“Look, smell, ask and cut” in the maintenance of if equipment

May 27, 2022

It is often found that a lot of energy and time are spent in the maintenance of if equipment, and the final reason is often very simple. For example, the connecting wire is connected falsely, the screw is not fastened, the water is cut off, a device is burnt out, etc. In order to shorten the maintenance time, we need to constantly sum up experience, be diligent in observation and master some maintenance skills. Just as doctors treat patients, it is necessary to look, smell, ask and cut the medium frequency power supply to determine the location of the fault.

Wang: Wang is to observe the parameters of the instrument when the equipment is running, and whether there are heating, redness, loose screws and other appearance phenomena in the equipment. Here, we mainly introduce the relationship between the parameters of the instrument and the running state of the equipment. During the operation of the intermediate frequency power supply, there is a close relationship between the intermediate frequency voltage, DC voltage and DC current. Whether the intermediate frequency power supply operates normally can be determined by observing the parameters of the three instruments. We know that the product of DC voltage and DC current is the intermediate frequency power, and the ratio of DC voltage and DC current can reflect the impedance matching state of the load. For example, for 250KW medium frequency equipment, the highest average value of DC voltage is 513v and the highest average value of DC current is 500A. If the DC voltage reaches 500V and the DC current is 500A when the equipment is running, its impedance reaches the best matching value. If the DC current is less than 500A, the impedance value is high; if the DC current is greater than 500A, the impedance value is low. That is to say, the matching condition of load impedance can be seen by observing the value of DC current and DC voltage.

The ratio of DC voltage to intermediate frequency voltage can reflect the working state of the inverter. For example, if the DC voltage is 510v and the intermediate frequency voltage is 700V, the leading angle of the inverter is 36 °. We use 700V / 510v=1.37. Generally, the ratio of intermediate frequency voltage to DC voltage is between 1.2 ~ 1.5. We all think that the inverter works normally. If the ratio is less than 1.2, the leading front angle is too small and the inverter is difficult to commutation; If it is greater than 1.5 times, the leading angle is too large, and the equipment may fail.

Smell: the so-called smell refers to listening to the sound of the equipment during operation. First, listen to whether there is noise, whether the sound is continuous, and whether there is dull reactor vibration sound in the medium frequency howling; The second is to listen to whether there is a fire sound, which is different from the usual sound.

Q: the so-called "ask" means to understand the condition of the equipment in case of failure, and try to be as detailed as possible. At the same time, it is also necessary to understand the operating condition of the equipment before failure.

Cut: the so-called cut is exact. It refers to measuring the waveform, voltage, time, angle, resistance and other parameters of each point with oscilloscope, multimeter and other test instruments to determine the cause of the fault. It is forbidden to directly run the equipment without any inspection after finding the fault point, because there are often other deeper reasons behind the fault point.