Technical Paper – Tushar Mogre (Director- TAS PowerTek … PQ compensation systems.pdf ·...

Technical Paper – Tushar Mogre (Director- TAS PowerTek P. Ltd)

Technical Paper – Benchmarking of PQ systems and various types of systems.

Power Quality (PQ) Improvement Systems on LT distribution:Benchmarking of PQ and Various methods & merits.

Abstract

Various aspects of Power Quality need to cater to issueslike:

Voltage Sags and Swells. Momentary mains cycles loss. Voltage surges and High frequency noise /

disturbance (sometimes called as transients orglitches)

Current surges and high fluctuation of loadcurrent (normally reflects onto voltage problems)

Current Harmonics and consequential VoltageHarmonics.

Inter-harmonics on Current and Voltages. Neutral floating or shifting. Earthing Problems. Power Outages and effect of Auto-Reclose

system. Load Shedding (Specifically with countries

where demand is much higher than generation) Power frequency Variations.

And some issues that are indirectly related to PowerQuality:

Reactive Power Compensation issues. Load unbalance between the phases and

Neutral loading. System Resonance – Parallel and Series. Maximum Demand control (kVA demand and

kW demand).

There are widespread efforts to make a system that isable to take care of all these issues through “UnifiedPower Quality Compensation System”. Unfortunately, theissues are many and each one requires a specializedapproach to take care of them. Additionally, if one tries totake care of all the issues in one system, it causes thesystem cost to go up causing economic issues.

These PQ issues too are dependent upon the ElectricalLoad types. Various types of industries, commercialcomplexes, urban household loads, rural electrical loadrequirements etc. are causing PQ issues of various types.But all the issues are never seen to be present at every LTinstallation. Only, few of the above mentioned issues maybe present on a specific given installation. Thus, it is seenthat instead of usage of Unified Control System whichdoes not fit into economics, most of the installations preferto cater to the specific PQ issues. This necessitates theusage of various systems that caters to one or few specificPQ issues present on a given specific installation.

Most of the Power Quality Audits, concentrate onmeasurement and the specific issues. Unfortunately, avery less emphasis is seen in such audit reports on thetype of systems to be used for taking care of the issues.Thus, concerned personnel have no option but to dependupon the various manufacturer’s for supply of suchsystems. Most of the suppliers to suit their product rangegive various glorified pictures. The best approach for everyinstallation has to first undergo the “PQ Benchmarking”process first by identifying the issues present on theinstallation. Then, has to specify the “GuaranteedTechnical Particulars” (GTP) of the product they wish toinstall for taking care of the PQ issues. After defining theGTP, the specific supplier’s products are to be evaluateddepending upon the benchmarking requirements. This canavoid purchase of system with unwanted features as wellas economics is maintained.

For a specific installation, Benchmarking is extremelyimportant. Some PQ issues may be present on theinstallation but all of them need not be necessarilyaddressed; as these may not cause any undesirable effecton the specific installation. The issues that really causethe problems too can be neglected if brought withinspecific limits. For this purpose, simple approach can workmany times as compared to usage of sophisticated PQcompensation equipments. Unfortunately, the PQcompensation equipment manufacturers too are manytimes approached for such benchmarking process andsuch benchmarking created is normally to suit the specificmanufacturer rather than the specific system needs.

If the Benchmarking is generated based upon theinstallation requirements, the specific type or types ofsystem/s specifications can guide the user to select theright type of system for their need. The approach of thisTechnical Paper is to create awareness about the rightapproach towards PQ needs and to introduce varioustypes of systems that can be used for specific need of PQissue/s.

In this technical paper, author wishes to highlight thebenchmarking approach and various types of systems fortheir applicability towards the earlier defined PQ issuesalong with their merits and demerits.

Now days, there are various types of systems that areavailable for taking care of more than one PQ issues.These are normally the part of FACTS product family. Still,the old approach of passive component approach is stilleconomical and can bring the results set by benchmarkingin many electrical installations.

The various systems for Voltage stability gives specificdescription about the systems like:

Solid state voltage stabilizers Servo control stabilizers On load Tap Changers for Transformers CVT – Constant Voltage Transformers. UPS – Uninterrupted Power Supply systems. Series boost – buck converter. High speed Thyristorised Power Factor

Correction (reactive power compensation)system.

The types of approach used normally for Mains Cyclesloss and momentary Power Outages with Auto Reclosesystems are:

Ferro resonant Transformers. UPS – Uninterrupted Power Supply systems. Synchronous generators with fly-wheel.

For Voltage Surges and transients: Lightning Arresters. Usage of Earth conductor over open distribution

lines. Usage of MOVs (Metal Oxide Varistors) – High

Power and normal grade. Capacitor filters, Low pass filters like T, L and Pi

filters. Zero Voltage Capacitor switching and

synchronous switching of loads.

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Shielding with differential and common modedisturbance filtering like low impedance powerconditioning.

For Current and Voltage Harmonics and Inter-Harmonics: Passive L-C shunt tuned and partially tuned

filters Low pass filters for 6-pulse converter type

systems like AC/DC drives & UPS. Usage of 12 pulse converters. Z-Winding Transformers for taking care of

triplen harmonics. Active filters – Static Synchronous

Compensators (STATCOM)

For Neutral Shifting and Earthing: Earthing grid enhancement. Usage of Isolation Transformer.

Additionally, for indirect issues of Power Quality, Thesystems that are used:

For Reactive Power Compensation: Usage of Auto PF correction systems (Normal

speed and High speed using thyristorisedswitching) or Static VAR correction systems.

Static Condensers (STATCON). Usage of appropriate rating capacitors.

For Unbalanced Loading: Passive Load balancing system – Fixed and

Dynamic. STATCOM system also offers this additional

feature. Individual phase Power factor correction

system.

System Resonance: Such phenomenon are quite rare onLT distribution. Still, in case of such phenomena seen,approach is towards adjustment of passive elements likeCapacitors and Reactors values and positioning inelectrical system.

Maximum Demand Control: Usage of maximum demand controller system.

Load Shedding (specifically with countries with wide –vegap between supply generation and demand.The issue in such case is complex and depending uponthe need, various types of systems have been designed insuch countries. This paper also briefly looks into suchsystem design and the related specific issues.

As can be seen in the systems listed above, some of thesystems are appearing in multiple types of PQ issues.Thus, termed as an Unified approach.

