Requirements documents for Design of Power Capacitors for Power Factor Improvement in a Power Distribution System submitted to: Professor Joseph Picone ECE 4522: Senior Design II Department of Electrical and Computer Engineering Mississippi State University Mississippi State, Mississippi 39762 September 14, 2000 submitted by: Page J. C., Parson L.B., Watson K.M., Wong C.S. Faculty Advisor: Dr. Stanislaw Gryzbowski Department of Electrical and Computer Engineering Mississippi State University Box 9571 Mississippi State, Mississippi 39762 email: {jcp2, lbp1, kmw2, csw1}@ece.msstate.edu DEPARTMENT OF ELECTRICAL AND COMPUTER ENGINEERINGExecutive Summary In the power distribution industry today, utility companies are trying to come up with a solution to increase the efficiency of distributed power. One way of achieving this task is by improving the power factor of a system by adding power factor correction capacitors. Power factor improvement is a very important aspect of power distribution. Without a good power factor, there cannot be an efficient means of transporting energy over long distances due to the losses associated with moving power through a wire. This action has led to multiple studies on power factor correction. In order to achieve maximum efficiency, we had to increase our power factor as close to unity as possible. We accomplished this controlled boost of power factor by installing the proper number of specifically designed high voltage power capacitors at the substation. In designing our capacitors, there were certain design constraints that had to be met and overcome. Our capacitors were designed according to established IEEE standard 18-1992. In addition, our capacitor bank was built around an average load on a typical substation. This typical substation is rated at 15kV and during the peak hours of the day, its load of 3MW draws a total of 2MVAR of reactive power. Using these typical specifications, a bank of forty (40) capacitors was designed with each capacitor contributing 50kVAR of reactive power. These forty (40) capacitors were also economically feasible. Another constraint that had to be overcome was the capacitors' exposure to environmental conditions. Our capacitors are able to withstand a corrosive environment and a wide variety of weather conditions such as extreme temperatures and lightning. Upon meeting all of the design constraints, our capacitors have long lifetime expectancy. In overcoming the design constraints, several techniques have been incorporated. We researched the problem thoroughly and took into account the design parameters. We contacted several manufactures to learn about the construction of capacitors. Certain calculations were performed to determine the dimensions and the physical construction of the capacitor. Next, we used simulation tools (SuperHarm, Excel, and PSpice) to prove our design were feasible. After these appropriate simulations were conducted, we tested the model capacitors in Mississippi State University's High Voltage Laboratory in order to verify their design functions and performance. We compared our test results with our design constraints and our goals were met. Due to the fact that using capacitors to correct a power factor has been around for many years, we are not the first to design and build a high voltage power capacitor. However, the innovativeness of our project comes into play when one considers the careful insulation process and materials used to extend the capacitors’ life and efficiency. The future of capacitor design to correct power factor will be based on finding new materials that provide better insulation between the foil sheets. Today, researchers are trying to employ new high-tech polymer as the dielectric in capacitors. This will allow for higher voltages and smaller physical dimensions of the capacitor to be attained.1. Problem Since the beginning of power production, there has been concern about the efficiency of power transmission and distribution. There are two main issues that drive this concern. The first concern is economics while the second is power quality. If one can deliver power at a more efficient rate than his rival, then he will be chosen as the major power supplier simply because he can offer power at a less expensive price than his rival. In order to offer power at a premium price, one has to minimize his losses associated with sending energy through a wire. To minimize the losses incurred when transmitting power, the overall power system must be made more efficient by minimizing the voltage drop between the generator and the substation, and decreasing the current present on the power lines. The way to accomplish this task is by addressing what is known as power factor correction. The power factor of a system is the ratio of the real power (generated by the "power-producing-current") to the apparent power (total current present). It expresses how efficiently the AC electrical power is transmitted and overall used. Inefficiency in a power system translates to wasted power, and as with any type of business, a utility company certainly does not like to waste its product. In an energy system, the majority of electrical loads are inductive loads such as induction motors. These types of loads produce electromagnetic fields in order to operate. Inductive loads draw two kinds of power from the utility system: real and reactive. The real or active power is the power that actually performs the work of creating motion, light, or heat while reactive power produces the electromagnetic fields necessary for the operation of induction motors. The real power is measured in kilowatts (kW) and the reactive power is measured in kilovolt-ampere-reactive (kVAR). These two types of power are combined to make up apparent power, which is the product of the voltage and current magnitudes; hence, it is measured in kilovolt-amperes (kVA). If the reactive power needed by a load increases while the real power needed stays the same, there will be more current drawn through the wires. This increase in current will in turn increase the voltage drop and power loss in the transmission line. Generally speaking, real power generates money while reactive power on a distribution system costs money. In order to produce the reactive power that is required by the inductive loads, power factor correcting devices known as power capacitors will be designed to function as small reactive power
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