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Power Quality Partnership
Harmonics in Power Systems
Copper Development Association
Power Quality Partnership
Copper Development Association
Fluke (UK) Ltd
MGE UPS Systems Ltd
Rhopoint Systems Ltd
Copper Development Association
Copper Development Association
• Established 1933
• website - www.cda.org.uk
• Technical helpline 01727 731200
• IEE Endorsed Provider
Copper Development Association
Harmonics in Power Systems
Background to Harmonics, Problems, Solutions and Standards
David Chapman, Copper Development Association
Harmonic Measurement and Power Quality Surveys
Ken West, Fluke (UK) Ltd
Total Harmonic Management
Shri Karve, MGE UPS Systems Ltd
Applying Predictive Techniques to Power Quality
David Bradley, Rhopoint Systems Ltd
Copper Development Association
Fundamental with third and fifth harmonics
1.100
Fundamental
Third harmonic
Fifth harmonic
0.000
0
90
-1.100
Copper Development Association
180
270
360
Composite waveform
1.600
0.000
0
90
-1.600
Copper Development Association
180
270
360
Loads that generate harmonics
 Switched mode power supplies (SMPS)
 Electronic fluorescent lighting ballasts
 Variable speed drives
 Un-interruptible power supplies (UPS)
These are all non-linear loads
Copper Development Association
How harmonics are generated – linear load
1.1
Current Waveform
Current
Load Line
Voltage
0.0
-1.2
Angle
0.0
1.2
Angle
Voltage Waveform
-1.1
Copper Development Association
How harmonics are generated – non-linear load
1
Current Waveform
Current
Load Line
Voltage
0
-1
0
Angle
1
Angle
-1
Voltage Waveform
Copper Development Association
A Common non-linear load
Copper Development Association
Current waveform for a typical Personal Computer
Desktop System
2.0000
1.5000
1.0000
Current (A)
0.5000
0.0000
0
90
180
-0.5000
-1.0000
-1.5000
-2.0000
Degrees
Copper Development Association
270
360
Harmonic profile of a typical Personal Computer
Desktop System
0.6000
0.5000
Current (A)
0.4000
0.3000
0.2000
0.1000
0.0000
1
2
3
4
5
6
7
8
9
Harmonic
Copper Development Association
10
11
12
13
14
15
16
17
Harmonic profile for electronic fluorescent ballast
Compact Fluorescent Lamp with HF Ballast
0.0600
0.0500
Current (A)
0.0400
0.0300
0.0200
0.0100
0.0000
1
2
3
4
5
6
7
8
9
Harmonic
Copper Development Association
10
11
12
13
14
15
16
17
Harmonic profile for magnetic fluorescent ballast
Compact Fluorescent Lamp with Magnetic Ballast
0.1400
0.1200
Current (A)
0.1000
0.0800
0.0600
0.0400
0.0200
0.0000
1
2
3
4
5
6
7
8
9
Harmonic
Copper Development Association
10
11
12
13
14
15
16
17
Six-pulse bridge
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Typical harmonic profile - six-pulse bridge
Six pulse bridge - harmonic current
25
20
15
%
10
5
0
1
2
3
4
5
6
7
8
9
10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25
Harmonic number
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Twelve-pulse bridge
Copper Development Association
Typical harmonic profile - twelve-pulse bridge
Twelve pulse bridge - harmonic current
25
20
15
%
10
5
0
1
2
3
4
5
6
7
8
9
10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25
Harmonic number
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Why have harmonics become so important?
Harmonic generating equipment has been in
use for decades
• Increase in the number of loads
• Change in the nature of loads
• Increase in those producing triple-Ns
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Equivalent circuit of a harmonic generating load
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Harmonic Diversity
80
70
60
50
% wrt RMS 40
30
20
10
0
Fund
41
3rd
20
5th
Harmonic
Copper Development Association
10
7th
5
9th
2
11th
1
No of Units (pairs)
Harmonic Diversity - THDI
THD
120
100
% wrt Fundamental
80
60
40
20
0
1
2
5
10
No of Units (pairs)
Copper Development Association
20
41
Problems caused by harmonics
 currents within the installation
