60MVA 132/11kV Contestable Connection Hemel Hempstead


JSM was awarded the contract to provide a 60MVA 132KV Connection a new Data Centre in Hemel Hempstead.




36 Months

Date Completed

June 2023

As part of the contestable works JSM provided full power system design & reporting, full civils design of the 132kV / 11kV substation inclusive of construction of a dedicated 11kV substation building, 132kV Dual transformer bund area and iDNO adoptable 132kV Switchgear compound. 

JSM also installed  and jointed 6.5km of dual circuit 132kV cables  along with 1.6km of 33kV dual circuit cables as part of DNO network reinforcement. In addition, in order to provide a temporary 11kV power supply to the customer, JSM installed and jointed 1.6km of 11kV dual circuit cables while the 132kV substation was constructed and cable works completed. 

Delivery and Approach

The delivery of the project was undertaken in separate phases with the 11kV building & cable installation being completed in July 2021 to provide temporary 11kV power to the customer to meet with their construction and commissioning requirements. 

Following successful energisation of the 11kV network, the 132kV bunded transformer compound, 132kV iDNO adoptable switchgear compound & 6.5km 132kV cable route was constructed to meet the DNO’s connection programme and energisation dates. 

This approach has meant that JSM have been flexible with project planning and construction to enable the customer to complete their commissioning and partial handover before the full 132kV load was available and prevent delays to the customers energisation requirements. 

The Challenges & Solutions 

There have been substantial challenges on each phase of the project. The customers commissioning requirements meant that full construction was not possible in the timeframes and JSM arranged a temporary 11kV ‘Bootstrap’ connection from a nearby substation to provide power to the customer’s 11kV substation. 

This requirement has resulted in having to stagger the construction works with initial focus being on the delivery of a live 11kV substation within an active construction site. Once the 11kV substation building and supplies were installed and energised, JSM achieved sectional completion of the project and were able to commence the construction of the dual bunded 132kV compound, installation of the dual 132kV / 11kV transformers and substantial 9.7M Durasteel blast wall. 

132kV GIS switchgear from Hitachi in Italy has also been installed on this project. This was the 2nd project on which JSM utilised PASS M0H switchgear during which JSM worked closely with the Hitachi factory team along with their installation & commissioning services teams to ensure the unit had all the necessary Sf6 handling work undertaken by suitable authorised operatives, some of which were flown in from mainland Europe to assist with completion of the project. 

 JSM are proud to announce that during May 2023, the connection of both 132kV cable circuits undertaken from the DNO owned 132kV Tower lines. This allowed full energisation of the iDNO adoptable GIS PASS M0H Switchgear and subsequent energisation of both customer owned 132kV / 11kV Grid transformers and full 11kV ring energisations. JSM have now achieved full practical completion of the project  and handed over to the iDNO and client.