Power Quality notes

POWER QUALITY

1 M.SURESH AP/EEE/KEC/PERUNDURAI

What is Power Quality ?What is Power Quality ?What is Power Quality ?What is Power Quality ?� Any power problem manifested in voltages, current, or

frequency deviations that results in failure or disoperation ofcustomer equipment.

� In broadest sense, power quality is a set of boundaries thatallows electrical systems to function in their intendedmanner without significant loss of performance or life.The term is used to describe electric power that drives anelectrical load and the load's ability to function properly withthat electric power. Without the proper power, an electricaldevice (or load) may malfunction, fail prematurely or notoperate at all


IEEE Definition

� Institute of Electrical and Electronic Engineers (IEEE) StandardIEEE1100 defines power quality as “the concept of powering andgrounding sensitive electronic equipment in a manner suitable for theequipment.”

� All electrical devices are prone to failure or malfunction whenexposed to one or more power quality problems. The electricaldevice might be an electric motor, a transformer, a generator, acomputer, a printer, communication equipment, or a householdappliance. All of these devices and others react adversely to powerquality issues, depending on the severity of problems.


TWO DIFFERENT CASESTWO DIFFERENT CASESTWO DIFFERENT CASESTWO DIFFERENT CASES

100 Watts Bulb

� Std. 100 W bulb requires 230 V to produce the required Lumens of light output.

� If Voltage drops 10% ?

� What happens if there is Complete Outage or blackouts ?

� If Voltage raises 10% ?

CRT Monitor of PC

� CRT Monitor for PC uses a 230 V AC Power Supply which is converted in to 5 V DC for logic circuits & high voltage DC to operate CRT.

� If Voltage drops 10% ?

� If Voltage raises 10% ?


POWER QUALITY ISSUESPOWER QUALITY ISSUESPOWER QUALITY ISSUESPOWER QUALITY ISSUESPower Quality Disturbances have been organized into sevencategories based on wave shape:� 1. Transients� 2. Voltage Sag � 3. Voltage Swell � 4. Interruption� 5. Waveform Distortion� 6. Voltage Fluctuations� 7. Frequency Variations









What is a Transient or Surge?What is a Transient or Surge?What is a Transient or Surge?What is a Transient or Surge?A“typical” lightning stroke can carry nearly3 billion kW at approximately 125million volts, with an average current ofmore than 20,000A.

Lightning also produces extremelypowerful, short-duration transientson power distribution systems — either bya direct strike or a near hit.

In most instances, a lightning strike-induced surge on local powerdistribution lines causes damage tosusceptible equipment.

It can also have secondary effects thatcause problems to susceptible electronicequipment in a building. CBs protectingutility lines can trip and then try to reclose.The resulting voltage sags and outagescan cause more problems to computersand other electronic devices than thevoltage transients themselves.13 M.SURESH AP/EEE/KEC/PERUNDURAI

� Continuous surges. These surges, which can range from250V to 1,000V, can come from operation of electricmotors or other inductive loads. Other causes include DCmotor drives, the power electronics of VSDs, DC powersupply switching, and even portable tools.

� Momentary surges. These surges, which can range from250V to 3,000V, can originate from the switching ofinductive loads.When you interrupt an inductor's current,a surge voltage will be generated. Its magnitude is describedby the equation e = L × di/dt,

� The opening and closing of electric motor startersor the use of arc welders and furnace igniters caninduce these surges. When the conductors carrying thesesurge currents are in proximity to conductors of signalingor data circuits, induced voltages will be generated withinthese circuits. The result is the introduction of electricalnoise and loop currents.

� Deenergizing inductive circuits with air-gap switchessuch as relays and contactors, can generate bursts of high-frequency impulses.

What is a Transient or Surge?What is a Transient or Surge?What is a Transient or Surge?What is a Transient or Surge?

Fig: Typical utility capacitor-switchingtransients can reach 134% of nominalvoltage "up line" from the capacitor.



Sources of TransientsSources of TransientsSources of TransientsSources of Transients

� Lightning�� Static�� Arc Welding

� Switching�� Contactor�� Relays�� SCR’s


What is a Transient or Surge?What is a Transient or Surge?What is a Transient or Surge?What is a Transient or Surge?

