Harmonics & There Filters 1
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Transcript of Harmonics & There Filters 1
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Pre
Abdul Mun
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What are Harmonics Sources of Harmonics
Effects of Harmonics
Standards for Harmonics Limitation
Harmonics Mitigation Active & Passive Filters
Selection of Filter for Specific Application
Conclusion
Plan of Presentation
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A harmonic is a signal or wave whose frequencyis an integral (whnumber) multiple of the frequency of some reference (fundamentawave.
currents or voltages with frequencies that are integer multiple(h=0,1,2,N) of the fundamental power frequency
Positive Sequence Harmonics ( 4th, 7th, 10th , . (6n+1) th ) Negative Sequence Harmonics ( 2nd, 5th, 8th (6n-1) th ) Zero sequence Harmonics ( 3rd, 6th, 9th, .. (6n-3) th )
What are Power System Harmonics
http://searchcio-midmarket.techtarget.com/definition/frequencyhttp://searchcio-midmarket.techtarget.com/definition/frequency -
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Current Harmonics are produced by Current Stiff Non linear Loads such as
Thyristor converter fed DC Motor DrivesCSI Based DC Drives
Switch Mode Power Supplies
Fluorescent Lamps
Personal Computers
a) Current Source nonlinear load
HARMONIC SOURCES
Thyristor rectifier for dc drives,
heater drives, etc.
Per-phase equiv
circuit of thyristor
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Diode rectifier for ac
drives, electronic
equipment, etc
b) Voltage source nonlinear load
Per-phase equiva
circuit of diode re
Voltage Harmonics are produced by either due to harmonic Current
demanded by non linear load with factor of source impedance or due to
Voltage Stiff Non linear Loads which involves voltage clamping & notchingsuch as
Diode Rectifiers with capacitive filter feeding DC Links
VSI Based AC Motor Drives
Switch Mode Power Supplies
Fluorescent Lamps
Personal Computers
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010 20 30 40
-1.0
-0.5
0.0
0.5
1.0
Time (mS)
Current
010 20 30 40
-1.0
-0.5
0.0
0.5
1.0
Time (mS)
Curr
ent
010 20 30 40
1.0
0.5
0.0
0.5
1.0
Time (mS)
Current
TYPE OF NONLINEAR
LOAD
TYPICAL WAREFORM THD%
1-
Uncontrolled Rectifier
80%
(high 3rd
component)
1-
Semicontrolled
Rectifier Bridge
2nd, 3rd, 4th,......harmonic
components
6Pulse Rectifier
with output voltage
filtering and without
input reactor filter
80%
5, 7, 11, .
INPUT CURRENT OF DIFFERENT
NOLINEAR LOADS
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010 20 30 40
-1.0
-0.5
0.0
0.5
1.0
Time (mS)
Curren
t
0 10 20 30 40-1.0
-0.5
0.0
0.5
1.0
Time (mS)
Current
0 10 20 30 40-1.0
-0.5
0.0
0.5
1.0
Time (mS)
Current
6 - Pulse Rectifier
with large output
inductor
28%
5, 7, 11, .
6 - Pulse Rectifier
with output voltage
filtering and with 3%reactor filter or with
continues output current
40%
5, 7, 11, .
12 - Pulse Rectifier 15%
11, 13, ..
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HarmonicsDetected on PCs
Recorded Current Waveform
Harmonic Spectrum for PC Load Current
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HarmonicsDetected on Fluorescent Lamps
Recorded Current Waveform
Harmonic Spectrum for Fluorescent Lamps
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HarmonicsDetected on Speed drive
Recorded Current Waveform
Harmonic Levels for Variable Speed Drive
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Voltage and current profiles in a
commercial building
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Effects of Harmonics on Power System
When a voltage and/or current waveform is distorted, it causes
abnormal operating conditions in a power system such as:
Voltage Harmonics can cause additional heating in induction and
synchronous motors and generators.
Voltage Harmonics with high peak values can weaken insulation
in cables, windings, and capacitors.
Voltage Harmonics can cause malfunction of different electronic
components and circuits that utilize the voltage waveform for
synchronization or timing.
Voltage Harmonics can cause problem in AVR of the small
Generator that is only source to power system.
Voltage Harmonics can cause problem in speed governor of a
small generator that is only source to power system
Current Harmonics in motor windings can create
Electromagnetic Interference (EMI).
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Current Harmonics flowing through cables can cause higher heat
over and above the heating that is created from the fundamen
component.
Current Harmonics flowing through a transformer can cause hig
heating over and above the heating that is created by the fundamen
component.
Current Harmonics flowing through circuit breakers and switch-g
can increase their heating losses.
RESONANT CURRENTS which are created by current harmonics athe different filtering topologies of the power system can cau
capacitor failures and/or fuse failures in the capacitor or ot
electrical equipment.
