Abstract: In view of the current status of transformer temperature rise testing, the automatic control system is improved by integrating electrical parameter monitoring and temperature measurement . Furthermore , the test processes are automatically controlled. This system can be used in conjunction with a PC, leveraging the PC's advantages for more convenient data processing and automatic control, reducing manual intervention, increasing the accuracy of the test, and improving the automation level of the power transformer temperature rise test process. Keywords: Transformer; Temperature rise test; Microcomputer control; Automatic control 0 Introduction Among all type tests and routine tests of transformers, the temperature rise test is the most unique. Currently, most manufacturers use the short-circuit method, with manual on-site operation. Temperature rise testing has the following characteristics: First, it is time-consuming; testing large transformers can take more than ten hours, and even small to medium-sized tests require eight or nine hours. Second, the testing process is monotonous and tedious, requiring monitoring the total loss applied to the transformer under test, adjusting the test power supply to ensure the applied total loss, and repeatedly measuring temperature values ​​over extended periods. Therefore, temperature rise tests are often conducted at night, where human fatigue is common, and the monotony of the process can easily affect measurement accuracy and even lead to operational errors. Thus, automating the testing process is essential. This automatic temperature rise test control system incorporates microcomputer technology, automatically measuring and recording relevant temperatures and making judgments, as well as measuring relevant electrical quantities during the test to monitor important parameters such as the total loss applied to the transformer under test in real time, and automatically adjusting the test power supply when deviations from predetermined values ​​occur. 1. Brief Description of Test Principle and Process 1.1 Temperature Rise Test Principle According to JB/T501–91 "Test Guidelines for Power Transformers", there are several methods for transformer temperature rise testing: direct load method; mutual load method; circulating current method; zero-sequence current method; and short-circuit method. The short-circuit method utilizes the losses generated by a short circuit in the transformer to conduct the temperature rise test. Currently, the short-circuit method is generally used. The short-circuit method requires the smallest power supply capacity and the lowest test voltage among all transformer temperature rise tests, making it the most commonly used method for temperature rise testing of large oil-immersed transformers. 1.2 Test Process The short-circuit method is used for the temperature rise test. First, determine the test power supply capacity and test current, connect the test circuit, and then begin the test. During the test, monitor the losses and current applied to the transformer under test and compare them with the set values. If they exceed the allowable error range, adjust the test power supply; and test the temperature of the test location once at predetermined intervals (generally 15–30 minutes), record the results, and make judgments on the measurement results. The temperature rise of the top layer oil is considered stable when the rate of change is less than 1 K/h and remains stable for 3 hours. The average value of the last hour is taken as the top layer oil temperature rise. Afterwards, the second stage of the test begins: winding temperature rise test (measuring hot resistance; cold resistance was measured before the temperature rise test). 2. Design of the Automatic Control System for Temperature Rise Test 2.1 Hardware Circuit Design The hardware circuit block diagram is shown in Figure 1. The applied electrical quantity in the test is signal conditioned, converted from analog to digital (A/D), buffered, and then sent to the microcontroller for automatic monitoring. After making a judgment, a control command is issued, converted from digital to digital (D/A), amplified, and transmitted to the test power supply adjustment system (generator excitation adjustment system) to achieve automatic adjustment of the test power supply; similarly, the temperature is automatically detected and recorded. The system has fast processing speed and accurate control. The microcontroller uses the cost-effective MCS-51 series 89C51, the ADC is AD674A, RAM is expanded, and address latches, multiplexers, and contactless switches are used. 2.2 Software Design The software consists of two parts: a lower-level computer program and a higher-level computer program. It includes: a main program, a T0 interrupt service subroutine, an ADC completion (external interrupt) service program, a power adjustment subroutine, and a higher-level computer (PC) program developed in a high-level language. The flowchart of the main program is shown in Figure 2. 2.2.1 Lower-Level Computer Main Program The lower-level computer main program includes: setting parameters such as loss, current, and temperature sampling intervals; power and temperature acquisition control; corresponding data processing and result determination. Timer T0 is used for power sampling timing. Judgment flag F1 (F1 setting see 2.2.2): F1=0, power processing is performed. The microcontroller processes the collected power data (voltage, current, etc. applied to the transformer under test during the experiment), calculates relevant parameter values ​​such as loss, and saves the data for experimental personnel to analyze the experiment. After simple data processing, the detected value is compared with the initially set parameter values ​​(loss, etc.). If the error exceeds the allowable range, the power adjustment subroutine is called. F1=1, clear F1, perform temperature processing, the microcontroller processes the collected temperature data appropriately, and determines the result. If the detected temperature change is less than 1K/h, continue for three hours. If the temperature change is not greater than 1K/h, the oil top layer temperature rise has stabilized. An alarm is triggered to prompt the staff to proceed to the next stage of the test: hot resistance measurement. 2.2.2 T0 Interrupt Service Subroutine In the T0 interrupt service subroutine, a 10-minute temperature sampling interval is timed using a loop counter. Before the time is up, the flag F1 is 0, and electrical sampling is selected. If the timer expires, F1 is set to 1, and temperature sampling is selected. A channel counter is used to cyclically select each channel for electrical or temperature. After selecting a channel, the AD conversion is started, and the program returns to the main program. 2.2.3 External Interrupt Service Subroutine The ADC conversion completion signal serves as the external interrupt source. In the interrupt service subroutine, the ADC conversion result is read, and the storage address is determined according to the F1 flag and the channel counter. After data storage, the program returns to the main program. 2.2.4 Host Computer Program (PC) The host computer program is programmed using the high-level language Visual C++ 6.0. In addition to realizing all the functions of the lower-level machine program, it can also perform more in-depth data processing and management, forming test logs and automatically filling in test reports. 3. Test Verification This system underwent a simple field test at Baoding Tianwei Group Baoling Company. Some of the measured data are shown in Table 1: Table 1 Oil Top Layer Temperature Rise Test. The test verified that the measurement data was accurate, the expected automatic control functions could be realized, and it basically met production needs. However, there are still shortcomings. Further improvements are needed in measurement accuracy and control accuracy. 4. Conclusion This system introduces microcomputer technology into the transformer testing process, making testing accurate and convenient. It integrates power (mainly loss) monitoring and temperature measurement, ensuring the accuracy and stability of the loss or current applied to the transformer during the test, and automating the monotonous temperature measurement and recording work, greatly improving the automation level of the temperature rise test process, reducing manual intervention, and fully adapting to the requirements of modern production. The author's innovation lies in introducing microcontroller control into the transformer temperature rise test process, replacing traditional manual timed temperature monitoring with automatic detection; and upgrading the manual adjustment of the test power supply to microcomputer-based automatic monitoring and adjustment, thus achieving automation of the entire test process. Modern microcomputer automatic control technology has played a crucial role in practical production. References [1]. Baoding Tianwei Baobian Electric Co., Ltd. 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