HV Switchgear - Transformer Separation

Are you thinking of the transformer that takes the HV down to LV, or the transformer that comes in from transmission down to HV for onward distribution ? There are normally things other than switch gear to consider (fuses, earth fault detection and breaking, zero sequence trips..  ) that also need a home. In the4 case of HV to LV,  terms of initial enclosure generally such things are not shared with the transformer which is in its own 'tank', but a single outer building or cage, yes very much so.

Very high voltages are often left outside. 

Mike.

Thank you for your reply, Mike. This question concerns a DNO supply HV transformer sharing an enclosure with its own control switchgear. The transformer is in an inner room, while the switchgear is in an outer room with direct ventilation. The designer plans to combine both into a single room to ensure good ventilation for the transformer. Not sure why the transformer is site where it is!

They do "package substations" where all the control/protection gear is practically bolted to the transformer - so I doubt there's any blanket ban on the two being close together. Things might be different if incorporated into a building though.

A transformer in an "inner" room sounds decidedly dodgy to me - under some rare conditions things can go bang with some considerable force - so much so that dedicated substation buildings are sometimes designed so the roof can be lifted off by the blast rather than attempt to contain things. When inside other buildings I've only seen them in an outer position with large louvres on large doors (and I suspect the doors themselves might be sacrificial too).

   - Andy.

The starting point is what type of transformer are we discussing - fluid filled, or dry type / cast resin? And if it is fluid filled, why type of dielectric fluid - mineral oil, an ester fluids, or another less flammable insulating fluid?

The suitability of locating high-voltage switchgear and the associated transformer within the same enclosure depends on the system design, equipment type, voltage level, installation environment, and the applicable regulations.

Your concern regarding fire separation is valid, particularly for oil-filled transformers, where fire risk, oil containment, ventilation, and arc-flash considerations must be carefully addressed. In many installations, transformers are separated from switchgear rooms to reduce the risk of fire propagation and to improve operational safety. However, some modern packaged substations and integrated switchgear-transformer units are designed and tested for installation within a common enclosure, provided they meet the required fire, insulation, protection, and safety requirements.

Relevant standards to consider include:

• IEC 61936-1 – Power installations exceeding 1 kV AC: requirements for design, installation, and safety of high-voltage installations.
• IEC 62271 series – High-voltage switchgear and controlgear standards, including requirements for switchgear assemblies and enclosures.
• IEC 60076 series – Power transformers, covering transformer design and performance requirements.
• BS 6622 / BS 9999 (where applicable in the UK) – Fire safety considerations for electrical installations and building design.

The key factors are usually:

• Transformer type (oil-filled vs dry-type)
• Fire rating and construction of the enclosure
• Oil containment arrangements
• Ventilation and pressure relief provisions
• Separation distances and access requirements
• Manufacturer’s installation instructions and certification

Rather than a blanket prohibition, the decision should be based on a documented risk assessment and compliance with the relevant standards. For oil-filled transformers, physical separation is often the preferred approach unless the enclosure has been specifically designed and approved for combined installation.

It would be useful to know the transformer rating, voltage level, whether it is oil-filled or dry type, and the country/standard framework being applied, as the requirements can vary.

Thank you for your reply, Andy. You raised a good point regarding the package arrangements. Unfortunately, I don’t have the information necessary to know what is proposed. However, I completely agree that the siting is rather peculiar. Since we are at RIBA Stage 4, I have asked if we can swap the locations of the equipment with the switchgear, which would solve the problem.

Thank you for your reply, TurboGen. I received information this morning from the M&E design team stating that it is a "dry transformer." However, I am still not convinced about the choice of its location, as it is clear that cooling is an issue.

Thank you for your detailed response, Terry, and for providing the references to the standards; they are very helpful. This morning, I received information from the M&E design team indicating that the transformer is a "dry type." This is a UK commercial transport project, but I currently do not have any additional information, such as the precise voltage level.

Many thanks all for your support and valuable contributions. Your assistance is greatly appreciated and will undoubtedly aid me in gathering the pertinent information required to effectively assess and respond to the inquiry presented to me yesterday.

Thanks Again all!

Dry transformers may be open winding or resin encapsulated, and open transformers are often seen in warmer parts of the world, not so much here.

In the UK normally at least the HV primary windings are encapsulated and often the secondary too, so the winding is a solid kebab like cylinder of insulating material with terminals.
In the pics below the green one is  a WEG one in Brasil,  the red one is a similar offering from Bowers in Derby , both I think are designed to IEC 60076-11:   
Again in Europe normally these would be inside some sort of enclosure, imagine something rather like a ventilated sheet metal shed and certainly no exposed terminals in an areas where personnel had access, and certainly not where they have to go to operate switchgear. 
Some of the rest of the world is more liberal, but with good reason we are not (!)
More fully encapsulated are attractive if the air cleanliness or humidity is not well controlled but the power rating for a given size and weight is lower. Also any permanent building will need access for the thing to be positioned, so allow for either tele-handler forks or some sort of hoist.

 
     
Any controls or indicators go on the outside of the enclosure, although panels can be removed (as here to allow visual inspection, when non energised !)

As regards cooling, the transformer makers publish installation advice and also how to be regs compliant in different jurisdictions, and it would be worth asking for that as much of that as possible it is not already available - the ventilation illustration is from one such makers manual.

If it is a UK DNO, they will also have their preferred pre-approved models and house rules about installation, and may well refuse to connect something they do not recognise, or at least expect a delay while evidence is collected so again, check with them for documentation.

M