Speed Sensing Protection Relay

Speed Sensing Protection Relay


DIN rail mounting protection relays for use in single and three phase systems. Available in 55mm x 112mm or 100 x 112mm DIN rail cases


For over protection, under protection and combined under & over protection available in AC current AC voltage & frequency versions. Millivolt trip, DC voltage trip, Reverse Power, Phase sequence & Phase balance relays also available in our extensive range of protection relays..

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Selection Guide

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.

Typical Applications

Pulses5V peak to peak
Frequency1000-10000Hz (speed of rotation RPM x number of teeth / 60)
Open circuit protectionOverspeed relay de-energised.
Rated value0-1mA = 133% of nominal speed
Load resistance< 10kOhm
Calibration Value0.75mm = 100% of nominal speed
RangeCrank 10 to 50%, Under 50 to 100%, Over 100 to 130%
RepeatabilityBetter than 0.5% of full span
Hysterysis2% (under, over) crank resets at 20% setting
Operating timeTypically 200mS
DC voltage24V ± 20%
WEIGHT&CASEApprox 0.5kg. 100mm case

Note: The three relays in this product are single pole changeover, the remainder of specification is under general specifications.

Technical Specifications

Product CodeM200-ST3
Normal running speed1800 rpm
Number of teeth on flywheel50
Magnetic pick up on output volts10 volt pk-pk

Ordering Information

Product CodeInputFreqAux

Connection Diagrams

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