distribution transformer is a device that is used wisely in many regions. What are a distribution transformer and the structure of them? Let's us show you.


A distribution of Vietnamtransformer



distribution transformer has another name that is a service transformer. It is a transformer that provides the final voltage transformation in the power grid, stepping down the voltage used in the distribution lines to the customer's level.


Typically, a distribution transformer rating is less than 200MVA, although some national standards can allow for units up to 5000 MVA to be called as distribution transformers. If the rating is more than 200MVA (or 5000MVA in some countries), it's called a power transformer.


Because distribution transformers are energized for 24 hours a day (even when they don't carry any load), reducing iron losses has an initial role in the transformer’s design. Usually, they don't operate at full load. At lower loads, they are designed to have maximum efficiency. Voltage regulation in these transformers should be kept to a minimum in other to have better efficiency. So they are designed to have small leakage reactance.


The distribution transformer has four parts: The Input Connection, the Output Connection, the Windings or Coils, and the Core.

a. Input Connections

Input Connections are also called the primary side because electricity goes into the transformer; it has to be connected to this site.

b. Output Connections

The output side has another name, which is the secondary side of the transformer. On that side, electrical power is sent to the electric device in your house or factories. Usually, the voltage in the transformer's output side (or secondary side) is lower than in the primary side.


One of the main differences between power transformer and distribution transformer is that a power transformer usually has one primary and one secondary or one input and output setup. A distribution transformer may have one primary and two or more secondaries, depend on the purpose.

c. Winding

The winding of the distribution transformer


All types of transformers have two windings, and the distribution transformer is the same. It is divided into the primary andthe secondary winding. The primary one has a function of drawing power from the source. The secondary winding transfers electric power to electrical equipment.

d. Core

The core of the distribution transformer


The transformer core provides a path that controls the magnetic flux created in the transformer. Typically, the core is not a solid bar of steel. It includes many laminated steel sheets, or layers folded neatly. This design is to eliminate or decrease heating.


The transformer's cores have two types used according to your demand: Core Type and Shell Type. The main difference of these types is how the primary and secondary coils folded around the steel core.


Core type - The windings are wrapped in the laminated core.

Shell type -The laminated core wraps the windings.


When the input voltage gets into the primary winding, alternating current starts to flow in this winding. As the current goes through it, a continuously changing and alternating flux is created in the transformer's core. When this magnetic field runs across the secondary winding, a new alternating voltage is formed in that one.


The main manor to determine the transformer types and the output voltage is the ratio of actual turns of wire in each coil. Say the number of turns of the primary and secondary winding is N1 and N2, the voltage in the two windings call U1 and U2; we have a formula: N1/N2 = U1/U2


If the output winding voltage is higher than the input voltage, then the secondary winding has more wire turns than the primary one. So, the output voltage increased higher, also called "a step-up transformer." Whereas, if the output voltage is less than the input voltage, it's called "a step-down transformer. Usually, a distribution transformer is also a step-down transformer.

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