Understanding of Harmonics in Power Distribution System Dr. Adel. M. Sharaf Department of Electrical...

Understanding of Harmonics in Power Distribution System

Dr. Dr. Adel. M. SharafAdel. M. Sharaf Department of Electrical & Department of Electrical &

Computer Engineering Computer Engineering

University of New BrunswickUniversity of New Brunswick

2/23/20062/23/2006 EE 6633 Seminar 1EE 6633 Seminar 1 22

OutlineOutline Power System Harmonics?Power System Harmonics? Why Harmonics are Troublesome? Nonlinear Loads Producing Harmonic Currents Harmonic Distortion? Negative Effects of Sustained HarmonicsNegative Effects of Sustained Harmonics Mitigation of the Effects of HarmonicsMitigation of the Effects of Harmonics Evaluation of AC Power System Harmonics? Conclusions Conclusions References References


What are Power System Harmonics? Harmonic: a mathematical definition, generally used when

talking about Integral orders of Fundamental frequencies Power system harmonics: currents or voltages with

frequencies that are integer multiples (h=0,1,2,…N) of the fundamental power frequency [1]

1st harmonic: 60Hz 2nd harmonic: 120Hz 3rd harmonic: 180Hz

Figure: 1 [2]


How are Harmonics Produced ?

Power system harmonics: presenting deviations from a perfect sinusoidal-waveform ( (voltage or current waveform).

The distortion comes from a Nonlinearity caused by saturation, electronic-switching and nonlinear electric loads, Inrush/Temporal/Arc/Converter/Limiter/Threshold Type Loads.

Figure: 2 Figure: 2 [1][1]


Why Bother about Harmonics?

50-60% of all electrical Ac Systems in North America operate with non-linear type loads

Power-Quality-PQ Issues & Problems Damage to Power Factor Correction capacitors Waveform Distortion can create

SAG/SWELL/NOTCHING/RINGING/… All can cause damage effects to consumer loads and

power systems due to Over-Current/Over-Voltage or Waveform Distortion

Additional Power/Energy Losses


Loads Producing Harmonic Currents

Electronic lighting ballasts/Controls Adjustable speed Motor-Drives Electric Arc Welding Equipment Solid state Industrial Rectifiers Industrial Process Control Systems Uninterruptible Power Supplies ( UPS )systems Saturated Inductors/Transformers LAN/Computer Networks


Current vs. Voltage Harmonics

Harmonic current flowing through the AC Power System impedance result in harmonic voltage-drop at the load bus and along the Feeder!!

Figure: 3 Figure: 3 [3][3]


How to Quantify Harmonic Distortion?

Total Harmonic Distortion-THD: the contribution of all harmonic frequency Currents/Voltages to the fundamental current. [3]

The level of THD-for Current or Voltage is directly related to the frequencies and amplitudes of the Offending Quasi-Steady State persistent Harmonics.

Individual Distortion Factor-(DF)-h quantify Distortion at h –harmonic-order


Calculation of THD

THD: Ratio of the RMS of the harmonic content to the RMS of the Fundamental [3]

(Eq-1)

Current THD-ICurrent THD-I (Eq-2)(Eq-2)

Voltage THD-VVoltage THD-V (Eq-3)(Eq-3)


Negative Effects of Harmonics Negative Effects of Harmonics

Overheating and premature failure of distribution transformers [1]

Increasing iron and copper losses or eddy currents due to stray flux losses Overheating and mechanical oscillations in the motor-load system [1]

Producing rotating magnitude field, which is opposite to the fundamental magnitude field.

Overheating and damage of neutral ground conductors [2]

Trouble sustained type Harmonics: 3rd, 9th, 15th … A 3-phase 4-wire system: single phase harmonic will add rather than

cancel on the neutral conductor Malfunction/Mal-Operation of Sensitive Tele-control and

Protection Relaying


Negative Effects of Harmonics (cont’ d) Negative Effects of Harmonics (cont’ d) False or spurious Relay operations and trips of circuit

breakers [2]

Failure of the Firing/Commutation circuits, found in DC motor-drives and AC drives with silicon controlled rectifiers (SCR-Thyristor) [1]

Mal-Operation instability of voltage regulator [1]

Power factor correction capacitor failure [1]

Reactance (impedance)-Zc of a capacitor bank decreases as the frequency increases.

