17-07-2012, 02:17 PM
FACTS and Custom Power Equipment for the Enhancement of Power Transmission System Performance and Power Quality
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INTRODUCTION
With the ongoing deregulation of the electric utility industry, numerous changes are continuously being introduced to a once predictable business. With electricity increasingly being considered as a commodity, transmission systems are being pushed closer to their stability and thermal limits, while the focus on the quality of power delivered is greater than ever. In the evolving deregulated utility environment, financial and market forces are, and will continue to, demand a more optimal and profitable operation of the power system with respect to generation, transmission and distribution. Now, more than ever, advanced technologies are paramount for the reliable and secure operation of power systems. Power electronic based equipment, such as Flexible AC Transmission Systems (FACTS), High-Voltage DC (HVDC), and Custom Power technologies constitute some of the most promising technical advancements to address the new operating challenges being presented today. These advancements are based on the high-performance capability of power electronic equipment to rapidly respond to system events, increase power transfer limits, and improve the quality of power delivered .The potential benefits of FACTS equipment are now widely recognized by the power system engineering community [1,2,3,4,5].As an advancement within the FACTS arena, voltage sourced converter based technology has been successfully applied in a number of projects [6,7,8,9,10,11,12,13].In addition to the applications described in the these references, there are several other recently announced voltage sourced converter based FACTS installations planned for operation in 2000 and 2001 in the USA, in the states of Texas and Vermont (no technical references are yet available for citation). All of these voltage sourced converter based applications are in addition to the established FACTS technologies of Static Var Compensation (SVC) [14] and Thyristor Controlled Series Compensation (TCSC) [15,16,17,18].As for the Custom Power requirements [19], utility distribution networks, sensitive industrial loads, and critical commercial operations can potentially suffer from various types of outages and service interruptions.
Application Example
In 1991, the world’s first commercial transmission system STATCOM (at the time known as SVG for Static Var Generator) was installed at the Inuyama substation of The Kansai Electric Power Company in Japan, for the objective of improving power system and voltage stabilization [6]. It has been successfully operating for nearly 9 years. Figure 2-5 shows an aerial view illustration of the Inuyama STATCOM installation. Table 2-1 shows the equipment specifications. Figure 2-6 shows the one-line
Diagram of this 80 MVA STATCOM. Shown in this figure are the eight 10 MVA voltage sourced converter stages connected via a line-side-series-connected multistage converter transformer to a 34.24 kV bus, and then through a main transformer up to the 154 kV transmission system. Each of the eight stages has the same output voltage, but shifted by 7.5 degrees from one to the other. With this 48-pulse system, minimal harmonics are generated.
DISTRIBUTION STATCOM FOR CUSTOM
POWER APPLICATIONS
System Requirements
The development efforts of advanced static compensation technology at the power delivery level
have resulted in a distribution STATCOM (DSTATCOM)that exhibits high speed control of reactive power to provide voltage stabilization, flicker suppression, and other types of system control. The DSTATCOM utilizes a design consisting of a GTO- or IGBT-based voltage sourced converter connected to the power system via a multi-stage converter transformer. The compact design has resulted in a size ratio improvement to nearly 1/3 the area and 1/5 the volume of a conventional dynamic compensation device ,namely, a distribution level SVC. This enables greater flexibility in terms of installation possibilities, and also provides a potential means to easily move the device to various locations around the power system. The following sections describe some equipment and control aspects of the D-STATCOM, along with an application example.