Electrical Mach...

A 230 V DC machine has an emf constant k = 212.21 V-s/Wb-rad and R_a = 0.278 Ω. The field is separately excited and produces 0.01 Wb per pole. Armature current, I_a = 36 A.

Which of the following is/are true?

An electro-mechanical energy conversion device is one which converts _______

The energy storing capacity of magnetic field is about ________ times greater than that of electric field.

What is the coupling field used between the electrical and mechanical systems in energy conversion devices?

The formula for energy stored in the mechanical system of linear motion type is ______

A 3600 rpm, 60 Hz, 13.8 kV synchronous generator has a synchronous reactance of 20 Ω. The generator is operating at rated voltage and speed with the excitation voltage. E_f (phase) = 11.5 kV and the torque angle is δ = 15°. Find the value of stator current (I_a) such that the maximum power can be converted from mechanical to electrical form without loss of synchronism if the field current is unchanged.

A DC machine has total armature ampere conductors of 4500 and total flux in the machine is 0.14 wb. The torque developed in the machine is _________ (in N-m/rad)

A 10 kW, 200 V, 1200 RPM series DC generator has armature resistance of 0.1 Ω, and field resistance of 0.3 Ω. The frictional and windage loss of the machine is 200 W and brush contact drop is 1 Volt per brush. Find the efficiency (in %) of the machine

The phasor diagram of a synchronous machine connected to an infinite bus is shown below. The machine is acting as a

A 1000 hp, 4 pole, 3 phase, 440 V, 50 Hz, Induction motor has a speed of 1440 rpm on full load. The number of cycles of the rotor voltage makes per minutes will be______

A 250 V, 700 W, 50 Hz, 6 pole single phase induction motor is rotating is clockwise direction with a speed of 960 rpm. The rotor resistance at standstill is 10 Ω. What is the effective rotor resistance is the backward branch of the equivalent circuit in ohms?

Two identical synchronous machines A and B running at same speed are connected to each other through an inductor. Machine A is supplying an active power to Machine B and Machine B is supplying reactive power to Machine A, then which among the following is correct?

A 6-pole alternator with 36 slots carries a 3-phase distributed winding. Each coil is short-pitched by one slot. The winding factor is given by

Which of the following graphs represents the speed-torque characteristic of a synchronous motor?

A three-phase synchronous motor rated at 800 hp, 2.4 kV, 60 Hz operates at unity power factor. The line voltage suddenly drops to 1.8 kV, but the exciting current remains unchanged.

Which of the following statements is/are true?

The flux per pole in a synchronous motor with the field circuit ON and the stator disconnected from the supply is found to be 25 mWb. When the stator is connected to the rated supply with the field excitation unchanged, the flux per pole in the machine is found to be 20 mWb while the motor is running on no-load. Assuming no-load losses to be zero, the no-load current drawn by the motor from the supply

A factory has an overall load of 2.4 MVA at 0.707 lagging pf. The MVA rating of a synchronous motor that would bring the total plant to unity power factor for the following condition is ________

The motor is used to drive a new load of 0.405 MW and the motor is 91% efficient.

Which of the following method would give a lower than actual value of regulation of an alternator?

A synchronous motor is operating on no-load at unity power factor. If the field current is increased, the pf will become

While comparing potential transformer to an auto transformer, a potential transformer transfers power ________

The following data were obtained from testing a 48 kVA, 4800/240 V, 50 Hz transformer.

OC test from LV side	240 V	2 A	120 W
SC test from HV side	150 V	10 A	600 W

 

The maximum efficiency (in %) of the transformer for 0.8 lagging power factor load is ________ (up to two decimal places)

The voltage regulation of a transformer at full-load 0.8 p.f leading is -2%. Its voltage regulation at full load 0.8 p.f lagging

A 6-pole, 50 Hz, 3 – phase induction motor running on full load with 4% slip develops a torque of 149.3 N-m at its pulley rim. The friction and windage losses are 200 W and the stator cu and iron losses equal to 1620 W. The efficiency at full load is ____

A 3-phase, 4 pole 50 Hz, star connected induction motor, during short circuit test, took 100 A and 30 kW. In case stator resistance is equal to stand-still rotor resistance, the starting torque is

A single phase 230V, 50Hz, 4 pole capacitor start IM has Z_m = 2.3 + 4j Ω and Z_a = 7 + 5j Ω  value of starting capacitor is