What is a DC Generator?
An electrical machine whose major function is to convert mechanical energy into electricity is known as a DC generator. Based on the electromagnetic induction principle of Faraday’s law, when a magnetic flux is generated by a conductor, then emf is produced. So, when the conductor circuit is closed, this electromotive force can cause a flow of current. Hence, it can be concluded that to generate electricity, a device is used, which is known as a DC generator that converts mechanical energy into electrical energy.
Water turbines, steam turbines, combustion engines etc. are several types of mechanical energy sources that are used in the assembly of power generating plants. The generator provides power to all the electrical power grids. On the other hand, an electric motor can perform the reverse function of the generator, whose main function is to convert electrical energy to mechanical energy.
Parts of a DC Generator
Without changing its construction, a DC generator can also be used as a DC motor. Therefore, both a DC motor and a DC generator come under the category of DC machines. Given below are some of the important parts of a DC Generator.
Stator
Rotor
Armature Windings
Yoke
Poles
Pole Shoe
Commutator
Brushes
Applications of DC Generators
DC generators have a wide range of applications, and some of them are listed below:
- DC generators, which are separately excited types, are widely used for power and lighting purposes.
- The stable current generator, arc lamps for lighting and a booster uses a series of DC generators.
- To compensate for the voltage drop within Feeders, DC generators are used.
- To provide a power supply for offices, hostels, lodges, etc. DC generators are widely used.
Important Questions on DC Generator
1) By keeping _____, the characteristics of a separately excited DC generator are drawn.
a) Both speed and field current constant
b) Both Speed and field current variable
c) Speed variable but field current constant
d) None of these
Correct Option: (b)
Explanation: The operation considered here assumes that by keeping both the speed and field current variable, the characteristics of separately excited DC generators are drawn.
2) Which among the following conditions is not desirable while connecting two DC generators in parallel?
a) Equal voltage rating
b) Voltage regulation of the same percentage
c) Prime movers with the same percentage speed regulation
d) Same current rating
Correct Option: (d)
Explanation: Apart from the same current rating, the other three conditions are desirable conditions for connecting two generators in parallel.
3. For supplying a ____, two generators are connected in parallel.
a) Large DC load
b) Small DC load
c) Any DC or AC load
d) None of these
Correct Option: (a)
Explanation: For supplying a large DC load, two generators are connected in parallel. It is necessary that more than one generator should be used in parallel. The benefit of this arrangement is that it provides the security that if one generator collapses, the others can provide the load.
4) With respect to variation in separately excited DC generators, the variation in terminal voltage of DC shunt generator will be _____.
a) Much rapid
b) Very slow
c) Will remain constant
d) None of these
Correct Option: (a)
Explanation: With the load in a shunt generator, the terminal voltage drops off much more rapidly as compared to the separately-excited generator. The reason behind it is the fall in field current with terminal voltage.
5) What is the reason for not using the differential compound generator in practice?
a) It is very costly
b) It is high in maintenance
c) High drop down in voltage
d) Its construction is difficult
Correct Option: (c)
Explanation: The differential compound machine gives the lowest voltage output at a given value of load current. So, the voltage of the DC differential compound generator is maximum when the load current increases drop down the terminal.
6) Internal/external characteristics start from _____ for series DC generators.
a) Non-zero positive voltage
b) Zero voltage
c) Negative voltage
d) None of these
Correct Option: (b)
Explanation: Apart from series DC generators, for all other DC generators, the external and internal characteristics start from a non-zero positive value of voltage. Both internal and external characteristics start from the origin of the series DC generator.
7) What will be the shaft power at the DC Generator?
a) Sum of rotational losses and mechanical power
b) Mechanical losses only
c) No mechanical and load losses
d) All of the above
Correct Option: (a)
Explanation: The sum of rotational losses and mechanical power is known as the shaft power.
8) At brush-commutator contact, the voltage drop is variable, and it is dependent on the armature current. Is it true or false?
a) True
b) False
Correct Option: (b)
Explanation: The above statement is false because at brush-commutator contact, the voltage drop is variable, and it is independent of armature current.
9) What is a DC Generator?
An electrical machine whose major function is to convert mechanical energy into electricity is known as a DC generator. Based on the electromagnetic induction principle of Faraday’s law, when a magnetic flux is generated by a conductor, then emf is produced.
10) What are the applications of DC generators?
DC generators have a wide range of applications, and some of them are listed below:
- DC generators, which are separately excited types, are widely used for power and lighting purposes.
- The stable current generator, arc lamps for lighting and a booster uses a series of DC generators.
- To compensate for the voltage drop within Feeders, DC generators are used.
- To provide a power supply for offices, hostels, lodges, etc., DC generators are widely used.
Practice Questions
1) How does a DC generator work?
2) What is DC current?
3) Write about the losses in a DC generator.
4) What are the types of generators?
5) What is AC current?
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