Discussion record of maintenance example of induction furnace

250kg GPRS medium frequency electric furnace, low power ＜ 100kW, works normally. As soon as the power is increased more than 150KW, the inverter tube will be burned immediately. The furnace body, cable, capacitor and control board have been checked, and no problem has been found. There are other reasons, please give us your advice

It may be the problem of pulse transformer or the turn off time of inverter thyristor.

KGPS medium frequency smelting furnace we now have a set of 1000kW

2 tons of smelting furnace appeared during commissioning. The power loss is too large.

The whole set of equipment can be started normally, and the main parameters are as follows

Medium frequency voltage: 1100, DC voltage: 760-800

Incoming voltage: 575, DC current: 1200

If frequency: 500

Transformer 1250kva without problem

The problem is:

When we are in Honglu, when the DC voltage is 140 and the current is 590, the power is only more than 80 kW

The high-voltage fuse is very serious. The 100A drop out fuse used for high-voltage has been blown out. Judging from the field situation, it is overloaded. Their high-voltage is 10000v, which is directly connected to our transformer

From our calculation point of view, the situation of high pressure burst is overload, but the cause can not be found

From the analysis of incoming power, when we drove to 80 kW, the incoming power was more than 200 kW

According to their safety requirements, the power supply cabinet of our door should be connected to the neutral line, but when it is not connected to the neutral line, the voltage of the cabinet is normal, but all the equipment is grounded. The neutral line of the cabinet is insulated from the shell. We can't find out where the zero line comes from

This is the above situation. Will the zero line cause too much loss? Will it send large voltage underground? Thank you for your help

Our company has a 500kW thyristor medium frequency power supply produced by Zhejiang University. The load is vacuum induction furnace. It has been used for nearly 6 years, and now it is often difficult to start the inverter. I hope the experienced master can help me solve it.

With medium frequency transformer, and a power supply with two different input voltage requirements of the furnace body, the matching of these two equipment and power supply also has some problems

You use an oscilloscope to test whether your inverter output waveform is normal. If there is a problem, you can check the capacitor on your control board to change the frequency. If it is appropriate, you can change your capacitor.

If transformer has an index called "rated transformation ratio". In fact, this index limits the impedance of load. You can check whether the actual impedance is lower than the limit of "rated transformation ratio". Especially when the impedance of zero start power supply (except sweep start) is very low, it is difficult to start.

10 tons of medium frequency voltage is generally 1000 V, 1500 v

Five KP tubes and two rectifier pulse transformers were suddenly burned in 250KW zero voltage starting intermediate frequency machine. After 12 hours of normal operation, all KK tubes and KP tubes were burnt out, and four rectifier pulse transformers were damaged. The failure point could not be found by using the multimeter to shake the meter. Now I'd like to ask you why.

At the same time, is there any large electrical equipment working?

When the pipe was burned, only one equipment was working, and there was no large power equipment around.

How about three phase balance of power frequency incoming line? What is the power when this happens? Is there a problem with the rectifier timing?

I have a question for you. I have been in contact with several SCR frequency conversion smelting equipment. The power [kW] to capacity [kg] ratio of Taiwan made equipment is almost 2:1, while that of mainland made equipment is 1:2. Why?

Smelting furnace:

According to the recommended value of national standard and industry practice, the specific power density (i.e. total power / rated capacity of furnace) of intermediate frequency furnace is about 500kW / T, higher than 600kW / T belongs to high power configuration, and higher than 800KW / T belongs to ultra-high power configuration.

According to the specific situation, the specific power density is high, the melting speed is fast, the required transformer capacity is correspondingly increased, and the furnace body size is different from the standard furnace body size.

In addition, how to calculate the compensation capacitance of IF circuit and how much to use are the most reasonable. The unit of capacitance is kvar, and its conversion with other physical quantities is?? For example: C, V,

In addition, if we can use other capacitors instead of water cooling capacitors, my heating system only works for 20 minutes. But the medium frequency heating system is required to be as small and light as possible. Of course, the failure rate should not be high

Several formulas: capacitance s = V.I (kvar. Kilovar)

Capacitive reactance = XC = V / I; capacitive reactance XC = 1 / & omega; C; angular frequency & omega; = 2 & PI; F

Capacitor capacitance C = 1 / & omega; XC = 1 / 2 & PI; FXC

In addition, you can choose the air-cooled capacitor, which is a little larger.

For the same 250 kW, 1000 Hz, 0.5 ton, capacitor boost medium frequency furnace, some machines are connected with a bypass inductor, which is connected to the output of two groups of KK thyristors, while some machines do not have this large inductor, for some reason. This inductor has been burnt out many times, and it is very difficult to repair. I implore the master to tell me if the machine connected with this inductor can be omitted? How does this inductance work in the circuit?

This inductor is used to discharge the DC component accumulated on the capacitor and protect the capacitor. In practice, it can be replaced by an electric welding machine.

It can be removed, but a capacitor must be connected in series beside the medium frequency voltage transformer, otherwise the DC component will burn the medium frequency voltage transformer

I used a constant power board, found it difficult to start when the frequency is low, please master advice.

The frequency is about 500Hz, smelting load, capacitor boost type

Can the minimum sweep frequency of the control board reach this frequency? If not, it is very difficult to start.

Is the frequency of your board properly adjusted, and is the pulse width appropriate

I bought a 0.75T medium frequency electric furnace, because I wanted to increase the power, I changed it to 1.0T, but I only changed the inverter tube to 1t. In the production, the thyristor was burnt out, one at a time. What's the reason

There are also some frequency requirements, and then the water jacket to change, small water jacket can not be used for 1500 KK, just change it

If it is impact start, replace it with 100 V large feedback transformer, replace it with 13 type water jacket, replace it with 200 mm inner diameter reactor and 8-10 capacitors, Wuxi 1000 special capacitor is the best; if it is constant power sweep start, replace it with 13 type water jacket, replace it with 200 mm inner diameter reactor and 8-10 capacitors, 1000 capacitor is the best,

It may also be that the converter inductance is too small, resulting in too large current rise rate and burning out the KK thyristor

I have a few stoves here. It's very easy to start when it's cold with light load and heavy load, but it's very difficult to start when it's hot. The frequency is low when it's hot

At about 800Hz, I use the constant power board of TC787. I heard that the constant power board of the current module is easier to start

So I tried it, but the result was the same. I sincerely ask the experts from all sides to help me.

What's your maximum frequency? Is it lower?

You're the main circuit, not the board

Its excitation frequency is not low, 1.6 times. May I ask which part of my main circuit may have problems?

