National Grid Gas Transmission Asset Management is responsible for the design, policy and delivery of work for the UK high-pressure pipeline (National Transmission System or NTS). If a new connection to the network were to ramp up gas pressure faster or slower than the system can handle, it would have an adverse impact on compressors and existing connections and could affect the safety and security of the network. Therefore, when a new connection to the network is requested by a National Grid customer, a ‘ramp rate study’ may be carried out to determine if the NTS can safely accommodate the rate.
It was taking National Grid about 3 months to run ramp rate studies internally, involving 1-3 analysts. Because the existing process was labour intensive, only 5 such studies could be requested in a year, meaning that National Grid was having to outsource work.
Generally, a ramp rate study starts by selecting the most challenging demand/supply scenario for the type of connection. The output from the simulation is a ‘transient alarm table’ that identifies pressure breaches in the network. On examining these outputs, an analyst carries out configuration changes (for example, turning on a compressor, shutting a valve, etc) in an attempt to ‘solve’ the scenario and bring the variables to within acceptable levels. Solving a scenario (and optimising a configuration) is a task for a human analyst. No automated solution has been found to be effective.
Setting up a new scenario in the existing system was onerous and ramp rate studies require 30-40 scenarios to be investigated.
After analysing the existing systems and processes, OCC and National Grid created a central datastore for ramp rate studies and delivered a desktop application that allows easy definition of sophisticated scenarios with multiple off-take/on-take nodes. The application also integrates with the systems used to run scenarios, monitor progress and communicate with stakeholders.
As well as making scenario creation more efficient, the project also automated and standardised the steps needed to run a study. The increase in turnaround means that 100% of ramp rate studies are now provided in-house. This improves the productivity of the department and removes the necessity to employ expensive third-party consultants, providing a better service for National Grid customers.
The application could also be suitable for other types of simulation study. You can read more on page 13 of this National Grid audit report: https://www.nationalgrid.com/sites/default/files/documents/Customer_Ramp_Rate_Studies.pdf.