality problems can cause: – Equipment malfunctions – Excessive wear or premature failure of equipment – Increased costs from downtime – Increased maintenance, repair time and expense – Outside consultant expense

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Why is Equipment Protection Important Today? • Electronic equipment is more sensitive to minor fluctuations. • New electronic loads create conditions that didn’t exist before. • We rely on the equipment more and have higher expectations

Electronic Loads are More Susceptible to Power Problems • New electronic devices are more sensitive than the equipment being replaced. – Lighting systems have electronic ballasts. – Motors have ASD’s or PLC’s – Offices have copiers, computers, faxes and laser printers.

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Electronic Devices Produce Problems

• Electronic devices produce harmonic distortion that degrades the sine wave provided by the utility.

200

60 Cycle Sine Wave

150 100

Voltage

• Utility systems were designed assuming loads were electromechanical...voltage and current would always be sine waves.

50 0 -50

-100 -150 -200 0.0000

0.0083

0.0167

Time (Seconds)

0.0250

• Many electronic devices are susceptible to power quality problems AND a source of power quality problems.

We’re “More Concerned” • Power Quality has been a problem since the conception of electricity, but only over the last 2 decades has it gotten considerable attention. – 1980's: large numbers of computers & microprocessors in business and homes. – 1990's: the network revolution and ever increasing equipment capability and speed.

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Solution Options • Improve the Supply – Utility: Less than a quarter of the problems. – Customer: Not every customer/device needs higher levels.

• Immunize the Equipment (Protection) – Manufacturer: Raises the cost of equipment. – Customer: End use equipment specifications.

• Control the Disturbance (Protection) – Utility: Some disturbances are un-avoidable and part of necessary operations. – Customer: How….and from what?

Electronic Equipment Protection • Backup Power Supplies – Auxiliary power during outages & interruptions. – Work for longer blinks & outages.

• Power Enhancers – Improve the characteristics of power coming in and produce a “clean” supply to the equipment. – No blink or outage protection.

• Power Synthesizers – Combine auxiliary power and “cleaning” capabilities. – Most expensive and highest maintenance.

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What Level is Needed? • Identify and prioritize equipment that is most important to the mission of the facility. – At what level will malfunction or failure cause major disruptions in manufacturing, sales or business processes? • Result in lost or off specification product? • Result in lost productivity? • Jeopardize employee or customer safety?

What Kind of Disturbances Cause Problems? • Interruptions – Outages & Blinks

• Voltage Fluctuations – Voltage Sags & Swells

• Transients – Really Fast Spikes, Surges, etc.

• Waveform Distortion – Harmonics, Noise & Interference

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Interruptions (Outages & Blinks) • Voltage falls below 10% of normal circuit voltage for any length of time. – The power is OFF!!!!!

(+)

Temporary Interruption

– Can be microseconds to hours or days. – If you noticed the lights blink…..chances are the power supplies in most electronic equipment thought the power was shut off. – Some interruptions can be so fast you don’t notice the lights “blink”.

Voltage

• How Long? seconds to minutes

(-) Time

Interruptions (Outages & Blinks) • Protection Options – Need Energy Storage!!!!! – Power Enhancers • Don’t Work…..no energy storage

– Power Synthesizers • • • • •

Battery Backup/Standby Supplies Uninterruptible Power Supply (UPS) Auxiliary Generator UPS with Auxiliary Generator Motor-Generator Sets

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What Should the Equipment Tolerate? • ITE (CBEMA) Curve

• Provides ride-through capability minimums for computing and office equipment. • Some power supplies tolerate levels much than those shown.

Data Processing Susceptibility 300 250

Rated Voltage (%)

– Information Technology Industry Council (formerly Computer & Business Manufacturers Association)

200 150 100 50 0 0.001

0.01

0.1

1

10

100

1000

Disturbance Duration (cycles)

What is a UPS? • Not all UPS systems do the same thing! • Standby Power Supplies (SPS), (Battery Backups) – Provide normal line power to equipment….switch to battery supply when an outage occurs.

• Line Interactive UPS • On-line UPS – Line supplies a rectifier that converts AC to DC, charges the batteries. Batteries supply an inverter that converts DC to AC, filters and regulates it, and supplies the load.

