GE 339

6–94 339 MOTOR PROTECTION SYSTEM – INSTRUCTION MANUAL
S3 PROTECTION CHAPTER 6: SETPOINTS
Acceleration protection (48)
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 the 7 or 8 seconds it would take for the
thermal model to operate. Furthermore, the starting torque applied to the driven
equipment for that period of time could cause severe damage.
If enabled, the Acceleration Protection will trip if the motor stays in the starting state and
does not reach the running state by the set acceleration time. Detection of starting and
running is as described in the motor status section of this manual. For two speed motor
applications, separate timer settings are provided for accelerating from stopped to low
speed, for accelerating from stopped to high speed, and for accelerating from low speed to
high speed.
If the acceleration time of the motor is variable, this feature should be set just beyond the
longest acceleration time.
PATH:
SETPOINTS > S3 PROTECTION > ACCELERATION
ACCEL TIME FUNC
Range: Disabled, Enabled
Default: Disabled
For details see Common setpoints
.
ACCELERATION TIMER
Range: 1.0 to 250.0 s in steps of 0.1 s
Default: 10 s
In single-speed motor applications, sets the maximum acceleration time before tripping.
In two speed motor applications, sets the maximum acceleration time before tripping
when low speed starting from a stopped condition.
OUTPUT RELAY X
For details see Common setpoints
.
BLOCK 1 to 3
For details see Common setpoints
.
TWO-SPEED MOTOR APPLICATION
PATH:
SETPOINTS > S3 PROTECTION > TWO SPEED MOTOR > HIGH SPEED ACCEL T
ACCEL T ON STOPPED
Range: 1.0 to 250.0 s in steps of 0.1 s
Default: 10.0 s
When a two-speed motor starts directly at high speed, this setting specifies the
maximum acceleration time before tripping.
ACCEL T ON LOW SPD
Range: 1.0 to 250.0 s in steps of 0.1 s
Default: 10.0 s
When a two-speed motor is switched from a low-to-high speed, this setting specifies the
maximum acceleration time before tripping.
Figure 6-41: Acceleration logic diagram