What is the Difference Between Power Transformers and Distribution Transformers?

Electrical Technology

Main Difference between Power Transformer and Distribution Transformer

The working principle of all transformers is the same i.e. electromagnetic induction whereas design, function, purpose of applications and winding configurations differentiate them for different applications such as residential and commercial (domestic and industrial). Both of them are widely used in power system (generation, transmission and distribution).

Similarly, the main purpose of all types of transformers (such as typical transformer, auto-transformer, current transformer, potential transformer, power transformer and distribution transformer etc.) is also same e.g. they step-up or step-down the level of voltage (or current) except changing the value of electric power or frequency etc.

In today’s article, we will show the main difference between distribution and power transformer but before, lets know briefly about them.

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What is a Power Transformer?

A transformer in the generating station or substation having very high MVA (mega Volt-Ampere) which is used to transmit the high capacity electric power through power lines to the distribution center is known as power transformer.

They are generally rated over 200 MVA with a voltage rating of 400+ kV, 200 kV, 110 kV, 66 kV, 33kV etc. They are designed to operate at full load with maximum efficiency.

The main purpose of a power transformer is to step up the low level of generated voltage to high level of voltage and transmit it over transmission lines to the distribution substation for further process.

Applications of Power Transformer

Power transformers are used to:

Step up the level of generated voltage to the high voltage level for transmission purposes.
Fed-up the transmission system via high voltage (with low current) which reduces the line losses.
Step-up or step down the level of voltage in the generating and substation according to the requirements.

What is a Distribution Transformer?

A transformer mounted on the utility pole near the consumer load points which step-down the high voltage to the safest rated voltage according to the utilization needs is known as distribution transformer.

Distribution transformers are generally rated for 11kV, 6.6 kV, 3.3 kV, 440V, 230V ,120V and 110V. They are designed to operate at maximum efficiency of 60-70% load as they don’t operate at full load all the time.

The main purpose of a distribution transformer is to step-down the high level of distributed voltage to low level of voltage according to the needs of consumers (both commercial and residential). The common voltage from the transformer secondary to the panels are 400V three phase and 230V single phase in the UK and IEC following countries while 120V, 240V single phase and 277, 480V three phase in the US.

Applications of Distribution Transformer

Distribution transformers are used to:
Step-down the level of high voltage to the low voltage according to the system (e.g. 230V, 400V, 120V, 240V etc.).
Distribute the electric power to the consumer units.
Provide both single phase and three phase power to the consumers according to their needs.

In brief, those transformers installed at the ending or receiving point of long and high voltage transmission lines are the power transformers (mostly step-up). On the other hand, The distribution transformers (generally pole mounted) are those installed near the load terminals (domestic and industrial) to provide utilization voltage at the consumer terminals (mostly step-down).

Difference Between Power Transformer and Distribution Transformer

Differences between Power Transformer & Distribution Transformer

The following comparison table shows some of the key differences between power and distribution transformers.

Power Transformer	Distribution Transformer
Step-up the level of low voltage to high voltage and transmit high electric power via transmission lines.	Step-down the level of high voltage to the low voltage and distribute electric power to the consumer units.
Mostly step-up while step down is also possible.	Only step-down – installed at the utility poles near consumer units.
Rated voltages are 33kV, 66 kV, 110 kV, 200 kV and 400 kV or above.	Rated Voltage are 11kV, 6.6 kV, 3.3 kV, 440V, 230V ,120V and110V
The power rating is more than 200 MVA.	The power rating is less than 200 MVA.
Designed for maximum efficiency at full load as they operate all the time e.g. 24/7/365.	Designed to be operated for maximum efficiency at 60-70% load as they don’t operate at full load all the day.
Operates at nearly full load and analyzed by commercial or maximum efficiency.	Operates at light loads during major parts of the day.
It withstands low load fluctuations.	It withstands high load fluctuations.
Higher flux density.	Lower flux density.
Mostly, primary winding is connected in Star while the secondary is connected in Delta.	Mostly, primary winding is connected in Delta while the secondary is connected in Star with Neutral point.
It has generally one primary and one secondary (Single Input / Output setup).	It may have one primary and tapped i.e. two or more secondary.
Time depended.	Independent of time.
Power transformers are used in power plants, generation stations and receiving end substations etc.	Distribution transformers are used to distribute the electrical power to the consumer applications.

Summary of Distribution VS Power Transformers

Below is the summary of some of the differences between power transformer and distribution transformer.

Power transformers are used in transmission networks of higher voltages for step-up and step-down applications (400 kV, 200 kV, 110 kV, 66 kV, 33kV) and are generally rated above 200MVA.
Distribution transformers are used for lower voltage distribution networks as a means to end user connectivity. (11kV, 6.6 kV, 3.3 kV, 440V, 230V) and are generally rated less than 200 MVA.
A power transformer usually has one primary and one secondary as well as one input and output setup. A distribution transformer may have one primary and one divided or “Tapped” secondary, or two or more secondary windings.
Power transformers generally operate at nearly full – load. However, a distribution transformer operates at light loads during major parts of the day.
The performance of the power transformers is generally analyzed by commercial or maximum efficiency because they are designed for maximum efficiency at full load. Whereas, the performance of a distribution transformer is judged by all day efficiency of transformer because they are designed to be operated for maximum efficiency at 60-70% load as they normally don’t operate at full load all day as there are peak hours for load in 24 hrs which are not the same at once all the time.
The rating of a high transformer is many times greater than that of a distribution transformer.
In a Power Transformer, the flux density is higher than the distribution transformer.
Power transformers, primary winding always connected in star and secondary winding in delta connections while in distribution transformers, primary winding connected in delta and secondary in star connection. read more about the comparison between star & delta connections.
At the end of the transmission line in a Substation, the power transformer connection is in Star-Delta.(to step down the level of voltage)
At the beginning of the transmission line (H-T), the connection of the power Transformer is in Delta – Star (to step up the level of voltage). Also, not that the same connection i.e Delta – Star connection is used in three phase step down distribution transformer as well.
Power transformers are used in power plants, generation stations and receiving end substations etc. while distribution transformers are used to distribute the electrical power to the consumer applications such as domestic and industrial (residential and commercial) applications.

Good to Know: All day efficiency = (Output in KWhr) / (Input in KWhr) in 24 hrs. All day efficiency is less than the Power efficiency. Read more Here.

Here is the table image chart to download as a reference.

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