4.3.4.3
Functionality
The high-impedance based restricted earth-fault protection function HREFPDIF
is used for the restricted earth-fault protection of generators and power
transformers.
The function starts when the differential neutral current exceeds the set limit.
HREFPDIF operates with the DT characteristic.
The function contains a blocking functionality. It is possible to block function
outputs, timers or the function itself, if desired.
4.3.4.4
Operation principle
The function can be enabled and disabled with the
Operation setting. The
corresponding parameter values are "On" and "Off".
The operation of HREFPDIF can be described using a module diagram. All the
modules in the diagram are explained in the next sections.
Figure 296: Functional module diagram
Level detector
The level detector compares the differential neutral current IDo to the set value of
the
Operate value setting. If the differential neutral current exceeds the Operate
value setting, the level detector sends an enable signal to the timer module to start
the definite timer.
Timer
Once activated, the timer activates the
START
output. The time characteristic is
according to DT. When the operation timer has reached the value set by
Minimum
operate time, the
OPERATE
output is activated. If the fault disappears before
the module operates, the reset timer is activated. If the reset timer reaches the
value set by
Reset delay time, the operation timer resets and the
START
output is
deactivated.
The timer calculates the start duration value START_DUR, which indicates the ratio
of the start situation and the set operation time. The value is available in the
monitored data view.
Blocking logic
There are three operation modes in the blocking function. The operation modes
are controlled by the
BLOCK
input and the global setting Configuration/System/
Blocking mode which selects the blocking mode. The
BLOCK
input can be controlled
by a binary input, a horizontal communication input or an internal signal of the IED
Protection functions
1MRS757644 H
570
620 series
Technical Manual
