ETAP - Harmonics.pdf · Slide 12. Phase Angle Relationship • Fundamental Frequency. ETAP.IT. ETAP...
Transcript of ETAP - Harmonics.pdf · Slide 12. Phase Angle Relationship • Fundamental Frequency. ETAP.IT. ETAP...
© 1996-2009 Operation Technology, Inc. – Workshop Notes: Harmonics
Harmonic Analysis
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Slide 2© 1996-2009 Operation Technology, Inc. - Workshop Notes: Harmonics
Types of Power Quality
Problems
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Slide 3© 1996-2009 Operation Technology, Inc. - Workshop Notes: Harmonics
Waveform Distortion
• Primary Types of Waveform Distortion
– DC Offset
– Harmonics
– Interharmonics
– Notching
– Noise ETAP.IT
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Slide 4© 1996-2009 Operation Technology, Inc. - Workshop Notes: Harmonics
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)ETAP.IT
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Slide 5© 1996-2009 Operation Technology, Inc. - Workshop Notes: Harmonics
Nonlinear Loads
• Sinusoidal voltage
applied to a simple
nonlinear resistor
• Increasing the
voltage by a few
percent may cause
current to doubleETAP.IT
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Slide 6© 1996-2009 Operation Technology, Inc. - Workshop Notes: Harmonics
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)
)cos(
13cos13
111cos
11
17cos
7
13cos
5
1(cos
32
1h
hh
dac
thI
tttttII
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Slide 7© 1996-2009 Operation Technology, Inc. - Workshop Notes: Harmonics
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 fractional-pitch winding) and Saturation
– Usually a voltage source
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Slide 8© 1996-2009 Operation Technology, Inc. - Workshop Notes: Harmonics
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
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Slide 9© 1996-2009 Operation Technology, Inc. - Workshop Notes: Harmonics
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 currentETAP.IT
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Slide 10© 1996-2009 Operation Technology, Inc. - Workshop Notes: Harmonics
Harmonic I and V
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Slide 11© 1996-2009 Operation Technology, Inc. - Workshop Notes: Harmonics
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)ETAP.IT
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Slide 12© 1996-2009 Operation Technology, Inc. - Workshop Notes: Harmonics
Phase Angle Relationship
• Fundamental Frequency
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Slide 13© 1996-2009 Operation Technology, Inc. - Workshop Notes: Harmonics
Phase Angle Relationship
• Third Order
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Slide 14© 1996-2009 Operation Technology, Inc. - Workshop Notes: Harmonics
Phase Angle Relationship
• Fifth Order
• Seventh Order
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Slide 15© 1996-2009 Operation Technology, Inc. - Workshop Notes: Harmonics
Order vs. Sequence
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Slide 16© 1996-2009 Operation Technology, Inc. - Workshop Notes: Harmonics
Characteristic Harmonics
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Slide 17© 1996-2009 Operation Technology, Inc. - Workshop Notes: Harmonics
Characteristic Harmonics
(cont’d)
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Slide 18© 1996-2009 Operation Technology, Inc. - Workshop Notes: Harmonics
Harmonic Spectrum
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Slide 19© 1996-2009 Operation Technology, Inc. - Workshop Notes: Harmonics
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
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Slide 20© 1996-2009 Operation Technology, Inc. - Workshop Notes: Harmonics
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
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Slide 21© 1996-2009 Operation Technology, Inc. - Workshop Notes: Harmonics
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
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Slide 22© 1996-2009 Operation Technology, Inc. - Workshop Notes: Harmonics
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
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Slide 23© 1996-2009 Operation Technology, Inc. - Workshop Notes: Harmonics
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
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Slide 24© 1996-2009 Operation Technology, Inc. - Workshop Notes: Harmonics
Parallel Resonance
• Total impedance at resonance frequency increases
• High circulating current will flow in the capacitance-inductance loop
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Slide 25© 1996-2009 Operation Technology, Inc. - Workshop Notes: Harmonics
Parallel Resonance
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Slide 26© 1996-2009 Operation Technology, Inc. - Workshop Notes: Harmonics
Capacitor Banks
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Slide 27© 1996-2009 Operation Technology, Inc. - Workshop Notes: Harmonics
Capacitor Banks
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Slide 28© 1996-2009 Operation Technology, Inc. - Workshop Notes: Harmonics
Capacitor Banks
Say, Seventh Harmonic Current = 5% of 1100A = 55 A
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Slide 29© 1996-2009 Operation Technology, Inc. - Workshop Notes: Harmonics
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
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Slide 30© 1996-2009 Operation Technology, Inc. - Workshop Notes: Harmonics
Parallel Resonance (cont’d)
Cause:
Impacts: 1. Excessive capacitor fuse
operation
2. Capacitor failures
3. Incorrect relay tripping
4. Telephone interference
5. Overheating of equipment
Source inductance resonates with
capacitor bank at a frequency
excited by the facilities harmonic
sources
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Slide 31© 1996-2009 Operation Technology, Inc. - Workshop Notes: Harmonics
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
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Slide 32© 1996-2009 Operation Technology, Inc. - Workshop Notes: Harmonics
Harmonic Distortion Measurements (cont’d)
1
2
2
F
F
THD
i
Where Fi is the amplitude of the ith harmonic,
and F1 is that for the fundamental component.
