4.3.1.4 Operation principle
The function can be enabled and disabled with the Operation setting. The
corresponding parameter values are “On” and “Off”.
The function can also be set into test mode by setting the Operation setting to “test/
blocked”.
The operation of the line differential protection and related measurements,
stabilized and instantaneous stages can be described using a module diagram.
GUID-44304073-30AC-4EEA-889C-2D9410DC1180 V3 EN
Figure 178: Functional module diagram. I_LOC_x stands for current of the local
end and I_REM_x for phase currents of the remote ends.
Stabilized low stage
In the stabilized low stage, the higher the load current is, the higher the differential
current required for tripping is. This happens on normal operation or during
external faults. When an internal fault occurs, the currents on both sides of the
protected object flow towards the fault and cause the stabilizing current to be
considerably lower. This makes the operation more sensitive during internal faults.
The low stage includes a timer delay functionality.
The characteristic of the low stage taking the apparent differential current into
account is influenced by various factors:
• Small tapped loads within the protection zone
• Current transformer errors
• Current transformer saturation
• Small asymmetry of the communication channel go and return paths
Section 4 1YHT530004D05 D
Protection functions
346 615 series
Technical Manual
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