� A Transient can be classified into two categories,� impulsive and oscillatory Duration < 50 ns to 50 ms

�� .00000005 seconds to .002 seconds�� .000005 seconds to .050 seconds



Transient OvervoltageTransient OvervoltageTransient OvervoltageTransient Overvoltage

� Transient overvoltage are brief, high-frequency increases in voltage on AC mains.


Capacitor Bank SwitchCapacitor Bank SwitchCapacitor Bank SwitchCapacitor Bank Switch



� There are two different types of transient overvoltage:a)low frequency transients : frequency components in the few-hundred-hertz region typically caused by capacitor switching .Low frequency transients are often called "capacitor switchingtransients".

� These transients are caused when a discharged power-factor-correction capacitor is switched on across the line. The capacitorthen resonates with the inductance of the distribution system, typically at400 - 600 Hz, and produce and exponentially damped decayingwaveform. The peak of this waveform, in theory, cannot exceed twicethe peak voltage of the sine wave, and is more typically 120% - 140% ofthe sine peak.



� b)high-frequency transients :frequency components in thefew-hundred-kilohertz region typically caused by lighting andinductive loads turning off. High frequency transients are oftencalled "impulses", "spikes", or "surges".

� Typical rise times are on the order of a microsecond; typicaldecay times are on the order of a tens to hundreds ofmicroseconds. Often, the decay will be an exponential dampedwaveform, with a frequency of approximately 100 kHz, whichcorresponds to the frequency of equivalent inductor/capacitormodel of low voltage power lines. Typical peak voltages for end-useapplications are hundreds of volts to a few thousand volts; severalthousand amps of current may be available.


Voltage Transients - Simulation

In this disturbance, the nominal voltage is increased to high value for a moment during fault, this isgenerated by rapid switching on the source side. In the above circuit the voltage transient is created usingrapid switching by breaker before the bus bar that is on the distribution side has been switched onand off by giving values in the switching times in the block parameters. After simulating we can see theoutput waveform in the scope of the above model.

The above waveform is done by including a negativegain in between the scope and the voltagemeasurement block, here the voltage transient willpersists for only a moment for that moment thevoltage value will be increased to a high value thusit is called voltage transient.


Introduction to the most common Introduction to the most common Introduction to the most common Introduction to the most common

disturbance on AC mainsdisturbance on AC mainsdisturbance on AC mainsdisturbance on AC mainsVoltage Sags (dips) , Voltage Swells and Flickering

� Voltage sags -- or dips which are the same thing -- are brief reductions in voltage,typically lasting from a cycle to a second or so, or tens of milliseconds to hundreds ofmilliseconds. It is caused by abrupt increases in loads such as short circuits or faults,motors starting, or electric heaters turning ON, or they are caused by abrupt increases insource impedance, typically caused by a loose connection

� Voltage swells are brief increases in voltage over the same time range.

Voltage swells are almost always caused by an abrupt reduction in load on a circuit with apoor or damaged voltage regulator, although they can also be caused by a damaged orloose neutral connection.

� Flicker : Random or repetitive variations in the RMS Voltage between 90% and 110% ofnominal can produce a phenomenon known as flicker in lighting equipment24 M.SURESH AP/EEE/KEC/PERUNDURAI

A typical voltage sag

� Voltage sags are the most common power disturbance. At a typical industrial site, it isnot unusual to see several sags per year at the service entrance, and far more atequipment terminals.

� Voltage sags can arrive from the utility; however, in most cases, the majority of sags aregenerated inside a building. For example, in residential wiring, the most commoncause of voltage sags is the starting current drawn by refrigerator and air conditioningmotors.

� Sags do not generally disturb incandescent or fluorescent lighting,motors, or heaters.However, some electronic equipment lacks sufficient internal energy storage and,therefore, cannot ride through sags in the supply voltage. Equipment may be able to ridethrough very brief, deep sags, or it may be able to ride through longer but shallowersags.


Simulation - Sag

� In this disturbance, the nominal voltage is reduced to get the fault period. This is generated bycreating a short circuit for a small period. In the above circuit the sag is created using short circuitby breaker. A load that has been switched ON and OFF by giving values in the switching times inthe block parameters. After simulating we can see the output waveform in the scope of the abovemodel.

The above waveform is done by including anegative gain in between the scope and thevoltage measurement block, here the voltage sagis persists for around 6 cycles you can note thatfor those 6 cycle the voltage value is reduced.