The inductance between power supply and capacitor is too large. It can reduce commutation inductance or copper bar spacing

I used the constant power board of a master in Shanghai (the board is not different from the constant power board in Xi'an and Jiangsu, except that the electronic protection and phase loss protection of water pressure are omitted, and the high and low frequency switches with automatic reset function and sweep frequency are added. The frequency of high frequency is between 1.6K ~ 0.8k, and that of low frequency is between 1.2k ~ 0.6k) to transform a 1.5t/h intermediate frequency furnace. After the transformation, it has been running normally for half a month Right, and then there is the following fault: once the machine is stopped and put in a lot of cold iron or just started (the current is very large, the voltage is very low, that is, heavy load), the angle will be very small and automatically start repeatedly, but in fact, I have adjusted the minimum angle to 1.3 times (the ratio of intermediate frequency voltage and DC voltage, the meter record is accurate) at no load, then I will adjust the minimum angle a little larger, or turn high and low frequency to high and low frequency After a change (high to low or low to high), it can start smoothly. Now I have adjusted the minimum angle to 1.6 times, but sometimes the above faults still occur. I don't know why? Thank you for your advice! The frequency of the machine is about 0.8k when the furnace is empty (measured by oscilloscope). When the medium frequency voltage is 850V, the voltage on the step-up capacitor is about 1100V, the inductance of the reactor is about 3.2mh, the current limit is 1500A, and the voltage limit is 850V.

Maybe the frequency is too low. You can change the frequency of the board to about 600-1500hz,

Of course, it's useless to change the board. Your board is a kind of frequency. You can modify the frequency of the board according to the actual situation of the furnace

Medium frequency melting furnace, incoming line 1000V, power 2500kw, the furnace ignites and burns four KK. After changing and changing the furnace, it starts up and everything is normal. After about 20 minutes, the same position burns the pipe again. Look at the chip, The breakdown point is at the control pole or on the control pole. The primary and secondary voltage withstand of the pulse transformer is normal. I suspect that the pulse is interfered when the power is high. Please ask how to check the interference source or other reasons. (the KK tube has been compressed and the water is normal.)

The harmonic voltage or current may be amplified by the built-in capacitor bank, or the harmonic voltage or current resonates with the furnace system. Measure the power quality, check the furnace parameters, simple calculation.

Can start a month since it is normal. And several other equipment are also in normal work, can be caused by outside line

The reason is that the trigger pulse of KK tube is not strong enough or steep enough.

The pulse amplitude is 3.5V, and the pulse current is 45mA. Now, if the intermediate frequency voltage is reduced to 1500V, it can work normally

If you don't measure the pulse steepness, you must measure it. And the 45 ma current is too small in quantity. Is it measured with an electric meter instead of an oscilloscope. I hope to compare the number of vulnerable bits with that of other bits

I have a 150kg, 2500 cycle medium frequency furnace in our department. Now the medium frequency voltage of empty furnace can reach 750 V. When there is iron, the current will be over-current at 400A. If the medium frequency voltage is adjusted to 600 V, the current will be over-current at 500A. After the over-current value is increased, the main line switch will trip. It's OK to run at 600V and 400A for a long time. Please give me your advice

The furnace is used for cast steel, with rated power of 250KW, rated frequency of 2500kh, voltage of 750V, if the current is greater than 400A, it will be over-current; if the voltage is 600V, if the current is greater than 500A, it will be over-current

It is preliminarily estimated that the angle may be too small, and the capacitor may be too much, because the rated current of 250KW furnace is 500A.

Most of the users didn't know that the constant power was a fault. They denied that the control board was broken. It took two months to realize the reality. Why? Because its electricity charges were more than 2000 yuan and 3000 yuan, respectively,

The faulty board has been replaced with a new one

All integrated circuits are in good condition!

The phenomenon is that the DC voltage rises to about 500V, the incoming line voltage is 400V, the DC voltage is 2000a, and the medium voltage is 800V. When the DC voltage rises to 2200A, the DC voltage drops 480v, and the intermediate frequency voltage is about 775v. Hope professional personnel to talk about this aspect of the problem!!!!!!!

The current is limited, or the inverter angle is not adjusted properly---

thank you:

It has been found that the fault board is not universal. After increasing the inductor of the power frequency incoming line, it was found that there was no such phenomenon. After further searching the components in the board, it was found that the rectifier diode of the current signal had poor characteristics. After replacing the diode, the fault was eliminated. After checking the diode, it was also found that the forward resistance became larger and the back voltage was abnormal. It is likely to be caused by harmonics, but one point explains to netizens that the surface temperature of one of the triodes is 72 degrees. Thank you for your concern.

There is a medium frequency furnace in our department that often burns out the inverter thyristor. There are four of them each time. How can I solve them? What are the reasons?

You should check the peripheral circuit of SCR, such as resistance capacitance absorption, voltage sharing resistance, etc., and check whether the over-current protection circuit is normal.

If the SCR is used for a long time, there will be heat dissipation problem. If the heat dissipation is not good, the thyristor will burn out. You can solve the problem of heat dissipation. If it doesn't work out. Consider replacing SCR with mercury contactor. Because of the low on resistance of mercury relay, it will not generate heat.

1. Check the waterway and radiator plane

2. Replace the pulse transformer

Problems in debugging??

In the commissioning of the new machine, the 2-ton 500Hz 800KW constant power board works normally without load. When it is smelted to 2 / 3 of the whole capacity, the swing of the needle (intermediate frequency voltage, DC voltage, intermediate frequency power) is very large, and even over-current occurs. About 10 minutes later, everything is normal again. What is the problem? Please do if friends help to analyze??

Let go of the cut-off value. Just cut off enough voltage.

Experts: Recently, I encountered a problem in the process of repairing the machine. I'd like to ask you for advice.

Phenomenon: 250KW zero pressure starter, in the process of normal furnace opening, the molten steel is nearly full, suddenly two inverter tubes are burned, after changing the tube, switch to another empty furnace to start up, and then burn another tube after one hour of normal operation. After changing the tube, it will work normally for about 5-10 minutes and burn another one. Since then, the tubes have been repeatedly burned. When the machine is cold, the first tube can last more than an hour, and the second one can only last a few minutes. In this way, eight tubes were burned, which two of them shared the same anode, and six of them were tubes in the same position.

The ratio of current, voltage, frequency, intermediate frequency voltage to DC voltage is normal after the machine is started. It is easy to start even the heavy furnace (full furnace has been condensed to normal temperature steel). Over current, limit current, over voltage and limit voltage have been adjusted again and work normally. The waterway and RC protection elements have also been checked repeatedly, and no problem has been found. No short circuit point was found.

Check: when replacing components; method, tools, pressure and cleanliness. Check the radiator for fouling.

Replacement, pulse transformer, resistance capacitance absorption, water jacket, feedback transformer

The diagonal thyristor is also replaced. The water cooling frame is also replaced

The main circuit should also be checked for poor contact

The damage of inverter should be considered from two aspects

1： The device suffers from overvoltage during operation. Overvoltage often comes from the sudden or instantaneous interruption of current in the process of equipment operation. Such as ignition, poor contact, etc.

2： The working temperature of the device is too high. It is usually damaged in a few hours. Check the radiator of the device, installation of the device and radiator, cooling water, etc.

