The synchro-check relay can be used to assist in the semi-automatic
parallelling of two ac power systems. The volt-free relay contacts change
state when the voltage level, phase relationship and frequency are within
the selected synchronising limits. Connecting two electrical systems that
are not closely matched can cause expensive damage and disturbance
to the electrical system. Using this relay will ensure that damage will
not occur.
Operation
As part of a manual control system, the operator will make adjustments to the generator
voltage (excitation) and frequency (engine speed) using a synchroscope or lamps and
will then attempt to manually close the breaker. This synchro check protector will
qualify that the two systems are closely matched before permitting the breaker to close.
As part of an automatic synchronising arrangement, this relay can be used as an
independent backup or checking device to ensure the two systems are suitably
matched before the breaker can close.
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. |
