Function Block - ABB RED615 Technical Manual

Section 4
Protection functions
4.3.4.2
4.3.4.3
4.3.4.4
432

Function block

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Figure 231: Function block
Functionality
The high-impedance-based restricted earth-fault protection HREFPDIF is used for
the restricted earth-fault protection of generators and power transformers.
HREFPDIF starts when the IDo, the differential neutral current, exceeds the set
limit. HREFPDIF operates with the DT characteristic.
HREFPDIF 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 the high-impedance-based restricted earth-fault protection
function can be described using a module diagram. All the modules in the diagram
are explained in the next sections.
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Figure 232: 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
1YHT530004D05 D
615 series
Technical Manual