Micom P631, Technical Manual, Page: 176 / 638

differential current as compared to the restraining current, and thus the desired
through-stabilization is achieved. Locking is restricted to the measuring system
where an external fault was detected.
There will be no blocking if the differential current exceeds the set threshold
DIFF: Idiff>> PSx.
Q6Z0111A
DIFF:
Id,1
303 303
DIFF:
Id,2
303 304
DIFF:
Id,3
303 307
DIFF:
Meas.system 1 trigg.
[ 041 124 ]
DIFF:
Meas.system 2 trigg.
[ 041 125 ]
DIFF:
Meas.system 3 trigg.
[ 041 126 ]
DIFF:
IR,3
303 308
DIFF:
IR,2
303 306
DIFF:
IR,1
303 305
DIFF:
Sat.discr. 1 trigg.
[ 041 115 ]
DIFF:
Sat.discr. 2 trigg.
[ 041 116 ]
DIFF:
Sat.discr. 3 trigg.
[ 041 117 ]
Fig. 3-87: Saturation discriminator
3.21.9 Overfluxing Stabilization
If the transformer is loaded with a voltage in excess of the nominal voltage,
saturation effects occur. Without stabilization, these could lead to differential
protection tripping. The fact that the current of the protected object under
saturation conditions has a high proportion of harmonics having five times the
system frequency serves as the basis of stabilization.
The P631 filters the differential current. The fundamental wave
I ( f
0
) and fifth
harmonic components I
(
5 ⋅ f
0
)
of the differential current are determined. If the
ratio
I
(
5 ⋅ f
0
)
I
(
f
0
)
exceeds the set value DIFF: Ov. I(5f0)/I(f0) PSx in at least one
measuring system, and if the differential current is smaller than 4·I
ref
, then
tripping is blocked selectively for one measuring system.
There will be no blocking if the differential current exceeds the set threshold
DIFF: Idiff>> PSx.
P631 3 Operation
3-120 P631/EN M/R-11-C // P631-310-650