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Sampling address synchronization
The same method as described in section 2.2.7.1 is employed in Mode 0 and Mode 2A where the
sampling synchronization must be established. It is not employed in Mode 1 and 2B because the
sampling address synchronization has already been established in the previous mode.
2.2.7.3
Differential Current Calculation
Synchronized sampling allows correct calculation of differential current even in the presence of
a transmission time delay. This processing is indicated in Figure 2.2.7.6. As indicated in the
figure, sampling synchronization is established between terminals A and B, and both the
sampling timing and sampling address match. The instantaneous current data and sampling
address are both sent to the other terminal. The GRL100 refers to the sampling address affixed to
the received data and uses local data with the same sampling address to calculate the differential
current. This allows both terminals to use data sampled at the same instant to perform the
differential current calculation, no matter how large the transmission time delay is.
Terminal A
Terminal B
Figure 2.2.7.6 Calculation of Differential Current with Transmission Delay Time
Protection in anomalous power system operation
Even when any of the terminals is out-of-service, the GRL100 in-service terminal can still
provide the differential protection using the out-of-service detection logic. For details of the
out-of-service detection logic, see Section 2.2.2.
When one terminal is out-of-service in a two-terminal line, the other terminal continues the
current differential protection using the local current irrespective of whether it is a master
terminal or a slave terminal.
When one terminal is out-of-service in a three-terminal line, synchronized sampling is
established between the remaining two terminals as follows and the differential protection is
maintained.
• If the master terminal is out-of-service, one of the slave terminals takes over the master
terminal synchronized sampling function and enables current differential protection
between the remaining terminals to be performed.
• If the slave terminal is out-of-service, the master and another slave terminal maintain the
differential protection.
When two terminals are out-of-service in a three-terminal line, the remaining terminal continues
the current differential protection using the local current irrespective of whether it is a master
terminal or a slave terminal.
2.2.8
Charging Current Compensation
When differential protection is applied to underground cables or long overhead transmission
0
1
2
i A(0)
i B(1)
i B(0)
i A(1)
0
1
2
i A(0)
Differential current calculation
i B(0)
⎯ 25 ⎯
6 F 2 S 0 8 3 5
3
4
t
t
3
4
Sampling address number
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