Level detector
The fundamental frequency component of the measured three phase voltages are
compared phase-wise to the set
Start value. If the measured value is lower than
the set value of the
Start value setting, the level detector enables the phase
selection logic module. The
Relative hysteresis setting can be used for preventing
unnecessary oscillations if the input signal slightly varies above or below the
Start
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
Voltage selection setting is used for selecting the phase-to-earth or phase-to-
phase voltages for protection.
For the voltage IDMT mode of operation, the used IDMT curve equations contain
discontinuity characteristics. The
Curve Sat relative setting is used for preventing
unwanted operation.
For more detailed description on IDMT curves and usage of
Curve
Sat Relative setting, see
Chapter 11.3.2 IDMT curves for undervoltage
in this manual.
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 (
Enable block
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
Num of start phases, the phase selection logic activates
the Timer.
Timer
Once activated, the Timer activates the
START
output. Depending on the value of
the set
Operating curve type, the time characteristics are selected according to DT
or IDMT.
For a detailed description of the voltage IDMT curves, see
IDMT curves for undervoltage protection
When the operation timer has reached the value set by
Operate delay time in the DT
mode or the maximum value defined by the IDMT, the
OPERATE
output is activated.
When the user-programmable IDMT curve is selected, the operate time
characteristics are defined by the parameters
Curve parameter A, Curve parameter
B, Curve parameter C, Curve parameter D and Curve parameter E.
If a drop-off situation occurs, that is, a fault suddenly disappears before the operate
delay is exceeded, the reset state is activated. The behavior in the drop-off situation
depends on the selected operate time characteristics. If the DT characteristics are
selected, the reset timer runs until the set
Reset delay time value is exceeded. If
the drop-off situation exceeds the set
Reset delay time, the Timer is reset and the
START
output is deactivated.
1MRS758755 C
Protection functions
REC615 & RER615
Technical Manual
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