I use the thyristor medium frequency power supply in Shanghai. Recently, there has been frequent over-current. The DC current can only be maintained at 300.kp. All KK tubes have been replaced. The circuit of RC absorption circuit elements is good, the waveform is normal, and the compensation capacitance test is normal. Please give me your advice,

You should use the equipment of Shanghai Automation. This kind of equipment was widely used from 1992 to 1997. Please check whether the following signal wires are in good contact. I mean the voltage and current signals. In addition, the resistance value of the over-current potentiometer should be 8 Ω. It's really not good. You can connect a 0 in parallel on the signal isolation transformer. 47uF / 160 aluminum case capacitor

Recently, our FM equipment is always burning capacitors, and only a few of them are burned. Listening to the teacher Fu, it's normal that the weather in Guangdong is humid. I think this is wrong. The damage to the equipment has nothing to do with the weather. A reasonably designed equipment should be able to overcome any bad weather. The capacitor used in our factory was originally produced by a factory in Wuxi, but now it can't be contacted. How to avoid the damage of the capacitor? Which one is durable. I work in the equipment section of the heat treatment plant, and I don't know much about the heat treatment equipment. I sincerely ask you to give me more advice.

If your capacitor is used with over frequency and over pressure, if you don't often check whether the connecting bolts are tight and whether the connecting cable on the capacitor is hot, these are the reasons for the damage of the capacitor.

50kg electric furnace

The coil is about 300 mm in diameter, 400 mm in height and 14 turns in diameter. It is wrapped and dipped with round copper tube of 28 mm in diameter. For reference only.

Our factory has a medium frequency machine, which is easy to over-current, reset and start normally, and it works normally. If you move the intercepting regulator a little, you can open the pipe

Which circuit is constant power or something? Because constant power over-current and cut-off are together. Try another board. If it is still the same, it has nothing to do with the over-current value. See if there is any bad contact. Untie the cable to see if most of them are broken. Also, check if the commutation inductors are touching each other, What's the insulation of reactor and furnace? I don't know where and how big your machine is. It's the same with KK

I have a very strange machine here. It's the Dongyang Hongtai 2T machine. It always burns KK, but I can't find the problem after checking. It's not necessary to burn a few. Sometimes it burns two, sometimes it burns six, The water jacket has been changed, the pipes have been changed, rose has tightened everything, the insulation has been checked, and no problem has been found. I didn't burn when I was there, I just left and burned again, and I feel dizzy. The rectifier circuit board of this machine always breaks down, and it's not easy to burn the pipes when the furnace is big

If the rectifier is broken, 4001 or 4060, make sure the air gap of your reactor is about 4cm high, and take a look at the cable

Now the rectification is good, and the reactor has also been done. They did it a few days ago, and the machine couldn't be turned on. I went to do it yesterday. The first few times it was turned on, that is, the voltage of the pipe was uneven. I changed it several times, and then it was turned on and off by air, and it burned as soon as it was started. I couldn't find any fault

I have encountered the problem you mentioned. It may be the problem of control circuit, which can be solved by modifying the control circuit.

Take a look at the inverter absorption circuit, as well as the voltage equalizing resistor. Check the power supply with the rectifier board. Check whether the inverter angle is appropriate in the situation you said. If the current is burned by shock, the inductance of the bridge arm will increase, which will affect the start-up

There is a medium frequency induction heating furnace in our factory. When the furnace is working with load, it is always over-current. When it is working with no load, the reactor sometimes makes a "sound". At this time, the pointer of the ammeter swings and immediately returns to normal. The manufacturer has been here for several days, and no problem has been found

Maybe there is something wrong with rectification, check the resistance and capacitance, and check whether the incoming line electricity is on fire. It's better to use the oscilloscope to see the waveform

We have checked the resistance capacitance absorption, and the rectifier bridge is OK, but one of the resistance capacitance absorption capacitors of the inverter bridge is broken down, a small hole is leaked, and the fault phenomenon is the same as the replacement test. We observed that the reactor emits & quot; noise & quot; during each no-load test; If the intermediate frequency voltage is adjusted up or down near 1020v, the reactor will be normal and there will be no sound.

The incoming line you use is 660V, if 1020v, DC 750 / 800V, it works normally,

I still don't understand why the reactor will ring irregularly near this voltage when it is no-load? If it is at full load, if this sound appears, it will shut down immediately.

Are you using a constant power board? If so, that's right, because the DC voltage is full and the angle is changing,

But the medium frequency voltage has not been adjusted to the maximum, and the DC voltage has not reached the maximum at this time. Why does it ring irregularly near this voltage when it is no-load? If it is at full load, if this sound appears, it will shut down immediately.

When the impedance is adjusted, it is a critical point where the angle changes from small to large,

The two rectifying bridges of the double distillation medium frequency power supply in our factory had two tubes of common anode [or common cathode] broken down at the same time, resulting in short circuit. What's more than that?

Add resistance and capacitance protection and check the reactor.

Is there any problem with the sampling signal of power frequency incoming line.

Take the dual trace oscilloscope to see the starting angle and range of phase shifting. I suspect there's something wrong with the starting angle.

I'm repairing a Xi'an constant power board machine these days. The phenomenon is over current and over voltage. The 1t distribution capacitor of the machine is 11000 kvar. At first, I played 4 KK, but I didn't find any problem after replacing it. It's just that the water temperature is too high. I asked to lower the temperature, and the current is limited to 1500, because I used 1500 / 1600 KK. I had nothing to do after one night's operation, but it was too slow. I put the current to 1800, turned on over current or over voltage, and kept jumping. The next day, I changed the medium frequency transformer, the inverter transformer, the heat sink, the reactor, the capacitor, the cable, the furnace, and the circuit board. I didn't jump when I started the machine. When I poured water, I started to jump again. When I started the machine, it was over-current and over-voltage, but it was not over-voltage when I started the machine. Like repeated starting, I started the machine again. I didn't jump when I started the machine, I don't know what the problem is when I turn the frequency up, the small angle up, the big angle down or jump

Today, we found a problem during debugging: when the incoming line voltage is 660V and the maximum DC voltage reaches 890v, the control angle is not at 0 degree, but about 18 degree. Why?

It is possible that there is a problem with the value of the resistance and capacitance shift term of your 3-phase circuit

Our company has four 8-ton intermediate frequency power supplies produced by Hangzhou Sida. Recently, a teacher broke down the thyristor at one position in one machine. After checking all relevant positions, no fault was found. Sometimes it can be turned on for 8-9 days, sometimes it can only be turned on for dozens of minutes. The water jacket, pulse transformer, resistance capacitance protection and circuit board are all replaced, but they still can't. The reactor has also been disassembled and inspected, and no sign of ignition has been found. The furnace and cables have also been inspected, and they are all normal. Since the 25th, the equipment has been normal again. So far, no cause has been found out. Please give me more advice!

