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COMMON ASPECTS BETWEEN GENERATORS AND MOTORS

The theoretical operation of synchronous generators and synchronous motors is almost the same. The main differences are the direction of stator current and the flow of power through these machines.

The construction of generators and motors, of the same kW ratings, used in the oil and gas industry is very similar. Variations that are noticeable from the external appearance exist mainly due to the location of the machine and its surrounding environment. It is uncommon for generators to be placed in hazardous areas, whereas it is occasionally necessary to use a synchronous motor in a hazardous area, e.g. driving a large gas compressor. Large induction motors are often used for driving oil pumps and gas compressors that need to operate in hazardous areas.

The rotor of generators may be either ‘cylindrical’ or ‘salient’ in construction. Synchronous motors nearly always have salient pole rotors. Machines with four or more poles are always of the salient pole rotor type. Cylindrical pole rotors are used for two-pole generators, and these generators are usually driven by steam or gas turbines at 3600 rpm for 60 Hz or 3000 rpm for 50 Hz operation and have power output ratings above 30 megawatts.

The methods of cooling and the types of bearings are generally the same.

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