Time Synchronization; Analog Signal Communication For Line Differential Protection - ABB RELION 650 Series Applications Manual

1MRK 505 363-UEN A
Operate current
[ in pu of IBase]
IdMin
IEC05000300 V1 EN-US
Figure 35: Overestimated charging current
If a high resistive fault is considered, the voltage in the fault location will not be much reduced.
Consequently, the value of the pre-fault "false" differential current will be a good estimation of
the actual charging current.
Subtracting the pre-fault charging current from the differential current under fault conditions
will make it possible to set
achieve maximum sensitivity. The stability at external faults will not be affected.
6.2.2.4

Time synchronization

Time synchronization of sampled current values is a crucial matter in numerical line differential
protections. The synchronization is made with the so called echo method, which can be
complemented with IRIG-B time synchronization. In applications with symmetrical
communication delay, that is, send and receive times are equal, the echo method is sufficient.
When used in networks with asymmetrical transmission times, the optional IRIG–B time
synchronization is required.
6.2.2.5

Analog signal communication for line differential protection

Line differential protection uses digital 64 kbit/s communication channels to exchange
telegrams between the protection IEDs. These telegrams contain current sample values, time
information, trip signals, block signals, alarm signals and eight binary signals, which can be
used for any purpose. Each IED can have a maximum of two communication channels.
On a two terminal line there is a need of one 64 kbit/s communication channel provided that
there is only one CT in each line end, as shown in Figure 36.
Application manual
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conditionally
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Idmin mainly without considering the charging current in order to
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Restrain current
[ in pu of IBase]
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Section 6
Differential protection
C
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Section 3
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