I have touched it on a small machine, and it's also very miserable. When I changed the light, it burned. Later, I mainly checked the signal circuit. I replaced the signal capacitor. I replaced the angle adjusting potentiometer. I removed all the capacitors and rebuilt them, Clean the insulated mahogany block. Take off the cable to see if it is in good condition, including whether the support of output copper bar is blackened. In addition, the thyristor. If the power is full, check the voltage drop waveform of the tube. It's better to replace the whole set that has not been burned with it. See if it is still at that position

The signal capacitance has also been changed, and the capacitor filter has been added on the pulse isolation transformer, but it has no effect! But recently, it's suddenly better. It's been running continuously for nearly half a month, and there's no problem. It's really strange!

Ask the problem: constant power line, a start-up, air switch on the over-current action, adjustable hours can start (air furnace) DC voltage 80 & or;; current 20A; intermediate frequency 150 & or;; in a point on the over-current - air switch on the over-current action, current limit does not work, check 2000 / 5 transformer, 5 / 0.1 transformer, circuit board for three, are not. 0.5 ton furnace -. When the fault occurred, all three KP1 / 3 / 5 were broken, and the circuit board was also broken. How do you solve this problem.

Disconnect the two lines of the inverter pulse, so that the inverter bridge can not work. Add the preload to observe whether the output waveform of the rectifier bridge is normal. If not, check the wiring and circuit board integrated block until the waveform is normal. Check the inverter pulse under the condition of DC 80 , to ensure that it is normal, Put the current and voltage limiting potentiometer in the middle position. If the starter is still abnormal, check the main circuit, resistance and capacitance absorption, water cable, reactance, LK inductance for poor contact, false welding, etc. If the starting voltage is changed properly, the general problem should be solved.

500 V wave abnormal

Can you tell me the position of the thyristor, and whether it is connected to the DC positive or negative? I've been in a similar situation. The thyristor is one of a group connected to the negative plate of the power supply.

It's the negative plate connection

If the thyristor connected to the negative end of the power supply is burned repeatedly, and no other reasons can be found, it is necessary to consider replacing the bracket of the thyristor. Because the inner wall of the waterway of the bracket is easy to scale and form an insulating layer, the water flow on the surface is very smooth, and the actual heat dissipation is not enough. A simple inspection method is to use a glass tube thermometer to directly measure the surface temperature of the thyristor shell, The surface temperature of the four thyristors is about the same. At full power, the temperature is about 50 ℃ (the water temperature is about 35 ℃). It is very convenient to use the temperature measuring gear of 9208 digital multimeter to measure. The temperature sensing head contacts with the thyristor porcelain shell (never touch metal), and the measured data is more accurate

Today, when we are debugging our medium frequency induction equipment, when the medium frequency voltage rises to the maximum, the DC voltage is 900v. The incoming line voltage of the power supply is 660V, and the theoretical calculation is only 891v. Why does this happen?

Inaccurate indication of DC voltmeter

I think it should be the superposition of harmonic voltage and fundamental voltage on the AC side, resulting in the phenomenon of high DC voltage. If you can provide me the electrical schematic diagram of your medium frequency furnace, I think I may be able to say more in detail!

It is equipped with a 1.5T electric furnace, 70cm internal diameter, 17 turns, 380 voltage, 8 KKS, 1500A / 1600V, and Shenghe brand tube reactance

. constant power line

Fault: after being installed and opened for three days, it is normal, medium frequency voltage is 900v, current is 1400A. But sometimes it will shut down, over-voltage and over-current. On the fourth day, when the medium frequency voltage is opened to more than 800, it will make a "choking choking" sound, and when it is higher, it will cause over-voltage and over-current

Sometimes it makes a "choking - choking" sound

Please check your inverter trigger transformer. According to the phenomenon you provided, it may be inter turn short circuit inside the transformer

At the beginning of this year, our factory installed a new set of 3-ton machine, which is made of five boards from Dongyang. It seems to work abnormally all the time. Sometimes KP is burned occasionally, sometimes KK is burned occasionally, but it's easy to operate for a period of time after changing it. It's just that the pipes are burned and there's not much burden for production. But the day before yesterday, three KKS were burned. I replaced them, checked everything, and started the machine again, But just after I turned on the medium frequency voltage of about 1000, I burned another KK, which was replaced by a new one. I thought it was because the tubes didn't match, so I replaced both. I checked the machine again, and the pulse waveform was also good. I measured the high voltage waveform when the starting voltage was low, which was also normal. Later, I turned it up, but when it reached 1000V, I burned two KKS again. Now it's the first time I changed a pair of burners, All of them were burned in the bottom four. I replaced the pulse transformer with the one on the top, but I still burned one of the four below. I don't know what happened. Please give me some advice. Thank you first!

Please check if there is a problem with the voltage and current signal

In my opinion, there are several points to pay attention to. First, the transformer that you take the signal is mainly the intermediate frequency voltage transformer and the isolation transformer. After changing, you also take the signal capacitance. Second, the angle is the problem. The capacitance must balance the angle. Third, it is like the cooling water jacket

Thank you for your advice, but my machine still hasn't solved the problem. Last night, I bought and replaced the medium frequency voltage transformer and the medium frequency furnace transformer, but as soon as I started the machine, it was still the same, and I played three KK, which means that the cooling water jacket hasn't been changed. But I think the water jacket that has only been used for half a year can't be bad. Besides, the water quality in my factory is still very good, very clear water, I don't think there is a problem of heat dissipation. The angle is 1.35 times, which should be normal. Does the capacitance balance refer to the large capacitance? The large capacitance is 14 sets in the factory, 7 sets on each side. I measured them and they are all OK. From the appearance, there is nothing special, so there should be no problem

The interference is usually caused by high current rather than voltage. Please take a careful look at whether the insulation board of the cable and the copper bar connected to the cable is blackened

Is the voltage point and current point of the protection too high, and the resistance and capacitance outside the thyristor are used for absorption? Is it good? Is the discharge reactance outside the capacitor available?

Check the capacitor carefully to see if there is poor internal contact of individual capacitors. If there is a fire inside the capacitor, it is difficult to find out and it is easy to burn KK

Add a small capacitor to the secondary of the pulse isolation transformer and give the signal to him for filtering

It is suggested that when the voltage is adjusted to the bottom, the oscilloscope should be used to check the output waveform of intermediate frequency voltage, whether the positive and negative half cycles of commutation waveform are symmetrical, and whether the peak is too large. If the commutation waveform is out of line, it is likely that the sampling signal of electric furnace is faulty (sampling transformer and series capacitor), or the resistance capacitance protection is faulty,

The problem of pulse transformer can be solved by substitution of Tangshan

Internal ignition of water cable

Encountered a similar fault, replaced many parts are not resolved. After that, the positive and negative series parallel diodes of the zero voltage starting signal part are all replaced and immediately work normally. You can try

