Virtual Labs

Control of Bus Voltages Through Onload Tap Changes

In a transformer, if N2 is number of secondary winding N1 is the number of primary winding then, if (N2/N1) ratio is greater than 1.It is called as ________

a: Step down transformer Explanation

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b: Step up transformer Explanation

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c: Isolation transformer Explanation

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d: All Explanation

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In a transformer, if N2 is number of secondary winding N1 is the number of primary winding then, if (N2/N1) ratio is lesser than 1.It is called as ________

a: Step down transformer Explanation

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b: Step up transformer Explanation

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c: Isolation transformer Explanation

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d: All Explanation

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Oil transformer usually consist of,

a: A conservator tank, buchholz relay Explanation

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b: Breather of dehydrating type Explanation

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c: Winding temperature-indicator, oil temperature indicatore Explanation

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d: All Explanation

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The tap changing control equipment includes _______

a: Control and paralleling equipment Explanation

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b: Line drop compensator equipment used along with the current transformer to provide voltage control at a point remote from the measuring point Explanation

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c: Automatic voltage regulating relay Explanation

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d: All Explanation

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32 step tap changes provide ________ voltage change in each step.

a: 5/4% Explanation

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b: 4/5% Explanation

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c: 5/8% Explanation

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d: 8/5% Explanation

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Conservator is an oil-expansion tank mounted _________ on the transformer.

a: Below the highest oil point Explanation

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b: Ground level Explanation

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c: Above the highest oil point Explanation

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d: Any of the them Explanation

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To prevent the moisture from entering the conservator, a __________ is provided that will dry the air as the breather takes place.

a: Low quality icon core operating at very low flex density so that the magnetizing current may be large Explanation

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b: Magnesium dioxide breather Explanation

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c: Silica gel breather Explanation

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d: Both Low quality icon core operating at very low flex density so that the magnetizing current may be large and Magnesium dioxide breather Explanation

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Advantage of using instrument Transformer is _______

a: Standard rated instruments may be used easily Explanation

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b: It provides safety for operating personal Explanation

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c: Standard rated instruments may be used easily and It provides safety for operating personal Explanation

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d: None Explanation

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Instrument transformers are classified as:

a: Potential transformer Explanation

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b: Current transformer Explanation

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c: Both Potential transformer and Current transformer Explanation

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d: None Explanation

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Potential transformers are made with

a: Low quality icon core operating at very low flex density so that the magnetizing current may be large Explanation

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b: High quality icon core operating at very high flex density so that the magnetizing current may be large Explanation

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c: High quality icon core operating at very high flex density so that the magnetizing current may be very small Explanation

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d: High quality icon core operating at very low flex density so that the magnetizing current may be very small Explanation

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High magnitude alternating current can be measured by a combination of _________ and _________.

a: Potential transformer and a low range ammeter Explanation

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b: Current transformer and high range ammeter Explanation

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c: Current transformer and low range ammeter Explanation

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d: None Explanation

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A current transformer must never be operated on open circuit for

a: There will be no secondary m.m.f. and since the primary current (and m.m.f.) is fixed, the core flux will increase enormously. This will cause large amount of eddy current and hysteresis losses and the resulting high temperature may damage the insulation or even the core Explanation

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b: As the secondary side is open, a very high voltage will be induced in the multi-turn secondary and this high voltage is dangerous to both life and to the insulation Explanation

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c: There will be no secondary m.m.f. and since the primary current (and m.m.f.) is fixed, the core flux will increase enormously. This will cause large amount of eddy current and hysteresis losses and the resulting high temperature may damage the insulation or even the core and As the secondary side is open, a very high voltage will be induced in the multi-turn secondary and this high voltage is dangerous to both life and to the insulation Explanation

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d: None Explanation

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In a power transformer, stepping down from 33kV to 11kV on load tap changes is provided along with 16 steps with 1.25% voltage changes in each step and a constant secondary voltage of 11kV is required. If the primary voltage changes from 33kV to 32kV then

a: The taps should be lowered 1 times Explanation

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b: The taps should be lowered 3 times Explanation

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c: The taps should be lowered 5 times Explanation

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d: The taps should be raised 5 times Explanation

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a: The taps should be lowered 2 times Explanation

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b: The taps should be lowered 3 times Explanation

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c: The taps should be lowered 5 times Explanation

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d: The taps should be lowered 7 times Explanation

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