Voltage SwellVoltage SwellVoltage SwellVoltage Swell

� A swell is the reverse form of a sag, having an increase in ACvoltage for a duration of 0.5 cycles to 1 minute’s time. Forswells, high-impedance neutral connections, sudden (especiallylarge) load reductions, and a single-phase fault on a three-phasesystem are common sources.


Simulation - Swell

In this disturbance, the nominal voltage is increased to get the fault period. In the above circuit the swell is createdusing rapid switching by breaker. A load that has been switched ON and OFF by giving values in the switching timesin the block parameters.After simulating we can see the output waveform in the scope of the above model.

The above waveform is done by including a negativegain in between the scope and the voltage measurementblock, here the voltage swell is persists for around 6cycles you can note that for those 6 cycle the voltagevalue is increased.




A Practical Approach

Induction Motor

� Voltage sags typically are due to starting on large loads,such as an electric motor or an arc furnace. Induction motorsdraw starting currents ranging between 600 and 800% oftheir nominal full load currents. The current starts at the highvalue and tapers off to the normal running current in about2 to 8 sec, based on the motor design and load inertia.Depending on the instant at which the voltage is applied to themotor, the current can be highly asymmetrical.



� Figure 1.contains the waveform of the starting current of a 50-hp induction motor with arated full-load current of 60 A at 460 V AC. During the first half of the cycle, theasymmetrical current attains a peak value of 860 A. When the circuit feeding the motorhas high impedance, appreciable voltage sag can be produced.

FIGURE .1Motor-starting current waveform. A 50-hp motor was started across the line. The motor full-load current was 60 A. The first half-cycle peak reached a value of 860 A.



� Figure 2 shows a 100-kVA transformer feeding the 50-hp motor just described. If thetransformer has a leakage reactance of 5.0%, the voltage sag due to starting this motor iscalculated as follows:

� Full load current of the 100-kVA transformer at 480V = 120 A.

� Voltage drop due to the starting inrush = 5.0 × 860 ÷(120 × √2) = 25.3%

� If the reactance of the power lines and the utility transformer feeding this transformerwere included in the calculations, the voltage sag would be worse than the value indicated.It is not difficult to see that any device that is sensitive to a voltage sag of 25% would beaffected by the motor starting event..33 M.SURESH AP/EEE/KEC/PERUNDURAI

Practical Approach

Arc FurnaceAn electric arc furnace is a system that heats charged material by means of an electric

arc. Arc furnaces range in size from small units of approximately one ton capacity used infoundries for producing cast iron products, up to about 400 ton units used for secondarysteelmaking (arc furnaces used in research laboratories and by dentists may have a capacityof only a few dozen grams). Temperatures inside an electric arc furnace can rise toapproximately 1800 degrees Celsius



Electric Arc

Graphite Electrode


A Practical ApproachArc furnaces are another example of loads that can produce large voltage sags inelectrical power systems. Arc furnaces operate by imposing a short circuit in a batchof metal and then drawing an arc, which produces temperatures in excess of 10,000°C,which melt the metal batch. Arc furnaces employ large inductors to stabilize the currentdue to the arc. Tens of thousands of amperes are drawn during the initial few seconds ofthe process

FIGURE

Typical current draw by arc furnace at the primary transformer. Large current fluctuations normally

occur for several seconds before steady state is obtained37 M.SURESH AP/EEE/KEC/PERUNDURAI

� Due to the nature of the current drawn by the arc furnace, which isextremely nonlinear, large harmonic currents are also produced. Severe voltagesags are common in power lines that supply large arc furnaces, which aretypically rated in the 30- to 50-MVA range and higher.

� Arc furnaces are operated in conjunction with large capacitor banks andharmonic filters to improve the power factor and also to filter theharmonic frequency currents so they do not unduly affect other powerusers sharing the same power lines.

� Utility faults are also responsible for voltage sags. Approximately 70% ofthe utility-related faults occur in overhead power lines. Some commoncauses of utility faults are lightning strikes, contact with trees or birds andanimals, and failure of insulators. The utility attempts to clear the fault byopening and closing the faulted circuit using reclosers, which can requirefrom 40 to 60 cycles. The power line experiences voltage sags or total lossof power for the short duration it takes to clear the fault.