Problems should be paid attention to when burning KK frequently

The main reason is that the large current and voltage are out of control, resulting in 1 high voltage out of control: when the medium frequency voltage rises to a certain value, the inverter will overturn, unable to operate under the condition of high impedance, the withstand voltage of components will be reduced or the cooling effect is not good, the insulation performance of the system will be reduced, and the machine will be short circuited to the ground when the medium frequency voltage rises, so check the medium frequency capacitor and furnace. Interference may also be caused. The trigger line of inverter should be far away from the main circuit, the large current is out of control, the back pressure angle of medium frequency voltage is too small, whether the trigger circuit has poor contact, and the consistency of turn off time should be paid attention to. For the resistance capacitance absorption circuit of the inverter, check whether the absorption capacitor is open circuit. It is not enough to measure its on-off. If the inverter absorption circuit is broken, it is easy to damage the inverter tube; check whether the electrical parameters of the tube meet the requirements, and whether the water cooling sleeve and other cooling water channels of the inverter tube are blocked and deformed. Whether the load has the phenomenon of sparking to the ground or not, the path leakage to the ground discharge will form a sudden high voltage, which will cause the breakdown of the inverter tube. If the operation angle is not right, it will also cause frequent over-current of the inverter tube, which will damage the tube. Without affecting the start-up, appropriately increasing the inductance of the intermediate frequency circuit from the intermediate frequency power supply to the furnace body can alleviate the damage caused by the excessive di / dt of the inverter.

As long as the incoming line voltage suddenly rises or falls (30-40v), there will be over-current protection, and the sharp fluctuation of the incoming line voltage is due to the relationship between the arc furnace under a 1000KVA transformer nearby. Do you have a good solution? Does it have anything to do with the inductance of the incoming line?

Control loop with low pass filter

Buy a wide voltage switching power supply ac110-260v / DC24V, 50W plus the most simple and reliable.

Does switching power supply resist harmonics

Our unit has a medium frequency induction heating furnace with double rectifiers. The incoming line voltage is 660V. When the medium frequency voltage is about 1080v, the reactor will make a noise irregularly. At this time, the ammeter will swing violently, and then it will be normal. When other medium frequency voltage values are close to it, it will be normal. At this time, before the front end of the reactor (i.e. bit filter), we can catch a wave with very high front value, which is superimposed on the DC voltage waveform, but not on the power supply incoming line side. At the same time, KP and KK tubes have never been burned in the past few months. I don't know why?

Whether to use constant power board, some constant power will appear this situation

I would like to ask you, in the commissioning of new equipment, the mechanical operation is normal, that is, a, phase current is always 100A larger than B, C, phase current. Observe the DC output waveform with an oscilloscope, and it is normal, 0 --- 500V.

There may be a tube in phase a with large reverse leakage current, please try to replace it

Today, I come across a strange intermediate frequency fault. I'd like to ask you for advice: This machine is a four board machine made in Wenzhou five or six years ago, 0.5t/h, capacitor voltage doubling, its feedback signal is the traditional current voltage synthesis signal, and the signal comes from both ends of the furnace. It can't start after a sudden stop, but it can start after the voltage doubling capacitor is short circuited. However, even if the leading angle is adjusted to the maximum, the voltage signal is removed or even reversed, the angle is very small, and the ratio of intermediate frequency voltage to DC voltage is only about 1.2. It can be seen that the reason why it can't start is that the leading angle is too small. I have carefully checked the synthetic signal circuit, and it can be confirmed that there is no problem. I once removed C401 from the inverter board, connected a 40 ohm resistor in series with the disk rheostat (150 Ohm) of the current signal, removed or even reversed the voltage signal, and tried to improve the leading angle, but all failed. I don't know why?

Take the capacitance of the signal and replace it with something related to the signal, including the wire

Originally, the capacitance used to take the signal was 180, but later it was changed to 360

The inverter board is broken. It is very likely that one of the two isolated resistors on the board is broken. The resistance value is about 500 ohm, and the power is about 5 watts, which means the secondary side of the isolation transformer is open.

If you can start without boosting the voltage, it means that the board is OK. Check carefully to see if there is a place where the start signal has been eliminated

The problem is that the furnace takes the signal transformer, and the primary side of the transformer has poor insulation or inter turn short circuit,

It's the inverter board. Later, I made a board and just plug it in.

Last time I met the word "stove". After it was put through the stove, it burned the computer, TV and light bulb in the office,

I had a headache. I had a headache. I've burned it several times. My machine is the line of Taizhou. It's not much compared with a small board in Xi'an. At that time, the furnace didn't stop when I was passing through the furnace. It was stopped manually,

There are only three ways - to add a filter, or to add a voltage regulator to civil appliances, or to connect other appliances to another power supply

The refitted medium frequency furnace, a 350kg furnace kk8 in Tangshan and a 250kg furnace in Wuxi all have the same fault. It is easy to start with light load, and sometimes half furnace can start, that is, when the furnace is almost full, it is difficult to start after manual shutdown.

Xi'an henggong large board line

The frequency is out of control

Circuit board C71 and micro capacitor, adjust W5 other excitation frequency potentiometer try

It's not good to use 0.068, 0.01 or 0.022. With 0.068, the measuring frequency of "heavy furnace time" is about 900hz.

If the converter inductance and reactor inductance are too large, short circuit the reactor or increase the reactor gap.

It's not good to increase the gap between reactors. When it is added to 4cm, the commutation inductance is appropriate.

Hello, I've also solved this problem. You can increase C71 a little, install core channeling inductor at the outlet of KK, and adjust the inverter angle ahead

Is there too few furnace rings? It's better to calculate the inductance of the furnace coil. Generally, small furnaces with less than 15 coils and less than 50 μ Heng inductance are prone to this kind of fault

There is a 46cm, 13 turns inside the furnace ring. One is 50cm internal diameter, 15 turns. Is that ok

46cm, too few 13 turns. The impedance is too small, and the boost condition is worse

The induction coil is 48CM. 16 turns. Double voltage. Each side of the capacitor is 1500kvar. How small UF is used for Xi'an henggong board. C71? Can it work normally

zero point four seven

There are as like as two peas in the three sets of 3 tons of medium frequency electric furnace. The incoming voltage is 1000V, the shell is aluminum, and 1 years after the furnace is started, 6 of the shell are melted, and the melting areas are the same. The middle parts of the right half of the furnace shell are all the same, and the aluminum panels on the top are also melted on the left side of the middle part, and each stove is the same, I do not know this is He Yuan. Because, please give me some advice. I'm very worried. Now I've changed the furnace shell. If the problem is not solved, it will melt down later. Experts, please help me! I would like to thank all the teachers first.!!!

Maybe your power is on the high side, you can reduce the power, increase the furnace shell or add water to cool it

The highest power is about 3500kW, DC voltage is 1300, DC current is 2700kw

The medium frequency voltage is 1700. Generally, the medium-term power of the furnace is about 32500, and the current is 2500. Like others, will the furnace shell melt if the power is too high? There are regular furnace grounding should be how to connect ah?

The power of your furnace is indeed a little high, but generally it should not melt the furnace shell. According to the situation you described, I think it is caused by the poor grounding of the furnace or the high induction current. You can check your grounding wire

It's about 3250kw.

