Requirements for transformer substations (KTP) under the code

Author: Viacheslav Yurdyk, Quality Engineer at LK Energy Group.
Acceptance of equipment at the plant (quality control department) and technical supervision on electrical installation sites.

Short answer

The PUE (PUE — the Ukrainian electrical installation code) does not describe a «correct KTP» in a single list — it sets the conditions under which a substation must stand and be serviced. The main ones: the site and installation height, separate rooms for different voltage classes, the width of aisles for racking equipment out, a climatic version matched to actual conditions, and a temperature regime per the manufacturer's requirements.

The practical takeaway for the client is simple. A substation is not chosen by transformer rating alone. Before buying, three things are worth checking: whether there is a graded site of the required height for it, whether the aisle is wide enough to rack the transformer out for repair, and whether the climatic version matches what will be around it. A mistake in any of the three is corrected by construction work, not by replacing a cabinet.

KTP, ZTP, ShchTP, BKTP: what is what

«Transformer hut» is a living colloquial synonym, but documents and designs use different words. The Rules give the definitions directly, and here they are in our own words.

(пп. 4.2.5–4.2.7)

🔑 What is useful here in practice. In the Rules the word «KTP» denotes a method of supply — the product arrives assembled or ready for assembly. So when you compare a «KTP» from two suppliers, you are comparing not the type of equipment but the scope of supply: what exactly will arrive on site and how much still has to be done there.

And an RP is not a substation. A distribution point distributes but does not transform. Confusion here costs money: the specification says «KTP» while the diagram calls for an RP — or the other way round.

Where and how a substation must stand

In the open air [п. 4.2.69]: - on a graded site, at a height of not less than 0.2 m above finished ground level; - next to the cabinets there must be a maintenance area; - in areas subject to snow drifts, not less than 1.0 m; - the layout must allow convenient racking out and transport of transformers and of the withdrawable part of the cells.

For outdoor switchgear up to 1 kV the requirements follow the same logic [п. 4.1.37]: a graded site, a height of ≥ 0.2 m, and if snow drifts exceed 1 m the cabinets are placed on raised foundations.

🔑 The last line is the most expensive one. «Convenient racking out of the transformer» sounds like a trifle at the design stage and turns into dismantling the fence seven years later, when the transformer has to be removed. This is the requirement that is easier to meet once, on paper.

Inside a building [пп. 4.2.70–4.2.71]: - indoor switchgear and substations may be in separate buildings, in built-in and attached premises; - attaching to an existing building using its wall is permitted provided measures are taken against damage to the waterproofing of the joint caused by settlement of the extension; - for built-in and attached substations in residential and public buildings additional requirements apply — NPAOP 40.1-1.32 and DBN V.2.5-23; - switchgear of different voltage classes is placed in separate rooms — but this requirement does not apply to KTPs rated 35 kV and below; - switchgear up to 1 kV may be placed in the same room as switchgear above 1 kV if one organisation will operate them.

🔑 The exception for KTPs rated 35 kV and below is precisely the economic point of a packaged substation. That is why a KTP allows the HV and LV sides to be fitted into one enclosure where conventional indoor switchgear would require two rooms.

Aisles: how much space to leave

This is the most common reason for rework after installation.

Maintenance aisle of indoor switchgear [п. 4.2.80] — measured in the clear between planes drawn through the most protruding parts:

For indoor switchgear (KRU) with withdrawable parts and for KTPs the rule is different — it is measured from the withdrawable truck [п. 4.2.81]:

• single-row arrangement — the length of the largest truck including all protruding parts plus at least 0.6 m;
• double-row — the length of the largest truck plus at least 0.8 m;
• in all cases the aisle must be at least 1 m and not less than the truck dimension across the diagonal;
• local narrowing of the aisle opposite withdrawable trucks is prohibited.

🔑 How to use this before buying. Take the truck length from the questionnaire and add 0.6 or 0.8 m — that is the minimum room width for a row of cubicles. If the room already exists and is narrower, the issue is not with the supplier: either the layout has to change or building work is required.

Climatic version and thermal regime

The Rules put it briefly, but the requirement is strong [п. 4.1.37]:

• the climatic version of the switchgear must match the environmental conditions;
• the switchgear must have an appropriate degree of protection against contact with live parts and ingress of solid foreign objects and liquids;
• within the switchgear it is necessary to maintain the temperature regime for the installed equipment in accordance with the manufacturer's requirements.