Details of all the stated issues in this Abstract are lookedinto the main technical paper.*****





Power Quality (PQ) Improvement Systems on LT distribution:Benchmarking of PQ and Various methods & merits.

The term – “PQ” on the electrical supplysystem has number of aspects to look into.The solutions to the various aspects of PQ aredifferent for different aspects. These aredepending upon the nature of the PQ issues.

Additionally, the electrical supply systemshave various needs in terms of PQ dependingupon the application requirement. Very little isspoken about the issues faced by industries aswell as other varieties of electrical consumers,which primarily uses the equipments runningon the LT supply system. (Voltage range of110Vac to 1000Vac). Every type of equipmentworking on electricity is designed with keepingin mind the level of adversities on electricalsupply system. Thus, for such equipments towork satisfactorily, the PQ benchmarkingshould be at better level than the equipmentdesign parameters for such adversities (PQissues) on supply system.

Most of the standards talk about maintainingthe PQ standards such that whatever oneconsumer of electricity does with regards tocreating any adversities on electrical supplysystem, the other consumers should not getaffected. Normally, the issue is alwaysdiscussed at PCC (Point of CommonCoupling). This is the view point from supplysystems utility that has primary responsibilityof giving the clean power to their consumers.But, what happens within a specific installationfor a consumer is always left to the discretionof the consumer provided such consumer isnot creating the PQ problems for otherconsumers. Thus, primary target for theconsumer is always to meet the requirementsas specified by electricity supply utility or isspecified by certain internationally knownstandards. Still, the electrical consumers aftermeeting this requirement give little attention totheir internal needs on PQ standards. Thisunknowingly causes losses to them.

It’s important for consumers to know thebenchmarking requirements of PQ dependingupon the need of their installation. Sometimes,the needs to improve PQ may not exist at all ifthe PQ issues that may be existent on supplyline may be well within the limits of thebenchmarking standards. Sometimes, ifconsumer meets the requirements of PQ forsupply utility needs, the internal benchmarkingstandards still can be exceeded. In such case,

even though there is no pressure fromelectrical utility, one has to look intoimprovement of PQ within the consumer areaso as to reduce the in house losses caused.Thus, in-house benchmarking on PQ issues isan important topic, even though in most of thecases it is neglected.

The approach towards PQ benchmarking withLT distribution within an installation is bestcarried out at the time of new installationwhere one can have a good control over theelectricity consuming equipment specificationsand is aware about the PQ issues that arepresent from Supply Utility side.But, with the consumers having existinginstalled equipments, the equipment changefor meeting the benchmarking is not a viableproposal due to economic aspect. In suchcase, depending upon the needs, thebenchmarking of PQ improvement equipmentselection based upon the exact needs seemsto be the right approach.

First, the benchmarking methods can bediscussed herein and further the variousequipments that can be selected based uponthe benchmarking needs and equipmentcapabilities can be discussed.





LT Electricity Consumer PQ Benchmarkingprocess:

The benchmarking process within a specificinstallation is normally governed by the variousfactors like:

Governed by supply utility. Measurednormally at point of supply (or meteringpoint).

Governed by the equipments used byconsumer. The equipment specificationswith regards to PQ requirements.

Processes for manufacturing goods qualitycontrol within the industry. Mainly theprocess reliability.

Other factors such as Human safety anddata communication requirements.

Based on these factors, the minimumbenchmarking needs can be defined withregards to various issues of PQ such as:

Voltage Sags and Swells. Momentary mains cycles loss. Voltage surges and High frequency

noise / disturbance (sometimes calledas transients or glitches)

Current surges and high fluctuation ofload current (normally reflects ontovoltage problems)

Current Harmonics and consequentialVoltage Harmonics.

Inter-harmonics on Current andVoltages.

Neutral floating or shifting. Earthing Problems. Power Outages and effect of Auto-

Reclose system. Load Shedding (Specifically with

countries where demand is muchhigher than generation)

Power Frequency variations.And some issues that are indirectly related toPower Quality:

Reactive Power Compensation issues. Load unbalance between the phases

and Neutral loading. System Resonance – Parallel and

Series. Maximum Demand control (kVA

demand and kW demand).

Once the minimum requirements are defined,with regards to each of these factors, theprocess for bringing the PQ issues within thebenchmarking stated can be worked uponbased on various methods that can beadapted.

The process of benchmarking within the giveninstallation requires activities like:1. Study of installation electrical distribution

diagram (SLD – Single line diagram) andidentify the critical points on the samewhere the PQ issues can be measured. i.e.identifying the points for survey.

2. Checking out the specifications of theequipments that are supplied from thespecified points in electrical diagram thatare selected for survey.

3. After identifying the survey points onelectrical installation diagram, defined thedifferent PQ issues that are needed to besurveyed. This should be based upon theequipment specifications too.

4. Check the supply utility standards andincorporate these too at PCC survey point.

5. With identified survey points, one needs todefine the survey standards for every PQissue identified. The survey standardshould specify the conditions like:

“overall time frame for survey” “time of survey – during specific

working shift OR during day ornight OR during specific seasonetc.”

“monitoring interval time betweenreadings acquired during survey”

“number of events for abnormalitiescaptured”

“load condition like – maximum orminimum loading”

“effect of other loads that are notmonitored – if to be kept on or off”

“effect of capacitor system forreactive power to be kept on or offor to be checked with both theconditions”

6. Define the right type of measurement andmonitoring equipments so as to get theauthentic results. The equipment may notbe able to monitor all the PQ issues definedin benchmarking. One has to select theright type of equipment so that resultsobtained are authentic.

The table as shown in the fig.1 can be madeso as to get clarity on benchmarking.

Once the table as in Fig.1 is defined, one hasto define the PQ issues requirements basedupon the electrical installation requirementsunder consideration.Fig.2 shows the typical way of defining suchbenchmarking needs.

After the preparation of such surveyrequirements (Fig.1) and the benchmarking





standards (Fig.2) for the specific requirements,the actual survey work can be commenced.

Once the survey is completed, the surveyresults needs to be analysed and checked ifany of the benchmarking requirements get

exceeded. One has to even define up to whatextent the benchmarking requirements havebeen exceeded. The requirement for the PQimprovement equipment’s specifications andfeatures has to be based upon the outcome ofthe benchmarking exercise.

Fig.1.

Fig.2.

