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IEC05000749 V1 EN-US
Figure 39: Current voltage characteristics for the non-linear resistors, in the range 10-200 V, the
average range of current is: 0.01–10 mA
6.2
Low impedance restricted earth fault protection
REFPDIF
IP14640-1 v6
6.2.1
Identification
M14843-1 v5
Function description
IEC 61850
identification
IEC 60617
identification
ANSI/IEEE C37.2
device number
Restricted earth-fault protection,
low impedance
REFPDIF
IdN/I
SYMBOL-AA V1 EN-US
87N
6.2.2
Application
IP14941-1 v1
M13940-3 v11
A breakdown of the insulation between a transformer winding and the core or the tank may
result in a large fault current which causes severe damage to the windings and the transformer
core. A high gas pressure may develop, damaging the transformer tank.
Fast and sensitive detection of earth faults in a power transformer winding can be obtained in
solidly earthed or low impedance earthed networks by the restricted earth-fault protection.
The only requirement is that the power transformer winding is connected to earth in the star
point (in case of star-connected windings) or through a separate earthing transformer (in case
of delta-connected windings).
The low impedance restricted earth-fault protection REFPDIF is a winding protection function.
It protects the power transformer winding against faults involving earth. Observe that single
phase-to-earth faults are the most common fault types in transformers. A sensitive earth-fault
protection is therefore desirable.
Section 6
1MRK 505 343-UEN B
Differential protection
108
Application manual
Summary of Contents for Relion 670 series
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