Phase failure detection method and circuit based on harmonic detection

Abstract

The invention relates to phase failure detection of a three-phase motor, in particular to a phase failure detection method and circuit based on harmonic detection. It can accurately judge all phase failure faults of three-phase motors. The phase failure detection method includes the following steps: 1), a collection step; 2), an extraction step; 3), a second harmonic detection step; 4), a second harmonic specific gravity determination step; 5), a judgment step. The open-phase detection circuit includes a current transformer, a three-phase half-wave precision rectification circuit, a voltage divider circuit, a 100Hz band-pass filter circuit, a single-phase full-wave precision rectification circuit, a large time constant low-pass filter circuit, and a comparator. The method of the invention is novel and reasonable, and can be realized by simple and ordinary analog circuits without relying on intelligent processors and complex mathematical operations, can accurately and reliably detect phase failure faults, and is not disturbed by unbalanced power supply.

Description

technical field [0001] The invention relates to phase failure detection of a three-phase motor, in particular to a phase failure detection method and circuit based on harmonic detection. Background technique [0002] There are two wiring methods for three-phase motors: star connection and delta connection, both of which have the possibility of external phase failure or internal phase failure. The so-called external phase failure is caused by the disconnection of the external power supply cable (core wire) or connection of the motor; the so-called internal phase failure is the phase failure caused by the disconnection of the internal circuit (such as winding) or connection of the motor. There are four typical situations of phase failure: 1. External phase failure of star connection, such as figure 1 , 2 2. The internal phase failure of the star connection method, such as image 3 , 4 3. The external phase failure of the angle connection method, such as Figure 5 , 6 4. ...

AI Technical Summary

Problems solved by technology

[0003] For the open phase fault of three-phase motors, the existing open phase detection methods and their characteristics are as follows: 1. Use current transformers to detect the three-phase power supply lines of the motor, and judge whether the lines are intact by detecting the current of the lines, but this method cannot detect 2. Use microcomputer protection, protection principle: when the three-phase electrical equipment works normally, the negative sequence current is zero; when a phase failure occurs, the negative sequence current will appear, among which, the negative sequence current Obtain according to the following steps: a. Use the current transformer to collect the current signal of the power supply line of each phase of the motor, and send it to an intelligent processor such as a single-chip microcomputer or ARM; b. The intelligent processor runs a microcomputer protection algorithm (such as: two-point product algorithm, reciprocal method, half cycle integral method, etc.) to calculate the vector value of the phase current; c, calculate the negative sequence current value by the vector value of the two phase currents

Microcomputer protection can accurately judge all phase failure faults, and its action is reliable, but it has high requirements for hardware circuits, and the software has a large amount of calculation. The calculation involves a large number of mathematical operations (such as derivation, trigonometric functions, etc.), and requires the use of high-performance processors.

Moreover, when the three-phase power supply is unbalanced, negative sequence current will also appear, causing the protection to operate, making it impossible to accurately determine whether the protection is activated due to phase failure.

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