# A current transformer must at all times have

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A current transformer must at all times have (a) a secondary load (b) short circuited secondary (c) either (a) or (b) (d) none of these

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Three phase step-up transformer installed at power house, just before commencement of transmission line, have:

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For a transformer, operating at constant load current, maximum efficiency will occur at?

A digital board has a unipolar square clock of 250MHz. If the clock on the board at all places should have all the harmonic components which have more than 10 % of DC value, the board has to be designed for at least —  A) 250MHz B) 750MHz C) 1250 MHz D) 2500 MHz

The kVA rating required for a transformer that must handle a maximum load current of 8 A with a secondary voltage of 2 kV will be: A. 4 kVA B. 0.25 kVA C. 16 kVA D. 8 kVA

The driving point impedance with poles at ω = 0(zero) and ω = ∞ (infinity) must have the  (a) s term in the denominator and an excess term in the numerator (b) s term in the numerator and an excess term in the denominator (c) s term in the numerator and equal number of terms in the numerator and denominator (d) s term in the denominator and equal number of terms in the numerator and denominator

The path of magnetic flux in a transformer should have?

When the SCR conducts, the forward voltage drop will   (a) 0.7 V at all load current (b) 2 to 2.5 V at all load current (c) increases slightly with load current (d) remains constant with load current

Full load copper loss in a transformer is 1600 watts. At half load the copper loss will be: A) 6400 watt B) 1600 watt C) 800 watt D) 400 watt

The voltage regulation of a transformer, with ohmic drop 2% and reactance drop 5% of the voltage at 0.8 lagging power factor, will be (a) 7% (b) 5.6% (c) 5.3% (d) 4.6%

In a transformer the voltage regulation will be zero when it operates at (A) unity p.f. (B) leading p.f. (C) lagging p.f. D) zero p.f. leading.

A simple phase transformer has a maximum efficiency of 90% at full load and unity power factor. Efficiency at half load at the same power factor is  (A) 86.7% (B) 88.26% (C) 88.9% (D) 87.8%

A single-phase, 50 kVA, 250 V/500 V two winding transformer has an efficiency of 95% at full load, unity power factor. If it is re-configured as a 500 V/750 V auto-transformer, its efficiency at its new rated load at unity power factor will be  (A) 95.752% (B) 97.851% (C) 98.276% (D) 99.241%

If the secondary turns of a transformer are doubled and at the same time primary voltage is reduced to half then the secondary voltage will

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The current transformer that is used to measure a 100 A current by 5 A ammeter is a_____.

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When secondary of a current transformer is open-circuited its iron core will be?

The secondary of a current transformer is always short-circuited under operating conditions because it?

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A highly conductive material must have?

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The inrush current of a transformer at no load is maximum if the supply voltage is switched on  (1) at peak voltage value (2) at zero voltage value (3) at half voltage value (4) at 0.866 time voltage value

A transformer at 25 Hz develops 20 W hysteresis loss and 50 W eddy current loss. If the applied voltage and frequency are doubled, the new core losses are (A) 140 W (B) 180 W (C) 240 W (D) 480 W

A large transformer operating at no load draws an exciting current Io of 5A, when the primary is connected to a 120 V, 60 Hz source. From a wattmeter test, it is known that iron losses are equal to 180 W. Calculate the reactive power absorbed by the core.  (A) 600 var (B) 572 var (C) 180 var (D) 360 var

The no-load current drawn by transformer is usually what per cent of the full-load current ?

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