Biased Differential (87Bd, 87Hs); Secondary Injection Testing - Siemens 7SR242 Duobias Technical Manual

2.1

Biased Differential (87BD, 87HS)

Voltage Inputs:
Current Inputs:
Disable:
Map Pickup LED:
The differential elements are subjected to CT multipliers, Vector Group Compensation and Zero Sequence filters
when applied to power transformers. The complexity of these features can cause confusion during testing and
lead to incorrect relay settings being applied. It is recommended that the accuracy of the differential elements are
tested by secondary injection with simplified differential settings applied to avoid ambiguity before reinstating the
required site settings which can be tested more thoroughly by primary injection followed by final checking with the
protected transformer on load.
2.1.1

Secondary Injection Testing

The settings used for Secondary Injection test purposes should be:
W1 ICT Multiplier 1x
Connection Yy0,0deg
Multiplier 1x
Connection Yy0,0deg
©2015 Siemens Protection Devices Limited
Chapter 6) 7SR242 Duobias Commissioning & Maintenance Guide
Figure 2-1 Biased Differential
None
W1-I (I ),W1-I (I ),W1-I
L1 A L2 B
46, 49, 50, 51, 50N, 51N, 50BF,
87BD, 87HS - Self Reset
(I ), and W2-I (I ),W2-I
L3 C L1 A
(I ),W2-I (I ),
L2 B L3 C
W1 ICT
W2 ICT
W2 ICT
Chapter 6 Page 17 of 62