Analysis of common faults in intermediate frequency furnace

November 15, 2019

 

Analysis of common faults in intermediate frequency furnace

 

1) Fault phenomenon: The device cannot be started. Only the DC current meter has an indication when starting, and there is no indication of DC voltage and intermediate frequency voltage.

Analysis:

a. The inverter trigger pulse has a pulse phenomenon;

b. Inverter thyristor breakdown;

c. Capacitor breakdown;

d. The load has a short circuit and grounding phenomenon;

e. The intermediate frequency signal sampling loop has an open circuit or a short circuit.

 

2) Fault phenomenon: It is difficult to start. After starting, the intermediate frequency voltage is more than twice the DC voltage, and the DC current is too large.

Analysis:

a. The IGBT is damaged in the inverter circuit;

b. The inverter thyristor has a non-conducting, that is, "three legs" work;

c. The IF signal sampling loop has an open circuit or a polarity error phenomenon;

d. The inverter leads the front angle phase shifting circuit to malfunction;

 

3) Fault phenomenon: It is difficult to start, DC voltage after starting, it is difficult to reach full load or it is difficult to get close to full load, and the reactor vibrates greatly and the sound is dull.

Analysis:

e. Rectifier thyristor open circuit, breakdown, soft breakdown or electrical parameter performance degradation

f. Missing a set of rectified pulses

g. Rectifier thyristor gate open or shorted

 

4) Fault phenomenon: It can be started, but it will stop immediately after starting, and the equipment will be continuously restarted.

Analysis:

h. The lead angle is too small;

i. The load oscillation frequency is at the edge of its excitation frequency

 

5) Fault phenomenon: After the equipment is started, when the power rises to a certain value, it is easy to over-current protection. Sometimes the original thyristor is burned out and restarted. The phenomenon remains the same.

Analysis:

j. If an overcurrent is generated at a low voltage immediately after startup, the inverter lead angle is too small for the thyristor to be reliably turned off.

k. Inverter thyristor water cooling jacket cooling effect is reduced

l. The channel connection wire has poor contact

 

6) Symptom: Nothing happens when the device starts up, and the control board lacks equal brightness.

Analysis:

Fast-blow blown

 

7) Fault phenomenon: The DC current has reached the rated value when the equipment is running, but the DC voltage and the intermediate frequency voltage are low.

Analysis:

This phenomenon is not caused by the IF power failure, but due to the low load impedance.

a. The series capacitor is damaged

b. The sensor has a short circuit between the turns

 

8) Fault phenomenon: When the equipment is running, the DC voltage and the intermediate frequency voltage have reached the rated value, but the DC current is small and the power is low.

Analysis:

This phenomenon is just the opposite of 7) the fault phenomenon, which is caused by the high load impedance.

a. The compensation amount of the load compensation capacitor is insufficient.

b. The contact resistance of the tank connection node is too large to clean the dust.

 

9) Fault phenomenon: The equipment is running normally, the DC current indication is too high. If the current is set at the rated value, the voltage is too low, and the indication of the de-power meter is inconsistent with the indication of the current voltmeter.

Analysis:

This phenomenon is usually caused by the dirt and oxide layers of the shunt and wiring increasing the contact resistance and increasing the voltage generated on the shunt.

 

10) Symptom: The equipment is operating normally, but there is no response and no protection after starting. Instructions.

Analysis:

a. The IF start switch is damaged.

b. Protection circuit failure, usually there is a problem with the frequency sweep circuit integration block NE556 on the circuit board.

c. The given signal is interrupted in the given circuit.

 

11) Fault phenomenon: Frequent burnout of the thyristor original, after replacement, burned out

Analysis:

Refer to fault E) for additional introductions as follows:

a. When the thyristor is turned off in reverse, the instantaneous glitch voltage subjected to the reverse voltage is too high, and the RC absorption is checked.

b. The load is reduced to ground insulation, and the ground is fired, or high voltage is formed at both ends of the thyristor

c. Pulse trigger loop fault, sudden loss of trigger pulse causes open thyristor

d. Load open circuit when the device is running

e. Load short circuit when the device is running

f. Protection system failure (protection failure)

g. Thyristor cooling water system failure

h. Reactor failure, causing current interruption on the inverter side, burning the thyristor due to magnetic saturation of the reactor and loss of current limiting

i. The inductance of the commutating inductor is too large, or the insulation is reduced to cause current instability.

 

12) Fault phenomenon: When the device is started, when the IF start switch is turned on, the main circuit switch protection trip or overcurrent protection

Analysis:

a. The power adjustment knob is at the highest position, and the instantaneous current impact is too large.

b. The current regulator is faulty, especially if the current transformer is damaged or the wiring is open, the current feedback suppression is started, and the current impact is too large.

 

13) Fault phenomenon: The intermediate frequency transformer burns out, and the starting device is still burned out after replacement.

Analysis:

This phenomenon generally occurs on the boost load device, mainly due to the open circuit of the snorkeling discharge. The two sets of capacitor voltages in the boost mode are inconsistent. The high voltage discharge is slow during discharge. When it is not discharged, it starts to charge and will accumulate on the capacitor. The DC charge is released by the discharge and discharge, and the open circuit is discharged through the intermediate frequency transformer. The capacity of the intermediate frequency transformer is small and burned out.

 

14) Fault phenomenon: bleed and discharge in the booster circuit, heat or burnout

Analysis:

a. Small discharge and discharge

b. Inverted pulse asymmetry

c. When the inverter thyristor has a burnout condition, the output voltage of the intermediate frequency is fluctuating, causing a large current flowing through the discharge and causing heat or burnout.

 

15) Symptom: The device can be started, the startup frequency is much higher than the original, sometimes it is not good to start.

Analysis:

a. There is a short circuit between the load coils

b. The load capacitor column has an open circuit

 

16) Fault phenomenon: easy to start, but the voltage is easy to overvoltage when boosting, sometimes overvoltage and overcurrent appear simultaneously

Analysis:

a. The inverter lead angle is too large, causing the inverter glitch voltage to be too high

b. The main circuit inside the power cabinet has virtual connection, insulation reduction, and sparking

c. The load coil or capacitor has a virtual connection, insulation reduction, and sparking

d. Inverter thyristor trigger has a problem, the connection is loose or the door is open

 

17) Fault phenomenon: The device can be started, but the voltage rise is not high, the reactor sound is loud and dull, the voltage rises when it is unstable, sometimes overcurrent and overvoltage protection, sometimes burns the thyristor, but the rectifier is good.

Analysis:

a. The reactor has a large inductance and magnetic saturation, which does not filter.

b. Reactor insulation is not good

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