 overloading of neutrals
 overheating of transformers
 nuisance tripping of circuit breakers
 over-stressing of power factor correction capacitors
 skin effect
 voltages within the installation
 voltage distortion & zero-crossing noise
 overheating of induction motors
 currents in the supply
Copper Development Association
Overheating of neutrals
In balanced three phase systems the
fundamental current cancels out
But triple-N harmonics
add arithmetically!
Non triple-N harmonics cancel in the neutral
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Harmonic neutral currents
Phase 1
Phase 2
Phase 3
Phase 1 3rd harmonic
Phase 2 3rd harmonic
Phase 3 3rd harmonic
0
120
240
3rd harmonic neut ral current
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360
480
600
720
Neutral conductor sizing
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Neutral conductor sizing
Copper Development Association
Neutral conductor sizing
Copper Development Association
Neutral conductor sizing
Neutral currents can easily approach twice the phase
currents - sometimes in a half-sized conductor.
IEEE 1100-1992 recommends that neutral busbars
feeding non-linear loads should have a crosssectional area not less than 173% that of the phase
bars.
Neutral cables should have a cross-sectional area that
is 200% that of the phases, e.g. by using twin single
core cables.
Copper Development Association
Sizing the neutral conductor
BS 7671:2001 - From January 2002
473 - 03 - 04
where neutral current is expected to exceed phase
current
473 - 03 - 05
where neutral cross-section is less than phase cross
section
- neutral overcurrent protection is required
Copper Development Association
Sizing the neutral conductor
For three phase circuits using single core cables:
• Use a neutral conductor sized for the actual
neutral current
• If the neutral current is not known, use a double
sized neutral cable
• Provide overcurrent protection
• But take account of the grouping factors!
• Take into account voltage drop
Copper Development Association
Sizing the neutral conductor
For multi-core cables :
• Multi-core cables are rated for only three loaded
cores - applies to both 4 and 5 core cables
• When harmonics are present the neutral is also a
current carrying conductor
• Cable rated for three units of current is carrying
more - three phases plus the neutral current
• It must be de-rated to avoid overheating
• Neutral must have overcurrent protection
• Grouping factor must be taken into account
Copper Development Association
Sizing the neutral conductor - thermal
2.5
Cable size multiplier
2.0
1.5
1.0
0.5
0
10
20
30
40
% third harmonic current in phase
Copper Development Association
50
60
70
Sizing the neutral conductor - IEC
2.5
Cable size multiplier
2.0
1.5
1.0
0.5
0
10
20
30
40
% third harmonic current in phase
Copper Development Association
50
60
70
Sizing the neutral conductor
2.5
Thermal
IEC
Cable size multiplier
2.0
1.5
1.0
0.5
0
10
20
30
40
% third harmonic current in phase
Copper Development Association
50
60
70
Neutral conductor protection
Neutral conductors should be appropriately
sized and provided with over-current protection.
The protective device must break all the phases,
but does not necessarily need to break the
neutral itself.
This implies a future need for 4 pole breakers
with double rated neutral poles.
Copper Development Association
Effect of harmonics on transformers
Transformers supplying harmonic loads must be
appropriately de-rated
 Harmonic currents, being of higher frequency,
cause increased magnetic losses in the core
and increased eddy current and skin effect
losses in the windings
 Triple-n harmonic currents circulate in delta
windings, increasing resistive losses, operating
temperature and reducing effective load
capacity
Copper Development Association
Increased Eddy current losses in transformers
Increase in eddy current loss can be calculated by:
Peh  Pef
h  h max

