8+FAQ About the Three-phase Overhead Transformer

The three-phase overload transformer is composed of a three-phase transformer and a heat sink connected to the transformer at the front and rear ends of the transformer.

The design of the three-phase overload transformer needs to take into account specific conditions such as the ability to withstand short circuits, the overload capacity, and the temperature rise limit in the product performance. It reflects the characteristics of the transformer product with high overload capacity.

A distribution transformer is a kind of isolation transformer.

The main use of this transformer is to alter voltages from high to low, like 240/120 V, to use in electric power distribution.

There are different types of transformers in the distribution system, such as single-phase, three-phase, underground, pad-mounted, and pole-mounted transformers.

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Three-phase Overhead Transformer: The Ultimate FAQ Guide

What Is An Overhead Transformer?

The most common kind of distribution transformer used is the single-phase oil-filled, pole-mounted transformer.

They are normally referred to as a “pole-top” or “overhead” transformer. Overhead transformers differ in their physical size and how they connect to produce different secondary voltage outputs.

Electric Pole Transformer | Single Phase Transformer

Pole Mounted Transformer
Pole Mounted Transformer

What Is a Three-phase Overhead Transformer?

The functions of a three-phase system, like a standard three-phase system, are to generate and distribute electricity.

It generates power on a larger scale to meet the demands of industries and commercial establishments.

These transformers are used to change voltages of electrical systems with three phases.

The three types of configurations are star-star, delta-delta, star-delta, and delta-star. 

Technically, three-phase overhead transformers are just overhead transformers with a three-phase system.

The only key differences of a three-phase overhead transformer from a standard three-phase system include sizes/rating, mounting locations, and applications.

Standard three-phase overhead transformer sizes are 3, 6, 9, 15, 30, 45, 75, 150, 225, 300, 500, 750, and 1,000 (kVA)

To get the specific sizes, it is better to consult your supplier.

In addition, be careful not to mention specific patents, products, and brand names not tied to the client’s company (Daelim).

Three Phase Epoxy-resin Dry Type Distribution Transformer Manufacturer – Daelim

What Are Differences Between Three-phase From A Single Phase Overhead Transformer?

In a single-phase power system, power lines are the input source.

But there is only a single primary and one secondary winding required to achieve the voltage transformation.

The single-phase transformer uses these two windings to transform the voltage.

A single-phase transformer has various models that differ in horsepower range, taps, mounting types, dimensions, kVA, and shipping weight.


Single Phase and Three Phase Pad-mounted Transformer From Daelim
Single Phase and Three Phase Pad-mounted Transformer From Daelim

Three-phase powers work differently because they are generated by rotating three windings or coils through a magnetic field within a generator.

The three windings are apart by 120 degrees.

They generate power as they rotate through the magnetic field. The generated power is sent out on three different lines, hence the term “three-phase” power.

Standard single-phase overhead transformer sizes are: 5, 10, 15, 25, 37.5, 50, 75, 100, and 167 (kVA).

Common electrical ratings of a single-phase power:

  • 5-1000 kVA
  • 65° C temperature rise
  • Standard: 60-hertz 

Are you looking to purchase a three-phase transformer? If you are, then you should know about the advantages and disadvantages of three-phase transformers.

Three-Phase Transformer: The Ultimate FAQ Guide

Advantages of Three-Phase Overhead Transformer

  • Inexpensive: Three-phase transformers are budget-friendlier. It is cheaper compared to three units of a single-phase transformer.
  • Lightweight: They are lighter in weight and smaller in size than single-phase transformers. They occupy smaller spaces.
  • Assembly: Easy to assemble.
  • Higher efficiency: It performs its functions more efficiently and delivers more power than a single-phase transformer.
  • Easier to install: A Pre-wired 3-phase transformer is ready to install, making the installation very easy and smooth.
  • Easy transportation: the materials used to build the core of a 3-phase transformer are very small compared to 3 single-phase transformers. They don’t only provide easy transportation but also lower shipping costs.

