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FIGURE 2.9.13 Single line-to-ground fault in resonant-grounded system.
FIGURE 2.9.15 Typical capacitor inrush/outrush reactor connection.
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.
FIGURE 2.9.14 Typical duplex-reactor connection.
I V * ( C / L )
peak LL eq. eq.
(2.9.5)
2.9.2.2.5 Duplex Reactors
Duplex reactors are usually installed at the point where a large source of power is split into two simultaneously
and equally loaded buses (Figure 2.9.14). They are designed to provide low-rated reactance
under normal operating conditions and full-rated or higher reactance under fault conditions. A duplex
reactor consists of two magnetically coupled coils per phase. This magnetic coupling, which is dependent
upon the geometric proximity of the two coils, determines the properties of a duplex reactor under
steady-state and short-circuit operating conditions. During steady-state operation, the magnetic fields
produced by the two windings are in opposition, and the effective reactance between the power source
and each bus is a minimum. Under short-circuit condition, the linking magnetic flux between the two
coils becomes unbalanced, resulting in higher impedance on the faulted bus, thus restricting the fault
current. The voltage on the unfaulted bus is supported significantly until the fault is cleared, both by the
effect of the reactor impedance between the faulted and unfaulted bus and also by the “voltage boosting”
effect caused by the coupling of the faulted leg with the unfaulted leg of duplex reactors.
The impedance of a duplex reactor can be calculated using Equation 2.9.1 and Equation 2.9.2, the
same as those used for phase reactors.
f 1/ 2
Leq
C
. eq
(2.9.6)
where
C eq = equivalent capacitance of the circuit, F
L eq = equivalent inductance of the circuit, H
V LL = 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.
2.9.2.3 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
FIGURE 2.9.16 550-kV capacitor inrush/outrush reactors.
© 2004 by CRC Press LLC
© 2004 by CRC Press LLC