A continuous stainless steel production line multi-trans rectifier cabinet motor grounding fault diagnosis method

Abstract

This invention belongs to the field of electrical equipment fault diagnosis technology, and provides a method for diagnosing grounding faults in the motors of multi-stage rectifier cabinets in continuous stainless steel production lines. The method includes: when a grounding alarm occurs in the rectifier cabinet, without shutting down the machine, firstly, using an oscilloscope, sequentially measuring the three-phase current waveforms of each motor; if a phase current waveform of a certain motor shows significant distortion, abnormal amplitude, or high-frequency interference, while the waveforms of the other two phases are normal, it is preliminarily determined that this phase has a potential grounding fault; then, using a multimeter, measuring the voltage to ground of the three-phase windings of the motor; if the voltage of a certain phase is significantly lower than the voltage of the other two phases or the corresponding phase voltage of a normal motor, and the multimeter displays an abnormal frequency of 1kHz to 2kHz, it can be further confirmed that this phase has a grounding fault; finally, based on the above electrical detection results, a physical inspection is performed on the suspected faulty motor to ultimately determine the fault point and handle it. This invention enables rapid and accurate diagnosis of grounding faults in the motors of rectifier cabinets in stainless steel production lines without shutting down the machine, reducing the probability of misdiagnosis and missed diagnosis, avoiding downtime losses, and improving production efficiency.

Description

Technical Field

[0001] This invention belongs to the field of electrical equipment fault diagnosis technology, and relates to the rapid location and troubleshooting of grounding faults in multi-transmission rectifier cabinets with multiple drive motors. Specifically, it is a method for diagnosing grounding faults in multi-transmission rectifier cabinet motors in a continuous stainless steel production line. Background Technology

[0002] In continuous stainless steel production lines, the electrical drive system typically consists of a rectifier cabinet driving multiple inverters to power multiple motors. For example, in one of our projects, the auxiliary drive G6 rectifier transformer at the entrance drives 171 motors. When a grounding fault occurs, traditional troubleshooting methods require shutting down the production line and measuring the insulation resistance of each motor individually to pinpoint the fault. However, continuous production lines operate at a tight pace, and shutdowns result in significant production losses and economic losses. Taking the aforementioned project as an example, checking each of the 171 motors individually would take an estimated 513 minutes, resulting in a loss of approximately 641 tons of stainless steel production and a direct economic loss of approximately 641,000 yuan. Furthermore, existing technologies lack mature methods for effectively troubleshooting grounding faults in multiple motors without shutting down the line. This not only leads to low troubleshooting efficiency and a tendency for the fault range to expand, but also carries the risk of misdiagnosis and missed diagnosis. In particular, the ability to identify weak grounding and intermittent grounding faults is insufficient, severely impacting production continuity and equipment safety. Summary of the Invention

[0003] The purpose of this invention is to provide a method for diagnosing grounding faults in the motors of multi-transmission rectifier cabinets in continuous stainless steel production lines. This method aims to solve the aforementioned problems and provide a way to quickly and accurately diagnose grounding faults without shutting down the system. It enables rapid fault location, reduces the probability of misdiagnosis and missed diagnosis, avoids downtime losses, and improves production efficiency.

[0004] The technical solution adopted by the present invention to achieve the above objectives is as follows: A method for diagnosing grounding faults in the motors of multi-transmission rectifier cabinets in a continuous stainless steel production line includes the following steps: S1. For each motor in the rectifier cabinet that has a grounding alarm, use an oscilloscope to measure the three-phase current waveform without shutting down the machine. S2. Observe the symmetry and stability of the current waveforms of each phase, and find the suspected faulty motor with two phases of normal waveforms and one phase of waveform showing obvious distortion, abnormal amplitude or high-frequency interference. S3. Use a multimeter in AC voltage mode to measure the voltage to ground of the three-phase windings of the motor suspected of having a fault, and verify the voltage. S4. Based on the above verification results, conduct on-site inspections of suspected faulty motors.

[0005] Furthermore, standard three-phase current waveforms of normal motors of the same model, under the same operating conditions and load are collected in advance to establish a reference library of normal motor current waveforms; the measured waveform of S1 is compared with the waveform in the reference library in terms of amplitude, distortion, harmonic content and symmetry to filter out misjudgments caused by load fluctuations.