h 1
I 2h h 2
where:
Peh is the total eddy current loss
Pef is the eddy current loss at fundamental
frequency
h is the harmonic order
Ih is the RMS current at harmonic h as a
percentage of rated fundamental current
Copper Development Association
K-Rating of Transformers
Two rating or de-rating systems for transformers:• American system, established by UL and
manufacturers, specifies harmonic capability of
transformer - known as K factor.
• European system, developed by IEC, defines
de-rating factor for standard transformers known as factor K.
Copper Development Association
K-Rating of Transformers - US System
First, calculate the K factor of the load according to:
K
h  h max

h 1
I 2h h 2
where:
h is the harmonic order
Ih is the RMS current at h in per unit of rated load current
Copper Development Association
K-Rating of Transformers - US System
Desktop System
0.6000
0.5000
Current (A)
0.4000
0.3000
0.2000
0.1000
0.0000
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
Harmonic
For this typical PC load, the K factor is 11.6
(See IEE 1100-1992 for a worked example)
Copper Development Association
K-Rating of Transformers - US System
Next, select a transformer with a higher K rating:
standard ratings are 4, 9, 13, 20, 30, 40 and 50.
NB - for non K-rated transformers:
The K factor describes the increase in eddy
current losses, not total losses.
Copper Development Association
K-Rating of Transformers - European System
In Europe, the transformer de-rating factor is calculated
according to the formulae in BS 7821 Part 4. The factor
K is given by:

e  I1 
K  1 
 
1 e  I 


 I
 nq  n

  I1
n2

2 n N



2




0.5
e is ratio of eddy current loss (50 Hz) to resistive loss
n is the harmonic order
q is dependent on winding type and frequency,
typically 1.5 to 1.7
Copper Development Association
K-Rating of Transformers - European System
Desktop System
0.6000
0.5000
Current (A)
0.4000
0.3000
0.2000
0.1000
0.0000
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
Harmonic
For the same PC load, the de-rating factor is 78%
Copper Development Association
K Factor
The methods for rating transformers
are discussed in CDA Publication 144
In addition, calculation software is
available on our web site:
www.cda.org.uk
Copper Development Association
K-Rating - Calculation software
Copper Development Association
K-Rating - Calculation software
Copper Development Association
Harmonic Diversity - K Factor
K Factor
16
14
12
K Factor
10
8
6
4
2
0
1
2
5
10
No of Units (pairs)
Copper Development Association
20
41
K-Rating or De-rating?
‘K-rated’ transformers are designed to supply harmonic
loads by :
• using stranded conductors to reduce eddy current
losses
• bringing secondary winding star point connections
out separately to provide a 300% neutral rating
Copper Development Association
K-Rating or De-rating?
‘De-rating’ a standard transformer has some
disadvantages: primary over-current protection may be too high
to protect the secondary and too low to survive
the in-rush current
 the neutral star point is likely to be rated at only
100% of the phase current
 it is less efficient
 future increases in loading must take the de-rating
fully into account
Copper Development Association
Effect of harmonics on transformers
Transformers supplying harmonic loads must be
appropriately de-rated
 Harmonic currents, being of higher frequency,
cause increased magnetic losses in the core
and increased eddy current and skin effect
losses in the windings
 Triple-n harmonic currents circulate in delta
windings, increasing resistive losses, operating
temperature and reducing effective load
capacity
Copper Development Association
Effect of triple-n harmonics in transformers
Triple-n harmonic currents circulate in delta windings they do not propagate back onto the supply network.
- but the transformer must be specified and rated to
cope with the additional losses.
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Skin effect
Alternating current tends to flow on the outer surface
of a conductor - skin effect - and is more pronounced
at high frequencies.
 At the seventh harmonic and above, skin effect
will become significant, causing additional loss
and heating.
 Where harmonic currents are present, cables
should be de-rated accordingly. Multiple cable
cores or laminated busbars can be used.
Copper Development Association
Skin effect - penetration depth
where:
1
d
2
  105
f
d is the depth of penetration, mm
f is the frequency, Hz, and
 is the resistivity of the
conductor
At the fundamental, 50 Hz
d = 9.32 mm
At the 11th harmonic, 550Hz
d = 2.81 mm
Copper Development Association
Circuit breakers
Nuisance tripping can occur in the presence of
harmonics for two reasons:
 Residual current circuit breakers are
electromechanical devices. They may not sum
higher frequency components correctly and
therefore trip erroneously.
 The current flowing in the circuit will be higher
than expected due to the presence of harmonic
currents. Most portable measuring instruments
do not read true RMS values.
Copper Development Association
Problems caused by harmonics
 currents within the installation
 overloading of neutrals
 over-heating of transformers
 over-stressing of power factor correction capacitors
 skin effect
 nuisance tripping of circuit breakers
 voltages within the installation
 voltage distortion & zero-crossing noise
 over-heating of induction motors
 currents in the supply
Copper Development Association
Voltage distortion
Copper Development Association
Reducing Voltage Distortion by Circuit Separation
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Effect of harmonics on induction motors
 Increased magnetic and copper losses
 Each harmonic generates a field which may rotate
forward (+), backward (-), or remain stationary (0)
1
2
3
4
5
6
7
8
9
10
11
12
+
-
0
+
-
0
+
-
0
+
-
0
• Zero sequence harmonics produce a stationary field,
causing over-heating and reduced efficiency
Copper Development Association
Effect of harmonics on induction motors
• The negative and positive sequence harmonics
together cause torque pulsing, vibration and
reduced service life
• Harmonics are induced in the rotor leading to
overheating and torque pulsing
Stator harmonic
1
Rotor harmonic
Harmonic rotation F
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5
6
B
7
6
F
11
12
B
13
12
F
17
18
B
19
18
F
Motor de-rating curve for harmonic voltages
1
De-rating Factor
0.95
0.9
0.85
0.8
0.75
0.7
0
2
4
6
Harmonic Voltage Factor (HVF)
Copper Development Association
8
10
12
Harmonic voltage factor
The Harmonic Voltage Factor (HVF) is defined as:
HVF 
n  V 2
n

