Name Values (Range) Unit Step Default DescriptionZSCurrSubtrW1 DisabledEnabled- - Enabled Enable zero sequence subtraction for W1 side,Off/OnZSCurrSubtrW2 DisabledEnabled- - Enabled Enable zero sequence subtraction for W2 side,Off/OnZSCurrSubtrW3 DisabledEnabled- - Enabled Enable zero sequence subtraction for W3 side,Off/On6.1.2.5 Monitored dataTable 28:T3WPDIF (87T) Monitored dataName Type Values (Range) Unit DescriptionIDMAG_A REAL - A Magnitude of fundamentalfrequency differential current,phase AIDMAG_B REAL - A Magnitude of fundamentalfrequency differential current,phase BIDMAG_C REAL - A Magnitude of fundamentalfrequency differential current,phase CIBIAS REAL - A Magnitude of the bias current,which is common to all phasesIDMAG_NS REAL - A Magnitude of the negativesequence differential current6.1.3 Operation principleThe task of the power transformer differential protection is to determine whether a faultis within the protected zone, or outside of the protected zone. The protected zone is limitedby the position of current transformers (see figure 31), and in principle can include moreobjects than just a transformer. If the fault is found to be internal, the faulty powertransformer must be quickly disconnected from the system.The main CTs are normally supposed to be Wye connected and can be grounded in anydirection (that is, either "ToObject" or "FromObject"). Internally the IED will alwaysmeasure the currents on all sides of the power transformer with the same referencedirection towards the power transformer windings as shown in figure 31.Section 6 1MRK 502 048-UUS ADifferential protection90Technical manual