I guess the connection between your two furnace shells is in the part of grounding wire. Did you connect the grounding wires of the left and right furnace shells together. The correct grounding should be that the two ground wires are not connected to each other, with an interval of at least three meters

I have a 12 pulse, 5 tonnage 1500kW medium frequency electric furnace, frequency 300Hz, every time the molten steel is almost finished, the power is reduced to the minimum, shut down, etc. when the machine is started again, the medium frequency can't start, use a multimeter to measure a broken KP tube, the resistance and capacitance absorption is good, I don't know what cause, please help the experts in medium frequency to analyze the fault, thank you!!

Use an oscilloscope to check the rectification pulse. Maybe the angle is wrong

It may be the problem of potentiometer or power regulating circuit, with recoil phenomenon

It's normal that the medium frequency power of a 12 pulse medium frequency machine in our factory drops to the minimum when tapping, but when the molten steel rises again after tapping, it suddenly trips. When KP is measured with a multimeter, it is broken, but it is always broken. It's good to check and find out. I don't know why,

Twelve pulse high-power equipment must be shut down when tapping, half charge should be added before starting up, and it can not be started up when the frequency is too low, otherwise the thyristor will have difficulty in commutation, which will cause KP burning.

If the same rectifier KP tube is burned, it may be caused by current sharing

Is the trip before or after the transformer? It is common to burn KP in front of the transformer.

Our factory has a kgps-1250 / 0. 4 medium frequency induction furnace, in recent use, the water-cooled guide rail is always broken down, and they all happen in different positions. After checking the furnace lining, no problem is found. Ask the expert for advice!

We also encountered this problem at the customer's place. We preliminarily judged that it might be the discharge caused by the partial induction electricity of the guide rail, which is mainly common in high-power diathermy furnace. It is suggested that the guide rail be reliably grounded at one end, and try to see.

You can try this method:

1. Separate the water path of the water-cooled guide rail from that of the inductor,

2. Insulate the water-cooled guide rail from the baffles at both ends of the inductor,

The guide rail must not be grounded.

Breakdown reason of water-cooled guide rail: it is caused by induced potential difference. It is suggested to weld short ring at 300 places between water-cooled guide rails to completely solve this problem.

I am in favor of welding the short circuit ring, but the distance should not be too long and the welding should be firm. 300 should be more appropriate, because the fractures are all short connections burned, and the serious guide rail burned out.

The current popular constant power board is bolt type, so it is very inconvenient to change the board. Excuse me, where can I buy the constant power board with row plug-in connection?

Recently, I changed several 1.5T low-pressure furnaces with chip type constant power board, two of which are extremely unstable, sometimes over-current, sometimes over-voltage, sometimes no problem in a few days, and it will not be difficult to start. When the machine is operated to 3 ~ 5 hundred volts (intermediate frequency voltage), that is, over-current, it can work normally for several days by changing the sweep frequency or the minimum angle. I used the first generation of constant power board to change a machine of the same size. Ask everybody prawn: does constant power board with chip have poor anti-interference ability, which is not suitable for large machines, or does it need to take other measures in the circuit?

I feel the same way. Small chipboard is better than integrated constant power

A 150 kg old machine has been in normal operation for more than two years. Now, as long as the intermediate frequency voltage exceeds 600 V, the machine will trip,

It's useless how to adjust the overvoltage protection. Please give me some advice

I've changed it in the middle, but I'm just about to change the board

Replace the inverter pulse transformer, check the compensation capacitor, and try to replace the standby furnace

Check whether there is a problem with the three-phase voltage

Check three-phase main circuit, try to replace KK tube, compensation capacitor and circuit board

Please describe the situation in detail

When the cold furnace is started up with charging, the power will not go up and the current will only be about 150, so the inverter angle will be adjusted

Increase the intermediate frequency voltage, just to 600 jump. So change the capacitor, KK tube, intermediate frequency transformer are useless. Now good

Frequency voltage to 400 on the jump

Turn the voltage to 350-400v and check the voltage and current of each KK.

You need to confirm that the current or voltage to a certain point before jumping, can use empty furnace and full furnace test

Determine the voltage, because the current is more than 250 at the start, and then gradually drop to below 150

Thank you for your advice. I changed a new board and burned two KK in one try. Everything was normal after I changed it

The machine is a four board machine produced by a factory in Wenzhou, Zhejiang Province, with 660V incoming line and 1.5t/h. At the beginning, a KK tube (2000a / 2000V) was burned, and the machine tripped due to over-current. After checking that there was no abnormality, it was replaced. Three more heats were produced, and the newly replaced pipes were burned again. Three more heats were produced, and then they jumped again. At this time, there was no tube burning and the furnace continued to open. Although there was an occasional overflow later, it was still from production to work. The next day at 8:00 p.m. normal start-up, normal production to about 7:00 a.m. on the third day, when there is 8 minutes of hot metal in the 11th furnace, the over-current begins, at this time, the DC current is about 2000 a, the intermediate frequency voltage is about 1250 V, and the DC voltage is about 950 v. But there was no control. The valve can be fully opened again. Sometimes the current is over-current every few minutes, sometimes it is over-current every few seconds. It's been like this for a few days: at six or seven o'clock in the morning, the eleventh heat, eight minutes of hot metal - it's not normal. Even if it's a new lining. When the machine jumps again this morning (over-current and over-voltage). I removed half of a shunt capacitor (2000kvar / 1200V) to reduce the current to 1600A or so. After filling the machine for a moment, the machine made abnormal sound, the voltage limiting lamp flashed, and the direct voltage and medium voltage decreased. At this time, if the power adjusting potentiometer is lowered, the sound of the machine will return to normal. If it is not lowered, it will soon be over-current or over-voltage again. Finally, two KK tubes are opened. The whole circuit board and two pulse transformers have been replaced, but the fault is still the same. The rest of the pulse transformers and signal machines make abnormal sounds, the voltage limiting lamp flashes, and the direct voltage and medium voltage drop. If the potentiometer is lowered, the sound of the machine will return to normal. If it is not lowered, there will be over-current or over-voltage soon

This phenomenon is caused by interference when limiting voltage

Frequency transformer, with 2000V withstand voltage meter hit, no abnormal!

When the machine doesn't break down, I will increase the angle, but there is no such phenomenon when limiting the pressure.

Check if the cable is broken. And if there is a short circuit between the intermediate frequency voltage transformer and the electric furnace, the megger can't shake out

After I replaced the signal transformer, there has been no fault for three days.

At the beginning, I burned a KK tube, which pair has been changed!

Try to replace the two diagonally, it should be the problem of KK or pulse transformer or current signal transformer

DC voltage and if voltage decrease? Have you considered KP?

.

How to do if voltage is low due to overload? ，

Reduce the compensation capacitance, but pay attention not to reduce too much when the frequency increases.

It shows that there is a problem in the matching design of the whole channel.

The only way is to move the shunt capacitor to the series capacitor. As for how much to move, experiment.

We can't simply reduce the shunt capacitance, otherwise the frequency rise is not good.

