Research On Motor Protection In Variable Frequency Speed Control System

In order to reduce power consumption rate, more and more power plants use the frequency control technology to transform the high-voltage motor, which can greatly improve the motor operating environment. The use of inverter technology in the motor will inevitably change the way of motor protection. In this paper, the inverter runs motor protection problems raised a reliable protection programs.In this paper, we introduced the AC frequency converter speed regulatio-n technology, including two kinds of control basic ways of frequency conversio n speed regulation and it’s principle. Through the research of high voltage freque ncy converter, we summed up the impact on the operational motor and the corre sponding improvement measures. Combined with the protection function of high voltage frequency converter, we proposed the protection scheme of operational motor with power frequency and variable frequency.Then in this paper, we research the problems and it’s corresponding solution s of operational motor with power frequency protection:First we analysis the is sue of differential motion protection, because inconsistent of transmission charact eristics of CT in two sides caused differential circuit through the too large unbala nced current, then make the device misoperation, we put forward effective solut ion to solve this kind of misoperation; Then we introduce the discriminant metho d of saturated CT, and put forward the discriminant method which suitable for e ngineering; Aim at the protection device misoperation caused by error in collect ed sampling data, we put forward the method to judge the error data and corres ponding treatment plan. Then in this paper, we research the protection and it’s s etting scheme of operational motor with variable frequency:First we research t he scheme of differential motion protection, make the sampling value differentia 1 motion protection as the main protection of motor, we analyze the principle a nd algorithm of sampling differential motion protection, and on the basis of this algorithm, we put forward the implementation scheme of differential motion pro tection; Base on the analysis of electrical quantities of operational motor, we pu t forward the current quick break protection scheme and the backup protection sc heme, including low voltage protection, over voltage protection and landing prote ction.At the end, we introduce the development of motor differential motion protection device from two aspects of hardware design and software design. First we introduce the overall design of the hardware of the device, and based on the design proposed the architecture of CPU device. Then we describe the concept of software platform based on graphic, and bring about the subassembly logic of differential motion protection based on the platform, complete the software development of differential motion protection.