Reactive Power

REACTIVE POWER

Synchronous Generators:

Ø   Synchronous machines can be made to generate or absorb reactive power depending upon the excitation (a form of generator control) applied.

Ø   The ability to supply reactive power is determined by the short circuit ratio.

Synchronous Compensators:

Ø   Certain smaller generators, once run up to speed and synchronized to the system, can be declutched from their turbine and provide reactive power without producing real power.

Capacitive and Inductive Compensators:

Ø   These are devices that can be connected to the system to adjust voltage levels .

Ø   A capacitive compensator produces an electric field thereby generating reactive power An inductive compensator produces a magnetic field to absorb reactive power.

Ø   Compensation devices are available as either capacitive or inductive alone or as a hybrid to provide both generation and absorption of reactive power.

1. Overhead lines and underground cables, when operating at the normal system voltage, both produce strong electric fields and so generate reactive power.

2.  When current flows through a line or cable it produces a magnetic field which absorbs reactive power.

3. A lightly loaded overhead line is a net generator of reactive power while a heavily loaded line is a net absorber of reactive power.

4. In the case of cables designed for use at 275 or 400kV the reactive power generated by the electric field is always greater than the reactive power absorbed by the magnetic field and so cables are always net generators of reactive power.

5.     Transformers always absorb reactive power.