POWER HARMONICSPOWER HARMONICS

Swagat pradhanSwagat pradhan

77thth Sem Elect.Engg. Sem Elect.Engg.

Roll No.- 0811013091Roll No.- 0811013091

INTRODUCTIONINTRODUCTION

A strange phenomenon is occurring in today’s office buildings A strange phenomenon is occurring in today’s office buildings and manufacturing plants.Transformers supplying seemingly and manufacturing plants.Transformers supplying seemingly average loads are overheating.Neutral conductors in average loads are overheating.Neutral conductors in balanced circuits are overheating from excessive loads.Circuit balanced circuits are overheating from excessive loads.Circuit breakers are trapping for no apparent reasons.Yet the breakers are trapping for no apparent reasons.Yet the standard troubleshooting procedures show everything to be standard troubleshooting procedures show everything to be normal.Then where lies the problem?In other word the normal.Then where lies the problem?In other word the answer is harmonics.answer is harmonics.

Harmonics in electrical system result in wave form Harmonics in electrical system result in wave form distortion.In general harmonics are periodic disturbance in distortion.In general harmonics are periodic disturbance in voltage and current.any non-sinusoidal periodic wave form voltage and current.any non-sinusoidal periodic wave form can be contributed as combination of sinewave of certain can be contributed as combination of sinewave of certain frequencies,amplitude phase angle.In simple terms frequencies,amplitude phase angle.In simple terms harmonics are multiple of the normal main power harmonics are multiple of the normal main power frequency.For example,3rd order has got frequency 150hz frequency.For example,3rd order has got frequency 150hz and 5th order has frequency 250hz.In a wave shape only the and 5th order has frequency 250hz.In a wave shape only the fundamental componenet of voltage and current contribute fundamental componenet of voltage and current contribute to power transmission.This non active power due to to power transmission.This non active power due to harmonics is referred as distortion power.harmonics is referred as distortion power.

The harmonic is introduced in the system at both ends i.e. at the generating end and The harmonic is introduced in the system at both ends i.e. at the generating end and at the receiving end(loads).A pure sinusoidal voltage is a conceptual quantity at the receiving end(loads).A pure sinusoidal voltage is a conceptual quantity produced by an ideal ac generator built with distributed stator and the field windings produced by an ideal ac generator built with distributed stator and the field windings that operate in uniform magnetic field.Since neither the winding distribution nor the that operate in uniform magnetic field.Since neither the winding distribution nor the magnetic field are uniform in a working ac machine,voltage waveform distortions are magnetic field are uniform in a working ac machine,voltage waveform distortions are created and the voltage time relationship deviates from pure sine function.As the created and the voltage time relationship deviates from pure sine function.As the deviation is in the form of a ic function which implies that the voltage distortion deviation is in the form of a ic function which implies that the voltage distortion contains harmonics.contains harmonics.

In contrast some loads cause the current to vary disproportionately with the voltage In contrast some loads cause the current to vary disproportionately with the voltage during each half cycle.These loads are classified as nonlinear loads and the current during each half cycle.These loads are classified as nonlinear loads and the current and the voltage waveforms are nonsinusoidal,containing distortions,where by the and the voltage waveforms are nonsinusoidal,containing distortions,where by the 50hz wave forms has numerous additional waveforms superimposed upon it,creating 50hz wave forms has numerous additional waveforms superimposed upon it,creating multiple frequencies within the normal 50 hz sine wave.The multiple frequencies are multiple frequencies within the normal 50 hz sine wave.The multiple frequencies are the harmonics of the fundamental frequency.The current distortions produce voltage the harmonics of the fundamental frequency.The current distortions produce voltage distortions.This is of no concern where there is a low impedence path from the power distortions.This is of no concern where there is a low impedence path from the power source,which has sufficient capacity so that loads placed upon it will not affect the source,which has sufficient capacity so that loads placed upon it will not affect the voltage.voltage.

CAUSES OF HARMONICSCAUSES OF HARMONICS

The nonlinear loads which are the causes of The nonlinear loads which are the causes of harmonics are as under:harmonics are as under:

1.Loads that make use of semiconductor 1.Loads that make use of semiconductor devices like transistor,thyristor i.e. static devices like transistor,thyristor i.e. static rectifiers,(ac/dc conversion using rectifiers,(ac/dc conversion using SCRs),static frequency converters,static SCRs),static frequency converters,static inverters like:inverters like:

- static power converters- static power converters - static rectifiers- static rectifiers - static uninterrupted power supplies- static uninterrupted power supplies - static inductor regulators - static inductor regulators

Variable impedance loads,using electric Variable impedance loads,using electric arcs,arc furnaces,welding units,flouroscent arcs,arc furnaces,welding units,flouroscent tubes,dischargelamps,light control etc. tubes,dischargelamps,light control etc.