n 5
n
where:
Vn is the RMS voltage at the nth harmonic as a
percentage of the fundamental, and
n is the order of each odd harmonic, excluding
triple-Ns
Copper Development Association
Harmonic problems affecting the supply
 Harmonic currents cause harmonic voltage
distortion on the supply that can affect
other customers. This distortion can
propagate onto the 11 kV grid and spread
widely.
 There are limits for harmonic voltage
distortion - a supplier may refuse to
supply power to a site that exceeds them.
Copper Development Association
Harmonic Standards
Electricity Association Engineering
Recommendation G 5/4 (2001)
BS EN 61000
IEEE Std 519-1992 Recommended Practices and
Requirements for Harmonic Control in Electrical
Power Systems
ISBN
Copper Development Association
1 - 55937 - 239 - 7
Why revise G5/3?
 Levels at 132kV higher than Grid Code allows
 Introduction of concept of Electromagnetic
Compatibility
 G5/3 didn’t include notching and burst harmonics
 Introduction of the EU Compatibility Directive and
developments in IEC and European Standards
 Better information on network harmonic impedance
(see ETR 112)
Copper Development Association
The Electromagnetic Compatibility concept
 Satisfactory operation of supply systems and
users’ equipment only when electromagnetic
compatibility exists between them
 Emission limits help fulfil this objective
 G5/4 seeks to limit harmonic distortion levels on the
network at the time of connection to below the
immunity levels of equipment
 Enforced via the Electricity Supply Regs, Grid &
Distribution Codes, and connection agreements
Copper Development Association
Harmonic Compatibility
Planning levels
Probability Density
Total supply
network
disturbance
Compatibility Level
Immunity
(test) levels
Emission
limits for
individual
sources
Disturbance Level
Copper Development Association
Susceptibility of
local equipment
Compatibility levels v Planning levels
 Compatibility levels in IEC 61000-2-2 & 61000-212, for 400V and 6.6kV to 33kV systems are based
on the immunity of capacitors
 The margins between planning levels and the
compatibility levels depend on voltage level and
range from 3% at lv and 5% at mv to 0.5% at ehv
 The margins are necessary to make allowance for
system resonance and for loads connected where
there is no consent required from the DNO
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Stage 1
 Applies only to lv connected loads
 Requires reference to other IEC standards e.g.
 IEC 61000-3-2 emissions from lv connected
equipment <16A
 IEC 61000-3-4 ditto >16A (To be 61000-3-12)
 Clarifies that levels may be modified by reference to
relevant fault levels rather than the notional ones
used to derive the table of emissions Table 7
Copper Development Association
Aggregate loads

