ABB RELION 620 Series Technical Manual page 565

1MRS757644 F
4.3.4.3
4.3.4.4
620 series
Technical Manual
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.
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.
GUID-75842EE4-C4B8-452A-8FA9-FDE60ED22DD4 V3 EN
Figure 286: 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.
Section 4
Protection functions
559