© 2003 Eaton Corporation. All rights reserved. Understanding Harmonics Richard Molloy Technology...

transcript

Understanding Harmonics

Richard Molloy

Technology Sales Manager, Power Quality

Agenda

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

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

Definition of Power Quality

‘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?

No definitive answer – entirely dependant on compatibility of equipment and supply

Power standards

Power standards are defined by the electricity regulator OFGEM

Standard EN 50 160 ‘Voltage characteristics of electricity supplied by

public distribution systems’

EN 50 160

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

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

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

Harmonics

Definition

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

Waveforms - Fundamental

Fundamental Wave, 50Hz

Waveforms – Fundamental and 2nd Harmonic

2nd Harmonic, 100Hz

Waveforms - Fundamental, 2nd and 3rd harmonic

2nd Harmonic, 100Hz

3rd Harmonic, 150 Hz

Fundamental + 2nd harmonic

Fundamental + 3rd harmonic

All wave-shapes can be reduced to a sine wave plus harmonics

Even a square wave

Square wave equation

.........tSin551tSin33

1tSin4

Switched mode power supply current waveform

Harmonic spectrum of SMPS

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

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

Effects of harmonics

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

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.

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

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

Mitigation measures

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

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)

Passive filters

Capacitor and reactor combination

Tuned to specific frequency

Requires higher voltage capacitors

Designed for a fixed system requirement

Harmonic production

Harmonics and capacitors

Impedance System

eCapacitanc System

Effects of Resonance

Freq IH 100 kvar 300 kvar 600 kvar (Hz) IC IS IC IS IC IS 150 100 3 103 9 109 21 121 250 100 9 109 31 131 91 191 350 100 18 118 88 188 1419 1519 550 100 62 162 769 669 177 77 650 100 115 215 265 165 145 45

Avoiding resonance with PFC capacitors

Calculate the Resonant Frequency

(Mvar) SizeCapacitor

(MVA) LevelFault System50of

Adding reactors

Effect of adding reactors

Hz NoCaps

600kvar

150 100 121 197.0 175.6 149.1 141.5 134.5

250 100 191 66.7 62.8 47.9 34 0

350 100 1519 75.7 73.7 66.8 61.5 51.9

550 100 302 79.2 77.7 72.8 69.4 63.5

650 100 237 79.8 78.3 73.7 70.6 65.2

Current flowing into supply in ASeries Reactor Tuned to the frequency shown below

Filters

Single Frequency Filter

Double Tuned Filter

2nd Order High Pass Filter

f (Hz)

f (Hz)|z|

f (Hz)

Harmonics In Practice

Sub-Statio

When others add to your system

Sub-Statio

Active harmonic conditioner

Harmonic current compensation, 2nd to 25th

Harmonic neutral current compensation

Global or selective harmonic current compensation

Site adjustable compensation parameters

Active harmonic conditioner

AHC points of connection

SUB BOARD 1

DIS BOARD

SUB BOARD 2

INCOMING SUPPLY

SUB BOARD 1

DIS BOARD

SUB BOARD 2 AHC GLOBAL

INCOMING SUPPLY

SUB BOARD 1

DIS BOARD

DIS BOARD AHC PARTIAL

INCOMING SUPPLY

SUB BOARD 1

AHC LOCAL

DIS BOARD

DIS BOARD AHC PARTIAL

INCOMING SUPPLY

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

Transformer based solutions

3rd Harmonic rejection transformers

Phase shifting transformers

Isolation or harmonic suppression transformers

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

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.

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

Thank you

© 2003 Eaton Corporation. All rights reserved. Understanding Harmonics Richard Molloy Technology...

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