Abstract This paper introduces the principle, composition, and design process of a high-voltage motor intelligent testing system based on PLC and configuration software. By using an industrial control computer as the host computer and a PLC as the slave computer, automatic control of high-voltage motor type testing is achieved. The system utilizes KingSCADA software and a Mitsubishi PLC intelligent control system, capable of verifying general performance items of high-voltage motors. Furthermore, the system features a user-friendly interface, convenient operation, and a simple structure. It can be applied to a computer-automated testing system for a high-power motor testing station, effectively improving the automation level of motor testing, making test data more objective and accurate, and facilitating better performance testing of motors. Keywords : High-voltage motor; KingSCADA; PLC; Intelligent control; Automatic testing Chapter 1 Introduction Previously, motor testing in China was non-intelligent, generally using manual single-machine control, resulting in poor timeliness and large errors, making it difficult to meet testing requirements. In recent years, China has made significant progress in intelligent motor testing. The testing equipment and technology in the domestic motor industry have developed rapidly, and various testing sensors and instruments are now relatively complete and stable in performance, providing favorable conditions for the development of motor testing systems. However, in practical applications, high-voltage motor testing systems still have the following shortcomings: low automation, insufficient reliability and safety, etc. The total investment in high-voltage testing systems is high, and motor quality inspection agencies, as investors, hope to modify existing low-voltage testing systems to develop testing systems capable of high-voltage motor testing. Meanwhile, due to various constraints, manufacturing enterprises lack complete type testing equipment and relevant professional technicians, often failing to accurately diagnose performance defects, analyze their causes, and propose clear improvement suggestions. All motors (including high-voltage motors) must undergo type testing and performance testing before leaving the factory, and can only be put into production or continue production after fully meeting technical requirements. The data from these tests include the motor's voltage, current, speed, power, slip, frequency, efficiency, temperature, and resistance. These parameters are obtained through various tests such as no-load testing, load testing, temperature rise testing, and torque testing, based on the accuracy and safety requirements of relevant national standards such as GB1032 Three-Phase Asynchronous Motor Test Method. The intelligent high-voltage motor testing system introduced in this paper has automatic testing functions, and through measurement data, it can effectively reflect the motor's performance and quality. 1.1 Introduction to Motor Type Testing Motor testing utilizes instruments, meters, and related equipment, in accordance with relevant standards, to inspect the electrical, mechanical, safety, and reliability performance of semi-finished and finished motors, or motor-based supporting products, during the manufacturing process. These tests can fully or partially reflect the relevant performance data of the tested motor. This data can be used to determine whether the tested product meets design requirements, its quality, and the goals and directions for improvement. Type testing is a comprehensive performance test that can accurately obtain the relevant performance parameters of the tested motor. Its purpose is to determine whether the electrical and mechanical parameters of the motor fully meet the technical requirements. All types of motors must pass this test before they can be put into production or continue production. International standards and those of countries such as the UK, Soviet Union, and Germany treat type testing as a performance test to check the characteristics and parameters of motors. This test is generally only conducted on the first or first few prototypes of various types of motors, hence the name type testing. Depending on the needs, the test may include all items specified in the standard, or only a portion of them. According to national standards, type tests shall be conducted under the following circumstances: 1. Newly designed and trial-produced products; 2. Products that have been identified and approved for small-batch trial production; 3. Products whose design or intentional changes are sufficient to cause changes in certain characteristics and parameters of the motor; 4. Products whose test structure deviates from the previous test structure in an unacceptable manner; 5. Periodic sampling tests after the product has been approved for production. 1.1.1 No-load test and load test There are many items in motor testing, such as no-load test, load test, locked rotor test, temperature rise test, etc. In this system design, only no-load and load tests are introduced and designed. Therefore, it is necessary to clarify their test objectives and test processes. 1. No-load characteristic test (1) Test objective: The no-load test of a three-phase asynchronous motor is to apply the rated voltage at the rated frequency to the stator. The test objectives are: a. To check the flexibility of the motor operation and whether there is abnormal noise and strong vibration; b. To obtain the core loss of the motor at the rated voltage and the mechanical loss at the rated speed through testing; c. To obtain the relationship curve between the no-load current and the no-load voltage through testing. This curve is actually a magnetization curve. It can reflect the working condition of the motor magnetic circuit, such as the performance of the core material and whether the selection of the rotor air gap is reasonable. (2) Test process: After starting the motor, keep it running under no-load at the rated voltage and rated frequency until the mechanical loss is stable. The standard for judging the stability of mechanical loss is: the difference between two readings of input power half an hour apart is not greater than 3% of the previous input power. In practical applications, it is generally determined by experience. For motors below 1KW, it generally runs for 15 to 30 minutes; for motors of 1 to 10KW, it generally runs for 30 to 60 minutes; and for motors above 10KW, it should run for 60 to 90 minutes. During the test, the voltage applied to the stator winding starts from 1.1 to 1.3Un and gradually decreases to the lowest possible voltage value until the current begins to rise. During this period, 7 to 9 points are measured. The following values ​​should be measured at each point: three-phase voltage (if the three-phase balance can be determined, only one phase can be measured), three-phase current, and input power P0. 