Showing papers in "Transactions of The American Institute of Electrical Engineers. Part Iii: Power Apparatus and Systems in 1957"

The calculation of the temperature rise and load capability of cable systems

Abstract: This Neher–McGrath paper describes a method of esti mating the steady-state temperature of electrical power cables for commonly encountered co nfigurations. By estimating the temperature of the cables, cables’ safe long-term c urrent-carrying capacity (termed “ampacity”) is determined. The paper described two-dimensional highly symmetric simplified calculations which have formed the basis for many cable applicat ion guidelines and regulations. Complex geometries, or configurations that require three-di mensional analysis of heat flow, may require more complex tools such as finite element analysis.

The Calculation of Radio and Corona Characteristics of Transmission-Line Conductors

Abstract: A method of calculating the corona and radio-interference generating characteristics of either single or bundled transmission-line conductors is presented. Briefly the calculations are made in six steps by following the simple procedure outlined in the section "Method of Calculation." The concept of representing a bundled conductor by an "equivalent diameter" is presented and confirmed by the test results. Using this concept, it is shown that a single 1.602-inch-diameter ACSR conductor is approximately equivalent to a 2-conductor bundle of 795-MCM ACSR "Drake" conductors or a 3-conductor bundle of 477-MCM ACSR "Hawk" conductors. Likewise a single 1.75-inchdiameter conductor is approximately equivalent to a 2-conductor bundle of 954-MCM ACSR "Cardinal" conductors.

Corona Measurement and Interpretation

Abstract: This discussion of the performance of the more common types of corona measurement circuits has emphasized certain points. They may be summarized as follows: 1. The coulomb charge in individual corona discharges and the number and phase of these individual discharges are considered the significant quantities in corona measurement. 2. The voltage step pulse produced by a single discharge varies directly as the pulse coulomb charge and inversely as the test specimen capacitance and the capacitance in parallel with it. This voltage is then divided between the detector input shunt capacitance and the series-coupling capacitance. 3. The observed shape of the pulse following the very rapid step change in voltage is determined by the inductance or resistance shunting the detector input. These produce, in the case of a resistance, a nonoscillatory exponentially decaying voltage, and in the case of an inductor an oscillatory decaying voltage. 4. A wide-band amplifier is needed to indicate a major fraction of the initial pulse height if the time constant of the exponential decaying is short. This is particularly true of the nonoscillatory pulse produced by a resistance input, where conventional narrow-band amplifiers have an output crest voltage which is only a small fraction of the input pulse crest. A much greater sensitivity may be achieved with a fairly narrow bandwidth amplifier tuned to the natural oscillation frequency of the input circuit having an inductance. A high Q in this input circuit is preferred to give maximum sensitivity. 5.

Synchronizing out of Phase

Abstract: Synchronous-machine torques due to out-of-phase synchronizing may be quite large; larger in fact than those encountered during a 3-phase short circuit. Previous works have presented various forms of equations to calculate these torques.1-3,6 With the advent of the widespread use of systems analyzers and computers, it becomes convenient to use more exact equations to calculate synchronous machine transient performance. The objectives of this paper are to present the derivation of the equations for the currents and electrical torques which occur when turbine generators are synchronized out of phase; to show how these electrical torques arise; to illustrate the application of these equations to the problem of calculating the transient mechanical torques in a large, multiunit turbine-generator set under these conditions.

Electrode Area Effect for the Impulse Breakdown of Transformer Oil

Abstract: In a previous paper (1), the necessary experimental and theoretical basis was established for a discussion of the effect of electrode area on the 60-cycle breakdown of transformer oil. A study of 1600 observations established the extremal nature (2) of such breakdown distributions and yielded an equation relating area and voltage which agreed closely with test results. This equation is: V A1 − V A2 = s v /σ N 1n A 1 /A 2 (1) where V is the modal strength and s v is the standard deviation of N measured breakdown values; σ N is a function of the number of breakdowns N only.

