Priciple of operation
MODEL 256 - PLL
The relay continuously monitors the voltage, phase displacement and frequency of two supplies. A single set point adjustment permits selection of suitable matching and a red LED illuminates when the relay is energised, indicating that the two supplies are well matched and it is safe to close the breaker.
MODEL 256 - PLD
This version operates in the same way as model 256-PLL but includes an additional dead bus detection function. If there is a requirement for a continuous supply or emergency power, then the generator can be connected without synchronising, thus ensuring continuity of supply. The absence of bus voltage will cause the relay to energise.
The relay provides one pair of normally open and one pair of normally closed contacts. An LED indicates relay energised state. The synchronising set point limits are user adjustable.