Capacitor bank acts as a sink for higher harmonic currents. The System-Series and parallel Resonance can cause dielectric

failure or rupture the power factor correction capacitor failure due to Over-Voltages & Over-Currents.


Harmonics and Parallel Resonance CircuitHarmonics and Parallel Resonance Circuit

Harmonic currents produced by variable speed motor-drives: can be Harmonic currents produced by variable speed motor-drives: can be amplified up to 10-15 times in parallel resonance circuit formed by the amplified up to 10-15 times in parallel resonance circuit formed by the capacitance bank and network inductancecapacitance bank and network inductance [5][5]

Amplified/intensified harmonic currents: leading to internal Amplified/intensified harmonic currents: leading to internal overheating of the capacitor unit.overheating of the capacitor unit.

Higher frequency currents: causing more losses than 60hz currents Higher frequency currents: causing more losses than 60hz currents having same amplitudehaving same amplitude

Figure 4: Parallel resonance circuit and its equivalent circuitFigure 4: Parallel resonance circuit and its equivalent circuit [5][5]


Harmonics and Series Resonance CircuitHarmonics and Series Resonance Circuit

The voltage of upstream AC Network can be also The voltage of upstream AC Network can be also distorted due to series/parallel resonance formed by distorted due to series/parallel resonance formed by capacitance of the capacitor bank and System/load capacitance of the capacitor bank and System/load inductance : Ca cause high harmonic current circulation inductance : Ca cause high harmonic current circulation through the capacitorsthrough the capacitors [5][5]

Parallel Resonance can also lead to high voltage distortion.Parallel Resonance can also lead to high voltage distortion.

Figure 5: Series resonance circuit and its equivalent circuit Figure 5: Series resonance circuit and its equivalent circuit [5][5]


Measure Equipments of Harmonics Digital Oscilloscope: Digital Oscilloscope: Wave shape, THD and Amplitude of each harmonic Wave shape, THD and Amplitude of each harmonic ““True RMS” Multi-Meter:True RMS” Multi-Meter: GGiving correct readings for distortion-free sine waves and typically

reading low when the current waveform is distorted

Use of Harmonic Meters-Single Phase or three Phase

Figure 6: “True RMS” Multi-MeterFigure 6: “True RMS” Multi-Meter [3][3]


Standards for Harmonics LimitationIEEE/IEC

IEEE 519-1992 Standard: Recommended Practices and IEEE 519-1992 Standard: Recommended Practices and Requirements for Harmonic Control in Electrical Power Requirements for Harmonic Control in Electrical Power SystemsSystems (Current Distortion Limits for 120v-69kv DS)(Current Distortion Limits for 120v-69kv DS)

Table 1:Table 1: Current Harmonic Limits Current Harmonic Limits [4][4]

Ratio

Iscc / Iload

Harmonic oddHarmonic oddnumbers (<11)numbers (<11)

Harmonic oddHarmonic oddnumbers (>35)numbers (>35)

THD-i

< 20 4.0 %4.0 % 0.3 %0.3 % 5.0 %5.0 %

20 - 50 7.0 %7.0 % 0.5 %0.5 % 8.0 %8.0 %

50 - 10050 - 100 10.0 %10.0 % 0.7 %0.7 % 12.0 %12.0 %

>1000 15.0 %15.0 % 1.4 %1.4 % 20.0 %20.0 %


Standard of Harmonics Limitation (cont’d)

IEEE 519-1992 Standard: Recommended Practices and IEEE 519-1992 Standard: Recommended Practices and Requirements for Harmonic Control in Electrical Power Requirements for Harmonic Control in Electrical Power SystemsSystems (Voltage Distortion Limits)(Voltage Distortion Limits)

Table 2:Table 2: Voltage Harmonic Limits Voltage Harmonic Limits [4][4]

Bus VoltageBus Voltage Voltage Harmonic limit Voltage Harmonic limit

as (%) of Fundamentalas (%) of Fundamental THD-v (%)THD-v (%)

<= 69Kv <= 69Kv 3.03.0 5.05.0

69 - 161Kv69 - 161Kv 1.51.5 2.52.5

>= 161 Kv >= 161 Kv 1.01.0 1.51.5


Mitigation Of Harmonics Mitigation Of Harmonics [1][1]

