When a new connection to the network is requested by a National Grid customer, a ramp rate study may be carried out to determine the consequences of bringing it online. If the new connection ramps up or down more quickly than the system can handle, it can lead to abnormal operating conditions which can have adverse impact on compressors and existing points of offtakes or affect the safety and security of the NTS. A ramp rate study endeavours to model this situation to determine if a particular ramp rate can be safely accommodated by the system.
At present a ramp rate study, carried out internally by National Grid, takes about three months and can involve between one and three network analysts (costing £25k -£35k to the customer). Normally, only one ramp rate study is carried out at a time. Up to five ramp rate studies can be requested in a typical year, and depending on workload, some work may be outsourced to a third party consultant. Studies carried out by the consultancy take between four to six months to complete (costing up to £50k to the customer).
The main tool used by National Grid to carry out a ramp rate study is Simone, a windows application which is a mathematical model of the gas transmission network. Generally, a study starts by selecting the most challenging NTS demand /supply scenario for the type of connection under study. For this scenario, the most challenging time of day is selected for the ramp up (first using the requested ramp rate) to start. The output from the simulation of the scenario is a "transient alarm table" that identifies pressure breaches in the network, as well as a number of graphs which show different variables against time. On examining these outputs, an analyst carries out configuration changes (e.g. turning on a compressor, shutting a valve, etc) in an attempt to “solve” the scenario by bringing the variables to within acceptable levels. Setting up a new scenario in Simone is onerous and typically between thirty to forty scenarios are investigated for a ramp rate study. Excel spreadsheet tools have been developed to facilitate this and scenario results are exported from Simone to an Access database via an Access application. In addition, various applications from the Microsoft Office suite are used to monitor the study's progress, record the results, create the final report, communicate with the customer, and generate audit forms. Information is transferred between these different applications by manual copying and pasting, which is timeconsuming and has the potential for error.
This project looks to develop an intelligent tool with the appropriate algorithms to speed up the ramp rates process, providing process improvements and increased functionality.
Benefits
Reduced time, and therefore cost, to carry out ramp rate studies.
