Showing papers in "Transactions of The American Institute of Electrical Engineers in 1947"

The Transient-Energy Method of Calculating Stability

Abstract: The transient-energy method is a newly developed means of checking and quantitatively evaluating the transient stability of a system of three, or possibly more synchronous machines. Each machine is represented by a constant-magnitude voltage behind a fixed reactance (usually the transient reactance) and all losses and nonsynchronous loads are assumed to be constant throughout the transient. The method is developed in this paper specifically for the 3-machine problem and is demonstrated in two examples. The potential energy required to displace the machine rotors from the relative positions which they would occupy in steady-state after-transient operation is the basic function utilized; it may be expressed as a scalar potential function of two rotor-difference angles. Two critical (zero-slope) points of the potential energy function are located graphically; those points are 1. The minimum, which is the locus of steady-state after-transient operation. 2. The minimax, the rotor-difference-angle combination at which stability may be lost with the smallest amount of transient energy. The potential energy of (2) with respect to (1) is computed and compared with the initial transient energy, calculated with respect to condition 1. If the allowable transient energy (former) exceeds the actual transient energy (latter), the system is stable.

Pulse Code Modulation

Abstract: A radically new modulation technique for multichannel telephony has been developed which involves the conversion of speech waves into coded pulses. An 8-channel system employing pulse code modulation (PCM) and embodying these principles was produced. The method appears to have exceptional possibilities from the standpoint of freedom from interference, but its full significance in connection with future radio and wire transmission may take some time to reveal.

Fundamental Basis for Distance Relaying on 3-Phase Systems

Abstract: In the preceding investigation the quantities upon which distance relays must depend for their operation have been determined for all possible types of faults occurring at a single location. It has been shown that the quantities obtained by the use of earlier distance relay connections for both line and ground faults do not give the closest approach to the desired result, a constant indication for all types of faults at a given location. It has been shown further that, by the use of different connections and certain auxiliary apparatus, a constant relaying indication may be obtained by the line relays for all types of line faults and by the ground relays for all types of faults involving ground, if the fault resistance is zero, and, if the fault resistance is not zero, that smaller deviations from the normal value will be obtained for a given fault resistance. The analysis has been based upon the assumptions of sine wave currents and voltages, constant circuit impedances, and negligible distributed capacitance in the faulted sections of line. It has been assumed further that the fault impedance is resistance only and that it is effectively constant throughout each cycle. All of these assumptions, except perhaps the latter, are reasonably valid as far as relaying is concerned, although some consideration must be given to the d-c component of the short-circuit currents with very high-speed relays.

Distortion in a Pulse Count Modulation System

Abstract: In the further development of pulse time multiplex systems the form of modulation known as pulse count modulation (PCM) has been studied both theoretically and experimentally. This work reviews briefly the principles of pulse communication and its extension to PCM. Unlike the conventional types of modulation, PCM is represented by a discrete scanning of the amplitude of the modulating signal rather than a continuous amplitude scanning, in addition to the discrete scanning in time which is common to the other forms of pulse modulation. The discrete nature of such a system introduces a type of distortion which is a function of the number of amplitude levels used. The relation between the numbers of levels and this type of distortion has been investigated and is discussed. Several types of signals are analyzed mathematically; namely, a single-frequency signal, a 2-frequency signal, and finally a continuous band of frequencies. In connection with the multifrequency case, the application of the Fourier transform to pulse amplitude modulation and its extension to PCM is introduced. In addition, the cross talk introduced in different channels of the modulating frequency is shown graphically for several amplitude levels.

Gaseous Insulation for High-Voltage Apparatus

Abstract: A group of halogenated gaseous compounds have been investigated to determine their impulse (1?x40-microsecond wave) and 60-cycle strength in uniform and nonuniform fields at pressures of 1,2, and 3 atmospheres. The scope of this investigation was confined to bare electrodes, and additional testing will be required to determine the behavior of these gases with various types of solid insulation. It has been found that sulphur hexafluoride (SF6) possesses superior insulating properties for high-voltage apparatus, even at these relatively low pressures. Data obtained in an approximately uniform field indicate that at 30 pounds gauge. pressure this gas approaches the impulse strength of oil. Therefore, certain classes of high-voltage apparatus advantageously may use this gas for their insulation, if other properties are adequate.

Diffusion of Electric Current Into Rods, Tubes, and Flat Surfaces

Abstract: Electric current density penetrates or ``soaks'' into an electric conductor starting from the surface during current transients in a manner physically and mathematically analogous to thermal diffusion in transient heat flow. This useful concept is used to explain physically and evaluate numerically transient resistance and inductance of conductors subjected to rectangular current wave impulses.

Burning of Wood Structures by Leakage Currents

Abstract: Wood pole or structure fires of leakage-current origin have caused serious wood-member damage and service interruption. These fires often occur at the end of prolonged dry periods. Operating experience indicates surface tree carbonization on crossarms and pocket burninig at the crossarm-pole junction to be the two general types of burn damage. Pocket burning on some properties has been responsible for the larger part of the cases that required wood-member replacement. Laboratory tests conducted on approximately 200 specimens indicate that a coincident occurrence of dry wood and selective wetting of pole and crossarm surfaces by a light rain or fog, wind directed, which leaves a dry wood area in series with the leakage path, can result in a fire of a pocket type. This dry area, being high in resistance in comparision with adjacent series wetted-wood surfaces, results in a voltage concentration across the dry zone. If the dry zone is sufficiently short for a given circuit voltage, electrical breakdown occurs across the dry zone. This electrical breakdown being located favorably in dry wood and encouraged by a breeze may result in a pocket burn. Shunting devices which by-pass leakage currents around dry high resistance areas have proven successful in laboratory tests in eliminating pocket fires within the by passed zone.

