Brain power

Imperial College is leading a project to make the electricity distribution system more intelligent, so alternative sources of power, such as wind farms and small-scale generation, can be integrated without overloading the ageing distribution system.

The recent UK Energy Review focused on the way electricity is generated, but the addition of small-scale, alternative energy sources is forcing the distribution system to behave in a way it wasn't designed to, which could lead to power cuts and other problems.

The three-year, £4m project, called AuRA-NMS (Autonomous Regional Active Network Management Systems), aims to develop control systems that will sit on top of the existing power distribution system and find the most efficient routes to channel electricity from both traditional, large-scale generators and the new, smaller scale sources.

The project involves six other UK universities, Switzerland's ABB and power generators EDF Energy and Scottish Power.

Tim Green of Imperial College's Control and Power Group, who is coordinating the project, explained that there are two different systems used to transmit electricity from generators to consumers.

High-voltage electricity is sent long distances via the transmission network, operated by the National Grid, while lower-voltage power for domestic and commercial consumers is supplied through a different system, known as the distribution network, handled by the regional electricity suppliers.

Historically, electricity has been generated in the UK in large amounts and because of this the distribution network was designed to be a passive system. 'The power comes down from the transmission network and just flows out to where the loads [electricity users] are,' Green said.

However, the smaller-scale generators now coming on line - such as wind farms, hydro-electric schemes, landfill gas generation and even domestic solar and wind systems - generate electricity at a lower voltage, so can't be connected to the high-voltage transmission network.

Instead, they feed into the distribution network. 'So instead of taking power outwards towards the loads, the system now has power flowing in both directions: out to the loads and in from generators.'

This is starting to cause problems. For example, some parts of Scotland have so many small-scale generators that the system is becoming congested, Green said.

Scottish Power also runs the north Wales distribution network, where there is huge potential for wind generation, 'but it's going to be difficult to put more in without something changing about the way they control distribution'.

The AuRA-NMS project aims to develop automated control systems to monitor and control energy flows through the distribution network, in either direction, to avoid causing stress on the infrastructure.

To help with this, the three companies are installing extra equipment on the network, including electricity storage equipment, instrumentation and additional communication channels.

Part of the problem is that much of the system's cabling and transformers are several decades old. Running these systems at full capacity for too long will reduce their lifetime and increase the possibility of failure, said Green.

'We want to limit power interruptions as far as possible,' he added. 'When interruptions do happen, we want a system that's as flexible as possible to reroute power to customers, getting them back on supply as soon as possible.'

Another part of the project concerns power storage. Renewable energy sources only generate electricity under certain conditions — when it's windy, sunny, or when the tide is running — that don't always coincide with demand peaks.

To address this problem, ABB has developed a very large battery capable of storing 370kW/hr of electricity and injecting 200kW of power into the network in around an hour. 'This isn't like a car battery,' said Green, 'it would have its own building.'

This battery would store the electricity when it is generated and release it back on to the distribution network when demand rises or generating capacity falls.

'The question is, can you do that cost-effectively?' Green asked. 'So we'll put it into our test network and try to economically optimise the way it runs, and see whether storage has a value that balances the cost of installing it.'

The project aims to carry out tests in power supply situations that are as real as possible, but this is difficult to accomplish. 'Doing full-scale tests of the controllers on a network is tough, because power companies don't want to put their customers' supplies in jeopardy,' Green explained.

'So we've devised a form of testing where we take live data off the network, do our control calculations and produce the signals as if our controller were running live. We can compare that data with what is really happening in the conventional network. And that's the point at which the power companies and ABB can say whether this has potential as a product.'