HVDC REACTORS APPLICATION BASIC AND TUTORIALS

REACTORS IN HVDC APPLICATIONS BASIC INFORMATION

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.

CAPACITOR INRUSH/ OUTRUSH REACTORS BASIC AND TUTORIALS

CAPACITOR INRUSH/ OUTRUSH REACTORS BASIC INFORMATION

What Are Capacitor Inrush/ Outrush Reactors?

Capacitor switching can cause significant transients at both the switched capacitor and remote locations.

The most common transients are:

• Overvoltage on the switched capacitor during energization

• Voltage magnification at lower-voltage capacitors

• Transformer phase-to-phase overvoltages at line termination

• Inrush current from another capacitor during back-to-back switching

• Current outrush from a capacitor into a nearby fault

• Dynamic overvoltage when switching a capacitor and transformer simultaneously

Capacitor inrush/outrush reactors (Figure 2.9.15) are used to reduce the severity of some of the transients listed above in order to minimize dielectric stresses on breakers, capacitors, transformers, surge arresters, and associated station electrical equipment.

High-frequency-transient interference in nearby control and communication equipment is also reduced. Reactors are effective in reducing all transients associated with capacitor switching, since they limit the magnitude of the transient current (Equation 2.9.5), in kA, and significantly reduce the transient frequency (Equation 2.9.6), in Hz.

where

Ceq = equivalent capacitance of the circuit, F

Leq = equivalent inductance of the circuit, H

VLL = system line-to-line voltage, kV

Therefore, reflecting the information presented in the preceding discussion, IEEE Std. 1036-1992, Guide for Application of Shunt Power Capacitors, calls for the installation of reactors in series with each capacitor bank, especially when switching back-to-back capacitor banks.

Figure 2.9.16 shows a typical EHV shunt-capacitor installation utilizing reactors rated at 550 kV/1550 kV BIL, 600 A, and 3.0 mH

550-kV capacitor inrush/outrush reactors.