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NETWORK / 24 / FEBRUARY 2017 1 2 3 National Grid will spend nearly £1.4 million producing the detailed designs for a 400kV 240MVA mobile substation bay (MSB) capa- ble of being commissioned within 10 days. Although mobile substations up to 500kV have been deployed before, the concept of rapidly interfacing a reus- able mobile transformer bay into an existing operational substation at 400kV remains untried and untested. National Grid currently installs su… cient transformer capacity to cater for an N-2 contingency to manage supply security during a transformer fault while one transformer is o† ine for maintenance. The exposure to this risk is limited to planned transformer main- tenance activity. Using a mobile substation will reduce the cost of main- taining a constant network, eliminate the restriction of outage seasons by allowing maintenance to take place throughout the year, and pro- vide a short-term solution for temporary or uncertain demand pro‰ les. This is a development pro- ject, so to see ‰ nancial ben- e‰ ts the design would have to be built. Assuming that the design is built, one mobile bay could avoid the replacement of There are hundreds of bushings across Britain's electricity network, with varying designs used across the diŒ erent voltage lev- els. This variety complicates maintenance because the exact design in use is not always apparent until an engineer attends the site and takes measurements. As a result, and with the lead time for ordering bushings three to four months, network operators hold stocks of bushings of multiple designs to ensure that like-for-like replacement is possible across their networks. This practice is costly in terms of storage as well as the bushings themselves, and a risk still remains that security of sup- ply will be aŒ ected if no replacement can be sourced upon failure. This project will design, manufacture and test a portable earthing device that is capa- ble of installing and removing portable earths in a safe and controlled manner. The use of an earth switch is preferable when working on equipment, but a suitable earth switch is not always available at the point of work. In such cases a portable earth is used, but the devices are o' en di… cult to install, pose a signi‰ cant manual handling risk, and o' en have to be ‰ tted from a MEWP because of the busbar height. This project will follow on from previous work carried out in 2009-11, which devel- oped a prototype portable device capable of installing and removing portable earths in a safe and controlled manner. This project will use the lessons learnt to produce a pro- totype that addresses the design issues that were found in the ‰ rst prototype, and look to develop a product that is cost-eŒ ective tomanufacture. Current installation methods pose risks. They include loss of control because of the weather as well as human factors, a lack of interlocking facilities resulting in the earth being applied to live bar in error, and a physically challenging process. The prototype is intended to save some costs by devising a more e… cient way of working. Financial savings are di… cult to estimate at this stage because the produc- tion cost of the portable earthing device is unknown. However, if used twice a month it could result in a saving of between £20,000 and £145,000 a year. Detailed design of 400 kV 240MVA mobile substation bay NGET – launched Development of a universal bushing NGET – launched Portable earthing device NGET – launched four 400kV 240MVA transformers. Assuming that the replacement of each transformer costs £5m and a mobile unit costs £13m, and deploying an MSB costs £200k, then build- ing one MSB would produce a total bene‰ t of £6.2m. The cost of the units is expected to fall following the production of the ‰ rst pro- totype, so the cost of rolling out the technol- ogy across the country – with six units for NG, two for SPET and one for SHE – would be in the region of £90m. The project aims to design and complete a trial installation of a universal bushing suitable for installation on transformers that comply with the British Electricity Boards Speci‰ cation for Transformers and Reac- tors (BEBS T2), initially at 33kV. This will be the ‰ rst trial in Britain in which a bush- ing will be ‰ tted to a transformer it has not been designed for. A universal bushing for use at higher voltages will be considered in a follow-on phase if the project is successful at 33kV. The resulting design will be shared with all network operators for use on their net- works. The total annual saving from this project could be up to £350,000. The ‰ gure is based on the cost of a single bushing fail- ure in 2016 that led to signi‰ cant delays to a construction project resulting from outage cancellations. N E W D E S I G N Portable earth £20k annual saving if used twice a month £145k if rolled out across the country and used daily