Q 1-5
Which loss is considered the most unreliable or complicated to measure in electric motor efficiency testing?
a) stator Cu loss b) rotor Cu loss c) stator Iron loss d) stray loss
d) stray loss
For a 6 pole induction motor operating at 49.5 Hz, the percentage slip at a shaft speed of 950 RPM will be
a) 4.0 % b) 5.0 % c) 0.04 % d) none of the above
a) 4.0 %
Higher chiller COP can be achieved with
a) higher evaporator temperature and higher condensing temperature b) higher evaporator temperature and lower condensing temperature c) lower evaporator temperature and higher condensing temperature d) lower evaporator temperature and lower condensing temperature
b) higher evaporator temperature and lower condensing temperature
All other conditions remaining the same in a refrigeration system, at which of the following condenser temperatures, the power consumption will be the least:
a) 32.6 deg C b) 35.9 deg C c) 40.8 deg C d) 43.4 deg C
a) 32.6 deg C
2 ton of refrigeration (TR) is equivalent to about
a) 100.8 kcal/min b) 7032 W c) 428.7 BTU/min d) all of the above
d) all of the above
A pure resistive load in an alternating current (AC) circuit draws
a) lagging reactive power b) active power c) leading reactive power d) none of the above
b) active power
A plant had installed three phase shunt capacitors to improve power factor at Motor Control Circuit (MCC). Busbar three phase Voltages at the main electrical panel of a plant were balanced but at the Motor Control Circuit (MCC),receiving three phase power from busbars, the line voltages were found to be unbalanced. The main reason for this unbalanced voltage at MCC among the following could be
a) PF capacitors were operating at higher supply frequency b) PF improvement in all phase was not uniform due to blown fuse in one phase of the 3 phase PF capacitors c) PF capacitors were operating at higher voltage then their rated values d) PF capacitors were operating at lower voltage then their rated values
b) PF improvement in all phase was not uniform due to blown fuse in one phase of the 3 phase PF capacitors
Increase in the delivery pressure of a compressor by 1 bar would reduce the power consumption by
a) 1 to 5 % b) 6 to 10 % c) 11 to 15 % d) none of the above
d) none of the above
The pressure of refrigerant in vapour compression system changes in
a) compressor b)expansion valve c) both (a) & (b) d) evaporator
c) both (a) & (b)
A fan with 25 cm pulley diameter is driven by a 2940 rpm motor through a V-belt system. If the motor pulley is reduced from 20 cm to 15 cm keeping the motor rpm and fan pulley diameter the same, the fan speed will reduce by
a) 1176 rpm b) 1764 rpm c) 588 rpm d) none of the above
c) 588 rpm
Select the incorrect statement: The advantage of PF improvement by capacitor addition in an electric network is
a) active power component of the network is not affected b) reactive power component of the network is not affected c) I2R power losses are affected in the system d) voltage level at the load end is affected
b) reactive power component of the network is not affected
A 50 kVAr, 415 V rated power factor capacitor was found to be having terminal supply voltage of 430 V. The capacity of the power factor capacitor at the operating supply voltage would be approximately
a) 53.67 kVAr b) 50 kVAr c) 46.57 kVAr d) none of the above
a) 53.67 kVAr
The FAD of a reciprocating compressor is directly proportional to a) pressure b) volume c) speed d) all of the above
c) speed
A 1.5 ton air conditioner installed in a room and working continuously for one hour will remove heat of
a) 3024 kcals b) 4536 kcals c) 3000 kcals d) 6048 kcals
b) 4536 kcals
In series operation of identical centrifugal fans, ideally
a) flow doubles b) static pressure doubles c) static pressure goes up by four times d) flow goes up by four times
b) static pressure doubles
“Heat Rate” of a thermal power station is the heat input in kilo Calories or kilo Joules, for generating
a) one kW of electrical output b) one kVAh of electrical output c) one kWh of electrical output d) one kVA of electrical output
c) one kWh of electrical output
A 75 kW rated squirrel cage induction motor installed with static PF correction capacitors across the motor terminals got damaged along with capacitors once supply was switched off due to power failure. The possible reason for the motor burn out among the following could be
a) motor was over sized b) motor was undersized c) charging current of the capacitors was more than the magnetizing current of the motor d) charging current of the capacitor was only 85% of the motor magnetizing current
c) charging current of the capacitors was more than the magnetizing current of the motor
Which of the following is not true of air receivers in a compressed air system?
a) smoothens pulsating air output b) increases the compressed air pressure c) stores large volumes of compressed air d) facilitates draining of moisture
b) increases the compressed air pressure
If the power consumed by a 1.5 TR refrigeration compressor is 2.5 kW , what is the energy efficiency ratio?
a) 2.1 b) 1.5 c) 0.6 d) 1.66
a) 2.1
The hydraulic power of a motor pump set is 8 kW. If the power drawn by the motor is 16 kW at 90% efficiency, the pump efficiency will be
a) 55.5% b) 50% c) 45% d) none of the above
a) 55.5%
Improving power factor at motor terminals in a plant will
a) increase active power drawn by motor b) reduce system distribution losses c) reduce contract demand with utility d) increase motor design power factor
b) reduce system distribution losses
An induction motor rated for 75 kW and 94 % efficiency, operating at full load, will
a) deliver 70.5 kW b) deliver 75 kW c) draw 75 kW d) deliver 79.78 kW
b) deliver 75 kW
Typical acceptable pressure drop in mains header at the farthest point of an industrial compressed air network is
a) 1.0 bar b) 0.7 bar c) 0.5 bar d) 0.3 bar
d) 0.3 bar
In the performance assessment of a refrigeration system, which performance ratio (energy efficiency) does not follow the trend “a higher ratio means a more efficient refrigeration system”?
a) Coefficient of performance(COP) b) Energy Efficiency Ratio (EER) c) kW per ton d) none of the above
c) kW per ton
The energy saving with variable speed drives in a pumping system will be maximum for systems with
a) pure static head b) pure friction head c) high static head and low friction head d) high static head with high friction head
b) pure friction head