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Insulation paper is primarily used in electric motors as slot cells, coil separators and phase insulation in integral horsepower equipment. The slot cell being defined as the basic ground insulation that provides mechanical and dielectric barriers from the magnet wire to the stator core. This definition emphasizes that the insulation paper forming the slot cell is mainly ground insulation.

Consideration is directed toward electromagnetic compatibility as viewed from the control aspect. Emphasis is placed upon an inter-system approach to the improvement of the over-all electromagnetic environment.

In the past few years it has become well established that presently available carbon black papers when used to screen the conductor or insulation of a high voltage cable increase the initial dielectric loss of that cable. Kitagawa1 developed a formula which relates this increase to the resistivity of the carbon black paper. This formula can be expressed to a first approximation, as Δ tan δ = ω CR where C is the capacitance of the insulation and R is the series resistivity of the carbon black layer. In the work discussed last year, we2 showed that the resistivity formula did not provide an adequate explanation for the increase in dielectric loss due to carbon black paper.

A microwave method for the measurement of fiber orientation in paper, is described. The method uses a dual mode microwave cavity where the modes have equal resonant frequencies and mutually perpendicular electric fields. The paper is inserted through the cavity so that the electric fields of both modes are in the plane of the paper. If the orientation of the fibers in the paper is not random the resonant frequencies will differ due to the dielectric anisotropy of the paper. This difference is measured and can be calibrated to give the amount of fiber orientation. Moisture and thickness variations in paper can cause calibration errors. However, if the variations are within certain limits, these errors can be eliminated by a suitable selection of the resonator bandwidths.

Assuming a certain stage of development has been attained, it will be possible in the future to use cables with superconductors if they are reliable and economical.1, 2 In addition to the development of superconductors, the cryogenic envelope, and cooling equipment, it is necessary to investigate feasible dielectrics at a few degrees K. This paper is intended to give information regarding the experimental determination of the breakdown strength of paper wrappings impregnated with supercritical helium which could be used in direct voltage cables with superconductors.

For voltage levels of 300 kV and above,1,2 oil-impregnated cellulose paper becomes less and less efficient as insulation in underground transmission cables because of the increasing dielectric losses. Above 500 kV cellulose paper will not be applied as a result of prohibitive dielectric loss heat as well as of excessive growth of insulation thickness, so that maintaining both sufficiently low thermal resistance and acceptable bending properties becomes difficult.

This paper is concerned only with the effect of the dissipation factor of the liquid upon the overall dissipation factor of impregnated paper insulation.

Since the early days of electricity supply (1890), impregnated paper based cables have been used for transmission and distribution purposes.1 Besides a long record of cable reliability, paper insulation has unique characteristics such as a ruggedness which provides easy taping and subsequent bending of the finished cable and a porous matrix which allows easy flow of the impregnant assuring a virtually void free composition with a high breakdown strength. However, the inherent electrical properties of the oil impregnated paper composition give rise to a limited power transmission capability for paper-oil insulated power cables at extra high voltage. This limitation has stimulated research on new transmission systems and new materials. This report is concerned with one of these efforts, namely, synthetic paper insulation.

The voltage endurance of liquid impregnated paper insulation is important in both test and service for high voltage equipment such as transformers, capacitors, and cable. It has been recognized for a long time that if electrical discharges occur, they may limit the life. Especially with cable, corona studies have been carried out for many years using both dielectric loss measurements (i. e., Schering Bridge) and several types of amplified band pass techniques for more direct measurement of corona pulses.

The use of capacitors in electric networks is becoming more and more common. The capacitor remains under the voltage of the network, and in addition it is subjected to various over-voltages appearing in the network. The latter will originate from lightning strokes and more frequently from switching operations. Due to the incompleteness of data on the capacitor dielectric strength under switching surges, the problem became of interest. The lightning and switching surges may cause a weakening of the dielectric strength of many types of equipment. Power capacitors, with their impregnated paper insulation, belong to this category of equipment.

Mica paper was invented at almost the same time in the United States and in France. It was during the war and that is probably the principal reason why its development was delayed.

