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Holly, Texas

STATCOM replaces critical urban generation for voltage control and stability


Since 2005, Austin Energy, the public utility serving Austin, Texas and the surrounding area, has been operating an ABB-supplied STATCOM on its 138 kV power system. The STATCOM, rated at 80 Mvar inductive to 110 Mvar capacitive, replaces the Holly oil- and gas-fired power plant near downtown Austin, which was constructed in the 1960s and early 1970s. Due to the plant’s age and reduced use, the availability of more cost-effective generation elsewhere, and concerns of nearby residents regarding noise and other environmental factors, Austin Energy decided to close the plant.

Retirement of the power plant without a reliable dynamic reactive power source would be detrimental to the transmission system’s voltage stability. Due to the abundance of high-tech sensitive loads in the region, a fast response to help recover from voltage sags is a particular concern for Austin Energy. Flexible AC Transmission Systems (FACTS) technology was considered as a possible solution. To provide the voltage stability and reactive power that would be lost with the closure of the generating plant, Austin Energy initiated a study to determine the size, type, location and connection voltage of a FACTS solution. Space was scarce at the Holly site and ambient noise was a major concern. In addition, some concerns existed about magnetic fields contributing to forces in rebar
and in an oil tank beneath the site. For these reasons, the study ruled out an SVC and instead recommended installation of a STATCOM at the Holly 138 kV bus, along with three 31 Mvar mechanically-switched capacitor banks (MSCs) controlled by the STATCOM. Austin selected an ABB STATCOM, also known as SVC Light®, which uses insulated-gate bipolar transistor (IGBT) power semiconductors.

To save space and to address ambient noise concerns, the complete STATCOM, except for the step-down transformers, is housed inside a two-story building. In addition, due to the acoustic noise screening requirements, the phase reactors and harmonic filters are enclosed and the step-down transformers are equipped with additional light-weight sound insulation walls.


Main data

System voltage: 138 kV
Dynamic var rating 80 Mvar inductive to 110 Mvar capacitive
VSC 3-level, neutral point clamping converter, IGBT based, pulse width modulated, Pulse number:21.
VSC rating 95 MVA
Control system Three-phase dynamic positive-sequence voltage control, by means of a closed-loop, high sped digital voltage controller. The control includes switching of three MSCs, each rated at 138 kV, 31 Mvar, for steady-state system voltage control.

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