Power Quality Management Harmonic Distortion
and Variable Frequency Drives
Voltage and Current Harmonic
Distortion Cause and Effect
23/09/2011
Marek Farbis, Mirus International Inc.
1
We will focus on
•
•
•
•
•
•
•
•
•
Introduction: the ideal vs. distorted waveform
Definition of harmonics
Effects of harmonic distortion
What is a cause for harmonic voltage distortion?
Definition and calculation of THD
VFDs and harmonics
Standards and recommendations
Harmonic mitigation techniques
Applications
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Marek Farbis, Mirus International Inc.
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Introduction
3-Phase, 480V, 60Hz Power Supply
V(A,B)
V(B,C)
V(C,A)
800
600
400
200
Volts
• Electricity generation is
normally produced at
constant frequencies of
50 Hz or 60 Hz and can
be considered practically
sinusoidal.
• Ideally, an electricity
supply should invariably
show a perfectly
sinusoidal voltage signal
at every customer
location.
• In reality however these
signals contain many
types of disturbances.
0
-200
-400
-600
-800
0.000
0.002
0.004
Marek Farbis, Mirus International Inc.
0.006
0.008
0.010
Time [sec]
0.012
0.014
0.016
0.018
Introduction
• The deviation of the voltage and current
waveforms from sinusoidal is described in terms
of the waveform distortion, often expressed as
harmonic distortion.
• In nearly all cases harmonic
distortion is produced by a
customer’s equipment (nonlinear loads) injecting electrical
noise into the power system i.e.
Variable Frequency Drives.
Marek Farbis, Mirus International Inc.
Definition of Harmonics
• In a periodic signal the primary, desired frequency is
the "Fundamental Frequency“.
• The term “harmonics” was originated in the field of
acoustics, where it was related to the vibration of a
string or an air column at a frequency that is a
multiple of the base frequency.
• A harmonic component in an AC power system is
defined as a sinusoidal component of a periodic
waveform that has a frequency equal to an integer
multiple of the fundamental frequency of the
system.
• French mathematician Jean Baptiste Joseph Fourier (1768-1830) found
that any function of a variable can be expanded in a series of sines of
multiples of the variable.
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Marek Farbis, Mirus International Inc.
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Harmonics - Components of a Distorted Waveform
Fundamental - 60 Hz
Distorted Waveform
Resultant
1.5
2
2
1
1.5
0.5
1
0
0.5
-0.5
0
-1
-0.5
-1.5
-1
5th Harmonic - 300 Hz
-1.5
1.5
-2
Time domain
1
0.5
60 Hz
0
Harmonic
Harmonic
Spectrum
HarmonicSpectrum
Spectrum
Fundamental
ofFundamental
%ofof
Fundamental
%%
100
100
-0.5
-1
80
80
300 Hz
60
60
-1.5
420 Hz
40
40
7th Harmonic - 420 Hz
1.5
20
20
1
0
0
11
1
33
3
55
5
77
7
Harmonic
Harmonic ##
Harmonic #
99
9
11
11
11
13
13
0.5
13
0
-0.5
Fourier Series
Frequency domain
-1
f(t) = Ao+A1sin(wt+q1)+A2sin(2wt+q2)+A3sin(3wt+q3) ...
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Marek Farbis, Mirus International Inc.
-1.5
8
Why is the harmonic distortion bad?
• Effect of penetration in the electrical system affecting
adjacent installations.
• Thermal effect on electric rotating machines, transformers,
capacitors, and cables (extra losses).
• Pulsating torques in rotating machines.
• Neutral conductor overloading.
• Increased risk of faults from overvoltage conditions
developed on power factor correction capacitors and
resonant conditions.
• Unexpected Fuse Operation.
• Abnormal operation of electronic relays.
• Abnormal operation of solid-state devices.
• Lower system power factor preventing effective utilization.
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What causes a voltage distortion?
• Relationship between System Impedance and
Voltage Distortion.
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Harmonic voltage distortion is caused by the flow of harmonic currents through system impedance.
ZTh
Relationship between
System Impedance and
Voltage Distortion.
