The operating voltage of high-voltage capacitors can reflect the voltage status of the substation busbar system and directly affect the lifespan and output function of capacitors. The active power loss inside high-voltage capacitors during operation mainly consists of two parts: dielectric loss and resistance loss, And the dielectric loss accounts for 989% of the total active power loss of high-voltage capacitors {Above. The dielectric loss of the high-voltage capacitor will directly affect the operating temperature of the capacitor, which can be expressed by the following formula: Pr is the active power loss of the high-voltage capacitor; Qc is the reactive power of the high-voltage capacitor; US is the tangent value of the dielectric loss angle of the high-voltage capacitor; 〇 is the grid angular frequency; C is the permittivity of the high-voltage capacitor; U is the operating voltage of the high-voltage capacitor.
According to the formula, the active power loss and reactive power loss of high-voltage capacitors are directly proportional to the square of the operating voltage of the high-voltage capacitor. As the operating voltage increases, the active power loss of the high-voltage capacitor will rapidly increase, and the speed of temperature rise will also increase, resulting in a decrease in the insulation life of the capacitor? In addition, the overvoltage of high-voltage capacitors during continuous operation is generally set at 1.10 times the rated voltage. When the capacitor is operated under overvoltage for a long time, it can cause overcurrent and damage to the capacitor; Therefore, the construction of high-voltage capacitors requires the installation of complete overvoltage protection devices.
Overcurrent caused by high order harmonics in the power grid
When the harmonic current in the power grid flows into the capacitor, it will be added to the fundamental current of the high-voltage capacitor, and its operating current will increase. At the same time, it will also increase the effective value of the peak voltage on the fundamental voltage of the high-voltage capacitor. If the capacitance reactance of the capacitor matches the system inductance, it will amplify the higher-order harmonics, resulting in over-current and over-voltage, causing partial discharge of the insulation medium inside the capacitor, resulting in bulge Faults such as fuse burst.