GE CT/VT Modules with Enhanced Diagnostics Conclusion

Internal CT secondary monitoring

The CT/VT input modules with enhanced diagnostics are monitoring internal CT circuitry integrity.

This is done to eliminate relay erroneous operation in case of CT secondary winding failure.

The secondary winding of CT is divided into two equal parts with a central tap in the middle.

CT current values from both halves of the CT secondary windings are run through

a differential amplifier to get a true current sample for the phasor calculations.

It also compares between each other by simply summing two samples together.

(Note that due to CT central tap, samples have different polarity.)

In case that values from different halves of the same CT accumulated over

one protection pass per adaptable per signal level do exceed the fixed error boundary,

failure is declared and protection is blocked.

CT secondary monitoring is performed at all four CT channels (A, B, C, and N) individually at each CT bank.

Conclusion

CT/VT modules with enhanced diagnostics, released on 23 October 2006 with firmware 5.2.

offer much higher security for internal CT/VT module error detection and prevent undesired operations of URs.

Every UR firmware released since version 5.2 supports CT/VT modules with enhanced diagnostics,

which greatly improves the security and reliability of the protection system.

To take advantage of this feature, a relay hardware and possibly firmware upgrade is required.

If the existing relay has a firmware version below 4.0. GE recommends purchasing a

UR Upgrade Kit that allows modernization of the obsolete relay hardware

while taking advantage of the relay modularity.

The UR Upgrade Kit contains a new CPU and CT/VT modules that can be

inserted in an existing relay case (case is fully backwards compatible).

If the relay currently has firmware version 4.0 to 5.0. the latest firmware

can be downloaded from the GE Multilin website, and Enhanced Diagnostic

CT/VT modules (8L, 8M, 8N, 8R, 8S, 8V) can be purchased from the GE Online Store.

Consult with your local GE representative if you have any questions on the upgrade process.