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1. Mid-frequency furnace is equipped with fuse protection
The fuse protection should be set for each single-frequency electric furnace capacitor, and the rated current of the fuse should not be greater than 1.3 times of the rated current of the protected capacitor. This can avoid the group explosion caused by the failure of a capacitor to be removed in time. The accident happened.
2. Intermediate frequency furnace to strengthen inspection, inspection and maintenance
Parallel capacitors should be periodically checked for power failure, at least once a quarter. Mainly check whether there are dust and other contaminants in the capacitor casing, porcelain casing, mounting bracket, etc., and carefully clean them. During the inspection, special attention should be paid to whether the connection of each joint is firm and loose; whether the casing is bulging, seeping (leaking) oil, etc. If any of the above phenomena are found, the capacitor must be taken out of operation and properly disposed of.
3. Strict control of operating voltage
The operating voltage of the intermediate frequency furnace shunt capacitor must be strictly controlled within the allowable range. That is, the long-term operating voltage of the parallel capacitor should not be greater than 10% of its rated voltage. If the operating voltage is too high, the service life of the capacitor will be greatly shortened. As the operating voltage increases, the dielectric loss of the parallel capacitor will increase, causing the capacitor temperature to rise, accelerating the aging speed of the capacitor insulation, causing premature aging, breakdown and damage of the capacitor insulation. In addition, under the action of excessive operating voltage, the insulating medium inside the capacitor will locally aging. The higher the voltage, the faster the aging and the shorter the life.
If the long-term operating voltage of the parallel capacitor is higher than 20% of its rated voltage, its service life will be about 0.3 times of the normal condition.
Therefore, according to the actual situation of the local grid operating voltage, the rated voltage value should be reasonably selected so that the long-term operating voltage is not more than 1.1 times the rated voltage of the capacitor. Of course, the actual operating voltage is too low, because the output of the shunt capacitor is very low. The reactive power is proportional to the square of its operating voltage. If the operating voltage is too low, the reactive power output from the capacitor will be reduced, the task of reactive power compensation cannot be completed, and the function of installing the parallel compensation capacitor should be lost. Therefore, in actual operation, we must try to keep the operating voltage of the shunt capacitor at 95% to 105% of its rated voltage for a long time, and the maximum operating voltage should not be greater than 110% of its rated voltage.
When the shunting switch is correctly selected to disconnect the parallel capacitor, the arcing effect between the static and dynamic contacts of the switch will cause the operating overvoltage to occur, except that the capacity of the switching (cut) switch is selected to be smaller than that of the shunt capacitor bank. In addition to the capacity of about 35%, it must also be a circuit breaker with high insulation recovery strength between the contacts, low arc reignition and good arc extinguishing performance.
Prevent harmonics from having many harmonic sources in the intermediate frequency furnace power grid. If the harmonics are too large at the grid point where the parallel capacitors are installed, if the parallel capacitors are directly input, the harmonics in the medium frequency electric furnace power grid will be larger, and the intermediate frequency furnace will be more The safety of shunt capacitors poses a great threat.
The method of installing a series reactor can effectively suppress the occurrence of harmonic components and inrush current, and has obvious effects on ensuring the safe operation of the parallel capacitor. Where necessary, the harmonic components of the parallel capacitor installation should be tested in advance, and the capacity of the series reactor to be installed should be determined according to the test results.
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