3 T steel shell melting furnace power supply protection

3 T steel shell melting furnace power supply protection function is designed for various abnormal conditions and faults of the power supply, mainly over current protection and over voltage protection.

The three-phase full-controlled rectifier bridge, when the rectification triggers the phase shift angle α>90°, the rectifier bridge enters the inverter working state of the feedback energy to the input three-phase grid. With this working characteristic, the self-fast protection of the power supply can be realized.

When the power inverter output load is short-circuited or inverter controlled, and the drive circuit is not normal, the inverter bridge input terminal short-circuit phenomenon will occur, causing short-circuit overcurrent of the power supply, and the overcurrent protection circuit monitors the three-phase incoming line current. When the current exceeds the setting value, the phase shift angle of the rectifier bridge is increased to 150°, so that it enters the inverter working state, and the overcurrent indicator light is illuminated.

Inverter bridge short circuit, the maximum short-circuit current value I dM of the rectifier bridge pull-in inverter process is related to the rectified output inductor value and the working state of the inverter bridge short-circuit time. Generally, the I dM does not exceed 3 times of the rated working current ( Further reduction of I dM is necessary to increase the inductance, which in turn affects the overall performance of the power supply. Since the thyristor overload capability of the fully controlled power electronic device is lower than that of the semi-controlled SCR, even three times the rated operating current The operation of the thyristor is also damaged. For this reason, the power supply of the device is connected with a protection thyristor TY7 at the input end of the inverter bridge. When the over-current pull-in inverter occurs, the TY7 is turned on at the same time, and the voltage drop after the TY7 is turned on (1.5V). The left and right) is far lower than the conduction voltage drop of the thyristor bridge arm, and thethyristor current is immediately transferred to TY7, so that the circuit current flowing through the thyristor during the short circuit has no overshoot.

3 T steel shell melting furnace overvoltage protection circuit is used to protect the inverter power device thyristor from overvoltage damage. The current type inverter has a large inductance due to the DC output. When the input end of the inverter is open ( When the load is open to the inverter control, the drive circuit will not work normally.) The stored energy on the inductor is not discharged, and the inverter has an overvoltage at the input end. The power supply is connected to the inverter at the input end. Clamp circuit, when the inverter input open circuit, the clamp circuit provides a release path for the inductor energy, and limits the voltage rise rate of the inverter input terminal, detects the input terminal voltage, and generates a pulse when the set value is exceeded. The TY7 is turned on, and after the TY7 is turned on, the inverter input terminal becomes a short circuit state, thereby effectively protecting the impact of the overvoltage on the thyristor , and the overvoltage is converted into an overcurrent, and the power rectifier bridge is pulled as described above. The inverter automatically stops.