Ranging from variable frequency motor- drive to other Ranging from variable frequency motor- drive to other nonlinear loads and equipmentsnonlinear loads and equipments

Power System Design:Power System Design: Limiting the non-linear load penetration to 30% of the maximum Limiting the non-linear load penetration to 30% of the maximum

transformer’s capacitytransformer’s capacity Limiting non-linear loads to 15% of the transformer’s capacity, Limiting non-linear loads to 15% of the transformer’s capacity,

when power factor correction capacitors are installed.when power factor correction capacitors are installed. Avoiding/Detuning resonant conditions on the AC System:Avoiding/Detuning resonant conditions on the AC System:

(Eq-4)(Eq-4) hrhr = resonant frequency as a multiple of the fundamental frequency = resonant frequency as a multiple of the fundamental frequency kVAsc kVAsc = short circuit current as the point of study = short circuit current as the point of study

kVARckVARc = capacitor rating at the system voltage = capacitor rating at the system voltage


Mitigation the Effects of Harmonics Mitigation the Effects of Harmonics [1] [1]

(cont’d)(cont’d) Delta-Delta and Delta-Wye TransformersDelta-Delta and Delta-Wye Transformers

Using two separate utility feed transformers with equal Using two separate utility feed transformers with equal non-linear loadsnon-linear loads

Shifting the phase relationship to various six-pulse Shifting the phase relationship to various six-pulse converters through cancellation techniquesconverters through cancellation techniques

Figure 7: Delta-Delta and Delta-Wye Transformers Figure 7: Delta-Delta and Delta-Wye Transformers [1][1]


Mitigation the Effects of Harmonics Mitigation the Effects of Harmonics [1][1] (cont’d)(cont’d)

Isolation-Interface TransformersIsolation-Interface Transformers The potential to “voltage match” by stepping up or The potential to “voltage match” by stepping up or

stepping down the system voltage, and by providing a stepping down the system voltage, and by providing a neutral ground reference for nuisance ground faults neutral ground reference for nuisance ground faults

The best solution when utilizing AC or DC drives that The best solution when utilizing AC or DC drives that use SCR/GTO/SSR.. as bridge rectifiersuse SCR/GTO/SSR.. as bridge rectifiers

Line Isolation-ReactorsLine Isolation-Reactors More commonly used for their low costMore commonly used for their low cost Adding a small reactor in series with capacitor bank Adding a small reactor in series with capacitor bank

forms a Blocking series Filter. forms a Blocking series Filter. Use diode bridge rectifier as a front end to avoid severe Use diode bridge rectifier as a front end to avoid severe

harmonic power quality problemsharmonic power quality problems


Mitigation the Effects of Harmonics Mitigation the Effects of Harmonics [1][1] (cont’d)(cont’d)

Harmonic-Shunt or Trap Filters:Harmonic-Shunt or Trap Filters: Used in applications with a high non-linear ratio to Used in applications with a high non-linear ratio to

system to eliminate harmonic currentssystem to eliminate harmonic currents Sized to withstand the RMS current as well as the value

of current for the harmonics Providing true distortion power factor correctionProviding true distortion power factor correction

Figure 8: Typical Harmonic Trap Filter [1]


Harmonic Trap Filters (cont’d)Harmonic Trap Filters (cont’d)

Tuned to a specific harmonic order such as the 5th, 7th, Tuned to a specific harmonic order such as the 5th, 7th, 11th,… etc to meet requirements of 11th,… etc to meet requirements of IEEE 519-1992 IEEE 519-1992 StandardStandard

The number of tuned filter-branches depends on the The number of tuned filter-branches depends on the offending steady-state harmonics to be absorbed and on offending steady-state harmonics to be absorbed and on

required reactive power level to be compensatedrequired reactive power level to be compensated

Figure 9: Typical Filter Capacitor Bank Figure 9: Typical Filter Capacitor Bank [5][5]


Harmonics Filter Types Harmonics Filter Types [6][6]

Isolating harmonic current to protect electrical Isolating harmonic current to protect electrical equipment from damage due to harmonic voltage equipment from damage due to harmonic voltage distortiondistortion

Passive Filter-Low cost: Passive Filter-Low cost: Built-up by combinations of capacitors, inductors Built-up by combinations of capacitors, inductors

(reactors) and resistors(reactors) and resistors most common and available for all voltage levelsmost common and available for all voltage levels

Active Power Filter APF:Active Power Filter APF: Inserting negative phase compensating harmonics into Inserting negative phase compensating harmonics into

the AC-Network, thus eliminating the undesirable the AC-Network, thus eliminating the undesirable harmonics on the AC Power Network.harmonics on the AC Power Network.