Voltage Sag @ Refinery – Utility Fault

FIGURE :Voltage sag at a refinery due to a utility fault. The sag caused the programmable logic controller to drop out, which resulted in interruption of power. The sag lasted for approximately 21 cycles.


FIGURE : Voltage sag caused by utility switching at an aluminum smelter. The sag lasted for five cycles and

caused motor controllers to drop out.

Voltage Sag @ Al. Smelter – Utility Fault


Voltage sag due to generator step Voltage sag due to generator step Voltage sag due to generator step Voltage sag due to generator step

load applicationload applicationload applicationload application

FIGURE :Voltage sag due to generator step load application. The nominal 480-V generator bus experienced a sag to 389 V that lasted for approximately 1 sec.


Voltage swell due to step load rejectionVoltage swell due to step load rejectionVoltage swell due to step load rejectionVoltage swell due to step load rejection

FIGURE :Voltage swell due to step load rejection. The nominal 480-V generator bus experienced a rise to 541 V that lasted for approximately 18 cycles.


InterruptionsInterruptionsInterruptionsInterruptions

An interruption is defined as the complete loss of supply voltage or load current.Depending on its duration, an interruption is categorized as instantaneous,momentary, temporary, or sustained. Duration range for interruption types are asfollows:

� Instantaneous - 0.5 to 30 cycles

� Momentary - 30 cycles to 2 seconds

� Temporary - 2 seconds to 2 minutes

� Sustained greater than 2 minutes

The causes of interruptions can vary, but are usually the result of some type of electricalsupply grid damage, such as lightning strikes, animals, trees, vehicle accidents,destructive weather (high winds, heavy snow or ice on lines, etc.), equipment failure, ora basic circuit breaker tripping.This interruptions can be observed in the above fig.

An interruption, whether it is instantaneous, momentary, temporary, or sustained, cancause disruption, damage, and downtime, from the home user up to the industrial user.A home, or small business computer user, could lose valuable data when information iscorrupted from loss of power to their equipment.

Fig - Momentary interruption


Momentary InterruptionsMomentary InterruptionsMomentary InterruptionsMomentary Interruptions


OutageOutageOutageOutage


Interruptions Interruptions Interruptions Interruptions ---- SimulationSimulationSimulationSimulation

In this disturbance, the nominal voltage will be zero for a period of time, this is generated by rapid switching onthe source side. In the above circuit the voltage interruption is created using rapid switching by breaker beforethe bus bar that is on the distribution side has been switched on and off by giving values in the switching times inthe block parameters.After simulating we can see the output waveform in the scope of the above model.

The above waveform is done by including a negative gain inbetween the scope and the voltage measurement block, herethe voltage interruption will persists for only a period of timefor that period the voltage value will be zero thus it is calledvoltage interruption or outages.


Causes of Sag, Interruptions Causes of Sag, Interruptions Causes of Sag, Interruptions Causes of Sag, Interruptions

OutagesOutagesOutagesOutages


Simplified Utility SystemSimplified Utility SystemSimplified Utility SystemSimplified Utility System


ExampleExampleExampleExample


Simplified Utility SystemSimplified Utility SystemSimplified Utility SystemSimplified Utility System


Waveform DistortionWaveform DistortionWaveform DistortionWaveform Distortion

There are five primary types of waveform distortion:

� 1. DC offset� 2. Harmonics� 3. Interharmonics� 4. Notching� 5. Noise


DC offsetDC offsetDC offsetDC offsetDirect current (DC) can be induced into an AC distribution system, often due to

failure of rectifiers and Geo Magnetic disturbances ( GMD).

It adds unwanted current to devices already operating at their rated level. Overheatingand saturation of transformers can be the result of circulating DC currents. When atransformer saturates, it not only gets hot, but also is unable to deliver full power to theload, and the subsequent waveform distortion can create further instability in electronicload equipment. Fig shows the DC offset

The solution to dc offset problems is to replace the faulty equipment that is thesource of the problem. Having very modular, user replaceable, equipment can greatlyincrease the ease to resolve dc offset problems caused by faulty equipment, with lesscosts than may usually be needed for specialized repair labor.


What are Harmonics?What are Harmonics?What are Harmonics?What are Harmonics?

Harmonics are sinusoidal voltages orcurrents having frequencies that aremultiples of the frequency at which thesupply system is designed to operate, thatcombine with the fundamental voltage orcurrent, and produce waveform distortion.


