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Reason for unbalanced protection action of DC filter capacitor
Release time:
2025-04-15
DC filter is a type of filter mainly used to block and short-circuit AC signals.
DC filter is a type of filter mainly used to block and short-circuit AC signals. Capacitors can be used for filtering to make the output waveform smoother. By connecting capacitors in series to improve voltage resistance and parallel to increase capacity, the output DC becomes more stable. As an important equipment of the converter station, the DC filter is installed between the DC high-voltage bus and the neutral bus, and is a means of suppressing DC side harmonics in the high-voltage DC transmission system.
The unbalanced protection of DC filters is used to protect capacitors from avalanche damage caused by overstress of the complete capacitor bank by faulty capacitor units. High voltage capacitors are expensive components in DC filters, capable of withstanding all DC voltages and most harmonic voltage drops on DC lines, thus requiring high sensitivity for unbalanced protection. Capacitors are generally divided into two equal capacity branches to detect faults. When the capacitor is damaged, the harmonic currents in the two branches will be unbalanced. However, due to the diversity of operating modes and the variability of harmonic voltages and currents in DC systems, the harmonic components in the harmonic currents flowing through DC filters vary over time. When the same capacitor is damaged, the unbalanced current is also different. In addition, under normal conditions of DC filters, the capacitance value may change due to manufacturing errors, aging of capacitor components, temperature, sunlight, and other external environmental parameters, which can also lead to current imbalance.
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