The PF-434 TRMS automatic phase switch is used to maintain the continuity of the power supply of a single-phase receiver in case of phase failure or when the phase exceeds preset parameters. The compact size of the device allows you to save space in the electrical cabinet.
By measuring the RMS value of the voltage (True RMS), the switch guarantees the correct operation even when operating with a severely disturbed power supply network.
Functioning
A three-phase voltage (3×230 V+N) is connected to the input terminals of the device. A single-phase voltage (230 V) of one of the phases appears at the output of the relay. The electronic circuit of the switch controls the voltage values of the supplied phases so that the output voltage is not lower or higher than the set values. The phase with the correct parameters is directed to the output switch. The device measures the RMS value (True RMS) of the voltage, so it is perfect for modern automation systems, where the supply voltage is often distorted due to the operation of nearby devices with pulse power supplies. The corresponding green LED light indicates that the phase is connected to the output of the switch. Phase L1 is the priority phase and if its parameters are correct for a minimum of 5 s, it will be connected to the output.
If phase L1 exceeds the upper or lower setting level (its voltage value is incorrect), the output will show the voltage of phase L2 or L3 in turn, depending on which phase is correct. If none of the other phases is correct, the output will be disconnected. If phase L3 is connected to the output and phase L2 returns to the correct parameters, it will be switched to the output (priority of phases from highest to lowest is L1, L2, L3). If the output phase voltage is 10 V below the set value or 10 V above the set value, the switchover will occur with a 10-second delay. If the phase goes outside this range, it will be disconnected immediately (approximately 200 ms).
The operating voltage range for all three phases is set using the Vmax and Vmin knobs. The Vmax knob determines the maximum permissible output voltage and the Vmin knob determines the minimum voltage. If the phase voltage is between the Vmin and Vmax thresholds, it is considered correct.
In addition, the device has a control contact for continuous monitoring of the output status. In this way, it is possible to detect anomalies such as a stuck contact of one of the contactors or a non-functioning contact. If, after all contactors have been switched off, a voltage of more than 20 V is still present at the output for more than 1 s, all LEDs will start flashing. The corresponding contactor will only be switched on when the voltage drops below 20 V. If the decay occurs up to 1 s, the LEDs will not start flashing. This protection detects a possible stuck contactor contact, or prevents the contactor from switching on if the output voltage is generated externally.
If the contactor of the selected phase is switched on and the output voltage after 1 s is at least 10 V lower than the input voltage, the contact is considered to be faulty. The phase is deactivated until there is a complete voltage loss on the device (reset). This situation is indicated by the flashing of the faulty phase LED. If the device detects that all 3 contactors are faulty, it will attempt self-repair and after 60 s, all of the outputs will be recognised as operational. If the situation persists and none of the contacts are operational, all outputs will be blocked until the power supply fails.
