Electricity North West gives UK debut to ABB's IS-limiter - the world's fastest fault current limiting and switching device
30/04/2015 Hitachi Energy UK Limited
Low Carbon Network Fund (LCNF) 'Respond' Smart Grid project will demonstrate how intelligent fault current management can address the challenges of integrating low carbon generation sources within existing network infrastructureABB's Is-limiter - the world's fastest fault current limiting and switching device - will make its UK grid debut as part of Electricity North West's 'Respond' project. This LCNF Smart Grid project will demonstrate how innovative solutions such as the Is-limiter can enable DNOs (Distribution Network Operators) to adapt their existing distribution network assets to handle the fault current challenges created by connecting increasing levels of low carbon generation.
Electricity North West Limited (ENWL) owns, operates and maintains the North West's electricity distribution network, connecting 2.4 million properties, and more than 5 million people in the region to the National Grid. It delivers more than 23 terawatts (TW) of electricity to customers over a network covering a diverse range of terrain, from isolated farms in rural areas such as Cumbria, to areas of heavy industry and urban populations including Manchester.
The two-year Respond project will actively monitor demand and generation on the ENWL network, continually assess the fault level and automatically enable innovative techniques when necessary. This is the first time that fault level will be actively managed on 6.6, 11 and 33 kilovolt (kV) networks in the UK.
As part of the project, ABB Is-limiters will be installed at up to five ENWL substations.
Normal substation circuit-breakers cannot provide protection against fault currents, as they are too slow to respond. In contrast, the Is-limiter can detect and limit a fault current at its first rise - in less than a millisecond - this ensures that the maximum instantaneous current is limited to a safe level that will not cause damage to the substation equipment.
The Is-limiter consists of an extremely fast switch, able to carry a high rated current but having a low switching capacity, and a high rupturing capacity fuse arranged in parallel. In order to achieve the desired short opening time, a small charge, similar to those used in automotive airbags, is used to open the main conductor switch.
"The Respond project is an important UK grid first for ABB's Is-limiter. However, it is already a tried and tested technology, with over 600 reference applications worldwide," said Peter Jones, ABB Technology Strategy Manager. "We are delighted to be involved in this trial showcasing a technology capable of delivering significant value and very short payback periods for DNOs and their stakeholders. The Is-limiter is a perfect fit with the new imperatives faced by DNOs to optimize their capital expenditure. It has the potential to improve network performance, boost connection capacity and help improve customer satisfaction, without the need for multi-million pound investments in new substation infrastructure."
What is a fault current?
Normal current and fault current are very different. Normal current is a steady flow of electricity through the network. Fault current occurs only when there is a fault on the network. It is an instantaneous surge of electrical energy, which is significantly higher in magnitude than normal current and flows towards the point of the fault.
Fault level is the potential maximum amount of fault current that will flow when a fault occurs. Additional demand and generation connecting to the network increase fault level. Fault level fluctuates throughout the day depending on the network configuration and customers' load / generation. The ability to actively manage and mitigate fault level is a valuable tool for DNOs.
How is the low carbon economy contributing to increased fault levels?
The UK's transition to a low carbon economy is encouraging greater use of electricity as reliance on fossil fuels reduces. Low Carbon Technologies (LCTs), and more two-way flows of energy arising from the connection of LCTs will present a range of new challenges to DNOs, one of which is an increase in fault current.
DNO networks are designed and operated to provide safe, reliable and cost efficient distribution of electrical energy. On occasion networks experience faults, when these occur, protective devices such as substation circuit-breakers safely interrupt the flow of fault current. The purpose of circuit-breakers is to remove fault current from the network safely and quickly.
All network equipment ie switchgear, cables and overhead lines etc, is designed with a fault current capability rating, also known as the fault level rating. The UK standard specifies that network switchgear has a fault level rating of three seconds (ie it can withstand the flow of fault current for up to three seconds). The purpose of the switchgear is to remove fault current from the network safely and within three seconds.
When new customer demand or generation such as a combined heat and power (CHP) plant connects to the network, the potential maximum fault current may rise above the network fault level rating. If the network has an excessive fault level then circuit-breakers may not be able to interrupt the flow of fault current and could fail disruptively.
What is the effect of fault currents on distribution networks?
Fault levels fluctuate on the network throughout the day and there may only be a short time period when switchgear ratings could be exceeded. The traditional solution to this issue is to replace existing switchgear with a type that has a higher fault level rating.
In Ofgem's RIIO (Revenue=Incentives+ Innovation+Outputs) - ED1 framework for setting price controls for network companies, the cost of replacement for a single substation is around £500,000 for high voltage (HV) and starts at £1.2 million for extra high voltage (EHV). DNOs are required to maintain safe operation, so even if the switchgear rating is only exceeded infrequently, this would trigger asset replacement. Installing expensive, higher specification switchgear in these circumstances could mean the extra fault level capacity installed is effectively unused for the majority of the time.
The cost of resolving this fault current issue and the connection time associated with the design, procurement and installation of new switchgear or complete substations can often make it uneconomic for a customer to accept a connection offer.
The Respond approach
Respond will be the first demonstration of near real time fault level assessment and adaptive mitigation techniques to overcome the fault level challenge faced by all DNOs at much lower cost. ENWL's approach is to handle fault level fluctuations using existing assets. This will be achieved by deploying intelligent software together with innovative technical and commercial fault level mitigation techniques.
A fault level assessment tool will assess the potential maximum fault current. When the potential fault current exceeds the existing switchgear rating, this software will issue an "enable" command to one of the innovative fault current mitigation techniques featured in the trial, such as ABB's Is-limiter, retrofitted alongside existing substation equipment.
Further information on the ENWL Respond project, including a video presentation, is available here: www.enwl.co.uk/about-us/the-future/respond
For more information, please contact:
Karen Strong
ABB Power Products & Power Systems Divisions UK-۬
Tel: +44 1785 825050-۬
Email: Karen.strong@gb.abb.com
Web: www.abb.co.uk/energy
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