Powers in nonsinusoidal situations-a review of definitions andphysical meaning

The author expands on the physical meaning of the reactive power in nonsinusoidal situations. The sinusoidal waveform case is surveyed, viewing the active current as a component of identical waveform with the voltage. This approach, when extended to nonsinusoidal waveforms, supports Fryze's model for apparent power, S²=p ²+Q²_F. It is proved that the total reactive power Q_F is composed from four distinctive types of elementary reactive powers. Each of the basic reactive powers is identified as the amplitude of an oscillation of instantaneous power. The separation of Q_F in Q ₁, the reactive power at the system frequency, and in Q_H, the reactive power at harmonic frequencies, is recommended as an effective mean for monitoring filter efficacy and power-factor compensation. Two major recommendations are supported by the results of this study: abolish the power model using distortion power, and measure the active power of the system frequency separately from the active power of the harmonics     

Basic mechanisms of generation and flow of harmonic signals inbalanced and unbalanced three-phase power systems

The basic mechanisms of generation and flow of harmonic signals in electric power networks are discussed. With regard to generation, the unbalanced operating condition of a six-pulse converter is studied. Guidelines which are applicable in the general case are obtained. With regard to flow of harmonic signals, a new relationship between distortion voltamperes and total harmonic distortion is derived. This relationship is very similar to the P/δ and Q/| V| relations which are well known in electric power flow studies     

A reduced model for power system observability: analysis andrestoration

An algorithm for observability analysis and restoration in power system state estimation is presented. The problem of P-δ, Q-V and complete observability is addressed. In the proposed algorithm, groups of buses are represented by supernodes and the problem of observability analysis and restoration is examined with a reduced network. The proposed algorithm is easily implemented and it is independent of the state estimation solution algorithm. In case of unobservability, the proposed methodology identifies directly the maximal islands and determines the number and the placement of the required pseudomeasurements for observability restoration. Results from several test cases are presented     

Investigation of alternative residual current compensation forimproving series compensated line distance protection

The effect of the residual compensation factor on the measuring accuracy of distance protection measurements when an earth fault occurs on a series compensated line is investigated. It is shown that, when conventional residual compensation is used, there will be an error in the impedance measurement which depends on the ratio I_sa (I_sa+K_cI_res ) where I_sa is the faulted phase current at the relaying point, K_c is the conventional residual compensation factor, and I_res is the residual current. It is also shown that this expression depends on load current and source conditions at the line ends. In consequence, errors of measurement and concomitant overreaching/underreaching can occur when conventional residual compensation methods, as applied to plain feeders, are used in series compensated applications. An alternative method of compensation has therefore been developed. This has been found to improve accuracy of measurement at the boundary and relay measurement integrity for other fault positions in series compensated line applications     

An approach for the regularization of a power flow solution aroundthe maximum loading point

A method which is capable of greatly widening the range where the power flow solution is regular is presented. This is achieved by giving some modifications to the conventional power flow solution method and eliminating the singular point or shifting it to region where the voltage is lower than that of the maximum loading point. Then, the continuous execution of V-P curves including the maximum loading point is realized. The efficiency and effectiveness of the method were tested in a practical 598-node system are compared with the conventional method     

Contribution to the discussion of `1987 ampacitytables-demystifying the myths'

The author discusses J. Nasilowski's remarks (see ibid., vol.26, no.4, p.605, 1990) on a paper by D.W. Zipse (see ibid., vol.25, no.5, pp.910-17, 1989). Nasilowski claimed that in M=(hS/R)^1/2, where M is the current coefficient of heating, h is the heat transfer coefficient, including both convection and radiation, S is the surface area of the conductor, and R is the resistance, M is constant for a specific material for a range of currents and for temperature rises up to about 60 K. The author argues that M is approximately constant only for a specific conductor and for restricted ranges of temperature rise and ambient temperature. In his reply, Nasilowski stresses the utility of the assumption that M =constant for calculations of steady state temperature rise of the conductors in a quiet air     

Destruction of living cells by pulsed high-voltage application

Destruction of living cells in liquid has been formed by pulsed high-voltage application to the liquid. S. cerevsaie (yeast cell) or Bacillus natto, dispersed in deionized water and one- and three-percent NaCl solution, were used in this experiment. Four different electrodes (plate-plate, needle-plate wire-cylinder, and rod-rod electrode) were tested. The survival rate of cells was measured against peak electric field E_p pulsewidth T _W, and pulse application number N. The experimental results indicate that the survivability roughly follows Weilbull distribution. Yeast cells dispersed in deionized water could be almost completely destroyed when the wire-cylinder electrode was used with E_p=20 kV/cm, T_W=100 μs, and N=200. The energy input to a unit volume of the liquid to complete the cell destruction, however, differed significantly with the electrode type. The wire-cylinder electrode required above 10-30 cal/cm ³ to destroy the yeast cell in deionized water to 10^-6 survivability. This value was less than that required more than 70 cal/cm³. Using the rod-rod electrode contained in a pressure vessel, an arc discharge was generated to produce an intensive shock wave, which also destroyed the cells by its mechanical force. In this case, 5-10 cal/cm³ of energy was required to decrease the survivability of yeast cells in deionized water to 10^-6. Though further studies are necessary, this results indicate a possibility of the cell destruction by pulsed high voltage to be used as an energy-efficient sterilization process     

