87T > 87T Common >
(Note that the above settings produce ICTOUT = 1.00)
87T-HB Select Operate
87T > 87T-BD >
Gn HB2 Element Enabled
Gn HB2 Bias Cross
Gn HB2 Setting 0.15 ⋅ I
Gn HB5 Element Disabled
Gn Element Enabled
Gn Setting 0.3 ⋅ I
rated
(0.3 ⋅ ICT
OUT
Gn S1 0.3x (OLTC = +10 % to -20 %)
Gn S1L 4 ⋅ I
rated
(1/0.14 ⋅ 0.5 = 3.6 ⋅ ICT
OUT
Gn S2 Type Line (Default value)
Gn S2 1.5x (Default value)
Gn Delay 0 s
Gn External Fault 2.4 ⋅ I
rated
Gn Clearance Time 0.3 s
87T > 87HS >
Gn Element Enabled
Gn Setting 8 ⋅ I
rated
(> I
3PH THRU FAULT
i.e. 1/0.14 = 7.14 ⋅ ICT
OUT
Gn Delay 0 s
Configuration > Binary Outputs > Output Matrix >
87BD BOn, Ln
87HS BOn, Ln
Configuration > Binary Outputs > Trip Config >
W1 CB Trip Contacts BOn
W2 CB Trip Contacts BOn
The Effects of An In Zone Earthing Transformer
The in zone earthing transformer is a source of zero-sequence fault current. An earth fault on the delta side of
the transformer external to the differential protection zone will cause zero sequence currents to flow in the
CTs on the delta side of the transformer without corresponding current to flow in the line CTs on the star side
of the transformer. If these zero sequence currents are allowed to flow through the differential elements they
may cause undesired tripping.
Protection and Automation Functions
5.22 87T Transformer Differential Protection
322 Reyrolle 7SR5, Transformer Protection Device, Device Manual
C53000-G7040-C015-1, Edition 11.2019
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