Equipment electrical maintenance knowledge

Induction melting furnace repair

Time: 2019-08-23

 The induction melting furnace is operating normally but can hear sharp clicks and hums while the DC voltmeter swings slightly.

Analysis and processing:

Observe the voltage waveform at both ends of the DC bridge of the inverter bridge with an oscilloscope. A cycle failure or an indefinite period fails briefly. The short-term failure of the parallel resonant inverter circuit can be self-recovery and the periodicity is short. The failure is generally caused by the rectification pulse of the inverter control part.

Disturbance, non-periodic short-term failure is generally caused by poor insulation between the intermediate frequency transformers.

Induction melting furnace maintenance 4: An abnormal sound occurs after the induction melting furnace is in normal operation for a period of time, and the meter reading shakes the induction melting furnace to be unstable.

Analytical treatment: After the induction melting furnace works for a period of time, the abnormal sound operation is unstable. The main reason is that the electrical characteristics of the induction melting furnace are not good. The electrical part of the induction melting furnace can be divided into two parts: weak current and strong electricity. Detection. First detect the control part to prevent damage

The main circuit power device, only in the case of the main power switch, only turns on the power of the control part. After the control part is working for a period of time, the oscilloscope is used to detect the trigger pulse of the control board to see if the trigger pulse is normal.

Under the premise that there is no problem in the control part, open the induction melting furnace. After the abnormal phenomenon occurs, observe the tube voltage drop waveform of each thyristor with an oscilloscope to find the thyristor with poor thermal characteristics; if the thyristor tube pressure The waveform is normal

At this time, we must pay attention to whether there are any problems with other electrical components, pay special attention to circuit breakers, capacitors, reactors, copper busbar contacts and main transformers.

Induction melting furnace repair 5: The induction melting furnace works normally but the power does not go up.

The normal operation of the induction melting furnace can only indicate that the components of the induction melting furnace are intact and the power is not up, indicating that the parameters of the induction melting furnace are not properly adjusted. The main reasons that affect the power of the induction melting furnace are:

(1) The rectification part is not adjusted, the rectifier tube is not fully turned on, and the DC voltage does not reach the rated value to affect the power output;

(2) The intermediate frequency voltage value is adjusted too high / too low to affect the power output;

(3) The interception cutoff value is improperly adjusted so that the power output is low;

(4) The furnace body and the power supply are not matched, which seriously affects the power output;

(5) If the compensation capacitor is configured too much or too little, the power output with the best electrical efficiency and thermal efficiency cannot be obtained, that is, the optimal economic power output cannot be obtained;

(6) The distributed inductance of the output loop and the additional inductance of the resonant tank are too large, which also affects the maximum power output.

Induction melting furnace maintenance 6: The induction melting furnace operates normally and breaks through the compensation capacitor. Analysis and treatment of the cause of the failure:

(1) The intermediate frequency voltage and operating frequency are too high,

(2) The capacitor configuration is not enough;

(3) In the capacitor boost circuit, the capacitance difference between the series capacitor and the shunt capacitor is too large, causing uneven voltage breakdown capacitance; (3) it is not good to break down the capacitor.

 Induction Melting Furnace Repair 7: The induction melting furnace operates normally but is frequently overcurrent.

Analysis and processing:

When the induction melting furnace is running, the waveforms of all electrical parameters are normal, that is, frequent overcurrent. When such a fault occurs, it is necessary to pay attention to whether electromagnetic interference and inter-line parasitic parameters are coupled due to improper wiring, such as strong wires and weak wires.

From the beginning, the power frequency line and the intermediate frequency line are arranged together, and the signal line is intertwined with the strong power line and the intermediate frequency line bus line.

Induction melting furnace repair 8 DC smoothing reactor

Fault phenomenon: The induction melting furnace works unstable, the electrical parameters fluctuate, the induction melting furnace has abnormal sound, and the overcurrent protection and the burning fast thyristor occur frequently.

Analysis and processing: In the maintenance of intermediate frequency power supply, the fault of DC smoothing reactor is a fault that is difficult to judge and handle. The faults that occur in DC smoothing reactors are:

(1) The user randomly adjusts the air gap of the reactor and the number of turns of the coil, changes the inductance of the reactor, affects the filtering function of the reactor, and causes the DC current of the output to be intermittent, resulting in unstable operation of the inverter bridge. Inverter failed to burn

Inverter thyristor. Arbitrarily adjust the air gap of the reactor and the number of turns of the coil. When the inverter bridge is short-circuited, it will reduce the ability of the reactor to block the current rise and burn the thyristor. Changing the inductance of the reactor at will also affect the starting performance of the induction melting furnace;

(2) The reactor coil is loose. If the coil of the reactor is loose, the electromagnetic force causes the coil to shake during the operation of the induction melting furnace, and the inductance is abrupt, which may cause the inverter to fail during light load starting and low current operation;

(3) The coil of the coil is not well insulated. Short circuit to ground or short circuit between turns, sparking discharge causes the inductance of the reactor to jump and strong electromagnetic interference, making the induction melting furnace unstable. Frequently generated abnormal sounds, over-current burnt thyristors, resulting in coil insulation

The insulation is not good. The reasons for the short circuit are: a cooling is not good, the temperature is too high, the insulating layer insulation is deteriorated and pyrophoric; b. the reactor coil is loose, the coil insulation layer and the coil insulation layer, the coil insulation layer and the core Insulation caused by relative motion friction

The layer is damaged; c. When the scale of the reactor coil is treated, the acid solution is infiltrated into the coil, and the acid solution corrodes the copper tube and forms a copper salt to destroy the insulating layer.

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