Short-circuit Load Research Articles

磁気飽和進相型安定器の動作特性モデル

A model for the analysis of a lead - peaked ballast characteristics is developed. The model is derived using the equivalent circuit method of magnetic circuit. The magnetic path is divided into nine parts, and are expressed by equivalent inductors respectively. Iron loss at each part is represented by an equivalent resistance. For a discharge load, the discharge voltage - current model is adopted. Using the developed model, input and output characteristics are calculated and compared with the measured values at no-load, short-circuit load and discharge load condition, respectively. The calculated results agree well with the measured results both in waveforms and effective values.

AutoCAD application upgrades power system analysis programs

An easy and simple method for the development of graphic programs and for documentation and display of results of power system calculations and planning is described. The resulting programs use commercially available firmware, which enables even an unskilled programmer to write powerful graphic output routines. The method is applied to a variety of planning software, such as load flow, short circuit, and permissible loading calculations. The program can run on any mainframe or personal computer (286 and higher) and needs only the appropriate firmware and suitable graphic output facilities (graphic printer or plotter, and a graphic screen). >

Operation and empirical modeling of the plasma opening switch

Experiments on the performance of plasma opening switches (POS) were conducted on two pulsed power generators, the BLACK-JACK 5 and ACE 1 accelerators. The results demonstrate the capability of the POS as a final switching stage in an inductive energy storage system. The rate of delivery of current to an e-beam load on BLACKJACK 5 is multiplied by as much as a factor of five over the rate obtained without the switch. Experiments with a range of switch conduction times from 50 ns to 2 mu s were designed to determine the scaling laws relating plasma density and geometry to the current that can be conducted by the switch and the peak voltage generated during opening into an inductively short-circuited load. The data, though moderately well correlated by a snowplow model of plasma dynamics, indicate that the physical processes governing switch behavior are not thoroughly understood. >

Compact pulsed power generator using an inductive energy storage system with two-staged opening switches

The pulsed power generator, named ASO-I, is extremely compact and light in comparison with a conventional pulsed power generator, which consists of a Marx bank and a water pulse forming line. The ASO-I has a two-staged opening switch, consisting of fuses in water and a plasma erosion opening switch, and can be operated hundreds of times a day at an output power of 230 kV and 35 kA. The parallel fuses are effective for power multiplication, and small differences in length of the parallel fuses do not influence the output power. The risetime of current through the short-circuit load decreases with the increase of the gap length of the spark gap, which is placed between the fuses and the load. The plasma erosion opening switch can be operated as a second opening switch, and the risetime of the current through the short-circuit load decreases from 250 to 10 ns. The maximum resistance of the plasma erosion opening switch is 3.5 Omega with an open-circuit load. >

Modelling and analysis of multiphase (twelve-phase) line transients

This paper is aimed at the modelling and analysis of multiphase line transients. For this purpose, the existing three-phase techniques are initially briefly reviewed for an insight into the various aspects such as modelling, solution and computational procedure, flexibility and suitability of applications. Next a Laplace transform method is chosen for its simplicity to yield a complete transient response and adapted to multiphase systems. Further, in order to validate the analytical developments and to compare the transient responses of systems of various phase orders, a sample system consisting of three alternative (three-phase, six-phase and twelve-phase) transmission lines is worked out for open-eneded, short-circuited and resistive load terminations. The salient features of results and conclusions are included.

Impedance control of microstrip antennas using reactive loading

It is shown that it is possible to change the input impedance of a microstrip antenna over a wide range without affecting its resonant frequency by moving short circuits along prescribed loci. This theory has been verified by experiment; specifically, it is shown that the resonant frequency of the mode is left relatively unchanged by the appropriate placement of the short circuit loads. The experiment also shows that the agreement between the predicted and observed input impedance is quite reasonable in most cases. There was qualitative agreement between theoretical antenna patterns and measured antenna patterns although the measured cross-polarized components in the double-loaded element were higher than expected from the theory. A single load, varying in position, was seen to provide a reasonable range of impedance variation while retaining a very nearly constant resonant frequency, although the resulting asymmetries in the magnetic current distribution caused a high level of cross-polarized fields. The use of two loads, instead, produced an even greater range of possible impedances, with reduced cross-polarization levels as well. >

A reflection coefficient bridge

The design of an unbalanced Wheatstone bridge is presented. The bridge measures the reflection coefficient of unknown impedances relative to an arbitrary reference level. A experimental unit was designed for a 25-Ω reference level. It measured high isolation with a 25-Ω load; the magnitude of the reflection coefficient with a short-circuit load differed from that with an open-circuit load by less than 0.1 dB.

Switching of low density diode plasmas

The switching action of low density injected carbon plasmas is investigated by a numerical collisionless two-dimensional electromagnetic particle simulation. The plasma switch is considered in a planar vacuum transmission line with input current per unit length ramped at 240 A/cm ns during 10 ns, and short circuit output. The calculations, done with C+ ions at 4×1012/cm3, exhibit switching of the current from the plasma switch to the short circuit load. At early times (1–2 ns) a sheath of positive charge forms at the cathode by depletion of the plasma electrons. The electric fields at the cathode are large enough to explain the formation of a denser cathode plasma. The mechanism of switching appears to be, for this density and load conditions, the magnetic limiting of drifting electrons. The ion motion seen plays an insignificant role in this particular case.