HarmonicsHarmonicsHarmonicsHarmonics� Harmonic distortion is the corruption of the fundamental sine wave at

frequencies that are multiples of the fundamental. (e.g., 150Hz is the thirdharmonic of a 50Hz fundamental frequency; 3 X 50 =150).

� Symptoms of harmonic problems include overheated transformers,neutral conductors, and other electrical distribution equipment, as well asthe tripping of circuit breakers and loss of synchronization on timingcircuits that are dependent upon a clean sine wave trigger at the zerocrossover point. Fig shows the waveform distortion

Fig: Harmonic Waveform Distortion54 M.SURESH AP/EEE/KEC/PERUNDURAI

A Pure Sine WaveA Pure Sine WaveA Pure Sine WaveA Pure Sine Wave


Fundamental with 5Fundamental with 5Fundamental with 5Fundamental with 5thththth harmonicsharmonicsharmonicsharmonics


Distortion produced by 5Distortion produced by 5Distortion produced by 5Distortion produced by 5thththth order order order order


Fundamental with 7Fundamental with 7Fundamental with 7Fundamental with 7thththth harmonicsharmonicsharmonicsharmonics


Distortion produced by 7Distortion produced by 7Distortion produced by 7Distortion produced by 7thththth order order order order


Fundamental with 5th & 7thHarmonics


Creation of Non Linear Wave formCreation of Non Linear Wave formCreation of Non Linear Wave formCreation of Non Linear Wave form





Potential sources of HarmonicsPotential sources of HarmonicsPotential sources of HarmonicsPotential sources of Harmonics• SMPS• Dimmers• Current regulators• Power electronic converters• Low power consumption lamps• Arc welding machines• Induction motor with irregular magnetizing current

associated with saturation of the iron• All equipment with built-in switching devices or with

internal loads with non-linear voltage/current characteristics



Causes for Harmonic Distortion

Harmonic distortion has been a significant problem with IT equipment in the past, dueto the nature of switch-mode power supplies (SMPS). These non-linear loads, andmany other capacitive designs, instead of drawing current over each full half cycle, “sip”power at each positive and negative peak of the voltage wave. The return current,because it is only short-term, (approximately 1/3 of a cycle) combines on the neutralwith all other returns from SMPS using each of the three phases in the typicaldistribution system. Instead of subtracting, the pulsed neutral currents add together,creating very high neutral currents, at a theoretical maximum of 1.73 times themaximum phase current. An overloaded neutral can lead to extremely high voltages onthe legs of the distribution power, leading to heavy damage to attached equipment. At thesame time, the load for these multiple SMPS is drawn at the very peaks of each voltagehalf-cycle, which has often led to transformer saturation and consequent overheating.Other loads contributing to this problem are variable speed motor drives, lightningballasts and large legacy UPS systems. Methods used to mitigate this problem haveincluded over-sizing the neutral conductors, installing K-rated transformers, andharmonic filters.



Why Worry?Why Worry?Why Worry?Why Worry?


Why Worry?Why Worry?Why Worry?Why Worry?


IEEE Harmonic StandardsIEEE Harmonic StandardsIEEE Harmonic StandardsIEEE Harmonic Standards

Bus voltage at Bus voltage at

PCCPCC

Individual Individual

voltage voltage

distortion (%)distortion (%)

THD (%)THD (%)

69 KV & below69 KV & below 3.03.0 5.05.0

69.001KV 69.001KV --

161KV161KV

1.51.5 2.52.5

161.001KV & 161.001KV &

aboveabove

1.01.0 1.51.5

71M.SURESH AP/EEE/KEC/PERUNDURAI

HarmonicsHarmonicsHarmonicsHarmonics� The electric power distribution system is designed to operate with sinusoidal voltages and

currents. But not all waveforms are sine waves. Electronic loads, for example, often drawcurrent only at the peak of the voltage waveform, which always means that the current isdistorted, and may distort the voltage as well. One convenient way to describe thesewaveforms is to make a list of sine waves that, when added together, reproduce thedistorted waveform. The sine waves in this list are always multiples, or harmonics, of thefundamental frequency (50 Hz or 60 Hz).

A typical input circuit of a single-phase supply.

