What Are The HVDC Application Reactors?

In an HVDC system, reactors are used for various functions, as shown, in principle, in Figure 2.9.25.

The HVDC-smoothing reactors are connected in series with an HVDC transmission line or inserted in the intermediate dc circuit of a back-to-back link to reduce the harmonics on the dc side, to reduce the current rise caused by faults in the dc system, and to improve the dynamic stability of the HVDC transmission system.

Filter reactors are installed for harmonic filtering on the ac and on the dc side of the converters. The ac filters serve two purposes simultaneously: the supply of reactive power and the reduction of harmonic currents.

The ac filter reactors are utilized in three types of filter configurations employing combinations of resistors and capacitors, namely single-tuned filters, double-tuned filters, and high-pass filters.

A single tuned filter is normally designed to filter the low-order harmonics on the ac side of the converter.

A double-tuned filter is designed to filter multiple discrete frequencies using a single combined filter circuit.

A high-pass filter is essentially a single-tuned damped filter. Damping flattens and extends the filter response to more effectively cover high-order harmonics. The dc filter reactors are installed in shunt with the dc line, on the line side of the smoothing reactors.

The function of these dc filter banks is to further reduce the harmonic currents on the dc line (see Figure 2.9.24 and Figure 2.9.25).

PLC (power-line carrier) and RI (radio interference) filter reactors are employed on the ac or dc side of the HVDC converter to reduce high-frequency noise propagation in the lines.

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