ABB REM 610 Technical Reference Manual

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ABB REM 610 Technical Reference Manual Manual pdf 124 page image

1241MRS 752263-MUMMotor Protection RelayTechnical Reference ManualREM 6105.2. Application examples5.2.1. Protecting a circuit-breaker controlled motorData of the squirrel cage motor stated by the manufacturer:Rated power, Pnm 4500 kWRated voltage, Unm 3300 VRated current, Inm 930 AStart-up current of the motor 6.2 x FLCStart-up time of the motor 11 sSafe stall time 19 sAmbient temperature 40∞CCT current ratio 1000/5 A (relay input = 5 A)Setting calculationsThe protected unit scaling factor is calculated as follows:1000A930A---------------- 5A5A-------× 1.075 1.08≈=For a direct-on-line started motor, p = 50%.At an ambient temperature of 40∞C the internal FLC equals the FLC of the motor.Thus the start-up current of the motor is 6.2 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 30 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 28 seconds, which will allow two cold starts.However, as the operate time when no prior load is longer than the safe stall time ofnineteen seconds, single motor start ups should instead be protected by the start-upsupervision. The start-up current, Is>, is set to equal the start-up current of the motorand the start-up time, ts>, to approximately ten per cent above the start-up time ofthe motor in order to leave a safety margin for operation. Thus ts> is set to 1 s x 1.1≈ 12 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 11 s/28 s ≈ 39% of the thermal capacity of the motor, therestart inhibit level, θi>, should be set to below 61 per cent, e.g. to 55 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.