A typical distorted current waveform, drawn by the supply above. Itonly draws current at the peak of the voltage waveform, because thediodes in BR1 only conduct when the AC voltage is higher than thevoltage on C1.

This is the same waveform, expressed as a frequency spectrum. Note that the frequency content of the waveform consists of odd multiples (3,5,7,9, etc.) of the fundamental. This is typical for electronic loads.


InterharmonicsInterharmonicsInterharmonicsInterharmonics

� Interharmonics are a type of waveform distortion that are usually the result of a signal imposed on the supply voltage by electrical equipment such as static frequency converters, induction motors and arcing devices. Cycloconverters (which control large linear motors used in rolling mill, cement, and mining equipment), create some of the most significant interharmonic supply power problems. These devices transform the supply voltage into an AC voltage of a frequency lower or higher than that of the supply frequency. Interharmonics can be clearly seen in fig

� The most noticeable effect of interharmonics is visual flickering of displays and incandescent lights, as well as causing possible heat and communication interference.

Fig .Interharmonic Waveform Distrotion

� Solutions to interharmonics include filters, UPS systems, and line conditioners.73 M.SURESH AP/EEE/KEC/PERUNDURAI


Harmonics are bad!

� Excessive losses and heating in motors, transformers and capacitors connected to the system

� Insulation failure due to overheating and over voltages� Malfunctioning of sophisticated electronic equipments

� Over loading and over heating of neutral conductors with loss of conductor life and possible risk of fire

� Saturation of transformers

� Interference with communication network


NotchingNotchingNotchingNotchingNotching is a periodic voltage disturbance caused by electronic devices, such as variable speed drives, light dimmers and arc welders under normal operation. This problem could be described as a transient impulse problem, but because the notches are periodic over each ½ cycle, notching is considered a waveform distortion problem. The usual consequences of notching are system halts, data loss, and data transmission problems. It can be seen clearly in fig

Fig - Notching

One solution to notching is to move the load away from the equipment causing the problem (if possible). UPSs and filter equipment are also viable solutions to notching if equipment cannot be relocated.76 M.SURESH AP/EEE/KEC/PERUNDURAI


NoiseNoiseNoiseNoiseNoise is unwanted voltage or current superimposed on the power system

voltage or current waveform. Noise can be generated by power electronic devices,control circuits, arc welders, switching power supplies, radio transmitters and so on.Poorly grounded sites make the system more susceptible to noise. Noise can causetechnical equipment problems such as data errors, equipment malfunction, longtermcomponent failure, hard disk failure, and distorted video displays. Fig . shows thenoise in the waveform.

There are many different approaches to controlling noise and sometimes it isnecessary to use several different techniques together to achieve the required result.Some methods are:

� • Isolate the load via a UPS

� • Install a grounded, shielded isolation transformer

� • Relocate the load away from the interference source

� • Install noise filters

� • Cable shielding


Voltage FluctuationsVoltage FluctuationsVoltage FluctuationsVoltage Fluctuations

� Since voltage fluctuations are fundamentally different from the rest of the waveformanomalies, they are placed in there own category. A Voltage fluctuation is asystematic variation of the voltage waveform or a series of random voltagechanges, of small dimensions, namely 95 to 105% of nominal at a low frequency,generally below 25 Hz.This can be clearly seen in fig.

Fig -Voltage Fluctuation

� Any load exhibiting significant current variations can cause voltage fluctuations.Arc furnaces are the most common cause of voltage fluctuation on the transmissionand distribution system. One symptom of this problem is flickering of incandescentlamps. Removing the offending load, relocating the sensitive equipment, or installingpower line conditioning or UPS devices, are methods to resolve this problem.


Frequency VariationsFrequency VariationsFrequency VariationsFrequency Variations

� Frequency variation is extremely rare in stable utility power systems, especially systemsinterconnected via a power grid. Where sites have dedicated standby generators or poor powerinfrastructure, frequency variation is more common especially if the generator is heavily loaded.IT equipment is frequency tolerant, and generally not affected by minor shifts in local generatorfrequency. What would be affected would be any motor device or sensitive device that relies onsteady regular cycling of power over time. Frequency variations may cause a motor to run fasteror slower to match the frequency of the input power. This would cause the motor to run inefficientlyand/or lead to added heat and degradation of the motor through increased motor speed and/oradditional current draw. Frequency variations can be seen in fig

Fig - Frequency Variation

� To correct this problem, all generated power sources and other power sources causing the frequencyvariation should be assessed, then repaired, corrected, or replaced.



