A 'DANGER' sign on a grey locker.

Why Should You Choose A Package Substation?

A package substation is installed to supply power to large facilities, such as tenant buildings, office blocks, data centres and other campuses where a large amount of power is required to be distributed safely and efficiently.

Once appointed, AF Switchgear personnel will work collaboratively with their clients, electrical engineers, contractors, and program managers, from the design stage all the way through manufacturing, testing, installation, and then, finally, commissioning. This is so we can provide a bespoke solution for each individual site and customer.

What Is The Main Reason To Install A Package Substation?

The main reason clients want to install package substations is to bring high-voltage electricity (typically 11kV) into a building and then to transform the voltage to around 400VAC, which enables power to be distributed.

A package substation usually consists of an RMU (Ring Main Unit) or a HV switch (High-Voltage switch), cast resin transformer, transformer housing, high-power copper or aluminium busbar which is directly connected to a main LV Switchboard.

Infographic detailing how power distribution works: DNO, Transformer, LV Switchboard, Power Distributed To A Building.

The main type of transformer (TX) that AF Switchgear supplies is one made from cast resin, which we buy from companies like Legrand, SGB, or Schneider Electric. 

Cast resin transformers (also known as dry-type transformers) can be copper or aluminium wound. Copper is a superior conductor to aluminium because the TX itself can be manufactured to a smaller size compared to its equivalent aluminium counterpart; however, aluminium is slightly more cost effective due to the material cost itself.

A cast resin transformer is typically housed in a purpose built steel housing (also fabricated by AF Switchgear) that has built-in vents to help naturally keep it cool by dissipating the heat produced by the transformer. 

If a higher power output is required from the TX or more ventilation is required on hotter days, then a forced ventilation system can be installed by the way of cylindrical fans, which forces cooler air up underneath the TX core and up across the cooling fins. The fans can be controlled via a thermostat and can be a useful way to keep the TX cool when ambient temperatures start to rise or when the TX is being loaded up with a high power demand, i.e., at peak usage times.

The maximum transformer size that can be used at low-voltage is around 4MVA. A transformer of this size could enable a current draw of up to 6300 Amps maximum per phase. This is especially important when considering short circuit withstand levels where a maximum of 100kA Icw is desired. AF Switchgear are manufacturers of switchboards that are type tested up to 100kA Icw.

What Are The Differences Between A Cast Resin Transformer And An Oil-Filled Transformer?

The difference between a cast resin transformer and an oil-filled transformer (sometimes called a Midel Filled Transformer) is in its construction. A cast resin transformer is cooled by air only and an oil filled is cooled by a mineral oil and air. The decision on whether to select a cast resin transformer or an oil-filled transformer does depend on each site as power requirements and locations vary.

For example, if there is sufficient space in an indoor environment, such as an office block basement, large tenant building, commercial property, or a data centre then a cast resin transformer is the perfect solution. On the other hand, an oil-filled transformer is ideal for outside use when space inside is especially restricted.

Cast Resin Transformers

An advantage of using a cast resin transformer is that you can directly couple the transformer to the LV switchgear via copper or aluminium bus bars. When coupled together the system is called a ‘package substation’. 

Being able to connect the transformer and switchgear this way helps to save installation time on site and money. Additionally, the package substation (the transformer and LV Switchgear) can be tested under factory conditions together once assembled in a controlled environment. 

Before a package substation is tested at the factory, the TX can be tested under load at the transformer factory, which can be witnessed for a fee. Occasionally, AF Switchgear will send a fabricated steel transformer housing that matches the specification requested by the engineer to the TX factory, so the testing can be simulated as if it was an ‘on site’ transformer. 

Cast resin transformer housings are manufactured by AF Switchgear at our fabrications plant, AF Fabrications. The housings are made out of cold-rolled CR4 non-ageing steel and can be painted any colour from the RAL colour system. 

The housings are always vented and can be lockable for safety and security reasons. Locks are usually the Castell Key type which corresponds with the switchgear coupled to the transformer. Also it is usually requested that the TX manufactures own identity label is fixed to the housing which details the technical ratings of the transformer and who it is manufactured by.

Oil-filled Transformers 

An oil-filled transformer is not dissimilar to that of a cast resin transformer (dry-type transformer) in terms of converting high-voltage to low-voltage electricity. However, they are built very differently.

The oil in oil-transformers is used to cool the transformer whilst in operation. There is a small risk of oil spillages over time, which is why oil filled TXs tend to be installed outdoors.

Oil-filled transformers (also known as oil-immersed transformers) are usually mounted in a steel oil tank or a bunded area which would contain the oil in event of a leak. Large power cabling will need to be installed to connect the transformer to the LV switchgear either by the way of a trench or a significant cable containment system. 

One advantage of oil-filled transformers is that they can be installed outdoors if needed due to their higher IP rating and do not require forced ventilation.

How Are Package Substations Installed?

A site survey will need to be carried out to check the accessibility of the building or the area where the package substation will be located. The team will check for steps, goods lifts access including the amount of weight they can hold, the size of the corridors if on route, doorway dimensions  as well as other aspects of the site that may interfere with the installation of the substation.

Package substations supplied by AF Switchgear are individually designed and built in the factory, according to the needs of the customer. Each build varies from site to site, in terms of size, switching arrangements and specification. The specification is usually determined by an electrical engineer or consultant. 

Along with the appropriate electrical safety checks a Factory Acceptance Test (FAT) can be carried out for a fee to ensure correct functionality of the system. A test like this is usually witnessed by the client and the client’s representatives for independent analysis.

After testing, the substation is taken apart into sections and wrapped. All components will be delivered to the site by either a Hiab lorry or a flatbed. A specialised installation team will wheel the transformer on rollers to the area where it is to be installed via the entry routes established at the site survey. 

Occasionally, a crane will need to be deployed to lift the equipment if a Hiab lorry is not suitable for the site.

Once the transformer is in place, the team will bolt the transformer to the switchgear and bolt the switchgear sections together before connecting the cables and building the housing around the transformer. 

Commissioning of the system is always carried out by AF Switchgear personnel to ensure the safe operation of the system and to validate the warranty. 

If you are in need of a package substation at your facility, then contact us today and we would be happy to assist.

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