Loads using strong magnetizing Loads using strong magnetizing currents,saturated currents,saturated transformer,inductance,reactors etc.transformer,inductance,reactors etc.

Office automation equipment like Office automation equipment like computers,UPS,printers etc.computers,UPS,printers etc.

CLASSIFICATION OF HARMONICSCLASSIFICATION OF HARMONICS

Each harmonics has a name,frequency and Each harmonics has a name,frequency and sequence.The sequence refers to phasor rotation sequence.The sequence refers to phasor rotation with repect to the fundamental frequency i.e. in an with repect to the fundamental frequency i.e. in an induction motor a positive sequence harmonic induction motor a positive sequence harmonic would generate a magnetic fieldthat rotated in the would generate a magnetic fieldthat rotated in the same direction as the fundamental.A negative same direction as the fundamental.A negative sequence harmonic would rotate in the reverse sequence harmonic would rotate in the reverse direction.The first nine harmonic with their effects direction.The first nine harmonic with their effects are listed below.are listed below.

NameName F F 2nd 2nd 3rd 3rd 44thth 55thth 66thth 77thth 88thth 9th9th

FrequencyFrequency 5050 100100 150150 200200 250250 300300 350350 400400 450450

SequencSequencee

++ -- 00 ++ -- 00 ++ -- 00

EFFECTS OF HARMONIC CURRENTEFFECTS OF HARMONIC CURRENT

Office building and plants:Office building and plants:

There are two basic types of nonlinear loads – single phase and three phase There are two basic types of nonlinear loads – single phase and three phase loads. Single phase loads are mostly prevalent in offices while three phases loads. Single phase loads are mostly prevalent in offices while three phases loads are wide spread in industrial plant.loads are wide spread in industrial plant.

For ex.the growth of harmonics in the electrical loads of a modern facility is For ex.the growth of harmonics in the electrical loads of a modern facility is natural as it uses advanced electric components like natural as it uses advanced electric components like communications,computers,servers etc.for the continuity of the communications,computers,servers etc.for the continuity of the communications holding on to the programs and data,UPS(uninterrupted communications holding on to the programs and data,UPS(uninterrupted power supply) systems are commonly used.power supply) systems are commonly used.

Electrically what happens is the incoming ac voltage is diode rectified and is then used Electrically what happens is the incoming ac voltage is diode rectified and is then used to charge a large capacitor.After a few cycles,the capacitor is charged to the peak to charge a large capacitor.After a few cycles,the capacitor is charged to the peak voltage of sine wave.The electronic equipments draw current from this high dc voltage voltage of sine wave.The electronic equipments draw current from this high dc voltage to power the rest of the circuit.to power the rest of the circuit.

The equipment can draw the current down to a regulated lower limit.Typically before The equipment can draw the current down to a regulated lower limit.Typically before reaching that limit the capacitor is charged to the peak in the next half cycle of the sine reaching that limit the capacitor is charged to the peak in the next half cycle of the sine wave.This process is repeated over and over.A capacitor basically draws a pulse of wave.This process is repeated over and over.A capacitor basically draws a pulse of current only during the peak of the wave.During the rest of the wave,when the voltage current only during the peak of the wave.During the rest of the wave,when the voltage is below the capacitor residual,the capacitor draws no current.the diode/capacitor is below the capacitor residual,the capacitor draws no current.the diode/capacitor power supplies to be found in office equipments are typically single phase nonlinear power supplies to be found in office equipments are typically single phase nonlinear loads.loads.

Harmonics have different effects on different components but all effects are subjected Harmonics have different effects on different components but all effects are subjected to damage and inefficient performance.to damage and inefficient performance.

NEUTRAL CONDUCTORNEUTRAL CONDUCTOR

In a 3 phase,4 wire system neutral conductors In a 3 phase,4 wire system neutral conductors can be severely affected by nonlinear loads connected to can be severely affected by nonlinear loads connected to the branch circuits . In a 4 wire system with single phase the branch circuits . In a 4 wire system with single phase nonlinear loads ,certain odd number of harmonics known as nonlinear loads ,certain odd number of harmonics known as triplensodd multiples of the third harmonic:3rd ,9th , 15th triplensodd multiples of the third harmonic:3rd ,9th , 15th etc. do not cancel ,but rather add together in neutral etc. do not cancel ,but rather add together in neutral conductor . In systems with many single-phase nonlinear conductor . In systems with many single-phase nonlinear loads , the neutral current can actually exceed the phase loads , the neutral current can actually exceed the phase current .This may cause excessive overheating as there is current .This may cause excessive overheating as there is no circuit in the neutral conductor to limit the current as no circuit in the neutral conductor to limit the current as there are in phase conductors .This flow of excessive there are in phase conductors .This flow of excessive current in neutral conductors can also cause higher than current in neutral conductors can also cause higher than normal voltage drops between neutral and ground. normal voltage drops between neutral and ground.