G5/4 requires that aggregate non-linear loads be
considered
• An individual non-linear equipment complying
with 61000-3-2 can be connected without
consideration
• Groups of non-linear equipment with
aggregate rated current <16A and complying
can be connected
• For >16A either 61000-3-4 or 61000-3-6 should
be used to assess emissions using diversity
rules from 61000-3-6 if necessary
Copper Development Association
Example of application - the problem

Connection of communication centre equipment
– 15 off rectifier equipment type R2948-15
– each equipment is rated at 12.37A
– each equipment meets BS EN 61000-3-2
– the connection will be at lv and single phase
– future expansion expected to 30 units

Can they be connected?

The customer says that no data on emissions is
available
Copper Development Association
The solution

Data must be available - cannot claim
BS EN 61000-3-2 compliance otherwise!

Data was obtained simply by e-mailing
the manufacturer in New Zealand

Simplified calculations were carried out
on a spreadsheet to check compliance
Copper Development Association
Product data sheet
Product Test
Harmonic Emissions
Product: R2948-15
Serial #: 1040171
Date tested: 07 October 1999
Product Compliance Group
0.5
Test Parameters
Input Voltage: 230v 50Hz
Output Voltage: 54v at no load
Output Current: 52A
Ambient temperature: +20°C
12.37A
EUT
EN61000-3-2
IP Currenty(A)
0.4
0.3
0.2
0.1
0.0
0 1
2 3
4 5 6
7 8
9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40
Harmonic (f1 = 50Hz)
Copper Development Association
The calculations

As a first estimate the current emissions are
multiplied by the number of units, and the result
compared with the values in Table 7 of G5/4.
This shows that there is no problem

