Siemens siprotec 7SD5 User Manual page 64

2 Functions
current balance of the distance protection (in Figure 2-4 for the device at location II),
above which compensation should take place. In general, a presetting of 85 % is suf-
ficient. A more sensitive (larger) setting has no advantage. Only in the case of a severe
system asymmetry, or a very small coupling factor (X
may a smaller setting be useful. A more detailed explanation of parallel line compen-
sation can be found in Section 2.5.1 under distance protection.
Figure 2-4
The current ratio may also be calculated from the desired distance of the parallel line
compensation and vice versa. The following applies (refer to Figure 2-4):
Current 7SD5 contains a saturation detector which largely detects the measuring errors result-
Transformer ing from the saturation of the current transformers and initiates a switchover to dis-
Saturation tance measurement. The threshold above which it picks up can be set in address
1140 I-CTsat. Thres.. This is the current level above which saturation may be
present. The setting ∞ disables the saturation detector. This parameter can only be
altered with DIGSI
pected, the following equation may be used as a thumb rule for this setting:
Circuit Breaker Information regarding the circuit breaker position is required by various protection and
Status supplementary functions to ensure their optimal functionality. The device has a circuit
breaker status recognition which processes the status of the circuit breaker auxiliary
contacts and contains also a detection based on the measured currents and voltages
for opening and closing (see also Section 2.23.1).
In address 1130 the residual current PoleOpenCurrent is set, which will definitely
not be exceeded when the circuit breaker pole is open. If parasitic currents (e.g.
through induction) can be excluded when the circuit breaker is open, this setting may
64
Distance with parallel line compensation at II
®
under Additional Settings. If current transformer saturation is ex-
P = Nominal CT burden [VA]
N
P = Nominal CT internal burden [VA]
i
P' = Actual connected burden (protection device + connection cable)
/X below approximately 0.4),
M L
7SD5 Manual
C53000-G1176-C169-1