Scope of work for Alternator

1.0      Comprehensive maintenance contract for alternator 500 KVA

2.1.             Maintenance of Alternator:

Depending on the individual site conditions frequent maintenance should be practiced. Before carrying out any maintenance work the generator should be stopped and isolated electrically from all external loads or supplies.

2.2.             General cleaning

Both interior and exterior of the machine (particularly the windings, bearing, ventilation opening, static exciter, etc. ) should be kept free from any oil or dust by blowing out frequently (Say every one months) with clear dry air at a pressure not exceeding 3.5 kg/cm². If the blowing is ineffective to remove oil or dust, the parts should be carefully cleaned with a rag lightly damped in white spirit.

2.3.             Connections

All the external and internal connections (including rotating rectifier assembly and excitation control unit) must be checked for tightness at joints and continuity. Fuse links shall make a good fit in the holders. All the hardware, including those of terminals should be tightened if necessary.

2.4.             Loss of Residual

If the generator residual is lost because of long storage or demagnetizing due to any mal operations, it will be necessary to disconnect the exciter field terminals at the exciter control unit and connect 12 volts battery directly across the field (with correct polarity) for a few seconds to re establish the residual.

2.5.             Rotating rectifier assembly

The health condition of the diodes cab be checked when required as follows:-

a.             The pig tail terminal of each diode is disconnected.

b.             At least 1.5 volts source (eg. AVO using 008, simpsong 200) on the appropriate range (say ohms x 1). The resistance of diode between stud and pig tail in both directions is measured.

2.6.             Diodes in good condition will show a low (up to a few 100 ohms) resistance in the forward direction and a very high resistance (up to 1 mega ohm) in the reverse direction. A high resistance in both directions or a low resistance in both directions indicates a faulty diode which should be replaced.

2.7.             Failure of surge suppressor can be detected by smell and appearance. Failure of fuses can be detected by checking its continuity using a multi-meter.

2.8.             Bearing

The roller bearing or ball bearing will run for long periods without any attention as the bearing housing is charged with right quantity of grease before dispatch. The bearings are to be lubricated with correct quantity of grease in the intervals stated on the name plate of the generator, in order to replenish any grease lost during running. Lithium based conforming to grade 3 / AP 3 (Castrol) / Mobilube no. 3 (Indian oil) or equivalent may be used. The bearings will be replaced under AMC if defective.  

2.9.             If the grease is caked before commissioning, it has to be completely replaced. Grease of different makes and grades should not be mixed. The original grease should be removed, unless it has become dirty, deteriorated or not caked.

2.10.           Unnecessary disturbance of the bearing cap should be avoided. Where disturbance is necessary great care must be exercised when handling the bearing and cover to avoid the ingress of dirt and moisture into the grease of bearing. When the machine has to be stationary for a long period, the rotor should be turned periodically to avoid settling of grease at the bottom of the housing.

2.11.           However, if alternator failure/winding burnt happens due to AMC negligence, same will be penalised.