Transgrid PACR: Maintaining compliance with performance standards applicable to protection relays

Market Network Service Provider
StageProject Assessment Conclusions Report
ConvenorAEMO NSP
Accepting submissions?No

Transgrid has published the Project Assessment Conclusions Report (PACR) to assess options for maintaining compliance with performance standards applicable to protection relays. The PACR is the final step in the Regulatory Investment Test for Transmission (RIT-T) process and follows the Project Assessment Draft Report (PADR) published in April 2024.

Protection relays are used throughout the transmission network to isolate network faults and reduce their impact on system security, system reliability and network infrastructure. A high population of protection relays has been identified to reach the end of their technical life by 2027/28, with manufacturer support, access to spares and defects rates being the largest drivers for remediation. The risk of failing to protect primary assets increases as technology becomes superseded by the manufacturer, manufacturer support ceases, and spare parts become scarce.

Redundant protection schemes are required to ensure the transmission system is adequately protected as outlined in the Network Performance Requirement under Schedule 5.1 of the National Electricity Rules (NER), therefore the condition issues affecting the identified protection relays on the ACT and NSW transmission network must be addressed. The Network Performance Requirements, set out in Schedule 5.1 of the NER, place an obligation on Transmission Network Service Providers (TNSPs) to provide redundant protection schemes to ensure the transmission system is adequately protected. Clause 5.1.9(c) of the NER requires a TNSP to provide sufficient primary and back-up protection systems (including breaker fail protection systems), to ensure that a fault of any type anywhere on its transmission system is automatically disconnected.

Additionally, TNSPs are required to disconnect the unprotected primary assets where the secondary system fault lasts for more than eight hours (for planned maintenance) or 24 hours (for unplanned outages). TNSPs must also ensure that all protection systems for voltages above 66 kV are always well-maintained and available other than for short periods (less than eight hours), while the maintenance of protection systems is being carried out. In the event of an unplanned outage, AEMO’s Power System Security Guidelines require that the primary network assets must be taken out of service within 24 hours.

A failure of the secondary systems would involve replacement of the failed component or taking the affected primary assets, such as lines and transformers, out of service. Though replacement of a failed secondary systems component is a possible interim measure, the approach is not sustainable as the stock of spare components will deplete due to the technology no longer being manufactured or supported. Once all spares are used, interim replacements will cease to be a viable option to meet performance standards stipulated in clause 4.6.1 of the NER.
If the need is not addressed by a technically and commercially feasible credible option in sufficient time (by 2027/28), the likelihood of not recovering from secondary systems faults and not maintaining compliance with NER performance requirements will increase.

Transgrid published a Project Assessment Draft Report (PADR) for maintaining compliance with performance standards applicable to protection relays in April 2024. In the PADR Transgrid presented one credible network option that would meet the identified need from a technical, commercial, and project delivery perspective. Option 1 involves renewal of individual assets including protection relays for transmission line, transformer, reactor, capacitor, busbar (and interzone) and those associated with under frequency load shedding (UFLS) schemes.

No submissions were received in response to the PADR during the consultation period which closed in June 2024 and no additional credible options have been identified.

The assessment in this PACR finds that Option 1 is the preferred option to meet the identified need at this stage of the RIT-T.

The estimated capital cost of this option is approximately $50.18 million ($2023-24) +/- 25 per cent. Transgrid is the proponent of the proposed network project.

In accordance with the requirements of the Rules, a summary of the PACR is made available on the AEMO website. A copy of the PACR can be obtained from Transgrid’s website or by emailing

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