Causes and solutions of common faults of medium frequency electric furnace
Why do electric heating capacitors in medium frequency electric furnaces often burn out?
The main reasons for this are as follows:
1. Lack of water. When the medium frequency electric furnace is used for a long time, there may be scale in the cooling pipe of the capacitor, or the water inlet system may be blocked by impurities, causing the electric heating capacitor to overheat and burn out. Therefore, during use, the flow of cooling water of the electric heating capacitor should be closely observed. If abnormal conditions are found, corresponding measures should be taken;
2. If the medium frequency voltage exceeds the standard, when the medium frequency electric furnace is used for a long time, if the medium frequency electric furnace is set too high, exceeding the rated voltage that the electric heating capacitor can withstand (common specifications are 750V, 1200V, etc.), it will cause the electric heating capacitor to overvoltage breakdown. If this happens, it is necessary to reduce the medium frequency voltage or replace the electric heating capacitor model with a higher withstand voltage rating.
3. When using the electric furnace, if the electric heating capacitor has poor insulation, it may cause the capacitor cathode to be grounded, which in turn causes the capacitor shell to break down. If this happens, the insulation of the capacitor cabinet needs to be reprocessed.
2. Why does the same set of thyristors of the medium-frequency electric furnace always break down?
1. During the use of the medium-frequency electric furnace, the cooling pipe of the capacitor may be scaled or the water inlet system may be blocked by debris, which may cause the electric heating capacitor to overheat and be damaged.
Therefore, during use, you should pay attention to the flow of cooling water of the electric heating capacitor. If you find that the flow is abnormal, you need to take corresponding measures.
2. When the intermediate frequency voltage is too high, if the medium-frequency electric furnace is used for a long time, if it is adjusted to exceed the rated voltage of the electric heating capacitor (the common specifications of the electric heating capacitor are 750V, 1200V, etc.), it will cause the electric heating capacitor to overvoltage breakdown. If this happens, you need to reduce the intermediate frequency voltage or replace the electric heating capacitor with a model with a higher withstand voltage rating.
3. If there is an insulation problem with the cathode grounding of the electric heating capacitor during the use of the electric furnace, it may cause the capacitor casing to break down. Once this happens, you need to reprocess the insulation of the capacitor cabinet.
3. Why do medium-frequency electric furnaces often burn out thyristors?
[Fault manifestation]
After the intermediate frequency power supply is started, when the power reaches a certain value, the overcurrent protection mechanism will be triggered, sometimes causing the thyristor to burn out. Even if it is restarted, the fault phenomenon still exists.
[Fault cause analysis and solution]
The causes of this fault are as follows.
(1) If the intermediate frequency power supply is prone to overcurrent under low voltage after starting, it may be because the inverter lead angle is too small, causing the inverter thyristor to be unable to be reliably closed, thereby triggering the overcurrent protection mechanism. For this fault, we need to adjust the inverter lead angle to solve it.
(2) If the water cooling jacket of the inverter thyristor stops working or the cooling effect deteriorates, it should be replaced.
(3) Check the tank connection wire to ensure that there is no poor contact and circuit breakage. If the tank connection wire has poor contact and circuit breakage problems, when the power rises to a certain value, it may cause sparking, thereby affecting the normal operation of the intermediate frequency power supply and triggering the overcurrent protection mechanism. Sometimes, during the sparking process, transient overvoltage may occur at both ends of the thyristor. If the overvoltage protection is not timely, it may cause the thyristor to burn out. Therefore, the tank connection wires should be carefully checked to ensure that they are connected reliably.
(4) If overvoltage and overcurrent occur at the same time, this may be caused by high current interference. Special attention should be paid to the interference of the electromagnetic field of the medium frequency high current on the control part and the signal line. The control line and the signal line should be isolated from the medium frequency high current wire, or shielding measures should be taken to solve this problem.
(5) The lining of the electric furnace is too thin. When the lining is thinned, the equivalent impedance will decrease, causing the medium frequency power supply to limit the current output. For a normal smelting system, the current output is limited mainly when smelting starts and the furnace is almost full of metal, which generally accounts for about 50% of the total smelting time. If the equivalent impedance of the electric furnace is too small, the output voltage is low when the current output is limited, and the current regulator on the main board cannot work stably. Once a disturbance occurs (such as adding material), the output current will fluctuate and exceed the protection upper limit, causing the overcurrent protection to operate. The thickness of the lining can be determined by measuring the metal mass in each furnace. If the amount of metal melted in a furnace exceeds 1.3 times its rated capacity, the lining should be replaced.
4. The temperature of the medium frequency melting furnace is very high.
1. The furnace lining is too thin.
2. The furnace temperature is too high
3. There is a problem with the induction coil of the circulating cooling water
4. Please confirm whether the current and voltage are in normal state.
