Siemens SIPROTEC 7SD610, Руководство пользователя

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Functions
2.15 Monitoring Functions
SIPROTEC, 7SD610, Manual
C53000-G1176-C145-6, Release date 02.2011
200
Sampling Frequency
The sampling frequency and the synchronism between the ADCs (analog-to-digital converters) is continuously
monitored. If deviations that may occur cannot be corrected by another synchronisation, the device sets itself
out of operation and the red LED „ERROR“ lights up; The device-ready relay relay drops off and signals the
malfunction by its „life contact“.
Measured Value Acquisition Currents
Up to four input currents are measured by the device. If the three phase currents and the earth current from the
current transformer starpoint or a separated earth current transformer of the line to be protected are connected
to the device, their digitized sum must be zero. Faults in the current circuit are recognised if
I
F
= |
I
L1
+
I
L2
+
I
L3
+ k
I
·
I
E
| >
Σ
I THRESHOLD +
Σ
I FACTOR ·
Σ
|
I
|
Factor k
I
(address 221 I4/Iph CT ) takes into account a possible different ratio of a separate
I
E
transformer
(e.g. cable core balance current transformer).
Σ
I THRESHOLD and
Σ
I FACTOR . are setting parameters.
The component
Σ
I FACTOR
Σ
|
I
| takes into account permissible current proportional ratio errors of the input
transformers which are particularly prevalent during large fault currents (Figure 2-83).
Σ
|
I
| is the sum of all
currents:
Σ
|
I
| = |
I
L1
| + |
I
L2
| + |
I
L3
| + |k
I
·
I
E
|
As soon as a summation current fault is detected after or before a system disturbance, the differential protection
is blocked. This malfunction is signalled as
„Failure
Σ
i“ (No. 289). In order to avoid a blocking due to trans-
formation errors (saturation) in case of high fault currents, this monitoring function is not effective during a
system fault.
Note
Current sum monitoring can operate properly only when the ground current of the protected line is fed to the
fourth current measuring input (
I
4
) of the relay. The I
4
transformer must have been configured with parameter
I4 transformer
(address
220
) as .
Figure 2-83 Current sum monitoring