The spreadsheet calculations would show that
the future increase to 30 units would give values
of emissions greater than the limits for triple-Ns
above 21st
Copper Development Association
Table 7: Stage 1 Max Harmonic RMS Current Emissions
for aggregate loads and equipment rated >16A per phase
Harmonic Emission
order ‘h’ current Ih
2
28.9
3
48.1
4
9.0
5
28.9
6
3.0
7
41.2
8
7.2
9
9.6
10
5.8
11
39.4
12
1.2
13
27.8
14
2.1
Harmonic Emission
order ‘h’ current Ih
15
1.4
16
1.8
17
13.6
18
0.8
19
9.1
20
1.4
21
0.7
22
1.3
23
7.5
24
0.6
25
4.0
26
1.1
27
0.5
Copper Development Association
Harmonic Emission
order ‘h’ current Ih
28
1.0
29
3.1
30
0.5
31
2.8
32
0.9
33
0.4
34
0.8
35
2.3
36
0.4
37
2.1
38
0.8
39
0.4
40
0.7
Harmonic Emission
order ‘h’ current Ih
41
1.8
42
0.3
43
1.6
44
0.7
45
0.3
46
0.6
47
1.4
48
0.3
49
1.3
50
0.6
Sample spreadsheet
Harmonic
number
3
Emission
from EUT
0.42
Emissions
15 units
6.3
Table 7
emissions
48.1
Emissions
30 units
12.6
5
0.21
3.1
28.9
6.2
7
0.16
2.3
41.2
4.7
9
0.11
1.65
9.6
3.3
15
0.03
0.43
1.4
0.8
21
0.035
0.525
0.7
1.05
Emissions in Amps (RMS)
Copper Development Association
Example flow chart for lv connection
START
N
N
Complies with
61000-3-4
Less than
16A
Y
Complies with
6.3.1
N
Y
Y
N
3 phase
Y
Complies
Complieswith
with
61000-3-2
61000-3-2
0
Y
Y
N
Complies
with Table 7
Y
Y
N
Mitigation required
Connect to network
Copper Development Association
N
Y
Complies
with Table 6
N
Complies with
6.2
<5 kVA
Go to Stage 2
N
Stage 2
 This applies only to:
 a load or aggregate load that doesn’t meet IEC
61000-3-2 and 61000-3-6, or Table 7 current
emissions, i.e. Stage 1
 PCC less than 33kV i.e. at 6.6, 11 or 22kV
 Current emissions can be less than Table 12, or a
simplified voltage assessment can be used based
on the harmonic impedance just described
Copper Development Association
Harmonic Measurements
Copper Development Association
Assessment of the connection of new
non-linear equipment under Stage 2
a)
measure voltage distortion present at PCC
b)
assess the voltage distortion which will be
caused by the new equipment, and
c)
predict the possible effect on harmonic
voltage levels by an addition of the results
of (a) and (b)
Copper Development Association
Assessment of the connection of new
non-linear equipment under Stage 2
If the results of (c) are less than
• the harmonic voltage planning levels for the
5th harmonic and
• the THD planning level
connection of the equipment is acceptable
Copper Development Association
Combination rules
 for harmonics up to and including the 5th and for
all triple-Ns, the measured and calculated values
of voltage distortion are assumed to peak at the
same time and to be in phase - linear addition
 for the other harmonics, an average phase
difference of 90 is assumed at the time of
maximum THD - rms addition
 the THD is then given by the rms addition of all
combined harmonics up to the 50th
Copper Development Association
The Challenge
to keep the harmonic voltage distortion at the point of
common coupling below levels permitted by G5/4
to keep harmonic currents below levels
that cause equipment overload and damage within the
installation
that are permitted by G5/4
Copper Development Association
Harmonic solutions
Steps to be taken to reduce voltage distortion on
the supply include, for example:
 Passive harmonic filters
 Isolation transformers
 Active harmonic conditioners
Copper Development Association
Passive harmonic filters
Filters are useful when
 the harmonic profile is well defined – such as
motor controllers
 the lowest harmonic is well above the
fundamental frequency
- but filter design can be difficult and, especially
for lower harmonics, the filters can be bulky and
expensive
Copper Development Association
Passive harmonic filter
Copper Development Association
f
Power Factor
I
V
Ip
Iq
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0

