Ofgem has approved a modification to the Grid Code that will further protect critical sites from being disconnected during emergency load shedding.
The decision will allow distribution network operators (DNOs) to exclude protected sites such utilities, hospitals and railways from the second tranche of demand they disconnect when instructed to do so by the Electricity System Operator (ESO).
The modification, designation GC0162, is part of wider effort to align the Demand Disconnection arrangements in Operating Code 6 (OC6) of the Grid Code with the rationing arrangements in the government’s Electricity Supply Emergency Code (ESEC). The need for alignment was identified as part of the Electricity Shortfall Prioritisation Review held by the Department for Energy Security and Net Zero earlier this year.
The ESEC sets out a Variable Rota Disconnection Plan to ensure electricity supplies are shared as equitably as possible between non-protected sites during a protracted shortfall. The plan requires DNOs to divide non-protected sites in their licence areas into 18 near equally sized load blocks. During a supply emergency, available supplies would be rotated through these blocks across eight three-hour periods each day according to a detailed rota contained in the ESEC.
The ESEC also lists a series of protected sites that should not be included in these load blocks and therefore subject to rationing. These include electricity generators, oil and gas facilities, water and sewerage installations, essential telecommunications infrastructure, hospitals, major railways, airports, ports and docks.
In mid-September, Ofgem approved the modification GC0161, which removed a stipulation in OC6 that the Demand Control arrangements established in the code, including Demand Disconnection, should not “unduly discriminate against, or unduly prefer, any one or any group of suppliers or network operators or non-embedded customers”. It also removed an explicit statement that the protection for critical sites provided by the ESEC should not apply to Demand Control under the Grid Code.
As well as protecting critical sites from emergency load shedding, the modification, which came into effect at the beginning of October, was intended to allow DNOs to align their load blocks for Demand Disconnection under the Grid Code with those for rationing under the ESEC to allow a smooth transition from one to the other. However, the modification only enabled DNOs to exclude protected sites from the first 20% tranche of demand to be disconnected.
Ofgem has now approved the follow-up modification GC0162, which amends the timing requirements for Demand Disconnection to allow protected sites to also be excluded from the second tranche (20% to 40%).
The regulator said: “Whilst this may extend the overall time of implementing Demand Disconnection greater than 20% of demand, NGESO confirmed that this would promote rather than hinder system security.
“This is because consecutive demand disconnections provide a stepped response that’s easier to manage, and the proposal ensures all DNOs interpret instructions in the same way, therefore providing consistent response.”
Ofgem noted that the alignment of the Demand Disconnection and ESEC load blocks introduces a “low risk of degradation” of Demand Disconnection and Low Frequency Demand Disconnection (LFDD) if both Demand Control measures are required simultaneously.
However, the regulator said: “DNOs are cognisant of this and will endeavour to minimise the risk of degradation in implementing this proposal. Overall, we consider the societal and coordinated system benefits of protecting critical customers outweighs the low risk of LFDD degradation.” It said the ESO will consider keeping additional frequency response available to mitigate this risk.
It also acknowledged the potential for Demand Disconnection to exacerbate supply shortfalls by disconnecting generators connected to distribution networks. Ofgem said the ESO and DNOs will therefore seek to avoid including load blocks with significant embedded generation in the second tranche of demand to be disconnected.
GC0162 will come into effect on 15 December.