ISRO Scientist or Engineer Electrical 2018

Two DC machines are mechanically coupled. One is operating as a motor and the other as generator. The iron and frictional losses of the machines will be identical when:

If the terminal voltage of a DC shunt motor is halved, keeping load torque varying as square of speed. Then, which of the following statements are correct?
i. Speed is halved
ii. Speed remains unaltered
iii. Armature current is doubled
iv. Armature current is unaltered

A DC shunt motor is excited from voltage source and its brush axis rotated by an angle ‘$$\alpha$$’ from the geometrical neutral axis. The torque developed will be proportional to:

If the current drawn by a DC series motor is increased from 10 A to 12 A (neglect saturation), what is the increase in torque expressed as percentage of initial torque?

Following data are obtained by slip test on a salient pole machine:
$$I_{dmax} = 10 A$$ $$I_{dmin} = 6.5 A$$
$$V_{dmax} = 30 V$$ $$V_{dmin} = 25 V$$
What is the direct axis reactance $$‘X_d’$$ and quadrature axis reactance $$‘X_q’$$?

Two mechanically coupled alternators deliver power at 50 Hz and 60 Hz respectively. What is the highest speed of the alternators?

A 3 Phase, 11 kV, 5 MVA alternator has synchronous reactance of 10 Ω per phase. Its excitation is such that the generated emf is 14 kV. If the alternator is connected to infinite bus the maximum output of the alternator at a given excitation is

The resultant flux density in the air gap of synchronous generator is lowest during:

A voltmeter gives 120 oscillations per minute when connected to the rotor of an induction motor. When the stator frequency is 50 Hz, what is the slip of the motor?

A 6 pole, 3 phase alternator running at 1000 rpm supplies power to an 8 pole, 3 phase, induction motor which has a rotor current of frequency 2 Hz. What is the speed at which the motor operates?