How to measure transformer efficiency

As an indispensable and important equipment in power system, transformer's main function is to transfer electric energy from one circuit to another through electromagnetic induction principle, and realize the voltage increase or decrease. In actual operation, the transformer will inevitably produce certain energy loss, so it is of great significance to evaluate its efficiency for energy saving and consumption reduction of power system.

The Efficiency of a transformer refers to the ratio of its output active power to its input active power, usually expressed as a percentage. The calculation formula is:

$$
eta = frac{P_{out}}{P_{in}} imes 100%
$$

Where $ P_{out} $ is the output power of the transformer; $ P_{in} $ is the input power; $ eta $ stands for efficiency.

First, the loss of transformer

The total loss of transformer is mainly composed of two parts:

1. No-load loss (iron loss): the loss caused by hysteresis and eddy current effect in the iron core when the transformer is in no-load operation;
2. Load loss (copper loss): When the current flows through the winding, the heat loss caused by the winding resistance is directly proportional to the square of the load current.

Therefore, the actual efficiency of the transformer changes with the load, and usually reaches the maximum efficiency under a certain load.

Second, the method of measuring transformer efficiency

1. Direct load method:

This is the most intuitive method. In actual operation, the power meter is used to measure the input power and output power of the transformer respectively, and it can be calculated by substituting it into the efficiency formula. This method is suitable for transformers with small capacity or under laboratory conditions.

2. No-load and short-circuit test method (indirect method):

This method does not need actual loading, and the iron loss and copper loss are measured by two experiments, and then the efficiency is calculated:

-No-load test: when the low-voltage side is open and the high-voltage side is connected with the rated voltage, the measured power is the no-load loss (iron loss).
-Short-circuit test: the low-voltage side is short-circuited, and the voltage on the high-voltage side is gradually increased to make the primary current reach the rated value. At this time, the measured power is the copper loss under the rated current.

Through the data of these two tests, the total loss can be calculated under any load condition, and the efficiency can be obtained by combining the output power.

3. Instrument measurement method:

Using high-precision intelligent power quality analyzer or transformer test system, the input and output power of transformer can be directly measured, and the efficiency and related loss can be automatically calculated, which is suitable for field test and automatic detection system.

Three, the factors affecting the efficiency of transformer

-load size: the efficiency varies with the load, and often reaches the maximum efficiency when the load is about 50%~75% of the rated value;
-Design and manufacturing process: high-quality silicon steel sheet, excellent winding material and structural design can significantly reduce the loss;
-Operating environment: Temperature, humidity and ventilation conditions will also affect the actual operating efficiency of the transformer.

Fourth, the significance of improving transformer efficiency

Improving transformer efficiency will not only help to reduce energy consumption and operating costs, but also reduce carbon emissions and promote the green and sustainable development of power system. With the promotion of "double carbon" goal, the application of high-efficiency and energy-saving transformers has been paid more and more attention.

In a word, measuring transformer efficiency is not only an important content of power equipment maintenance, but also one of the key links of energy saving and emission reduction. Through scientific testing methods and reasonable operation management, the overall operation efficiency of transformer can be effectively improved, which provides guarantee for building an efficient and environmentally-friendly power system.