Differentiate between DC motor and AC dynamo.
Answers
Answer:
Difference Between AC and DC Generator
Sl. No.
Differentiating Property
AC Generator
DC Generator
1
Definition
AC generator is a mechanical device which converts mechanical energy into AC electrical power.
DC generator is a mechanical device which converts mechanical energy into DC electrical power.
2
Direction of Current
In an AC generator, the electrical current reverses direction periodically.
In a DC generator, the electrical current flows only in one direction.
3
Basic Design
In an AC generator, the coil through which the current flows is fixed while the magnet moves. The construction is simple and costs are less.
In a DC generator, the coil through which the current flows rotates in a fixed field. The overall design is very simple but construction is complex due commutators and slip rings.
4
Commutators
AC generator does not have commutators.
DC generators have commutators to make the current flow in one direction only.
5
Rings
AC generators have slip-rings.
DC generators have split-ring commutators.
6
Efficiency of Brushes
Since slip-rings have a smooth and uninterrupted surface, they do not wear quickly and are highly efficient.
Both brushes and commutators of a DC generator wear out quickly and thus are less efficient.
7
Short Circuit Possibility
As the brushes have high efficiency, a short circuit is very unlikely.
Since the brushes and commutators wear out quickly, sparking and short circuit possibility is high.
8
Armature
In case of AC generators, the armature is always the rotor.
In case of DC generators, the armature may be either rotor or stator.
9
Rotating Parts
The rotating part in an AC Generator is low current high resistivity rotor.
The rotating part in a DC generator is generally heavy.
10
Current Induction
In AC generator, the output current can be either induced in the stator or in the rotor.
In DC generator, the output current can only be induced in the rotor.
11
Output Voltage
AC generators produce a high voltage which varies in amplitude and time. The output frequency varies (mostly 50Hz to 60Hz).
DC generators produce a low voltage when compared to AC generator which is constant in amplitude and time i.e. output frequency is zero.
12
Maintenance
AC generators require very less maintenance and are highly reliable.
DC generators require frequent maintenance and are less reliable.
13
Types
AC generators can of varying types like 3 Phase generators, Single phase generators, synchronous generator, induction generator, etc.
DC generators are mainly two types which are Separately excited DC generator and Self-excited DC generator. According to field and armature connection, they can be further classified as DC series, shunt or compound generators respectively.
14
Cost
The initial cost of AC generator is high.
The initial cost of DC generator is less when compared to AC generators.
15
Distribution and Transmission
The output from AC generators is easy to distribute using a transformer.
The output from DC generators is difficult to distribute as transformers cannot be used.
16
Efficiency
AC generators are very efficient as the energy losses are less.
DC generators are less efficient due to sparking and other losses like copper, eddy current, mechanical and hysteresis losses.
17
Applications