Reactors are also called inductors. When an electrical conductor is connected to the power supply, it will cause an electromagnetic field in a certain space occupied by it. Therefore, all electrical conductors that can carry current are inductive in a general sense.
The inductive load must absorb the active current and reactive current of the power grid to operate, so that the power grid can improve the transportation of reactive current, and the loss of the power grid line will increase. The capacitor cabinet automatically inputs the required amount of capacitors according to the line inductive load loss and reactive current to provide a moderate amount of reactive current, thereby improving the power factor of the line. In the case of compensating the output power, the capacitor usually suffers from the impact of harmonic voltage and harmonic current, which leads to the destruction of the capacitor and the reduction of the power factor. Therefore, harmonic correction must be carried out under compensation.
For example, a diode rectifier circuit using capacitor filtering or inductive filtering on the DC side of the inverter is also a serious harmonic pollutant. The harm and damage of the harmonics caused by the operation of the inverter to the machine and equipment, the damage of the resonance current to the inverter, and the damage of the capacitor compensation cabinet to the inverter when it is automatically switched on. The harmonic current sent by the inverter is introduced into the system, which will cause a large current on the capacitor. If we install an input reactor at the incoming line of the inverter, we can minimize all kinds of negative effects and injuries, thereby ensuring the safe and stable operation of the inverter.
Inverters belonging to non-linear devices also consume reactive power. For example, when the three-phase bridge rectifier power circuit adjusts the working voltage, the fundamental wave current lags behind the grid working voltage during operation, which consumes a lot of reactive power. In addition, this kind of equipment will also cause a lot of harmonic currents, and the harmonic sources consume reactive power.
In high and low voltage reactive power compensation equipment, series reactors are generally equipped with two key points:
1) Limit the closing surge current so that the surge current will not exceed 20 times;
2) Suppress the high-order harmonics of the power supply system for maintenance of capacitors. Therefore, the efficiency of series reactors in reactive power compensation equipment is very critical.
The reactors used in the power supply system generally include series reactors and parallel reactors. The series reactor is mainly used to limit the short-circuit fault current, and it is used to limit the high-order harmonics in the power grid in parallel or in series with the capacitor in the filter.
The reactor and the capacitor are connected in series, and its main function: when a short-circuit fault occurs, the current on the series reactor is very large, so it also has the function of maintaining the bus voltage level, so that the working voltage on the bus does not fluctuate much, ensuring that it is very common The reliability of the operation of the customer's electrical equipment on the faulty line.
As everyone knows, series reactance and capacitors cannot be randomly formed, because the objectivity, diversity and contingency of power harmonics, as well as the differences in the structure and characteristics of the power grid to which the capacitor equipment belongs, promote the harmonic response of the capacitor equipment and the series reactance rate. Selection has become a difficult problem, and this is also a topic that requires practical scientific research. The characteristics of the power circuit have been changed after the capital investment of the capacitor bank in series reactor. The series reactor not only has the advantages of suppressing surge current and harmonics, but also has the disadvantages of its additional increase in power consumption and construction project investment and operation costs.
The capacitor compensation cabinet automatically controls the switching of the capacitor bank to keep the power factor in a high range during normal operation. If the adjustment is not good, it is very likely that oscillation will occur at low load, that is, compensation at low load. The capacitor is constantly switched on and off, and it cannot work stably. When the capacitor is put into the system, because there is no charge on the two pole pieces of the capacitor, it is equivalent to a short-circuit fault in an instant, and the charging current decays exponentially. This current transition is called "surge", which is the moment when the normal operating voltage is exceeded. Voltage. In essence, a surge is a strong pulse generated in just a few millionths of a second. The surge caused by the frequent switching of capacitors is very harmful to the inverter: the accumulation of several small surges leads to the fading of the rectifier diode and the DC bus capacitor characteristics, which reduces the service life of the inverter and even burns; a large surge immediately causes Inverter fuse is blown, rectifier diode penetrates, etc.
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