Micom P634 - Saturation Discriminator; Measured Operating Data of Differential Protection

saturation conditions has a high proportion of harmonics having five times the
system frequency serves as the basis of stabilization.
The P634 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 a
measuring system, and if the differential current is smaller than 4·I
ref
, then
tripping is blocked selectively for that measuring system.
3.21.9 Saturation Discriminator
Up to a certain limit, stability in the event of external faults is ensured by means
of the bias. Due to the triple-slope tripping characteristic, the stabilization is
particularly pronounced for high currents. However, as an additional safeguard
for through-currents with transformer saturation, the P634 is provided with a
saturation discriminator.
After each zero crossing of the restraining current, the saturation discriminator
monitors the occurrence of the differential current over time. For internal faults,
the differential current appears after a zero crossing together with the restraining
current. In the case of passing currents with transformer saturation, however, a
differential current will not appear until transformer saturation begins.
Accordingly, a locking signal is generated on the basis of level monitoring of the
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.
62Z9006A
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 ]
DIFF:
Sat.discr. trigg.
[ 019 201 ]
Fig. 3-97: Saturation discriminator
3.21.10 Measured Operating Data of Differential Protection
The differential and restraining currents are displayed as measured operating
data provided that the set thresholds are exceeded.
3 Operation
P634
P634/EN M/R-42-A // P634‑311‑653 3-139