S7 Motor Starting - GE 469 Instruction Manual

5.8

S7 Motor Starting

5.8.1 Acceleration Timer
 ACCELERATION
TIMER
5.8.2 Start Inhibit
 START
INHIBIT
5–68

PATH: SETTINGS S7 MOTOR STARTING
[] ACCELERATION TIMER
TRIP: Off
ASSIGN TRIP RELAYS:
MESSAGE
Trip
ACCELERATION TIMER
MESSAGE
FROM START: 10.0 s
The thermal model protects the motor under both starting and overload conditions. The
acceleration timer trip 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 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
value in seconds. If the current does not fall below the overload curve pickup level
START
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 soft-starters allow current to ramp up slowly while others limit current to less
than FLA throughout the start. Since the 469 is a generic motor relay, it cannot
differentiate between a motor with a slow ramp up time and one that has completed a
start and gone into overload. 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 protected by the overload curve.

PATH: SETTINGS S7 MOTOR STARTING
[]
MESSAGE
The Start Inhibit feature prevents motor starting if there is insufficient thermal capacity.
The largest
THERMAL CAPACITY USED
by (1 + ) and stored as the
TC USED MARGIN
capacity margin ensures a successful motor start. If the number is greater than 100%,
100% is stored as
LEARNED STARTING CAPACITY

ACCELERATION TIMER

START INHIBIT
START INHIBIT
BLOCK: Off
TC USED
MARGIN: 25%
value from the last five successful starts is multiplied
LEARNED STARTING CAPACITY
. A successful motor start is one in which
469 MOTOR MANAGEMENT RELAY – INSTRUCTION MANUAL
CHAPTER 5: SETTINGS
Range: Off, Latched, Unlatched
Range: Trip, Trip & Auxiliary2, Trip &
Aux2 & Aux3, Trip & Auxiliary3
Range: 1.0 to 250.0 s in steps of 0.1
ACCELERATION TIMER FROM
Range: On, Off
Range: 0 to 25% in steps of 1
. This thermal