1. The conductor EMF and current are in _____ direction and developed torque is in _____ for generating mode.
a) same, opposite
b) same, same
c) opposite, same
d) opposite, opposite
Explanation: The conductor emf and current will be in same direction and the developed torque is in opposite direction for a generator.
2. If the armature terminal voltage is more that its induced EMF, the DC machine given is ________
a) motoring mode
b) generating mode
c) regenerative mode
d) none of the mentioned
Explanation: As the terminal voltage is lesser than armature voltage, the supply is fed to the machine and so it will be acting like a motor
3. Consider a 200V, 25kW, 30A DC machine lap connected with armature resistance of 0.4 ohms. If the machine is later wave wound, then the developed power is?
a) 25 kW
b) 12.5 kW
c) 20 kW
d) 50 kW
Explanation: The power of the machine remains unaltered by the type of connections.
4. If the DC machine is held constant at 3000 rpm. The DC voltage is 250V. If the field is held constant with 250V. Is this machine generator or motor?
a) Motor
b) Generator
c) None of the mentioned
d) Any of the mentioned
Explanation: From the speed and emf relation, E = 250*2950/3000
= 245.8 V
This is less than the terminal voltage. Hence it is a motor
5. A shunt generator has an induced voltage on open circuit of 127 V. When the machine is on load the terminal voltage is 120 V. The load current if the field resistance be 15 ohm and armature resistance be 0.02.
a) 342 A
b) 350 A
c) 358 A
d) 8 A
Explanation: Ia*Ra = E-V
= 127 – 120
= 7 V
Ia = 350 A
Ish = 120/15
= 8 A
I = 350 – 8
= 342 A
6. Consider a DC generator running at the rated speed of 2000 rpm, suddenly there is an insulator falls on the field circuit and breaks it. Then __________
a) the motor stops in a few rounds
b) it continues to run but as dc motor
c) it continues to run as a motor
d) none of the mentioned
Explanation: As the field circuit gets broken there is interruption in the flux to the dc machine, and as a result the motor stops in few seconds.
7. If a self excited DC generator is failed to run, this refers to ________________
a) zero residual voltage
b) field MMF, that it is not cumulative
c) resistance is greater than critical resistance
d) any of the mentioned
Explanation: Any of the reasons are valid for no build up of an emf.
8. The self-excited dc generator with gradual build up of residual voltage and EMF corresponds to __________
a) positive feedback
b) negative feedback
c) saturation
d) any of the mentioned
Explanation: It responds to a positive feedback because the gain is always more than one in the linear region.
9.The critical resistance refers to __________
a) the resistance above which machine does not excite
b) the resistance below which machine does not excite
c) the resistance at which machine does not excite
d) any of the mentioned
Explanation: After taking a glance at the magnetization curve, it can be concluded that the emf will not build up if the resistance is greater than critical resistance.
10. If a DC shunt generator fails to start, the most primitive action would be __________
a) reversing field connection to armature
b) reversing direction of rotation
c) any of the mentioned applicable ways
d) none of the mentioned
Explanation: The first measure is to check if the field winding as properly connected with additive polarity so that the flux is aiding in nature.