ELECTRICAL RESILIENCE


The original Ottermill low voltage air circuit breaker in its withdrawn position (left), and an EDS Ottermill retrofit such circuit breaker (right).


fixed portion of the switchboards was in very good condition, and suitable for continued operation. With-ever increasing financial pressure


facing Oxford University Hospitals NHS Foundation Trust, Electrical Distribution Solutions was able to offer an innovative, technically sound, and cost-effective retrofit solution.


Extending existing switchboard’s life The proposed solution was to replace the obsolete low voltage air circuit breakers with retrofit low voltage air circuit breakers, which would significantly extend the life of the existing switchboard at a cost of much less than one third of a new switchboard. The retrofit solution negates the


requirement for complex planning, civil, cabling, and cable jointing/termination, and extended periods of time where the hospital electrical distribution system would be at risk. The Electrical Distribution Solutions


retrofit low voltage air circuit breaker utilises a modern air circuit breaker which has been engineered to directly fit in place of the old low voltage air circuit breakers without, in most cases, the requirement for a busbar outage. All interface points, such as contacts and interlocks, are identical and operate the same way as the old circuit breaker. The retrofit circuit breakers incorporate a modern intelligent electronic


60 Health Estate Journal February 2022 ‘‘


An EDS retrofit low voltage air circuit breaker replacing the Ottermill type OMA24 bus-section.


It was necessary to undertake tests to ensure that both transformers were in phase


device which affords much improved functionality. It allows enhanced grading with upstream and downstream protection devices, along with remote closing, opening functionality, and metering facilities, which can be incorporated into the Trust’s building management scheme. The project at John Radcliffe Hospital


involved the replacement of 14 low voltage breakers, as follows: n Four Ottermill OMA 12 50 kA, 1250 A, incoming ACBs.


n Two Ottermill OMA 12 50 kA, 1250 A, Bus coupler ACBs.


n Five Ottermill OMA 25 50 kA, 2500 A, incoming ACBs.


n Four Ottermill OMA 25 50 kA, 2500 A bus coupler ACBs.


Installation considerations As with undertaking any work on an electrical distribution system, of paramount importance is health and safety. Guidance for electrical compliance in the NHS is the HTM 06-02: Electrical safety guidance for low voltage systems.


Of equal importance when undertaking this work on the John Radcliffe Hospital distribution system was that, where possible, we should maintain the N+1 requirements as set out in Health Technical Memorandum 06-01: Electrical services supply and distribution (2017 edition).


As the project involved the


replacement of incomers and associated bus couplers, in theory both transformers being of the same phase rotation would allow the bus coupler to be closed before the incomer is opened. The John Radcliffe Hospital distribution network was operated with both incomers closed and the bus coupler open. This has been the case for many years. In order to utilise this arrangement, it was necessary to undertake tests to ensure that both transformers were in phase. Having undertaken testing and proven that the transformers associated with each switchboard were in phase, it was now clear that the system’s N+1 status could be maintained throughout the installation work, thereby maintaining continuity of supplies to all parts of the hospital – to the extent that very few, if any, hospital staff were even aware of the major work being undertaken on the electrical distribution system. Thanks to Mark Martin and his team, all Permits to Work and Sanctions to Test were issued promptly and very professionally,


Page 1  |  Page 2  |  Page 3  |  Page 4  |  Page 5  |  Page 6  |  Page 7  |  Page 8  |  Page 9  |  Page 10  |  Page 11  |  Page 12  |  Page 13  |  Page 14  |  Page 15  |  Page 16  |  Page 17  |  Page 18  |  Page 19  |  Page 20  |  Page 21  |  Page 22  |  Page 23  |  Page 24  |  Page 25  |  Page 26  |  Page 27  |  Page 28  |  Page 29  |  Page 30  |  Page 31  |  Page 32  |  Page 33  |  Page 34  |  Page 35  |  Page 36  |  Page 37  |  Page 38  |  Page 39  |  Page 40  |  Page 41  |  Page 42  |  Page 43  |  Page 44  |  Page 45  |  Page 46  |  Page 47  |  Page 48  |  Page 49  |  Page 50  |  Page 51  |  Page 52  |  Page 53  |  Page 54  |  Page 55  |  Page 56  |  Page 57  |  Page 58  |  Page 59  |  Page 60  |  Page 61  |  Page 62  |  Page 63  |  Page 64  |  Page 65  |  Page 66  |  Page 67  |  Page 68