A stator flux-oriented voltage source variable-speed drive based onDC link measurement

The authors present a new control strategy for variable speed drives, which is aimed at improving or even replacing existing volts per hertz (V/f) open loop variable-speed drives. This strategy uses only the DC link current and voltage, which are readily available in a V/f drive for protection purposes, to implement closed loop flux and torque control. Stator flux and electromagnetic torque feedback signals are derived from the DC link voltage, the DC link current, and inverter switching states. Digital implementation is seen to be possible with slight modification on existing V/f drives. Practical considerations in implementing such a system are emphasized, and experimental results are presented to show the feasibility of the scheme     

Theory for finite-phase traveling-wave boundary-guided transport oftriboelectrified particles

Numerical simulations are used to picture synchronous and asynchronous domains of traveling-wave pumping of charge-conserving particles (having mass m, charge q, radius a, and mobility b) in terms of the dimensionless frequency Ω=(ω/k)/(bE₀), mass M=(m/q) (kb) (bE₀), and gravitational acceleration G=mg/qE₀, where k and ω are the wavenumber and angular frequency of the imposed wave and E₀=kV, where V is the peak voltage. The effects of having a finite number of phases consisting of discrete electrodes covered by a semi-insulating layer are highlighted. The time-average velocity in the direction of wave travel is found to be synchronous (have velocity ω/k) for 0<Ω<Ω*<1, where Ω* is reduced by having finite phases. Because the discrete electrodes result in hops of higher magnitude, they tend to result in a conversion to asynchronous hopping and `certain' modes at a lower frequency than with a sinusoidal wave. At low M, they can also result in the stalling of particle pumping as the frequency is raised. Predicted effects of image forces, dielectric layer thickness, bulk conductivity, and surface conductivity as well as particle sticking and slipping are discussed     

Influence of an insulating spacer on the V-tcharacteristics of a coaxial gas-insulated cable. II. Tests on EHV buses

For pt.I see ibid., vol.3, no.1, p.16-25 (1988). The V- t characteristics of EHV buses were evaluated for two configurations with rated voltages of 550 and 800 kV. The bus dimensions were 6 m in length and 17.8/53.3 cm and 20.3-61 cm in diameter, respectively. They were each fitted with two tripod-type epoxy spacers. The results show a pronounced influence of the supporting spacers on the V-t characteristic, corresponding to a reduced withstand voltage and less dispersion in the measured breakdown voltages. A statistical method is presented for deriving the V- t characteristics of a gas-insulated system from those of the individual components     

Xerographic properties of a-Se:Te photoconductors

It is shown that the dark decay of the electrostatic surface potential on a corona-charged a-Se:Te alloy photoreceptor occurs via electric field-enhanced xerographic depletion discharge (FEXDD) in which Poole-Frenkel-assisted thermal emission of holes from deep mobility-gap states and their subsequent sweep out generates a negative bulk space charge. The theoretical model development is applied to explain the observed experimental dark discharge data over a wide range of charging (initial) voltages. It is shown that although the time required for the surface potential to decay to its half value t_1/2 initially increases with the charging voltage V₀ at the highest charging voltage, t_1/2 actually decreases with V₀. Results obtained from cycled-up xerographic experiments on single and double-layer photoreceptors are also reviewed and discussed in conjunction with transient photoconductivity experiments     

Fully digital, vector-controlled PWM VSI-fed AC drives with aninverter dead-time compensation strategy

A dead-time compensation method in vector-controlled pulse width modulator (PWM) voltage source inverters (VSIs) is proposed. The method is based on a feedforward approach that produces compensating signals obtained from the I_d-I_q current and inverter output angular frequency references in the rotating reference (d-q) frame. It provides excellent inverter output voltage distortion correction for both fundamental and harmonic components. The correction is not affected by the magnitude of the inverter output voltage or current distortions. Since this dead-time compensation method allows current loop calculations in the d- q frame at a slower sampling rate, with a conventional microprocessor than calculations in the stationary reference frame, a fully digital. vector-controlled speed regulator with just a component current control loop is realized for PWM VSIs. Simulations and test results obtained for the compensation method are also described     