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Un-interruptible Power Supply (UPS) • Provide continuous, uninterrupted AC power from an isolated, regulated source regardless of the quality of the primary AC line. • Can be used for interruptions, sags, swells, and voltage fluctuations. • Some success has also been achieved with impulsive and oscillatory transients, long duration over- and undervoltages and noise.

SPS vs True UPS Devices • It generally takes a few milliseconds for an SPS to switch to the battery backup source. • Effective when the equipment being protected can withstand the transfer time. • SPS’s are less expensive than UPS’s and for most small systems can be used in place of a UPS and still gain “most” of the protection from interruptions/outages.

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SPS Advantage/Disadvantage • Advantages – – – –

Lower cost than a true UPS device. Higher efficiency (less losses) than a true UPS device. Low operating hours on power components. Smaller physical size.

• Disadvantages – No power conditioning during normal operating mode. – Produces short interruption of power to load when switched. – Battery/Inverter problems not detected until critical point in time.

On-Line UPS Advantage/Disadvantage • Advantages – Continuous regulated power to load – Higher system reliability – Excellent output performance for sensitive loads

• Disadvantages – Higher cost – Lower efficiency – Larger physical size

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UPS & Auxiliary Generator • Allows computers & other mission critical equipment to operate during lengthy outages. – Generator starts automatically upon loss of utility power and the source to the UPS will automatically transfer to the generator. – Generators are available that utilize different fuels including gasoline, natural gas, propane or diesel.

Motor-Generator (MG) Sets • An electric motor driving a generator. • Converts electrical energy into mechanical energy and back again to isolate “short” disturbances from the equipment it supplies. – Ride Through

• The mechanical shaft isolates the electrical load from incoming disturbances such as voltage transients, swells and sags.

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MG Sets Advantages/Disadvantages • Advantages – Ride through many shorter interruptions. • Inertia keeps the rotor rotating for 10-15 seconds after the power shuts off which is long enough to ride through a high percentage of problems.

– Long Life – Simple, rugged device – Low harmonic distortion content at all load levels.

• Disadvantages – Will not ride through extended outages. – Degrade and fail gradually over time rather than all at once. – Expensive for smaller systems

Voltage Fluctuations (Sags & Swells) • Sag

Voltage Sag (+)

– Voltage falls below 90% of normal but stays above 10% of normal for any amount of time.

Voltage

Less than 1 minute

• Swell

• If it’s long enough, you notice lights dimming or getting brighter. • Sags are much more common than swells

(-) Time

Voltage Swell (+)

Less than 1 minute

Voltage

– Voltage rises above 110% of normal but below 180% of normal for any amount of time.

(-) Time

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Sags & Swells - Protection Options • Power Enhancers – – – –

Reduced Voltage Starters on large offending motors Voltage Regulators Constant Voltage Transformers (CVTs) Power Conditioners

• Power Synthesizers – Battery Backup Systems (Sometimes) • May not switch fast enough for short duration events.

– UPS – Motor-Generator Set

Voltage Regulators • Maintain voltage output within a desired limit or tolerance regardless how much input voltage varies. – Can offer some surge protection, but do not provide good isolation like computer grade transformers. – Protection against swells or noise and limited protection from fast voltage changes depending upon the response time of the regulator. – Voltage regulators respond best to slow changes in voltage.

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Constant Voltage Transformers (CVT’s) • Also known as ferroresonant transformers.

– Used for sags, swells, longer term over- and under-voltages.

• Especially attractive for constant, low-power loads like electronic controllers (PLC’s) where they provide ride-through capability. • Variable loads, especially those with high inrush currents, (Drives) present more of a problem for CVT’s.

CVT Ride Through

– A common solution is to protect the controls with a CVT. – With the CVT, the controller can ride through most voltage sags…but not an interruption.

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Voltage (%)

• It is not uncommon for electronic controls to trip from voltage sags caused by motor starts.