False tripping of circuit breakers and protective relays.
Effects of Harmonics on Power System
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How to quantify Harmonics
Total Harmonic Distortion-THD: the contribution of all harmonic
frequency Currents/Voltages to the fundamental current
THD: Ratio of the RMS of the harmonic content to the RMS of the
Fundamental
Current THD-I
Voltage THD-V
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How to quantify Harmonics
Distortion Factor is the ratio of fundamental component of current or
voltage to the RMS value of distorted voltage or current respectively
DF =
1
2
1
~
h
hI
I
DF = 21
1
THD
I
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Standards of Harmonics Limitation
IEEE/IEC
IEEE 519-1992 Standard: Recommended Practicesand Requirements for Harmonic Control inElectrical Power Systems(Current Distortion Limits for120v-69kv DS)
Table 1: Current Harmonic Limits
Ratio
Iscc / Iload
Harmonic odd
numbers (35)
THD-i
< 20 4.0 % 0.3 % 5.0 %
20 - 50 7.0 % 0.5 % 8.0 %
50 - 100 10.0 % 0.7 % 12.0 %
>1000 15.0 % 1.4 % 20.0 %
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Standard of Harmonics Limitation
IEEE 519-1992 Standard: Recommended Practices andRequirements for Harmonic Control in Electrical PowSystems(Voltage Distortion Limits)
Table 2: Voltage Harmonic Limits
Bus Voltage Voltage Harmonic limitas (%) of Fundamental
THD-v (%)
= 161 Kv 1.0 1.5
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METHODOLOGY FOR
COMPUTING DISTORTION
Step 1: Compute the individual current harmonic distortion at eadedicated bus using different Software programs (i.e. SIMULINSPICE, etc.) or tables that provide the current distortion nonlinear loads.
Step 2: Compute the voltage and current harmonic content at the PoinCommon Coupling (PCC) which is located at the input of industrial power system.
- Each individual harmonic current at the PCC is the sumharmonic current contribution from each dedicated bus.
- The load current at PCC is the sum of the load currcontribution from each dedicated bus.
- The maximum demand load current at PCC can be found computing the load currents for each branch feeder and multiby a demand factor to obtain feeder demand. Then the sum offeeder demands is divided by a diversity factor to obtain maximum demand load current.
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Step 3: Choose a base MVA and base KV for the system use the following eq
in order to compute individual and total current and voltage ha
distortions at PCC and any other point within the power system.
Ib= Base current in Amps Ampsb
b
kV
MVA
3
103
= System impedance = p.u.sc
b
MVA
MVA
MVAb= Base MVA, MVAsc= short circuit MVA at the point of interest
VH= Percent individual harmonic voltage distortion =
Volts100s
b
hZh
I
I
sZ
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h = harmonic order
100%
2
1
2
2
V
V
THD h
h
100I
I
%THD
1
2
2h
2
h
i
IH= Percent individual harmonic distortion =100
I
I
L
h
Isc= Short Circuit current at the point under consideration.
IL= Estimated maximum demand load current
S.C. Ratio = Short circuit RatioD
sc
L
sc
MVA
MVA
I
I
MVAD= Demand MVA
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ONCE THE SHORT CIRCUIT RATIO IS KNOWN, THE IEEE CU
HARMONIC LIMITS CAN BE FOUND AS SPECIFIED IN TABLE I O
IEEE 519-1992 POWER QUALITY STANDARDS
USING THE ABOVE EQUATIONS VALUES OF IDIVINDUAL AND
VOLTAGE AND CURRENT HARMONIC DISTORTION CAN BE COM
AND COMPARED WITH THE IEEE LIMITS
Step 4: Determine preliminary filter design.
Step 5: Compute THDv and THDi magnitudes and impedance
frequency plots with filters added to the system, one atSIMULINK or PSPICE software programs can be used
adjustments.
Step 6: Analyze results and specify final filter design.
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Mitigation of Harmonics
Mitigation of power system harmonics can be categorized as corrective
solutions and precautionary solutions.
Precautionary (Preventive) solutions aim to avoid harmonics and the
consequences.
oPhase cancellation or harmonic control in power convertors.
oDeveloping procedures and methods to control, reduce or eliminate
harmonics in power system equipment; mainly capacitors, transformers and
generators.
Corrective (remedial) solutions are the techniques to overcome the
existing problems.
oThe use of active and passive filters
oReconfiguration of the feeders or reallocation of capacitor banks to
overcome the resonance.
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Mitigation of Harmonics
Delta-Delta and Delta-Wye Transformers
Using two separate utility feed transformers with equal
non-linear loads Shifting the phase relationship to various six-pulse
converters through cancellation techniques
Figure 7: Delta-Delta and Delta-Wye Transformers
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Mitigation of Harmonics
Isolation-Interface Transformers
The potential to voltage match by stepping up orstepping down the system voltage, and by providing aneutral ground reference for nuisance ground faults
The best solution when utilizing AC or DC drives thatuse SCRs/GTO/SSR.. as bridge rectifiers
Line Isolation-Reactors More commonly used for their low cost
Adding a small reactor in series with capacitor bankforms a Blocking series Filter.
