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Model description and maintenance methods of resonant capacitors

2023-04-06

The intermediate frequency electric capacitor uses a coarsened polypropylene film and is immersed in a high-performance liquid as a composite medium, with high-purity aluminum foil as the electrode plate; The shell is a rectangular aluminum alloy oil tank, often equipped with water-cooled pipes. Mainly used in controllable or adjustable AC power systems with a rated voltage not exceeding 3.6kV and a frequency of 50kHz and below, specifically designed to improve the power factor of induction heating, melting, stirring or casting devices, as well as similar applications.

 

Model and meaning of intermediate frequency capacitor: RFM30.75-1000-1S

R series code (electric heating) F liquid medium code (diarylethane)

M Solid medium code (polypropylene film)

3. Design number 0.75 represents the rated voltage (KV)

1000 represents Nameplate capacity (Kvar)

1 represents rated power (KHz)

S endnote number (water-cooled)

 

Parallel capacitors should be regularly powered off for inspection, at least once a quarter, mainly to check whether there is dust or other dirt in the capacitor shell, ceramic sleeve, installation bracket, and other parts, and carefully clean them. During inspection, special attention should be paid to whether the connections of each connection point are firm and loose; Check if the shell is bulging or leaking oil. If the above phenomena are found, the capacitor must be removed from operation and properly handled.

 

Strictly control the operating voltage, and the operating voltage of parallel capacitors must be strictly controlled within the allowable range. The long-term operating voltage of parallel capacitors should not exceed 10% of their rated voltage. If the operating voltage is too high, it will greatly shorten the service life of the capacitor. As the operating voltage increases, the dielectric loss of the parallel capacitor will increase, causing the temperature of the capacitor to rise, accelerating the aging rate of the capacitor insulation, causing premature aging and breakdown of the internal insulation of the capacitor, leading to damage. In addition, under the action of excessively high operating voltage, the insulation medium inside the capacitor will undergo local aging. The higher the voltage, the faster the aging and the shorter the lifespan.

 

If the long-term operating voltage of a parallel capacitor is higher than 20% of its rated voltage, its service life will be about 0.3 times that of normal conditions. Therefore, the rated voltage should be reasonably selected based on the actual operating voltage of the local power grid, so that its long-term operating voltage is not greater than 1.1 times the rated voltage of the capacitor. Of course, low actual operating voltage is also very unfavorable, because the reactive power output by parallel capacitors is directly proportional to the square of their operating voltage. If the operating voltage is too low, it will reduce the reactive power output of the capacitor, unable to complete the task of reactive compensation, and losing the role that installing parallel compensation capacitors should play. So in actual operation, it is necessary to try to maintain the operating voltage of the parallel capacitor at 95% to 105% of its rated voltage for a long time, and the maximum operating voltage should not exceed 110% of its rated voltage value.

 

Control the operating temperature. In normal environments, it is generally required that the temperature of the hottest point of the parallel capacitor shell should not exceed 60 ℃. Otherwise, the cause must be identified and dealt with.

 

Timely handle abnormal operating conditions. If abnormal situations such as bulging, joint heating, and severe oil leakage are found in the parallel capacitor of the medium frequency electric furnace during operation, it must be removed from operation. For malignant accidents such as fuel injection, fire, and explosion that have occurred, power outage inspection should be carried out immediately to identify the cause of the accident and handle it before replacing the capacitor with a new one to continue operation.