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Function Dependencies
Hysteresis or Dead Band
When comparing a measured value against a pick-up value, some
amount of hysteresis is needed to avoid oscillation near equilibrium
situation. With zero hysteresis any noise in the measured signal or
any noise in the measurement itself would cause unwanted
oscillation between fault-on and fault-off situations.
PICK UP LEVEL
> PICK UP
Figure 3.3 – Behavior of a greater than comparator
PICK UP LEVEL
< PICK UP
Figure 3.4 – Behavior of a less than comparator
Application Modes
The application modes available are the feeder protection mode
and the motor protection mode. In the feeder protection mode all
current dependent protection functions are relative to nominal
current I
derived by CT ratios. The motor protection functions
n
are unavailable in the feeder protection mode. In the motor
protection mode all current dependent protection functions are
relative to motor's nominal current I
mode enables motor protection functions. All functions which
are available in the feeder protection mode are also available in
the motor protection mode. Default value of the application
mode is the feeder protection mode.
The application mode can be changed with SetPointPS software
or from CONF menu of the device. Changing the application
mode requires the configurator password.
Protection Functions
Hysteresis_GT
Example: In overcurrent
and overvoltage stages, the
hysteresis (dead band) acts
according this figure.
Hysteresis_LT
Example: In undercurrent
and under frequency stages,
the hysteresis (dead band)
acts according this figure.
The motor protection
mot.
857-UM001A-EN-P – July 2009
3-5
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