Understanding Harmonics
Richard Molloy
Technology Sales Manager, Power Quality
© 2003 Eaton Corporation. All rights reserved.
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
© 2003 Eaton Corporation. All rights reserved.
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
Fundamental Wave, 50Hz
2nd Harmonic, 100Hz
Waveforms - Fundamental, 2nd
and 3rd harmonic
Fundamental Wave, 50Hz
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
i
4I m

Sin t  13 Sin3 t  15 Sin5 t  .........
Switched mode power supply
current waveform
Desktop System
2.0
1.5
Current (A)
1.0
0.5
0.0
0
90
180
-0.5
-1.0
-1.5
-2.0
Degrees
270
360
Harmonic spectrum of SMPS
Desktop System
0.6
0.5
Current (A)
0.4
0.3
0.2
0.1
0.0
1
2
3
4
5
6
7
8
9
10
Harmonic
11
12
13
14
15
16
17
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
IL
IH
Harmonics and capacitors
System Impedance
X L  2 fL
IL
IH
IC
System Capacitanc e
XC 
1
2 fC
Effects of Resonance
Freq
(Hz)
150
250
350
550
650
IH
100
100
100
100
100
100 kvar
IC
IS
3 103
9 109
18 118
62 162
115 215
300 kvar
600 kvar
IC
IS
IC
IS
9
109 21
121
31 131 91
191
88 188 1419 1519
769 669 177
77
265 165 145
45
Avoiding resonance with PFC
capacitors

Calculate the Resonant Frequency
System Fault Level (MVA)
f o  50
Capacitor Size (Mvar)
Adding reactors
Effect of adding reactors
Freq
Current flowing into supply in A
Series Reactor Tuned to the frequency shown below
Hz
150
No
Caps
100
600
kvar
121
182
Hz
197.0
189
210
225
250
Hz
Hz
Hz
Hz
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
Filters

Single Frequency Filter
|z|
f (Hz)


Double Tuned Filter
2nd Order High Pass
Filter
|z|
|z|
f (Hz)
f (Hz)
Harmonics In Practice
SubStation
When others add to your system
SubStation
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
INCOMING SUPPLY
SUB BOARD 1
SUB BOARD 2
DIS BOARD
DIS BOARD
AHC points of connection
INCOMING SUPPLY
SUB BOARD 1
SUB BOARD 2
DIS BOARD
DIS BOARD
AHC GLOBAL
AHC points of connection
INCOMING SUPPLY
SUB BOARD 1
SUB BOARD 2
DIS BOARD
DIS BOARD
AHC GLOBAL
AHC PARTIAL
AHC points of connection
INCOMING SUPPLY
SUB BOARD 1
SUB BOARD 2
DIS BOARD
AHC LOCAL
DIS BOARD
AHC GLOBAL
AHC PARTIAL
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
© 2003 Eaton Corporation. All rights reserved.
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.