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
Why is Equipment Protection Important Today? • Electroni Electronicc equipmen equipmentt is more sensitive to minor fluctuations. • New electronic electronic loads 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 electronic devices 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.
Electronic Devices Produce Problems • Utility systems were designed assuming loads were electromechanical...voltage and current would always be sine waves.
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60 Cycle Sine Wave
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• Electronic devices produce harmonic distortion that degrades the sine wave provided by the utility.
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• 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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Time (Seconds)
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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.
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
Interruptions (Outages & Blinks) • Voltage falls below 10% of normal circuit voltage for any length of time. – The power is OFF!!!!!
Temporary Interruption (+)
• 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.
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seconds to minutes
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Time
– Some interruptions can be so fast you don’t notice the lights “blink”.
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
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.
Data Processing Susceptibility 300
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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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Disturbance Duration (cycles)
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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.
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
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.
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 (+) Less than 1 minute
– Voltage falls below 90% of normal but stays above 10% of normal for any amount of time.
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• 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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Voltage Swell (+)
Less than 1 minute
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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.
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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Ride Through Without CVT's
Ride Through With CVT's
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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
Impulsive Transient (+)
– Lightning – Switching Operations
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• Breakers • Capacitors & Transformers
– Fault Clearing/Breaker Operations
• Customer System – Lightning – Arcing Devices – Starting & Stopping Motors – Breaker Operations – Capacitor Switching
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Oscillatory Tranients
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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.
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.
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.
Waveform Distortion Resultant Waveform 250
• Harmonic distortion and/or noise created by the operation of electronic devices.
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• Effects: – motors, transformers & wiring overheat
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Line Notching
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– Data errors – Control system errors
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– 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
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.
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.
