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

A single 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

87.8%

B

86.7%

C

88.26%

D

88.9%

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

A

0.2 to 0.5 per cent

B

2 to 5 per cent

C

12 to 15 per cent

D

20 to 30 per cent

In testing a pile by load test, pile platform is loaded with one and half times the design load and a maximum settlement is noted. The load is gradually removed and the consequent rebound is measured. For a safe pile, the net settlement (i.e. total settlement minus rebound) per tonne of test load should not exceed

A

10 mm

B

15 mm

C

20 mm

D

25 mm

An ideal transformer will have maximum efficiency at a load such that

A

copper loss = iron loss

B

copper loss

C

copper loss > iron loss

D

none of the above

In a step down transformer, there is a charge of 15A in the load current. This results in changing of supply current of

A

Less than 15 A

B

Greater than 21 A

C

More Than 21A

D

None

When the axis of load lies in the plane of rivet group, then the most heavily loaded rivet will be the one which (where, Fa is the load shared by each rivet due to axial load and Fm is the shearing load due to moment in any rivet.)

A

Is at the maximum distance from CG of the rivet group

B

Is at the minimum distance from CG of the rivet group

C

Gives the maximum angle between the two forces Fa and Fm

D

Gives the minimum angle between the two forces Fa and Fm

The simply supported beam 'A' of length '$$l$$' carries a central point load 'W'. Another beam 'B' is loaded with a uniformly distributed load such that the total load on the beam is 'W'. The ratio of maximum deflections between beams 'A' and 'B' is

A

$$\frac{5}{8}$$

B

$$\frac{8}{5}$$

C

$$\frac{5}{4}$$

D

$$\frac{4}{5}$$

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

A

avoids core saturation and high voltage induction

B

is safe to human beings

C

protects the primary circuit

D

none of the above

In a given transformer for given applied voltage, losses which remain constant irrespective of load changes are

A

friction and windage losses

B

copper losses

C

hysteresis and eddy current losses

D

none of the above

If a transformer is continuously operated the maximum temperature rise will occur in

A

core

B

windings

C

tank

D

any of the above

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

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