Comparison between Advantages and Disadvantages of Several Temperature Rising Test Methods

In the temperature rising test of transformer , the heat source is mainly from the loss of winding, iron core and structural parts (such as iron core clamp, tension screw, winding press board, box wall etc.). Oil, air, or water are cooling agents. When the subjects were due to the losses caused by the transformer through heating and cooling medium heat balance, the temperature rise can be stable at a certain value. Therefore, in the process of temperature rising test, the cooling methods and actual conditions should be taken into consideration, and the appropriate test methods should be used.  

This is the method we explain in detail the several temperature rising test, several methods for transformer temperature rise test is introduced in detail in this paper, the advantages and disadvantages of several methods in detail, to facilitate the test according to the test environment of free choice.

(1) The direct load method can be adopted if the site is qualified. The measurement results are accurate, but load regulation is difficult.

(2) The method of mutual load and the method of circulating current. If there is a suitable auxiliary transformer or a special voltage regulating transformer for temperature rising test, it can also obtain more accurate results. But in fact, it is difficult to implement the transformer substation. It is limited to test the distribution transformer indoors.

(3) Short circuit method is that apply to test current at low voltage. Although the iron core is very small, it will not heat up, but measures can be taken to heat the oil (iron core is correspondingly hot) to make up the defect that the core is not heating. With the method of equivalent heat source, the result shows that the temperature rise of winding and upper oil is not very different from that of actual oil, but the temperature rise of core is different. But this test method does not require additional equipment, so for oil immersed transformers, this method is often used for testing. However, for dry-type transformer, because there is no intermediate cooling medium heat source, direct contact with the cooling medium, such as short circuit method of temperature rise test, the core is not only heat, but also can increase the radiating surface, which will cause great error to the test. Therefore, the dry transformer can not be tested by short circuit method.

The temperature rising test of transformer should be based on specific conditions and requirements, select the appropriate method, and according to the test current and voltage required to select the power supply, transformers, meters and wires.