Methodology for characterizing electric power system response and locating the energized capacitor banks using conventional power quality data
Abstract
A relatively small harmonic current with frequencies near or at the
power system parallel resonant frequencies could excite the power system into
a resonance condition. While a capacitor bank is not the root cause of the
condition, it facilitates and helps cause the problem. This is because when the
capacitor bank is energized, the system resonant frequency could shift closer
to existing harmonic frequencies produced by nonlinear loads. Therefore, the
objective of this dissertation is to quantify the power system characteristics
corresponding to the parallel resonant frequencies and system damping. Additionally,
since a capacitor bank actively facilitates the resonance condition,
the relative or exact location of the involved bank must be determined.
This dissertation first presents a practical and accurate methodology to
estimate system parallel resonant frequencies by performing spectral analysis
of the voltage and current transient data immediately after the capacitor bank
switching. The proposed method is also robust in that the accuracy of the
resulting estimates is not affected by prevalent harmonics in the system.
This dissertation provides two efficient algorithms for estimating the
system damping parameters using the Hilbert and analytic wavelet transforms.
These algorithms take advantage of the principle of an asymptotic or weaklymodulated
signal, for which the signal phase varies much more rapidly than the
amplitude. The zero-input voltage response or free response of the capacitor
bank energizing can be categorized into these asymptotic signals, and one can
assign a unique time-varying amplitude with the system damping information
and phase pair by building analytic signals. System model reduction theory
also allows us to interpret or quantify this damping as an effective X/R ratio.
This dissertation defines two fundamental signatures of shunt capacitor
bank energizing. It demonstrates that these two signatures can be utilized
to accurately determine the relative location of an energized capacitor bank
whether it is upstream or downstream from the monitoring location. This dissertation
also presents an efficient and accurate methodology for finding the
exact location of an energized capacitor bank. Once a PQ monitor is found
to be upstream from the capacitor bank by the relative location finding algorithm,
the proposed algorithm can further determine the exact location of
the switched capacitor bank by estimating the distance between the PQ monitor
and the energized capacitor bank. Thus, one can pinpoint the energized
capacitor bank causing the resonance.
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