2. Load test (1) Test purpose: The purpose of the load test is actually to measure the working characteristic curve of the motor, consider whether the efficiency and power factor are qualified, and obtain the necessary data for analyzing the motor's operating performance. (2) Test process: The test should be carried out when the motor under test is close to the hot state. Under the rated power and rated frequency, change the load and measure 6 to 8 readings within the range of 1.25 to 0.25 times the rated power. At each point, measure the following at the same time: three-phase voltage, three-phase current, input power, power factor, slip, and output torque. The slip is actually calculated by measuring the rotor speed. 1.1.2 Motor test standard In order to realize the system design in this test, it is necessary to meet the accuracy and safety requirements of relevant national standards such as GB1032 Three-phase asynchronous motor test method: 1. Test power supply 1) The sinusoidal distortion rate of the voltage waveform of the test power supply (the percentage of the root of the sum of the squares of the effective values ​​of each harmonic other than the fundamental component contained in the voltage waveform to the effective value of the fundamental component) should not exceed 5%, and should not exceed 2.5% when conducting temperature rise test. 2) The three-phase voltage symmetrical system of the test power supply should meet the following requirements: The negative sequence component and the zero sequence component of the voltage should not exceed 1% of the positive sequence component; during temperature rise testing, the negative sequence component should not exceed 0.5% of the positive sequence component, and the influence of the zero sequence component should be eliminated. The difference between the frequency of the test power supply and the rated frequency should be within ±1% of the rated frequency. 2. During the measurement instrument test, the accuracy of the electrical measuring instruments used should be no less than 0.5 class; the accuracy of the three-phase wattmeter should be no less than 1.0 class; the accuracy of the current transformer should be no less than 0.2 class; the accuracy of the frequency converter should be no less than 0.5% class (no less than 1% during inspection testing); the accuracy of the digital tachometer and slip meter should be no less than 0.1% ± 1 digit; and the accuracy of the torque meter and dynamometer should be no less than 1% (actual measured efficiency should be no less than 0.5%). When selecting instruments, the measured value should be within 20%-95% of the instrument's range. 3. Measurement Requirements When performing electrical measurements, the following requirements shall be followed: 1) Three-phase current shall be measured using a three-current transformer (or two-current transformer) method. 2) When using current transformers, the total impedance (including connecting wires) of the instruments connected to the secondary circuit shall not exceed their rated impedance value. 3) During the test, the readings of each instrument shall be taken simultaneously. When measuring three-phase voltage or three-phase current, the average value of the three-phase readings shall be taken as the actual measured value. 1.2 Characteristics of Automatic Motor Testing and Current Status of Motor Testing In the past, motor testing often used ordinary pointer instruments, with manual reading and recording, followed by manual data processing and curve plotting or experimental report writing. Due to factors such as power supply fluctuations, frequency fluctuations, and load fluctuations, the instrument pointers may oscillate. In order to accurately read the measured parameters at a certain moment, several people often need to read the meters simultaneously, resulting in low work efficiency. Moreover, due to the non-synchronous nature of meter reading and various human errors in reading, recording, and calculation, the experimental data is highly dispersed, the accuracy of the test is low, and the repeatability is poor. This testing method has now been basically phased out. Another measurement method is to use various electronic measuring instruments, such as multi-functional electrical parameter testers, which can measure the torque, speed, output power, etc. of motors under various conditions. These instruments are generally composed of single-chip microcomputers, with high measurement accuracy, digital display, and relatively complete functions, which improves the degree of automation. However, the processing of data and the synchronization of readings during the test process are still not ideal. The digital automatic test system developed on the basis of digital instruments can control the measurement process, process test data, and record and display measurement results. The automatic test system for motors using microcomputers far surpasses the traditional experimental methods in terms of test functions, measurement accuracy, and other indicators. This has brought motor testing into a new era. [21] In recent years, due to the continuous strengthening of computer functions and the emergence of various human-machine interface software, a visual monitoring screen has been provided for motor testing. This has taken a big step forward in motor testing. 1.3 Main contents and requirements of system design This project implements a high-voltage electrical control system. Based on the demonstration of various high-voltage detection implementation schemes, a scheme will be selected for design. Using prototypes with a rated voltage of 10kV and a rated power of less than 500kW (H400 or below) as test objects, an automatic control system was designed to perform general performance testing of high-voltage motors. Suitable transformers, voltage regulators, high-voltage facilities, and cables were selected to enable the testing of general performance items of high-voltage motors, meeting the accuracy and safety requirements of relevant national standards such as GB1032 Test Method for Three-Phase Asynchronous Motors. The system design included drawing schematic diagrams, main circuit diagrams, control circuit diagrams, and measurement circuit block diagrams; designing the control flow and program; performing range division; selecting appropriate instruments and equipment and setting their parameters. 