Hitachi Relion 670 Series Applications Manual page 77

1MRK506375-UEN Rev. N
Section 6
6.1 Low impedance restricted earth fault protection
REFPDIF
6.1.1 Function revision history
Document
revision
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6.1.2 Identification
Function description
Restricted earth fault protection, low
impedance
6.1.3 Application
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).
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. Therefore, a sensitive earth fault
protection is desirable.
A restricted earth fault protection is the fastest and the most sensitive protection, a power transformer
winding can have and will detect faults such as:
Railway application RER670
Application manual
Differential protection
Product History
revision
2.2.1 -
2.2.1 -
2.2.2 -
2.2.3 -
2.2.3 -
2.2.4 -
2.2.4 The upper limit of ROA setting range is changed from 90 degrees to 119 degrees.
2.2.5 -
2.2.6 -
2.2.6 -
IEC 61850
identification
REFPDIF
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GUID-BFAA47D8-C2B6-4EC2-9129-B031333BAD19 v3
IEC 60617 ANSI/IEEE C37.2
identification device number
87N
IdN/I
SYMBOL-AA V1 EN-US
Section 6
Differential protection
IP14640-1 v6
M14843-1 v6
IP14941-1 v1
M13940-3 v12
71