Differential Protection; Low Impedance Restricted Earth Fault Protection Refpdif; Identification; Application - ABB RELION 650 Series Applications Manual

1MRK 505 363-UEN A
Section 6
6.1 Low impedance restricted earth fault protection
REFPDIF
6.1.1

Identification

Function description
Restricted earth-fault protection,
low impedance
6.1.2

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) 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.
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:
• earth faults in the transformer winding when the network is earthed through an
impedance
• earth faults in the transformer winding in solidly earthed network when the point of the
fault is close to the winding star point.
The restricted earth-fault protection is not affected, as a differential protection, with the
following power transformer related phenomena:
• magnetizing inrush currents
• overexcitation magnetizing currents
• load tap changer
• external and internal phase faults which do not involve earth
• symmetrical overload conditions
Application manual

Differential protection

IEC 61850
identification
REFPDIF
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 v5
IP14941-1 v1
M13940-3 v11
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