Most the PQ improvement equipmentsuppliers would always influence therequirements and needs. These are basedupon the type of equipment specifications theymanufacture and need not necessarily matchthe requirements as defined in thebenchmarking process. One has to be carefulon such decision making process. Theequipments that take care of PQ issue may beinadequate or sometimes over doing thethings. Both these has problematic impact.Inadequacy in such equipments can cause theissue to remain unresolved and overcompensating may cause the equipment costto go up and would cause un-necessaryfinancial burden.

Additionally, one even has to look into theaspect if the selected PQ compensatingequipment is causing other PQ issue (whilethe original issue is resolved). The example ofthis can be seen in further part of this technicalpaper where “Introduction of Capacitors forReactive Power Compensation can cause therise in Harmonics”.

Further part of the paper gives the overview onthe various equipments used for PQimprovement along with their merits anddemerits.

Time frameData loginterval

Number ofevents

1.1Voltage Sags & Swells of morethan 1min Krykard ALM-35 24hrs 10 seconds -Not Applicable-

Maximum and MinLoad dring normal24hrs days work

-Not Applicable- Capacitor On

1.2 Voltage Outages

On Existing PowerDistribution panel -Energy Manager - Rish12

1 year -Not Applicable- Count the eventsper year

Normal work -Not Applicable- Normal status

1.3 Continuous Harmonics Krykard ALM-35 24hrs 1 min -Not Applicable- Maximum Load -Not Applicable-

Withcapacitors ONand withcapacitors OFF

1.4 Neutral Voltage (Neutralfloating)

Krykard ALM-35 24hrs 10 min -Not Applicable- Maximum Load -Not Applicable- Capacitor On

1.5 Power Values exceeding MDand Reactive Power needs

Krykard ALM-35 24hrs 15 min Count eventswithin 24 hrs.

Maximum Load Normal status Capacitor On

2.1 Continuous Harmonics Krykard ALM-35 8 hrs shift 1 min -Not Applicable- Maximum LoadAll other loads ONand All otherloads OFF


2.2 Voltage Disturbances Dig Storage Oscilloscope- Tektronics - 6 channel

8 hrs shift continuousCapature withsingle trigger asmany as possible.

Maximum LoadAll other loads ONand All otherloads OFF


3.1

Survey PointNo:Sr. No.

PCC -Transformer

Incomer

PQ Benchmarking at : XYZ Electrical Installation

Load Point -1 onSLD

Monitoring Requirements CapacitorStatus

Other LoadConditionLoad ConditionInstrument used

PQ Issues to besurveyed for:

1.1 Voltage Sags & Swells of more +10% to -15%

1.2 Voltage Outages Less than 3 times per year.

1.3 Continuous HarmonicsV-THD% < 2% I-THD% < 8% 3rd Harmonic < 5%

1.4 Neutral Voltage (Neutralfloating)

< 1.5 Volts-AC RMS value

1.5 Power Values exceeding MDand Reactive Power needs

MD-KVA < 3200 KVA kVAR < 150 kVAR

2.1 Continuous Harmonics V-THD% < 3% I-THD% < 12%

2.2 Voltage DisturbancesHF Disturbancesfrequency > 1kHZ < 650Volts-peakamplitude

3.1

RequirementsSr. No. Survey PointNo:

PQ Issues to besurveyed for:

PCC -Transformer

Incomer

Load Point -1 onSLD





PQ improvement Equipments and theirfeatures, usage merits and de-merits:

Let’s take a look at the PQ improvementEquipments based upon the PQ issuessolving.

Voltage Sags and Swells:

Almost all the installations are worried aboutthis PQ issue. Unless the supply utility poweris within the benchmarking needs, one has tolook out for taking care of such issues byconnecting the appropriate equipments.

The equipments used for taking care of theissue are:

Solid state voltage stabilizers Servo control Voltage stabilizers On load Tap Changers for Transformers CVT – Constant Voltage Transformers. UPS – Uninterrupted Power Supply

systems. Series boost – buck converter. High speed Thyristorised Power Factor

Correction (reactive power compensation)system.

Solid State Voltage stabilizers:Normally uses the semiconductors likethyristors for controlling the voltage.Even though the voltage (RMS value) iscontrolled well, normally tends to generate theharmonics on the supply system. Thus, usageof these is in limited low power applications.Specifically, dedicated to single machine.

The fig.3 depicts the typical scheme and theinput / output wave-shapes.

Fig.3.

Servo Control voltage Stabilizers:

Uses the auto transformer with variablevoltage that can be controlled by position ofthe wiper arm. The position of wiper co trolsthe output voltage. The positioning of the wiperarm is controlled by servo controlled motor.Sometimes individual phase control servocontrol too is adapted.

Fig.4 shows the typical scheme used withservo control voltage stabilizer.

The merits of this method are: Good voltage regulation. Almost no harmonics generated. Moderately good efficiency.

The de-merits of this method are: Regular maintenance. Correction for sudden voltage changes

takes few seconds. i.e. no instantaneouscorrection.

Limitation on output capacity so usage isrestricted to low to medium LT powerrequirements. (Typical 1kVA to 450kVA).

Fig.4.

On Load Tap Changer for Transformers:

The transformer supplying the electricalinstallation can be fitted with the equipmentcalled “On Load Tap Changer”. The varioustaps of the transformer are selectedautomatically to control the output voltageregulation. Typical schematic is as in Fig.5.

Input AC

Output wave(Load voltage)





Fig.5.Merits: Higher rated capacity control (Normally

available up to 10MVA). Voltage regulation fairly good (within the

difference between the tap voltage ratio). Almost no harmonics generated.

De-merits: Comparatively high cost of equipment. Voltage regulation only against the input

supply (utility supply) voltage variations. Voltage disturbances (transients) during the

tap changing process. Regular Maintenance needed. Considered by many as “Prone to break-

down”.

CVT – Constant Voltage Transformers:

Technology uses the effect of magnetic coresaturation to maintain the output voltageregulation.

Merits: High speed control over voltage regulation

and suitable for fast changing inputvoltages.

Voltage regulation with regards to highspeed load changes is good.

No mechanical moving parts thusextremely low maintenance requirements.

De-merits: Output voltage waveform is non-sinusoidal

creating harmonics issues. Transformer efficiency not good (higher

core losses)

UPS – Uninterrupted Power Supply:

This technology has wide spread use. It usesthe battery stored power and uses powerelectronics technology to maintain the outputvoltage regulation.Typical scheme of UPS is as in Fig.6.

Fig.6.

Merits: Extremely good output voltage regulation to

fast changes in input voltages as well as forfast changes in loads.

