5th March Sud Khatri

7/28/2019 5th March Sud Khatri

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INTRODUCTION

A harmonic of a wave is a

component frequency of the

signal that isan integer multiple of

the fundamental frequency,

i.e. if the fundamentalfrequency is f, the harmonics

have frequencies 2f, 3f, 4f, . . .

etc
http://en.wikipedia.org/wiki/Wavehttp://en.wikipedia.org/wiki/Frequencyhttp://en.wikipedia.org/wiki/Integerhttp://en.wikipedia.org/wiki/Fundamental_frequencyhttp://en.wikipedia.org/wiki/Fundamental_frequencyhttp://en.wikipedia.org/wiki/Integerhttp://en.wikipedia.org/wiki/Frequencyhttp://en.wikipedia.org/wiki/Wave


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PROBLEM

1) East Bus harmonic filter experienced failureof fifth harmonic reactor, fuses, and capacitor

cans. 2) West Bus harmonic filter experienced

failure of fuses and capacitor cans.


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SOLUTION

The East Bus fifth harmonic filter may not be

filtering properly for several possible reasons.


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REASONS GIVEN

First, measurements have shown an unbalance inthe phase currents to the entire filter shown anunbalance in the phase currents bank of 12.7%13.1%. Phase-B current is 282 A, while Phase-A

and Phase-C are 347 and 343 A, respectively, onaverage. So some capacitors were underratedand some were overrated.


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REASONS GIVEN

Second, the inductance of the East Bus fifth

harmonic was estimated to be 25 mH, which

gives a tuned frequency of 3.9th harmonic.

No design data were available from the

manufacturer, and the rewind shop did not

conduct an inductance test on either the

rewound or undamaged reactors


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REASONS

Voltage rating of the capacitors was

underrated for applications at 13.8 kV, putting

undue stress on the for applications at 13.8

kV, putting undue stress on the capacitors in

the steady state and providing no margin for

transient conditions. Since the rating of

voltages had increased since installation.


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SOLUTION GIVEN

The capacitors which were underrated ,were

replaced by new capacitors.

The inductance which was making filter to

remove 5th harmonic,was dimensionally

corrected to make it tuned to 5th harmonic.


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Problems Caused by

Harmonics

Transformer over-heating

Circuit breaker trips

Fuse blowing

Equipment malfunction

Increased KVA demand

rms and peak

Total Power Factor reduction

Wasted energy


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OTHER POSSIBLE SOLUTIONS

We can use harmonic filter at transformer

end, so that transmission line is free from

carrying harmonic current.


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We can also use harmonic filter at the load

end ,so that the harmonics which were

introduced at transmission line can also be

removed.


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We can use power quality meters at regular

distances in system to measure wave

distortion quantitatively.


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The rating of inductance and capacitance

used should be such that they can withstand

the temporary surges, so that they do not

damage during surges.

5th March Sud Khatri

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