ZCh
cable
xfmr
Harmonic
Current
Source
UTILITY
ZSh
ZSh
CUSTOMER/UTILITY
ZTh
ZCh
Sinusoidal
Voltage
Source
VS
VL
Ih
Non-linear
Load
~
VS = Ih x ZSh
VFD1
VT
<- The voltage will be the least distorted nearest to the
source.
Ohm’s Law:
V h = Ih x Z h
VT = Ih x (ZSh+ZTh) <- Voltage Distortion at the Transformer at h
VL = Ih x (ZSh+ZTh+ZCh) <- more distorted nearer the load, as the
harmonic current flows through larger amounts of impedance.
Where:
ZSh – impedance of the source at harmonic h,
Where:
Zh – impedance at hth harmonic, ZTh – impedance of the transformer at harmonic h,
ZChpower
– impedance
of cables
at harmonic
h,
Ih – current
of travels
hth harmonic,
While
current
only along the
path of the
non-linear
load, voltage
Vh – voltage
of hthall
harmonic,
distortion
affects
loads connected to that particular bus or phase.
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Total Harmonic Distortion
• “Fundamental Current” refers to the current
carried in the fundamental frequency, Ih1 (60 Hz).
• “current Total Harmonic Distortion” refers to the
ratio of all harmonic currents to the fundamental
current.
hmax
iTHD 
2


I
 h
h2
I h1
100%
Ratio of the root-sum-square (RSS) value of the harmonic content of the current to the
RMS value of the fundamental current.
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Standard Variable Frequency Drive
(PWM)
DIODE BRIDGE
IGBT ‘S = FAST KNIFE SWITCHES
IGBT = Insulated-Gate Bipolar Transistor
CONTROL VOLTAGE & FREQUENCY
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Marek Farbis, Mirus International Inc.
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VFD, 6-Pulse Rectifier Current Waveform
VFD input current
300.0
200.0
Current [Amps]
100.0
0.0
0.017
0.022
0.027
0.032
-100.0
-200.0
-300.0
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time [msec]
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VFD, 6-Pulse Rectifier and Harmonics
For simple diode bridge rectifiers:
h=n·p±1
h = harmonic number
p = # of pulses in rectification scheme
n = any integer (1, 2, 3, etc.)
ia
% Fund.
.
100
When, p = 6
60
40
20
h=n·6±1
h = -- 5,7,--,11,13,--,17,19...
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80
0
1
3
5
7
9
11
13
15
17
19
21
23
25
harmonic
Current Waveform and Spectrum
Marek Farbis, Mirus International Inc.
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Harmonic distortion limits
• IEEE Standard 519 – 1992
– IEEE Recommended Practices and Requirements
for Harmonic Control in Power Systems.
• IEEE Standard C57.110 – 1986
– IEEE Recommended Practice for Establishing
Transformer Capability When Supplying Nonsinusoidal Load Currents.
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IEEE Standard 519 General Overview
 Introduced in 1981
(Latest revision 1992)
 ‘Recommended Practices and Requirements for
Harmonic Control in Electrical Power Systems’
o Sets limits for voltage and current distortion at Point
of Common Coupling.
o Recognizes responsibility of both User and Utility.
 Widely adopted in N. America Becoming more common
globally
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IEEE Standard 519-1992, “Recommended Practices and Requirements for
Harmonic Control in Electrical Power Systems”
Definition of Terms
Point of Common Coupling
(PCC)
UTILITY
XFMR
ZSh
A point of metering, or any point
as long as both the utility and the
consumer can either access the
point for direct measurement of
the harmonic indices meaningful to
both or can estimate the harmonic
indices at point of interference.
CUSTOMER/UTILITY
XFMR
ZTh
ZCh1
ZCh2
VFD1
Within an industrial plant the PCC
is the point between the nonlinear
load and the other loads.
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MOTOR1
Marek Farbis, Mirus International Inc.
ZCh3
ZCh4
VFD2
MOTOR3
MOTOR2
19
IEEE Standard 519-1992, “Recommended Practices and Requirements for
Harmonic Control in Electrical Power Systems”
Definition of Terms
Point of Common Coupling
(PCC)
UTILITY
XFMR
ZSh
A point of metering, or any point
as long as both the utility and the
consumer can either access the
point for direct measurement of
the harmonic indices meaningful to
both or can estimate the harmonic
indices at point of interference.
