Power Factor Relay
Working principle, Parameters and Connection diagram
1 - Power factor relay:
APFC relay is used for monitoring the system power factor and also controlling the capacitor for connecting and disconnecting to the busbar. When the power factor is monitored in low below pre set value as 9.9 then a signal is provided to the capacitor contactor coil for capacitor connect into busbar. After maintaining the power factor the outgoing signal is disconnected.
Generally three types load are used in domestic or industrial like as resistive, inductive and capacitive. Mostly inductive load is used in industries like as motors, compressors, electrical choke, transformers and arching welding etc. Due to more inductive load the power factor is affected as low and system will start to take more current. So capacitor is used for improving power factor.
The APFC relay is used for controlling to the capacitors which is installed in capacitor bank panel for improving power factor. Capacitor is connected to the parallel with busbar. APFC relay monitors and controls the capacitors for connecting and disconnecting to the busbar as per requirement
2 - Working principle of APFC relay.
APFC is the main function of controlling the capacitor bank panel or power factor control panel. Fourteen or
sixteen numbers capacitors are installed with contactors. All contactor coils holding supply is provided from
APFC relay.
APFC relay monitors the power factor of system which should be default as 9.8. If the power
factor is low then it provides signal to the contactor holding coil as per sequence1 to 16. After connecting
one capacitor then APFC relay again monitors the power factor. If the power factor is low then it provides to
the signal next capacitor.
3 - Connection diagram of power factor relay.
4 - Relay setting parameters:
| Sr.No. | Parameters | Setting range |
|---|---|---|
| 1 | frequency | : 50, +/- 2.5 % |
| 2 | Auxiliary supply |
: 240V AC ± 15% or |
| 3 | Current | : 5A/ 1A from CT secondary |
| 4 | Target pf setting | : .7 lag to .9 lead |
| 5 | Supply for contactor | : 250 Volt AC, 5A |
| 6 | LED | : Capacitor status, Alarm, Auto/ Manual, Lead or leg pf |
| 7 | Parameters display | : pf, kVAR, Voltage, Target pf, CT ratio, Alarm condition. |
| 8 | pf control range | : 1% to 120% of rating. |
| 9 | Temp | : 0 to 60 degree centigrade. |
5 - Why it is used?
In industries, Power factor loss is the cause of penalty by gov electricity board and other second reason is
due to low power factor the system takes a excess current. Penalty and energy loss is the two major caused of
using power factor improvement system so the power factor relay is used for monitoring and controlling for it.
Capacitors are used for improving power factor so we will have to connect capacitor into line as parallel.
We can avoid penalty and power loss by using power factor improvement system.
