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

1 BACKGROUND
0BInvestment Evaluation Summary
TNM-GS-809-0720
Farrell Substation was established in 1982 to provide a connection point for the Pieman River power development and is
a critical node in the Tasmanian transmission network. It connects up to 618 MW of generation to the Tasmanian power
system and, in turn, the national electricity grid via Basslink. Under certain generation scenarios, Farrell Substation can
transmit up to one third of Tasmania’s generation requirement. In addition, the substation is critical to providing a secure
and reliable electricity supply to customers located on the west coast of Tasmania. The load supplied from Farrell
Substation is predominantly for mining and minerals processing and in 2007 the maximum demand was approximately
70 MW.
Farrell Substation is located on Tasmania’s remote west coast and is frequently exposed to inclement weather conditions.
On a number of occasions each year, the substation can not be accessed by road because of snow and ice. In addition, the
substation is approximately two hours drive from the nearest fault response centre. Therefore, adequate remote control
and monitoring facilities are essential to ensuring the security, reliability and availability of the transmission network.
The two existing bus bar protection schemes (one each on the 220 kV and 110 kV) were commissioned in 1983 as part of
the original substation development. The protection relays are now 25 years old and are well beyond their nominal
service life of 15 years. They are Brown Boveri type INX2 static low impedance schemes and are the only bus bar
protection schemes of this type in Transend’s transmission network.
2 PROJECT OVERVIEW
This project comprises the replacement of the 220 kV and 110 kV bus bar protection schemes at Farrell Substation. The
bus bar protection schemes will be replaced with new duplicate schemes on both the 110 kV and 220 kV bus bars.
The new bus bar protection schemes will be installed in the existing relay room at Farrell Substation. New multi-core
cabling will be required within the relay room to connect the new panels to Current Transformer, trip, control, AC/DC
supplies, disconnector imaging and SCADA circuits. The project also includes the installation of a small quantity of
cabling from the switchyard to the control building, but it does not include provision for new multi-core cabling between
assets located in the switchyard. Preliminary investigations indicate that there is sufficient spare capacity in the existing
multi-core cabling to accommodate the requirement for additional signalling from the primary plant. It may be a
requirement to utilise or install auxiliary relays if detailed designs identify that there are insufficient spare cable cores.
The 220 kV bus bar protection scheme will need to accommodate ten substation bays: A4 (transformer T1), B4
(transformer T2), H1 (Sheffield–Farrell No. 1 transmission line), J1 (Sheffield–Farrell 220 kV No. 2 transmission line) ,
D1 (Farrell–Reece No. 1 transmission line), E1 (Farrell–Reece No. 2 transmission line), A1 (Farrell–Tribute
transmission line), B1 (Farrell–John Butters transmission line), (Farrell–Bastyan transmission line), and A7 (bus coupler
bay).
The 110 kV bus bar protection scheme will need to accommodate seven substation bays: A5 (transformer T1), B5
(transformer T2), N1 (Farrell–Que-Savage River–Hampshire transmission line), S1 (Farrell–Rosebery transmission line),
T1 (Farrell–Rosebery–Queenstown transmission line), P1 (Farrell–Mackintosh transmission line) and B7 (bus coupler
bay).
3. INVESTMENT TIMING
The Farrell Substation bus bar protection replacement project has been programmed to commence in early 2009, with
final commissioning in June 2010. The project has been attributed a high priority because of the high likelihood and
impact of critical protection scheme failures.
NPV analysis demonstrates that it is most efficient to start this project in 2009.
The 110 kV bus zone has proven more unreliable than the 220 kV system, so it is proposed to undertake works on this
system first. The project is proposed to be staged as follows:
1. Commission the new 110 kV Bus Zone Protection B scheme (GE Multilin type B90), maintaining the existing
Brown Boveri type INX2 scheme in service. Use the existing spare protection CT of bays for new bus bar
protection scheme
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