Harmonic Analysis
©1996-2013 ETAP/Operation Technology, Inc. – Workshop Notes: Harmonics
Types of Power Quality
Problems
©1996-2013 ETAP/Operation Technology, Inc. - Workshop Notes: Harmonics
Slide 2
Waveform Distortion
• Primary Types of Waveform Distortion
– DC Offset
– Harmonics
– Interharmonics
– Notching
– Noise
©1996-2013 ETAP/Operation Technology, Inc. - Workshop Notes: Harmonics
Slide 3
Harmonics
• One special category of power quality
problems
• “Harmonics are voltages and/or currents
present in an electrical system at some
multiple of the fundamental frequency.”
(IEEE Std 399, Brown Book)
©1996-2013 ETAP/Operation Technology, Inc. - Workshop Notes: Harmonics
Slide 4
Nonlinear Loads
• Sinusoidal voltage
applied to a simple
nonlinear resistor
• Increasing the
voltage by a few
percent may cause
current to double
©1996-2013 ETAP/Operation Technology, Inc. - Workshop Notes: Harmonics
Slide 5
Fourier Representation
• Any periodic
waveform can be
expressed as a sum
of sinusoids
• The sum of the
sinusoids is referred
to as Fourier Series
(6-pulse)
2 3
I ac
1
cos3 t
5
I d (cos t
I h cos(h t
h
1
1
1
cos7 t
cos11 t
cos13 t
7
11
13
)
h 1
©1996-2013 ETAP/Operation Technology, Inc. - Workshop Notes: Harmonics
Slide 6
Harmonic Sources
• Utilities (Power Grid)
– Known as “Background Harmonic”
– Pollution from other irresponsible customers
– SVC, HVDC, FACTS, …
– Usually a voltage source
• Synchronous Generators
– Due to Pitch (can be eliminated by fractionalpitch winding) and Saturation
– Usually a voltage source
©1996-2013 ETAP/Operation Technology, Inc. - Workshop Notes: Harmonics
Slide 7
Harmonic Sources (cont’d)
• Transformers
– Due to magnetizing branch saturation
– Only at lightly loaded condition
– Usually a current source
• Power Electronic Devices
– Charger, Converter, Inverter, UPS, VFD, SVC, HVDC,
FACTS, …
– Due to switching actions
– Either a voltage source or a current source
©1996-2013 ETAP/Operation Technology, Inc. - Workshop Notes: Harmonics
Slide 8
Harmonic Sources (cont’d)
• Other Non-Linear Loads
– Arc furnaces, discharge lighting, …
– Due to unstable and non-linear process
– Either a voltage source or a current source
• In general, any load that is applied to a
power system that requires other than a
sinusoidal current
©1996-2013 ETAP/Operation Technology, Inc. - Workshop Notes: Harmonics
Slide 9
Harmonic I and V
©1996-2013 ETAP/Operation Technology, Inc. - Workshop Notes: Harmonics
Slide 10
Classification of Harmonics
• Harmonics may be classified as:
– Characteristic Harmonics
 Generally produced by power converters
– Non-Characteristic Harmonics
 Typically produced by arc furnaces and discharge
lighting (from non-periodical waveforms)
©1996-2013 ETAP/Operation Technology, Inc. - Workshop Notes: Harmonics
Slide 11
Phase Angle Relationship
• Fundamental Frequency
©1996-2013 ETAP/Operation Technology, Inc. - Workshop Notes: Harmonics
Slide 12
Phase Angle Relationship
• Third Order
©1996-2013 ETAP/Operation Technology, Inc. - Workshop Notes: Harmonics
Slide 13
Phase Angle Relationship
• Fifth Order
• Seventh Order
©1996-2013 ETAP/Operation Technology, Inc. - Workshop Notes: Harmonics
Slide 14
Order vs. Sequence
©1996-2013 ETAP/Operation Technology, Inc. - Workshop Notes: Harmonics
Slide 15
Characteristic Harmonics
©1996-2013 ETAP/Operation Technology, Inc. - Workshop Notes: Harmonics
Slide 16
Characteristic Harmonics
(cont’d)
©1996-2013 ETAP/Operation Technology, Inc. - Workshop Notes: Harmonics
Slide 17
Harmonic Spectrum
©1996-2013 ETAP/Operation Technology, Inc. - Workshop Notes: Harmonics
Slide 18
Harmonic-Related Problems
• Motors and Generators
– Increased heating due to iron and copper losses
– Reduced efficiency and torque
– Higher audible noise
– Cogging or crawling
– Mechanical oscillations
©1996-2013 ETAP/Operation Technology, Inc. - Workshop Notes: Harmonics
Slide 19
Harmonic-Related Problems
(cont’d)
• Transformers
– Parasitic heating
– Increased copper, stray flux and iron losses
• Capacitors (var compensators)
– Possibility of system resonance
– Increased heating and voltage stress
– Shortened capacitor life
©1996-2013 ETAP/Operation Technology, Inc. - Workshop Notes: Harmonics
Slide 20
Harmonic-Related Problems
(cont’d)
• Power Cables
– Involved in system resonance
– Voltage stress and corona leading to dielectric
failure
– Heating and derating
• Neutrals of four-wire systems (480/277V; 120/208V)
– Overheating
• Fuses
– Blowing
©1996-2013 ETAP/Operation Technology, Inc. - Workshop Notes: Harmonics
Slide 21
Harmonic-Related Problems
(cont’d)
• Switchgears
– Increased heating and losses
– Reduced steady-state current carrying capability
– Shortened insulation components life
• Relays
– Possibility of misoperation
• Metering
