4.5 REPRESENTATION OF LOADS

The loads generally consist of industrial and domestic components. The magnitude of the load changes continuously such that the load forecasting problem is truly a statistical one. An industrial load consists mainly of large three phase induction motors with sufficient load constancy and predictable duty cycle, whereas the domestic load mainly consists of lighting, heating and many single-phase devices used at random by householders. The design and operation of power systems both economically and electrically, are greatly influenced by the nature and magnitude of loads. In general, there are three ways of load representation. They are:

1. Constant power representation: This is used in load flow studies both specified MW and MVAR are taken to be constant.

    

2. Constant current representation: The load current equation can be written as is the power factor angle. It is known as constant current representation because the magnitude of current is held constant.

    

3. Constant impedance representation: This representation is generally used in stability studies. The load specified in MW and MVAR at nominal voltage is used to compute the load impedance. Thus,
   

   This is regarded as constant throughout the study.