Relationship Between Corona and Radio Influence on Transmission Lines, Laboratory Studies I-Point and Conductor Corona

Abstract: 1. When a quasipeak-type RN meter is used for the measurement of a corona noise, it is advisable to calibrate the meter with a pulse generator. 2. A procedure of calibration and a calibration chart are given. Consistent readings have been obtained for all the meters so calibrated. 3. Within the range of measurements the RN meter readings are linearly proportional to the voltage of square pulses and to the pulse width between 2 and 200 millimicroseconds above which the increase is no longer linear. 4. A given RI level can result from a variety of corona patterns characterized by the number, magnitude polarity, width, and distribution of pulses. These characteristics can sometimes be used to differentiate between the types of corona noise. 5. A good correlation between corona pulses and RI values can be obtained for a given setup if the repetition rate is known for each group of pulses of equal magnitude 6. Sudden jumps of RI were observed when an electrode with sharp points was subjected to a critical voltage. The instability was associated with the onset of corona pulses in the positive half cycle of the applied voltage. 7. Since moist insulating points cause much higher corona pulses and RI than metal points, it is possible that vegetation deposits on transmission-line conductors are more liable to cause RI than are surface imperfections. 8.

A New Approach to Loss Minimization in Electric Power Systems

Abstract: In this paper the power losses are studied for an electrical utility. The power and reactive volt-amperes may be specified at the loads. If so, either the voltage or the current vector at the load is also specified. A similar set of specifications may be made for certain of the generator inputs to the electric network. In addition, voltage current vector inputs may be established at other generator nodes. It is presumed that the foregoing restrictions do not preclude the possibility of varying either the voltage or the current vector at several other generator locations. It should be noted that the electric network is assumed to be passive and, if desired, may be grounded at one or more points in addition to those ground connections assumed at the loads and generators. With these restrictions established and the remaining free or manipulative generator voltage or current vectors chosen, loss minimization may be studied. First, the electric network is considered by itself. The necessary and sufficient conditions to be met with the manipulative variables in order to minimize the losses in the electrical network are established. Second, the generator station losses are considered in conjunction with the electric network. This time, the necessary conditions, and also a set of sufficient conditions, are established for the same manipulative variables in order that the over-all loss be minimized. In the latter approach, allowance is made for the fact that the cost per kilowatt-hours is not the same at each station and in the network.

Stray-Current Losses in Stranded Windings of Transformers

Abstract: Previous solutions of the stray loss problem in transformer windings have been made on the assumption that the winding turns contain only one conductor. In a stranded winding this solution represents only the eddy-current loss component of the total stray losses. A second loss component is caused by circulating currents flowing back and forth between the strands. This circulating-current loss depends upon the relative physical location of the strands throughout the winding. Considering various types of stranding, this paper gives equations and charts for the circulatingcurrent loss in a number of different coil constructions as well as for the eddy-current loss.

A Hypothesis Concerning Lightning Phenomena and Transmission-Line Flashover

Abstract: 1. There are differences among the lightning current data obtained by various investigators. These differences appear to be a function of the height and the terminating ground impedance of the structure on which the measurements were made. 2. There is agreement among the data obtained by magnetic links when the results were obtained from direct readings on tower or diverter rods or by the summation of readings made at each end of the ground wire of a stricken span. 3. Comparison of data obtained at sea level or at a high altitude (14,000 feet) based on measurements made of strokes to tower rods or ground wires as in conclusion 2, show no appreciable difference due to altitude. This appears to be contrary to the previously drawn conclusion based on a comparison of the high-altitude diverterrod data to sea-level lightning-current data based on the summation of tower currents. 4. There is disagreement among the lightning current magnitudes obtained as in conclusion 2 and those obtained by the summation of tower currents. 5. Lightning stroke data measured at the ESB are in disagreement with those obtained as in conclusion 2 by a factor of about two to one, particularly at the higher currents. 6. Examination of oscillograms obtained at the ESB show variations in the current wave shape that may be attributed to reflections occurring from the base of the building and other reflection zones around Manhattan Island. Thus, there are indications that the lightning stroke is not a constant current source.