An advanced darlington transistor for switch mode power control

A recently developed three-stage Darlington transistor is described which has been specifically designed for direct off-line power control. The device features fast, low-loss switching with direct drive from an integrated circuit. The transistor has been designed with a very extensive safe operating area so that a snubber network is not required. The device is sufficiently robust to survive a number of system fault conditions and when used in conjunction with a suitable drive circuit, it can even withstand a short circuit load without damage.

Study on shock wave-explosive energy converter of PZT 95/5 ferroelectric ceramics

Abstract Satisfactory agreement between experimental results and theoretical calculations of wave-explosive energy conversion in cases of inductive, resistive and short circuit loads were obtained for a Pb(Zr97.5Ti2.5)O3+1wt%Nb2O5 PZT.

Short Circuit Tests on a 3o, 230kV Rigid Bus Assembly

This paper describes the results of full scale, 3-phase short-circuit tests on a rigid bus assembly designed for 230kV operation. An investigation was conducted into the momentary withstand capabilities of the installation under actual short circuit conditions. A comparison of test results was made with methods proposed in the literature for the structural design of substation bus systems to withstand short circuit loads. Results indicate that existing design procedures are conservative.

Measurement of short circuit load losses in large three phase power transformers using an alternating current comparator bridge

The application of a high-voltage alternating-current-comparator capacitance bridge to the measurement of the short circuit load losses of large three phase power transformers at rated current is described. Input of the transformer current to the bridge is provided through a 1000/1 ratio two-stage current transformer with a single turn primary winding Insulated for 50 kilovolts. Voltage input is provided through a loss-free gas dielectric capacitor which serves as the reference. Measurements on typical transformers ranging in size from 450 MVA to 750 MVA; with currents from 600 to 2100 amperes and short-clrcuit power factors from one percent to four percent, are discussed. Comparisons to appropriately corrected wattmeter measurements (aided by low-loss capacitors connected in parallel with the transformer) indicate an overall agreement of better than one percent.

The Response of Substation Bus Systems to Short Circuit Conditions Part I: A Comparison of Design Methods

The four methods proposed in the literature for the structural design of substation bus systems to withstand short circuit loads are compared in the case of a single, simple element of a substation. These comparisons show that the continuous, dynamic design method, which treats the distributed mass of each element, will provide more reliable designs than will the methods presently in use. They also suggest that this method will provide more economical alternatives for renovation of existing substations, where the cost penalty can be especially severe if the traditional static method is used. It is concluded that the development of the continuous dynamic method for use on a routine basis is warranted, in spite of its computational complexity.

Cross-modulation figure of merit for transistor amplifier stages

This article concerns itself with comparison of transistor amplifier configurations in relation to their cross-modulation distortion characteristics. Only the base-emitter junction nonlinearity is considered, since this nonlinearity is considered to be the most significant contributor to cross-modulation distortion. For this case investigations have shown that since cross modulation occurs because of a third-order nonlinearity, the cross-modulation distortion is therefore proportional to the square of the interfering voltage which appears across the base-emitter junction. In this article the cross modulation of the transistor stage is analyzed from its equivalent circuit rather than from the theoretical device characteristics, It is assumed that the transistor stage gain and input impedance remain relatively constant with small signal voltage excursions. Using these hypotheses, a figure of merit factor is derived for comparison of transistor and transistor amplifier configurations with respect to their cross-modulation distortion characteristics. This figure of merit factor is then used to compare the relative cross-modulation susceptibility of the common collector, common emitter, and common base configurations. All three configurations are compared in the hypothetical voltage-generator and short-circuit load case. The derivation of the equations is shown in Appendix I. For this case it is shown that the three configurations have equal figures of merit. The latter two configurations are then analyzed and compared for the more practical matched input and matched output (maximum power transfer) case. Familiar formulas for transistor gain and input impedance in the low-frequency equivalent model are used for this analysis. Derivations of the equations are shown in Appendix II. The effect of feedback on the cross-modulation figure of merit is then analyzed using both degenerative and regenerative types of feedback. It is then shown that by use of the analysis of the low-frequency model, together with the analyses of the effects of feedback, a high-frequency analysis of cross-modulation figure of merit can be made. This analysis is most applicable to wide-band VHF amplifiers, such as used in Community Antenna Television trunk cascades. A convenient means for analysing cross modulation in the more complicated high-frequency circuit is thus described. Other types of stages, such as push-pull and parallel outputs, are also discussed in regards to the defined cross-modulation figure of merit. A set of conclusions concerning the defined cross-modulation figure of merit is then reached.