CUSTOMER/UTILITY
XFMR
ZTh
ZCh1
ZCh2
Within an industrial plant the
PCC is the point between the
nonlinear load and the other loads.
23/09/2011
Rarely
convenient to
measure on
Utility Side.
VFD1
MOTOR1
Marek Farbis, Mirus International Inc.
ZCh3
ZCh4
VFD2
MOTOR3
MOTOR2
20
IEEE Standard 519-1992, “Recommended Practices and Requirements for
Harmonic Control in Electrical Power Systems”
Definition of Terms
The harmonic current limits are based on the size of the load with
respect to the size of the power system to which the load is connected.
UTILITY
XFMR
Short-Circuit Ratio (ISC/IL):
Ratio of the short-circuit current (ISC) available at
the PCC to the maximum fundamental load
current (IL).
CUSTOMER/UTILITY
XFMR
ZTh
IL
Maximum Load Current (IL):
Recommended to be the average current of the
maximum demand for the preceding 12 months.
ZCh2
VFD1
MOTOR1
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Marek Farbis, Mirus International Inc.
ISC
ZSh
ZCh1
ZCh3
ZCh4
VFD2
MOTOR3
MOTOR2
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IEEE Standard 519-1992, “Recommended Practices and Requirements for
Harmonic Control in Electrical Power Systems”
Recommended Current Distortion Limits
Table 10.3, p72
Current Distortion Limits for General Distribution Systems (120 V Through 69,000 V)
Maximum Harmonic Current Distortion in Percent of IL
Individual Harmonic Order (Odd Harmonics)
ISC/IL
<11
11h<17
17h<23
23h<35
35h
TDD
<20*
4.0
2.0
1.5
0.6
0.3
5.0
20<50
7.0
3.5
2.5
1.0
0.5
8.0
50<100
10.0
4.5
4.0
1.5
0.7
12.0
100<1000
12.0
5.5
5.0
2.0
1.0
15.0
>1000
15.0
7.0
6.0
2.5
1.4
20.0
Where:
ISC = maximum short-circuit current at PCC.
IL = maximum demand load current (fundamental frequency component) at PCC.
TDD = Total Demand Distortion (harmonic current distortion calculated in % of maximum demand load current)
THD = Total Harmonic Distortion (calculated based on actual load)
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IEEE Standard 519-1992, “Recommended Practices and Requirements for
Harmonic Control in Electrical Power Systems”
Recommended Voltage Distortion Limits
Table 10.2, p70
Low-Voltage System Classification and Distortion Limits
Special
Applications1
General
System
Dedicated
System2
Notch Depth
10%
20%
50%
THD (voltage)
3%
5%
10%
16 400
22 800
36 500
Notch Area (AN)3
NOTE: The Value AN for other than 480 V systems should be multiplied by V/480
1 Special applications include hospitals and airports.
2 A dedicated system is exclusively dedicated to the converter load.
3 In volt-microseconds at rated voltage and current.
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IEEE Standard 519-1992, “Recommended Practices and Requirements for
Harmonic Control in Electrical Power Systems”
Current Distortion Criteria
• Intended to limit for the harmonic current injection from
individual customers, so they will not cause unacceptable
voltage distortion levels.
– Current harmonics will distort voltage in proportion to
impedance of power system.
• Short circuit current, ISC is a measure of system impedance.
– Higher ISC means lower impedance, therefore lower voltage
distortion.
• Short circuit ratio, ISC/IL allows for higher distortion levels at
lighter loads.
– As the size of the user load decreases with respect to the size of
the system, the % of harmonic current that the user is allowed
to inject into the utility increases.
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Effect of a Stiff Source, ISC/IL > 100
400 Hp VFD
vTHD = 2 %
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Marek Farbis, Mirus International Inc.
iTHD = 127 %
25
Effect of a Weak Source, ISC/IL = 8
400 Hp VFD
vTHD = 16 %
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Marek Farbis, Mirus International Inc.
iTHD = 25 %
26
Load Level contribution to Harmonics
• A load’s maximum contribution to harmonic
distortion is at rated load.
– Harmonic current in Amps at full load is highest even
if iTHD might be higher at lighter loads.
