Page 34 - Energize April 2021

TECHNICAL

other precautions are taken and the circuit breaker is adequately Practical Considerations
rated for the specific application. The following additional aspects should be taken into account when
Oscillation frequency and magnitude are determined by the studying and designing shunt reactor installations:
inductance and stray capacitance associated with the reactor, circuit • Most installations of the kind described here contain more than
breaker and network components in close proximity to the circuit one shunt reactor on the transformer tertiary, in order to provide
breaker. These capacitances are generally very low, resulting in high fine voltage control.
frequency switching transients that are especially harsh on circuit • Some form of control is required to operate the various steps
breaker contact surfaces. The oscillation frequency can be reduced and this control should take into account the control system of
by means of surge capacitors placed between the reactor and the any tap changer that may be present on the transformer primary
circuit breaker. or secondary.
The effect of such surge capacitors is shown in Figure 4. The • Surge arresters are commonly applied to the reactor and
frequency of the switching transient is reduced from more than 40 transformer tertiary to avoid excessive voltages during
kHz to less than 6 kHz by the introduction of a 100 nF capacitor switching.
between phase and earth. The reduced oscillation frequency results • The selection of the right switching equipment results in
in less contact wear and therefore longer life of the circuit breaker, increased reactor life.
as well as reduced reactor inter-turn stress levels. • Appropriate magnetic and electrical clearances between
For voltages up to 34,5 kV, reactor switchers have been reactors and other substation equipment must be observed
developed by some manufacturers especially for shunt reactor and all footings must be designed for use together with air core
application, providing reduced turn-to-turn stress on the reactor reactors.
during switching and resulting in increased reactor life.
Conclusion
As the demand for more energy grows, modern transmission/
distribution systems are operated close to security limits. The ability
to control transmission voltages to the extent possible with shunt
reactors is highly attractive from a commercial and technical point
of view. The pressure to increase available power to the end user
results either in new generation or increasing the efficiency of the
system/reducing losses.
Shunt reactors are used in transmission systems to increase
the capabilities of transmission lines by injecting inductive power
to the system. This results in fewer transmission losses and
consequently, less new generation is required, indirectly reducing
carbon dioxide emissions. n

Figure 4 For more about GE’s Grid Solutions, visit www.gegridsolutions.com

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