Switchgear Equipment for Tidd High-Voltage Test Lines

Abstract: The approach to terminal switching equipment herein described presents a new concept for higher voltage switchgear. It is believed that this concept, while not confined to higher voltages alone, will provide all the functional advantages of conventional switching equipments along with great economies in space and cost. At the same time, it should result in increased safety and decreased maintenance.

The hysteresis motor-advances whick permit economical fractional horsepower ratings

Abstract: The theory of the development of torque in a hysteresis motor is analyzed from both the hysteresis lag angle and total loop energy points of view. A new development, comprising the use of a closed slot stator in co-operation with a hysteresis rotor, which permits building hysteresis motors of high power output at high efficiency is explained qualitatively and supplemented by considerable quantitative experimental data. A new method of stator construction, permitting the use of closed slot stator laminations assembled on a mandrel with non-magnetic bearing supporting spiders, wound externally in either a d-c type of armature winding machine or with form-wound coils, impregnated with a thermosetting resin and baked to form a unitary structure, is described. The electrical design of the machine is covered and quantitative data on both design details and operating characteristics are given on several models.

Outage Expectancy as a Basis for Generator Reserve

Abstract: Probability calculations furnisha useful means whereby the average frequency and duration of generator outages on a power system, as shown by experience records may be converted into a consistent measure of the expectancy of multiple outages upon which the provision of reserves is based. This paper gives the mathematical development of relatively simple formulas for this purpose and methods of calculation and of exhibiting the results in tangible form. Use of these formulas does not require familiarity with technical probability mathematics.

Machine Computation of Power Network Performance

Abstract: The planning of modern power system expansion demands that voltages, phase angles, power flow, and reactive power flow throughout the network be determined in advance of actual system changes. Determination by calculation of these quantities increases in difficulty to such an extent, as the system increases in size, that, for large interconnected systems, it heretofore has been considered necessary to use a network analyzer for this work. Since the first a-c network analyzer was put in service at the Massachusetts Institute of Technology in 1929 the scale model method of handling complex power system problems has grown in popularity, and the number and size of analyzers in the United States has been increasing steadily. To date, 14 network analyzers have been constructed, and more are on order, all at a total cost approaching two million dollars. A widespread, but misguided, belief prevails among power system engineers that the foregoing problems are not solvable practically except with the aid of an analyzer. It is the purpose of this paper to set forth certain principles and methods which so facilitate the handling of problems of power flow in networks that the mathematical solution appears more feasible than the analyzer solution. The methods and equations presented in this paper have been tested by recomputing an actual network analyzer study by mathematical means for comparison. Data and answers from this study are tabulated in this paper. The mathematical solution was first made with a key calculating machine.

Frequency Division Techniques for a Coaxial Cable Network

Abstract: A description is given of developments employing frequency division techniques by which the telephone-message-carrying potentialities of the coaxial cable system are realized. By these methods 480 high quality telephone messages are prepared for transmission over the line and restored to original condition at main terminal points. At intermediate points appropriate groups of channels may be removed, inserted, bridged, or relocated in the frequency spectrum of the line.

Some Fundamentals of a Theory of the Transductor or Magnetic Amplifier

Abstract: The old d-c presaturated reactor has experienced a revival with the appearance of the metallic rectifier. The combination of these two devices is studied with an idealized magnetization curve as a basis. Two typical connections are chosen as examples, namely one polyphase connection without self-excitation and one single-phase connection with self-excitation. The behavior is very similar to that of grid-controlled rectifiers. There is a marked difference as to the dynamic properties of the two connections. Much more rapid response is obtained at correct design than generally expected, making the application to quick-acting regulators often quite possible.

The Interruption of Charging Current at High Voltage

Abstract: The switching of high-voltage transmission lines and underground cables occasionally produces overvoltage surges on electric power systems. While operating experience generally has been satisfactory voltages of 66 kv and below, there have been transient disturbances of considerable magnitude at the higher voltages. The length of many of the transmission lines and the importance of maintaining continuity of service on heavily loaded interconnections have stimulated a critical analysis of the problem. However, in contrast to the extreme overvoltages predicted by theoretical studies, a review of several hundred field tests over the past ten years, including many tests with voltage records by cathode ray oscillographs, discloses practically no cases of line or bus surge voltages on solidly grounded systems reaching transient peaks as high as 2? times normal line-to-ground crest voltage. This paper attempts to evaluate the effect of both the circuit constants and the characteristics of the various types of interrupters used in modern high voltage oil circuit breakers on the magnitude of switching surges. Particular attention is given to the advantages and disadvantages of such oil flow pistons or low ohmic value resistors in parallel with the main arc extinguishing devices.

Air-Borne Magnetometers for Search and Survey

Abstract: Air-borne magnetometers developed during the war for the detection of submerged enemy submarines now have become important tools for aerial geophysical exploration. The instruments described utilize the second harmonic outputs produced by the magnetic field in saturated core inductors for field measurement and for control of servo stabilizing systems acting around two axes to maintain the measuring element in alignment with the earth's field. The field to be measured is compared continuously with that produced in the measuring inductor, winding by an accurately controlled direct current. The sensitive element usually is towed in a bombshaped bird sufficiently removed from the airplane to escape the effects of its magnetic field. A continuous record is produced which, when keyed with position records obtained by photography or shoran, may be used in the preparation of maps of total magnetic field intensity.