ABB REM 610 Technical Reference Manual

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ABB REM 610 Technical Reference Manual Manual pdf 133 page image

1336.1.2.3. Checking the set safe stall time for cold startsBy 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. The total start-up time should permit as manycold starts as stated by the motor manufacturer.In applications where, for instance, three cold vs two hot starts are allowed, the totalstart-up time of the motor may allow too many cold starts. In this case, the thermalprotection can be supplemented by using the cumulative start-up time counter forlimiting the number of cold starts. Alternatively, setting the weighting factor to 40per cent, instead of to 50 per cent, has at times proved useful.The operate time when no prior load with the selected safe stall time setting can alsobe calculated as follows:operate time = × ×⎛⎝⎜ ⎞⎠⎟⎛32 15 62. ln intinttIFLAIFLAxstartstart⎝⎝⎜ ⎞⎠⎟ −⎧⎨⎪⎪⎩⎪⎪⎫⎬⎪⎪⎭⎪⎪21 1025.(8)6.1.2.4. Checking the set safe stall time for a single startIf the safe stall time of the motor is shorter than the operate time when no prior load,a single motor start up should instead be protected by the start-up supervision.6.1.2.5. Restart disable level, 49 RESTDISThe restart disable level can be calculated as follows:49 RESTDIS start-up time of the motoroperate time whe= −100% nn no prior load margin× +⎛⎝⎜ ⎞⎠⎟⎛⎝⎜ ⎞⎠⎟100% (9)For instance, if the start-up time of the motor is 11 seconds and the calculatedoperate time of the thermal protection element when no prior load 25 seconds, onemotor start up will use 11 s/25 s = 45% of the thermal capacity of the motor.Therefore, the restart disable level must be set to below 100% - 45% = 55%, e.g. to50%.6.1.2.6. Prior alarm level, 49 ALARMTripping due to a beginning overload can be avoided by reducing the load of themotor at a prior alarm.The prior alarm level can be set to a level, which will allow the use of the motor’sfull thermal capacity without causing a trip due to long-time overload.Motor Protection RelayTechnical Reference Manual - ANSI VersionREM 610REM 6101MRS755537