The 250 series speed sensing relay monitors rotating equipment and
provides three output contacts which can be used to initiate alarm or
shutdown signals. The relay also provides a tachometer output for speed
indication. Speed sensing relays are ideally suited for engine and gas
turbine monitoring and the protection of generator sets.
Operation
The speed sensing protector monitors the speed of rotation using a low cost magnetic
pickup. Speed sensors are often used in generator set engines, gas turbines, motors,
gear boxes or any rotating machines. The relay will detect under-speed, over-speed and
stopped conditions and the set point relays can be used to raise an alarm or shut down
the equipment. The relay provides three user adjustable trip levels with LED relay state
indication and a speed indicator output signal.
The product also offers an analogue output that can be used to monitor or display the
speed. The product operates from the 12V or 24V dc battery supply and speed is
measured and calculated from the number of sensor pulses per revolution. Since the
sensor is magnetic, a rotating steel component such as the flywheel which has gear
teeth can be used. This will result in a large number of pulses per revolution and lead to
greater accuracy.
The protector continuously monitors the rotation speed and updates the analogue
output signal. An output of 0.75mA indicates normal speed (100%) while 1mA
indicates 133% of nominal speed. The calibration point can easily be user adjusted.
Three set point control adjustments allow setting of the desired speed limits for
cranking, under-speed and over-speed.
Cranking Relay
The cranking relay detects if the engine is running or stopped. This relay can be used
to ensure the cranking motor is disconnected once the engine has started running.
Set the cranking set point just above the cranking motor speed. A red LED illuminates
when the relay is energised, indicating a trip condition. The crank relay will only reset
when the input frequency falls below 20% of the crank set point.
Under-Speed Relay
The under-speed relay detects when the normal running speed has been achieved.
This can be used to enable the generator's electrical protection. It can also be used to
trigger load shedding. A red LED illuminates when an under-speed condition exists.
Over-Speed Relay
The overs-peed relay detects a stuck throttle or overshoot. A break in the sensor load
will de-energise the over-speed relay and can be used to shut down the engine. A red
LED indicates over-speed trip.
Fail Safe Operation
The relay will detect an open circuit speed sensor and de-energise the over-speed relay. |
