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NETWORK / 17 / July/augusT 2017 Centre for Energy systems In- tegration at Newcastle univer- sity, the technology is unlikely to become a critical part of the day-to-day operations of the networks, but will be of critical importance when it is needed – if a storm knocks out significant infrastructure over wide areas, for example. "In those kinds of situations, having the ability to drive substa- tions out to those areas could be extremely valuable. They're the kind of things you won't be using regularly but will be extremely valuable when they are needed," says Taylor. "If you've got a very remote area and you're doing some work or there's been a fail- ure on the network, can you just drive up in a van with protection, transformers and backup genera- tors – or energy storage applica- tions – and plug it into the grid to support the network and provide a substation in a remote area?" Mobile substations offer strong potential to provide value in such situations, but there are already tried and tested technolo- gies and solutions available to networks that they will have to go up against. In recent years, as the addition of distributed generation assets has increased networks' susceptibility to intermittency problems, networks have invested in mobile generation, both in terms of infrastructure and con- tracting of providers, to provide backup power. Up against existing solutions as steve White, head of network control and operations at uK Power Networks, says, this approach works well to restore power in unexpected or unique scenarios. "Mobile generation is a good practical solution, for what would be very unusual scenarios, to restore customer supply. "We contract our suppliers for mobile generation and they can deliver large quantities of mobile generation within a very short period which can be connected to restore supply." He adds: "There's a limit to what you can do in that regard, but it's relative to ship- ping out a mobile substation or transformer and connecting it up at 33kV or higher and it's very fast. Mobile generation is very fast." For uK Power Networks, particularly its london network, the density of customers and layout of the network means that mobile substations are not as strong an option as they would be for networks with more remote operations, and that works in favour of the continuing use of mobile generation. However, Taylor believes mobile substations and packaged control rooms may increasingly be seen as a better choice than to mobile generation because they are quieter and also more envi- ronmentally friendly compared with any diesel generator-based mobile generation options. "I think the DNOs do have lots of mobile generator sets that they can take out and plug in, but they are noisy and polluting so if you could turn up with a cleaner, quieter substation with battery power instead I think that would be something that customers would appreciate," says Taylor. as well as reducing noise and emissions, adoption of mobile substations is also driven through P26 compliance, which dictates that networks should be built in a manner that allows for suitable resilience. Through this require- ment, networks must ensure that backup power is available, so op- erations can be restored if a stra- tegic point in the network goes down. In many of the networks, mobile substations could serve as a valuable asset in ensuring that P26 requirements are met. Citing such requirements, Rachael Taljaard, technical con- sultant at smarter grid solutions, suggests that mobile substations are "definitely becoming more important". "If you think you're going to have an issue, then you can mobilise mobile substations to get things up and running again and then focus on fixing the problems." Overall – and as Taylor suggests – the role and impact of mobile substations will, as intended, be restricted to those occasions where networks are either caught out by an unex- pected issue or to enable short- term work to be carried out with minimal disruption. However, against an increasing range of de- mands, from sweating assets for longer to more quickly connecting distributed generation assets, that role will is likely to be bigger than before. protection relay to a certain threshold and see if the current goes above it, then there's a short circuit to trip the circuit breaker. Today, the fault current that will flow could be quite different, depending on the mix of generators that are connected at the time of the fault." This emerging lack of clarity about fault levels is growing in large part because, in the past, detection and protection of fault levels was pretty straightforward. With the overwhelming majority of generation on the transmission network, the distribution network was relatively easy to protect. Re- cently, however, more and more generation is switching from transmission to distribu- tion networks. "Because of all this distributed genera- tion, you've essentially got more genera- tion coming off the transmission network and going onto the distribution network," says Randolph Brazier, head of innovation and development at the Energy Networks Association, "and that means that the fault levels are changing. The fault level on the distribution network is getting larger and the fault level on the transmission network, depending on the area, is getting lower." As a result, fault detection is becoming more difficult. Existing protection systems are fast becoming outdated and insufficient, and networks are having to develop new systems. "Obviously, from a protection point of view, that changes the sort of protection system you go for," says Brazier. "Tradi- tionally, you would just use overcurrent on the distribution network, but as more and more distributed generation is connected you might need more complicated forms of protection." Protection focus for next 30 years Explaining the significance of the chal- lenge to the networks, Ian Cameron, head of innovation at UK Power Networks, says: "Variable fault current for us is arguably one of the biggest protection focuses that we are going to face over the next 30 years, mainly as we approach a position where distrib- uted generation approaches about 50% of generation." Although UKPN thinks the issue will become more significant in the coming years, it and the other networks are already working to change their approach to protec- tion to account for the new challenges and makeup of the network. Central to these new approaches are new network technolo- gies that create new ways of both detecting and fixing faults. Of particular importance is the ability to respond more quickly to faults, with the AutomAtion, protection And control