Engineering a mobile substation is not a simple exercise. It requires a clear understanding of the specific requirements not only from an electrical perspective but also from a road ordinance viewpoint of the country in which the solution will be deployed.
This is according to Coenraad Vrey, managing director of Zest Energy, who explains that the company’s interaction with various utilities including Eskom for more than ten years has keenly developed its understanding of the stringent design requirements on both electrical and mechanical components. As a result, Zest Energy is able to develop fit-for-purpose mobile substation solutions.
According to Vrey, the two most important components of a mobile substation are the high-tech transformer and the trailer, which must comply with road ordinance legislation in regard to weight and equipment dimensions. The effects of trailer deflection and movement on the integrity of the transformer are also important design considerations.
Since each country’s road ordinance specifications are different, mobile substations need to be designed in accordance with the relevant requirements of the country in which they are intended for use.
“Zest Energy utilises trailer designs with proven industry technology to assist with manoeuvrability. We make use of combination trailer configurations to better distribute the overall weight and to ensure that we do not exceed the axle weight limitations of the specific country,” says Vrey.
The heart of the mobile substation is the trailer itself. This comprises a gooseneck, articulated steerable axle system, air suspension, ABS braking system, trailer stabilisation legs and fold away type access platforms, which allows safe access to the secondary plant.
Essentially, a mobile substation should meet all or most of the attributes of a fixed substation, with the added benefit of mobility, which affords the customer the flexibility to move the unit to wherever it is needed.
Vrey explains that while the standard configuration of a high voltage substation is consistent, certain customers have specific requirements which are informed by their own reticulation requirements and specifications.
It is not difficult to adjust the design to conform to these requirements, but it is essential to have an understanding of these requirements up front.
“Mobile substations are custom engineered to ensure that they can be configured for individual applications and will seamlessly integrate into the existing electrical network,” he says.
The main idea is to facilitate the deployment of a mobile substation as quickly as possible, and these units therefore need to be engineered to ensure the highest level of mobility for transportation without the need for escort vehicles and special permits.
This means that the weight and the physical size must be taken into account, as well as the weight distribution of the substation components. Height is also a restriction, both from an installed space perspective as well as in terms of safe passage of the trailer under bridges and other structures during transport,” says Vrey.
Another factor that needs to be considered is that the components that make up the installation need to be able to withstand the impacts of being transported on road networks.
“When it comes to ensuring the optimum mobility of the substation, it is essential to take into consideration the forces applied to the equipment during transportation. This requires an in depth understanding of each of the elements and how these are affected, to minimise internal movement,” Vrey points out.
Electrical network considerations are critical and Zest Energy leverages WEG’s 20 years of experience in engineering transformer technology that allows for multi ratio primary and secondary voltage transformers.
This will permit customers to use the mobile substation in areas where different voltage reticulation networks are found, thus improving operation flexibility. “We also factored into the design the specifications of the utility with respect to electrical equipment.
Every utility has its own specifications for primary and secondary plant and Zest Energy strives to ensure that we offer equipment that is in line with these standard specifications” he adds.
Vrey cites the example of Eskom’s standard protection schemes, which were incorporated in the overall mobile substation solution.
Zest Energy ensured that all these specifications and standards were analysed as part of the overall design process, to ensure complete compliance with Eskom’s requirements.