Series compensation is a technology that connects reactive power compensation devices in series to the line for reactive power compensation. Its main application areas are rural power distribution, high-voltage long-distance transmission, and electrified railway power supply. Here we introduce the classification of series compensation devices in series resonance.
Series compensation devices are used on transmission lines to improve the stable transmission capacity of the system, improve line electrical parameters, and achieve the power of three lines transmitted by two lines, which not only increases transmission power but also saves investment. There are usually two types of capacitors used for series compensation: external fuse capacitors and internal fuse capacitors.
1. External Fuse Capacitors
External fuse capacitors have the fuse device installed outside the capacitor unit. According to IEC standards, the fusing current of the external fuse should be more than 1.43 times the rated current of the protected capacitor, generally taken as 1.5 times. For the variable frequency series resonance withstand voltage test device, capacitors used for series compensation also need to consider that the fuse should not blow when the capacitor bank is short-circuited and discharged at both ends. Otherwise, when a system fault occurs and the series compensation capacitor bank is taken out of operation, the bypass gap or shunt switch bypassing the capacitor bank may cause the external fuses of the capacitor bank to operate.
2. Internal Fuse Capacitors
Internal fuse capacitors have the fuse installed inside the capacitor. Each phase of the capacitor bank consists of 320 capacitor units. For the variable frequency series resonance withstand voltage test device, this capacitor is an oil-immersed all-film capacitor with an actual design electric field strength of 170V/um. The protection level of the capacitor bank is 2.3pu, and the protection voltage is 230. Since the recovery voltage after the fuse of the capacitor unit is blown is relatively high, the manufacturing of the fuse is relatively difficult. When a certain capacitor element fails, only the fuse of that capacitor element blows, disconnecting that capacitor element. After the faulty capacitor element is disconnected, the capacitor unit can still operate normally. For the variable frequency series resonance withstand voltage test device, the capacitor capacity is relatively small. According to the design example of the capacitor bank, a single capacitor unit only loses 1/52 of its capacity.
