Wiring Method and Filtering of Power Capacitor Capacitor Bank Reactors

The wiring of capacitors is usually divided into two ways: triangular and star. In addition, there is a distinction between double triangles and double stars.   
Triangle connected capacitors directly bear the voltage between the lines. When any capacitor is broken down due to a fault, a two-phase short circuit is formed, and the fault current is large. If the fault cannot be quickly removed, the fault current and arc will cause the insulation medium to decompose and produce gas, causing the fuel tank to explode and affecting adjacent capacitors. Therefore, this type of wiring is rarely used in 10kV systems, only a small amount is used in 380V distribution systems.  
In the high-voltage power grid, star connected capacitor banks are currently widely used both domestically and internationally. The inter pole voltage of star connected capacitors is the phase voltage of the power grid, and the insulation withstands a lower voltage. The manufacturing design of capacitors can choose a lower working field strength. When one capacitor in the capacitor bank experiences a breakdown or short circuit due to a fault, the fault current will be reduced to a certain range due to the impedance limitation of the other two healthy phases, and the impact of the fault will be reduced.  
The structure of star connected capacitor banks is relatively simple and clear, and the construction cost is economical. When applied to higher voltage levels, this type of connection is more advantageous.  
The biggest advantage of star wiring is that multiple protection methods can be selected. After a few capacitors fail and break through a short circuit, a single protective fuse can quickly cut off the faulty capacitor without causing the capacitor to explode.  
Due to the above advantages, high-voltage capacitor banks of various voltage levels are now commonly connected in star configuration.  
In addition to widely using star connection for capacitor banks in high-voltage power systems, double star connection is also widely used domestically and internationally. The so-called double star connection refers to dividing capacitors into two star connected capacitor banks with equal or similar capacitors, which are connected in parallel to the power grid bus. The neutral points of the two capacitor banks are connected by a low transformation ratio current transformer.  
This type of wiring can utilize the current protection device connected to its neutral point. When a capacitor fault breaks down and is cut off, an unbalanced current will be generated, causing the protection device to act and disconnect the power supply. This protection method is simple and effective, and is not affected by system voltage imbalance or ground faults.  
For capacitor banks with large capacity, if the capacity of a single unit is small and the number of parallel units per phase is large, double star wiring can be chosen. If the voltage level is high and there are many series sections per phase, it is advisable to use a single star connection to simplify the structural layout.  
The primary side of the capacitor is connected with a series reactor and a parallel discharge coil. The function of the discharge coil is to quickly and reliably release the charge on the capacitor after disconnecting the power supply. Due to the frequent operation of switching on and off the capacitor bank, the interval may be very short. After the power supply is disconnected, there is a large amount of charge stored between the electrodes of the capacitor bank, which cannot disappear quickly. In a short period of time, there is a high DC voltage between the electrodes. When the power is switched on again, it will cause voltage superposition, which will generate high overvoltage and endanger the safe operation of the capacitor and the system. Therefore, it is necessary to install a discharge coil and connect it in parallel with a capacitor to form an inductive capacitance parallel resonant circuit, so that electrical energy can be consumed in the resonance. The discharge coil should be able to reduce the capacitor terminal voltage to 50V within 5 seconds after the capacitor is disconnected from the power supply.