Aluminum melting furnaces are widely used in steel, casting, special steel and other related fields. Different application fields have different requirements for medium frequency power supplies. Only when they master the basic working principle of these circuits and the basic characteristics of power devices can they be quickly and accurately Analyze and judge the cause of the fault and take effective measures to eliminate the fault. There is a lot of knowledge about Aluminum melting furnaces. Here are three major failures of the Aluminum melting furnace.
Three major failures of the Aluminum melting furnace
1, boot, the device can not start normally
Fault phenomenon: DC current is large at startup, DC voltage and intermediate frequency voltage are low, and the equipment sounds dull.
Analysis and processing: The thyristor with a bridge arm of the inverter bridge may be short-circuited or open circuit, causing the three-arm bridge of the inverter bridge to operate. Observe the thyristor voltage drop waveform on the four bridge arms of the inverter bridge with an oscilloscope. If the voltage drop of the thyristor on one of the bridge arms is one line, the thyristor has been punched through; if it is a sine wave, the thyristor is not turned on. . Replace the thyristor that has been replaced; find out why the thyristor is not conducting.
2, the equipment can start, but the working condition is wrong.
Fault phenomenon: The device can start normally and smoothly, when the power rises to a certain value, overvoltage or overcurrent protection.
Analysis and processing: Find the cause of the fault in two steps:
1) First run the equipment at no load and observe whether the voltage can rise to the rated value. If the voltage does not rise to the rated value, and the current is overcurrent protection near a certain value of the voltage. This may be caused by insufficient compensation capacitor or thyristor voltage, but it is not excluded from the ignition of a certain part of the circuit;
2) If the voltage can rise to the rated value, the device can be transferred to heavy-duty operation to see if the current value can reach the rated value. If the current cannot rise to the rated value, and the current is over-current protection at a certain value, This could be a large current disturbance. Pay special attention to the interference of the electromagnetic field of the medium frequency and large current to the control part and the signal line.
3. Faults that are prone to occur when the equipment is in normal operation
Symptom: The device is operating normally, but in the normal overcurrent protection action, burn multiple KP thyristors and fast melt.
Analysis and processing: In the case of overcurrent protection, in order to release the energy of the smoothing reactor to the grid, the rectifier bridge is switched from the rectified state to the inverting state. At this time, if а>1500, it may cause active inverter subversion and burn multiple thyristors. And fast-melting, the switch trips, and is accompanied by a huge current short-circuit explosion. Large current and electromagnetic force impact on the transformer, which will damage the transformer in severe cases.