Power Factor Correction

The active power produced by the active current can alone be turned into an effective use for the consumer; while the reactive power produced by the reactive current does not yield usable power, and consequently, is not registered on the active performance meter. The reactive power has, however, a negative effect on generators, transformers, and conductor lines, while causing voltage drops and fi nancial losses due to additional electric heating.

The reactive power required for the creation of the magnetic fields around motors, transformers, and conductor lines continuously oscillates between the current generators and the consumers. A more cost effective way to provide this reactive power is to produce it by placing capacitors close to the consumers of reactive power (motors, transformers), thus relieving the line between generator and consumer of the transport of the reactive current portion. This way, several more current consumers can be connected to an existing supply system without having to extend or amplify that system if the capacitors are suitably positioned.

Individual Power Factor Correction

The power factor correction capacitor is connected directly to the terminals of the consumer and will be switched together with it. The advantages of this method are: Relief of the conductor lines and switches, no capacitor switches or discharge resistors are needed, and the installation is simple and cheap. The individual compensation is the best solution for large consumers (e.g. motors), particularly if they are in continuous operation.

Individual Power Factor Correction of 3-Phase Motors

The motor and the capacitor are connected in parallel. They are both switched in and out by means of one and the same switchgear and also monitored by a common protective device. A discharge device is not required, because discharging takes place through the motor windings.

The switchgear must be rated to be capable of withstanding the inrush current of the capacitor and the connection lines must be capable of withstanding the full load current of the motor. The capacitor, in this case, has to be installed in close proximity to the motor.

Individual Power Factor Correction of Power Transformers

The direct connection of the capacitor to a power transformer,which is jointly switched in and out, is feasible and permissible both at the H.V. side and the L.V. side.

In cases where harmonics exist in the line, the line should be checked to determine whether the capacitors and the power transformer are connected in series and create a resonance.

Care should be taken not to overcompensate the power transformer during low load operation in order to avoid an unacceptable rise in voltage.

Individual Power Factor Correction of Welding Machines

The output of capacitors for welding transformers and resistance welding machines only needs to be in the range of 30% to 50% of the nominal transformer capacity. For welding rectifi ers, a capacitor output of about 10% of the nominal capacity of the transformer/rectifi er is suffi cient.

Group Power Factor Correction

The  group power factor correction capacitors are connected to the secondary distribution system which feeds a number of individual motors, operating either continuously or at intervals.

The motors and the capacitors are each switched in and out separately and are monitored by separate protective devices. The capacitors can be switched in or out individually or in groups.

Central Power Factor Correction

In large installations where many individual electrical appliances of various size (motors etc.) operate at different times and for different periods, the power factor correction capacitors are centrally connected to the main buss bar. The capacitors can be switched either manually or, by means of power factor control relays, automatically.