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4.8 S7 MOTOR STARTING
S START INHIBIT
S [ENTER] for more
a) FUNCTION
The Start Inhibit feature helps to prevent tripping of the motor during start if there is insufficient thermal capac-
ity. The largest value of THERMAL CAPACITY USED from the last five successful starts is multiplied by (1 + TC
USED MARGIN) and stored as A3 LEARNED DATA\MOTOR STARTING\LEARNED STARTING CAPACITY. This thermal
capacity margin ensures that a motor start will be successful. If the number is greater than 100%, 100% is
stored as LEARNED STARTING CAPACITY. A successful motor start is one in which phase current rises from 0 to
greater than overload pickup and then, after acceleration, falls below the overload curve pickup level. If the
Start Inhibit feature is enabled, each time the motor is stopped, the amount of thermal capacity available
(100% – THERMAL CAPACITY USED) is compared to the LEARNED STARTING CAPACITY. If the thermal capacity avail-
able does not exceed the LEARNED STARTING CAPACITY, or is not equal to 100%, the Start Inhibit Block will
4
become active until there is sufficient thermal capacity. When a block occurs, the lockout time will be equal to
the time required for the motor to cool to an acceptable temperature for a start. This time will be a function of
the S5 THERMAL MODEL\THERMAL MODEL\COOL TIME CONSTANT STOPPED setpoint.
If this feature is turned "Off", the THERMAL CAPACITY USED must reduce to 15% before an overload lockout
resets. This feature should be turned off if the load varies for different starts.
b) EXAMPLE
If the THERMAL CAPACITY USED for the last 5 starts is 24, 23, 27, 25, and 21% respectively, the LEARNED START-
ING CAPACITY is 27% × 1.25 = 33.75% used. If the motor stops with 90% thermal capacity used, a start block
will be issued.
When the motor has cooled and the level of thermal capacity used has fallen to 66%, a start will be permitted.
If the COOL TIME CONSTANT STOPPED setpoint is programmed for 30 minutes, the lockout time will be equal to:
4-54
ð
START INHIBIT
ENTER
BLOCK: Off
ESCAPE
TC USED
ESCAPE
MARGIN: 25%
MESSAGE
TC
TC
=
used
66%
=
90%
t
=
ln
=
9.3 minutes
469 Motor Management Relay
4 SETPOINT PROGRAMMING
Range: On, Off
Range: 0 to 25%, step: 1
t – τ ⁄
×
e
used_start
⁄
t – 30
×
e
66
×
----- -
–
30
90
4.8.2 START INHIBIT
GE Power Management
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