[dw_7SR5_function87Tsettingsexample7, 1, en_US]
Figure 5-59
Relay Currents – External Earth Fault with In Zone Earthing Transformer
To prevent undesired tripping the ICT connections should be such as to cause the zero sequence currents to
flow in a closed delta CT secondary connection of low impedance instead of in the differential relay operating
coil. As the transformer vector group has already been considered on the star side a Ydy0 ICT is used on the
delta side winding.
Protection and Automation Functions
5.22 87T Transformer Differential Protection
Reyrolle 7SR5, Transformer Protection Device, Device Manual 323
C53000-G7040-C015-1, Edition 11.2019
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