The cosine of angle between voltage and current in an a.c circuit is known as power factor (p.f) . Low power factor is undesirable from economic point of view. Normally,the p.f of the whole load on the supply system is lower than 0.8 . The low p.f is mainly due to the fact most of the power loads are inductiveand therefore take lagging current. In order to improve the power factor ,some device having leading p.f should be connected in parallel with the load. One of such devices can be capacitor. The capacitor draws aleading current and partly or fully neutralises the lagging reactive component of load current. This raises the power factor of the load. With the following equipments power factor can be improved :
- Static capacitors : Power factor can be improved by connecting capacitors in parallel with the equipment operating at lagging p.f .For 3-phase loads, the capacitors can be connected in delta or star.
- Synchronous condensors : A synchronous motor takes a leading current when over-excited and therefore behaves as a capacitor.An over excited synchronous motor running on no load is known as synchronous condensor. When such a machineis connected in parallel with the supply,it takes a leading current which partly neutralises the lagging reactive component of the load. Thus p.f is improved.
- Phase advancers : It is a source of reactice power and sometime it also act as the load balancing device. This device is widely used to improve the power factor of induction motors.