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

4.3 CURRENT TRANSFORMERS
0BInvestment Evaluation Summary
TNM-GS-809-0720
The 110 kV current transformers in service at Meadowbank Substation (nine single phase units) are Laur Knudsen type
A8ZX units that were manufactured in 1963. A number of identical current transformers installed elsewhere in the
transmission system have been identified as having high percentage power factor readings. This type of current
transformer utilises a silica gel breather that requires the transmission circuit to be removed from service for
maintenance. This deficiency impacts adversely on transmission circuit availability.
The Current Transformer Asset Management Plan (TNM-PL-809-0605) recommends that the Laur Knudsen type A8X
current transformers be progressively replaced with current transformers installed with the dead-tank circuit breakers
because they are generally in poor condition and require frequent maintenance in comparison to modern equivalent units.
The current transformers will be 52 years old when decommissioned.
The average preventive maintenance costs associated with 110 kV current transformers at Meadowbank Substation is
$5 500 per three phase set.
4.4 DISCONNECTORS
The 110 kV disconnectors installed at Meadowbank Substation comprise the following types:
� ABB type DBRP - 1 unit (age 12 years);
� Stanger type DR2 - 3 units (average age 46 years); and
� Switchgear Pty Ltd type DBR-4 - 1 unit (age 46 years).
Generally, the ABB, Stanger and Switchgear Pty Ltd disconnectors in service at Meadowbank Substation are in a
serviceable condition. Given that these disconnectors have proven to be reasonably reliable, they will be refurbished and
retained in service at this time.
The average preventive maintenance costs associated with 110 kV disconnectors at Meadowbank Substation is $2 000
per unit.
Details of each disconnector type are provided in the Extra High Voltage Disconnector and Earth Switch Asset
Management Plan (TNM-PL-809-0606).
4.5 POST INSULATORS
The 110 kV post insulators (approximately 45 units) installed at Meadowbank Substation are a multi-piece construction
that comprise individual insulators bolted together to achieve the required voltage rating. The multi-piece design post
insulators are susceptible to mechanical failure in certain operating environments due to moisture freezing within the
post insulator, causing the porcelain components to crack. Transend has experienced a significant number of mechanical
and electrical failures of EHV multi-piece post insulators over the past 10 years. The consequences of failure have
included an increased safety risk to personnel working in switchyards, considerable disruption to electricity supply and
the requirement for unplanned outages to facilitate replacement of post insulators.
The post insulator asset management plan (TNM-PL-809-0614) recommends the progressive replacement of all multipiece
post insulators.
4.6 CONTROL BUILDING
The control building at Meadowbank Substation was designed for the secondary and ancillary systems associated with
the 110 kV assets. There is insufficient space available in the control building to facilitate the planned replacement of
secondary and ancillary systems without disrupting the existing equipment. Extending the control building is not feasible
without major 110 kV asset relocations. Due to this constraint, a new switch house was constructed in 2001 for the
22 kV switchgear and associated protection and control systems. This project includes the extension of the 22 kV switch
house be to provide a greenfield area for the planned replacement of secondary and ancillary equipment. Replacing
secondary and ancillary equipment at greenfield locations is common practice for transmission network service providers
and has been adopted by Transend for a number of previous projects. This approach has the following advantages:
� the likelihood of interruption to electricity supply is minimised;
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