It is on this third requirement that most sites fail — and it is the hardest one to see at the buying stage. Equipment is rated for a certain ambient air temperature: in our data sheets this is climatic version U1 with an upper operating temperature of +40 °C. If the transformer chamber stays significantly hotter in summer, the product is working outside the conditions it was designed for, and the question is not for the equipment manufacturer but for the ventilation.

🔴 A real example from our own measurements. At one site a pyrometer registered up to 88 °C on the surface of the equipment in the transformer chamber. A surface is cooler than what is inside, so the oil in the tank was hotter than this figure. By how much exactly a surface measurement does not show: for that a transformer is fitted with temperature signalling devices and thermometers, and the staff servicing it are required to monitor the temperature of the upper oil layers [п. 4.7 глави 4 розділу VII ПТЕЕС]. The limit for the upper oil layers with natural cooling is 95 °C [п. 4.12 глави 4 розділу VII]. So 88 °C on the surface is not «almost within limits» — it is a reason to reach for the built-in instruments. The cause was not the equipment: forced ventilation had been removed from the substation, as there was nothing to power it from.

More on operating standards — on the PTEES page.

Auxiliary supply: the thing remembered last

A substation consumes electricity itself: cubicle heating in winter, lighting for maintenance, ventilation, power for drives, automation and telemechanics, sockets for tools. The Rules explicitly require maintaining the temperature regime — and heating and ventilation must be powered from something too.

Technically these are two products that almost never make it into the client's first cost estimate:

• Auxiliary transformer (TVP): it powers the facility itself — control circuits, heating, lighting. The presence of an auxiliary transformer, incidentally, does not turn a distribution point into a substation: it feeds only auxiliary loads, not consumers;
• Auxiliary distribution board (ShchSN): a separate metered circuit for everything listed above, usually with its own consumption meter.

🔑 Why this is not an option but part of the scope. Without a dedicated board, auxiliary loads get hung «wherever they fit» — and then it is impossible either to measure the substation's own consumption or to de-energise part of it for repair without stopping the facility. Whoever provides for an auxiliary board at the diagram stage does not rebuild the board on site.

Fire requirements: when a water main is not required

A provision that removes unnecessary cost from smaller facilities [п. 4.2.68]:

• a fire-fighting water main is required at substations with outdoor transformers of 110 and 150 kV with a unit rating of 63 MV·A and above, with transformers of 220 kV and above regardless of rating, and also at enclosed substations of 110 kV and above;
• at substations with outdoor transformers of 35 to 150 kV with a unit rating of less than 63 MV·A a fire-fighting water main and fire reservoirs are not provided.

So for a typical distribution substation of an industrial plant the Rules do not require a separate fire-fighting water main. Oil collection pits, however, must be of the closed type.

What is new in the 2026 edition for generation

Two provisions worth keeping in mind for anyone building a solar plant or installing a battery system:

1. Chapter 4.2 explicitly covers the main step-up substations of wind and solar power plants and the connection points of generating units of wind and solar plants to the internal network of those plants [п. 4.2.3]. In other words, the substation requirements are not «something for big power engineering» but apply directly to solar plant equipment.
2. Switchgear and low-voltage assemblies through which electricity storage or generation installations are connected must be marked with the sign «W026 — Warning: battery charging» to DSTU EN ISO 7010 [п. 4.1.37]. A detail that is easy to miss during manufacture and then has to be added on site.

Which documents must arrive with the substation

This is not a requirement of chapter 4.2 but a requirement placed on the owner by the PTEES — but this set can only be collected at the moment of delivery:

• the product data sheet and certificates;
• as-built single-line diagrams of primary and secondary connections;
• factory test reports;
• the operating manual.

The full list with clause references — on the PTEES page.

🔑 In practice. If the data sheet and the test report did not arrive with the substation, collecting them later is nearly impossible, while every inspection and every subsequent test will ask for them: the results of new measurements are compared precisely against the manufacturer's original data.

Frequently asked questions

We will price a substation for your site

LK Energy manufactures KTPs and switchgear for 0.4–35 kV at its own plant in Odesa. Send a single-line diagram or a completed questionnaire and we will select the configuration and design for your conditions.

This material is provided for information only and is neither an offer nor legal advice. We do not publish the full text of the Rules — only quotations with clause numbers; obtain the official text from the source indicated above.

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See also

• PUE:2026 — what changed and how to use it
• PTEES: key requirements for operation
• Earthing under the PUE
• Cable laying under the PUE
• Selecting a circuit breaker: rating, Icu, selectivity
• Climatic versions U1 and UHL
• Equipment test standards before commissioning