S7 Motor Starting; Acceleration Timer - GE MOTOR MANAGEMENT RELAY 469 Instruction Manual

4 SETPOINT PROGRAMMING

4.8 S7 MOTOR STARTING

S ACCELERATION TIMER
S [ENTER] for more
The thermal model protects the motor under both starting and overload conditions. The acceleration timer trip
feature may be used to complement this protection. For example, if the motor always starts in 2 seconds, but
the safe stall time is 8 seconds, there is no point letting the motor remain in a stall condition for 7 or 8 seconds
when the thermal model would take it off line. Furthermore, the starting torque applied to the driven equipment
for that period of time could cause severe damage.
If enabled, the ACCELERATION TIMER TRIP element functions as follows. A motor start is assumed to be occurring
when the 469 measures the transition of no motor current to some value of motor current. Typically current
rises quickly to a value in excess of FLA (e.g. 6 x FLA). At this point, the Acceleration Timer will be initialized
with the ACCELERATION TIMER FROM START value in seconds. If the current does not fall below the overload
curve pickup level before the timer expires, an acceleration trip will occur. If the acceleration time of the motor
is variable, this feature should be set just beyond the longest acceleration time.
Some motor softstarters may allow current to ramp up slowly while others may limit current to less
than FLA throughout the start. Since the 469 is a generic relay for protection of all motors, it cannot
differentiate between a motor that has a slow ramp up time and one that has completed a start and
NOTE
gone into an overload condition. Therefore, if the motor current does not rise to greater than full load
within 1 second on start, the acceleration timer feature is ignored. In any case, the motor is still pro-
tected by the overload curve.
GE Power Management
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ACCELERATION TIMER

ENTER
TRIP: Off
ESCAPE
ASSIGN TRIP RELAYS:
ESCAPE
Trip
MESSAGE
ACCELERATION TIMER
ESCAPE
FROM START: 10.0 s
MESSAGE
469 Motor Management Relay
4.8 S7 MOTOR STARTING
4.8.1 ACCELERATION TIMER
Range: Off, Latched, Unlatched
Range: Trip, Trip & Auxiliary2, Trip & Aux2 & Aux3,
Trip & Auxiliary3
Range:1.0 to 250.0 sec., step 0.1
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