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While the manufacturer may be more concerned with keeping production costs low, the end user will be more interested in the usability and functionality of the final product.
For many industries, the product development process follows four key steps: concept initialisation, research and development, design prototyping (including type testing) and finally full-scale production. During the research stage, it’s vital that the correct questions are asked to ensure the product is fit for purpose. When designing an enclosure for electrical equipment, this research is usually undertaken when the customer provides an initial specification. The specification writer may not be aware of all criteria that impact on the enclosure design, therefore it is our responsibility to ask those key questions to establish a comprehensive specification.
Function of the equipment to be protected
Whether the enclosure is housing control equipment or power components such as resistors, inductors etc. consideration must be given to the by-products of the equipment, predominantly we are talking about heat losses. This is especially true in the case of power resistors, which convert electrical energy to heat. Cressall is a specialist at ensuring sufficient ventilation is provided in the enclosure design.
Other considerations are; equipment operating voltage and therefore the air gap clearances required, component layout to practical build and air circulation, vibration and expansion/contraction over time.
One of the most important considerations when designing an enclosure is the environment that it will be operating in. At Cressall, we design power resistors for a range of industries including oil and gas, renewable energy, marine and offshore, electricity generation, transmission and distribution. Each one of these industries presents slightly different working conditions for the equipment.
Selecting the correct material for the enclosure is an important consideration. For many of Cressall’s own enclosures, the preferred material is 316L stainless steel, which has a good long-term corrosion resistance. Cressall also fabricates enclosures from other grades of stainless steel such as 304 as well as pre-galvanised steel and hot-dip galvanised steel.
In addition, further mechanical considerations exist depending on the installation location of the equipment such as wind loading, ice loading and seismic shock. Where these apply, Cressall uses tools such as CFD (Computational Fluid Dynamics) and FEA (Finite Element Analysis) to assess the proposed design for the geographical parameters, accelerating the design process.
Level of protection provided
While the material of the enclosure itself protects the majority of its contents, in environments such as marine vessels, ingress protection is vital in stopping dust, moisture and other contaminants from affecting the resistor. The BS EN 60529 standard provides quantified levels of protection for people from the equipment and the equipment itself from the outside environment. These levels are described by an IP (ingress protection) code number designating protection from liquids and solid objects. Adherence to the relevant ingress protection level will ensure safe operation in service.
However, this is where the equipment manufacturer can assist the specifying customer who may not understand the full impact placing too high a requirement of the IP level can be for the enclosure manufacturer. A higher level literally places tighter restrictions on openings in the enclosure panel work which can restrict ventilation. Therefore, with a thorough understanding of the equipment the designer can propose a suitable level to meet all requirements.
Accessibility of the equipment
The enclosure must allow suitable access for both installation and in-service operation and maintenance. Often some electrical equipment is installed and commissioned with very little access to the internals of the enclosure being required thereafter.
In many other instances access is regularly required. The enclosure cost can be optimised to suit the frequency and duration of requirements to access the equipment housed by the enclosure, for example it can have simple bolted covers or alternatively more expensive hinged and lockable doors.
Fabrication, assembly and installation
Many manufacturers design and build products at a central location from which the assembled equipment is shipped to the end user, often exporting overseas. Enclosures for electrical equipment can become large pieces of equipment, especially in high voltage applications where the air gap clearances are high. The designer must carefully consider how the enclosure will be fabricated, assembled, shipped and installed to ensure a cost effective solution is delivered. The key interface points such as the mounting fixings, incoming electrical connections also need to be considered to suit the site layout. Once the enclosure has arrived at its destination, it then needs to be installed. This could be at ground level or at an elevated position. Consideration needs to be given to how the enclosure will be lifted into position, for example lifting eyes, lifting beams or forklift channels.
The path to design success
The design and build of an enclosure is not a one-way conversation. As is so often the case, communication in the design phase is critical to future success. While the chosen manufacturer may have the experience to make recommendations and assumptions, the client must also input into the design process making clear the site information and operational conditions. Communication between all relevant parties coupled with a considered design approach will ensure the electrical enclosure design.
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