Modern Mining: Featured News

With the increasing demand for modular plants and removable mining equipment, Boksburg-based MCA Projects, part of the MCA Group, has seen a rising demand for modular removable mobile or modular substations. In this article, Brian Teeling, who runs MCA Projects, looks at the pros and cons of the various mobile substation options.

Mobile substations can be categorised or identified in three different ways – there is the standard containerised substation, the E-House and the modular substation.

A typical E-House. These are generally fully custom built and of prefabricated construction.

The containerised substation, probably the most popular version of the mobile substation, typically consists of a standard 12 or 6 m shipping container that has either been used once (‘a once used’ is the term that normally describes a brand new shipping container) or is a second-hand shipping container that has been customised to suit the specific requirement of an electrical substation.

Standard containerised substations generally maintain the structural framework of the original container with modifications to mainly the interior floor, walls, ceiling and doors. With minimal steel fabrication required and the convenient sizing of this option, the standard containerised substation is by far the most cost-effective option as it requires the least amount of labour intensive fabrication and is particularly easy to transport in comparison to an E-House or a modular substation.

An E-House (‘Electrical House’) is typically a fully custom-built, prefabricated construction that is designed to suit a specific application and house whatever equipment is required. E-Houses come in various shapes and sizes and can vary depending on the application. Some look like normal prefabricated buildings while others form part of a mobile machine, for example on a stacker or a reclaimer.

E-Houses are fully customised and particularly expensive due to labour-intensive steel fabrication. They can also be costly to transport and often need to be moved via abnormal load trucks and placed on special vessels for sea freighting, which takes time and costs money. When it comes to E-Houses, the end-user would be advised to consider whether this is the correct solution, given the costs of logistics and erection.

The modular substation is a much larger substation that may consist of two or more containerised substation sections or E-House sections which have been joined together to create a much larger substation. These are ultimately used where time constraints are a major factor or where the conditions on site are too extreme for civil works. These units are typically constructed in a convenient location, tested and cold commissioned, broken up into multiple sections and then re-assembled on site.

A typical example of a modular substation could be a 12 m and a 6 m container that are placed in line with each other having interleading doors or, alternatively, are joined completely on site, with a bus-trunking joining the busbars of two sections of an MV or LV board – this is a relatively cost effective way of getting a board that is too big for a 12 m container into one complete substation. There are many different modular substations and versions but, since they are all transported in modules or sections, we would consider them to be ‘modular substations’.

There are several factors to consider when choosing a mobile substation for an application.

Safety should always be the most important consideration when it comes to the design and selection of a mobile substation, as it is an area of fatal risk if the engineering and design does not address safety considerations adequately.

To reduce the risk of fire, one needs to ensure that the standard wooden floors that come with the container as a standard are removed and replaced with metal clad flooring. Wooden floors are a severe fire risk, as even a small electrical fault can generate massive amounts of heat which could potentially set the entire container alight, compromising the entire operation and capital investment. As a minimum, a simple fire detection system should be installed that can detect smoke within the substation. It is extremely important to shut down any air conditioning or HVAC systems in the event of a fire, as these will fuel the fire to the extent that the entire substation could burn down in a matter of minutes.

The risk posed by arc flash and high fault currents should also be considered. Arc flash is one of the hot topics in industry and has recently been added as a consideration to the Mine Health and Safety Act in South Africa. The Act now calls for the employer to consider the risk and potential incident energy that could be emitted by a potential arc flash and the potential danger therefrom.

With that being said, the most important question to ask is, “what happens if things go bang”? It is critical that the electrical engineering team and mobile substation manufacturer have the answers to this very important question. My advice is to only make use of fully type-tested equipment which has been tested in accordance with the latest SANS/IEC standards. In addition, the installation must be carried out within the guidelines provided in the OEM manuals.

The installation of fully type-tested equipment ensures that – in the event of an arc flash incident – the potentially fatal hot metallic gases and excess pressure are diverted away from personnel and equipment and out of the mobile substation in a controlled manner, thus ensuring a safe space for both people and equipment.

In respect of the economics of a mobile substation installation, one needs to aim for a careful balance between cost and functionality. Careful evaluation of equipment, availability and application all need to be considered when executing a project. It is important to shop around and look at different manufacturers and technologies in the market and make appropriate choices based on the demands of the project. It is very important to not only consider the cost of the substation itself but also the civil and transport costs associated with implementing the design.

Finally, choosing the correct air conditioning, HVAC or pressurisation units is critical to successful operation and maintenance of mobile substations. These are much better conductors of heat than brick buildings and failure of AC or HVAC systems could result in equipment failing within a matter of hours.

It is of utmost importane that these units are sized in accordance with the ambient temperature and humidity on site. Consideration must also be given to the size of the substation as well as the heat dissipation and the power losses of the equipment within the substation. It is always best to seek the advice and expertise of a reputable manufacturer of mobile substations and ensure that the units are sized correctly and sourced from a reputable supplier.

Contact Modern Mining

Title: Editor
Name: Arthur Tassell
Email: mining@crown.co.za
Phone: +27 11 622-4770
Fax: +27 11 615-6108

Title: Advertising Manager
Name: Bennie Venter
Email: benniev@crown.co.za
Phone: +27 11 622-4770
Fax: +27 11 615-6108

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