Transend - Appendix 5 Renewal capital expenditure - Australian ...

� loss of back-up protection functionality.
0BInvestment Evaluation Summary
TNM-GS-809-0720
Transend has not recorded any failures of the Mitsubishi MPC-SB protection relays over the last four years (out of the total of
six devices presently in service in the transmission network) but Transend is aware that an identical relay in the Tasmanian
Power System failed due to an internal fault during March 2008.
The failure rates for this type of protection technology have increased over the last few years and further failure rate increases
are expected as the condition of the components continue to deteriorate. The components of these devices fail randomly and
cannot be accurately predicted.
In addition both the Reyrolle type THR and Mitsubishi MPC relays types suffer the following asset management issues:
� they are no longer either manufactured or supported by the manufacturer;
� spares are no longer available from the manufacturer;
� spares held by Transend are aged and are likely to be prone to the same failures as the in-service assets; and
� the relays do not have ancillary or monitoring functionality.
Table 1 - Transmission line protection scheme failures involving THR and MPC protection relays over the last 4 years
Station Type Device
Outage duration of
Protection scheme
(estimated average)
Description of Failure
Ulverstone THR A121B 8 hours Relay incorrectly indicating VT failure,
requires VT detection card replacement.
Ulverstone THR A121B 8 hours Relay has VT Fail alarm. Cause is found to
be a faulty backplane. Relay replaced.
Farrell THR T121B 8 hours VTS card failed, incorrectly indicating VT
fail. Card replaced
Farrell THR D121 4 hours During testing, relay failed to operate for
zone 2 R-W phase fault. Card replaced.
Refer to the EHV Transmission Line Protection Asset Management plan (TNM-PL-809-0701) for further details regarding
management of these types of schemes.
4.2 ASSET MAINTAINABILITY
The recent failures of these protection devices have challenged Transend’s capabilities of performing corrective maintenance
on this technology of relays. At the present time a small number of experienced protection technicians are familiar with
testing and potentially repairing these relays. An adequate number of spares are held for these devices and in most cases,
faults have been resolved using spare cards within the 16 hour period allowed for unplanned maintenance as stated in the
‘NEMMCO Protection Systems Outage procedure’. However, these spares have all been recovered from de-commissioned
assets and are thus prone to the same failures as the in-service equipment. Spare parts for this type of equipment are no longer
available from the manufacturer.
The THR and MPC relays age, technology and lack of self supervision dictate that routine maintenance be performed twice
as often (every three years) than modern devices. Field staff have also noted that the devices are more likely to fail under
routine testing conditions, so accelerating the routine testing interval is likely to create more relay faults. This circumstance
also brings into question the ongoing reliability of this technology, that is, the relays although seemingly healthy, may fail
when called on to operate.
© Transend Networks Pty Ltd 4 of 7