POWER HARMONICS- SOURCES, ISSUES AND MITIGATION

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POWER SYSTEM HARMONICS:SOURCES,ISSUES AND MITIGATION

Presented by-

ASHIK.S & ROOPESH.R.NAIR

AMMINI COLLEGE OF ENGINEERING

HISTORY OF HARMONICS

Power system have always had harmonics present.

In early 1890’s harmonics were associated with distorted current and voltage waveform shape on transmission system.

Over the last fifteen years, the proliferation of electronic device has brought subject up-front and personal.

As the number of electronic devices increased, so did the number of other harmonics creating devices.

There has been an explosion of microprocessor based equipment which are also non-linear loads. Examples include computer systems, variable frequency drives, AC/DC converters, electronic ballasts, X-ray machines, MRI equipment.

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LINEAR LOADS

Linear loads occur when the impedance is constant; then the current is proportional to or the same as the voltage

A linear element in a power system is a component in which the current is proportional to the voltage.

Typical linear loads are incandescent lights and motors, heaters

ASHIK.S AND ROOPESH.R.NAIR, AMMINI COLLEGE OF

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NON-LINEAR LOADS

Non linear loads occur when the impedance is not constant; then the current is not proportion or the same as the voltage.

The current drawn by non-linear loads is not sinusoidal but is periodic, meaning that the current wave looks the same from cycle to cycle

Typical non-linear loads are electronic switch mode power supplies, DC/AC drive and induction furnace/arc furnace.

There are basically two types of non-linear loads: single phase and three phase.


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CAUSES OF HARMONICS?

Harmonics are created by a non-linear loads that draw a current in abrupt pulses rather than a smooth sinusoidal manner.

Harmonic resonance occurs when the capacitor reactance and the system reactance are equal.

All electronic loads generate positive & negative sequence harmonic currents, single phase electronic loads connected phase neutral in a 3 phase 4wires distribution system, also generate zero sequence harmonic currents

Appliances:

TV set, air conditioners, washing machines, microwave ovens and vacuum cleaners.

Fax machines, photocopies, printers and so on.


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SOURCES OF HARMONICS

☞ Adjustable drive systems

☞Arc Furnaces

☞Switching Mode Power Supplies

☞Computers, TV sets

☞HVDC Transmission

☞Electric Traction

☞Wind & Solar power generation

☞Battery charging & Fuel cells

☞Fluorescent lighting, Electronic ballasts…ASHIK.S AND ROOPESH.R.NAIR, AMMINI COLLEGE OF

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EFFECTS OF HARMONICS

☞ Increased Cu loss leading to Excessive heating.

☞Harmonic Torques.

☞Voltage distortion in weak system.

☞Harmonic voltages increase hysteresis and eddy current losses, also

additional 𝐼2R losses mainly in Converter transformers.(Transformer

derating).

☞Power factor also deteriorates.

☞Phenomenon of Flicker.


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☞Excessive neutral currents.

☞Effects measuring instruments.

☞Misoperation of relays.(False tripping of ground relay due to

triplen harmonics)

☞Parallel resonance between Cable capacitance and system

inductances, incase of long cables.

☞Introduces Electromagnetic interference in adjacent signal or

control cables via radiated and conducted emissions.


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PROBLEMS DUE TO HARMONICS

Large load currents in the neutral wires of a 3 phase system.

Overheating of standard electrical supply transformers which

shortens the life of a transformer and will eventually destroy it.

High voltage and current distortion exceeding

Poor power factor conditions result in monthly utility penalty

fees for major users (factories, manufacturing and industrial)

with a power factor less than 0.9.

Resonance that produces over-current surges.


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False tripping of branch circuit breakers.

Waste energy/high electric bill

Capacitors: can be affected by heat rise increases due to power loss and

reduced life on the capacitors.


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MITIGATION


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There are many ways to reducing harmonics. The primary

methods used today to reduce harmonics are:

Power System design: harmonics can be reduced by

limiting the non-linear load to 30% of the maximum

transformer’s capacity.

Isolation transformers: An isolation transformer provides a

good solution in many cases.


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METHODS TO MITIGATE HARMONICS

1.Passive filters.

2.Active filters.

Filters are used to suppress harmonics as well as to support reactive

power.

3.Operation with higher pulse number.

4.Using K-factor transformers.


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PASSIVE FILTERS

1.Single tuned filter:

Based on series resonance of RLC circuit. The circuit is

designed to resonate at the frequency equal to the frequency

of the component which needs to be filtered.

It is confined to a particular frequency.ASHIK.S AND ROOPESH.R.NAIR, AMMINI COLLEGE OF

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2.Double tuned filter:

This filter is tuned to two frequencies equal to the frequency of the

significant harmonic components in the magnitude spectrum.


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3.High pass filters:

These filters are designed such that all the components of frequencies

higher than a particular frequency are filtered.

• Passive filters are cheap, easy design and reliable.

• But they cause resonance problems, fixed reactive power

compensation and large size.ASHIK.S AND ROOPESH.R.NAIR, AMMINI COLLEGE OF

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ACTIVE FILTERS

Active power filters are Power electronic converters to inject

harmonic currents into the system.

They can eliminate voltage and current harmonics;

compensate for reactive power. No resonance problems, can

support variable reactive power compensation. Expensive,

complex control.


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New generation of harmonic filters

Very high Speed IGBT ensuring response time of a few milliseconds

Capable of generating wide spectrum of harmonic currents to

inject into the network to cancel the harmonic current drawn from

the source by nonlinear loads

Additionally they can generate both capacitive and inductive

reactive power in a step-less manner improving the PF of the load.


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ACTIVE FILTERING

Parallel type Series type

HYBRID FILTERS

A combination of passive and Active filter

Active filters are used to handle the dynamically varying harmonic

component and passive filters handle more predictable narrow

band in addition to providing capacitive reactive power

compensation at fundamental frequency.


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Hybrid of series active and parallel passive

Hybrid of parallel active and series passive

CONCLUSION

It is essential to know the effects of the harmonics, sources of

the harmonics for a power engineer to ensure that the systems

will work well within the safety zone, owing to standards.

Also, the various harmonic mitigation techniques discussed are

to be understood well for a design engineer to protect the power

system from harmonics.


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REFERENCES

☞Power system Harmonics- Jos Arrillaga, Neville R. Watson.

☞Control of Harmonics in Electrical Power systems,

from American Bureau of Shipping(ABS).

☞POWER SYSTEM ANALYSIS, Short circuit load flow and

Harmonics-J. C. Das

☞IEEE transactions on Power Apparatus & Systems, Power

system Harmonics: An Overview, Vol.PAS-102, No.8,

August1983.


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☞ IEEE transactions on Power Apparatus & Systems, vol.PAS-104,

No.9, 1985. The effects of Power system Harmonics on Power

system equipment and Loads.

☞Mitigation of Harmonics in a Neutral Conductor for Three-

Phase Four-Wire Distribution System using Series Active

Power Filter 2015 IEEE paper

☞A Review of Harmonic Mitigation Techniques –by Gonzalo

Sandoval & John Houdek, © 2005

☞Harmonic Mitigation In Minigrid Integrated Distributed

Power System-2016 International Conference on Circuit, Power

and Computing Technologies [ICCPCT]


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THANKYOU

ASHIK.S AND ROOPESH.R.NAIR, AMMINI COLLEGE OF ENGINEERING 27

POWER HARMONICS- SOURCES, ISSUES AND MITIGATION

Engineering

Transcript of POWER HARMONICS- SOURCES, ISSUES AND MITIGATION