What Is a Medium Voltage Transformer?

Medium voltage generally covers systems from 1 kV up to 36 kV. In distribution practice the common levels are 11 kV, 22 kV and 33 kV, and a transformer connected to any of them is called a medium voltage transformer.

This article explains what makes MV transformers different from low voltage units, and what to specify when you buy one.

What counts as medium voltage

Definitions vary slightly by standard and by country, but for power distribution the practical range is 1 kV to 36 kV. Above that you are in high voltage transmission territory, which uses different designs, clearances and test regimes.

Typical ratings and configurations

Ratings. 500 kVA to 3150 kVA and above for industrial intakes

Primary. 11 kV, 22 kV or 33 kV

Secondary. 400 V, 415 V, 433 V, 690 V or another MV level

Vector group. Dyn11, Dyn5, YNd11 as required

Cooling. ONAN, ONAF, KNAN, AN or AF

Insulation level is the defining difference

The higher the system voltage, the higher the required insulation level. Standards such as IEC 60076-3 define the lightning impulse withstand level (BIL) and the applied voltage level for each system voltage and earthing arrangement.

This is why a 33 kV transformer is physically larger and more expensive than an 11 kV unit of the same kVA, more insulation, larger clearances and higher rated bushings.

Where MV transformers are used

Industrial intake substations, factory and plant distribution, commercial building substations, renewable generation connection, data and process facilities, and utility-style distribution points.

Frequently Asked Questions

Is 33 kV medium or high voltage?

33 kV sits at the top of the usual medium voltage range. It is treated as medium voltage in distribution practice, though it requires the clearances and insulation discipline associated with higher voltages.

Can I use one transformer for both 11 kV and 22 kV?

A dual-ratio or tapped primary design can cover both, but the insulation level and switchgear must be rated for the highest voltage.

Which voltage should I choose?

Usually you do not choose, the utility offers a supply voltage based on the load and the local network. Your transformer is then built to match.

Related Products, Applications and Support

Not sure which rating fits your project? Send us your load list and we will size it for you, or email info@xsdfftransformer.com, call +86 158 6789 7761 or WhatsApp +852 5416 2620.