[0006] Furthermore, the oscilloscope described in S1 uses a dual-channel or three-channel oscilloscope to simultaneously acquire the U, V, and W phase currents, and compares the waveforms at the same time and under the same triggering conditions. If only one phase shows distortion, increased noise, or peak shift, while the other two phases remain symmetrical and sinusoidal, the faulty phase can be accurately located.

[0007] Furthermore, S1 isolates inverter carrier interference, line-to-line coupling interference, and on-site electromagnetic interference by shortening the measurement line and using a differential probe.

[0008] Furthermore, in S2, for motors suspected of having faults but with unclear fault characteristics, continuous waveform monitoring for 1 to 3 minutes is performed to observe whether periodic distortion or instantaneous drops occur, and to identify intermittent grounding faults.

[0009] Furthermore, in S3, the voltage difference between the three phases of the faulty motor and the voltage difference between the faulty motor and the normal motor in the same phase are calculated. When the difference exceeds the set threshold, a fault is determined.

[0010] Furthermore, in S4, the oscilloscope waveform characteristics, voltage measurement data, rectifier cabinet grounding alarm signal, and motor overcurrent fault code are analyzed to form a multi-verification mechanism.

[0011] The beneficial effects of this invention are: 1. It enables rapid and accurate diagnosis of grounding faults without shutting down the machine, avoiding the tedious work of measuring the insulation of each motor over a large area, and achieving a high accuracy rate in troubleshooting.

[0012] 2. It saved time in troubleshooting, greatly improved production efficiency, and prevented misdiagnosis or missed diagnosis.

[0013] 3. Because the troubleshooting was conducted without shutting down the machine, production losses were reduced, and equipment damage caused by the escalation of the fault was avoided.

[0014] 4. The ability to identify weak grounding and intermittent grounding faults is significantly improved, and the anti-interference performance is excellent. It provides an efficient and reliable new method for troubleshooting grounding faults in multi-transmission systems and has important value for promotion and application. Attached Figure Description

[0015] Figure 1 This is a waveform diagram of the U-phase grounding current of the tension roller motor 1B1 in an embodiment of the present invention; Figure 2This is a normal current waveform diagram of the V phase of the tension roller motor in embodiment 1B1 of the present invention; Figure 3 This is a normal current waveform diagram of phase W of the tension roller motor in embodiment 1B1 of the present invention. Detailed Implementation

[0016] The present invention will be further described below with reference to embodiments: Taking the grounding fault investigation of the No. 2 RAP line of the stainless steel production line in the company's cold rolling plant as an example, the fault phenomenon is as follows: starting at 20:00 on a certain day, the pickling support roller EPN1-DR18 (4KW), the plate roll motor of the 4th stand of the rolling mill (18KW), and the pickling extrusion roller EPN1-SR01.1 motor (4KW) successively reported an overcurrent fault of 140V, and the G6 rectifier cabinet showed a grounding alarm.

[0017] The specific steps for fault diagnosis are as follows: S1. For each motor in the G6 rectifier cabinet that has a grounding alarm, without shutting down the machine, use a three-channel oscilloscope to simultaneously collect the three-phase current waveforms of each motor and compare them with the pre-established normal waveform reference library for the same model of motor.

[0018] S2. Observe the symmetry and stability of the current waveforms of each phase, and find the suspected faulty motor with two phases of normal waveforms and one phase of waveform showing obvious distortion, abnormal amplitude or high-frequency interference. When investigating the 1B1 tension roller motor, its U-phase current waveform was found to be as follows: Figure 1 As shown, the waveform exhibits obvious distortion, violent amplitude fluctuations, and high-frequency interference, which is significantly different from a normal sine wave. The high-frequency noise superimposed on the waveform and the waveform distortion characteristics are the core basis for judging the grounding fault, indicating that there is a potential grounding fault in this phase. The V-phase current waveform is as follows: Figure 2 As shown, the waveform is a standard sine curve with stable amplitude, no obvious distortion or high-frequency interference, conforming to the current waveform characteristics during normal motor operation and consistent with the reference library waveform; the W-phase current waveform is as follows. Figure 3 As shown, it is also a standard sine curve with stable amplitude, no obvious distortion or high-frequency interference, and is symmetrical and consistent with the V-phase waveform; this further verifies that the U-phase is the faulty phase.