Coupled transmission lines revisited

The author presents a very satisfying and disarmingly simple way of introducing students to the parallel line coupler, which derives its S matrix directly from a knowledge of its eigenvectors and eigenvalues. For a pair of symmetrical coupled lines, the eigenvectors can be found by inspection, and the eigenvalues determined easily by means of flow graphs. The elements of the S matrix are then known, being linear combinations of the eigenvalues     

Single-stage AC electrostatic precipitation

Measurements are reported on the collection efficiency of a laboratory-scale single-stage electrostatic precipitator (3 cm plate spacing) excited by AC voltages (V_rms~8 kV, f =20→500 Hz) biased to give no time-average. With f=60 Hz, an effective migration velocity of 3.5 cm/s is observed. Previously published works on the charging and migration of particles in AC coronas and on the effects of finite turbulent diffusivity on the precipitation process are combined to predict the experimentally observed dependence of the efficiency on the magnitude and frequency of the applied voltage. When applied to the experimental situation reported here, the model reduces to one of complete mixing, with the effective particle migration velocity being predicted in terms of the velocity that is achieved with DC charging and a charging time constant that is either estimated or obtained from charging experiments     

Apparent power definitions for three-phase systems

It is shown that currently used apparent power definitions, namely the arithmetic VA, S_A and the vector VA, S_V, both lack an important property: the system power losses are not a linear function of the apparent power squared, S_A² or S _V². The only apparent power definition known today, that holds this property for all the possible situations-balanced, unbalanced, sinusoidal or nonsinusoidal-has the mathematical expression suggested by F. Buchholz; and explained by W. Goodhue. This paper gives a set of basic examples meant to emphasize the merit of Buchholz-Goodhue approach     

Mode ordering algorithms for sparse vector method improvement

Three node-ordering algorithms that enhance sparse vector methods without losing sparse matrix method efficiency are presented. The performance of the algorithms is compared with that of the minimum-degree algorithm for eight test systems up to 661 nodes. For the factorization of a sparse matrix into U^tU, the new algorithms give a similar or even better sparsity for U, while clearly improving the sparsity of U^-1      

A simple packet retransmission strategy for throughput and delayenhancement on power line communication channels

A new communication protocol is developed and evaluated for use on power line distribution networks. The protocol involves retransmission of unacknowledged packets, which are sent in either single or multiple ( N) copies in accordance with estimates of communication link quality. Multiple packet copies can be code-combined at the receiver using majority voting on each bit position in order to reduce packet error rates. Adaptive link quality estimates are based on the receipt or absence of positive acknowledgements. Information throughput efficiency is calculated and N optimized in terms of system variables. The performance benefits of code combining are demonstrated. The algorithm is implemented and tested using a five-station intrabuilding power line communications network operating at 1.2, 2.4, 4.8 and 9.6 kbit/s data rates. Substantial throughput and delay improvement occur on poor quality links without degrading performance on good links     

The onset of electrothermal convection in nonpolar liquids on thebasis of a dissociation-injection conductivity model

The onset of convection for a layer of nonpolar liquid subjected to an adverse thermal gradient and intense electric field is examined. The electrical conductivity is determined via a recent physiochemical model based on dissociation and injection charge generation. Convective instabilities and overstabilities are predicted as a function of strength of injection C and residual conduction C₀. Physical and mathematical arguments show that for values of C bigger (smaller) than 2√2C₀ , the regime is approximately injection dominated (conduction dominated). It is also shown that dissociation always plays a stabilizing role, which is contrary to the injection which can have either a stabilizing or a destabilizing effect due to its indirect coupling with thermal perturbations     

A line-current measurement based state estimator

The authors present a method for state estimation when the measurement set consists basically of node voltages and line currents. The key idea is that P-&thetas; observability can be reached provided inequality constraints are added to the estimation process. These constraints simply state that P⩾0 for a generator bus and P⩽0, for a load bus. Simulation results confirm that the method may be applicable to medium-sized subtransmission networks, the only major exception being radial networks with more than one feeder bus     

The relationship between virtual time and quality factor forheavy-current test circuits

The use of deviations in virtual time for plotting the time-current characteristics and evaluating the thermal effect of the DC component of a fault current is discussed. The relationship between the virtual-time deviation, the initial EMF phase making angle and the Q factor is used as the basis of a newly developed method for evaluation of the Q factor. This method is particularly useful in the range of higher values of Q, where other methods are not as efficient. For example, the most common DC component damping method is very vulnerable to even small errors in the estimation of the value of this component. In the method presented here, the main contributing factor is that the evaluation of Q is based on measuring the constant component of the virtual-time deviation, which in turn is directly proportional to the time constant of the circuit. The only major shortcoming of the method is the need to maintain the test current until the quasi-steady state is reached