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How to Differentiate between Power Transformers and Distribution Transformers

How to Differentiate between Power Transformers and Distribution Transformers

Are you a professional engineer looking to set up a power system and need to evaluate the transformers you need? Are you eager to know the critical differences between power and distribution transformers? Then keep on reading this article as we walk you through the stark differences between power and distribution transformers.

This article discusses the applications, loadings, and physical characteristics of the two transformers. All these characteristics have unique behavior for both types of transformers that helps to differentiate between them. They include the operating voltage, the type of network the transformers are commonly used in, the core type, the size of the transformer, available ratings, efficiency, flux density, etc.

To understand the differences between the two types, let’s first review what power transformers and distribution transformers are and explain their applications and working principles.

What is a Power Transformer?

A power transformer alters an electrical power signal’s voltage and current characteristics to facilitate its flow in circuits with different power considerations and ratings. Like all other transformers, power transformers are considered static electrical machines due to the absence of moving parts. Tap-changers and protective valves do move, but not during the stable operating periods of the transformer. Power transformers can be used as step-down or step-up transformers to increase and decrease the voltage and current levels of the electrical signals as required. This voltage and current level changing process of a transformer only applies to AC supplies and works on the principles of mutual inductance. The power and frequency of the electrical signal on either side of the power transformer remain the same, which means that the same power is transferred between circuits that work on different voltage and current levels.

In terms of application and usage, power transformers are typically installed at different power-generating stations to facilitate the processes of power generation and transmission. They are also used to match and interconnect two different power stations, which might not generate or transmit the power at the same voltage level. Thus, power transformers add to the power-delivering capacity of the system operating at the same voltage levels through an interconnected web of transformers and power stations. Such an interconnected system has many other benefits like system reliability, uptime, maintenance, islanded operations, etc., which would not be possible without power transformers.

Figure 1. An Iron-core Power Transformer:

What is a Distribution Transformer?

A distribution transformer alters an electrical power signal’s voltage and current characteristics to facilitate consumption at households, offices, commercial markets, and zones. The output power of a distribution transformer is directly consumable. Thus, these transformers can be commonly seen in cities and towns where the end consumers need direct access to electrical energy. They operate with AC supplies and work on the principles of mutual induction. In addition to this, they, too, do not alter the power and frequency profiles of the incoming electrical power signals.

Figure 2. A Pole-Mounted Distribution Transformer:

The Differences between Power Transformers and Distribution Transformers

Now that we have reviewed the two transformers, we are ready to learn about the different parameters used to differentiate between power and distribution transformers. These parameters include their maximum usage ratings, the networks they are used in, their designed ratings, applications, and sizes.

Below, we have mentioned twelve parameters and explained how the two transformers differ based on them.

1. Type of Network

The first parameter to consider is the type of network that suits both types of transformers.

Power transformers and distribution transformers perform better when used for certain types of networks. Power transformers are used in high voltage transmission networks, and distribution transformers are used in low voltage distribution networks.

2. Size

Power transformers are much larger than distribution transformers because they are designed with more specifications in mind.

3. Designed Efficiency

Power transformers are the first transformers of a complete power system circuit, as they are used at the source. Thus, they are designed to give maximum efficiency, i.e., around 99.5%. In contrast, distribution transformers are designed to provide 50-70% efficiency.

4. Availability of Ratings

Power transformers have available units for voltage ratings between 33kV to 700kV. In comparison, distribution transformers are used in much lower voltage networks and come in voltage ratings between 230V to 33kV.

5. Efficiency Formula

The efficiency formula for a power transformer is a simple ratio of the transformer’s output power to its input power. On the other hand, the efficiency formula for a distribution transformer is measured by taking the ratio of the transformer’s output to input in kilowatt-hours. This measurement is done for 24-hour periods.

6. Application

Power transformers are used at power generating stations and power transmission substations. On the other hand, distribution transformers facilitate the domestic and industrial consumption of electrical energy.

7. Maximum Rating of Usage

A power transformer has to deliver power to the rest of the system, so it must be able to handle the flow of tremendous amounts of electrical power at any given time. Power transformers commonly have a maximum power rating of 200 MVA or above. In contrast, the distribution transformers have to deliver much less power and have a rating of less than 200 MVA.

8. Operating Condition

Power transformers deliver power to more Loads and always function at full Load. The distribution transformers operate at less than full Load.

9. Flux Density

Power transformers have a greater flux density than distribution transformers.

10. Load Fluctuation

The Load connected to a distribution transformer represents a smaller portion of the power system than the total Load connected to a power transformer. Thus, the Load constantly fluctuates in the case of a distribution transformer, but rarely for power transformers.

11. Usage

Power transformers and distribution transformers have different functions. Power transformers perform several functions in high voltage networks that require them to either step up or down the voltage as required. On the other hand, distribution transformers are only used to connect end-users to the power system to facilitate a unidirectional power flow by stepping down the voltage.

12. Design of the Core

The last difference between the two types is their core design. Power transformers must operate at maximum efficiency, which is only possible when the core design allows maximum flux density. These cores are also meant to operate close to the saturation point of the B-H curve. This will enable designers to reduce the core mass. Distribution transformer cores come in various types, but the E-core Kernel design is one of the most common configurations.

This guide has covered the critical differences between power and distribution transformers based on several important parameters. If you still have questions, we are one call or email away! Don’t hesitate to contact us to get in touch with our experts for help. You can also look through the articles we have published on our website to understand power and distribution transformers better.

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