[0019] S3. Using a multimeter in AC voltage mode, the three-phase voltage to ground of motor 1B1 was measured. The results showed that all three phases were around 24V, with a frequency of 1.58KHz. In contrast, the three-phase voltage to ground of the normally functioning motor 1B2 was 440V. The voltage difference between the three phases of motor 1B1 and the voltage difference between the same phase of motor 1B2 and motor 1B2 were calculated. Both exceeded the set threshold, further confirming that there was a grounding fault in phase U of motor 1B1. Meanwhile, after shortening the measurement line and using a differential probe to isolate the inverter interference, the measurement was performed again. The U-phase current waveform of motor 1B1 still showed distortion characteristics, thus eliminating the influence of external interference.

[0020] S4. Based on the above verification results, conduct on-site inspection of the suspected faulty motor.

[0021] An on-site inspection of motor 1B1 revealed that the U-phase insulation at the connection point between the hard wire and the flexible wire was damaged, causing grounding. After re-insulating the connection, the fault was eliminated and the system returned to normal.

[0022] Subsequently, the same method was used to check the motors connected to the G14 and G15 rectifier cabinets, and no abnormalities were found, ensuring the safe and stable operation of the entire system.

Claims

1. A method for diagnosing grounding faults in the motor of a multi-transmission rectifier cabinet in a continuous stainless steel production line, characterized in that: Includes the following steps: S1. For each motor in the rectifier cabinet that has a grounding alarm, use an oscilloscope to measure the three-phase current waveform without shutting down the machine. S2. Observe the symmetry and stability of the current waveforms of each phase, and find the suspected faulty motor with two phases of normal waveforms and one phase of waveform showing obvious distortion, abnormal amplitude or high-frequency interference. S3. Use a multimeter in AC voltage mode to measure the voltage to ground of the three-phase windings of the motor suspected of having a fault, and verify the voltage. S4. Based on the above verification results, conduct on-site inspections of suspected faulty motors.

2. The method for diagnosing grounding faults in the motor of a multi-transmission rectifier cabinet in a continuous stainless steel production line according to claim 1, characterized in that: Before fault diagnosis, collect the standard three-phase current waveforms of normal motors of the same model, under the same working conditions and load, and establish a reference library of normal motor current waveforms; compare the amplitude, distortion, harmonic content and symmetry of the measured waveform of S1 with the waveforms in the reference library to filter out misjudgments caused by load fluctuations.

3. The method for diagnosing grounding faults in the motor of a multi-transmission rectifier cabinet in a continuous stainless steel production line according to claim 1, characterized in that: The oscilloscope described in S1 uses a dual-channel or triple-channel oscilloscope to simultaneously acquire the U, V, and W phase currents. By comparing the waveforms at the same time and under the same triggering conditions, if only one phase shows distortion, increased noise, or peak shift, while the other two phases maintain a symmetrical sinusoidal pattern, the faulty phase can be accurately located.

4. The method for diagnosing grounding faults in the motor of a multi-transmission rectifier cabinet in a continuous stainless steel production line according to claim 1, characterized in that: In S1, by shortening the measurement line and using a differential probe, the inverter carrier interference, line-to-line coupling interference, and on-site electromagnetic interference are isolated.

5. The method for diagnosing grounding faults in the motor of a multi-transmission rectifier cabinet in a continuous stainless steel production line according to claim 1, characterized in that: In S2, for motors suspected of having faults but with unclear fault characteristics, continuous waveform monitoring for 1 to 3 minutes is performed to observe whether periodic distortion or instantaneous drops occur, and to identify intermittent grounding faults.

6. The method for diagnosing grounding faults in the motor of a multi-transmission rectifier cabinet in a continuous stainless steel production line according to claim 1, characterized in that: In step S3, the voltage difference between the three phases of the faulty motor and the voltage difference between the faulty motor and the normal motor in the same phase are calculated. When the difference exceeds the set threshold, a fault is determined.

7. The method for diagnosing grounding faults in the motor of a multi-transmission rectifier cabinet in a continuous stainless steel production line according to claim 1, characterized in that: In S4, the waveform characteristics of the oscilloscope, voltage measurement data, rectifier cabinet grounding alarm signal, and motor overcurrent fault code are analyzed to form a multi-verification mechanism.

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