DurationDurationDurationDuration

� ��Transient or Surge (Impulse)

� ��Transient or Surge (Oscillatory)

� �� Sag

� �� Swell

� �� Momentary Interruption

� �� Interruption

� �� Outage

� �� Harmonics

� �� Unbalance

� �� .00000005 -- .002 sec

� �� .000005 -- .050 sec

� �� .008 -- 1 min

� �� .008 -- 1 min

� �� .008 -- 3 sec

� �� 3 sec to 1 min

� �� Greater than 1 min

� �� Steady State Condition

� �� Steady State Condition


Customized SolutionsCustomized SolutionsCustomized SolutionsCustomized Solutions








FlickerFlickerFlickerFlicker� Flicker is a very specific problem related to human perception and incandescent light bulbs.

It is not a general term for voltage variations. Humans can be very sensitive to light flicker that is caused by voltage fluctuations.Human perception of light flicker is almost always the limiting criteria for controlling small voltage fluctuations. The figure illustrates the level of perception of light flicker from a 60 watt incandescent bulb for rectangular variations. The sensitivity is a function of the frequency of the fluctuations and it is also dependent on the voltage level of the lighting.


Voltage RegulationVoltage RegulationVoltage RegulationVoltage Regulation

� The term "voltage regulation" is used to discuss long-term variations in voltage. It does not include short term variations, which are generally called sags, dips, or swells.

� The ability of equipment to handle steady state voltage variations varies from equipment to equipment. The steady state voltage variation limits for equipment is usually part of the equipment specifications. The Information Technology Industry Council (ITIC) specifies equipment withstand recommendations for IT equipment according to the ITI Curve (formerly the CBEMA curve). The 1996 ITI Curve specifies that equipment should be able to withstand voltage variations within +/- 10% (variations that last longer than 10 seconds).


Other DisturbancesOther DisturbancesOther DisturbancesOther Disturbances� The most common disturbances on AC power systems are voltage sags or dips. Other

problems, such as transient overvoltage and brief interruptions, occur almost everywhere. Problems with harmonics, voltage regulation, and flicker occur at a wide range of sites. Some other disturbances that occur at specific locations include:

� Frequency variations. On utility grids, these are rare events, usually associated with catastrophic collapses on the grid. However, at sites with back-up diesel generators, they are common.

� High frequency noise.This can be caused by anything from arcing brushes on a motor, to local radio transmitters.

� Mains signaling Some utilities intentionally place small signals on the mains voltage to act as control signals (for example, they may control a capacitor switch, or they may instruct revenue meters to go to a different rate structure).

� EFT Extremely Fast Transients are nano-second range transient overvoltage. Due to their high frequency content, they do not travel well over the mains circuits, getting damped out within a few meters. However, they can be caused by nearby contact arcing.

� Unbalance On three-phase systems, the voltages and currents on each phase should, in theory, match the voltages and currents on the other phases. Sometimes they don't.89 M.SURESH AP/EEE/KEC/PERUNDURAI

IEEE PQ Standards


Electromagnetic Compatibility

� Electromagnetic compatibility is the capability of electrical and electronic systems,equipments, and devices to operate in their intended electromagnetic environmentwithin a defined margin of safety, and at design levels or performance, withoutsuffering or causing unacceptable degradation as a result of electromagneticinterference.

Eg: Switching off your electronics devices when you are taking a flight

� As more electronics products e.g. handphones, radio transmitters, solid stateswitching devices, motor drives devices are developed and push to the market, theincrease of electromagnetic pollution is on the rise everyday. These devices causedemissions to the environment where it was used.

� As a result of these emissions, they will affect other electronic equipment which issusceptable to these emissions. As more microprocessors are used to replace analog ormechanical means of a product, it become apparent that the issue of EMC cannot beignored. Ignoring this will caused the product to suddenly malfunction or even causeddamage to properties or lives.


EMC StandardIn order to ensure that the equipments are designed to perform as close as possible in its environment,

the European standards making body CENELEC(European Committee for Electrotechnical Standardization) has been mandated to produce standards for use with the European EMC Directive. For telecommunications equipment ETSI(European Telecommunications Standards Institute) is the mandated standards body.