– Affected readings
©1996-2013 ETAP/Operation Technology, Inc. - Workshop Notes: Harmonics
Slide 22
Harmonic-Related Problems
(cont’d)
• Communication Systems
– Interference by higher frequency
electromagnetic field
• Electronic Equipment (computers, PLC)
– Misoperation
• System
– Resonance (serial and parallel)
– Poor power factor
©1996-2013 ETAP/Operation Technology, Inc. - Workshop Notes: Harmonics
Slide 23
Parallel Resonance
• Total impedance at resonance frequency
increases
• High circulating current will flow in the
capacitance-inductance loop
©1996-2013 ETAP/Operation Technology, Inc. - Workshop Notes: Harmonics
Slide 24
Parallel Resonance
©1996-2013 ETAP/Operation Technology, Inc. - Workshop Notes: Harmonics
Slide 25
Capacitor Banks
©1996-2013 ETAP/Operation Technology, Inc. - Workshop Notes: Harmonics
Slide 26
Capacitor Banks
©1996-2013 ETAP/Operation Technology, Inc. - Workshop Notes: Harmonics
Slide 27
Capacitor Banks
Say, Seventh Harmonic Current = 5% of 1100A = 55 A
©1996-2013 ETAP/Operation Technology, Inc. - Workshop Notes: Harmonics
Slide 28
Capacitor Banks
Resistance = 1% including cable and transformer
CAF = X/R = 7*0.0069/0.0012 =40.25
Resonant Current = 55*40.25 = 2214 A
©1996-2013 ETAP/Operation Technology, Inc. - Workshop Notes: Harmonics
Slide 29
Parallel Resonance (cont’d)
Cause:
Source inductance resonates with
capacitor bank at a frequency
excited by the facilities harmonic
sources
Impacts: 1. Excessive capacitor fuse
operation
2. Capacitor failures
3. Incorrect relay tripping
4. Telephone interference
5. Overheating of equipment
©1996-2013 ETAP/Operation Technology, Inc. - Workshop Notes: Harmonics
Slide 30
Harmonic Distortion
Measurements
• Total Harmonic Distortion (THD)
– Also known as Harmonic Distortion Factor
(HDF), is the most popular index to measure the
level of harmonic distortion to voltage and
current
– Ratio of the RMS of all harmonics to the
fundamental component
– For an ideal system THD = 0%
– Potential heating value of the harmonics relative
to the fundamental
©1996-2013 ETAP/Operation Technology, Inc. - Workshop Notes: Harmonics
Slide 31
Harmonic Distortion
Measurements (cont’d)
– Good indicator of additional losses due to
current flowing through a conductor
– Not a good indicator of voltage stress in a
capacitor (related to peak value of voltage
waveform, not its heating value)
Fi 2
THD
2
F1
Where Fi is the amplitude of the ith harmonic,
and F1 is that for the fundamental component.
©1996-2013 ETAP/Operation Technology, Inc. - Workshop Notes: Harmonics
Slide 32
Harmonic Distortion
Measurements (cont’d)
• Individual Harmonic Distortion (IHD)
- Ratio of a given harmonic to fundamental
- To track magnitude of individual harmonic
IHD
Fi
F1
• Root Mean Square (RMS) - Total
- Root Mean Square of fundamental plus all
harmonics
- Equal to fundamental RMS if Harmonics are
zero
Fi 2
RMS
1
©1996-2013 ETAP/Operation Technology, Inc. - Workshop Notes: Harmonics
Slide 33
Reducing System
Harmonics
• Add Passive Filters
– Shunt or Single Tuned Filters
– Broadband Filters or Band Pass Filters
– Provide low impedance path for harmonic
current
– Least expensive
©1996-2013 ETAP/Operation Technology, Inc. - Workshop Notes: Harmonics
Slide 34
Reducing System
Harmonics (cont’d)
• Increase Pulse Numbers
– Increasing pulse number of convert circuits
– Limited by practical control problems
©1996-2013 ETAP/Operation Technology, Inc. - Workshop Notes: Harmonics
Slide 35
Reducing System
Harmonics (cont’d)
• Apply Transformer Phase Shifting
– Using Phase Shifting Transformers
– Achieve higher pulse operation of the total
converter installation
• In ETAP
– Phase shift is specified in the tab page of the
transformer editor
©1996-2013 ETAP/Operation Technology, Inc. - Workshop Notes: Harmonics
Slide 36
Reducing System
Harmonics (cont’d)
• Either standard phase shift or special phase
shift can be used
©1996-2013 ETAP/Operation Technology, Inc. - Workshop Notes: Harmonics
Slide 37
Reducing System
Harmonics (cont’d)
• Add Active Filters
– Instantly adapts to changing source and load
conditions
– Costly
– MVA Limitation
©1996-2013 ETAP/Operation Technology, Inc. - Workshop Notes: Harmonics
Slide 38
Voltage Distortion Limits
Recommended Practices for Utilities (IEEE
519):
Bus Voltage
Individual
Total Voltage
Distortion
Distortion
(%)
THD (%)
69 kV and below
3.0
5.0
69.001 kV through 161kV
1.5
2.5
161.001 and above
1.0
1.5
At
PCC
In ETAP:
Specify Harmonic Distortion Limits in Harmonic
Page of Bus Editor:
©1996-2013 ETAP/Operation Technology, Inc. - Workshop Notes: Harmonics
Slide 39
Current Distortion Limits
Recommended Practices for General
Distribution Systems (IEEE 519):
©1996-2013 ETAP/Operation Technology, Inc. - Workshop Notes: Harmonics
Slide 40