Failure analysis of mediate frequency furnace - Part 2


Through above inspection methods, user can figure out most failure reason, then user can turn power on, do further inspection. The main power switch-on of mediate frequency power has manual & auto types, to switch-on system, user should cut off power cable, to ensure main circuit not work. User can do these inspection after control power connected.


1.    link the probe of oscilloscope between rectifier SCR gate and cathode, the oscilloscope keep synchronization with power, push start button to check triggering pulse wave, it must dual pulse, range bigger than 2V, then push the stop button, the pulse disappear immediately, repeat this action 6 times, and check each thyristor, if gate without pulse, user can move the probe to pulse transformer original rim, if original rim has pulse but second rim without pulse, that mean pulse transformer broken, otherwise the problem is transmit wire or main control board.


2.    link the probe of oscilloscope between inverter SCR gate and cathode, the oscilloscope set as internal synchronization, user can see inverter triggering pulse after control power connected, it is a series of peak pulse, range should bigger than 2V, user can read pulse cycle by oscilloscope time scales and count out triggering pulse frequency, in normal condition, this frequency should higher 20% than power cabinet marked frequency, this is start frequency. Push start button, gap turn big between pulse, frequency turn low, in normal condition, this frequency 40% lower than power cabinet marked frequency. After above inspection, user can move total unable start failure. Abnormal working after start, it has several spects:

a.    Rectifier lack-phase
b.    Inverter three bridge arm on working


3.    Induction coil failure, its normal failure is:
Coil leakage: need make up welding
Liquid steel stick on the coil: must clean up
Coil short circuit: coil deformation by over heat


Hope our above inspection tips can help you to check mediate frequency furnace failure, the best way is to familiar your furnace structure and feature, know normal failure reasons. Welcome to read this article, we are DoMelting Technologies Co. your professional furnace and  parts provider.

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