There are 3 types of standards :

� a) Product or product family standards, relating to a specific product or product family group. The product standards take precedence over the generic standards and are drafted to cover the particular range of product types. These standards should refer to the Basic Standards for test methods wherever possible. It wil consist of defining what tests to carry out, what levels or limits, and what operating conditions and performance criteria to apply. These are prepared by IEC, CENELEC or CISPR.

� b) Generic Standards relating to a particular environment of use. At present these are for: (i) Domestic, Commercial and Light Industry (ii) Industrial environment

� c) Basic Standards, to provide general information and relate to the disturbing phenomena and testing and measuring techniques. Basic standards do not contain limits or performance criteria. They serve as a reference for product standards and will not normally be listed in the Official Journal, but will be referred to in product or generic standards.


EMC Standard

List of Product Standards related to household electrical appliances

� i) EN 55014 Limits and methods of measurements of radio disturbance charateristics of household electrical appliances, portable tools, and similar electrical apparatus (CISPR 14).

� ii) EN 55015 Limits and methods of measurement of radio disturbance characteristics of electrical lighting and similar equipment (CISPR 15).

� iii) EN 55104 Electromagnetic compatibility - immunity requirements for household appliances, tools and similar apparatus (CSIPR 14-2)

Generic Standards - Emissions

� i) EN 50081 Part 1 Generic emission standard, part 1: Residential, commercial and light industry environment.

� ii) EN 50081 Part 2 Generic emission standard, part 2: Industrial environment.

Generic Standards - Immunity

� i) EN 50082 Part 1 Generic immunity standard, part 1: Residential, commercial and light industry environment.

� ii) EN 50082 Part 2 Generic immunity standard, part 2: Industrial environment93 M.SURESH AP/EEE/KEC/PERUNDURAI

EMC Standard� Basic Standards

� i) EN 61000-3-2 Electromagnetic compatibility (EMC). Limits. Limits for harmonic current emissions (equipment input current up to and including 16 A per phase)

� ii) EN 61000-3-3 Electromagnetic compatibility (EMC). Limits. Limitation of voltage changes, voltage fluctuations and flicker in public low-voltage supply systems, for equipment with rated current 16 A per phase and not subject to conditional connection.

� iii) EN 61000-4-1 Electromagnetic compatibility (EMC). Testing and measurement techniques. Overview of IEC 61000-4 series.

� iv) EN 61000-4-2 Electromagnetic compatibility (EMC). Testing and measurement techniques. Electrostatic discharge immunity test. Basic EMC publication.

� v) EN 61000-4-3 Electromagnetic compatibility (EMC). Testing and measurement techniques. Radiated, radio-frequency, electromagnetic field immunity test.

� vi) EN 61000-4-4 Electromagnetic compatibility (EMC). Testing and measurement techniques. Electrical fast transient/burst immunity test. Basic EMC publication.

� vii) EN 61000-4-5 Electromagnetic compatibility (EMC). Testing and measurement techniques. Surge immunity test.

� viii) EN 61000-4-6 Electromagnetic compatibility (EMC). Testing and measurement techniques. Immunity to conducted disturbances, induced by radio-frequency fields.

� ix) EN 61000-4-7 Electromagnetic compatibility (EMC). General guide on harmonics and interharmonics measurements and instrumentation, for power supply systems and equipment connected thereto.

� x) EN 61000-4-8 Electromagnetic compatibility. Testing and measurement techniques. Power frequency magnetic field immunity test. Basic EMC publication.

� xi) EN 61000-4-9 Electromagnetic compatibility (EMC). Testing and measurement techniques. Pulse magnetic field immunity test. Basic EMC publication.

� xii) EN 61000-4-10 Electromagnetic compatibility (EMC). Testing and measurement techniques. Damped oscillatory magnetic field immunity test. Basic EMC publication.

� xiii) EN 61000-4-11 Electromagnetic compatibility (EMC). Testing and measurement techniques. Voltage dips, short interruptions and voltage variations immunity tests.

� xiv) EN 61000-4-12 Electromagnetic compatibility (EMC). Testing and measurement techniques. Oscillatory waves immunity test. Basic EMC publication.


The Bigger Picture


The Bigger Picture





Power Quality notes

Documents