Siemens 7SR242 Duobias - 2.1 Biased Differential (87 BD, 87 HS)

7SR242 Duobias Commissioning & Maintenance Guide
©2010 Siemens Protection Devices Limited Chapter 6 Page 14 of 57
2.1 Biased Differential (87BD, 87HS)
Figure 2-1 Biased Differential
Voltage Inputs: None
Current Inputs: W1-I
L1
(I
A
),W1-I
L2
(I
B
),W1-I
L3
(I
C
), and W2-I
L1
(I
A
),W2-I
L2
(I
B
),W2-I
L3
(I
C
),
Disable: 46, 49, 50, 51, 50N, 51N, 50BF,
Map Pickup LED: 87BD, 87HS - Self Reset
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 W1 ICT
Connection Yy0,0deg W2 ICT
Multiplier 1x W2 ICT
Connection Yy0,0deg