The effect of switching surges on the dielectric strength of Askarel impregnated capacitor paper is less than for standard impulses and approximately the same for A.C. From the practical point of view the small variation in breakdown strength resulting from a change in the wave front duration from 35/110 µ sec to 600/2000 µ sec can be neglected in the design of capacitors.

Mica in the form of mica paper will soon make its appearance as a component, in electrical insulation. This revolutionary advancement in the use of mica will make available to the electrical manufacturer products which have heretofore been impossible to produce.

This session is devoted to the insulation probieros in the manufacture and use of transformers. These probieros resuit from the progress in delermining the life of equipment from many viewpoints. New matcrials and ways of using them, processes, quality control, and corona effects, are illustrated as problems in the papers being presented.

Cellulose papers expand and contract when the humidity of the atmosphere with which they are in equilibrium changes. This phenomenon — known as hygroexpansivity — plays a significant role in the manufacture of such electrical components as capacitors, cables and transformers due to the shrinkage and consequent mechanical instability which the units suffer on being dried before impregnation. While many investigations have been made of the phenomenon, most of the work has been hampered and made useless by the failure of the researchers to establish repeatable data. It was the purpose of this work to determine why the effect was not reproducible within close limits and from the results to understand the mechanism of hygroexpansivity.

In dielectric materials, measurements of the low frequency ac conductivity can often reveal certain features of the electrical conduction mechanism which are often not apparent from the data derived through dc or higher frequency ac measurements alone. In the not too distant past, low frequency measurements were difficult and tedious due to the rudimentary measuring techniques available and the associated instrumentation problems. However, the recent development of a low frequency bridge by Harris1 has changed the situation entirely; now low frequency measurements may be carried out with relative ease in the range from 10−3 to 1 Hz, using the Harris technique.

It has been shown1 that the distribution of the gradient in a dielectric under dc conditions generally depends on the rate of the voltage variation. This fact has already been studied in connection with a voltage polarity reversal1,2 in extra-high-voltage dc power cables, but it can also be of importance to define a correct testing procedure for the same cables. Conversely, an analysis of the transient behavior of the dielectric may also be useful from a physical point of view, in order to get a deeper knowledge of the phenomena involved.

In composite materials, the laminating industry has been built on the principle of locating things where they would do the most good. Way back in 1922 at General Electric Company I began to appreciate that the same base materials in the same proportions would give twice as much strength if they were disposed in laminate fashion than if they were randomly mixed. Throughout the years, these structures have been applied, originally to give greater strength and stiffness; but more recently through the whole gamut of qualities, to toughness and controlled permeation of films. Let me review some of those earlier days with you.

Silicone fluids have numerous electrical applications in both energy conversion equipment and communications type apparatus. To aid engineers in the application of these fluids and to determine the general characteristics of these dielectrics, a study was made of their electrical properties. The measurements were made on fluids of commercial purity.

Fiber Modified Isomica provides the electrical design engineer the tools needed to overcome many critical insulation problems at a reasonable cost. The unimpregnated nature of the tape coupled with its physical strength makes it suitable for many taping applications previously not considered for reconstituted mica products. The very high mica content suggests a practical way of obtaining the reliability of mica insulation in a wide variety of rotating electrical apparatus.

Immediately following the breakdown of a liquid dielectric a variety of dynamic events appear. Initially, a highly luminescent, thin, plasma column is formed followed by a radially expanding mechanical shock wave. In the process, a gaseous bubble composed of vaporized dielectric is created. The study described here is concerned with this bubble. Specifically, investigations were made into the effects of hydrostatic pressure upon the dynamics of the gas bubble.

Space is both an environment and an insulating medium. Space, viewed as an environment, is characterized by great temperature extremes, bursts of dangerous particulate and electromagnetic radiation, extremely low gas pressures, and swarms of particles and clouds of dust. Space as an insulating medium is characterized by a heat transfer process that is limited solely to radiation, the high dielectric strength associated with an essentially ion free environment, and the Jack of deterioration of materials caused by oxygen, water, and other similar terrestrial causes of corrosion and decomposition.

