hobut protection relays : speed sensing

The M200-ST3 protection relay is most commonly used to detect the speed of engines used in generating sets. The pick up, situated close to the flywheel, produces a high frequency pulse train which is directly proportional to the number of teeth passing it. The frequency is converted, by the ST3 into a mA signal, that is directly proportional to the rotational speed of the flywheel. The relay provides the user with the following adjustments which allows control of start up, normal running and protects against under and over speeds of the generator.

Adjustment of crank speed is 10 to 50%

Adjustment of under speed is 50 to 100%

Adjustment of over speed is 100 to 133%

A mA output signal proportional to the input frequency

Typical start up is as follows

When the speed of the morot (or as frequency rises) reaches the crank set point, the crank relay energises (disengaging the crank starter) when the under speed set point is reached, the under speed relay is energised. The motor is now in normal running condition with all relays energised. Should an under or over speed condition occur the appropiate relay is de-energised. Two other safety features are incorporated. , if the pick up sensor input lead breaks, the over speed relay will de-energise. The crank relay will only de-energise when the input frequency goes below 20% of the setpoint. The mA signal can be fed to digital or analogue meters scaled in speed, or to provide a control signal to a PLC etc.

INPUT
Pulses	5V peak to peak
Frequency	1000-10000Hz (speed of rotation RPM x number of teeth / 60)
Open circuit protection	Overspeed relay de-energised.
OUTPUT
Rated value	0-1mA = 133% of nominal speed
Load resistance	< 10kOhm
Calibration Value	0.75mm = 100% of nominal speed
SETPOINT
Range	Crank 10 to 50%, Under 50 to 100%, Over 100 to 130%
Repeatability	Better than 0.5% of full span
Hysterysis	2% (under, over) crank resets at 20% setting
Operating time	Typically 200mS
AUXILIARY
DC voltage	24V ± 20%
WEIGHT&CASE	Approx 0.5kg. 100mm case
Note: The three relays in this product are single pole changeover, the remainder of specification is under general specifications.

Product Code	M200-ST3
Normal running speed	1800 rpm
Number of teeth on flywheel	50
Magnetic pick up on output volts	10 volt pk-pk

1	Calibration at temperature other than 23ºC
2	Setpoints factory set. Specify frequency of crank, under speed and over speed settings required