Suitable for other PQ issue like Cycle Loss,Power Outages and Voltage transients etc.

Normally available with fairly good outputsinusoidal waveform.

De-merits: High cost of equipment. Efficiency is not good as compared to other

methods. Backup battery needs regular maintenance. Output surge current handling (load surges)

capacity is poor. Generates Harmonics on supply system

from where it draws the power. (unlessspecial design features to reduceharmonics are incorporated).

Series Boost – Buck Converters:

Technology uses series transformer which iscontrolled through power electronics basedsynchronous inverter technology.Series transformer is connected with the load.The transformer control winding is controlledthrough the synchronous AC source whoseoutput is controlled with appropriate polarity toincrease or decrease the output voltage onhigh speed basis.

Typical scheme can be as seen in fig.7.

Fig.7.





Merits: Output voltage regulation is extremely good

and suitable for fast changing load as wellas changes in input voltage.

Output voltage is without harmonics. Additional advantage for utilization against

other PQ issues like maintaining limits onHarmonics at PCC and some extent thereactive power control.

Bi-directional control over voltageregulation. i.e. able to effectively control thesags and swells with single equipment withsame efficiency.

De-merits: High cost of equipment. Energy efficiency is not good because it

has to handle the entire load current incontrolling elements.

High Speed Thyristorised Power FactorCorrection System:

This system is primarily used for reactivepower compensation, still has good effect onvoltage regulation with regards to loadvariation.The technology used is to switch ON/OFF thecapacitors and inductors (if needed) usingPower Electronic devices like thyristors. Thecapacitors are controlled based upon thereactive power needs on supply system.Sometimes, even the IGBT based STATCON“Static Condenser” technology is used forreactive power compensation.

By maintaining the power factor near unityalmost on instantaneous basis, it gives goodvoltage regulation against normal inductivesource impedance.

The Phasor representation with regards toLagging, Leading and Unity Power factor withregards to practical loads like transformer withcertain output impedance is depicted as shownin Fig.8 (a). Whereas Fig.8 (b) shows laggingPF phasor representation showing under-voltage with lagging PF. Fig.8 (c) shows over-voltage with leading PF and Fig.8 (d) showslow voltage change with Unity PF.

(a)

(b)

(c)

(d)

Fig.8.

The basic schematic of the Dynamic PowerFactor Correction System is as shown in theFig.9.

Fig.9.

Merits: As the system is used primarily for

Reactive power compensation, its usage asvoltage regulator is an added benefit.

Speed of compensation is very fast.Normally within 2 to 5 supply cycles.

System efficiency is good. Almost zero maintenance.





De-merits: Cannot compensate for input voltage

changes given by utility. Such system needs to be adequately

protected against harmonics otherwise cangive enhancement to harmonics on supplyline.





Momentary mains cycles loss:

The momentary mains cycles loss isconsidered in the range of 0.5 cycles to 30cycles in the mains voltage.The mains cycle loss is considered as totalloss of voltage during some cycles or reductionin voltage below an acceptable limit for somecycles in mains supply.Many times it is caused due to starting of highpower induction motors.

The loss of cycles for some installations maynot be critical and can even be neglected. Butin some industries like Semiconductorindustries, this is of prime importance. In suchindustry, loss of cycle can create huge lossesto its production and such industries have tobe equipped with compensating equipment soas to achieve the “Ride through” effect.

The types of equipments used for providingcompensation against this PQ issue are:

Ferro resonant Transformers. UPS – Uninterrupted Power Supply

systems. Synchronous generators with fly-wheel.

Ferro resonant Transformers:

These are the transformers in category of CVT(constant voltage transformers) but use theeffect of saturation energy in conjunction withCapacitors to create the resonance effect.Normally such kind gives good output voltageregulation effect up to 30% Under voltagecycle losses and for total voltage absent cangive the ride through effect for very few cycles(typically up to 5 cycles) after which thevoltage amplitude diminishes belowacceptable limits.Typical schematic of Ferro-Resonanttransformer schematic is as in Fig.10.

Fig.10.Merits:

Effective against cycle loss with amplitudenot lesser than 30% of the rated voltagevalue.

Harmonic values even though present dueto saturation effect are not very high.

Extremely good voltage regulation effecteven against the continuous voltage sagsand swells.

Robust construction without anyelectromechanical moving parts. Givesgood reliability and low maintenancerequirements.

De-merits: Usage with lower power ratings. This is

because the transformer needs to beoperated at much lower loading conditionas compared to design of normaltransformer of same rating.

With higher loading than design, thevoltage suddenly drops down near zero.

Due to higher design parameters, the costis comparatively high.

UPS – Uninterrupted Power Supply:This equipment is already discussed inprevious section of voltage sags and swells.Normally used with primary reason forsustained voltage regulation and thus is veryeffective with Cycle loss even of longerduration.

Synchronous Generators with Fly-wheel:

As the name suggests, the synchronousmachines that are mechanically coupledthrough a fly-wheel are used. Thesynchronous machines with normal supply aremade to run at synchronous speed in motoringmode. During the cycle loss, the moment ofInertia in flywheel (mechanical energy)continues to run the synchronous machines ina generator mode to go on supplying theelectrical system and create a ride througheffect.The dimensions of the fly-wheel and loadingconditions determines the time duration of theride through effect.

Typical scheme is as in Fig.11.





Fig.11.

Merits: Effective against the longer duration cycle

losses. Well designed system gives the ridethrough effect up to 30 seconds.

No harmonics generated. During normal motoring operation,

synchronous machine with over-excitationcan compensate for Reactive Powerrequirements.

Good reliability against loading conditions.De-merits: Mechanically moving parts gives rise to

human safety and maintenance issues. During normal motoring mode,

considerable power is lost. Thus, system isconsidered in-efficient for wastage ofpower.

Extremely complex design needing trainedmanpower for maintenance andrectification issues.





Voltage Surges, Load Current surges andhigh frequency transients / disturbances:

This topic of Voltage Surges and transient /disturbances is bit complex. There are variouscategories these phenomena are segregated.= Short duration high voltage peak transientswith high energy content.= High frequency disturbances riding on sinewave voltages – can be momentary orrepetitive.= Glitches of short duration causingundervoltage spikes or overvoltage spikes ofvery low energy contents.

These are mainly caused due to Lightning strikes. Capacitor switching. Load switching. Short circuit faults. High power semiconductor switching with

line commutation. Switching of SMPS and Converter type

loads.