IEEE Std 519 uses TDD (Total Demand Distortion) for
this purpose.
– If IEEE Std 519 limits can be met at full load, then both
voltage distortion and harmonic overheating would be
satisfied at all load levels.
• More practical to use a load’s rated current as the
Demand Current.
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WHAT METHODS ARE USED TODAY TO MITIGATE
HARMONIC CURRENTS GENERATED BY PWM VFD’S ?
1.) DO NOTHING.
2.) ADD AC LINE REACTORS OR DC LINK CHOKES
3.) TUNED TRAP FILTER
4.) LOW PASS FILTERS
5.) 18-PULSE VFD’S
6.) VFD/CW ACTIVE FRONT ENDS (AFE).
7.) VFD WITH PARALLEL ACTIVE HARMONIC FILTER
8.) MIRUS LINEATOR™ AUHF.
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LINEATOR™ Advanced Universal
Harmonic Filter with 600V-480V AUTOXFMR
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APPLICATIONS
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Case Study, Current Distortion
McQuay 400Hp VFD Chiller
with Mirus Lineator.
Competitive 500Hp VFD chiller
with 5% AC Line reactor.
400.0
250.0
350.0
200.0
300.0
150.0
250.0
200.0
100.0
150.0
50.00
100.0
50.00
A 0.000
A 0.000
-50.00
-50.00
-100.0
-150.0
-100.0
-150.0
-200.0
-250.0
-200.0
-300.0
-350.0
-250.0
-400.0
7/20/2011
1:33:27.264 PM
16.669 (ms)
3 ms/Div
7/20/2011
1:33:27.281 PM
7/20/2011
1:39:39.267 PM
16.672 (ms)
3 ms/Div
A1 W aveform
163.27 Arms, 7.69 %THD
A1 W aveform
216.05 Arms, 42.81 %THD
100
100
80
7.7 % THD at 65% Load = 5% TDD
60
80
40
20
20
1
5
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10 15 20 25 30 35 40 45 50
7/20/2011 - 1:33:27.264 PM
42.8 % THD at 65% Load = 27.8% TDD
60
40
0
7/20/2011
1:39:39.284 PM
0
1
5
10 15 20 25 30 35 40 45 50
7/20/2011 - 1:39:39.267 PM
Marek Farbis, Mirus International Inc.
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Case Study, Voltage Distortion result
McQuay 400Hp VFD chiller
with Mirus Lineator.
Competitive 500Hp VFD chiller
with 5% AC Line reactor.
800.0
600.0
600.0
400.0
400.0
200.0
200.0
V 0.000
V 0.000
-200.0
-200.0
-400.0
-400.0
-600.0
-600.0
-800.0
7/20/2011
1:33:27.264 PM
16.669 (ms)
3 ms/Div
7/20/2011
1:33:27.281 PM
8/23/2011
11:54:34.219 AM
16.669 (ms)
3 ms/Div
U1 W aveform
587.71 Vrms, 0.86 %THD
U1 W aveform
466.20 Vrms, 3.55 %THD
100
100
80
80
60
60
40
40
20
20
0
1
5
23/09/2011
8/23/2011
11:54:34.236 AM
10 15 20 25 30 35 40 45 50
7/20/2011 - 1:33:27.264 PM
0
1
5
10 15 20 25 30 35 40 45 50
8/23/2011 - 11:54:34.219 AM
Marek Farbis, Mirus International Inc.
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Summary
• By drawing non-sinusoidal current, VFD’s
generate harmonics.
• The flow of harmonic currents through the power
system impedance creates voltage distortion.
• Excessive voltage distortion will cause equipment
malfunction.
• IEEE Std 519 harmonic limits can be met by
application of appropriately designed harmonic
treatment.
• Harmonic treatment method must perform in
‘Real World’ conditions and when supplied by
generator.
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How to Ensure your VFD Installation Meets IEEE 519 Limits
• Perform harmonic survey to
Or
determine existing conditions
• Obtain harmonic spectrum of • Specify LINEATOR™ FOR
ALL LARGER VFD
load from manufacturer
APPLICATION
• Use modeling software to
analyze various treatment
methods and system
conditions
• Analyze impact on Generator
or UPS
• Anticipate effect of future
system or load changes
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Thank you
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