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1) Parallel-passive filter for current-source nonlinear loads
TYPES OF FILTERS
Harmonic Sinc
Low Impedance
Cheapest
VA ratings = VT(Load Harmonic current + reactive current of the filter)
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2) Series-passive filter for voltage-source nonlinear loads
Harmonic damp
High-impedance
Cheapest
VA ratings = Load current (Fundamental drop across filter + Load Harmonic
Voltage)
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3) Basic parallel-active filter for current source in nonlinear loads
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4) Basic series-active filter for voltage-source in
nonlinear loads
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5) Parallel combination of parallel active and parallel passive
6) Series combination of series active and series passive
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7) Hybrid of series active and parallel passive
8) Hybrid of parallel active and series passive
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ACTIVE FILTERING
Parallel type Series type
SHUNT ACTIVE FILTERS
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SHUNT ACTIVE FILTERS
By inserting a parallel active filter in a non-linear load location we can inje
a harmonic current component with the same amplitude as that of the load
to the AC system. They damp harmonic propagation in a distribution feed
or between two distribution feeders.
C
FL
Equivalent circ
SERIES ACTIVE FILTERS
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SERIES ACTIVE FILTERS
By inserting a series Active Filter between the AC source and the load
where the harmonic source is existing we can force the source current to
become sinusoidal. The technique is based on a principle of harmonic
isolation by controlling the output voltage of the series active filter.
Equivalent Circ
The series active filter exhibits high impedance to harmonic current andconsequently blocks harmonic current flow from the load to the source.
RESULTS OF ACTIVE FILTERING
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-2500
-1500
-500
500
1500
2500
0 5 10 15 20 25 30 35 40
I
[A]
Time [ms]
0
5
10
15
20
25
30
2 5 8 11 14 17 20 23
[%I
1]
Harmonics
-5000
-2500
0
2500
5000
0 10 20 30 40
Time [ms]
IDynacomp[A
]
0%
5%
10%
15%
20%
25%
30%
35%
2 5 8 11 14 17 20 23
Harmonics
[%I1]
RESULTS OF ACTIVE FILTERING
Input current of a 6-pulse Rectifier driving a DC machine without any input filter
Input current with Active Filtering
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-1000
-500
0
500
1000
0 5 10 15 20 25 30 35 40
U
[V]
Time [ms]
0
2
4
6
8
10
12
14
2 5 8 11 14 17 20 23
[%U
1]
Harmonics
-1000
-500
0
500
1000
0 5 10 15 20 25 30 35 40
U[
V
]
Time [ms]
0
2
4
6
8
10
12
14
2 5 8 11 14 17 20 23
[%U
]
Harmonics
Typical 6-pulse drive voltage waveform
Voltage source improvement with active filtering
3 HYBRID ACTIVE PASSIVE FILTER
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3- HYBRID ACTIVE-PASSIVE FILTER
Compensation of current harmonics and displacement
power factor can be achieved simultaneously.
HYBRID ACTIVE-PASSIVE FILTER
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HYBRID ACTIVE PASSIVE FILTER
Single-phase equivalent circuit Single-phase equiva
for 5thHarm
HYBRID SERIES AND SHUNT
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HYBRID SERIES AND SHUNT
ACTIVE FILTER
At the Point of Common Coupling provides:
Harmonic current isolation between the sub transmission and
the distribution system (shunt A.F)
Voltage regulation (series A.F)
Voltage flicker/imbalance compensation (series A.F)
SELECTION OF AF S FOR SPECIFIC
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SELECTION OF AF S FOR SPECIFIC
APPLICATION CONSIDERATIONS
AF Configuration with higher number of * is more preferred
Compensation for
Specific Application
Active Filters
Active
Series
Active
Shunt
Hybrid of
Active Series
and Passive
Shunt
Hybrid of A
Shunt an
Active Ser
Current Harmonics ** *** *
Reactive Power *** ** *
Load Balancing *
Neutral Current ** *
Voltage Harmonics *** ** *
Voltage Regulation *** * ** *
Voltage Balancing *** ** *
Voltage Flicker ** *** *
Voltage Sag&Dips *** * ** *
Conclusion
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Conclusion
The harmonic distortion principally comes fromNon linear-Type Loads.
The application of power electronics is causingincreased level of harmonics due to Switching!!
Harmonic distortion can cause seriousFailure/Damage problems.
Harmonics are important aspect of power operationthat requires Mitigation!!
Over-Sizing and Power Filtering methods arecommonly used to limit Overheating Effects ofSustained Harmonics.
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