This part of the scope GB/T 25117 applies to the combined system composed of electric motors, indirect converters, and their control systems on locomotives and vehicles. Its purpose is to specify the performance characteristics of the electric transmission system composed of locomotive and vehicle converters, AC motors, and their control systems—— Test methods for verifying these performance characteristics. The combination system is divided into the following two types: a) AC motors powered by indirect converters (mainly auxiliary motors, such as cooling ventilation motors), with no control between their mechanical output (torque, speed) and the converter, which can be regarded as the motor working through a busbar (variable frequency variable voltage or constant frequency constant voltage) for power supply; b) There is a controlled (parallel or non parallel) AC motor between the mechanical output and the indirect converter. The first type of system shall be tested in accordance with GB/T 25123.2-2010 and GB/T 25122.1-2010. This section is applicable to the second category, mainly traction transmission systems. GB/T 25123.2-2010 is applicable to AC motors powered by converters, GB/T 25122.1-2010 is applicable to power electronic converters, and GB/T 25119-2010 is applicable to electronic equipment. This part is applicable to combined systems composed of motors, converters, and their control systems. Therefore, GB/T 25123.2-2010 elaborates on the test methods for verifying whether electric motors meet their technical conditions, while GB/T 25122.1-2010 elaborates on the test methods for verifying whether inverters meet their technical conditions. Obviously, some of the tests in this section can replace the corresponding tests in the above standards. The user and manufacturer should reach an agreement to avoid duplicate testing. Conducting a complete set of combination tests is complex and often requires a large amount of power, which may not necessarily be feasible in factories. Therefore, users and manufacturers can negotiate that the test can be conducted in the factory or on rolling stock. The experiment can also be conducted separately, with some conducted in the factory and some conducted on the circuit. At the time of drafting this section, only the following combinations of electric motors and inverters have been used in traction transmission systems: asynchronous motors powered by voltage source inverters- Asynchronous motor powered by current source inverter; -- A synchronous motor powered by a current source inverter. This section can also be applied to other combinations that may be used in the future. The DC input of the inverter (see Figure 1) can be the power supply network or the intermediate DC link, which is provided by the AC power grid rectifier (2.2.1 in GB/T 25122.1-2010), the DC power grid chopper (2.2.2 in GB/T 25122.1-2010), or a self-contained power source (such as an onboard generator, battery, or other electronic power source, see 1.1 in GB/T 25122.12010)