Automatic Capacitor Controls Panel
Capacitors are used in general electrical usage to improve system power factor. Usage of elements like motor in electrical circuit contributes to pull down power factor resulting in drawing higher currents to the same power as 3 E1.cos . Voltage of the system remaining constant at low power factor current being inversely proportional to the same. The current would increase this demands a higher size cable, more voltage drop and loss of energy too.

Most important to the electricity authority is the voltage drop. When a common transformer is used by number of clients, they are interested in the electrical well being of all users on the same transformer. Hence when voltage drops due to high current, It affects the neighboring above and hence they insist upon 0.9 PF to be maintained so that any one person do not contribute to this trouble.

Hence electricity authority insists upon the use of 33% capacitor on the particular transformer used when the customer owns the transformer. Hence say for 1000 KVA transformer installation of 350 KVA r capacitor becomes mandatory. But this is not the end of it. Even after this installation the power factor of the system goes down. It is up to the user to bring up the system PF to 0.9 by use of additional capacitor, the quantity of which could be decided with the knowledge of present PF value the desired PF value. PF penalty will be levied by supply authority if lower PF than 0.9 is observed on the system as well it may lead to disconnection of the system.

Originally use of capacitors with use of a number of switches, switched on/off manually for purpose was used. But with fast load value changing in the system such manual arrangement becomes tedious. Hence automatic power factor correction relays have come to vogue by which step selection becomes fully automatic.

We have got up to 14 step relays which could be efficiently used to suit our requirements. A main line CT and main line voltage is sampled out to operate this relay. Hence an additional CL’s CT’s would be needed in the main panel for the relay operation.

Tapped CT’s could be used in place of normal CT where load has not developed and after the load is developed lower tap could be shifted to the full value. This is view of the fact that the relays need 10-15% of total load current as a minimum for operation.

Wherever transformers are used idle for a length of time in the day the following float capacitor advised to be used to compliment no load loses of the transformer.

  • Up to 315KVA – 5% of transformer KVA
  • Up to 1000KVA – 6% of transformer KVA
  • Above 1000KVA – 8% of transformer KVA

Since this does not fall as a load to APFCR separate capacitor kept floating is necessary. These however add on to APFCR during load running.

Capacitor usage on HT can also be undertaken. They will be out door unit without APFCR unit. Now a Days HT contacters are available, Hence APFCR will be delayed switching also can be installed.