Our department has a 2-ton furnace (produced in Nanchang). The inner diameter of the induction coil is 82cm, the incoming voltage is about 780v, the power is about 2600kw when full of water, and the scrap is OK. Smelting a furnace for about an hour, we can get about 2.5 tons of column steel embryo. After a shift, the power consumption is as high as 750 degrees / ton. It's said that for a furnace as big as mine, the power consumption per ton of steel embryo should be about 650 degrees. Why is there so much difference? What's the problem? In addition to the size of the furnace, the quality of scrap and the operator, what other factors affect the power consumption?

In terms of speed and power, we should not consume so much power. Induction ring is not big, in the steel-making plant, the general induction ring is 880. What is the incoming voltage?

780V

The power consumption per ton of steel should not be greater than 600kwh, and the 780v incoming line is no problem. I think we should consider the following aspects: 1) materials. 2) output (if you think about 1t effluent, the power consumption must be large). 3) production management (including equipment operation management). 4) equipment efficiency (because there are no operation parameters for reference, it is inconvenient to express opinions. The above is only for reference. According to zbk46-87, the efficiency of the equipment should be more than 90%.

The purchased high frequency induction heating equipment has the function of automatic frequency tracking, and the heating material is non-magnetic material. By measuring the working frequency of the equipment, it is found that the working frequency is related to the size and shape of the heating coil, and the working frequency has little change with the presence or absence of the load (the heated workpiece is non-magnetic material). But I am puzzled that the working frequency decreases with the increase of the current of the heating coil, and the manufacturer says that the working frequency has nothing to do with the current. How does current affect working frequency?

I hope you can give me advice, thank you!!

The increase of current indicates that the load is changing. The load is also a part of the whole system. It will form a coupling with the inductor, which will affect the inductance of the inductor and the frequency.

The operating current is definitely related to the operating frequency. The higher the frequency, the shallower the current penetration (skin effect), so the power and current decrease.

Low voltage 1200kW power supply with four ton furnace, can you do it? What should the induction loop do? Please give me some advice.

If it's 380V, it's not easy to start. If it's 660V, the coil diameter is 920 and the height is 1100. If it's too slow, you can make it by yourself. If it's too slow, you can make 19 coils of magnetic pig iron, or make it into double 10 left and right rotation parallel connection, the effect is better. 80 minutes is OK. The copper tube is fed up and down with 30 * 40, and the middle double tube is fed out,

I would like to ask you whether medium frequency furnace or power frequency furnace is better for smelting brass. What are their advantages and disadvantages

If it is brass with high zinc content, the problem of dust should be considered, and the melt churning of medium frequency furnace is smaller. In other aspects, there is little difference between medium frequency and power frequency. At present, intermediate frequency furnace has a little more advantages. If you have any other questions, please continue to contact.

Generally speaking, it is better to smelt brass in medium frequency furnace.

1。 Due to high frequency, small stirring force, it is not easy to oxidize and burn;

2。 Medium frequency furnace has high efficiency, low failure rate and energy saving.

wait

A 200kW medium frequency induction furnace produced by Zhejiang University electrical engineering factory of our factory often burns the medium frequency transformer (voltage signal), and the start-up and operation are normal, but it burns the transformer irregularly (in operation)

A 0.22-1uf1.6-6.3kv capacitor is connected in series on the primary side

What's the use of adding capacitor? There will be no tributary component in the medium frequency transformer of 200kW heating furnace.

Self made transformer can, but we must pay attention to the process, insulation treatment should be done between layers, each layer should be padded with a layer of polyester film. The primary and secondary sides are insulated. No less than 5 floors. The first reason is that the ratio of turns is not right, and the interlayer is not insulated

The series capacitor only blocks the invasion of DC voltage. Whether there is or not, the series capacitor is not serious

The 5 ton steel shell furnace in our factory is always hot

Scalding is mainly reflected in the furnace shell and silicon steel sheet (Note: there are 8 even silicon steel sheets around the induction coil) fixed bracket, they are mutually insulated

It is estimated that there is something wrong with the grounding of the furnace. I have encountered it on the aluminum shell furnace, which is so hot that it even melts the furnace shell. Would you like to find out if the grounding is not well connected?

A one ton boiler has no reaction when it is started up after full furnace shutdown and charging. The capacitance, silicon and cable have been checked. It uses the adjustable module constant power board. It's normal to use it for one year. Now this problem suddenly appears. The start-up of an empty furnace ring is still unsuccessful, the sound of frequency sweep is very slight, and sometimes the over-current protection.

Try changing the board

Change a given potentiometer

There may be something wrong with your cable

A 250kg furnace is normally operated during the day. After 12 o'clock at night, when the incoming line voltage is lower than 350V, there is no cause of over-current. It jumps more than ten times an hour, and sometimes it is over-voltage. However, the 15V power supply of the circuit board is good. It uses the old-fashioned constant power board of Xi'an. I doubt whether it is the interference from the line, but there is no way to determine or solve it. Please raise your finger Teach! (the load on their side is heavy after 12:00 p.m., and the voltage drops even after 10000 v. most of the load is medium frequency furnace.)

When the board is changed, sometimes before the over-current, the direct voltage, medium voltage and direct current will suddenly drop together. At the same time, the sound of the reactor will suddenly coarsen, but it will soon recover. If it can't recover, the over-current will occur, and the furnace has been changed. I wonder if the turns of the reactor will be less? The inner diameter of reactance coil is 152, a total of 64 coils, the air gap is 23, and the outer diameter of iron core is 148. After one shift, the iron core temperature is higher, reaching 115 ℃; the maximum power is 250KW, and the maximum frequency is 950hz

Line voltage too low: will affect the + 15V voltage, power ripple is too large, there may be interference. It is suggested to switch to wide voltage switching power supply.

Reactor overheating: magnetic saturation, inductance close to zero, inverter is easy to fail. It is recommended to increase the air gap.

DC voltage, intermediate frequency voltage and DC current decrease at the same time: if the rectification offset is too large, adjust W4.

There is something wrong with the synchronization signal. The phase shift angle is not enough.

If it is a small DSP board in Xi'an, it has circuit board power supply voltage (18V) too low protection and reactor

Replace the inverter radiator, because the radiator will have junction temperature in the second half of the night

If the incoming line voltage is too low, the power of transformer or intermediate frequency equipment will be reduced. When the boiler water is almost full, the current will rise, and the voltage will start to drop, and then there will be frequent over-current. There is also an open circuit of current feedback resistance, which will also cause frequent over-current

The main problem is the power supply, for example, the waveform and frequency of the power supply, the purity of the shop assistant and so on

I repaired a 0.5 ton furnace, and the medium frequency voltage can't be adjusted. The maximum voltage can only be adjusted to 650 v. I don't know why. It's the same with changing the control board. How much should the medium frequency voltage be?

