The main cause of overvoltage is because the circuit is usually connected with an inductive component. When the circuit is switched off or on, the voltage in the circuit tends to exceed the normal value when switching from one component to the other, and when the fuse is blown. Sometimes lightning strikes can also cause overvoltage.
There are several protection measures for thyristor overvoltage:
1. Resistor protection can use capacitors to absorb overvoltage. The essence is to convert the energy that causes the overvoltage into the electric field energy and store it in the capacitor, then release it into the resistor to consume it. This is the basic method of overvoltage protection.
The RC absorber element can be connected in parallel to the AC side (input), DC side (output) or component side of the rectifier.
2. Selenium Reactor Protection Selenium Reactor (Selenium Rectifier) ​​is a non-linear resistance element with steep reverse characteristics. When the voltage on the selenium stack exceeds a certain value, its resistance is rapidly reduced, and the overvoltage energy can be consumed on the non-linear resistor through a large current, and the selenium stack is not damaged.
The selenium stack can be used alone (Figure 1) or in parallel with the RC element.
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