How to reduce the probability of SCR burnout

Oct 24, 2022

Silicon controlled rectifier is the heart of medium frequency power supply of medium frequency furnace, and its correct use is crucial to the operation of equipment. It is normal that several thyristors are occasionally damaged during the use of intermediate frequency furnace. If silicon is burned frequently, it will cause alarm. The working current of silicon controlled rectifier is several thousand amperes, and the voltage is usually one or two kilovolts. Good main control board protection and good water cooling conditions are necessary.

Overload characteristics of silicon controlled rectifier: the damage of silicon controlled rectifier is called breakdown. Under normal water cooling conditions, the current overload capacity can reach more than 110%; No voltage overload capability, that is, silicon is definitely damaged under overpressure. Considering the surge voltage, manufacturers often select silicon components based on 3-4 times of the working voltage when manufacturing equipment. For example, when the rated working voltage of the intermediate frequency cabinet is 1750V, two 2500V withstand silicon elements are selected to work in series, which is equivalent to 5000V withstand voltage.

Correct installation pressure of silicon controlled rectifier: 150-200KG/cm2. When the equipment leaves the factory, it is generally pressed with an oil press. This value cannot be reached with the maximum strength of an ordinary wrench manually, so there is no need to worry about the silicon being crushed during manual pressure loading; If it is loosened, it will burn silicon due to poor heat dissipation.

The radiator structure of silicon controlled rectifier: water-cooled cavity+multi copper column support. If the circulating water is too hard, it will scale inside the water chamber, causing poor heat dissipation; If leaves and other sundries enter the water chamber, the water flow will also be blocked.

The factory test temperature of silicon controlled rectifier is 100 ℃ (junction temperature). Generally, the circulating water temperature of the electric cabinet is kept below 45 ℃ to ensure its normal operation. The hand-held infrared thermometer is very useful. The 350 ℃ thermometer is only a few hundred yuan, not too expensive. It can be used to measure the thyristor temperature and radiator temperature of the working power supply, so that abnormal points can be found in time and faults can be handled.

The panel size of the radiator must match the panel size of the component to prevent the component from being damaged due to pressure deviation and deflection. The radiator table top must be flat and smooth. It is recommended that the surface roughness of radiator table is less than or equal to 1.6mm, and the flatness is less than or equal to 30mm. During installation, the component table and radiator table shall be kept clean and free of dirt such as oil stain.

During installation, keep the silicon element mesa completely parallel and concentric with the radiator mesa. During installation, it is required to apply pressure through the center line of the element so that the pressure is evenly distributed in the entire contact area. When the user installs manually, it is recommended to use a torque wrench to alternately and evenly exert force on all fastening nuts, and the pressure should meet the specified requirements.

When reusing the water-cooled radiator, pay special attention to check whether the table surface is smooth and flat, whether there is scale and blockage in the water chamber, especially whether the table surface is sagging, and if so, replace it.