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In the DT mode, the function operates after a predefined operate time and resets
when the fault current disappears. The IDMT mode provides current-dependent
timer characteristics.
The function contains a blocking functionality. It is possible to block function
outputs, timers or the function itself, if desired.
4.2.2.4
Operation principle
The function can be enabled and disabled with the
Operation setting. The
corresponding parameter values are "On" and "Off".
The operation of (F)DEFxPDEF can be described using a module diagram. All the
modules in the diagram are explained in the next sections.
Figure 141: Functional module diagram
Level detector
The magnitude of the operating quantity is compared to the set
Start value and
the magnitude of the polarizing quantity is compared to the set
Voltage start value.
If both the limits are exceeded, the level detector sends an enabling signal to the
timer module. When the
Enable voltage limit setting is set to "False", Voltage start
value has no effect and the level detection is purely based on the operating quantity.
If the
ENA_MULT
input is active, the
Start value setting is multiplied by the Start
value Mult setting.
The operating quantity (residual current) can be selected with the setting
Io signal
Sel. The options are "Measured Io" and "Calculated Io". If "Measured Io" is selected,
the current ratio for Io-channel is given in Configuration > Analog inputs > Current
(Io,CT). If "Calculated Io" is selected, the current ratio is obtained from the phase-
current channels given in Configuration > Analog inputs > Current (3I,CT).
The operating quantity (residual voltage) can be selected with the setting
Uo
signal Sel. The options are "Measured Uo" and "Calculated Uo". If "Measured Uo"
is selected, the voltage ratio for Uo-channel is given in Configuration > Analog
inputs > Voltage (Uo,VT). If "Calculated Uo" is selected, the voltage ratio is obtained
from the phase-voltage channels given in Configuration > Analog inputs > Voltage
(3U,VT).
Example 1: Io is measured with cable core CT (100/1 A) and Uo is measured from
open-delta connected VTs (20/sqrt(3) kV : 100/sqrt(3) V : 100/3 V). In this case,
"Measured Io" and "Measured Uo" are selected. The nominal values for residual
current and residual voltage are obtained from CT and VT ratios entered in Residual
1MRS758755 C
Protection functions
REC615 & RER615
Technical Manual
295
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