What is a Distribution Transformer : Construction and Its Types

At present, discovering a convenient as well as a suitable area for installing a distribution transformer is one of the main challenges faced by the distribution company. Especially in urban areas, it is severe so power departments need to plan for an appropriate place for installation by considering the load, load center, possibility & further development, etc. This type of transformer can be arranged on a single pole or H pole based on the size, weight, and requirements of the transformer. Accordingly, the choice for installation of this transformer can be done by the distribution company depending on the capability and availability of space.

What is a Distribution Transformer?

Definition: A distribution transformer is also known as a typical kind of isolation transformer. The main function of this transformer is to alter the high voltage to the normal voltage like 240/120 V to use in electric power distribution. In the distribution system, there are different kinds of transformers available like single phase, 3-phase, underground, pad-mounted, pole-mounted transformer.


Generally, these transformers are available in different sizes with efficiencies along with insulating oil. These transformers are available in various sizes and efficiencies. The selection of this transformer mainly lies in the requirement and budget of the user. There are four types of distribution transformer connections available like star-star, delta-delta, star-delta, delta-star and Zig Zag/delta zigzag.

Distribution Transformer Construction

The designing of a distribution transformer can be done similarly to small size transformers. The main parts of this transformer mainly include Oil Tank, Conservator, Buchholz Relay, Breather Unit, Oil Indicator, Temperature Detector, Pressure Relief Device, Thermal Relay, Radiator, and Bushing.

  • The oil tank is used to soak the windings by placing it in.
  • A conservator is arranged above the oil tank at the outside of the transformer frame. It is connected to the main tank with the help of a metallic tube. The oil within the tank can be easily contacted & enlarge throughout loading so that the temperature of the oil can be increased & decrease.
  • Buchholz relay is used when a conservator tank is used. Because it indicates errors like loss of oil once it goes low, improper flow of oil between the tank & transformer.
  • Breather Unit includes silica gel that absorbs moisture in the oil. It changes its color from blue color to pink color it is not capable to absorb moisture in the oil.
  • The oil indicator indicates the level of the oil within the conservatory unit.
  • The temperature detector monitors the temperature of the oil. If the temperature of the oil increases to a certain level then the transformer will be disconnected from the service.
  • Pressure relief device decreases the pressure within the transformer to avoid an explosion of the transformer.
  • Thermal relay is used as an indicator for the temperature of the winding
  • The radiator is used to increase the transformer’s cooling efficiency.
  • The bushing is used to connect the internal windings of the transformer with the help of an exterior electrical network.

Types of Distribution Transformer

Based on the application or requirement, these transformers are categorized into different types like single phase, three phases, underground, pad-mounted, pole-mounted transformers.

Single Phase

These transformers are specially used for networks wherever a three-phase supply is not required. Usually, these are used for repairing overhead distribution loads in residential. These are also applicable in industrial lighting, light commercial loads & power applications.


Three Phase

This kind of transformer is used to hold electrical energy from the main distribution circuit to a minor distribution circuit. This type of transformer transmits the current to a secondary distribution circuit and also reduces the voltage of the primary distribution circuit. These transformers reduce the voltage supply for the primary circuit based on the consumer requirement.


This voltage always changes & can be dissimilar for the users of commercial, residential & light industry. These transformers work on different levels of voltage & frequency based on the standards existing in different countries. These transformers are available in single-phase & three phases. Single-phase is used in residential applications whereas 3-phase with a pad is used in underground primary circuits.


This type of transformer includes a locked steel cupboard that is arranged on a concrete pad. This type of transformer is installed in places where they do not have space for a fenced enclosure. This transformer is used with electric power distribution lines at an overhead electrical line for reducing the primary voltage to supply for the customers. A single transformer of this type can serve many homes/a large building. The power rating of this transformer ranges from 75 kVA to 5000 kVA and includes fixed switches & fuses.


Pole Mounted

These transformers are mounted on an electrical service pole at the height of the overhead cables. These are used for changing high distribution voltage to low like 120/240 volt power. These types of transformers are used in a wide rural area, ranges from 16 kVA to 100kVA. These are available in small size and easy to fit on single-pole structures. These transformers are reliable to harsh climates when they used in remote areas.


Tanks of the transformer can be shaped and protected from the corrosive materials & accumulation of water. In coastal areas, tanks can be protected from zinc sprays whereas, in highly corrosive regions, stainless tanks are used.


The uses of the distribution transformer include the following.

  • This transformer changes from high voltage electricity to low voltage electricity, used in homes & businesses.
  • The main function of this is to step down the voltage to provide isolation between two windings like primary & secondary
  • This transformer distributes the power to remote areas which are generated from the power plants
  • Generally, this transformer distributes the electrical energy to industries with less voltage under 33KV and 440volts to 220volts for domestic purposes.


1). Which transformer is used in an electrical distribution system?

A step-down transformer is used in an electrical distribution system

2). What is the difference between distribution & power transformer?

The power transformer is used in transmission networks with high voltages whereas a distribution transformer is used in low voltage distribution networks.

3). What are the types of transformers?

The different types of transformers are step up, step down, power, distribution, instrument, potential, comprising current, single-phase, 3-phase, auto, etc.

4). Why transformers are rated in kVA?

Because they do not change the power factor (PF) of their output power.

5). What is the formula for kW to kVA?

Apparent power (kVA) = Actual power (kW) / power factor (pf)

Thus, this is all about an overview of the distribution transformer. It is used to distribute the electrical energy in industries with a voltage less than & 440v to 220v for domestic purposes. It works with less efficiency and they are small in size, easy to install, include low magnetic losses. Here is a question for you, what are the connections used in the distribution transformer?