Motor selection, installation, operation, maintenance, and troubleshooting: 700 solutions

Author: Chief Editor: Zhang Gaichu et al
Publisher:
Publication Date: 1998-02-01
Features: Synopsis This book explains various aspects of common electric motors and their starting, control, and protective devices in a question-and-answer format. The content includes motor selection, installation, wiring, acceptance, handling, and storage; the selection, installation, use, maintenance, and troubleshooting of common starting, control, and protective devices for motors; the use, maintenance, and troubleshooting of three-phase asynchronous motors, single-phase asynchronous motors, synchronous motors, DC motors, and other types of motors; as well as coil impregnation, drying, and testing after motor repairs. The book covers a wide range of practical content and is suitable for junior and intermediate electricians and motor repair personnel, as well as for students and teachers of electrical engineering in technical schools. Excerpt: Power drives have become the foundation and core of highly electrified and automated modern industrial production. Achieving electrification and automation in industrial enterprises is of great significance for improving product quality, enhancing working conditions, increasing reliability, and boosting productivity. 2. How are electric motors classified? Electric motors are machines that use electrical energy to perform work. Through electric motors, electrical energy obtained from power supply lines is converted into mechanical energy to drive various production machinery. There are many types of electric motors, which are broadly classified into DC motors and AC motors based on the type of power supply used. DC motors are primarily used for machinery requiring uniform speed control and high starting torque (e.g., trams). AC motors are further divided into synchronous motors and asynchronous motors (also known as induction motors). Synchronous motors are generally used for machinery requiring high power or constant speed (e.g., air compressors, blowers, pumps, ball mills, and continuous rolling mills). Asynchronous motors are divided into three-phase asynchronous motors and single-phase asynchronous motors. Three-phase asynchronous motors are further classified into squirrel-cage motors and wound-rotor motors based on the type of rotor. Among these, squirrel-cage motors are further divided into three types based on the slot shape of the rotor and the conductor material: conventional squirrel-cage motors (primarily small motors), suitable for general machinery with minimal speed variation and no need for speed control; deep-bar rotor motors, with deeper rotor slots, mostly used for high-power mechanical equipment; and double-squirrel-cage motors, where the conductors in the rotor slots are made of low-resistance copper or aluminum. The characteristics of these motors are a high starting torque, but the maximum torque decreases as the starting torque increases. They are suitable for loads requiring high starting torque and constant speed, such as conveyors, crushers, mixers, and reciprocating pumps. Additionally, there is another type of double-squirrel-cage motor where the conductors in the rotor slots are made of high-resistance material. These motors have a high starting torque but a lower maximum torque, with a large slip rate, allowing speed adjustment. They are suitable for loads such as shearing machines or presses. Wound-rotor motors can operate within a certain speed range, produce high starting torque, and significantly reduce starting current. Therefore, they are often used for machinery with strict requirements for starting and speed control (e.g., hoists and bridge cranes). Single-phase asynchronous motors have many functions and are widely used. In industry, they can be used for electric tools, blowers, control and transmission devices, while in daily life, they are used for fans, refrigerators, washing machines, vacuum cleaners, and air conditioners, among others. Additionally, electric motors can be classified based on protective type, operating environment, installation method, and structural dimensions, among other factors, though detailed explanations are not provided here. 3. How can the meaning of domestic motor model numbers be understood? The performance, application, and structural features of electric motors are generally identifiable from their model numbers.