**136.**As compared to air, hydrogen has ___________

thermal conductivity and __________ density.

(A) lower ………. lower

(B) lower…….. higher

(C) higher……… lower

(D) higher ………. higher.

Get Answer

**137.** A machine is specified as 50 kW maximum continuous rating. The machine

(A) cannot be overloaded

(B) can be overloaded 10% only

(C) can be overloaded 20% for half an hour only

(D) can be overloaded 20% for two hours only

Get Answer

**138.** A short time intermittent rating of electric motors is considered while selecting motors for

(A) blowers

(B) punching machines

(C) reciprocating compressors

(D) sirens.

Get Answer

** 139.** Short time rating machines have usually

(A) low operating times and longer shut down times

(B) low operating times and shorter shut down times

(C) longer operating times and shorter shut down times

(D) longer operating times and longer shut down times.

Get Answer

** Questions 140 to 142 refer to data below : **

The rate of temperature rise as measured from a temperature time

curve of a transformer is 0.0803 °C per minute and 00605 °C per minute,

when the temperature rise is 20.5 °C and 28.5 °C respectively.

**140.** The temperature rise at any time t is given by

(A) θ = θf ( 1- e -t/T )

(B) θ = θf ( 1+ e -t/T )

(C) θ = θf ( 1+ e t/T )

(D) θ = θf ( 1+ e -t/T )

Get Answer

** 141.** The final steady temperature rise will be

(A) 15.5°C

(B) 35.5°C

(C) 52.5°C

(D) 72.5°C.

Get Answer

**142.** The heating time constant is

(A) 102 minutes

(B) 204 minutes

(C) 306 minutes

(D) 398 minutes.

Get Answer

** 143**. A. 3 φ, 52 slot, 8 pole machine can have a coil-span of

(A) 4

(B) 71/2

(C) 6

(D) 8.

Get Answer

** 144.** In case of induction motors the value of air gap flux density usually taken is

(A) 0.1 to 0.2 Wb/m2

(B) 0.35 to 0.6 Wb/m2

(C) 1.05 to 1.35 Wb/m2

(D) 2.15 to 2.55 Wb/m2.

Get Answer

**145.** Larger values of air gap flux density can be adopted while designing induction motors of

(A) larger output

(B) larger diameter of rotor

(C) both (A) and (B) above

(D) none of the above.

Get Answer

**146.** Higher values of flux density can be taken while designing machines for

(A) low voltages

(B) smaller number of poles

(C) both (A) and (B) above

(D) none of the above.

Get Answer

**147..** A 5 HP cage induction motor has power factor

of 0.75 at 750 rpm. A motor of 100 HP at 750 rpm can be expected to

have a power factor of

(A) 0.88

(B) 0.75

(C) 0.72.

Get Answer

**148.** An induction motor of 100 HP at 750 rpm is

expected to have power factor of 0.88. A 100 HP induction motor at 1500

rpm can be expected to have power factor of

(A) 0.91

(B) 0.88

(C) 0.81.

Get Answer

**149.** An induction motor of 10 HP at 750 rpm has

efficiency of 83%. An induction motor of 100 HP at 750 rpm can be

expected to have an efficiency of

(A) 81%

(B) 83%

(C) 90%

(D) 99.9%.

Get Answer

**150.** An induction motor of 20 HP at 750 rpm has

efficiency of 85%. Another induction motor of 20 HP operating at 1500

rpm can be expected to have an efficiency of

(A) 80%

(B) 82%

(C) 85%

(D) 88%.

Get Answer