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What are the main causes of thyristor breakdown?
Overvoltage breakdown is one of the main reasons for thyristor breakdown. There is no time for thyristor to accept overvoltage. Even in a short time of a few milliseconds, overvoltage will be broken down. Therefore, in practical application circuits, RC absorption circuits must be connected at both ends of thyristor to prevent sudden overvoltage caused by various irregular interference pulses. If thyristor breakdown occurs frequently, please check whether the components of the absorption circuit can be burnt out or fail.
In fact, over-current breakdown and over-thermal breakdown is the same thing. Over-current breakdown is the current in the SCR chip when the internal thermal effect, so that the chip temperature rises, when the chip temperature reaches 175 ℃, the chip will fail and can not be restored. Under normal operating conditions, this thermal breakdown will not occur as long as the working current does not exceed the rated current of thyristor. As the principle of overcurrent breakdown is caused by temperature rise, and the process of temperature rise requires a certain period of time, overcurrent (hundreds of milliseconds to a few seconds) will not break down in a short period of time.
The over-thermal breakdown mentioned here refers to the thermal breakdown that occurs under the condition that the working current does not exceed the rated current of the thyristor. The main reason for this breakdown is that the auxiliary heat dissipation installation of the thyristor is poor, which causes the breakdown of the thyristor chip temperature to be too high. Regarding the use of water cooling, the main check is whether the inlet water temperature is too high (the general request water temperature should be below 25 ℃, but the maximum cannot exceed 35 ℃), and whether the flow rate is sufficient; For air-cooled work, check whether the number of revolutions of the fan is normal and the ambient temperature cannot be too high, but whether it is air-cooled or water-cooled.
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