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© 2003 Eaton Corporation. All rights reserved.
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
© 2003 Eaton Corporation. All rights reserved.
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
Fundamental Wave, 50Hz
Waveforms - Fundamental, 2nd and 3rd harmonic
2nd Harmonic, 100Hz
Fundamental Wave, 50Hz
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
mIi
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
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
IH
IL
Harmonics and capacitors
IH
IL
IC
fL 2X
Impedance System
L
fC 2
1X
eCapacitanc System
C
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
Freq
Hz NoCaps
600kvar
182Hz
189Hz
210Hz
225Hz
250Hz
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
|z|
f (Hz)
|z|
f (Hz)|z|
f (Hz)
Harmonics In Practice
Sub-Statio
n
When others add to your system
Sub-Statio
n
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
AHC points of connection
SUB BOARD 1
DIS BOARD
DIS BOARD
SUB BOARD 2
INCOMING SUPPLY
AHC points of connection
SUB BOARD 1
DIS BOARD
DIS BOARD
SUB BOARD 2 AHC GLOBAL
INCOMING SUPPLY
AHC points of connection
SUB BOARD 1
DIS BOARD
DIS BOARD AHC PARTIAL
SUB BOARD 2 AHC GLOBAL
INCOMING SUPPLY
AHC points of connection
SUB BOARD 1
AHC LOCAL
DIS BOARD
DIS BOARD AHC PARTIAL
SUB BOARD 2 AHC GLOBAL
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
© 2003 Eaton Corporation. All rights reserved.
Conclusions
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
© 2003 Eaton Corporation. All rights reserved.
Thank you