GE 469 Instruction Manual

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Contents

5–66 469 MOTOR MANAGEMENT RELAY – INSTRUCTION MANUALCHAPTER 5: SETTINGS5.8 S7 Motor Starting5.8.1 Acceleration TimerPATH: SETTINGS ZV S7 MOTOR STARTING Z ACCELERATION TIMERThe thermal model protects the motor under both starting and overload conditions. Theacceleration timer trip may be used to complement this protection. For example, if themotor always starts in 2 seconds, but the safe stall time is 8 seconds, there is no pointletting the motor remain in a stall condition for 7 or 8 seconds when the thermal modelwould take it off line. Furthermore, the starting torque applied to the driven equipment forthat period of time could cause severe damage.If enabled, the Acceleration Timer functions as follows. A motor start is assumed to beoccurring when the 469 measures the transition of no motor current to some value ofmotor current. Typically current rises quickly to a value in excess of FLA (e.g. 6 x FLA). At thispoint, the acceleration timer will be initialized with the ACCELERATION TIMER FROM STARTvalue in seconds. If the current does not fall below the overload curve pickup level beforethe timer expires, an acceleration trip will occur. If the acceleration time of the motor isvariable, this feature should be set just beyond the longest acceleration time.Some motor soft-starters allow current to ramp up slowly while others limit current to lessthan FLA throughout the start. Since the 469 is a generic motor relay, it cannotdifferentiate between a motor with a slow ramp up time and one that has completed astart and gone into overload. Therefore, if the motor current does not rise to greater thanfull load within 1 second on start, the acceleration timer feature is ignored. In any case, themotor is still protected by the overload curve.5.8.2 Start InhibitPATH: SETTINGS ZV S7 MOTOR STARTING ZV START INHIBITThe Start Inhibit feature prevents motor starting if there is insufficient thermal capacity.The largest THERMAL CAPACITY USED value from the last five successful starts is multipliedby (1 + TC USED MARGIN) and stored as the LEARNED STARTING CAPACITY. This thermalcapacity margin ensures a successful motor start. If the number is greater than 100%,100% is stored as LEARNED STARTING CAPACITY. A successful motor start is one in whichACCELERATION [ACCELERATIONTIMERRange: Off, Latched, UnlatchedMESSAGE ASSIGN TRIPRELAYS:Range: Trip, Trip & Auxiliary2, Trip &Aux2 & Aux3, Trip & Auxiliary3MESSAGE ACCELERATIONTIMERRange: 1.0 to 250.0 s in steps of 0.1START [START INHIBITBLOCK: OffRange: On, OffMESSAGE TC USEDMARGIN: 25%Range: 0 to 25% in steps of 1