Disadvantages of Three-Phase Transformers

When it comes to purchasing a transformer, it is important to know everything about it.

The three-phase transformer is no exception. Here are some of the disadvantages of three-phase transformers so you can be informed.

  • The significant cost of a standby unit: The cost of a single piece of equipment is high. It is hard to repair or fix problems. In a 3-phase transformer, there is a common core shared across all three units. Therefore, if the unit is defective or damaged, it must be shut down.
  • Cost of fixing: Repair costs for 3-phase transformers are higher because it is very costly to change the components. Therefore service recovery, the spare unit cost is high.
  • Reduced capacity: Since the 3-phase transformer is self-cooled, the transformer’s power is also reduced.
  • Faulty correction: When there is a fault in any phase of a 3-phase transformer, it transfers to the rest of the two phases. Therefore, the whole unit must be replaced.

How Is a Transformer Sized Or Rated?

Sizing your transformers is simple. It uses a straightforward formula to generate your kVA requirements from the current and voltage of your electrical load.

Most kVA ratings are whole numbers, and most of them come in multiples of five or 10 to 15, 150, 1,000 kVA, and so on.

If your transformer is rated at 1.5 kVA and you want it operated at 25 volts, multiply 1.5 by 1,000 to get 1,500 and divide 1,500 by 25 to get 60.

Analysis of Performance Data of High Voltage Distribution Transformer

What Are the 3 Wires from Pole to House?

Static Wire

The top line of the utility pole is the static wire.

The static wire is like a lightning conductor, breaking off any excess charges from the power lines when lightning strikes during a thunderstorm.

This wire is connected to the grounding conductor.

How to ground the pad-mounted substation

instrument transformers
instrument transformers

Primary and Secondary Lines

Primary and secondary lines are located under the MGN.

The primary line carries electricity to a substation at 5 to 30 kV. Being supported by crossbars on older types of utility poles.

The secondary line is also named the secondary service drop.

The service drop leads from utility pole lines to a house. It consists of three-conductor wires.

Two of them are insulated wires carrying electricity from the transformer.

The third one is a bare neutral wire connecting to the grounding wire.

These lines have voltages of 120 to 240 volts.

What are the main neutral grounding methods of power systems?

Transmission Lines

Below the static line, there are three power lines known as the transmission lines.

Transmission lines are typically labeled as “A,” “B,” and “C”.

They can conduct high voltage electricity from a power plant to a substation.

A substation decreases the amount of voltage from 69 to 500 kVdown to five to 30 kV.

Power is then sent out on feeder lines connected to buildings and homes.

Does Every House Have A Transformer?

In most suburban neighborhoods, the distribution lines are underground.

There are green transformer boxes at every house or two.

Two wires run out of the transformer, and three wires run to the house.

The two from the transformer are insulated. Meanwhile, the third one is bare.

Bare wires are the ground wires. These two insulated wires each carry 120 volts.

DAELIM’s professional advice is to get the best-quality three-phase distribution transformers for safety purposes, lesser maintenance, longevity, and overall acquire the best value out of you or your company’s money

This is why DAELIM, one of the top companies in the world specializing in three-phase distribution transformers, will provide and share with you their 15 years of expertise to be knowledgeable of three-phase distribution transformers, pole-mounted transformer locations, and pole-mounted transformer specifications. Contact them today to learn more.

About Bin Dong

Hello, I am Bin, General manager of Daelim which is a leading transformer manufacturer. As a expert, I am glad to share my experience in transformer to you. I believe our professional team can always provide you with high quality service and we are ready to provide you with one stop solution. If you have problems when you are looking for the equipment, what you need to do is tell us.

Custom Three-Phase Overhead Transformer

The common three-phase overload transformers on the market are mainly oil-immersed transformers. The limitation of specific values can be involved according to your requirements.

Daelim has a professional transformer design and production team. They have gone through more than fifteen years of work and can perfectly fulfill your needs.

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