[dw_7SR5_function87Tsettingsexample13, 1, en_US]
Figure 5-65 Auto Transformer with Earthed Neutral Point
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 (81HB2) must be Enabled as the magnetizing inrush
currents in each phase will not balance.
[dw_7SR5_function87Tsettingsexample14, 1, en_US]
Figure 5-66 AC Connections for Auto-Transformer Overall Protection
For the connections shown below the neutral-point currents are monitored and connected to the device, all
currents flowing into the protection zone are measured. The HV, LV and neutral currents are summed. Internal
faults are detected with high sensitivity.
Higher sensitivity for earth faults can be achieved where the neutral-point current is measured and included in
a restricted earth fault protection.
The differential protection does not monitor the tertiary winding, this must be separately protected. For the
connections below it is recommended that the CT ratios are all identical and that Yy0 vector correction
settings are used.
Protection and Automation Functions
5.22 87T Transformer Differential Protection
328 Reyrolle 7SR5, Transformer Protection Device, Device Manual
C53000-G7040-C015-1, Edition 11.2019
To Next Page
Loading...
