Percentage Restrained Differential Operation - ABB RELION 650 Series Applications Manual

Section 6
Differential protection
6.2.3.2

Percentage restrained differential operation

Line differential protection is phase-segregated where the operate current is the vector sum
of all measured currents taken separately for each phase. The restrain current, on the other
hand, is considered the greatest phase current in any line end and it is common for all three
phases. Observe that the protection may no more be phase-segregated when there is an in-
line power transformer included in the protected circuit. These are usually of the Dy or Yd type
and the three phases are related in a complicated way. For example, a single-phase earth fault
on the wye side of the power transformer is seen as a two-phase fault on the delta side of the
transformer.
Operation : Line differential protection function is switched on or off with this setting. If the
parameter
by the remote end IED.
The characteristic of the restrained differential function is shown in Figure 41. The restrained
characteristic is defined by the settings:
1. IdMin
EndSection1
2.
EndSection2
3.
SlopeSection2
4.
5. SlopeSection3
82
Operation is set to Off this IED is switched over to Slave mode and trip is initiated
1MRK 505 363-UEN A
M12541-104 v4
Application manual