Electrical Power System Essentials

5.1 INTRODUCTION

Electrical power systems can be regarded as one of the most complex systems designed, constructed and operated by humans. The consumers are supplied with the requested amount of active and reactive power at constant frequency and with a constant voltage. Loads are switched on and off continuously, and because electricity cannot efficiently be stored in large quantities, the balance between the amount of generated and consumed electricity has to be maintained by control actions.

The active power balance is controlled by the generators. There is also another option, and that is to reduce the active power consumption by disconnecting parts of the load (this is called load shedding), but this is merely an emergency measure and not common practice. The reactive power balance can be controlled by rotating equipment (generators and motors) and by static components (capacitors and inductors). The synchronous generator is the most important component in the system for maintaining the active and the reactive power balance.

Let us look at what happens in a simple system, in which a generator is supplying a variable load, when suddenly more active or reactive power is consumed and no control actions are taken. When we neglect losses, we can write for the active power balance:

P_m the mechanical power supplied to the generator axis by the prime mover [W]

P_e the electrical (active) ...