Protection Of Auto Transformers - Siemens 7SR242 Duobias Technical Manual

6.5 Protection of Auto Transformers

The transformer has a phase shift of zero. To prevent undesired tripping of the overall differential protection for
external faults a zero sequence shunt is required, this is implemented by selecting ICT Connection setting on
both sets of CT inputs to Ydy0. The inrush inhibit (81HBL2) must be Enabled as the magnetising inrush currents
in each phase will not balance.
Fig. 6-8: AC Connections for Auto-Transformer Overall Protection
Fig. 6-9: AC Connections for Auto-Transformer Overall and REF Protection
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