If the DC output voltage can reach above 500V, it should be due to improper adjustment of inverter parameters, that is, the angle before current leading is small, the inverter power factor is 1.1 times of DC voltage / intermediate frequency voltage, which can be adjusted by adjusting the power factor adjustment potentiometer. Generally, the adjustment range of intermediate frequency voltage is 650v-800v. In order to improve the smelting speed, some users adjust the intermediate frequency voltage above 900v at the expense of others At the cost of other indicators. If the adjustment is invalid, it may be the parameter problem of the phase-shifting circuit or slot circuit, so it is necessary to make appropriate adjustment.

There is a 0. 5 ton electric furnace, constant power line, double voltage line, 4 pieces

Fault: medium frequency voltage 800 and current 500 of light furnace are normal. When the furnace is opened for more than half a year, if the medium frequency voltage is 800 a and the current is 650a, it will be over-voltage and over-current, and the sound of "thump" will appear at the same time. Only when the voltage is 700 and the current is 650a can it be normal.

Sometimes it's normal to put the over-current up to 820, that is, sometimes the sound of "click" will cause over-voltage and over-current.

Two new pumps were used for pulse variable pressure gas

The inverter inductance is not suitable or try to change the board.

Check if there is water leakage in some places and the insulation is wet.

Two new 3000kW medium frequency electric furnaces [6 tons] will interfere with each other if they are started at the same time. What's a good solution

Both of these two furnaces are 12 pulse double rectifiers, and the current of each other's double rectifiers will be seriously unbalanced when they operate at the same time. The power supply is a six phase transformer, and two furnaces share one transformer.

Re connect the ground wire

The manufacturer has separately added a diode to the output side (front end of reactor) of two rectifier bridges in one of the two sets of electric cabinets. In order to contain interference, the effect is not good. Is this reasonable

Diodes are added to make the current continuous, which should be added to each set of rectifier bridge arm of each set of power supply

The interference will not only make the current of the two rectifier bridges unbalanced (the difference is 300-400a), but also make the current of the two rectifier bridges unstable

The solution of 3000kW interference is another transformer, two furnaces can't share one, the other transformer is rectifier transformer, the impedance voltage should not be less than 6.95%

Try it. Use 18 2mm thick copper tube to wind 240mm diameter hollow inductor under the air switch. The rectifier control circuit of the cabinet should be symmetrical, and the phase sequence should be symmetrical. The trigger part of the rectifier should be strongly triggered, and the trigger pulse voltage should not be less than 12V. The resistance capacitance protection resistance of KP silicon should be non inductive resistance, and the power should not be less than 300W. The star and angle voltage of transformer should be 660V, The phase difference shall not be greater than 1 v. in addition, the 5th, 7th, 11th and 13th harmonic filtering devices must be added.

The air core inductor has been cut off at the load side of air switch, but the effect is not good

The rating plate of the reactor is 6.9mh

It should be judged whether the control circuit is disturbed or the main circuit is disturbed? Try the following methods:

1. Turn off the current sharing function of the control panel temporarily to see if the interference is reduced.

2. Connect a 0.47 UF capacitor and a 47 ohm capacitor to the rectifier silicon control pole to see what the effect is?

1. Increase the width of trigger pulse.

2. Increase the value of rectifier resistance capacitance absorption capacitance.

3. In the rectifier output (reactance back-end) and a dummy load, do the next test.

This phenomenon may also be due to poor ground entry effect, that is, large ground resistance

If this phenomenon still exists after the grounding problem is solved, the anti-interference device must be added in front of the power transformer of the control circuit

A induction furnace (250KW) with constant power sweep start control operates normally under low power 120kw, but as soon as the power is increased, the inverter thyristor will be burned immediately, and the electric heating capacitor, cable and cable head, reactor, resistance capacitance protection, and ground insulation of equipment components are all OK

You can check if there are any problems with the furnace, such as poor insulation, poor ignition, poor lining, damp new furnace, poor heat dissipation of thyristor, etc

If you change the radiator, there may be some sludge in it, so the heat dissipation is not good

Replace the pulse trigger board of the thyristor that often breaks down,

It was found that it was caused by the soft breakdown of a diode on the inverter pulse transformer board. Everything was normal after replacement!

If the diode is broken, the intermediate frequency machine can still work. Do you think it's strange? In fact, some faults of the intermediate frequency machine can't be understood with conventional theoretical knowledge. For example, when I encounter a fault, the reactor will jump when I start the machine. You will think it's lack of phase. In fact, it's not. The answer is a KK tube

Why does the DC current decrease with the increase of full charge temperature?

When steel (iron) is heated and melting furnace is cold, RD is very small. In cold state, the frequency is low and the current is high. In the hot state, the frequency increases automatically, the RD increases and the current decreases.

If the current is large in the cold state, the current in the full furnace is larger than that in any period (because the closer the molten steel is to the full furnace, the higher the temperature is). Why?

Under the condition of the same burden weight, the transfer resistance RD of the cold furnace is small, but the current is certainly large. With the increase of temperature, when the temperature exceeds the Curie point, the magnetic characteristics change, the transfer resistance Rd increases, and the current will decrease (of course, the decrease of current is also related to the increase of the channel impedance due to the increase of the channel frequency). Of course, if the medium frequency power supply is full, the weight of the charge is different from that of the cold furnace, and it must be greater than that of the cold furnace. Therefore, with the increase of the burden weight, the natural current is larger. At the same time, in order to shorten the furnace discharging time, the furnace manufacturer also intentionally reduces the inverter power factor, increases the intermediate frequency voltage and increases the power (current) during the temperature rising period.

As we all know, metals are generally magnetic materials (except copper and stainless steel). Medium frequency furnace uses induction heating to melt the charge. When the charge is below the cold state and Curie point temperature, the metal is still magnetic material, so the current is too high. When the charge is heated and the temperature exceeds the Curie point, it will become non-magnetic material, and the main magnetic flux of the furnace will be lower The leakage flux will increase and the current of the equipment will decrease with the increase of the leakage flux

Eddy current plays a significant role, otherwise the induction heating of non-magnetic materials such as copper and aluminum will become a problem.

There is a medium frequency power supply in our factory, which is often over-current. It is a diathermy furnace. I used to turn on the DC voltage only to 300V for many times, and the DC current will suddenly increase. The medium frequency voltage changes very little, but the DC voltage becomes much smaller. At this time, the ratio of medium frequency voltage and DC voltage increases to about 3. Check the back voltage of the inverter silicon with a multimeter (no oscilloscope). It is found that there are two voltages on one side, one is large and the other is small. It is suspected that one of them is not connected, but it can only be used for one or two days after several times of silicon replacement, and then the furnace will be over charged if there is not much charging. It's still the same after changing the water jacket. Changing motherboard is the same as changing silicon.

Try changing the pulse

Now it has been basically found out that the thyristor is not up to standard. Just change the thyristor of a regular factory

My opinion is not necessarily correct, I think: 1000kvar connected in parallel, 3000kvar connected in series, so that the induction coil voltage can be increased to about 2250v, can improve the smelting speed

Yiphee Electric Furnace Co.,Ltd specializes in producing induction smelting furnace.Tel(WhatsApp):+86-13450756789, yiphee@yiphee.cn