ERL F-PRO 116, User Manual

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5-8 F-PRO 116 User Manual D05125R01.20
The function can also be used as high impedance Restricted Earth Fault protection (REF) for
transformer by using external stabilizing resistor and metrosil. The main purpose of the Restricted
Earth fault is to sense the internal earth fault in the transformer. For any external earth fault REF
relay will not operate. But in the case of internal fault, the differential fault current will initiate
operation of REF function. In the star side of the transformer, whenever the external fault occurs,
the current will flow through the affected phase of the line current transformer and
simultaneously the balancing current flows in the neutral of transformer. As a result, the
differential current in the relay circuit will be zero.
64/50 – Instantaneous SEF Protection Logic diagram
Figure 5.7: Logic Diagram of 64/50 Function
Table 5.8: 64/50SEF Instantaneous SEF Settings (No. of Stages – 2)
Setting Description Range
Function Activation Enable/disable
Pickup ISEF>>
0.005 to 3.000 A (1 A) / 0.025 to 15.000 A (5 A)
Pickup Delay 0.00 to 999.99 seconds
Inrush Blocking Enable/disable