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6 - 55
Siemens AG ⋅ May 1998
2. Bay unit 1 is injected with a constant current I
1
via
the test set. After initiation by the feeder protecĆ
tion (trip signal) in bay 2, the measured value of
bay 2 is continuously unbalanced. The current in
bay 2 is slowly increased until the protection trips.
3. The differential current is then I I
1
+ I
2
I and the
stabilizing current is I I
1
I+II
2
I.
The stabilizing factor is then differential current/
stabilizing current
k=II
1
- I
2
I/II
1
I+II
2
I
6.5.5.2 Checking the time delay with mode of
operation "forced bus zone unbalance"
The test set-up for the measurement of the time
delay with mode of operation "unbalance" is illusĆ
trated in Fig 6.6. This test is performed with a setting
of 250 ms for T-CBF (DA 6204/ZE).
FeeĆ
der 1
Master
unit
Bay
unit 2
FO
FO
BF initiation
Bay
unit 1
FeeĆ
der 2
D The two feeders are normalized to the same value
(same CT transformation ratio).
D The polarity of the CTs is connected such that the
current (approx. 2 I
N
) before unbalance correĆ
sponds to an external short-circuit (through curĆ
rent) (Diff current approx. zero).
Time measurement is started when the feeder
protection trip signal is simulated for feeder 2. The
timer is stopped by the trip signal of the busbar
protection.
D The measured time corresponds to the delay time
for unbalance plus protection trip time.
6.5.6 General recommendations for setting
the protection
6.5.6.1 Busbar protection
a) Differential current supervision (DA 6305/ZE;
DA 6306/ZE)
Range: 0.05 to 0.80 I
no
Recommended setting for the bus-section specifĆ
ic protection (DA 6305/ZE) = 0.10 I/I
no
Recommended setting for the check zone
(DA 6306/ZE) = 0.10 I/I
no
Time for protection blocking/alarm
(DA 6304/ZE)
Range: 1.0 to 10 s
Recommended setting (DA 6304) = 2.0 s
b) Differential current pick-up for tripping
(DA 6102/ZE; DA 6104/ZE)
Range: 0.2 to 4.0 I
no
Setting depends on short-circuit current.
Setting value v 0.6 I
sc min
3-phase
0.3 I
sc min
2-phase
1.0 I
sc min
1-phase
Firstly, the smallest fault current which can be exĆ
pected in the event of a short-circuit must be deĆ
termined.
From that value and the above mentioned data,
the maximum permissible setting value is calcuĆ
lated.
c) Stabilizing factor k (DA 6101/ZE;
DA 6103/ZE)
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