1.4 Main Work Completed in This Paper The main work completed in this paper is as follows: (1) Analyze the requirements of type test, and consult and search the literature on motor test at home and abroad; (2) Study the high voltage test method standard and test scheme, and determine the overall scheme; (3) Design the main circuit system of motor test; (4) Select instruments and meters according to the standard accuracy requirements and design the measurement circuit; (5) Design the electrical control system, including the host computer, the slave computer, the protection system and the communication between the host computer and the slave computer; (6) System design outlook and summary of this paper. 1.5 System Architecture According to the main content of the design, the system architecture between the chapters of the paper is shown in Figure 1.1: Chapter 2 System Overall Scheme Design At present, the main components of the automatic motor test system are very similar, mainly including: microcomputer system and its external equipment, test hardware platform, and various digital test instruments. There are two main types of test methods: one is that the process control of the test is realized by the test hardware platform, and the microcomputer system only performs data processing, curve drawing, etc. For example, the automatic motor test system developed by the Electromagnetic Research Institute of Zhejiang University in 1995 uses a microcomputer interface controller to realize the control. Another example is the automatic motor testing system developed by Westinghouse Electric Corporation in the United States, where the entire testing process is implemented by a PLC. With the development of microcomputer technology, the performance of microcomputers has become increasingly powerful, and software development has made control extremely convenient and flexible. Therefore, most systems now use microcomputers to control the control logic and control the equipment through communication ports. This is because software running on microcomputers is very flexible to write, many functions are very easy to implement, complex logical operations and judgments can be performed, and the calculation speed is very fast, greatly increasing the system's flexibility. The high-voltage motor intelligent testing system designed in this project, like traditional motor testing, must first have a general concept to achieve load testing: The high-voltage motor testing system must first consider providing an adjustable high-voltage power supply to the motor under test. Given that this system performs load testing on the motor, the load must be varied, so an adjustable high-power load must also be provided, and this load must be smoothly adjustable. In this system, the load is implemented using another load motor M2 with the same voltage and power as the motor under test. To ensure the system operates according to the set requirements, a PLC must be used for control. Furthermore, during the test, all parameters must be uploaded to the host computer via a measurement system and data acquisition system, and monitored through configuration software. 2.1 System Functions: 1) The system should be able to smoothly adjust the frequency of the inverter unit within the allowable range (ensuring the load motor is not overloaded); 2) The system should be able to smoothly adjust the load of the tested motor; 3) The system should be able to automatically control the inverter power supply and load according to the test requirements; 4) The system should be able to acquire data in real time as required and transmit the data to the host computer via a serial port, with the software providing a visual menu; 5) The system should be able to automatically cut off the circuit or issue an alarm signal in case of abnormal conditions (such as overvoltage, overload, etc.). 2.2 System Composition This intelligent testing system differs from traditional motor testing systems. This system not only performs motor testing but also achieves automated control and data acquisition, and enables microcomputer-based on-site monitoring of parameter changes. More importantly, the tested motors are 10kV high-voltage motors, requiring consideration of high-voltage protection. Therefore, the system design undoubtedly involves more control and protection modules. Based on the system design and control requirements, the testing system is divided into a control subsystem, a high-voltage subsystem, an adjustable load subsystem, a measurement system, a data acquisition subsystem, and a configuration monitoring system. The control subsystem consists of a host computer (industrial control computer), a slave computer (PLC), and control devices. The host computer uses KingSCADA software for on-site monitoring; the slave computer uses a Mitsubishi PLC for control. The data acquisition system utilizes sensors, transmitters, and A/D converters to transmit data to the host computer via an RS-485 interface, or directly uploads data to the host computer using high-precision intelligent instruments with built-in RS-485 interfaces. The configuration interface monitors the test results in real time. Meanwhile, the configuration software also provides the tester with a visual monitoring screen, which is beneficial for real-time on-site monitoring. The system composition diagram is shown in Figure 2: 2.3 System Working Principle In Figure 2, the control and its high-voltage protection device, the tested motor, and the adjustable load in the dashed box constitute the main circuit system. The PLC controls the operation of the main circuit system as required. When the voltage and load of the tested motor meet the requirements, the measurement system starts, measures various parameters on the tested side and the load side in the main circuit, and then transmits the data to the industrial control computer through the data acquisition system. The configuration interface monitors the data. The PLC and the industrial control computer are connected through a serial interface, and the industrial control computer can control the on-site workflow through the PLC. The entire operation constitutes an intelligent motor testing system.