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Case Studies

Guernsey Electricity

  • Supply of 38 retrofit circuit breakers – 11kV, 25kA (400-1250A)
  • Upgrade of 4 x double busbar 400A panels to 1250A rating
  • Conversion of 1600A oil circuit breaker to 2000A double busbar switchgear earth truck

"The reliability and future proofing of this board is of paramount importance and crucial to our electricity network infrastructure. Switchgear Support Ltd has played a significant and important role in this. Guernsey Electricity Limited have developed a good working relationship with Switchgear Support since their inauguration and our thanks go to them for being able to meet our requirements"

Sean McCracken, Electrical Maintenance Engineer, Guernsey Electricity
Guernsey Electricity Limited is a limited liability company wholly owned by the States of Guernsey and the Company is the sole provider of electrical energy to the island of Guernsey.  Guernsey Electricity has been providing electricity to the island for over one hundred years.  Until 2000 all electricity was generated on-island, but since then the completion of a cable link to France, via Jersey, has given the opportunity to import low carbon electricity from the European grid.

But, whether importing from the European grid or generating on-island the Power Station, Brush Switchgear VTD (double busbar) switchboard, forms the backbone of the islands 11kV network. 

Retrofit oil to vacuum Switchgear

At the main power station at Vale, Northside is installed a very unique switchboard.  Starting life as  Brush Switchgear single busbar, oil based (ocb) type VSI panels, the switchgear was modified to become the type VTD double busbar switchgear in the late 1960’s – a massive undertaking by Brush Switchgear at the time.  Over the ensuing 40 years, switchgear extension panels have been added, with the switchboard now comprising 52 oil free panels.

Approximately twelve years ago, Guernsey Electricity embarked on a phased programme of retrofitting this primary double busbar switchboard, recognising that this type of switchgear, with its cast resin bushings throughout, was in immaculate condition and the only cause for future concern was the oil circuit breakers – maintenance considerations, availability of spares, expertise/operator familiarity ongoing reliability etc.

In 2010, Switchgear Support Ltd were requested to supply the final four vcb’s to complete the double busbar retrofit programme. 
(Image No.2: Part section of 52 panel Brush Switchgear type VTD switchgear [double busbar])

In addition, following inspection of the remaining 11kV substations utilising Brush Switchgear ocb’s, we supplied an additional thirty four 11kV, 25kA vcb’s to enable Guernsey Electricity to upgrade all of their remaining Brush Switchgear type VSI ranges from oil to vacuum.

Circuit upgrades from 400A – 1250A

Over forty years of service, the network requirements are bound to change, thus creating possible constraints with the existing double busbar switchgear.   Guernsey Electricity approached Switchgear Support Ltd to assist with the conversion of four of its double busbar 400A rated panels, which needed to be converted to a 1250A rating (maximum rating for the switchgear frame size).
Switchgear Support Ltd were only too happy to assist and provided the following original design components to maintain the certified rating of the original switchgear:
  • Retrofit 1250A vacuum circuit breakers
  • New primary bushings (busbar, feeder, CT, cable box)
  • New cable box
  • New primary copper connections
  • Addition of new cast resin VT’s for the new protection/metering duties

Switchgear Support Ltd were able to provide all of the materials and technical support to allow Guernsey Electricity engineering staff to undertake the modification programme themselves.

OCB conversion to earthing truck

Due to increasing operational demands, Guernsey Electricity realised that they had no earthing trucks for the 1600A circuits of the Brush Switchgear type VTD equipment.

Following the phased retrofit of the 1600/2000A circuits over the previous years, Guernsey Electricity had surplus equivalent rated oil circuit breakers. Switchgear Support Ltd were approached to see whether they could convert a 1600A ocb into an earthing truck, certified for such duties. 

(Image No.3: Original 1600A ocb)

Following an initial feasibility study by Switchgear Support Ltd that proved this could be achieved, we took receipt of the 1600A ocb into our workshops and modified the ocb to a fully certified 20kA (50kA peak) Earthing ocb by modifying the ocb internals, bushings and earthing connections, ocb top plate to accommodate earthing (internal connections brought through tank), disable the shunt trip assembly and removal of the internal butt contact assembly.

(Image No.4: Converted 1600A Earthing Truck)

“Over the years we have formed a very close relationship with Guernsey Electricity and were only too pleased to assist in resolving the requirements of our customer – from the simple supply of retrofit vacuum circuit breakers to the more specialist requirement of the ocb-earth truck conversion, with Switchgear Support Ltd probably being the only company in the world capable of this modification, ensuring that the original earthing truck design was not compromised”

Dave Johnson, Director of Switchgear Support Ltd


Photos courtesy of Guernsey Electricity