A three-phase Y-connected synchronous motor with a line-to-line voltage of \(440\) V and a synchronous speed of \(900\) rpm operates with a power of \(9\) kW and a lagging power factor of \(0.8\). The synchronous reactance per phase is \(10\) ohms. The machine is operating with a rotor current of \(5\) A. It is desired to continue carrying the same load but to provide \(5\) kVAR of power factor correction to the line. Determine the required rotor current to do this.
A\(7.88\) A
B\(8.06\) A
C\(8.62\) A
D\(8.28\) A
#22📜 EE Board October 1991📘 1001 RojasHard
A \(3{,}600\) volts three-phase star connected turbo synchronous generator of synchronous reactance of \(0.5\) ohm per phase and negligible resistance is supplying \(30{,}000\) kVA at \(0.8\) pf lagging to a large power system. If the steam supply is cut-off, calculate the amount of current that the generator will then carry assuming negligible losses.
A\(3901\) A
B\(3823\) A
C\(3094\) A
D\(3870\) A
#23📜 EE Board October 1994📘 1001 RojasHard
A wye-connected turbo alternator having a synchronous reactance of \(0.5\) ohm and negligible resistance is connected to a large power system having a busbar voltage of \(13.8\) kV supplying a load of \(15{,}000\) kVA at \(0.80\) lagging power factor. If the steam supply is cut-off, what armature current will the machine carry assuming negligible losses?
A\(256.55\) A
B\(525.62\) A
C\(384.26\) A
D\(627.55\) A
#24📜 EE Board October 1994📘 1001 RojasHard
A \(1{,}000\) kVA, \(6{,}600\) V wye-connected three-phase alternator having a reactance of \(8.8\ \Omega\) and a negligible resistance is supplying power to a constant frequency busbar. The open circuit emf at this instance is \(4{,}311\) V per phase. If the steam supply is suddenly cut-off, the armature current in amperes is nearest to
A\(57\) A
B\(60\) A
C\(59\) A
D\(56\) A
#25📜 EE Pre-Board March 2013📘 PowerhouseHard
A 200-hp, 2,200 V, 3-phase star connected synchronous motor has a synchronous impedance of 0.3 + j3 Ω per phase. Determine the induced emf per phase if the motor works on full load with an efficiency of 94% and a power factor of 0.8 leading.
A1,354 V
B1,360 V
C1,402 V
D1,522 V
#26📜 EE Pre-Board August 2013📘 PowerhouseMedium
A 10-hp, 230 v, three-phase Y-connected synchronous motor has a reactance of 3 ohms per phase a negligible resistance. To what voltage must the motor be excited to deliver full-load at unity power factor and 90% efficiency?
A242 v
B254 v
C262 v
D248 v
#27📜 EE Pre-Board August 2013📘 PowerhouseMedium
The input power to a 600-v synchronous motor is measured by means of a two-method. One wattmeter reads 64 kW and the other reads 36.5 kW. The motor is known to be operating at leading p.f. Determine the line current drawn.
A110 A
B104 A
C112 A
D107 A
#28📜 EE Pre-Board August 2014📘 PowerhouseMedium
A 500 volts 1 synchronous motor is taking 50 amperes at a p.f. of 0.8 leading. The output is 25 Hp and the effective resistance of the armature is 0.25 ohm. Find the iron and friction losses.
A375 w
B650 w
C725 w
D175 w
#29📜 EE Pre-Board August 2014📘 PowerhouseMedium
The output of a 200-volt 1 synchronous motor, taking a current of 20 amperes is 4 HP, its effective armature resistance is 0.5 ohm. The iron and friction losses amount to 400 watts. What is the motor power factor?
A0.896
B0. 846
C0.796
D0.916
#30📜 EE Pre-Board March 2016📘 PowerhouseEasy
A 5,000 kVA synchronous condenser operates with a leading p.f. of 0.032. The losses are 180 kW. What is the power input to the motor?
A5,160 kW
B5,320 kW
C160 kW
D320 kW
#31📜 EE Pre-Board August 2017📘 PowerhouseMedium
A 500 volt, single-phase synchronous motor is taking 50 amperes at a p.f. of 0.8 leading. The output is 25 HP and the effective resistance of the armature is 0.25 ohm. Find the iron and friction losses.
A1,350 W
B625 W
C1,975 W
D725 W
#32📜 EE Pre-Board March 2018📘 PowerhouseMedium
A 440-volt single-phase synchronous motor is taking 50 amperes at a pf of 0.9 lagging. The effective resistance of the armature is 0.8 ohm. If the iron and friction losses amount to 600 watts, find the horsepower output.
