Mobile substations incorporating HV GIS, WG B3.4

In recent years several utilities have reported on the use of ‘mobile’ substations employing a high level of off-site construction. There is a growing interest in such ‘build off-site’ solutions as transmission and distribution owners come under pressure to respond rapidly to changing user demands. The ability to respond to these demands is one element in delivering smarter grids for the 21st Century.

The early adopters of mobile substation technology have gained valuable experience regarding the design, testing, implementation and use of mobile substations.  WG B3.41 was established to undertake this task and has now produced Technical Brochure 907.  The Australian member on the WG was Jose Lopez-Roldan who produced this article.

In some circumstances, depending on the application, it may not be appropriate for mobile substations to fully comply with conventional standards regarding, for example, foundations, environmental conditions or testing requirements.

The scope of the brochure is:

• Drivers for deployment of mobile substations
• Benefits of using mobile substations.
• Experience of implementation and operation, including relevant case studies
• Applicability of existing standards
• Guidelines for specification and design

The WG established 3 categories of mobile substations:

1. a) Type A mobile substation: “short term emergency type unit” typically used for:

• Unplanned deployment to replace failed equipment, bays or the complete substation
• Planned deployment to support maintenance works or to provide short time network enhancement.

1. b) Type B mobile substation: “intermediate type unit” typically used for:

• Unplanned deployment to replace failed equipment, bays or substations (longer deployment time than emergency type)
• Planned deployment to support infrastructure works or to provide network enhancement for a longer period of time.

1. c) Type C mobile substations: “semi-stationary type unit” typically used for:

• Planned deployment as an alternative to a conventional substation where resources (e.g. skilled labour) are not readily available or costs are high
• Planned deployment as an alternative to a conventional substation when site works are difficult or impossible (eg offshore substation).

Figure 1 shows an example of the three types of mobile substations.

Figure 1 Examples of mobile substations type A, B and C

In Australia, an example of the implementation of mobile substation A, is the NOMAD 66-33kV/22-11 kV developed by Ergon in Queensland to be used in most single transformer substations up to 11.5 MVA.

Mobile substations are very adaptable to cover different requirements for different applications users may have. This flexibility is also related to risks when transporting, installing, and testing mobile substations on site. This risk situation needs to be understood before energizing the mobile substation. An increased risk appetite can be acceptable in emergency situations where power needs to get restored quickly and time for intensive on-site testing is not available.

In addition to the risk evaluation, it is important to determine the objective of the use of the mobile substation. A clear understanding of the expected outcome of operating the mobile substation will streamline preparation and mobilization aspects such as choosing the correct mobile substation type, transport options, installation, safety, risks, and on-site testing considerations.

Existing technical standards have been reviewed and considered as fit for purpose. There is no recommendation for adjusting or upgrading these standards for the use of mobile substations.

Further details on the recommendations of the Working Group as well as a detailed overview of case studies from a variety of users are discussed in the CIGRE Technical Brochure 907.

The TB is free for members and 200 euros for non-members