Ride Through Without CVT's

60 40 Ride Through With CVT's

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0.1

1

10

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1000

Sag Duration (cycles)

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Overvoltages & Transients • Lightning is the nemesis of communication stations, tall structures and other buildings housing sensitive electronic equipment. • Lightning Damage Problems: – Direct strike problems – Swells and transients which can arrive via power, communications or signal lines, even though the lightning strike may be some distance from the building or installation.

Transients - Causes • Distribution System

(+)

Voltage

– Lightning – Switching Operations • Breakers • Capacitors & Transformers

• Customer System – Lightning – Arcing Devices – Starting & Stopping Motors – Breaker Operations – Capacitor Switching

(-) Time (seconds)

Oscillatory Tranients

(+)

Voltage

– Fault Clearing/Breaker Operations

Impulsive Transient

(-) Time

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Lightning Protection • Degree of lightning protection needed in a facility: – Strategic importance of the equipment housed in the facility – Level of strike exposure.

• Effective protection involves the integration of several concepts.

Lightning Protection System • Capture the strike on purpose designed air terminals at designated points. • Conduct the strike to ground safely via purpose-designed downconductors. • Dissipate energy to the earth with minimal rise in potential through a low impedance ground system. • Eliminate earth loops/differentials by creating an equipotential plane system. • Protect equipment from swells and transients on – incoming power lines. – telecommunications and signal lines.

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Transients – Protection Options • Power Enhancers – – – –

Surge Suppressors Lightning Protection/Arrestors Power Conditioning Line Reactors/Chokes

• Power Synthesizers – Standby Power Systems • Provide no protection

– UPS • Limited to low energy transients

– Motor Generator Set

Transient Voltage Surge Suppressors (TVSS) • Simplest, least expensive way to condition power by clamping voltage when it exceeds a certain level and sending it away from the equipment it protects. – Excess voltage is sent to MOVs which convert it to heat which dissipates over time.

• Most effective with impulsive transients and short term swells and have limited success with oscillatory transients.

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Levels of Protection • High Energy Devices = Service – High energy suppressors are installed at service entrances and considered the minimum necessary protection level even if other power conditioners are employed. – Generally clip high voltages to less than 600 volts.

• TVSS Devices = Equipment – Transient voltage surge suppressors (TVSS) can be installed at the terminals of the sensitive electronic loads. – Generally do not do well with high voltage transients like lightning.

Power Line Filters • Suppress transients, swells, and noise before they get to the clipping level of common surge protectors. – Power line filters limit noise and transients to a safe level by slowing down the rate of change of these problems and keeping electronic systems safer than surge protectors can. – EMI/RFI Filters, Line Reactors & Chokes

• More expansive than surge suppressors.

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Waveform Distortion Resultant Waveform

– motors, transformers & wiring overheat – Data errors – Control system errors – Burned circuit boards

• Harmonic Distortion has become a significant issue.

200 150

Voltage

100 50 0 -50 -100 -150 -200 -250

Time

(+)

Line Notching

Voltage

• Harmonic distortion and/or noise created by the operation of electronic devices. • Effects:

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(-)

Time

Waveform Distortion - Causes • Distribution System – Customer produced harmonics feeding back into the distribution system and moving down the line. – EMF and Noise from faulty electrical equipment that is about to fail.

• Customer System – Electronic Office Equipment – Adjustable Speed Drives (ASD’s) – Electronic Control Equipment – Lightning

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Distortion - Protection Options • Power Enhancers – – – – –

Line Reactors/Chokes Harmonic Filters Isolation Transformers Power Conditioners Constant Voltage Transformers

• Power Synthesizers – Backup Power Supply….No protection – Some UPS systems…if large enough, the harmonics cause problems for the UPS. – Motor-Generator Set…motor becomes victim

Line/Load Reactors & Chokes • A type of “Filter”. • These devices are used as protection from oscillatory transients and waveform distortion. • They are increasingly being incorporated into many newer and existing ASD installations.

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Isolation Transformers • Protect sensitive electronic equipment by buffering electrical noise and rejecting common mode line-to-ground noise including harmonic distortion. • Effective at protecting from oscillatory transients, harmonics, noise and in some cases impulsive transients. • Provide a "separately derived" power source and permit single point grounding.

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