Transpower Mobile Station 110kV/33-22-11kV (TPMS)




The Transpower Mobile Substation (TPMS) project involved design and construction of a 110kV mobile substation for use at limited capacity Transpower substations. Mitton ElectroNet undertook project management from conceptual design through to commissioning. ElectroNet undertook the construction project management and was ultimately responsible for the build of the TPMS which is currently the highest voltage, 110 kV/33-22-11 kV mobile substation in New Zealand.


$ 2.6M (Design, construction)

Key Dates

Commenced: July 2011
Completed: December 2013


This case study showcases an ability to innovate and collaborate to design and construct a fitout which was the first of its kind to be undertaken in the industry within New Zealand. The construction team faced unique and difficult challenges - to successfully mount a complete, fully operational substation on a mobile platform, capable of deploying easily from one site to another.

Throughout the project, both design and build teams were required to be innovative in their thinking to overcome multiple challenges from ‘seemingly’ simple tasks such as running an earth grid throughout the trailers to the more complex demands of voltage interlocking systems.

Innovation and Collaboration

The ability of MEL and ENS to collaborate and drive innovation was fundamental both to the success of the project; and overcome challenges faced. These include:

Challenge: a standard 110kV Hypact circuit breaker would not meet the physical dimensional safety requirements for transportation on a public road.
Solution: we worked with manufacturer and identified a collapsible type to meet the height restriction and shortened the stands and re-configured the mechanism boxes to meet the width restriction.

Challenge: 110kV bay on MS1 required a physical barrier to meet safety requirements during deployment in a substation and for security when on the road. However, the physical distances between the barrier and electrical equipment available for transport, do not meet the “minimum approach distances” required during deployment.
Solution: we worked with trailer manufacturer to develop a hydraulic aided fold out barrier that suits both transport and deployment requirements. A door is built into the barrier for access control and clear panels are installed at strategic locations for monitoring the interior from the outside.

Technical Complexity

The 18 MVA, fully self-contained unit was developed in conjunction with Transpower and a transport designer to produce a design which met all power system and safety requirements while still being fully mobile. The result is a complete and independent Transpower substation, which is fully transportable on New Zealand’s roads, and able to be moved to 16 identified substation sites on an ‘as required’ basis.

The successful design and construction of the TPMS enables a grid owner to divert power around a Transpower substation to maintain supply during planned outages and ensure reliable supply to the end customer. Many aspects of the design and construction of the TPMS were totally new. This level of innovation was achieved through a collaborative approach between Mitton ElectroNet and ElectroNet. This included:

  • MEL had previous expertise in building mobile substations and was engaged by Transpower to perform the lead design. The starting point was taking the initial design and developing the discussion with Transpower to achieve a feasible design that met Transpower’s requirements.
  • MEL prepared a Preliminary Design Report for sign off, and then prepared the detailed design. MEL focused on the primary, power and detailed layout design and was also responsible for checking interface issues and keeping a combined drawing register. The nature of the project meant that a collaborative partnership was developed to deliver the complete solution to Transpower and included ElectroNet Services, TRT and BECA among some of the specialist companies involved.

As the project was large and complex, specialised industry skills were required to ensure an effective outcome for all parties. Robust project management skills and oversight practises were used to manage relationships, and project related activities to achieve a successful outcome for Transpower.

Construction of the TPMS was undertaken at the Stoke Substation. Both trailers (MS1 & MS2) were moved from TRT in Hamilton to Stoke where the major electrical fit out was undertaken. This was the first fitout of this nature undertaken in the industry in New Zealand and the construction team were faced with some unique and difficult challenges. Throughout the project the team was required to be innovative in their thinking to overcome these challenges.

The project required significant co-ordination between a number of different construction subcontractors and design teams and the early engagement of ENS and Mitton ensured that a number of construction issues were overcome at the early stages of design and build.


This project was awarded Transpower’s 2014 STAR Award for Best Performance Health & Safety – Team. Excellent communication between all parties across the planning, design and construction phases was key to full delivery against all client requirements. In addition to this, early engagement of the build contractors ensured potential issues were overcome before the build started. Simple thin cableways that allowed cables to be run the length of the trailer may have caused considerable construction issues if the construction contractor had not been engaged throughout the design. Considerable time was spent in meeting and communicating with all stakeholders to firm up the requirements. Communication was key to keep everybody up to date and informed of any issues that arose during the project and the design interfaces were managed. The project did take longer than initially planned primarily due to changes in Transpower’s requirements and an incident at a substation (unrelated to this project) that put the mobile sub project on hold. The original estimated budget was $5.8 million with the final cost being $6.7 million. The project changed considerably from the original scope the main changes to scope included changes to the transformer, addition of SCADA satellite and cell phone communications system, addition of revenue metering and changes to the timeframes. Having successfully completed the construction TPMS was commissioned successfully at the Murchison Substation and has gone on to other sites where it has been equally successful.