Medium frequency electric furnace fault Q & A

Nov 12, 2021

1. Q: a 5T medium frequency furnace always burns KK thyristor (2500A / 3000V) and always burns the same thyristor. What's the matter?

A: first, check whether the water cooling system of the pipe is smooth and whether the resistance capacitance absorption is intact. Check whether the water-cooled radiator has been replaced. The water path of the radiator is not smooth or the contact surface is uneven. This is likely to happen. Is the incoming line voltage 1350v? Is KK thyristor 8 or 16? If it is 8, it is only possible that the withstand voltage is not enough. If it is 16, consider whether there is a problem with the furnace.

2. Q: for a 10 ton medium frequency furnace, the incoming voltage is 1450v, the resistance capacitance absorption at the incoming end is removed (resistance 250K Ω / 400W, capacitance 4KV / 4uf), and the resistance heats and smokes immediately after the wiring is restored. Remove and clean the dust, measure the resistance and capacity, and check the capacitance with a megger. No problem is found. When the circuit is connected again, the resistance does not smoke, but a capacitor explodes in about two hours. What is the reason and how to solve it?

A: this may be because the resistance and capacitance do not match. Try a resistance of about 500w50 Ω and a capacitance of about 2 micro method 3KV.

3. Q: 250kg medium frequency furnace, low power (100kW) works normally. When the power increases to 150KW, burn the inverter tube immediately. The furnace body, water cooling cable, capacitor and if control board have been checked. What is the reason for the problem?

A: it may be the problem of pulse transformer or the shutdown time of inverter thyristor.

4. Q: 500kW thyristor medium frequency power supply and vacuum induction furnace under load have been used for nearly 6 years. Recently, it is often difficult to start the inverter. How to solve it?

Answer: test whether the inverter output waveform is normal with oscilloscope. If there is a problem, check whether the capacitance changing the frequency on the if control board is appropriate. You can change the capacitance. The intermediate frequency transformer has an index called "rated transformation ratio", which actually limits the impedance of the load. You can check whether the current actual impedance is lower than the limit of "rated transformation ratio". Especially when the impedance of zero start power supply (except scan start) is very low, it is very difficult to start.

5. Q: for the medium frequency furnace with 1000V incoming line and 2500kw power, the furnace was ignited and burned for 4 KK. After replacement, it was started up, everything was normal, and the pipe was burned again 20 minutes later. Look at the chip. The breakdown point is beside or on the control pole. The primary and secondary withstand voltage of the pulse transformer is normal. It is suspected that it is disturbed at high power. How to check the interference or what other causes?

A: it may be that the harmonic I voltage or current of the built-in capacitor group is amplified, or there is resonance between the harmonic voltage or current and the furnace system. Measure the power quality, check the parameters of the furnace, and make a simple calculation.