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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 un-noticed.

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 DevicesProduce Problems

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

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

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

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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!!!!!

• How Long?– 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”.

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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– Information Technology

Industry Council (formerly Computer & Business Manufacturers Association)

• Provides ride-through capability minimums for computing and office equipment.

• Some power supplies tolerate levels much than those shown.

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Data Processing Susceptibility

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 under-voltages 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 falls below 90% of

normal but stays above 10% of normal for any amount of time.

• Swell– Voltage rises above 110% of

normal but below 180% of normal for any amount of time.

• If it’s long enough, you notice lights dimming or getting brighter.

• Sags are much more common than swells

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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• It is not uncommon for

electronic controls to trip from voltage sags caused by motor starts.– 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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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

– Lightning– Switching Operations

• Breakers• Capacitors & Transformers

– Fault Clearing/Breaker Operations

• Customer System– Lightning– Arcing Devices– Starting & Stopping

Motors– Breaker Operations– Capacitor Switching

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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 down-conductors.

• 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 VoltageSurge 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• Harmonic distortion and/or

noise created by the operation of electronic devices.

• Effects: – motors, transformers &

wiring overheat– Data errors– Control system errors– Burned circuit boards

• Harmonic Distortion has become a significant issue.

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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.