Harmonics & There Filters 1

8/12/2019 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


Harmonic Spectrum for Fluorescent Lamps


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HarmonicsDetected on Speed drive


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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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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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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Harmonics & There Filters 1