6. synchronous generator tests-a

8/18/2019 6. Synchronous Generator Tests-A

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Synchronous GeneratorTests

To obtain the parameters of asynchronous generator, we performthree simple tests as described below.

The Resistance Test

The Open-Circuit Test

The Short-Circuit Test


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The Resistance Test

This test is conducted to measure-windingresistance of a synchronous generatorwhen it is at rest and the eld winding isopen.

The resistance is measured between twolines at a time and the average of thethree resistance readings is taken to bethe measured value of the resistance, RL,from line to line. If the generator is Y-connected, the per-phase resistance is :

R A = 0,5 R L


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The Open-Circuit Test

The open-circuit test, or the no-loadtest ,is performed by :1) enerator is rotated at the rated

speed.!) "o load is connected at the

terminals.#) $ield current is increased from % to

ma&imum.') (ecord values of the terminal

voltage and eld current value.


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Circuit diagram to perform open-circuittest


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ith the terminals open, * + %, so + / . *t is thus possible to construct a plot

of +

or T

vs * $

graph. This plot is calledopen-circuit characteristic 0 22) of agenerator. ith this characteristic, it ispossible to nd the internal generated

voltage of the generator for any giveneld current.


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Open-circuit characteristic (OCC of agenerator


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The 22 follows a straight-linerelation as long as the magneticcircuit of the synchronous generatordoes not saturate.3ince, in the linear region, most ofthe applied mmf is consumed by theair-gap, the straight line isappropriately called the air-gapline.


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The Short-Circuit Test

The short-circuit test providesinformation about the currentcapabilities of a synchronousgenerator. *t is performed by1) enerator is rotated at rated speed.!) +d4ust eld current to %.#) 3hort circuit the terminals.') 5easure armature current or line

current as the eld current isincreased.


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3ince 6 3 77 ( + , the e8uation reducesto:


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322 is essentially a straight line. To understand why this characteristic is a straight line, look at the e8uivalent circuit belowwhen the terminals are short circuited.


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hen the terminals are short circuited, the armature current * + is:

!rom both tests, here we can "nd the internal machine impedance (# $ from OCC, % $ from SCC :


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3hort 2ircuit (atio

Ratio of the eld current re uired for therated !oltage at open circuit to the eldcurrent re uired for rated armaturecurrent at short circuit.


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6. synchronous generator tests-a

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