Nonequilibrium ionization in magnetoplasmadynamic power generation - theory and experiment

Test results from a closed-loop magnetoplasmadynamic (MPD) generator experiment at gas temperatures in the range of 1000°-1100 °F are examined in the light of the theory of magnetoplasmadynamic electrical power generation with nonequilibrium ionization. The effective electrical conductivities measured under virtual short-circuit electrical load conditions in a segmented-electrodes constant-area-duct experiment when the magnetic field is applied, are compared with the thermal equilibrium ionization conductivities, which are calculated using electron densities derived from Saha's equation with the corresponding gas temperatures inserted. This comparison gives a verification of the presence of magnetically-induced nonequilibrium ionization in the MPD generator duct. Next, the energy balance equation is used to derive the electron temperature. The electron temperature is in turn used to calculate the resultant nonequilibrium electron density. This is done using two approaches. One approach uses an ion balance equation, which balances the rate of generation of ions by the hot electrons with the rate of loss of ions by recombination. The other approach derives the electron density from Saha's thermal equilibrium equation using the electron temperature instead of the gas temperature. The calculated nonequilibrium conductivities resulting from the use of these two approaches are compared with those obtained by experiment.

Current-Limited Rectifiers

Several ac rectifier circuits have the property, inherent in the rectification process, of limiting their output current to a specified maximum. They are technically simple and can be used as the foundation for power supplies that remain undamaged and absorb little power with a short-circuited load. In combination with a dc regulator, such a rectifier provides a constant-voltage supply with desirable overload characteristics. A modified bridge rectifier is especially useful.

Short-circuit characteristics and load performance of inductor-type alternators

Short-circuit characteristics and load performance of inductor-type alternators

Short-circuit characteristics and load performance of inductor-type alternators

The paper develops a graphical method of determining the short-circuit current of an inductor alternator, taking into account the effect of a damping circuit which prevents oscillations of the total flux. It is shown that the short-circuit current depends mainly on the important ratio of maximum to minimum flux and on the leakage. The equivalent circuit for the inductor alternator is determined from the open-circuit voltage and short-circuit current. The ratio of these values varies owing to saturation effects, but can be taken as constant for a given excitation and independent of the load circuit. Compensation of the internal inductive reactance by series condensers for an alternator with constant and variable speed is considered, and the transient- and steady-voltage changes are investigated. The reason for the voltage drop of the fully compensated machine being many times greater than the resistive drop is given. The effect on the speed/torque characteristic of series-condenser compensation is shown. The paper explains that the damping winding increases the effective excitation for a load circuit having a lagging power factor and reduces for a leading power factor. An unusual type of instability arising when paralleling series-compensated alternators is investigated, and a remedy for this phenomenon is given.

Electric Shut-Down in London

THE sudden cessation of the supply of electricity over London and part of the south-east of England during midday on July 29 proves that even with the best machinery a breakdown in the supply is a possibility that has to be guarded against. Luckily it is an extremely rare occurrence. The trouble started apparently when the engineers were re arranging sections of the supply at the Battersea power station. A small section becoming overloaded, the automatic circuit breaker came into action. When the circuit breaker was closed the currents in two of the sections were probably not in synchron ism and so a huge current circulated in the link connecting Battersea with the neighbouring station at Deptford West. The former had an output of 70,000 kilowatts at this moment and the latter of 90,000. The devices at Battersea declined to take the short circuit load, and several of the machines at Deptford shut down. The Barking Power Station had now to take the load, but the circuit breaker at Northfleet opened and the whole system ceased to operate. The effect was that the whole of the south-east area of the grid was suddenly deprived of 280,000 kilowatts of generating plant. The stations at Norwich and Brighton cleared themselves from the grid, the latter for about an hour. This affected the Southern Railway. The trouble was probably caused by the engineers taking advantage of the light load in summer to cut out certain transmission connexions for overhauling and so the grid system was not in full commission. It was not able to face the loss of Battersea, Barking and Deptford and still keep the whole system working. Notes on this shut-down are given in the Electrical Times of August 2.

Comparison of methods of loading large A-C. and D-C. generators and rotary converters for factory temperature tests

A satisfactory test should duplicate as completely as possible the conditions under which the machine is guranteed to operate, and the conditions of test should be more severe and not less severe than the conditions of operation. Four methods of loading a-c. generators are described and illustrated by test results: (a) Separate open circuit and short circuit loading is unreliable because the test conditions are radically different from operating conditions but this method may be the only possible method on account of minimum testing equipment required. (b) Alternate open circuit and short circuit loading more nearly approaches operating conditions but results do not check with actual load unless test conditions are modified, from those theoretically determined. Experience is not, as yet, available to empirically determine proper test conditions. (c) Direct-current open delta loading still more closely approximates operating conditions in that current and voltage are simultaneously present. The method is somewhat limited in application due to the presence of direct current in the armature. The proper field current for use in the test is shown to be that corresponding to open circuit normal voltage. The test results check well with actual operation. (d) Zero power factor loading affords the nearest approach to actual operating conditions that has been suggested. It exactly corresponds with operating conditions except for the differences due to power factor, and these, in general, result in more severe conditions than actual loading. Test results are closer to results from actual loading than by any other method described. A direct check on field coil temperatures and exciting voltage is afforded. The application of the method is only limited by the expensive test equipment sometimes required. The zero power factor method of loading is recommended for adoption by the Institute as the preferable method. For d-c. generators and rotary converters, only one satisfactory method of loading has been suggested. This is the familiar loading-back method which is recommended.