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NETWORK / 32 / SEPTEMBER 2017 INDUSTRY INSIGHT WESTERN POWER DISTRIBUTION I n January 2013, Western Power Distribution (WPD) began a project called FlexDGrid supported by £17 million of funding through tier two of the Low Carbon Networks Fund (LCNF) – the precursor to the National Innovation Competition. The aim was to enable more synchronous generation to connect to the 11kV network in and around Birmingham City Centre, without the need for costly reinforcements, by modelling, managing and mitigating fault levels. Fault levels refer to the volumes of cur- rent that flow through a network when a short circuit occurs as "all the energy and current rushes to that point", WPD inno- vation and low carbon networks engineer Jonathan Berry explains. "When you connect a synchronous generator, such as a com- bined heat and power plant, that adds an additional current contribution when a fault occurs." This can raise fault levels beyond what the network is able to cope with, in which case expensive upgrades are required for new generation to be connected safely. In one instance, WPD was forced to spend £4 mil- lion and three years replacing transformers Future grid comes to fruition The future of synchronous generation in Birmingham is being facilitated by the FlexDGrid project. at a primary substation in Birmingham to accommodate less than 3MW of new distrib- uted generation. The upgrade involved the early retirement of still healthy assets and increased network losses by 745,000kWh per year. Modelling built on assumptions In an effort to avoid the need for such rein- forcements, the FlexDGrid project sought to better understand how the 11kV network in Birmingham responds to faults and how this changes with the connection of new synchronous generation. The company has itself admitted that its models of the grid were previously "built on lots of net- work assumptions", leading to conserva- tive estimates of the volume of generation which could be safely connected without upgrades. To resolve the issue, WPD increased the detail and granularity of its models, feed- ing in up-to-date network arrangement and connection data. It says removing uncer- tainty and assumptions from its models has enabled the release of more connection capacity. The enhanced modelling also facilitated the creation of a fault level guidance tool for planners and engineers and led WPD to update the fault modelling policy for all four of its license areas. Active fault management The second strand of the project saw WPD install fault level monitors at ten primary substations sites to create an active fault level management system. The devices, which were developed as part of a separate tier one LCNF project, work by triggering small disturbances on the network which can then be used to calculate fault levels. "Previously we've only been able to meas- ure fault level at a specific point when a fault has actually happened," says Berry. "Now we can generate the make and break values that would occur if a fault happened, without a fault actually happening on the network." Among other things, this enabled the company to verify the models developed during the initial phase of the project by comparing the real world data to the mod- els' predictions. "It also allowed us to look at how we can offer flexible and alternative connections to customers who have previ- ously been restricted or limited from con- necting to the network," Berry adds. WPD is now examining the possibility of developing a mobile fault level monitor which can been moved between sites. Mitigation: fault current limiters For the final stage, the company deployed fault current limiters to "effectively act as a sponge to soak up the excess fault level", thereby increasing the connection capacity of the network. WPD was able to meet its target of increasing the connection capacity by 50MW using the technology. Berry says the fault current limiters may be added to WPD's suite of standard assets following the success of the trial. The project reached its conclusion at the end of March and the closedown report was pub- lished in July. "When you connect a synchronous generator, such as a combined heat and power plant, that adds an additional current contribution when a fault occurs."