The Research On Digital Relays For Induction Motors

In the Medium-low distribution power system, digital relays are developing towards control and protection integration. This paper discusses new digital series protective equipment, which can meet the functional requirements of measurement, protection, control and communication, based on this hardware platform we produce a motor protective device to apply to medium-low power plant,110kV and low voltage level transformer substation and industrial factories.The paper systematically expounds design principles and functional requirements of the system and proposes overall technical scheme. To meet measurement, protection, control and communication multi-functions requirements, we designs the digital protection device by layers and modules scheme, with high-performance, strong-universality and well-expansibility. Thereinto, the hardware platform consists of the 32-bit floating-point DSP-based protection module plug and ARM-based control module plug, the software consists of bottom DSP protection system and upper ARM monitor system. The DSP protection system is designed in modular form of logic flow charts, change of high and low sampling frequency and time-sharing protection task management are used to satisfying requirement of system. By these means, the performance and maintainability of the software system is improved.The paper briefly introduces some common faults and abnormal running states of motors, particularly analyses the main protective principles and algorithms. And based on the analysis, some kinds of motor protection schemes are proposed to meet many field demands.After analyzing the motor state character of this special device, the paper introduces some methods of motor state detection, and applies the adaptive protection to motor protection, proposes the directional adaptive current instantaneous protection and the adaptive difference current instantaneous protection, then, analyses the scheme of the adaptive overheat protective and deduces its algorithm.Based on the hardware platform and software platform, the paper finishes the development of the motor backup protection device. At last, the paper describes the static simulation and dynamic simulation experiments for the device, and analyzed the results of the experiments.