CIRCUIT BREAKERS:CIRCUIT BREAKERS:

A peak sensing electronic trip A peak sensing electronic trip circuit breaker responds to the peak of circuit breaker responds to the peak of current waveforms .As a result it won’t current waveforms .As a result it won’t always respond properly to harmonic always respond properly to harmonic current .Since the peak of the harmonic current .Since the peak of the harmonic current is usually higher than normal this current is usually higher than normal this type of circuit breaker may trip prematurely type of circuit breaker may trip prematurely at a low current .If the peak is lower than at a low current .If the peak is lower than the normal the breaker may fail to trip the normal the breaker may fail to trip when it should.when it should.

BUS BARS AND CONNECTING LUGS:BUS BARS AND CONNECTING LUGS:

Neutral bus bars and Neutral bus bars and

connecting lugs are sized to carry the full connecting lugs are sized to carry the full value of the rated phase current.They can value of the rated phase current.They can become overloaded when natural become overloaded when natural conductors are overloaded with with conductors are overloaded with with additional sum of triplen harmonics .As the additional sum of triplen harmonics .As the triplen harmonics are zero sequence triplen harmonics are zero sequence harmonics these get add up at the neutral harmonics these get add up at the neutral and because if which the phase current and because if which the phase current flows through the neutral current .flows through the neutral current .

ELECTRICAL PANELS :ELECTRICAL PANELS :

Harmonics in electrical panel Harmonics in electrical panel can play a lively tune .Panels that are can play a lively tune .Panels that are designed to carry 50Hz current can designed to carry 50Hz current can become mechanically resonant to the become mechanically resonant to the magnetic fields generated by higher magnetic fields generated by higher frequency harmonic currents .When this frequency harmonic currents .When this happens ,the panel vibrates and emits a happens ,the panel vibrates and emits a buzzing sound at the harmonic frequency .buzzing sound at the harmonic frequency .

TRANSFORMERS:TRANSFORMERS:

Commercial buildings Commercial buildings commonly have transformer in a commonly have transformer in a delta-star configuration .Single phase delta-star configuration .Single phase nonlinear loads connected to it nonlinear loads connected to it produce triplen harmonics which produce triplen harmonics which algebraically add up in the algebraically add up in the neutral .When this neutral current neutral .When this neutral current reaches the transformer it is reflected reaches the transformer it is reflected into the delta primary winding where into the delta primary winding where it causes transformer overheating and it causes transformer overheating and failure .Another transformer problem failure .Another transformer problem results from core loss and copper results from core loss and copper loss . Transformers are normally rated loss . Transformers are normally rated for a 50Hz phase current load for a 50Hz phase current load only .Higher frequency harmonic only .Higher frequency harmonic currents can cause to increased core currents can cause to increased core loss due to eddy current and hystresis loss due to eddy current and hystresis , resulting in more heating than that , resulting in more heating than that would occur at the same 50Hz current would occur at the same 50Hz current ..

GENERATORS:GENERATORS:

Generators are subjected to same Generators are subjected to same kind of overheating problems as kind of overheating problems as transformers .Because these are also connected transformers .Because these are also connected to harmonic producing loads such as data to harmonic producing loads such as data processing equipments and other non linear loads processing equipments and other non linear loads .In addition to overheating ,certain types of .In addition to overheating ,certain types of harmonics produce distortions at the zero harmonics produce distortions at the zero crossing of the current wave form which causes crossing of the current wave form which causes interference and instability for the generator’s interference and instability for the generator’s control unit .control unit .

DETECTING HARMONICSDETECTING HARMONICS To determine the harmonic problem the true rms To determine the harmonic problem the true rms

value and instantaneous peak value of the wave value and instantaneous peak value of the wave shape should be measured .shape should be measured .

