Processing method of protection sampling signals of variable-frequency electric motor protection device

Abstract

The invention relates to a processing method of sampling signals of a variable-frequency electric motor protection device. The line-in side of an electric motor, which is connected with a bus, is provided with a first CT (Computerized Tomography) group, a second CT group is mounted at the end of the electric motor, a third CT group is mounted at the neutral point of the electric motor, and the three CT groups are accessed in a variable-frequency electric motor protection device or the first CT group and the third CT group are accessed in a common protection device, and the second CT group and the third CT group are accessed in the variable-frequency electric motor protection device. In the variable-frequency operation of the electric motor, differential protection is formed by sampling currents of the second CT group and the third CT group. The variable-frequency electric motor protection device filters the acquired current signals by utilizing the orthogonality of an Fourier algorithm, eliminates the influence of the DC component and various higher harmonic components, adjusts sampling interruption time by adopting a real-time frequency tracking method, ensures the fixed number of sampling points in each cycle and then calculates the steady-state amplitude values of related analog quantities under variable frequencies. The invention improves sampling stability and accuracy.

Description

technical field [0001] The invention relates to a sampling signal processing method of a high-frequency motor protection device in the fields of power plants, petrochemicals, steel and the like, and a protection device using the method. Background technique [0002] The frequency conversion technology based on power electronics technology and modern control communication technology, its basic principle is to rectify the 50Hz frequency power supply into DC, then chop it and restore it to AC. The frequency of the restored AC power supply is adjusted according to the needs of fluid flow regulation. , that is to adjust the motor speed through frequency conversion technology, so that the motor power can be "distributed on demand", and then realize the efficient adjustment of fluid flow, so as to achieve the purpose of improving efficiency, saving energy and reducing consumption. At the same time, after the motor is converted to frequency conversion, the starting current of the mo...

AI Technical Summary

Problems solved by technology

At present, the commonly used microcomputer protection devices are all designed according to the general technical conditions of industry standard microcomputer protection, that is, digital sampling calculation is performed by sampling with a fixed frequency of 50Hz, which cannot meet the requirements of motor microcomputer protection after the inverter is installed. Due to technical problems on site, only Can use the traditional relay method (the method is complicated and cannot realize the automatic function) or simply give up the differential protection, which has a great impact on the safe operation of the motor itself

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