Distribution Transformers

Power transformer or distribution transformer

The line is drawn by where the unit sits and how hard it works. A power transformer sits in a substation, is usually above 5 MVA, and runs near full load for long periods. A distribution transformer sits at the end of the line feeding actual customers, is usually below 2500 kVA, and spends most of its life lightly loaded with short peaks. That difference in duty is why they are designed to different efficiency curves. A distribution transformer is optimised for low no load loss because it is energised all the time and loaded some of the time.

The forms it takes

Pad mounted, sitting on a concrete pad at ground level, which is what underground distribution uses and what we sell. Pole mounted, hung on the distribution pole, which is overhead distribution. Vault or submersible, installed below grade in dense urban areas. Unit substation, bolted directly to switchgear on both sides. The transformer inside is broadly the same machine, the enclosure and connections are what change.

Ratings you can actually buy

Three phase pad mounted runs 45, 75, 112.5, 150, 225, 300, 500, 750, 1000, 1500, 2000 and 2500 kVA. Single phase runs 25, 50, 75, 100 and 167 kVA. Anything off that list is a special order with a longer lead time and a worse price, so design to a standard rating wherever the load allows.

What drives the price

Copper and aluminium cost, the kVA, and the lead time you are willing to accept. A rating bought from stock costs more per kVA than the same rating bought from a production slot, because somebody financed the inventory. Under about 750 kVA the price per kVA climbs sharply, since the tank, cabinet, bushings, switches and freight cost roughly the same at 75 kVA as at 500.

What is a distribution transformer

The transformer that takes medium voltage from the utility distribution system, typically 12470 or 13200 volts, and reduces it to the voltage a building uses, typically 480Y/277 or 208Y/120. It is the last transformer in the chain before the customer.

What is the difference between a power transformer and a distribution transformer

Size, location and duty. Power transformers sit in substations, are usually above 5 MVA and run near full load. Distribution transformers sit at the customer end, are usually below 2500 kVA and are energised continuously but loaded intermittently, so they are designed for low no load loss rather than peak efficiency at full load.

What are the major brands of distribution transformers

In the US market the names you meet most are ERMCO, Howard Industries, Central Moloney, Prolec GE, Eaton, ABB and Virginia Transformer, alongside stocking distributors like Maddox and Sunbelt Solomon. There are 172 companies holding a UL listing to build liquid filled pad mounted units for this market, and only 32 of them are TAA eligible.

How much does a distribution transformer cost

It moves with metal prices and lead time, so we quote rather than publish. What holds is the shape. Price per kVA falls steeply as rating rises, so a 75 kVA unit costs far more per kVA than a 500 kVA unit, and stock costs more per kVA than a production slot.