4.2.1.3 Functionality
The earth-fault function (F)EFxPTOC is used as non-directional earth-fault
protection for feeders.
The function starts and operates when the residual current exceeds the set
limit. The operate time characteristic for low stage (F)EFLPTOC and high stage
EFHPTOC can be selected to be either definite time (DT) or inverse definite
minimum time (IDMT). The instantaneous stage EFIPTOC always operates with the
DT characteristic.
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.
4.2.1.4 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)EFxPTOC can be described by using a module diagram. All the
modules in the diagram are explained in the next sections.
Figure 139: Functional module diagram
Level detector
The operating quantity can be selected with the setting
Io signal Sel
. The selectable
options are "Measured Io" and "Calculated Io". The operating quantity is compared
to the set
Start value
. If the measured value exceeds the set
Start value
, the level
detector sends an enable-signal to the timer module. If the ENA_MULT input is
active, the
Start value
setting is multiplied by the
Start value Mult
setting.
The protection relay does not accept the
Start value
or
Start value Mult
setting if the product of these settings exceeds the
Start value
setting
range.
The start value multiplication is normally done when the inrush detection function
(INRPHAR) is connected to the ENA_MULT input.
Timer
Once activated, the timer activates the START output. Depending on the value of the
Operating curve type
setting, the time characteristics are according to DT or IDMT.
When the operation timer has reached the value of
Operate delay time
in the DT
Protection functions
1MRS758755 C
278 REC615 & RER615
Technical Manual
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