Powerful–CB

Start date: January 2017 End date: August 2021 Total funding: £5,301,041.47 Network Licensee Compulsory Contribution: £518,121.93

UK Power Networks is developing and trialling two new fault limiting circuit breakers that are significantly smaller and more efficient than any similar device currently in use. The project aims to make it quicker and cheaper for distributed generation, especially Combined Heat & Power units, to connect to the network. This high-speed protection could allow hundreds of megawatts of low-carbon electricity sources to connect to the electricity network more safely and cheaply.


The project aims to recruit a commercial customer that has a Combined Heat and Power generator installed to trial one of the new fault limiting circuit breakers. It is hoped this will enable more of the electricity it generates to be put into the network.

It will trial a second device at an 11kv substation to increase its capacity for a number of customers to benefit from.

We will talk to commercial-scale customers so that we can identify their requirements from a commercial, technical and logistical perspective. This will include taking into account their arrangements for factors such as installation, ownership, operation and maintenance.  


We estimate that by 2050, FLCBs could save customers around £400m (in net present value terms) in reinforcement costs in GB. These savings would be associated with around 460MW of additional DG connections in GB. Moreover, the increase in distribution connected CHP has the potential to deliver up to 3,800 kilotonnes of cumulative reduction in CO2 emissions by the year 2050, the equivalent of emissions generated by 800,000 vehicles in one year.


Tackle fault level issues in areas which have physical space constraints 

  • Design, build, install and trial an FLCB that will fit in customer premises in a dense urban environment where space is a premium
  • Trial the technology for up to 2 years, in order to see faults occur on the network
  • Evaluate the success of the trial, both technically, commercially and logistically from both UKPN and the participating customer perspective.


Trial two different methods to tackle fault level in the network

  • Trial one technology at a customer site, to minimise contribution to fault level to enable higher connection capacity to a fault level constrained substation. This will provide customers the benefit of increased fault level headroom at substation level
  • Trial one technology at an 11kV substation, to increase fault level headroom for a number of customers to benefit from. It will minimise the fault level contribution of the generator, using advanced power electronics which operate 20x faster than traditional vacuum filled circuit breakers.


Better understand the requirements for these technologies beyond the two trial sites

  • Enable the transition for the technology to be used in BAU across the UKPN networks
  • Talk to customers to identify requirements from a commercial, technical and logistical perspective such as connection arrangements and installation/ownership/operation/maintenance arrangements
  • Keep talking to customers who have expressed an interest but have not been selected as a trial site through a customer working group
  • Engage with UKPN planners and other internal stakeholders


Provide the UKPN connections planners with an alternative option to reinforcement in fault constrained network areas

  • Ensure the specifications allow connection to the network
  • Working with internal stakeholders to manage transition to BAU


Share the knowledge as the project progresses

  • Arrange dissemination events 
  • Work with customers outside UKPN connection areas and other DNOs to determine the suitability of the technology outside London


Fault level constraints can sometimes impact the connection of distributed generation due to small fault level headroom in substations.  Traditionally, when a new connection exceeds headroom, time-consuming or costly network reinforcement can be required, which can render the connection not commercially viable or result in reduced capacity being connected.  This is particularly true in dense, urban areas such as London.   The technology being trialled will help more distributed generation, such as efficient CHP units, to connect to the network more quickly and at lower cost. 

Traditional fault limiting devices are much too large to be installed in the densely populated cities where many CHP devices are found. The brand new device being built for this project will be significantly smaller than anything existing at the moment, and will take advantage of advanced power electronics to not only reduce the size but also the operation speed.  The trial aims to ease fault level constraints using two methods.  Increasing the headroom available to all customers using a device at the substation and minimising the impact on fault current at a generator premises, allowing quicker and cheaper connection for that individual generator.

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Powerful-CB: Preliminary Safety Case

The report presents the independently produced preliminary safety case report for the two methods to trial FLCB introduction to the UK Power Networks (UKPN) network.