ABB REG670 - Low Impedance Restricted Earth Fault Protection REFPDIF

security if the primary system DC time constant is very long, thus giving risk of
current transformer saturation, even for small currents. It is recommended to set
OperDCBiasing = On if the current transformers on the two sides of the generator are
of different make with different magnetizing characteristics. It is also recommended
to set the parameter OperDCBiasing = On for all shunt reactor applications.
7.4 Low impedance restricted earth fault protection
REFPDIF
7.4.1 Identification
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
87N
7.4.2 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. 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:
• 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.
1MRK 502 071-UEN - Section 7
Differential protection
Generator protection REG670 2.2 IEC and Injection equipment REX060, REX061, REX062 175
Application manual