A medium voltage transformer usually sits quietly in a substation room or on a pole, far from the showroom floor, which is exactly why so many buyers choose it with less care than they give to the machinery it feeds. That single decision can cost a plant tens of thousands in energy losses, downtime and early replacement. This overview explains what a medium voltage transformer is, how it works, which types exist, which parameters actually drive the price, and how to buy a factory-direct unit without being taken advantage of.

What Is a medium voltage transformer?

A medium voltage transformer is a static electrical device that steps voltage up or down inside the medium voltage range, generally from 1 kV to 36 kV. In distribution work, the two dominant classes are the 10 kV class and the 35 kV class. The transformer takes the voltage delivered by the grid and converts it to the low voltage used by end equipment, commonly 400 V or 230 V, or works in reverse as a step-up unit in renewable energy collection systems.

Rated capacities typically span 30 kVA to 6300 kVA, with smaller units serving commercial buildings and larger units feeding industrial plants, mining operations and solar or wind farms. Because it operates continuously, even a small efficiency difference compounds over a service life of twenty years or more.

How a medium voltage transformer Works

Inside the tank or enclosure sit two windings wound around a laminated magnetic core. Alternating current in the primary winding creates a changing magnetic flux in the core, and that flux induces a voltage in the secondary winding. There are no moving parts, so reliability comes down to design margin, material quality and manufacturing discipline rather than mechanical wear.

Two loss categories matter. No-load loss, also called iron loss or core loss, is present whenever the transformer is energised, even with no load connected. Load loss, or copper loss, grows with current. The sum determines efficiency and temperature rise. This is why lower-loss designs such as the S13, S20 and S22 oil-immersed series and the SCB14 and SCB18 dry-type series cost more upfront but often pay for themselves within a few years of operation.

Main Types of medium voltage transformer

• Oil-immersed transformer. The core and windings are submerged in insulating oil that provides insulation and carries heat to the tank walls. Common series include S11, S13, S20 and S22, along with three-dimensional wound core designs. Oil-immersed units handle high capacity and harsh outdoor environments well.
• Dry-type transformer. No liquid is used. Insulation relies on cast resin or impregnated materials, which removes fire and leakage risk and makes these units suitable for indoor installation in hospitals, data centres, shopping malls and underground substations. Typical series are SCB10, SCB13, SCB14, SCB18 and SGB10.
• Amorphous alloy transformer. The core is made from amorphous metal rather than grain-oriented silicon steel, cutting no-load loss dramatically. SH15 and SCBH15 series are widely chosen where the transformer runs lightly loaded for long periods.
• Special-purpose units. Mining transformers, rectifier transformers, lightning arrester transformers, capacity-regulating transformers and load tap changing transformers are engineered for particular duty cycles and are usually custom designed.

Key Parameters Buyers Should Check Before Ordering

• Rated capacity in kVA and the expected load profile
• Voltage ratio and vector group, for example Dyn11 or Yyn0
• Impedance percentage, which affects short-circuit current and voltage regulation
• No-load loss and load loss against the applicable energy efficiency standard
• Cooling method, such as ONAN for oil-immersed units or AN/AF for dry-type
• Insulation level and temperature rise limits
• Tap changer type and tap range, plus whether off-circuit or on-load tap changing is required
• Enclosure rating, cable entry and dimensions for the available space

Where medium voltage transformers Are Used

Distribution networks, industrial production lines, water treatment plants, mines, tunnels, ports, charging infrastructure, and renewable energy projects all depend on them. Solar farms and wind projects use step-up units to raise inverter output to collection voltage, while process industries may require rectifier transformers to feed DC drives. Preassembled substations and compact substations package the transformer together with high and low voltage switchgear to shorten installation time on site.

Why Two Quotes for the Same Transformer Differ So Much

Price differences rarely come from thin air. The gap usually reflects copper versus aluminium windings, the grade and thickness of core steel, whether the core is stacked or wound, loss levels, tank steel thickness and anti-corrosion treatment, and the quality of bushings, gaskets and pressure relief devices. A cheaper quote often hides material substitution that only becomes visible after several years of heat cycling and oil leakage.

Buying directly from the manufacturer removes distributor margins. Runsheng Transformer Co., Ltd., for example, supplies oil-immersed units at factory-direct prices with manuals, inspection reports, test certificates and lifelong quality tracking, so the savings come from the supply chain rather than from cutting materials.

How to Select a Reliable manufacturer

• Confirm the product range covers your voltage class and capacity, from 30 kVA to 6300 kVA
• Ask for type test reports, routine test reports and material certificates
• Check compliance with national standards and IEC requirements
• Request references in your own industry
• Clarify warranty terms, spare parts availability and after-sales response time

Installation, Operation and Maintenance Essentials

Good installation protects the investment. Keep the unit well ventilated, maintain required clearances, ensure correct earthing, and verify oil level, silica gel condition and sealing before energising. During operation, monitor temperature, sound level, oil level and terminal connections. A simple annual inspection covering oil testing, cleaning of bushings and tightening of connections prevents most failures. For dry-type units, keep the windings free of dust and confirm that cooling fans operate correctly.

Final Thoughts

A medium voltage transformer is a long-term asset, not a commodity. Comparing quotes on price alone is the fastest way to lose money. Compare losses, materials, test documentation and service instead, then negotiate on supply chain efficiency. Sourced well, a single unit can serve reliably for decades while quietly lowering your electricity bill every month.

For specifications, drawings or a quotation, contact Runsheng Transformer Co., Ltd. at phone +86 13406394988, e-mail runsheng@7813transformer.com, or WhatsApp 008613508930968.