1. Understanding Harmonics Richard Molloy Technology Sales Manager, Power Quality

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

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

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

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

6. Power standards • Power standards are defined by the electricity regulator OFGEM • Standard EN 50 160 • ‘Voltage characteristics of electricity supplied by public distribution systems’

7. Long term interruptions 10 to 50 Short term interruptions 30 to 1000 Dips 30 to 1000 Short-term over-voltage <1.5kV Steady state voltage 230V +/- 10% for 95% of time Voltage unbalance <2% for 95% of time EN 50 160

8. Total harmonic distortion </= 8% for 95% of time Transient over-voltages Majority <6kV Frequency 50Hz +/- 1% for 99.5% of time Frequency 50Hz +/- 2% for 100% of time EN 50 160

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

10. Harmonics

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

12. Waveforms - Fundamental Fundamental Wave, 50Hz

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

14. Waveforms - Fundamental, 2nd and 3rd harmonic Fundamental Wave, 50Hz 2nd Harmonic, 100Hz 3rd Harmonic, 150 Hz

15. Fundamental + 2nd harmonic

16. Fundamental + 3rd harmonic

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

18. Switched mode power supply current waveform

19. Harmonic spectrum of SMPS

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

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

22. Effects of harmonics • Overloading of capacitors • Damage to sensitive electronic equipment • Excessive currents in neutral conductor

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

24. Effects of Triple-N harmonics

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

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

27. Mitigation measures • Neutral up-sizing • Passive filters • Active harmonic conditioners • Transformer based solutions

28. Neutral up-sizing • All neutrals in the system, including switchgear etc., must be rated for the neutral current as well as phase currents • 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 • Above 7th harmonic (350 Hz), skin effect should be considered • Cables should be de-rated in accordance with IEC 60364-5-523 / BS 7671 (Appendix 4)

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

30. Harmonic production IL IH

31. Harmonics and capacitors IL IH IC

32. Effects of Resonance

33. Avoiding resonance with PFC capacitors • Calculate the Resonant Frequency

34. Adding reactors

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

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

37. Harmonics In Practice Sub-Station

38. When others add to your system Sub-Station

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

40. Active harmonic conditioner AHC

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

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

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

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

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

46. Transformer based solutions • 3rd Harmonic rejection transformers • Phase shifting transformers • Isolation or harmonic suppression transformers

47. Conclusions

48. Conclusions • 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 • A combination of good design practice and effective harmonic mitigation measures is required

49. Conclusions • The power quality required will be dependant upon the equipment to be operated at any given location • 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.

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