– 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)
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Slide 33© 1996-2009 Operation Technology, Inc. - Workshop Notes: Harmonics
Harmonic Distortion Example
Find THD for this waveform
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Slide 34© 1996-2009 Operation Technology, Inc. - Workshop Notes: Harmonics
Harmonic Example
• Find THD for this Harmonic Spectrum
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Slide 35© 1996-2009 Operation Technology, Inc. - Workshop Notes: Harmonics
Adjustable Speed Drive –
Current Distortion
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Slide 36© 1996-2009 Operation Technology, Inc. - Workshop Notes: Harmonics
Adjustable Speed Drive –
Voltage Distortion
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Slide 37© 1996-2009 Operation Technology, Inc. - Workshop Notes: Harmonics
Harmonic Distortion Measurements (cont’d)• Individual Harmonic Distortion (IHD)
- Ratio of a given harmonic to fundamental
- To track magnitude of individual harmonic
1F
FIHD i
• Root Mean Square (RMS) - Total
- Root Mean Square of fundamental plus all
harmonics
- Equal to fundamental RMS if Harmonics are
zero
1
2
iFRMS
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Slide 38© 1996-2009 Operation Technology, Inc. - Workshop Notes: Harmonics
Harmonic Distortion Measurements (cont’d)
• Arithmetic Summation (ASUM)
– Arithmetic summation of magnitudes of all
components (fundamental and all harmonics)
– Directly adds magnitudes of all components to
estimate crest value of voltage and current
– Evaluation of the maximum withstanding ratings
of a device
1
iFASUM
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Slide 39© 1996-2009 Operation Technology, Inc. - Workshop Notes: Harmonics
Harmonic Distortion Measurements (cont’d)
• Telephone Influence Factor (TIF)
– Weighted THD
– Weights based on interference to an audio
signal in the same frequency range
– Current TIF shows impact on adjacent
communication systems
2
1
2
1
i
ii
F
FW
TIF
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Slide 40© 1996-2009 Operation Technology, Inc. - Workshop Notes: Harmonics
Harmonic Distortion Measurements (cont’d)
• I*T Product (I*T)
– A product current components (fundamental
and harmonics) and weighting factors
H
h
hh TITI1
2)(
where Ih = current component
Th= weighting factor
h = harmonic order (h=1 for fundamental)
H = maximum harmonic order to account
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Slide 41© 1996-2009 Operation Technology, Inc. - Workshop Notes: Harmonics
Triplen Harmonics
• Odd multiples of thethird harmonic(h = 3, 9, 15, 21, …)
• Important issue forgrounded-wye systemswith neutral current
• Overloading and TIF problems
• Misoperation of devices due to presence of harmonics on the neutral
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Slide 42© 1996-2009 Operation Technology, Inc. - Workshop Notes: Harmonics
Triplen Harmonics
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Slide 43© 1996-2009 Operation Technology, Inc. - Workshop Notes: Harmonics
Winding Connections
• Delta winding provides ampere turn balance
• Triplen Harmonics cannot flow
• When currents are balanced Triplens
behave as Zero Sequence currents
• Used in Utility Distribution Substations
• Delta winding connected to Transmission
• Balanced Triplens can flow
• Present in equal proportions on both sides
• Many loads are served in this fashion
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Slide 44© 1996-2009 Operation Technology, Inc. - Workshop Notes: Harmonics
Implications
• Neutral connections are susceptible to overheating when serving single-phase loads on the Y side that have high 3rd Harmonic
• Measuring current on delta side will not show the triplens and therefore do not give a true idea of the heating the transformer is subjected to
• The flow of triplens can be interrupted by appropriate isolation transformer connection
• Removing the neutral connection in one or both Y windings blocks the flow of Triplen harmonic current
• Three legged core transformers behave as if they have a “phantom” delta tertiary winding
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Slide 45© 1996-2009 Operation Technology, Inc. - Workshop Notes: Harmonics
Modeling in Harmonic
Analysis
• Motors and Machines
– Represented by their equivalent negative
sequence reactance
• Lines and Cables
– Series impedance for low frequencies
– Long line correction including transposition and
distributed capacitance
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Slide 46© 1996-2009 Operation Technology, Inc. - Workshop Notes: Harmonics
Modeling in Harmonic
Analysis (cont’d)
• Transformers
– Leakage impedance
– Magnetizing impedance
• Loads
– Static loads reduce peak resonant impedance
– Motor loads shift resonant frequency due to
motor inductance
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Slide 47© 1996-2009 Operation Technology, Inc. - Workshop Notes: Harmonics
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
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Slide 48© 1996-2009 Operation Technology, Inc. - Workshop Notes: Harmonics
Reducing System
Harmonics (cont’d)
• Increase Pulse Numbers
– Increasing pulse number of convert circuits
– Limited by practical control problems
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Slide 49© 1996-2009 Operation Technology, Inc. - Workshop Notes: Harmonics
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 editorETAP.IT
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Slide 50© 1996-2009 Operation Technology, Inc. - Workshop Notes: Harmonics
Reducing System
Harmonics (cont’d)• Either standard phase shift or special phase
shift can be used
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Slide 51© 1996-2009 Operation Technology, Inc. - Workshop Notes: Harmonics
Reducing System
Harmonics (cont’d)• Add Active Filters
– Instantly adapts to changing source and load
conditions
– Costly
– MVA LimitationETAP.IT
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Slide 52© 1996-2009 Operation Technology, Inc. - Workshop Notes: Harmonics
Voltage Distortion Limits
Recommended Practices for Utilities (IEEE
519): Bus Voltage
At
PCC
Individual
Distortion
(%)
Total Voltage
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
In ETAP:
Specify Harmonic Distortion Limits in Harmonic
Page of Bus Editor:ETAP.IT
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