ENGINEERING ARTICLES

Solid insulating materials can be classified into two main categories: organic and inorganic. There are a large number of solid inorganic insulants available, including the following: • ALUMINA: produced by heating aluminum hydroxide or oxyhydroxide; it is widely used as a filler for ceramic insulators. Further heating yields the corundum structure, which in its sapphire form is used for dielectric substrates in microcircuit applications. • PORCELAIN: a multiphase ceramic material that is obtained by heating aluminum silicates until a mullite phase is formed. Because mullite is porous, its surface must be glazed with a high-melting-point glass to render it smooth and impervious to contaminants for use in overhead line insulators. • ELECTRICAL-GRADE GLASSES: which tend to be relatively lossy at high temperatures. At low temperatures, however, they are suitable for use in overhead line insulators and in transformer, capacitor, and circuit breaker bushings. At high temperatures,...

The effective resistance offered by a conductor to high frequencies is considerably greater than the ohmic resistance measured with direct currents (dc). This is because of an action known as the skin effect, which causes the currents to be concentrated in certain parts of the conductor and leaves the remainder of the cross section to contribute little toward carrying the applied current. When a conductor carries an alternating current, a magnetic field is produced that surrounds the wire. This field continually is expanding and contracting as the ac current wave increases from zero to its maximum positive value and back to zero, then through its negative half-cycle. The changing magnetic lines of force cutting the conductor induce a voltage in the conductor in a direction that tends to retard the normal flow of current in the wire. This effect is more pronounced at the center of the conductor. Thus, current within the conductor tends to flow more easily toward the surface o...

A typical modern power system is a high-order multivariable process whose dynamic response is influenced by a wide array of devices with different characteristics and response rates. Stability is a condition of equilibrium between opposing forces. Depending on the network topology, system operating condition and the form of disturbance, different sets of opposing forces may experience sustained imbalance leading to different forms of instability. A systematic basis for classification of power system stability is given below. Need for Classification Power system stability is essentially a single problem; however, the various forms of instabilities that a power system may undergo cannot be properly understood and effectively dealt with by treating it as such. Because of high dimensionality and complexity of stability problems, it helps to make simplifying assumptions to analyze specific types of problems using an appropriate degree of detail of system representation and appropriate ...

“Power system stability is the ability of an electric power system, for a given initial operating condition, to regain a state of operating equilibrium after being subjected to a physical disturbance, with most system variables bounded so that practically the entire system remains intact”. The definition applies to an interconnected power system as a whole. Often, however, the stability of a particular generator or group of generators is also of interest. A remote generator may lose stability (synchronism) without cascading instability of the main system. Similarly, stability of particular loads or load areas may be of interest; motors may lose stability (run down and stall) without cascading instability of the main system. The power system is a highly nonlinear system that operates in a constantly changing environment; loads, generator outputs and key operating parameters change continually. When subjected to a disturbance, the stability of the system depends on the initial o...

The term alternative energy is referred to the energy produced in an environmentally friendly way (different from conventional means, i.e., through fossil-fuel power plants, nuclear power plants and hydropower plants). Alternative energy considered in this dissertation is either renewable or with high energy conversion efficiency. There is a broad range of energy sources that can be classified as alternative energy such as solar, wind, hydrogen (fuel cell), biomass, and geothermal energy. Nevertheless, as mentioned in the previous section, at present the majority of the world electricity is still generated by fossil fuels, nuclear power and hydropower. However, due to the following problems/concerns for conventional energy 5 technologies, the renewable/alternative energy sources will play important roles in electricity generation. And, sooner or later, today’s alternatives will become tomorrow’s main sources for electricity. Conventional generation technologies are not environme...

The five major factors that contribute to the renewed interest in distributed generation (DG) system: Electricity market liberalization  Developments in DG technologies  Increased customer demand for highly reliable electricity. Environmental concerns. Constraints on the construction of new transmission lines. ADVANTAGES OF DISTRIBUTED GENERATION SYSTEMS: UTILITY PERSPECTIVE: On-site power supply avoids transmission and distribution losses. Increasing the efficiency compared with central power generation. Diversification of power sources. A possible solution to constraints on new transmission lines. Provides cleaner power by using renewable sources such as wind and sun. Better quality of power. Hedge against uncertain load growth and high market. CUSTOMER PERSPECTIVE: Improving energy efficiency and reducing greenhouse- gas emission through combined heat and power (CHP) plants and renewable sources. Improved reliability by having back-up ge...

Distributed Generation (DG) also called as site generation, dispersed generation, embedded generation, decentralized generation, decentralized energy or distributed energy, generates electricity from the many small energy sources. In recent years, micro electric power systems such as photovoltaic generation systems, wind generators and micro gas turbines, etc., have increased with the deregulation and liberalization of the power market. Under such circumstances the environment surrounding the electric power industry has become ever more complicated and provides high-quality power in a stable manner which becomes an important topic. Here DG is assumed to include Wind power Generation (WG) and Fuel Cells (FC), etc. Wind energy is the world‘s fastest-growing energy technology. It is a clean energy source that is reliable, efficient and reduces the cost of energy for homeowners, farmers and businesses. Wind turbines can be used to produce electricity for a single home or building, o...