The Problem
The zero missing phenomenon (ZMP) is a recognised protection challenge in transmission networks that occurs when current through a circuit breaker fails to cross zero during switching or fault events. Extra high voltage (EHV) circuit breakers require the current to pass through zero in order to interrupt fault currents safely. When ZMP prevents this zero crossing, the breaker may fail to operate correctly, potentially resulting in catastrophic equipment failure.
ZMP is most associated with heavily shunt-compensated circuits and is expected to become more prevalent as renewable generation and long cable installations increase.
Current risk management approaches rely on conservative offline modelling and worst-case simulations rather than real-time detection. As a result, network operators face:
- Unnecessary restrictions on circuit breaker operation
- Delayed or constrained fault isolation
- Reduced network utilisation and operational flexibility
- Increased risk of equipment damage and customer interruptions and customer minutes lost (CI/CML).
Although mitigation measures such as pre-insertion resistors (PIR) and point-on-wave (POW) switching can reduce the likelihood of ZMP in some switching scenarios, they are ineffective for all operating conditions, particularly faults adjacent to shunt reactors.
Preferred Output
SP Energy Networks are seeking to assess the feasibility of a real-time ZMP measuring device which will allow informed, automated decision-making in breaker operations. The solution will allow systems to employ mitigating measures only when the phenomenon occurs. Some key considerations will need to include:
- Accuracy in detection (critical)
- Consideration of any modifications required to existing assets (cost implications)
- Consideration if a new solution will be required (cost Implications)
- Consideration of the effects on the wider network.
Deadline
The deadline for this opportunity is 11.59pm on 28 August 2026. Please submit your submit your proposal above.
Q&A Registration
The Q&A session for this opportunity will take place on 30 July 2026 at 2pm. You can register by clicking the button at the top of this page, or directly below. Please pre-submit any questions for the Q&A by 5pm on 28 July 2026.