Principle Of Operation; Algorithm And Logic - ABB Relion 670 Series Technical Reference Manual

Section 5
Differential protection
5.1.2
5.1.2.1
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Communication Channels
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Figure 50: Five terminal line with master-slave system
Current samples from IEDs located geographically apart from each other, must be time
coordinated so that the current differential algorithm can be executed correctly. In IED,
it is possible to make this coordination in two different ways. The echo method of time
synchronizing is normally used whereas for applications where transmit and receive
times can differ, the optional built in GPS receivers can be used.
The communication link is continuously monitored, and an automatic switchover to a
standby link is possible after a preset time.

Principle of operation

Algorithm and logic

In Line differential protection function, measured current values from local and remote
line ends are evaluated in order to distinguish between internal or external faults, or
undisturbed conditions.
The local currents are fed to the IED via the Analog Input Modules and thereafter they
pass the Analog to Digital Converter, as shown in figure 51.
Protected zone
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Technical reference manual