© 2003 Eaton Corporation. All rights reserved. Understanding Harmonics Richard Molloy Technology Sales Manager, Power Quality

Agenda l Introduction l Definition of ‘Power Quality’ l Identification of power quality problems l Harmonics – causes and effects l Mitigation techniques l Conclusion

The cost of poor power quality l Cost of power quality problems to European industry & commerce is estimated at €10 billion per annum l Expenditure on preventative measures is less than 5% of this

Definition of Power Quality l ‘A supply that is always available, always within voltage and frequency tolerance, with a pure, noise free, sinusoidal wave shape’ Source – Leonardo Power Quality Initiative

How good is good enough? l No definitive answer – entirely dependant on compatibility of equipment and supply

Power standards l Power standards are defined by the electricity regulator OFGEM n Standard EN n ‘Voltage characteristics of electricity supplied by public distribution systems’

EN l Long term interruptions10 to 50 l Short term interruptions30 to 1000 l Dips30 to 1000 l Short-term over-voltage<1.5kV l Steady state voltage230V +/- 10% for 95% of time l Voltage unbalance<2% for 95% of time

EN l Total harmonic distortion </= 8% for 95% of time l Transient over-voltagesMajority <6kV l Frequency50Hz +/- 1% for 99.5% of time l Frequency50Hz +/- 2% for 100% of time

Identification of problems l Harmonic distortion l Voltage sags (‘dips’, ‘brownouts’) l Voltage swells (‘surges’) l Outages (‘power cuts’, ‘blackouts’) l Transient voltage surges (‘spikes’) l Earthing (‘grounding’) l Poor power factor

© 2003 Eaton Corporation. All rights reserved. Harmonics

Definition l Waveforms with frequencies that are multiples of the fundamental frequency (50Hz UK & Europe, 60Hz North America)

Harmonic production l Half wave rectifier l Full wave rectifier l Thyristor Switching l or t I I I I t t t

Waveforms - Fundamental Fundamental Wave, 50Hz

Waveforms – Fundamental and 2nd Harmonic 2nd Harmonic, 100Hz Fundamental Wave, 50Hz

Waveforms - Fundamental, 2nd and 3rd harmonic

Fundamental + 2nd harmonic

Fundamental + 3rd harmonic

All wave-shapes can be reduced to a sine wave plus harmonics l Even a square wave l Square wave equation

Switched mode power supply current waveform

Harmonic spectrum of SMPS

Causes of harmonics l Harmonic currents are caused by the use of non-linear loads: n Switched mode power supplies n HF fluorescent ballasts n Compact fluorescent lamps n Inverters Variable frequency drives UPS systems

Effects of harmonics l Erroneous operation of control systems l Excessive heating in rotating machines l Overloading of transformers l Overloading of switchgear and cables l Nuisance tripping of circuit breakers

Effects of harmonics l Overloading of capacitors l Damage to sensitive electronic equipment l Excessive currents in neutral conductor

Effects of Triple-N harmonics l Triple-N harmonics are odd multiples of 3 times fundamental frequency, i.e., 3 rd, 9 th, 15 th etc. l They are all in phase and sum in the neutral conductor l Switched Mode Power Supplies (SMPS) produce a lot of 3 rd harmonic - this is especially problematic in commercial buildings due to the vast number of computers, office equipment etc.

Effects of Triple-N harmonics

l A 3-phase star connected system with a balanced linear load has no current flowing in the neutral l Where a lot of 3 rd (or other triple-N) harmonics are present, neutral currents can be considerably in excess of phase currents l This causes overheating of neutral conductors. Note these may only be 50% rated in older buildings l Neutrals do not normally have over-current protection

Limits on Harmonic Distortion l Harmonic currents flowing back to the supply cause harmonic voltage distortion due to the supply impedance l Governed by Engineering Recommendation G5/4 l Title : ‘Limits for Harmonics in the U.K. Electricity Supply System’. l Guidance ONLY

Mitigation measures l Neutral up-sizing l Passive filters l Active harmonic conditioners l Transformer based solutions

Neutral up-sizing l All neutrals in the system, including switchgear etc., must be rated for the neutral current as well as phase currents l A 4 or 5 core 3 phase cable is rated for current flowing in the phase conductors only. Current in the neutral can cause overheating of the cable l Above 7 th harmonic (350 Hz), skin effect should be considered l Cables should be de-rated in accordance with IEC / BS 7671 (Appendix 4)

Passive filters l Capacitor and reactor combination l Tuned to specific frequency l Requires higher voltage capacitors l Designed for a fixed system requirement

Harmonic production IHIH ILIL

Harmonics and capacitors IHIH ILIL ICIC

Effects of Resonance

Effect on power factor capacitors l Increase in current loading l Increase in dielectric loss n Dielectric Loss = l Increase in Dielectric Stress n Dielectric Stress =

Avoiding resonance with PFC capacitors l Calculate the Resonant Frequency

Adding reactors

Effect of adding reactors Current flowing into supply in A Series Reactor Tuned to the frequency shown below

Voltage across the capacitor at various tuning frequencies

Filters l Single Frequency Filter l Double Tuned Filter l 2nd Order High Pass Filter |z| f (Hz) |z| f (Hz) |z| f (Hz)

Harmonics In Practice Sub- Station

When others add to your system Sub- Station

Active harmonic conditioner l Harmonic current compensation, 2 nd to 25 th l Harmonic neutral current compensation l Global or selective harmonic current compensation l Site adjustable compensation parameters

Active harmonic conditioner AHC

AHC points of connection SUB BOARD 1 DIS BOARD SUB BOARD 2 INCOMING SUPPLY

AHC points of connection SUB BOARD 1 DIS BOARD SUB BOARD 2 AHC GLOBAL INCOMING SUPPLY

AHC points of connection SUB BOARD 1 DIS BOARD AHC PARTIAL SUB BOARD 2 AHC GLOBAL INCOMING SUPPLY

AHC points of connection SUB BOARD 1 AHC LOCAL DIS BOARD AHC PARTIAL SUB BOARD 2 AHC GLOBAL INCOMING SUPPLY

AHC advantages l Continued guaranteed effective harmonic compensation l Easy to use and install l Auto configures l NOT susceptible to harmonic overload l Expandable l Compatible with electric generators l Connected anywhere

Transformer based solutions l 3rd Harmonic rejection transformers l Phase shifting transformers l Isolation or harmonic suppression transformers

© 2003 Eaton Corporation. All rights reserved. Conclusions

l As more electronic equipment is used in industry and commerce, harmonics have become a major power quality problem – more harmonics are generated, and more equipment is adversely affected by these harmonics l A combination of good design practice and effective harmonic mitigation measures is required

Conclusions l The power quality required will be dependant upon the equipment to be operated at any given location l A holistic approach to power quality is required – one solution is unlikely to address all the problems – a combination of equipment will be required to achieve the quality required.

Power quality measurement l Most power quality problems can be measured or monitored – if you suspect a problem, we can conduct a PQ survey to identify: n Harmonic distortion n Transient voltage disturbance n Power factor n Load survey n Unbalance n Flicker

© 2003 Eaton Corporation. All rights reserved. Thank you