Question
What is the difference between direct current generator and alternating current generator?
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Sl.No.
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Differentiating Property
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AC Generator
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DC Generator
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1
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Definition
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AC generator is a mechanical device which converts mechanical energy into AC electrical power.
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DC generator is a mechanical device which converts mechanical energy into DC electrical power.
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2
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Direction of Current
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In an AC generator, the electrical current reverses direction periodically.
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In a DC generator, the electrical current flows only in one direction.
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3
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Basic Design
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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.
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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.
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4
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Commutators
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AC generator does not have commutators.
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DC generators have commutators to make the current flow in one direction only.
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5
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Rings
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AC generators have slip-rings.
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DC generators have split-ring commutators.
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6
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Efficiency of Brushes
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Since slip-rings have a smooth and uninterrupted surface, they do not wear quickly and are highly efficient.
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Both brushes and commutators of a DC generator wear out quickly and thus are less efficient.
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7
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Short Circuit Possibility
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As the brushes have high efficiency, a short circuit is very unlikely.
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Since the brushes and commutators wear out quickly, sparking and short circuit possibility is high.
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8
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Armature
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In case of AC generators, the armature is always the rotor.
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In case of DC generators, the armature may be either rotor or stator.
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9
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Rotating Parts
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The rotating part in an AC Generator is low current high resistivity rotor.
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The rotating part in a DC generator is generally heavy.
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10
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Current Induction
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In AC generator, the output current can be either induced in the stator or in the rotor.
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In DC generator, the output current can only be induced in the rotor.
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11
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Output Voltage
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AC generators produce a high voltage which varies in amplitude and time. The output frequency varies (mostly 50Hz to 60Hz).
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DC generators produce a low voltage when compared to AC generator which is constant in amplitude and time i.e. output frequency is zero.
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12
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Maintenance
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AC generators require very less maintenance and are highly reliable.
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DC generators require frequent maintenance and are less reliable.
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13
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Types
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AC generators can of varying types like 3 Phase generators, Single phase generators, synchronous generator, induction generator, etc.
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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.
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14
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Cost
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The initial cost of AC generator is high.
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The initial cost of DC generator is less when compared to AC generators.
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15
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Distribution and Transmission
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The output from AC generators is easy to distribute using a transformer.
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The output from DC generators is difficult to distribute as transformers cannot be used.
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16
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Efficiency
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AC generators are very efficient as the energy losses are less.
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DC generators are less efficient due to sparking and other losses like copper, eddy current, mechanical and hysteresis losses.
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17
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Applications
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It is used to power for smaller motors and electrical appliances at homes (mixers, vacuum cleaners, etc.)
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DC generators power very large electric motors like those needed for subway systems.
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