ABB REM 610 Technical Reference Manual

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ABB REM 610 Technical Reference Manual Manual pdf 141 page image

1416.4. Protecting a contactor controlled motorData of the squirrel cage motor stated by the manufacturer:Rated power, Pnm 900 kWRated voltage, U nm 380 VRated current, Inm 1650 AStart-up current of the motor 6.0 x I nmTwo 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:2000165055 1 212 1 21AAAA× = ≈. . (16)For a direct-on-line started motor, p = 50%.At an ambient temperature of 50°C the internal FLA is 0.9 x FLA of the motor.Thus, the start-up current of the motor is 6.0/0.9 = 6.67 x the internal FLA.The safe stall time setting, t 6x , is calculated or selected from the trip curves at priorload 1 x FLA. A safe stall time setting of 25 seconds is selected, permitting a start-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 elementwill trip 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, 48/14 PICKUP, is set to equal the start-up current of the motorand the start-up time, 48/14 TDLY, to approximately ten per cent above the start-uptime of the motor in order to leave a safety margin for operation. Thus 48/14 TDLYis 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.Motor Protection RelayTechnical Reference Manual - ANSI VersionREM 610REM 6101MRS755537