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PROTECTION
Acceleration Time
4–160
Many motors have quite a time margin between acceleration-time and the stall limit. It is
advantageous to detect stalling during a start as early as possible to minimize re-starting
delays once the cause of the stall is remedied, e.g. neglecting to release a fan brake.
The Acceleration Time element compares actual starting time with a pre-determined time
setting (defined under System>Motor as Max. Acceleration Time) and operates when it is
exceeded. This element has the functionality to adapt the tripping time for starts with
lower starting current, and it stores acceleration time and current of the last five starts.
The element uses currents configured under Setpoints > System > Current Sensing and
motor status asserted by the Thermal Model protection element. Both the signal source
and thermal protection must be configured properly in order for the Acceleration Time
protection to operate.
The following figure shows examples of constant and variable acceleration currents and
explains measurement of the acceleration time and current. Part "a" represents a constant
current start and part "b" represents a variable current start.
The element stores the basic statistics for the last five successful starts. The following
values are retained, available for display and accessible via communications:
•
Date and time of starting.
•
Acceleration time (seconds).
•
Effective acceleration current (multiplies of FLA).
•
Peak acceleration current (multiplies of FLA).
Recorded effective acceleration current and time could be used for fine-tuning of the relay
settings.
Figure 4-52: Sample Acceleration Currents: (a) Constant Current Start and (b) Variable
Current Start
Path:
Setpoints > Protection > Group 1(6) > Motor > Acceleration Time
FUNCTION
Range: Disabled, Trip, Alarm, Latched Alarm, Configurable
Default: Disabled
The setting enables the Acceleration Time functionality.
CURRENT
Range: 1.00 to 10.00 x FLA in steps of 0.01
Default: 6.00 x FLA
The setting is only used in the Adaptive mode. The setting defines a constant current
that when applied to the motor accelerates the motor within the normal acceleration
time. The setting is used to adapt the tripping action when the current is changing
significantly during the start, such as due to voltage dips.
869 MOTOR PROTECTION SYSTEM – INSTRUCTION MANUAL
CHAPTER 4: SETPOINTS
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