Industry & Manufacture

General Article

What Is the Efficiency of Dry-Type Transformer?

Transformers play a critical role in power supply systems, connecting the supply and load systems. The efficiency of a transformer is a key factor in its performance and aging, and it is important to understand how to measure and optimize it for maximum effectiveness.

Measuring Transformer Efficiency

The average efficiency of a power transformer is typically between 95% and 99%, with large power transformers reaching up to 99.7%. Measuring the output or input of a transformer under load conditions is not necessary, as wattmeter readings are usually inaccurate by 1-2%.

Calculating Transformer Losses

Using open-circuit (OC) and short-circuit (SC) tests, you can calculate the rated core and wound losses of the transformer to use in efficiency calculations. Copper losses are dependent on the currents flowing through the primary and secondary transformer windings, while core losses depend on the transformer’s rated voltage.

Operating Transformers at Constant Voltages and Frequencies

Efficiency is particularly important when operating transformers at constant voltages and frequencies. The heat generated by the transformer can impact the oil’s properties, and the appropriate cooling method will depend on the temperature rise. Temperature rise limits the rating of the equipment.

Optimizing Transformer Efficiency

To optimize transformer efficiency, it is important to select the appropriate cooling method, monitor the temperature rise, and regularly test and maintain the transformer. By taking these steps, you can ensure that your transformer operates at maximum efficiency and performance, minimizing the risk of downtime and failure.


This post was written by Justin Tidd, Director at For nearly a half a century, Becker Mining has been at the forefront of mining transformers Becker/SMC is the industry’s leader in increasingly more sophisticated electrical control systems. Most of the major innovations, design features and specialized electrical components have been developed by Becker/SMC.