National Grid Gas Transmission
James McCormick, Steve Johnstone, box.GT.email@example.com
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Gas Transmission Networks
The National Transmission System (NTS) consists of 7,615 km of high pressure gas pipelines, 246 Block Valve installations, 87 multijunctions where pipelines connect, 183 Exit Points and 23 Compressor Sites.
Remote isolation valves are currently installed at Multi-junctions, Compressor Sites and Entry Points to allow a pipeline to be isolated remotely by Gas Network Control Centre. In addition to these, there over 200 block valve sites, which have local operated valves and would require staff to visit the site to operate the valves. Remote isolation valves are also installed at 73 Exit Points to isolate the site from the pipeline however there are 39 Exit Points where the main pipeline isolation valve can only be operated locally at the site.
The risk to the pipeline network is controlled by a number of processes and procedures to avoid damage to a pipeline; however in the event of severe damage, leak or rupture, it would be necessary to isolate and de-pressurise the affected section of the pipeline. In
case of emergency the current approach would be to send staff to the block valves either side of the incident to isolate the pipeline. In the event of a major incident then the nearest remote operable valves would be used and the gas supply to the exit points between the two remote valves would be lost. This approach relies on a quick response time from staff to attend site and sufficient equipment to gain access to the valves which is some cases are located in below ground pits which would require any accumulated water to be pumped out before the valve could be operated.
The traditional way to provide electrical power to these types of facilities is to use the local electricity company’s services to provide the supply. The cost for this can be extensive and therefore prohibitive. There are alternative methods to get power to remote sites which National Grid are looking to investigate.
Where possible it is preferable to reduce the carbon footprint, the most common configuration to do this is to use PV Cells and/or wind turbines with an electrical supply. The electrical supply will take over from the renewable sources when the demand for the
system is greater that the renewable sources can supply.
Alternatively without using an electrical supply, batteries can be used as a permanent supply, with the renewable sources providing power for the system and charging the batteries, which then provide the power when the renewable source is insufficient. Another possibility could be to use a generator instead of renewable sources where they may not be suitable. These last two options tend to
be more suitable for lower power applications.
This approved strategy for local to remote conversion at strategic Block Valve and Exit Points will ensure that National Grid emergency arrangements for the NTS pipeline network are updated for new technologies and will meet the requirements of the Pipeline Safety Regulations and the Gas Safety (Management) Regulations.
Therefore, to support the delivery of this strategy a source of renewable energy is to be investigated for these remotely located sites in order to send signals to and from the GNCC to open and close the valve remotely.
This project also aims to gain knowledge about the use of alternative energy sources that are fit for purpose to power gas facilities on the National Transmission System.