ABB REG670 - Operation Principle

Name Type Values (Range) Unit Description
IDL3MAG REAL - A Magnitude of
fundamental freq. diff.
current, phase L3
IBIAS
REAL - A Magnitude of the bias
current, which is common
to all phases
IDNSMAG
REAL - A Magnitude of the
negative sequence
differential current
Table 46: T3WPDIF Monitored data
Name Type Values (Range) Unit Description
IDL1MAG REAL - A Magnitude of
fundamental freq. diff.
current, phase L1
IDL2MAG
REAL - A Magnitude of
fundamental freq. diff.
current, phase L2
IDL3MAG
REAL - A Magnitude of
fundamental freq. diff.
current, phase L3
IBIAS
REAL - A Magnitude of the bias
current, which is common
to all phases
IDNSMAG
REAL - A Magnitude of the
negative sequence
differential current
6.1.7 Operation principle
The task of the power transformer differential protection is to determine whether a
fault is within the protected zone, or outside of the protected zone. The protected zone
is limited by the position of current transformers (see Figure
32), and in principle can
include more objects than just a transformer. If the fault is found to be internal, the
faulty power transformer must be quickly disconnected from the system.
The main CTs are normally supposed to be star connected. The main CTs can be
earthed in anyway (that is, either "ToObject" or "FromObject"). However internally
the differential function will always use reference directions towards the protected
transformer as shown in Figure
32. Thus the IED will always internally measure the
currents on all sides of the power transformer with the same reference direction
towards the power transformer windings as shown in Figure 32. For more information
see the Application manual.
1MRK502052-UEN B Section 6
Differential protection
113
Technical manual