Standby Power Supply System (Generator)

Standby or emergency power can be supplied through AC (alternating current) generator and diesel engine

AC Generator

A generator is a machinery that converts mechanical energy to electrical energy by electromagnetic action to generate electrical power.

Synchronous generator, the principle of which is reverse as that of an electric motor, is an AC generator, which generates electric power synchronizing to rotating rate of magnetic field passing through armature windings.

Frequency of the synchronous generator is determined according to the rate of rotation, and accordingly, the frequency decreases as the rate of rotation becomes lower than the synchronous rate.

Therefore, the rate of the engine for the synchronous generator should be regulated to maintain the level of synchronous rate.

The O&M issues to be taken care of are mentioned overleaf:


• Oil or dust on windings or air vent sleeves obstructs air ventilation and leads to overheating of the generator and deterioration of insulators, which may cause short circuit and ground fault. The dust should be blown-off by a compressed air and the oil and grease should be removed with cloth, cleansing oil, etc.

• In the case of severe accumulation of oil and dust, it is recommended to have the winding cleaned and varnished with insulation paint after drying thoroughly, by a professional cleaning company.

• Insulation coating over terminals should be checked for overheat or discolouration due to cracks or slacks.


• Pay full attention to any abnormal noise from bearings during running to detect any defect at early stage. It is the simplest way to check bearing conditions.

• Grease should be supplied through the openings periodically while the generator is running. If a drain valve is provided to the grease chamber, always open the valve during filling grease to purge out old grease.

Brush (Static excitation system)

• Worn brush reduces brush pressure and causes sparks that may make the surface of a slip ring rough. To prevent it, always check for abrasion, unsymmetrical wear or damage to brush, and pressure of the brush holder. The brush-lifting device should be inspected to ensure that it works properly.

• Brushes should be replaced with new ones when the wear level reaches the designated value. The newly installed brushes should preferably be of the same material and shape as the currently used ones.

Exciter (brushless)

• Exciters hate moisture and dust. Dust should be blown-off by low-pressure compressor and wiped with dry cloth.

• Check bolts and nuts on terminal area and terminal block for looseness, wires for discolouration and conditions of earthing and installation.