The principle and application of high current temperature rise test using simulated load method

The high current temperature rise test is an important indicator to measure the performance of electrical equipment, especially in the factory inspection test of transformers and circuit breakers. Although there are many types of transformers and circuit breakers and their functions are very different, the process of temperature rise test is basically the same. The following explains the principle and application of the large current temperature rise test system using the simulated load method for the large current temperature rise test.

The temperature rise test of dry-type transformers with simulated load method needs to be carried out step by step. Carry out a no-load test, let the exciter core heat up, wait until the temperature is stable, and then perform a short-circuit test until its temperature is stable, and measure the temperature rise of the winding under the no-load test and the temperature rise of the winding under the short-circuit state respectively. According to the temperature rise in the two stages, the total temperature rise is calculated.

The no-load temperature rise test uses an open circuit on one side and a rated voltage on the other side. Place the thermometer at the point that needs to be measured, and then let the iron core generate heat due to no-load loss until the temperature is stable. Since the winding does not generate heat during the no-load test, the heat exchange process between the iron core and the winding cannot be effectively displayed. The measured value is only a reference value and cannot be evaluated as the actual temperature rise. When the temperature of the iron core stabilizes, the temperature rise of the winding is measured.

The measured temperature rise is obtained indirectly by measuring the change of the winding resistivity, and belongs to the average temperature rise. After cutting off the power, it will first measure a value, and then measure a value every 30 seconds, continuously measure ten times, and then measure once every 10 minutes. The measured value needs to use a semi-logarithmic coordinate to make a curve, and then measure its instantaneous thermal resistance value according to the extrapolation method. The short-circuit temperature rise test is carried out after the no-load temperature rise test. The connection method of the short-circuit temperature rise transformer is the same as the no-load temperature rise test. The low-voltage side is short-circuited and the high-voltage side is used for power supply. After the testing of the test circuit is completed, the rated current is applied to the high-voltage side, and the transformer generates heat due to the short-circuit of the winding. After the temperature rise is stable, the thermal resistance of the high- and low-voltage windings is tested.

The short-circuit temperature rise of the high and low voltage windings is calculated. The test method and calculation method are the same as the no-load temperature rise test. The actual temperature rise of the windings is calculated according to the temperature rise of the high and low voltage windings measured during no-load and short-circuit conditions.

The mutual load method uses an auxiliary transformer with the same test voltage ratio and connection group. One winding is used for rated excitation, and the other winding is connected in parallel through the auxiliary transformer and the end of the test product with the same name. By adjusting the input voltage of the load auxiliary transformer, Adjust the load current to reach the rated value. The power supply of the auxiliary transformer can be the same as or different from the rated excitation power supply, but no matter what kind of power supply, it should be ensured that the phase and frequency of the power supply are exactly the same, so as to ensure the smooth progress of the test.

Since in the actual test process, there are often many factors that affect the test results, it is necessary for the tester to take these factors into consideration. Under the existing conditions, effective measures should be taken to reduce the interference of external factors. Obtain more accurate data.