True rms :refers to the root mean square ,or True rms :refers to the root mean square ,or equivalent heating value of a current or voltage equivalent heating value of a current or voltage wave shape .True rms meters give current readings wave shape .True rms meters give current readings correctly compared to conventional meters which correctly compared to conventional meters which give correct reading for pure sine waves only and give correct reading for pure sine waves only and typically read low when confronted with a distorted typically read low when confronted with a distorted current wave form .Such meters have a capacity of current wave form .Such meters have a capacity of measuring the electrical characteristics f the measuring the electrical characteristics f the waveform by sampling many points along the waveform by sampling many points along the waveform .waveform .

Another important parameter which is needed is Another important parameter which is needed is crest factor .It is the ratio of the peak value to rms crest factor .It is the ratio of the peak value to rms value of the wave forms .for a sine wave ,the crest value of the wave forms .for a sine wave ,the crest factor is 1.414.Greater the difference from 1.414 the factor is 1.414.Greater the difference from 1.414 the higher the harmonic content .For voltage harmonic higher the harmonic content .For voltage harmonic wave forms ,the typical case factor is below wave forms ,the typical case factor is below 1.414,i.e.a ‘flat top’ wave form For single phase 1.414,i.e.a ‘flat top’ wave form For single phase current harmonica ,the typical crest factor is much current harmonica ,the typical crest factor is much above 1.414.Three phase current waveforms often above 1.414.Three phase current waveforms often exhibit the “double hump” wave form .So the crest exhibit the “double hump” wave form .So the crest factor comparison method should not be applied to factor comparison method should not be applied to three phase load current .three phase load current .

SOLVING THE PROBLEMSOLVING THE PROBLEM Harmonics without doubt cause a lot of problem like excessive Harmonics without doubt cause a lot of problem like excessive

over heating of electrical system and thus ultimately reduces over heating of electrical system and thus ultimately reduces the life of the equipment ,so its removal is essential .The the life of the equipment ,so its removal is essential .The following are some methods to address some typical following are some methods to address some typical harmonics problems .harmonics problems .

IN OVERHEAD NEUTRALS:IN OVERHEAD NEUTRALS:

In 3-phase 4-wire system ,the 50Hz portion of the neutral In 3-phase 4-wire system ,the 50Hz portion of the neutral current can be minimized by balancing the loads in each current can be minimized by balancing the loads in each phase .The triplen harmonic neutral current can be reduced by phase .The triplen harmonic neutral current can be reduced by adding harmonic filters at the load end .Another solution can adding harmonic filters at the load end .Another solution can be pulling in extra neutrals-ideally one neutral for each phase .be pulling in extra neutrals-ideally one neutral for each phase .

In new construction ,undercarpet wiring and modular office In new construction ,undercarpet wiring and modular office partitions wiring should be specified with individual neutrals partitions wiring should be specified with individual neutrals and possibly an isolated ground separate from the safety and possibly an isolated ground separate from the safety ground ground

DERATING TRANSFORMERDERATING TRANSFORMER

The transformer can be protected from harmonics by The transformer can be protected from harmonics by limiting the amount of load placed on it .This is called “derating” the limiting the amount of load placed on it .This is called “derating” the transformer.This is done by determining the transformer.This is done by determining the derating factor.derating factor.

Harmonic derating factor = (1.414)(true rms phase Harmonic derating factor = (1.414)(true rms phase current)/instantaneous phase current current)/instantaneous phase current

Typically HDF varies from 0.5 to 0.9 .Typically HDF varies from 0.5 to 0.9 . The KVA derated = (HDF)(KVA nameplate)The KVA derated = (HDF)(KVA nameplate)

HARMONIC FILTRATION SYSTEM:HARMONIC FILTRATION SYSTEM:

The data recorded by the true RMS Power Analyzer is The data recorded by the true RMS Power Analyzer is analyzed and evaluated .If harmonics distortion is more than the analyzed and evaluated .If harmonics distortion is more than the prescribed limit ,then a filter system is to be installed at various feeder prescribed limit ,then a filter system is to be installed at various feeder lines /load centers .The filter system mainly consists of capacitor banks lines /load centers .The filter system mainly consists of capacitor banks along with a series reactor ,tuned for the predominant harmonic along with a series reactor ,tuned for the predominant harmonic frequency .Thus the filter system will inject the reactive power into the frequency .Thus the filter system will inject the reactive power into the network,below the harmonic frequency ,the same will be inductive network,below the harmonic frequency ,the same will be inductive

CONCLUSION:CONCLUSION:

Due to the development of modern protective and filtering Due to the development of modern protective and filtering devices, now-a-days harmonics were not a serious matter devices, now-a-days harmonics were not a serious matter of concern .But still research has been going on in order of concern .But still research has been going on in order to reduce this problem up to a large extent .to reduce this problem up to a large extent .