What’s the Problem?
The UK wide transition towards net zero is resulting in an increase in grid connections of inverter- based resources (IBRs), such as solar, wind and battery storage.
IBR connections are on the 132 kV distribution network and are connected via a step-up transformer with a 132 kV Yn configuration. The increase of connections and the Yn earthing configuration provide low impedance for earth- level fault current. Thus, pushing the fault level towards or beyond its rating for existing 132kV equipment resulting in the degradation of circuit breakers (CB) and other network equipment.
A neutral earthing resistor (NER) can be used to reduce the earth- fault current by adding additional resistance resulting in an increase of impedance of fault current path. However existing 400/132 kV transformers have been designed with graded insulation and are typically solidly earthed. Therefore, the introduction of an NER could cause the neutral voltage to rise during an earth fault, creating electrical stresses that existing insulation may not be designed to withstand.
Preferred Output
National Grid (NGET) is seeking innovative approaches to enable effective NER installation (or equivalent solution) to control fault levels, maintain equipment ratings and ensure system stability without compromising transformer integrity.
A potential project must investigate one of the following:
- Investigation of risks of neutral voltage displacement if an NER is installed
- Investigation of the effects on transformer insulation at the neutral side if an NER is installed.
A potential project can explore one or more of the following solution archetypes:
- Potential of a new standard/NGET specific requirement for the fault management of new embedded generation connections, arrangement and how they connect to 400kV, 275kV and 132kV network eg only accept floating busbars in future
- Addition of the NER to the NGET SGT (132kV side) – this must be based on favorable results from investigations 1 & 2
- Possible reduction of the X/R ratio of the fault current exploring passive/active management of X/R ratio during a fault scenario.
Deadline
The deadline for this opportunity is 11.59pm on 2 October 2026. Please submit your proposal above.
Q&A Registration
The Q&A for this opportunity will take place on 7 September 2026 at 10am. You can register to attend above. Please email your questions by 5pm on 3 September 2026, marking your message with the name of the opportunity.