by Reza <aghamolaei@[EMAIL PROTECTED]
>
Jul 3, 2007 at 05:33 AM
Dear friend :
The capacitor rating (rated KVAR) required for desired power factor
calculated as below:
Qc = P. (tan 1 - tan 2)
Where:
P: Load active power
1: phase displacement angle before compensation
2: phase displacement angle of desired Cos 2
The desired Cos should be between 0.9 to 1 , over
compensation(Qc>P.tan 1) and lead Cos must be avoided as this gives
rise to capacitive reactive power which stresses the conductors in
the same way as inductive power , and in addition unwanted voltage
increase can occur.
Types of compensation:
1-Single compensation:
The capacitor is coupled directly to the terminals of load and
switched in Common with it.
Advantage: reduced load on distribution, lines no separate switches
required for capacitor, simple and inexpensive installation.
This technique is used when relatively large loads (e.g. motors) are
as far as possible in continues operation.
2-Group compensation:
The capacitor bank is connected to the distribution bus feeding, for
example a large number of small motors running continuously or
intermittently. The motors and capacitors are switched by separate
switches and supervised by separate protection systems.
Advantage: automatic control of Cos , thus keeping the Cos closer
to the desired value.
