ZAHRA RST-25 Voltage Relay Three Phase A+ Quality
Electronic Voltage Protection Phase Sequence Relay
Model Name: Zahra RST-25
2. Operation Instructions
The electronic phase filure relay RST 25 offers phase failure, phase shift, phase flashing, asymmetric,phase sequence and also under and overvoltage control
The RST 25 can be connected as following in the installation diagram:
FIG 1: Connection of the relay before operation.
When the relay is connected as in FIG 1, the three yellow LED’s L1, L2 and L3 light up when the power supply A1 phase L, the A2 Neutral, and the three phases “L1”, “L2” and “L3” are properly connected.
If there is no under of overvoltage, phase failure of phase sequence, the green LED lights up, (terminals 11 and 14 are closed) and the relay is ready for operation.
FIG 2: Connection of the relay after operation.
When the relay is connected as in FIG 2, (the power supply A1 phase L, the A2 Neutral are properly connected) after operation, the three phases “L1”, “L2” and “L3” are properly connected, and there is no under of overvoltage, phase failure, phase sequence, the green LED lights up (terminals 11 and 14 are closed) and the relay is ready for self retaining.
It is also possible to connect the power supply after operation in FIG 2.
By both FIG’s 1 and 2, the terminal “PE” must be grounded.
The desired undervoltage limit can be adjusted down to -25% UN.
The desired overvoltage limit can be adjusted up to +25% UN.
When adjusting overvoltage and undervoltage limit, the asymmetric limit is also adjusted.
7. Time Delay
The switch off time can be adjusted by the potentiometer “Time Delay” from 0.1……5 seconds. With this function it is possible to adjust the time for the identification of the failure.
8. Contactor Control
If a phase fails during operation at load or one of the contacts of the contactor or circuit breaker is defect, (contact bounce or scorched contacts), RST 25 recognizes the failure, and also the feedback voltage, and switches off depending on the setting of “Time Delay”
The RST 25 controls the phase shift. If there is a phase failure during operation the angle from the feedback boltage is 30℃ and the RST 25 recognizes this failure.