Some of the electricity consuming equipmentsare capable of handling some type oftransients and disturbances. Still one has totake care that such phenomenon are notexceeding the specified values or if someequipments can give undesirable effects fortheir performance.

The types of equipments for taking care ofsuch PQ problem are:

Lightning Arresters. Usage of Earth conductor over open

distribution lines. Usage of MOVs (Metal Oxide Varistors) –

High Power and normal grade. Capacitor filters, Low pass filters like T, L

and Pi filters. Zero Voltage Capacitor switching and

synchronous switching of loads. Shielding with differential and common

mode disturbance filtering like lowimpedance power conditioning.

Lightening Arresters:

This equipment is primarily used at the HTside of the Electrical installation. (on primaryside of the supply transformer). Sometimesgiven by supply utility or sometimes used bythe consumers themselves. As the namesuggests, it’s use is to reduce the amplitude ofhigh energy surges created by lightningstrikes. It reduces the extent of the high energysurges by creating low impedance path and

bypassing some of the energy content toearthing.

The technology uses MOV blocksencapsulated in polymer housing. The polymerhousing is resistant for natural elements likesunlight and humidity (rain water). Earliertechnology used porcelain housing.Sometimes resistance graded gap structuretoo is incorporated.

On transmission lines, the periodically placedLine arresters (Lightning Arresters) are placedto reduce the effect of Lightning Strikes. Thiscan be seen as shown in fig.12.

Fig.12.

Merits: Effective against the high energy lightning

strikes. New technology design give a good

reliability and almost zero maintenance.De-merits: Does not nullify the entire effect of surges. Capable of handling the specified levels of

Energy. Beyond which is susceptible fordamage.

Cannot be used for other disturbances thatare having amplitude equal or lower thansupply voltage.

Usage is limited only on specified voltageHT feeders.

Usage of Earth Conductor over distributionlines:Creating the low impedance conductor overthe open distribution lines is another effectivemethod against the Lightning strikes.This method is many times used by supplyutility and is used in the area that is Lightningstrike prone.

The LT distribution lines are rarely transmittingpower in open conductors on overhead poles.Still, with some large size industries, suchmethod is adapted and Earth conductor puttingover the higher level of distribution poles is anadapted practice.





Fig.13.Fig.13. shows the arrangement of such earthconductors over the transmission poles forLightning Strikes.

Merits: Effective method. Prevents the Lightning strike on the power

carrying conductors.De-merits: Additional cost of conductor. Additional Pole length needed.

Usage of MOV of normal and High energygrade:

The metal oxide varistors uses the non linearcharacteristic for its conduction. With highervoltage applied, it starts conducting rapidly.It’s like effect of 2 series back to backconnected Zener Diodes, but has much higherenergy handling capabilities.

Many times, the electricity consumingequipments too use MOVs to handle thehigher voltage surges to protect its internalcritical circuitry.

Merits: Effective against High voltage transients. Can handle high frequency surges

effectively. Effective against intermittent as well as

continuous high voltage transients anddisturbances (glitches).

De-merits: Limitation on Energy handling capacity. Selection of right type of MOV needs

elaborate study of requirement. i.e. Voltagesurge characteristics and maximum energyvalue to be handled.

High energy MOVs are costly.

Capacitor Filters and Low Pass filters like T, Land Pi Filters:

The passive elements like Capacitors andInductors in various configurations are used.They provide the excellent filtering effectagainst the PQ issues like High frequencyvoltage disturbances, spikes and even againstload generated harmonics.

One has to be careful while designing theappropriate filter configuration against theissues like “voltage regulation against loadchanges”, “Shunt and Series resonance”,“Harmonics enhancement” etc.

Merits: Strong and Rugged design giving very little

maintenance requirements. Highly economical.

De-merits: Specific design to match the site

conditions. Any changes in loading conditions on

supply lines needs necessary designchanges.

Careful approach while designing the filterswhich otherwise can give rise to theproblems like voltage regulation, resonanceand harmonic enhancement.

Zero Voltage Capacitor Switching andSynchronous Switching of Loads:

Switching ON of Capacitors through aconventional electromechanical switchgenerates high momentary transients onsupply system. Thus, many times there islimitation on the biggest size capacitor bankthat can be switched on.The thyristor technology based “Zerodifferential voltage” switch can give theadvantage of almost zero surges as well asable to give a faster switching ON and OFFresponse time to the capacitor switches.

The various loads like Transformer switch ONand OFF, SMPS switch ON generates thetransients on the supply line.Inductive loads like transformers if made toswitch ON during the sine wave peak reducethe transients (momentary DC shift).Synchronous switches using solid statetechnology in conjunction withelectromechanical technology (for conductionloss reduction) is normally used with suchissues.

The SMPS switch ON again is like capacitorswitching and Zero differential voltagedetection switch ON is really effective.





The typical zero differential voltage switch-onscheme of a 3-phase capacitor is as shown inFig.14 (a) and the switching on waveforms asshown in Fig.14 (b).

(a)

(b)

Fig.14.

Merits: Zero differential voltage detection switching

on of capacitors and SMPS almosteliminates the voltage disturbances onsupply system.

Capacitor switching fast responses can beachieved. – Without waiting for capacitorsto be discharged to zero DC voltage beforethey can be switched ON.

Well designed system is quite rugged andhas reduced maintenance requirements.

Can be provided with additional protectionto the capacitors with the same technology.

De-merits: On state conducting watt losses are higher

as compared to conventionalelectromechanical switches.

Higher costs.

Shielding with differential and common modedisturbance filtering like low impedance powerconditioning:

This approach is normally used with low powerrequirements. This is even incorporated in theelectrical equipment design to protect theequipments against the high frequencydisturbances.

These type of disturbances are evencategorized as EMI (Electro-MagneticInterference) and are divided into commonmode and differential mode disturbances.

Common mode disturbances are thedisturbances that are between all the threephases and neutral lines with respect to Earthpotential.Differential mode disturbances are thedisturbances that are in between differentphases and between phases to neutral.

High frequency common mode and differentialmode filters uses high frequency (ferrite core)reactors and capacitors in right configuration.

Merits: Simple design and rugged construction. Combined common mode and differential

mode filters are available easily for thespecific applications.

Low cost.De-merits: Lower power application usage. Not suitable for high energy transients.





