N. H. Malik

Steady State Analysis and Performance of an Isolated Self-Excited Induction Generator

A general analysis to predict the steady state performance of an isolated self-excited induction generator feeding a balanced R-L load is presented. In the analysis the effect of machine core losses has also been considered. It is shown that besides voltage and frequency the analysis can be used to predict the minimum value of terminal capacitance required for excitation as well as for maintaining a constant terminal voltage. Comparison of the predicted and the experimental results shows a good agreement.

Capacitance Requirements for Isolated Self Excited Induction Generators

Capacitance requirements for isolated self excitd induction generators are discussed. It is shown that numerical methods based upon the steady state as well as operational equivalent circuit give similar predicted values. An analytical method is proposed to compute, Cmin, the minimun capacitance value required for self excitation under no load conditons. It is shown that Cmin is inversely proportional to the square of the speed. Furthermore, it is inversely proportional to the maximum saturated magnetizing reactance. The theoretical results are verified experimentally for a number of test machines and a good agreement is observed between the theoretical and the experimental values. The influence of load impedance and its power factor on the terminal capacitance required to maintain self excitation under steady state is also examined and it is shown that when machine is loaded, the terminal capacitance should be several times that required at no load. Furthermore, the influence of terminal capacitor upon the maximum available output power fron isolated induction generators is also examined.

Electrical insulation in power systems

Introduction to electrical insulation in power systems gas dielectrics air insulation SF insulation liquid dielectrics solid dielectrics vacuum dielectrics composite dielectrics high voltage cables generation and measurement of testing voltages new measurement and diagnostic technologies insulation testing.

Operation of a Fixed Capacitor-Thyristor Controlled Reactor (FC-TCR) Power Factor Compensator

A fixed capacitor-thyristor controlled reactor (FC-TCR) type of power factor compensator with thyristor-controlled series R-L load is analysed using an approximate and also a more exact circuit. The variation of power and power factor before and after compensation is examined for both cases. It is shown that considerable power factor improvement can be achieved in the circuit for low values of load thyristor firing- angle. However, for higher values of firing-angle, any improvement is obtained at the expense of additional. power losses.

Statistical evaluation of water tree lengths in XLPE cables at different temperatures

Accelerated aging of two types of commercially produced medium voltage XLPE insulated cables was carried out under the combined stresses of three types consisting of ionic aqueous species, elevated electrical stress and temperature cycling. After 1000 h of aging, the water tree parameters were evaluated. Results show that external ionic species exert profound impact on the generation of bow tie and vented water trees, while impurities inherently present in the cable components also contribute significantly. Temperature cycling increases the bow tie trees by an order of magnitude, while morphology of insulation influences the level of water tree degradation. The water tree population and their lengths were subjected to Weibull and log-normal models of statistical distributions and the data were found to fit better on the log-normal model. For a better statistical inference, a computer based Monte Carlo simulation was devised and used to precisely discriminate the two models. Simulation results further confirm that both types of water trees fit better on the log-normal model. The most likely mechanism for water tree degradation is fatigue based and hence mechanistic by nature.

Influence of sand/dust contamination on the breakdown of asymmetrical air gaps under lightning impulses

The authors review the important parameters of particles which are present in the environment when sand/dust storms occur. Basic features of the experimental system are summarized. Extensive measurements of breakdown voltages and times to breakdown are carried out under clean and polluted conditions using rod-plane and sphere-plane gaps. It is shown that when positive lightning impulse voltages are applied to asymmetrical gaps from 5 cm to 2 m, the presence of sand/dust contamination can cause a breakdown voltage reduction. However, the presence of particles can greatly affect the breakdown characteristics of rod-plane and sphere-plane gaps under negative lightning impulses. For gaps with moderately nonuniform field distributions, the particles can decrease V/sub 50/ by >

Experimental study and design of smart energy meter for the smart grid

The demand for energy is increasing as a result of the growth in both population and industrial development. To improve the energy efficiency, consumers need to be more aware of their energy consumption. In recent years, utilities have started developing new electric energy meters which are known as smart meters. A smart meter is a digital energy meter that measures the consumption of electrical energy and provides other additional information as compared to the traditional energy meter. The aim is to provide the consumer and supplier an easy way to monitor the energy. Smart meters are considered a key component of the smart grid as these will allow more interactivity between the consumers and the provider. Smart meters will enable two-way and real-time communication between the consumers and the provider. Considering the increase of electricity demand in Saudi Arabia, smart meters can decrease the overall energy consumption. This paper presents the development of a GSM and ZigBee based smart meter. This meter can measure the energy and send the information to the service provider, who can store this information and notify the consumer through SMS messages or through the internet.

Economic and environmental dispatch at highly potential renewable area with renewable storage

Economic/Environmental Dispatching (EED) is an important multiobjective optimization problem to decide the amount of generation to be allocated to each thermal generating unit including renewable sources so that the total cost of generation and emission of polluting gases is minimized without violating system constraints. Here, the problem is EED of hybrid power system including solar, wind and storages of renewable energies. High potential renewable area ensures the availability of renewable sources in some extent. A consistent optimum EED can be obtained by extracting maximum renewable energy during their availability and using them for both available and unavailable periods with the aid of their storages. This paper illustrates the optimization of EED with renewable storage using MATLAB simulations. The simulations have been done using IEEE-30 test bus (with 6 generators) data.

Electrical Stress Distribution in Three-Core Belted Power Cables

A charge simulation method is used to calculate the stress distibution in a three core belted power cable having circular conductors. Each conductor is represented by Nc infinite line charges arranged in a circular pattern inside the conductor. The sheath is represented by Ns infinite line charges arranged in a circular pattern outside the sheath. Values of Nc and Ns are slected so that the percentage potential error is below 1% even when inter conductor spacing is very small. The variation of stress with location, time and cable parameters is studied in the entire cable crossection. The locations of maximum stress points are determined and magnitudes of these stresses are calculated using typical cable design parameters. The results are presented in a normalized format so that they can be readily applied.

Performance of rod-rod gaps in the presence of dust particles under lightning impulses

Investigations have been made to evaluate the performance of rod-rod gaps of two different shapes in the presence of simulated dust storms. Breakdown voltages and time lags have been determined for a range of gap spacings from 5 cm to 125 cm for standard lightning impulses. It was found: that the influence of particles in gap spacings of >or=50 cm is small and is not of much practical importance, but in spacings >