8 SELECTION OF ALTERNATOR FOR LINEAR LOADS

To select the rating of ac generator for linear loads the maximum connected load and the base load which is always connected has to be considered. In arriving at a total load figure it is always wise to select the standard rating larger than that estimated. This despite the fact that all the loads may not be operating at the same time and hence a smaller machine could have been selected. Future operating conditions and future growth are very difficult to estimate. An allowance of 15% to 29% excess capacity designed into a set now is a small price to pay compared with the cost of completely new larger unit that may be required to drive additional load in few years time.

8 NON LINEAR LOADS

Over a period of time the loads applied to AC generators have become more complex and more care has to be exercised in the sizing of the generators to ensure satisfactory performance.

8 CHARACTERISTICS OF NON-LINEAR LOADS

a) A non linear load is one in which the load current is not proportional to the instantaneous voltage. Often the load current is not continuous.
b) These are essentially electronic loads such as Computers, UPS equipments and variable speed motor drives.

There are two main non linear loads commonly being applied to ac generators
a) Gas discharge lighting loads and
b) Semiconductor thyristor / rectifier loads.