Current and Voltage Harmonics and Inter-harmonics:

This topic is probably the most widelydiscussed topic in PQ. Harmonics on supplysystem is like a cancer and without knowing itspresence; it can cause multiple issues withsupply related issues like higher energyconsumption, maintenance issues,breakdowns in equipments, communicationsystem reliability etc.

Generation of non sinusoidal current loadingnormally gives rise to voltage harmonics dueto the source impedances. Thus, the load thatgenerates such non-sinusoidal currents cangenerate the harmonic issues for normal linearloads too.

Capacitors used for Power Factor correctionabsorb the harmonics and can even enhancethe levels of harmonics on supply lines.

The recent energy conservation typeequipments normally create non-sinusoidalloading on supply system and thus creatingharmonics. Some of the examples of the loadsthat create harmonics on supply lines are:

Variable speed drives (VFD & DC drives) Uninterrupted Power Supplies (UPS) SMPS – used with household and control

equipments. Fluorescent lamps of different types and

LED lamps. Induction furnaces and Arc furnaces. (even

generate inter-harmonics) CNC machines and automation servo

drives. Welding machines.

The non-sinusoidal waveform as per “FourierSeries” mathematical theory are the highfrequency sinusoidal components. These highfrequency components are further categorizedinto zero sequence, +ve sequence and –vesequence components on 3 phase electricalsupply system. Such categorization helps interms of analyzing the nature of problems andthe solutions that can be offered.

In general, it’s always good to get rid ofharmonics on supply system, whatevercategory it may fit into.

The detailed analysis of harmonics is muchlengthier topic, thus this technical paper willnot get into those details and proceed with thevarious solutions available for harmonicmitigation.

The various type of approach and equipmentsused for Harmonic mitigation are:

Passive L-C shunt tuned and partially tunedfilters

Low pass filters for 6-pulse converter typesystems like AC/DC drives & UPS.

Usage of 12 pulse converters. Z-Winding Transformers for taking care of

triplen harmonics. Active filters – Static Synchronous

Compensators (STATCOM)

Let’s take a look at each one on basis of theirspecific advantages and limitations.

Passive L-C shunt tuned and partially tunedfilters:

Probably the oldest approach againstharmonic mitigation method. The approach isto filter the individual harmonic number thatcan be prominent specific to the site condition.The series Inductor and Capacitor (L-C)combination is put in shunt with the supplysystem. Series L-C combination gives very lowimpedance at its resonance frequency.Resonance frequency of L-C series circuit is

__ ____ ___ ___ ___ ___ ___ ___

1 ÷ (2 LC). By this method, the specificharmonic on supply system sees almost zeroimpedance and gets filtered through the L-Cfilter.

In case of supply system is with wide spectrumof harmonic numbers, for every harmonicnumber, one has to put a separate L-C filter.

Additionally, such filter is a shunt filter, itcannot see the direction from where theharmonics are generated and takes theapproach of general non-directional filter.

The typical LT supply distribution in theindustry is shown in Fig.15 (a) and Fig.15 (b)shows the 5th and 7th Harmonic that getsfiltered near the harmonic generating load.

(a)





(b)

Fig.15.

One has to be extremely careful whiledesigning of this filter. The design needs totake into account the specific site relatedimpedances of source and loads and variousloading conditions. One even has to take thenote of reactive power generated by such L-Ctuned filters.

Merits: Simplified rugged construction by passive

electrical components like Reactors andCapacitors.

Almost zero maintenance. Comparative lower cost if system is with

one or two harmonic numbers that areprominent.

Offers additional capacitive reactive powercompensation on supply system.

De-merits: Site dependent design. Requires complete

nodal analysis survey and systemimpedance calculations for designing.

Vulnerable to system resonance –specifically with changes in loadingconditions.

Can offer leading PF with low loadingconditions and can cause over-voltageissues.

With wide band spectrum of harmonicnumbers present on supply, the costinvolvement is high.

Design is bulky due usage of air corereactors (to avoid saturation effect drift intuned frequency).

Low pass filters for 6-pulse converter typesystems like AC/DC drives & UPS:

A lot of applications in today’s industry usesthe equipments like AC/DC drives and UPSwhich uses the full wave rectifiers by usage ofpower semiconductors. Such rectifiers typicallygenerate prominent 5th and 7th harmonics on

supply system. Total Harmonic Distortion oncurrent is typically ranging between 40% to65%.

The approach of this method is to reduce thecurrent harmonics generated by suchapplications.

The simplistic approach is to put the seriesreactors. These approach even thougheffective to certain extent normally does notbring down the current harmonics to desirablelevels. Typical THD% brought down in currentharmonics ranges in 25% to 40%.

Better approach is to put the series reactor incombination with shunt L-C tuned filters for 5th

and 7th harmonic. Such approach gives farimproved results. Typically, the currentharmonic THD% comes down to less than10%. (7.5% to 10% is typical range).

Fig. 16 shows the typical schematic for suchLow pass filters.

Fig.16.

Merits: Extremely effective – gives value for money

solution. No hassles (normally) of resonance

problems. Provides some reactive power

compensation. Rugged construction using passive

elements like Inductors, capacitors andresistors.

De-merits: Useful only for six pulse converter type of

applications. Need to put power consuming resistors to

avoid overvoltage issues during lowerloading conditions.





Usage of 12 pulse converters:

In case of very high power requirements withsix pulse converters, this approach is used. Itis normally used based upon the application.This approach is used with applications like:

Induction Furnaces. High power AC/DC drives used with Steel

rolling mills.

It uses the star and delta windings of thetransformer on the secondary. The output ofthese windings is 60 phase shifted withrespect to each other. Thus, overall effect ofsix pulse converters on the secondary windingis seen by primary winding of transformer as a12 pulse converter.The effect of 12 pulse converter is to generateharmonic numbers 11th and 13th. Higherharmonics being higher frequency componentscan be much easily filtered out and do nottravel higher distances on electrical networks.

The typical schematic for 12 pulse converter isas shown in Fig.17.

Fig.17.

Merits: Extremely effective approach for specific

applications. Transformer impedance itself acts like

added filter for 11th and 13th harmonicgenerated.

No need of added series reactors or lowpass filters that are used for six pulseconverters.

De-merits: Needs specially designed transformer with

higher K-Factor. (Typical K-Factor is 13) Some attention may have to be given to

11th and 13th harmonics on primary of thetransformer.

Product design need to use two numbers ofsix pulse converters and thus can add upthe cost.

Z-winding transformer for taking care of TriplenHarmonics:

Triplen harmonics are 3rd, 9th, 15th,--- etc.These harmonics on 3-phase supply systemnormally show zero sequence characteristics.

