ABB RELION REX640 Technical Manual page 860

Protection functions
Figure 484: Functional module diagram
Level detector
The fundamental frequency component of the measured three phase voltages are
compared phase-wise to the set
the set value of the
selection logic module. The
unnecessary oscillations if the input signal slightly varies above or below the
value setting. After leaving the hysteresis area, the start condition has to be fulfilled
again and it is not sufficient for the signal to only return back to the hysteresis area.
The
phase voltages for protection.
For the voltage IDMT mode of operation, the used IDMT curve equations contain
discontinuity characteristics. The
unwanted operation.
The level detector contains a low-level blocking functionality for cases where one
of the measured voltages is below the desired level. This feature is useful when
unnecessary starts and operates are wanted to avoid during, for example, an
autoreclose sequence. The low-level blocking is activated by default (
value is set to "True") and the blocking level can be set with the Voltage block value
setting.
Phase selection logic
If the fault criteria are fulfilled in the level detector, the phase selection logic detects
the phase or phases in which the fault level is detected. If the number of faulty
phases match with the set
the Timer.
Timer
Once activated, the Timer activates the START output. Depending on the value of
the set
or IDMT.
860
Start value setting, the level detector enables the phase
Voltage selection setting is used for selecting the phase-to-earth or phase-to-
For more detailed description on IDMT curves and usage of
Sat Relative setting, see
protection
in this manual.
Operating curve type , the time characteristics are selected according to DT
For a detailed description of the voltage IDMT curves, see
IDMT curves for undervoltage protection
Start value . If the measured value is lower than
Relative hysteresis setting can be used for preventing
Curve Sat relative setting is used for preventing
Chapter 11.3.2 IDMT curves for undervoltage
Num of start phases , the phase selection logic activates
1MRS759142 F
Curve
Enable block
Chapter 11.3.2
in this manual.
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REX640