Siemens 7SR242 Duobias, Technical Manual

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©2015 Siemens Protection Devices Limited Chapter 7 Page 54 of 64
6.3 Transformer with Primary Connections Crossed on Both
Windings
Yd11 Transformer Connected as Yd9 (90
0
)
The phase-shift between the W1 and W2 primary systems may necessitate that primary connections to each
winding of the transformer have to be crossed. Fig. 6.4-1 shows a typical arrangement where a Yd11 transformer
is arranged to give a primary system phase-shift of 90 by crossing of its main connections. There are two
optional methods of configuring the 7SR24 relay.
Solution 1
Figure 6-5 shows W1 and W2 CT secondary wiring crossed over to replicating the crossovers on the transformer
primary connections:
Figure 6-5 – AC Connections: Yd9, 90
0
Transformer – Non-standard Secondary Connections
Notes:
An advantage of the above is that the 7SR24 relay can be set to correspond to the vector group shown on the
main transformer rating plate i.e. Yd11, +30° simplifying installation. This approach is also applicable where the
transformer is used to reverse the system phase sequence – see section 6.5.
A disadvantage is that ‘non-standard’ secondary wiring connections are used.
Relay instruments will indicate ’transformer’ quantities rather than system quantities.