APF-Used only for for low voltage networksAPF-Used only for for low voltage networks


Harmonic Filter Types (cont’d) Harmonic Filter Types (cont’d) [7][7]

Unified Switched Capacitor Compensator USCS:

The single line diagram (SLD) of the utilization (single-phase) or (three-phase- 4-wire) feeder and the connection of the Unified Switched- Capacitor Compensator (USCS) to the Nonlinear-Temporal Inrush /Arc type Loads or SMPS-Computer/LAN-Network loads.

Figure 10 Figure 10 [7][7]


Harmonics Filter Types (cont’d) Harmonics Filter Types (cont’d) [7][7]

The USCS is a switched/modulated capacitor bank using a pulse-width modulated (PWM/SPWM) Switching Strategy. The switching device uses either solid state switch SSR-(IGBT or GTO).

Figure 11 [7]


Need To Evaluate System Harmonics? [1]

The application of capacitor banks in systems where 20% or more of the load includes other harmonic generating equipment.

The facility has a history of harmonic related problems, including excessive capacitor fuse operation or damage to sensitive metering/relaying/control equipment.

During the Planning/Design stage of any facility comprising capacitor banks and nonlinear harmonic generating equipment.


When to Evaluate System Harmonics? [1] (cont’d)

In facilities where restrictive Electric Power Utility Company Standards/Guidelines limit the harmonic injection back into their system to very small magnitudes.

Industrial/Commercial Plant expansions that add significant harmonic generating nonlinear type equipment operating in conjunction with capacitor banks.

When coordinating and planning to add any emergency standby generator as an alternate/renewable power source


ConclusionsConclusions

The harmonic distortion principally comes from Nonlinear-Type Loads.

The application of power electronics is causing increased level of harmonics due to Switching!!

Harmonic distortion can cause serious Failure/Damage problems.

Harmonics are important aspect of power operation that requires Mitigation!!

Over-Sizing and Power Filtering methods are commonly used to limit Overheating Effects of Sustained Harmonics.


ReferencesReferences [1] [1] www-ppd.fnal.gov/EEDOfficewww-ppd.fnal.gov/EEDOffice--w/Projects/CMS/LVPS/mg/8803PD9402.pdfw/Projects/CMS/LVPS/mg/8803PD9402.pdf

[2] [2] www.pge.com/docs/pdfs/biz/power_quality/power_quality_notes/harmonics.pdfwww.pge.com/docs/pdfs/biz/power_quality/power_quality_notes/harmonics.pdf

[3] [3] www.metersandinstruments.com/images/power_meas.pdfwww.metersandinstruments.com/images/power_meas.pdf

[4][4]httphttp://://engr.calvin.edu/PRibeiro_WEBPAGE/IEEE/ieee_cd/chapters/CHAP_9/c9toc/c9_frame.htmengr.calvin.edu/PRibeiro_WEBPAGE/IEEE/ieee_cd/chapters/CHAP_9/c9toc/c9_frame.htm

[5] [5] www.nokiancapacitors.com.es/.../EN-TH04-11_ 2004- Harmonics_and_Reactive_Power_Compensation_www.nokiancapacitors.com.es/.../EN-TH04-11_ 2004- Harmonics_and_Reactive_Power_Compensation_in_Practice.pdfin_Practice.pdf

[6][6]http://rfcomponents.globalspec.com/LearnMore/Communications_Networking/http://rfcomponents.globalspec.com/LearnMore/Communications_Networking/RF_Microwave_Wireless_Components/Harmonic_FiltersRF_Microwave_Wireless_Components/Harmonic_Filters

[7][7] A.M. Sharaf & Pierre Kreidi, POWERQ UALITYE NHANCEMEUNSTI NGA UNIFIEDSW ITCHED CAPACITOCRO MPENSATOR, CCECE 2003 - CCGEI 2003, Montreal, Mayimai 2003

0-7803-7781-8/03/$17.00 0 2003 IEEE


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