The changing nature of assets connected to the gas network present “a very real problem that needs a solution” in the event of a gas supply emergency, National Grid Gas Transmission (NGGT) said at a meeting that kicked off examination of the emergency arrangements.
NGGT said it was in discussion with BEIS, HSE and Ofgem over its concern, and kicked off the a discussion on the problem statement: “When there is a shortage of gas which leads to an impact on electricity generation there is currently no robust methodology, tools or coordinating party to compare the impact on gas and electricity consumers. This may result in an uncoordinated response that leads to unnecessary safety and/or financial consequences to consumers and wider societal impact”.
The discussion was referred to by a meeting particpant as “long overdue”. The evolution of the electricity system operator to become more independent of National Grid has also made more pressing the consideration of information flows between the two systrems during an emergency.
Gas supply emergencies are very rare because the system has diverse sources – storage, as well as gas pipelines and LNG terminals – it responds over hours instead of miliseconds (as with the electricity network) and the pipeline network itself represents a form of storage as it can be ‘packed’ with extra gas. However, the advent of fleets of gas engines that are connected to the distribution networks – which are not operated by NGGT – is just one change that has caused NGGT to begin its reassessment of emergency arrangements.
In a gas emergency NGGT can call on the power sector to respond by powering down gas generation, at first by using commercial options that incentivise the market to switch to other forms of generation. NGGT has direct contact with such plant as they are connected to its high pressure network. If the emergency continues other measures are used such as interrupting demand customers.
Gas engines, however, are invisible to NGGT’s control room. They are just one among a large number of customers connected on each gas disribution network (GDN), and it is the GDN entry point which is the ‘customer’ visible to NGGT.
In fact, the gas engines may not be obvious to the GDN operator either, because complex contracts structures mean that the gas user who contracts with the GDN may have a different designation than the site.
GDN supplies are the last to be interrupted, not least because they are providing gas to end users, including domestic customers. Many of these end users are vulnerable. For safety reasons every user would require individual home visits to restart the gas supply if it were interrupted – a more costly and disruptive return to service than interrupting electricity supplies, which can be remotely restarted.
Gas engines can ‘free ride’ on this effectively ‘guaranteed supply’. And in the event of a gas emergency that involves switching off transmission-connected gas turbines, they are almost certain to start up to take advantage of the resultant high prices in the electricity market. That means the reduced gas demand on NGGT’s network will be immediately eroded by increased demand from the GDNs.
The gas engine fleets may be among the large users within a GDN area (although that varies widely) and the neither the GDN nor NGGT is routinely informed when such plant are started up.
This interaction is a relatively new one for the gas and electricity systems, which were previously linked only at the transmission level and with emergency arrangements that applied between large parties.
Other changes such as the addition of LNG to the system have raised questions such as whether the electricity supply to LNG terminals and to NGGT’s compressor stations are safeguarded in an emergency. Another participant noted that ‘black start’ capability to recover the electricity system after a blackout also relies increasingly on gas.
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