A Study of Ferroresonant Conditions on Distribution Circuits Involving Cable-connected Power Transformers

As far as electric utilities are concerned, ferroresonance is undesirable on distribution or transmission systems because it may result in either transient or sustained over voltages under certain conditions. Lightning arrestor flashover, excessive transformer hum, transformer damage, cable damage, and phase reversals have been attributed to ferroresonance. The probability of ferroresonant conditions resulting in damage to equipment has only relatively recently risen to an appreciable level. The difference lies in the fact that the farroresonant circuit is nonlinear due to the inductive component. This component is a saturable core reactance, which has its impedance value dictated by the saturation characteristic of the iron core. This nonlinear element accounts for the fact that three modes of irregular voltage may be possible on the same circuit. One mode is an unstable, transient overvoltage that quickly disappears. A second mode is a sustained voltage of nearly normal value. The third mode is a sustained overvoltage that can reach destructive values under certain conditions, and this high mode represents a ferroresonant overvoltage condition. If a ferroresonant circuit appears within a power system, the inductive component will in most oases be the winding of an unloaded transformer. An early report of 60 years ago attributes over voltages on a test circuit to ferroresonance. The subject was apparently not of great concern until after World War II as evidenced by the amount of attention it has received within the past 25 to 30 years. Several tests have been conducted on ferroresonance, including network analyzer studies, actual field tests on existing equipment, and extensive laboratory tests. Although the subject has been covered in quantity, there are at least two good reasons for researching ferroresonance. The first reason is supported by the complexity of the subject. Ferroresonance is affected by several factors, many of which are not readily apparent in most of the available literature. One goa1 of this thesis will be to present a discussion of ferroresonance that is more clear and complete. The second reason lies in the fact that the prediction of ferroresonance, using system parameters, does not appear to be entirely satisfactory. The second goal of this thesis will be to present a fresh approach to this problem via a computer solution. The computer program will be an attempt to solve for ferroresonant over voltages given information about the primary cable and transformer involved. A solution will be presented for one situation only. This will consist of an unloaded, ungrounded wye-connected transformer bank supplied by a length of underground cable with only one phase energized. If the solution is accepted for this case, it could be applied to other situations

Radiative properties of a plasma moving across a magnetic field. II: Numerical results

A theoretical analysis developed in a companion paper to treat the early‐time evolution of plasmas moving across a background magnetic field is applied to the modeling of low‐beta, barium chemical releases in the magnetosphere. The results indicate that radiation damping plays an important role in defining the plasma cloud evolution, causing a rapid decay of the polarization field and a loss of plasma kinetic energy and momentum on time scales comparable to several ion gyroperiods. The radiation spectrum consists of a burst of chirped, high‐frequency (in the range of the cloud plasma frequencies) waves, followed by a pulse of whistler waves, and subsequently by ion cyclotron emission. Scaling laws are derived for the plasma momentum and energy loss rates and predictions for the braking time, the amplitude and spectrum of the radiation field, and the total radiated power are presented for conditions relevant to the recent Combined Release and Radiation Effects Satellite (CRRES) experiments [Phys. Fluids B 4, 2249 (1992)].Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/70589/2/PFBPEI-5-4-1306-1.pd

Radiative properties of a plasma moving across a magnetic field. I: Theoretical analysis

The early‐time evolution of plasmas moving across a background magnetic field is addressed with a two‐dimensional model in which a plasma cloud is assumed to have formed instantaneously with a velocity across a uniform background magnetic field and with a Gaussian density profile in the two dimensions perpendicular to the direction of motion. This model treats both the dynamics associated with the formation of a polarization field and the generation and propagation of electromagnetic waves. In general, the results indicate that, to zeroth order, the plasma cloud behaves like a large dipole antenna oriented in the direction of the polarization field which oscillates at frequencies defined by the normal mode of the system. The magnitude of the radiation field and the amount of plasma momentum and energy carried away by and stored instantaneously in the fields are discussed only qualitatively in this paper, quantitative results for specific cloud parameters and scaling laws for the magnitude of the fields and the slowing down of the plasma cloud are presented in a companion manuscript.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/70196/2/PFBPEI-5-4-1289-1.pd

Self‐consistent electrostatic potential due to trapped plasma in the magnetosphere

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/94921/1/grl6791.pd

A Coulomb collision algorithm for weighted particle simulations

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/95216/1/grl7782.pd

Pitch‐angle scattering of cometary ions: Computer simulations

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/95535/1/grl5552.pd

RISK-RETURN ANALYSIS OF INCORPORATING ANNUAL LEGUMES AND LAMB GRAZING WITH DRYLAND CROP ROTATIONS

Profitability and risk, 1988-2001, are examined for lamb-grazed field pea as a fallow alternative with wheat, or an extended wheat-sunflower-millet rotation. Switching from conventional wheat-fallow to an extended rotation with grazed-peas increases profitability (2.3% to 7.3%), and reduces risk (below 0% target in only 2 versus 7 of 14 years).Crop Production/Industries,