ABB REM 610 Technical Reference Manual

Also see for REM 610: Operator's manual Product guide Installation manual Technical reference manual Product guide

Contents

ABB REM 610 Technical Reference Manual Manual pdf 126 page image

1261MRS 752263-MUMMotor Protection RelayTechnical Reference ManualREM 6105.2.3. Protecting a contactor controlled motorData of the squirrel cage motor stated by the manufacturer:Rated power, Pnm 900 kWRated voltage, Unm 380 VRated current, Inm 1650 AStart-up current of the motor 6.0 x InmTwo cold starts allowedStart-up time of the motor 9 sSafe stall time 21 sAmbient temperature 50∞CCT current ratio 2000/5 A (relay input = 5 A)Setting calculationsThe protected unit scaling factor is calculated as follows:2000A1650A---------------- 5A5A-------× 1.212 1.21≈=For a direct-on-line started motor, p = 50%.At an ambient temperature of 50∞C the internal FLC is 0.9 x FLC of the motor. Thus,the start-up current of the motor is 6.0/0.9 = 6.67 x the internal FLC.The safe stall time setting, t6x, is calculated or selected from the trip curves at priorload 1 x FLC. A safe stall time setting of 25 seconds is selected, permitting astart-up time slightly longer than the one stated by the motor manufacturer.By selecting the correct trip curve from the trip curves at no prior load according tothe previously selected or calculated safe stall time setting, the total start-up time ofthe motor can be read from the curve. In this case, the thermal protection stage willtrip in approximately 20 seconds, which will allow two cold starts.As the operate time when no prior load is shorter than the safe stall time of 21seconds, no start-up supervision will be required to protect the motor against singlestart ups. Still, start-up supervision is recommended in order to shorten the operatetime in case of a locked rotor condition.The start-up current, Is>, is set to equal the start-up current of the motor and thestart-up time, ts>, to approximately ten per cent above the start-up time of the motorin order to leave a safety margin for operation. Thus ts> is set to 9 s x 1.1 ≈ 10 s.As the safe stall time is longer than the start-up time of the motor, no speed switchwill be required.As one motor start-up uses 9 s/20 s ≈ 45% of the thermal capacity of the motor, therestart inhibit level, θi>, should be set to below 55 per cent, e.g. to 50 per cent.The prior alarm level, θa>, is set to 80...90 per cent of the trip level.The time constant multiplier, Kc, is set to 4...6.