Second shunt wave detection method

The shunt meter waveform detection method for rectifier bridge fault determination is a simple and practical method, because the general power rectifier bridge is equipped with a shunt meter for measuring the output current of the power, so it is very convenient to measure.

Using this measurement method, it is necessary to understand the relationship between the waveform of the output voltage of the rectifier bridge on the shunt and the current of each branch of the thyristor and how to use the oscilloscope to correlate the measured waveform with the ABC three-phase of the anode voltage. As mentioned above, the thyristor positive output current is the sum of the thyristor anode + A + B + C three-phase current, and the thyristor rectifier bridge anode output current is the thyristor anode - A - B - C three-phase current And, usually, the conduction angle of the inductive load is 120°, so the voltage measured from the shunt should be approximately a straight line; and for the resistive load, the waveform of the current on the shunt and the thyristor The working angle is related, but when the trigger angle of the thyristor is less than 60°, the current waveform is continuous, and when the trigger angle of the thyristor is greater than 60°, the waveform of the current is intermittent, and the waveform is as shown in the figure.

In order to determine the position of the ABC three-phase current waveform, the oscilloscope needs to be positioned by external triggering. If you use a dual-turbo oscilloscope, you can achieve precise positioning by measuring the trigger pulse on a thyristor.

Third arm current detection method

The bridge arm current detection method of the rectifier bridge is the most direct method, that is, the current of each branch bridge arm is measured by a clamp-type ammeter, and the thyristor operation condition of the bridge arm is judged by comparing the branch currents of the respective bridge arms. Good or bad. It can be seen from the figure that the on-time of each bridge arm is only one-third of the output current of the entire rectifier bridge, so under normal circumstances, the effective value of the thyristor current of each bridge arm is only this rectification. The bridge output current is 0.25 times the rms value. Obviously, this method is very intuitive and can accurately determine the thyristor of the faulty bridge arm based on the measurement results.

But unfortunately, most of the power branch current is not convenient to measure, that is, the method is good, but it is limited by the structure of the thyristor rectifier cabinet. In order to avoid the difficulty of measuring the current of each thyristor bridge arm, the method of measuring the three-phase current of each rectifier bridge ABC can be used to judge the conduction of two thyristors in each phase (in this case, each phase under normal conditions) The effective value of the current is approximately 0.816 times the effective value of the output current of the thyristor rectifier bridge.

Type of fault of the fourth thyristor rectifier circuit

The three-phase thyristor rectifier circuit can be mainly divided into three-phase full-wave full-control, three-phase full-wave half-control and three-phase half-wave full-controlled rectifier bridge. Since the latter two are generally not used, this paper mainly discusses the three-phase full-wave full-controlled rectifier bridge, which is customarily called the three-phase full-control bridge.

The faults of the thyristor rectifier bridge generally include the cooling system fault, the fuse break fault and the thyristor conduction fault. However, the cooling system of the thyristor rectifier cabinet in China is generally forced air-cooled by the fan, so the fault of the cooling system is very It's easy to identify, and it's easy to find a solution, so it's not discussed in this article. The fuse breakage has a corresponding signal indicator in almost all thyristor rectifications. Therefore, after the fuse is found to be faulty, it is only necessary to check whether the corresponding device in series with the fuse is intact, and then replace the fuse.

When the conduction check of the thyristor rectifier bridge is off-line, it can be checked by the small current test of the single bridge respectively, and the thyristor bridge running on the line has at least two due to the redundant design. And the above rectifier bridges are operated in parallel, so it is difficult to judge the conduction of the single thyristor bridge by checking the output voltage waveform of the thyristor bridge. Even if the multi-bridge is operated in parallel, the bridge can be exited separately. The method is used for measurement, but since the thyristor rectifier bridge generally has a high voltage in actual operation, it is not convenient to directly measure its output voltage waveform. It seems that there is no introduction to the on-line fault detection of the thyristor rectifier bridge running online, so it is of great practical significance to study the on-line fault diagnosis of the thyristor rectifier bridge.