7/21/2019 Pt Selection Scheme

1/1

https://www.facebook.com/groups/PowerSystemProtection/

Feroz Hakkim

THE PT SELET!"# SHE$E

The normal scheme is provide bus - PTs in the Substations and no PTs for transformer bays.Hence, the PT signal of that particular bus, which is fed to the transformer, should be usedfor the metering and relay circuits of the transformer. The PT selection scheme enables to

select the PTs between the buses where the transformer is connected to, so as to avoidproviding separate PT for the Transformer bay, ie the scheme switches between the bus PTs

as per the current feeding arrangement of the transformer. The PT selection may becontrolled by the auxiliary contacts of the isolators which are wired to the selection scheme,

by which the current feeding arrangement can be sensed.

The scheme in the gure is for a !" # bus arrangement scheme, where the feeders to thebus are supplied by PT through "$ %wired through brea!er auxiliary of bus incomer& and

bus# by PT# through "#$, while both the brea!ers are in '( status. )f one of the brea!erschanges to '**, say if brea!er is o+, then the ( contacts of " %"-b& will connect the

bus feeders to PT# through "#-a..and vice versa..

Feroz HakkimThe same scheme can be wired to sense PT voltage by providing ac coil for "and "#... and connecting the coil directly to the corresponding PT signals...

%utti #ateshPower system protection ommissioning engineers are best groups in thiscategory %/entors are also maintaining these groups with their best !nowledge e+orts. Than!s a lot.

https://www.facebook.com/feroz.hakkimhttps://www.facebook.com/feroz.hakkim