Example 2 of troubleshooting induction furnace

A fault phenomenon: the equipment cannot be started, only DC ammeter has indication, DC voltage and intermediate frequency voltmeter have no indication.

Fault analysis and treatment are as follows:

A. the trigger pulse of inverter has pulse missing phenomenon. Use an oscilloscope to check the inverter pulse (preferably on the G-K of the thyristor). If there is a lack of pulse, check whether the connecting line has poor contact or open circuit, and whether the front stage has pulse output.

B. breakdown of inverter thyristor. Use a multimeter to measure the resistance between a and K. in the case of no cooling water, the value between a and K should be greater than 10k ohm. When the resistance is 0, it is broken. If there are two damages during the measurement, the connecting copper bar of one can be removed, and then judge whether it is one or two damages, replace the thyristor, and check the cause of thyristor damage.

C. capacitor breakdown. Use X1K gear of pointer multimeter to measure whether there is charging and discharging phenomenon at the common end of each column of capacitor. If there is no indication that the column is broken, remove the damaged capacitor pole.

D. the load is short circuited and grounded. 1000V megohmmeter (megger) can be used to measure the resistance of coil to ground (when there is no cooling water), which should be greater than 1 megohm, otherwise the short-circuit point and grounding point should be excluded.

E if signal sampling circuit has open circuit or short circuit. Observe the resistance value of each signal with an oscilloscope to find the open circuit point or short circuit point. Focus on checking if the primary side of intermediate frequency feedback transformer is open (caused by virtual connection of discharge inductance).

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