The single phase harmonic prone loads on 3phase supply system normally create theproblems of “Triplen Harmonics”.The effect of triplen harmonics is that theygather together in neutral causing Neutraloverloading and Neutral shifting issues.

The tuned filters for taking care of 3rd harmonicare normally very bulky and costly due to theaddition of neutral phenomenon.

The better approach is therefore to use Z-winding transformers that effectively cancel outthe zero sequence components and reflectedcurrent on primary is without such zerosequence components (i.e. without or verylittle triplen harmonics)

(a)

(b)

(c)

Fig.18.

Schematic of a 3-phase Z-winding transformeris as shown in Fig.18(a) and the phasorrelation to input and output for fundamentalcomponents are in Fig.18(b). Fig.18(c) showsthe zero sequence third harmonics phasorscancelling each other.





Merits: Effective value for money solution against

“Triplen Harmonics” on 3-phase supplysystem.

Energy efficient solution with transformerefficiency of @ 99%.

Provides effective solution with Neutralfloating issue by galvanic isolation of loadwith triplen harmonics.

Rugged construction with littlemaintenance.

De-merits: Effective against only zero sequence

component harmonics.

Active Filters – Static SynchronousCompensators (STATCOM):

A recent addition of product in FACTS(Flexible AC Transmission Systems) family. Anextremely effective solution for the Harmonicmitigation.

Uses the Power Electronics (IGBT inverters) tocounter generate reverse harmonics on supplysystem. It uses Microprocessor basedmethods like Digital Signal Processing (DSP)to monitor supply harmonics on line and onreal time basis. It then controls the PowerElectronics IGBT based inverter to generatethe exact reverse harmonics on supply line.This cancels the load generated currentharmonics that can be seen at PCC (Point ofCommon Coupling).

This method has added advantage of able toprovide variable reactive power compensationas well as load balancing in three phases.

Probably the best known method for harmonicmitigation with present day technology.

(a)

(b)

(c)Fig.19.

Fig.19(a) shows the positioning of ActiveHarmonic filter on supply line.Typical Current wave-shapes as can be seenby Load current, Active Harmonic filter and thesupply system transformer are as depicted inFig.19(b).Typical schematic of active harmonic filterblock diagram is as in Fig.19(c).

Merits: Highly suitable for Loads with wide band

spectrum of harmonic numbers. Bring down THD% factor to much lower

level than any other method available withtoday’s technology. Typically below 5%current THD% factor.

Added benefit of automatic reactive powercompensation and 3-phase load balancing.

Resistant to system resonance. Real time high speed response makes it

suitable even for intermittent harmonics.De-merits: Efficiency is not as good as other methods.

Typically works between 94% to 97%efficiency.

Extremely high cost – thus sometimesdifficult to justify the economic angles.

Specialized technology. Thus, needsspecialist to take care of anycommissioning, maintenance and repairrelated issues.





Neutral Floating (shifting) and Earthingproblems:

There are various type of Neutral Earthingstandards used depending upon the country ofusage and utility adapted standards.

The LT supply distribution for human safetyreasons as well as for connected equipmentsafety reasons, cannot be left floating withrespect to Earth potential.Neutral therefore is normally earthed at singlepoint (i.e. near supply transformer orgenerator). Sometimes the earthing is carriedout through some impedances. This isnormally to limit the level of fault currentsagainst Earth Faults.

There are various reasons for getting thedifference between Neutral and Earthingpotential.Major reasons seen are:

Long length of LT cables from source toload point.

Excessive Neutral current due to unbalanceloading in 3-phases.

Excessive Neutral current due to loadtriplen harmonics.

Increase in resistance of Earth pits. This ismany times seasonal and observed duringdry seasons where earth resistance is seenhigher.

Earth fault problems in connectedequipments.

Connection problems between Neutral andEarth pit grid points.

There are some specific equipments neededto resolve these issues. Still, the approach isto identify the exact reason for shift in Neutraland Earth potential. Once the reason is known,the solution is normally simple like:

Improving value of earth resistance(bringing it lower) by water addition or byusage of specialized compounds.

Reduction in Neutral currents by eitherreducing phases unbalance or by takingcare of triplen harmonics problems.

Checking the earth fault reason in theconnected equipment that has fault andrectifying this.

Improvement in earth pit grid network onwide spread area if existing earthresistance is at inadequate level.

Some equipments used additionally apart fromabove mentioned approach for taking care ofNeutral Shifting issues are:

Isolation Transformer.

Dynamic Load balancing betweenphases.

Isolation Transformer:

Sometimes, usage of “Isolation Transformer”can help to resolve the issues due to longercable lengths. With some critical laboratoryequipments where there is very criticalrestrictions between Neutral to Earthprotection, usage of Isolation transformer isquite effective.The neutral earthing on secondary of suchisolation transformer which is very close toloads can help reducing the Neutral to Earthpotential in such case.

Dynamic Load balancing between phases:

The usage of passive elements like shuntinductors and shunt capacitors across the linesand line to neutral are used for balancing outthe loads between the phases.Where the load is fairly fixed and does notchange, the fixed calculated values of reactorsand capacitors can suffice to the issue.But, in case of the loads where unbalance ischanging on continuous basis, the dynamicswitching of reactors and capacitors isachieved by special “Dynamic load balancingController”.

The equipments used for Harmonic filteringlike “STATCON” have this specific feature ofdynamic load balance. This equipment iscapable of generating inductive and capacitivereactive power on supply lines thus can beeffectively utilized to generate this additionalfeature that can be useful.





Power Outages and Effect of Auto-Reclose:

Power outages in third world countries arequite frequent phenomena even though everyutility company is trying to improve onto thereliability.Thus, in such Power Outage prone countrieswhere demand is higher than supply or wherethe technology up gradation in distribution isneeded, normally electrical consumer isalways better equipped to take care of suchissues.

Unfortunately, in the countries where suchphenomenon is rare, power outages createsadditional challenge. Here one has to becareful enough to ensure that back-up systemsare well maintained and able to give adequatebackup arrangement. This is needed to becarried out with regular checkups as the actualutilization of such systems is rare.

Where, the outages are regular phenomena,or in the countries where there is plannedoutage (Load Shedding) the approachnormally is to segregate loads into two or threeparts like:

o Highly Critical loads.o Normally Critical loads.o Non-Critical loads.

