Question
What is the difference between direct current generator and alternating current 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 | It is used to power for smaller motors and electrical appliances at homes (mixers, vacuum cleaners, etc.) | DC generators power very large electric motors like those needed for subway systems. |
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