This set of DC Machines Multiple Choice Questions & Answers (MCQs) focuses on “Parallel Operation of DC Generator”.
1. For connecting two generators in parallel, they should have __________________
a) Same current rating
b) Same ohmic rating
c) Same voltage rating
d) All ratings must be same
View Answer
Explanation: For connecting two DC generators in parallel we equal voltage ratings. As the generator voltage is easily adjustable in a range, so the condition stated above is not a must. But, it is desirable condition.
2. While connecting two DC generators in parallel, which of the following is not a desirable condition?
a) Same voltage rating
b) Same percentage voltage regulation
c) Same percentage speed regulation of the prime movers
d) Same current rating
View Answer
Explanation: Same voltage rating, same percentage voltage regulation, same percentage speed regulation are the desirable conditions for connecting two generators in parallel, though these conditions are not a must.
3. We connect two generators in parallel _____________
a) For large DC load
b) For small DC load
c) For any DC load
d) For any AC or DC load
View Answer
Explanation: We connect two generators in parallel for supplying large DC load. It is desirable to use more than one generator in parallel. This arrangement provides the security that if one generator gives way, the other(s) can feed part load.
4. Load sharing of two generators connected in parallel is determined by __________
a) Internal characteristics
b) External characteristics
c) Both internal and external characteristics
d) It doesn’t depend on load sharing
View Answer
Explanation: Two generators are connected in parallel such that, summation of current carried by both generators is equal to load current. In such cases we need to see external characteristics on loaded condition.
5. For a parallel operation of 2 DC shunt generators, we get net external characteristics ___________
a) Starting from the same no-load point and between generator 1 and generator 2
b) Starting from the same no-load point and below generator 1 and generator 2
c) Starting from the same no-load point and above generator 1 and generator 2
d) Can’t be determined
View Answer
Explanation: The load sharing by these generators is determined by addition of external characteristics of both of generators. Thus, at no load generators will have common point, on y- axis so parallel characteristic will start from same point and will lie above of both.
6. When two compound generators are connected in parallel, when load current in generator 1 is increased __________
a) Both generator will share same load
b) Generator 1 will start running as motor
c) Generator 2 will be overloaded
d) Generator 2 will start running as motor
View Answer
Explanation: If load current in G1 increases, load current in G2 decreases. Series excitation and internal voltage in G1 increases and for G2, these quantities decrease. Finally, all load shifts, which may turn to run G2 as a motor. All this leads to heavy overloading of G1.
7. While running two compound motors in parallel, we connect equalizer ring between ___________
a) Two armatures
b) Two fields
c) Two load points
d) Anywhere
View Answer
Explanation: A low-resistance equalizer connection is made directly between the two armatures before the series fields. Any emf variations of the armatures causes equalizing circulating current which do not affect the current through the series windings. Thereby the parallel operation is stabilized.
8. When two DC series motors are connected in parallel, the resultant speed is __________
a) More than the normal speed
b) Loss than the normal speed
c) Normal speed
d) Zero
View Answer
Explanation: When two DC series motor are connected in parallel then the resultant speed is increase the normal speed. If the voltage across each motor is assumed to be V, then current through each motor in parallel connection will be I/2. So, speed α (voltage/current) α (V/Ia/2). Hence the resultant speed is more than normal speed.
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