The backup systems in case of outages arethen selected based upon the category ofcriticality.

The critical loads are normally given with online back up using: Uninterrupted Power Supply (UPS) Automatic On line Generator set driven

through prime-mover like steam turbine,Diesel engine depending upon theavailability of fuel of such prime-mover.

Specifically for Outages that are plannedand where electricity cost is on Timedependent basis (TOD metering), aspecially designed equipment with backupthrough stored energy is utilized.

Making arrangement with utility supplycompany for alternate emergency feederand transfer of load through a high speedsynchronous switch. (many times solidstate switches too are used)

For auto-reclose effect, the measure suchas fly wheel operated synchronousmachines is used.

For normally critical loads, the approach is tokeep the off line generator set which can beswitched ON based upon the requirements or

by AMF (auto mains failure) system operatedgenerator set.

The non-critical loads are normally kept offduring such outages.

Segregating the loads based upon criticalityhas the advantage of limiting the capacity ofthe backup system and reducing additionalcost investments.

Let’s just take a little extra look on theelectrical supply equipment that has plannedoutages due to wide gap between demand andsupply in those countries.

Planned Outage equipments and TODmetering equipments are mainly segregatedinto two main categories:a) Rural Agricultural Supply applications.b) Urban electrical loads. – Household and

small offices / shops.

The category (a):The rural agricultural area has major loads asElectric pumps. These pumps are driven bystandard 3-ph induction motors. Suchelectrical pump loads contribute to almost 80%of electrical loads in Rural – Agricultural areas.

Thus, distribution companies utilize a specialapproach to curb down the loading by supplyof 3-phases to the specific areas for few hoursand balance time giving single phase supplyso that there pump motor loads cannot beswitched on.For this purpose, specialized LT load sheddingcontrol systems are installed on the LT side ofDistribution transformers by utilities.

Such systems in modern day technologycomes along with features like: Selection of 3-phase supply or 1-phase

supply with pre-programmed intervals. GSM / GPRS wireless connectivity to

control the schedules from remotelocations.

Transformer on line monitoring for bettermaintenance standards.

Electricity power monitoring – specificallyuseful against the thefts of electricity insome countries.

The category (b):

The urban areas, utilities cannot disconnectthe power due to shortages. Thus, a separateapproach of “Time of Day” (TOD) meteringapproach is adapted by supply utilities. Duringthe peak demand hours of the day, the





electricity is charged at much higher valuethan few non critical hours when it is chargedat normal rates. Sometimes it is even chargedmuch lower during very low consumptionhours like late hours in the night.Most of the electricity distribution companies inIndia have 4 steps tariff as per the timecriticality.

Under such case, the consumers are advisedto connect the specially designed systems.The features of such specially designedsystems are:

Usage of Battery Storage of ElectricalEnergy during least tariff hours.

Utilize the stored energy during peak tariffhours.

Switching OFF the non-critical loads duringpeak hours and in applications like waterheaters, use low tariff hours for heating.

Keeps control over critical and non-criticalloads depending upon TOD.

Some added features that are convenient fromuser viewpoints that are added in this like:

GSM / GPRS control for communicatingwith user through messaging on mobilephones.

Pre-set and user set programmingschedules.





Power Frequency Variation:

This problem can be more prominent with thesupply system with is with smaller localizedsupply system. Here the effect of high loadvariation can create the impact on the supplysystem.

Big size grid utility supply normally does notget affected by the LT consumer loads. Thus,very high variation in Power Frequency isnever a major issue and normally it isneglected in most LT installations.

With localized generator supply system, bestapproach is to improve the generator controlsystem and capacity such that such highfrequency variation is not supplied.

Normally, electrical consuming equipments aredesigned to take care of smaller variations infrequency. And the processes that can getaffected with speed changes in the motorsconnected due to frequency variations arefitted with more accurate method of speedretention like VFDs in close loop speedcontrol.





Some important issues indirectly related toPQ for other Electrical equipments:

The one important issue here is connectedwith Reactive Power control equipments.

These equipments are fitted on LT distributionto take care of Transmission and Distribution(T & D) losses in current carrying conductors.The consumers normally fit such equipmentsto avoid Power Factor related penalties and /or to avail financial benefits offered by utilitycompanies against better Power Factor.

Power Factor Controlling equipments:

These are: PF improvement capacitors. Capacitors Automatic switching (using

contactors and high speed switchingthyristors)

The capacitors used either fixed or switchedfor the purpose of Power Factor improvementhas an important known bad effect onHarmonics on electrical supply system. As oneknows that impedance offered by capacitor onAC system is Xc = 1 ÷ (2 f C).The harmonics are high frequencycomponents thus offer low value of Xccapacitive impedance for such higherfrequency components. This provides an easypath to the harmonics on Electrical Distributionnetworks. This most of the times createsenhancement in harmonics on supply lines.

Such effect as can be well understood is badfor the other equipments connected on thesame supply lines and even has deterioratingeffect on the Capacitors themselves.

Normally, the introduction of line reactors inseries with capacitors which has overall effectof resonance frequency that is away fromharmonics can take care of the problem.Such reactors are normally known as“Detuned Reactors” and for the prevalentharmonics, the resonance frequency isadjusted at a value much lower than theharmonic frequencies.

For non-triplen harmonics, the resonancefrequency is adjusted at @ 187Hz and 225Hzfor 50Hz and 60Hz respectively. Similarly forsupply system with triplen harmonicspresence, the resonance frequency is adjustedat 134Hz and 160Hz for 50Hz and 60Hzsupply systems respectively.

One can even know from such introduction of“Detuned Reactors” that the impedanceoffered by such L-C combination would giveinductive reactance to the harmonics butwould be offering capacitive reactiveimpedance to Fundamental mains frequencyof 50Hz or 60Hz.

Typical Impedances seen by L, C and L-Ccombinations for non-triplen harmonics with50Hz supply system application of PFcorrection capacitors can be as shown inFig.20.

Fig.20.

- Tushar Mogre.

(Graduate Engineer – Mumbai University)(BEE – EM)

DirectorTAS PowerTek Pvt. Ltd.Nasik, India.(Company specialized in PQ audits andproviding PQ solutions).

*****

References: Most of the technical paper is written byauthor by self experience working in the field.One reference book is used for preparation of the paper.

1. Book – Electrical Power Systems Quality (2nd

edition) – Roger C. Dugan, Mark F.McGranaghan, Surya Santoso, H. WayneBeaty.

*****



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