Parameter: Gn 87T-HS > Delay
•
Default setting: 0 s
A 5 ms setting is recommended to compensate for transient overreach.
Settings Example
Selected applications for differential protection are described in the following. Setting instructions for the
necessary setting parameters are given for these applications.
Transformer Differential Protection (87T)
This section covers the transformer overall differential protections, the biased differential and high-set differ-
ential elements. Transformer design limitations necessitate that the protection CTs are located on the line side
of the HV and LV windings, therefore the zone of differential protection covers both transformer windings.
[dw_7SR5_function87Tsettingsexample1, 1, en_US]
Generally the procedure to calculate relay settings is carried out in the following order:
Establish System Parameters
•
Transformer rated power, impedance and rated winding voltages.
•
Transformer winding connections.
•
Transformer OLTC range
•
CT ratios for each set of line and neutral CTs.
Calculate ICT Settings
•
ICT Multipliers, ICT Connections
Calculate Required System Settings
•
87T-BD function and 87T-HS function
Calculate Required Relay Settings
•
87T-BD function and 87T-HS function
Example n – 2-Winding Transformer
A 90 MVA with vector group Yd11 is selected, the neutral side is solidly grounded.
Protection and Automation Functions
5.22 87T Transformer Differential Protection
318 Reyrolle 7SR5, Transformer Protection Device, Device Manual
C53000-G7040-C015-1, Edition 11.2019
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