2
Power Factor
POWER
Ip
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0

2
Power Factor
POWER
Iq
0
Copper Development Association

2
f
Power Factor
V
IL
I1
I5
Copper Development Association
0
I7

2
Power Factor
G
active
power
reactive power
M
Copper Development Association
Power Factor Correction
G
CAPACITOR
active
power
reactive power
M
Copper Development Association
Power Factor Correction
G
CAPACITOR
active
power
reactive power
M
Copper Development Association
Power Factor Correction
• Diversity
• Self Excitation
• Harmonics
M
M
Copper Development Association
M
M
Power Factor Correction
Control
M
M
M
Copper Development Association
M
Power Factor Correction
• Transformer overloading
• Step voltage
Control
• Bank Size
• Switch-fuse & Cable load
ratings
M
M
M
M
Copper Development Association
• Load make/break rating
of main isolator/switchfuse
Power Factor Correction Bank Sizing
Required improvement in % wattess
X kW Maximum Demand
equivalent to {tan(cos-1PFA) - tan(cos-1PFR)} X MD (kW)
or
kVArh (actual) - kVArh (required)
running hours X load factor
Copper Development Association
Power Factor Correction
• Capacitor Discharge time required for
standard Power Factor banks (1 minute)
• Rapidly switching loads require Zero
crossing Thyristor or IGBT switched
steps
e.g. Spot Welders
Lift motors
Cranes
Copper Development Association
Harmonic Resonance
TO POWER SYSTEM
LV
CONVERTOR
M
HARMONICS
Copper Development Association
AMPLIFIED
HARMONICS
Detuned or Blocking Banks
SOURCE IMPEDANCE WITH FILTER IN CIRCUIT
Capacitive
0.3000
Fo = 189 to 204 Hz
0.2500
Y = Ln (Z+1)
0.2000
Inductive
0.1500
5th
11th
7th
0.1000
0.0500
Frequency
Copper Development Association
592
580
568
556
544
532
520
508
496
484
472
460
448
436
424
412
400
388
376
364
352
340
328
316
304
292
280
268
256
244
232
220
208
196
184
172
160
148
136
124
112
100
0.0000
Filter Banks - 5th Harmonic
SOURCE IMPEDANCE WITH FILTER IN CIRCUIT
Capacitive
0.3000
Fo = 235 to 245Hz
0.2500
7th
Y = Ln (Z+1)
0.2000
0.1500
Inductive
0.1000
0.0500
10
0
10
7
11
4
12
1
12
8
13
5
14
2
14
9
15
6
16
3
17
0
17
7
18
4
19
1
19
8
20
5
21
2
21
9
22
6
23
3
24
0
24
7
25
4
26
1
26
8
27
5
28
2
28
9
29
6
30
3
31
0
31
7
32
4
33
1
33
8
34
5
35
2
35
9
36
6
37
3
38
0
0.0000
Frequency
Copper Development Association
Filter Banks 5th & 7th Harmonic
SOURCE IMPEDANCE WITH FILTER IN CIRCUIT
0.5000
0.4500
0.4000
Y = Ln (Z+1)
7th
5th
0.3500
0.3000
0.2500
0.2000
0.1500
0.1000
0.0500
Frequency
Copper Development Association
592
580
568
556
544
532
520
508
496
484
472
460
448
436
424
412
400
388
376
364
352
340
328
316
304
292
280
268
256
244
232
220
208
196
184
172
160
148
136
124
112
100
0.0000
Third harmonic filters
10 Amps
R
N
S
T
E
Copper Development Association
30 Amps
Load
10 Amps
10 Amps
Third harmonic filters
10 Amps
R
I3 =300Amps
Amps
N
Load
S
T
10 Amps
v
E
Copper Development Association
10 Amps
Delta Interconnected-Star Transformer
R
S
T
R
S
T
N
Copper Development Association
N
Harmonic reduction transformers
Load
I3
Interconnected Star
Transformer sized for
harmonic currents only
Copper Development Association
Isolating transformers
Delta-star isolating transformers reduce propagation
of harmonic current into the supply.
 Transformers should be adequately rated to
cope with the harmonics
 Although the transformer effectively
establishes a new neutral, don’t use half-sized
neutrals
 Provide a well rated four wire feed so that the
transformer can be isolated for service
Copper Development Association
Isolating transformers
Copper Development Association
Isolating transformers
Copper Development Association
Isolating transformers
Copper Development Association
Isolating transformers
Copper Development Association
Active filters
 Where the harmonic profile is unpredictable or
contains a high level of lower harmonics,
active filters are useful
 Active harmonic conditioners operate by
injecting a compensating current to cancel the
harmonic current
Copper Development Association
Harmonic solutions
 Keep circuit impedances low
 Rate neutrals and multi-core cables generously 1.73 to 2 times normal size
 Always use true RMS meters
 Provide a large number of separate circuits to
isolate problem and sensitive loads
 Take harmonics into account when rating
transformers
 Provide appropriate filtration where required
Copper Development Association
Harmonics in Power Systems
Copper Development Association
www.cda.org.uk
Copper Development Association