Reverse Power Relay
Working principle, Parameters and Connection diagram
1 - Reverse power relay:
Reverse power relay is an electronic, microprocessors based protection device which is used for monitoring and stopping the power supply flowing grid side to the DG side. If accidentally leakage current is received by generator then it can start to running as motor. This situation may be very dangerous for generator set.
In LT panel if the DG supply is running then grid supply should be switched off and if the grid supply is running then DG supply should be switched off. When one source is on then second source accidentals starts to leakage current resultant a large fault may be occurred and system can be fail. So for prevention of other source leakage the RPR relay is used.
2 - Connection diagram of over current relay.
3 - Working principle of reverse power relay.
The main function of RPR is to stop the reverse current from grid side to DG side. It is called a another name directional reverse current relay. The current CTs are installed to the grid side and output is connected with RPR relay. During change over from DG to grid the generator will stop after cooling period. If the leakage current from gird side then RP relay is activated and provides a trip signal to he circuit breaker.
After tripping RPR trip LED is activated and blinking. The reset button comes out in tripping condition. It can be manually reset for normal operation.
4 - Relay setting parameters:
| Sr.No. | Parameters | Setting range |
|---|---|---|
| 1 | Voltage | : 110/415V AC |
| 1 | Current | : 1A to 5A |
| 2 | frequency | : 50, +/- 2.5 % |
| 3 | Auxiliary supply |
: 24V to 110V AC/DC ± 15% or 95V to 240V AC/DC ± 15% |
| 4 | RPR Setting of Current | : 1% to 15% (in steps of 1%) |
| 5 | RPR Setting of Time Multiplier | : 0 to 1.5 in steps of 0.1 |
| 6 | Pickup Current | : Same as set current |
| 7 | Reset Current | : 95% - 90% of pickup current |
| 8 | Reset time | : less than 100mS |
| 9 | Instantaneous trip time | : Less than 100mS |
5 - Why it is used?
When diesel generator or turbine behave in reverse condition because alternate start to move as motor due to receiving leakage current from grid side. This situation may be very dangerous for generator and turbine. For stopping reverse current from grid side the RPR is used.
