Dry-type transformer 10 kV: a reliable solution for distribution networks 

A 10 kV dry transformer is not just an alternative to an oil transformer. This is a technical solution that we have seen in work at housing and communal services substations in Kazan, in the workshops of machine-building enterprises near Yekaterinburg and in modernized distribution points in the north of the Krasnoyarsk Territory. Where the use of oil is prohibited, where fire safety is important, where there is no room for regular maintenance, a 10 kV dry transformer becomes the only logical choice.

Why 10 kV is the “breaking point” for distribution networks

Voltage 10 kV is not a random number. This is the operating level at which transmission ends and distribution begins: from the RP to the TP, from the TP to the consumer. This is where conflicts between reliability and operational safety most often arise. Oil-filled transformers require sealed rooms, fire suppression systems, and constant monitoring of oil levels and moisture. Dry - work in the open air, in basements, within the walls of shopping centers. We tested them in conditions where temperatures ranged from −45 °C to +40 °C and relative humidity reached 98%. None of the samples failed when tested at 35 kV for one minute - as required by GOST R 52719-2023.

Behind the dryness: a design that works without compromise

A 10 kV dry transformer is not just windings without oil. This is a three-level protection system:

• Windings made of copper busbar or aluminum tape, filled with epoxy resin with a high thermal conductivity coefficient;

• Active part in a vacuum chamber, where all air inclusions are removed - the main cause of partial discharges;

• Housing made of galvanized steel or AISI 304 stainless steel, with IP54 or IP65 - protection from dust, splashes and even direct rain.

We measured the heating of the windings at 120% load: after 2 hours the temperature did not exceed 115 °C - within the permissible limits for insulation class F. This means a service life reserve of more than 30 years, subject to compliance with the operating conditions.

Where it “doesn’t survive” - and why it’s important to know

The 10 kV dry transformer is not universal. He is weak in two cases - and this is a fact, not a flaw. Firstly, with frequent short circuits with currents above 25 kA: its mechanical resistance is lower than that of its oil counterpart. Secondly, with prolonged overload above 150% for several hours, heat dissipation is limited. But in 92% of Russian distribution networks such conditions do not occur. Where they exist, we offer a hybrid solution: a dry transformer as the main one and an oil transformer as a reserve. This is what they did at the plant in Tula: they reduced the risk of fire by 100% and maintained emergency preparedness.

How to choose - without costly mistakes

In practice, clients often confuse the three parameters. And they pay for it twice:

• Rated power (kVA)- not the same as active power (kW). Consider the cos φ of the load: at 0.8 - 1000 kVA it gives only 800 kW of useful power.

• Cooling method: AN (natural) or AF (forced). When installed in a closed panel - only AF with thermal sensors and automatic fan switching.

• Accuracy class of measuring windings: if the transformer is used for metering, class 0.2S is needed, not 0.5.

Wenzhou Qiaonasen Electrical Equipment Co., Ltd. designs a 10 kV dry-type transformer taking into account these nuances. Configurators, technical data sheets in Russian and connection diagrams for specific customer specifications are available on the qnasen.ru website - from Novosibirsk to Baku.

Reliability does not start with the certificate, but with the person who verifies it.

TR CU Certificate of Conformity is the required minimum. But real reliability is determined by how each stage is carried out: incoming inspection of the epoxy resin, measuring the dielectric loss tangent after pouring, testing for a 75 kV impulse voltage. At the production base in Wenzhou, each product undergoes 17 control operations - including a 48-hour load test. We don't just supply dry-type 10 kV transformer. We guarantee that it will work as specified in the passport - even if it is installed in an unheated distribution point in Yakutia.