QUESTION 14
1.
A machine has a 480-V, 3-phase electrical motor as an integral part of the machine. The total machine load
requirement is 10 A at 480 V. If the building has a 240-V, 3-phase electrical system, determine the minimumkVA 3-phase transformer required. Write only the answer without the units.
2 points
QUESTION 15
1.
Calculate the percentage voltage regulation of a transformer in which ohmic drop is 2% and the reactance drop
in 5% of the voltage at 0.8 lagging power factor.
4 points
QUESTION 16
1.
The power input to a 500 V, 50 Hz, 6 pole 3 phase squirrel cage induction motor running at 975 rpm is 40 KW.
The stator losses are 1 kW and the friction and windage losses are 2 KW. Calculate:
a) Slip.
2 points
QUESTION 17
1.
The power input to a 500 V, 50 Hz, 6 pole 3 phase squirrel cage induction
motor running at 975 rpm is 40 KW. The stator losses are 1 kW and
the friction and windage losses are 2 KW. Calculate:
b) Rotor copper loss in kW.
2 points
QUESTION 18
1.
The power input to a 500 V, 50 Hz, 6 pole 3 phase squirrel cage induction
motor running at 975 rpm is 40 KW. The stator losses are 1 kW and
the friction and windage losses are 2 KW. Calculate:
c) Mechanical power developed in kW.
2 points
QUESTION 19
1.
The power input to a 500 V, 50 Hz, 6 pole 3 phase squirrel cage induction
motor running at 975 rpm is 40 KW. The stator losses are 1 kW and
the friction and windage losses are 2 KW. Calculate:
d) The percentage efficiency.
2 points
QUESTION 20
1.
The shaft output of a three-phase 60- Hz induction motor is 80 kW. The frictionand windage losses are 920 W,
the stator core loss is 4300 W and the stator copper loss is 2690 W. The rotor current and rotor resistance
referred to stator are respectively 110 A and 0.15 W . If the slip is 3.8%, what is the percent efficiency?
6 points
QUESTION 21
1.
A 6 pole 3 phase induction motor develops 30 HP including mechanical lossestotalling 2 HP, at a speed of 950
rpm on 550 V, 50 Hz mains. If the powerfactor is 0.88 and core losses are negligible, calculate:
(i) The slip
2 points
QUESTION 22
1.
A 6 pole 3 phase induction motor develops 30 HP including mechanical lossestotalling 2 HP, at a speed of 950
rpm on 550 V, 50 Hz mains. If the powerfactor is 0.88 and core losses are negligible, calculate:
(ii) The rotor copper loss in kW.
2 points
QUESTION 23
1.
A 6 pole 3 phase induction motor develops 30 H P including mechanical lossestotalling 2 H P, at a speed of 950
RPM on 550 volt, 50 Hz mains. If the powerfactor is 0.88 and core losses are negligible, calculate:
(iii) The total input power if the stator losses are 2 kW.
2 points
QUESTION 24
1.
A 6 pole 3 phase induction motor develops 30 HP including mechanical lossestotalling 2 HP, at a speed of 950
rpm on 550 V, 50 Hz mains. If the powerfactor is 0.88 and core losses are negligible, calculate:
(iv) The line current.
2 points
QUESTION 25
1.
Three single-phase, 50 kVA, 2300/ 230 V, 60 Hz transformers are connected to form a 3-phase, 4000V / 230-V
transformer bank. The equivalent impedance of each transformer referred to low-voltage is 0.012 + j 0.016 Ω .
The 3-phase transformer supplies a 3-phase, 120 kVA, 230 V, 0.85 power-factor (lagging) load.
a) Calculate the secondary line current.
2 points
QUESTION 26
1.
Three single-phase, 50 kVA, 2300/ 230 V, 60 Hz transformers are connected
to form a 3-phase, 4000V / 230-V transformer bank. The equivalent impedance of
each transformer referred to low-voltage is 0.012 + j 0.016 Ω . The 3phase transformer supplies a 3-phase, 120 kVA, 230 V, 0.85 power-factor (lagging)
load.
a) Calculate the primary line current.