Harold A. Peterson

Superconductive energy storage inductor-converter units for power systems

Large magnets with superconductive windings could serve to perform a power system function analogous to pumped storage hydro. A conventional Graetz bridge converter as used in dc transmission provides an ideal interface between the three-phase power system and the superconductive magnet or inductor. Such Inductor-Converter or I-C units, when properly controlled, provide significant power system benefits. Power reversibility is achievable within a few cycles without switching. Power system electromechanical oscillations can be damped effectively. Computer studies reveal that this damping capability may be useful even with smaller inductor sizes when energy storage in large amounts is not the primary objective. In sizes greater than 1,000 MWh, economic studies show promise.

Damping of Power Swings in a Parallel AC and DC System

In an earlier paper, the authors presented a method of simulating a transmission system including ac and dc lines in parallel, and established the validity of the simulation. In this paper the method, which utilizes a direct and quadrature axis representation, is used to study with the aid of an analog computer the electromechanical oscillations in a system consisting of one machine tied to an infinite bus through two parallel transmission lines, one of which is ac and the other dc. Results make it clear that with proper dynamic control of power flow in the dc line, a substantial degree of damping of transient power swings may be achieved.

An Analog Computer Study of a Parallel AC and DC Power System

Overall critical evaluation of the dynamics of EHV dc-power transmission requires that a variety of system conditions and effects of many parameters be studied. Problems can be strictly electrical or electromechanical. In general, those that fall in the former category are of short time duration, while those in the latter may be either of intermediate duration, on the order of 1 second, or of long duration, from 2 to 40 seconds. The approach used, whether it be 1) a physical model such as a transient network analyzer; 2) an analog computer, sometimes called an electronic differential analyzer, or 3) a digital computer, will depend upon the specific problem at hand. The capabilities and limitations of the analog computer in providing solutions to electromechanical problems are outlined in this paper, and the results reported give insight into the dynamic performance characteristics of a dc link under constant current or power control, with or without a parallel ac line.

A Dynamic Surge Arrester Model for Use in Power System Transient Studies

The valve-type surge arrester with current-limiting gap has dynamic performance capabilities which provide improved protection against system transient overvoltages. This paper interprets these dynamic characteristics as revealed in laboratory tests and translates them to a set of differential equations which can be solved with the aid of a computer. Alternatively, the differential equations can serve as an important guide in developing an equivalent circuit, and hence a physical model for the arrester which might be found useful in direct analog studies. Comparison between laboratory test results and computer results establish the validity of the simulation. Extension of the approach to more general system voltage transient studies is contemplated.

A Method for Reducing Dead Time for Single-Phase Reclosing in EHV Transmission

Most faults on transmission lines are single line to ground (SLG). For such faults single-phase reclosing would result in an improvement in transient stability over the alternative of three-phase reclosing. The improvement is offset by the capacitive coupling from the other two energized conductors because it tends to sustain current in the original fault arc path, thereby lengthening the time required for arc deionization. An increase in dead time is therefore required which decreases the net improvement. This paper presents a novel method of nullifying the capacitive coupling effect. The method requires the addition of a capacitor, connected across the terminals of each breaker pole, proportional to the particular line being switched.

Superconductive Inductor-Converter Units for Pulsed Power Loads

Pulsed power loads of increasing magnitudes up to several hundred megawatts or more must be supplied in the near future. High energy physics research laboratory experiments and the longer range foreseeable needs for successful nuclear fusion reactors such as the University of Wisconsin Tokamak reactor designs are representative examples. Such large pulsed power demands are at best undesirable if not prohibitive, even for the largest electric power systems. Techniques for storing energy in superconductive inductors employing thyristorized converters are described. Circuits which serve to minimize both the pulsed power and corresponding reactive volt-ampere requirements from the three phase power system are presented. Exploitation of these circuits and related concepts from the control standpoint should provide a basis for designing power conditioning interface equipment to meet the challenging requirements of very large pulsed power loads looking to the future.

Parallel Operation of AC and DC Power Transmission

A preliminary account has already been given of the EHV composite ac-dc study initiated last year at the University of Wisconsin [1]. This paper presents additional results obtained in the study of parallel EHV ac-dc power transmission in a basic 2-machine equivalent system. The consequences of 3-phase faults on inverter commutation are evaluated, and circumstances leading to inverter commutation failure (shoot-through) are made clear for various conditions of initial loadings and faulting. The consequences of inverter shoot-through onsystem stability are also evaluated for the 2-machine case. The characteristics of the control arrangement for a dc line are expected to be of special significance in determining the final overall performance of composite ac-dc systems.

Superconducting Energy Storage

Energy storage with large superconducting magnets is one of the possible new components in a power system. Serious feasibility studies are under way in the United States at the University of Wisconsin and at the Los Alamos Scientific Laboratory. The preliminary opinion by both groups is that such units should be technically feasible. As of the date of this writing (summer 1973), there is less certainty that such units can be designed, constructed, and operated economically.

Microwave Thickness Detector

A device is described which is capable of continuously measuring the thickness of moving conducting materials. The details of two independent methods, one utilizing the amplitude and one the phase of reflected microwave energy, are explained and compared. Experimental results verify that increments of the order of 1/40 mm are clearly detectable.