Alstom MiCOM P54 Series, Technical Manual, Page: 198 / 1024

P54x/EN OP/La4 Operation
(OP) 5-24
MiCOM P543, P544, P545 & P546
OP
1.1.6 Mesh corner and 1½ breaker switched substations
If differential protection is applied in a mesh corner or 1½ breaker switched substation, a
P544 or P546 should be preferred to use it as they do have two independent CT inputs and
therefore each one generates its own restrain. See also
P54x/EN AP
.
P113 4E Na
END Y
P4037ENa
P543 or
P545
CTY
Communication Channel
P544 or
P546
Protected Line
To Busbar 2
CTX2
CTX1
To Busbar 1
END X
Figure 10 Breaker and a half application
As shown in Figure 10, a P544 or P546 relay should be used at the End X as the line is fed
from a breaker and a half substation configuration. At End Y, a P543 or P545 should be
installed.
Relay calculations for differential and bias currents are as follows for this case are as follows:
At End X
I diff = Ī
CTX1
+ Ī
CTX2
+ Ī
CTY
I bias = ( │ I
CTX1
│ + │ I
CTX2
│ + (Additional bias if non zero) or │ I
REMOTE
│ )/2
In this case Additional bias is zero as the P54x at the remote end has one single CT
(P543 or P545).
Additional bias (to be sent to end Y) = is calculated on a per phase basis by scalar summing
both local currents (ICTX1 and ICTX2) and selecting the largest of the three calculated. This
current is included in the transmitted message.
At End Y
I diff = Ī
CTY
+ Ī
CTX1
+ Ī
CTX2
I bias = ( │ I
CTY
│ + (Additional bias if non zero) or │ I
REMOTE
│ )/2
In this case Additional bias is the one sent by End X (relay with two CT inputs;
P544 - P546).