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

0BInvestment Evaluation Summary
TNM-GS-809-0720
Reference Compliance obligation Substation issue Project objective
NEMMCO
Operating
Procedure
SO_OP6100
S8.1.3.1
‘Unless agreed to the contrary, after sixteen
hours from the unplanned outage of one
protection of a duplicated scheme the power
system equipment must be switched out of
service unless the protection scheme has been
repaired or temporary protection installed.’
5 CUSTOMER CONSULTATION
Maximum allowable period for an
unplanned outage of one protection
of a duplicated scheme is 16 hours.
The existing protection schemes are
unreliable and are likely to fail.
Provision of an upgraded
220 kV transmission line
protection schemes will
minimise risk of any future
unplanned outage being
greater than 16 hours.
Transend will liaise with all relevant stakeholders regarding the planned works at Farrell and Sheffield substations. Outages
will be required for each of the transmission lines to implement the works. Some of these outages will constrain generation,
so it is important that planned outages be well coordinated to ensure that the impact of the planned outages is minimised.
6 BENEFITS
Replacement of the 220 kV transmission line protection schemes at Sheffield and Farrell substations will provide the
following benefits:
� the likelihood of unplanned transmission line protection scheme outages will be reduced, thereby improving the
reliability and security of the transmission network;
� the occurrence of events that cause power flows through Farrell Substation to be constrained will be reduced;
� obsolete, unreliable and difficult to maintain protection schemes will be replaced with modern, reliable equipment that
incorporate self supervision functions, thereby reducing ongoing operations and maintenance costs;
� ensure ongoing compliance with the NER;
� additional disturbance recording and distance to fault facilities will be provided, thereby improving power system
analysis and fault response capability;
� allow full compliance with Transend’s internal design standard for the protection of EHV transmission lines;
� reduction in the risk of non-operation of the transmission line protection schemes. If faults are not cleared
appropriately then faults can result in damage to primary equipment, system instability issues and forced outages; and
� reduction in the risk of mal-operation of the transmission line protection schemes due to partial failure of the scheme.
Mal-operation of the scheme (ie operation of the scheme when there is no fault present) can result in forced outages
and system instability issues.
7 OPTIONS ANALYSIS
The following viable options have been considered to address the identified investment needs and compliance issues
associated with the Sheffield–Farrell 220 kV transmission line protection schemes:
� maintain the existing transmission line protection schemes and defer replacement; and
� replace transmission line protection schemes.
An alternative option that included replacing the Main A protection scheme (THR relay) and deferring the replacement of the
Main B protection scheme (MPC relay) additional schemes was considered but discounted because this option would not
provide any material benefits since the existing protection schemes would still be susceptible to failure. It would also create a
technological mismatch between the relays protecting a particular transmission line.
The viable options are discussed in further detail in the following sections.
© Transend Networks Pty Ltd 6 of 7