Some present developments in the area of laminated, low-loss and combined substrates for use in electronic equipment are discussed. The tailoring of these materials, particularly in light of their intended fabrication, to meet specific engineering needs is reviewed in terms of several concrete applications. Some of the properties which appear critical for the successful use of these materials are noted and used to provide insight concerning future trends in materials engineering in this area.

The major growth area within the printed circuit market is expected to be as a result of the development of flexible and multi-layer circuits. The continuing pressures on designers of electrical and electronic equipment for smaller and lighter packaging has greatly increased the demand for thin, multi-layer and flexible, wiring packages. In the automotive field, dashboard wiring is rapidly being replaced with flexible circuitry. Computer, appliance and meter manufacturers are among the many circuit users finding benefits in flexible multi-layer circuitry. Mechanical pattern generation methods lend themselves to the production of flexible circuits, where the insulating film to which the pattern is bonded is tough, flexible, and possesses good electrical properties.

According to Time magazine, the dreadful summer of 1955 will be remembered for a long time to come in the Eastern United States. Beginning in July, the region was withered by drought and a heat wave, the worst on record, with temperatures in the 90's for a large part of the month. Then Hurricanes Connie and Diane flooded the Northeast, killing more than 250 people and causing property damage well in excess of $1.5 billion (1).

Measurements of temperature histories of epoxy/glass prepreg layers during multilayer printed wiring board lamination have been recently obtained. In the present paper, it is shown that the temperature histories may be predicted by an analysis of the transient heat flow process within the MLB. The analysis requires a knowledge of the press platen temperature history during laminations and the thermal resistance of the padding material. Theoretically predicted results show close agreement with the experimental data for both 5 layer and 15 layer MLB's using the "hot press" as well as the "cold press" cycles. The present method may be used in the design of MLB lay-ups, in particular the determination of the necessary padding thickness to achieve heating rates which give adequate timing "windows" for cure pressure applications. The present theory has been applied to study the effect of kraft paper padding on the prepreg temperatures. Results are shown for both 15 and 5 layer laminations employing the hot press as well as cold press cycles. The number of kraft paper sheets used is shown to have a significant bearing on the temperatures.

Five years ago, the author presented to this Conference a paper entitled “A New Approach to the Analysis of Insulating Liquids”. In addition to presenting theories concerning the behavior of insulating oils, this paper described the Doble Oxidation Test which furnishes information during an accelerated life test that is indicative of the oil quality and its probable service performance by determining the time to the first appearance of sludge or an acidity of .25 KOH/g. Published as a suggested method in the 1958 Annual Report of ASTM Committee D-9, it is currently under study by Committee D-27. A new equally pertinent test which measures power factor has been developed. The combination of both provides information of far greater value than does either test alone.

Mineral oil and askarel have been in general use in transformers, capacitors, cables, and switchgear for many decades. With the exception of polybutenes, no other dielectric liquids have gained acceptance for use in high voltage power apparatus, primarily because oil and askarel are so inexpensive and possess such excellent electrical properties in combination with kraft paper.

A method of measuring the mean rms level of a low duty cycle acoustic signal using an inverting circuit and an integrating digital voltmeter (DVM) is described. The technique has the capability of taking many measurements which are recorded, in one configuration, through a data coupler on paper tape for analysis on a time share computer. The important system characteristics are noted and an estimate of the system error is tabulated.

The results of a study of the propagation mechanism of impulse creepage discharges over oil-immersed Kraft board is reported in this paper. This study was carried out using Leica and high-speed Boys cameras to record the progression of the discharges and using a special probe technique to measure the discharge potentials at various points along the channel. The electrode configuration used in these experiments consisted of a rod electrode on one side of a sheet of one-eighth inch Kraft board and a grounded copper surface deposited on the opposite side. Capacitance probes were imbedded in the copper surface to measure the approximate potentials of streamers passing along the rod side of the insulation. Impulse waves (1.5 × 7000 μsec) were applied to the rod at 120 kv which was about three times the corona starting level. The entire test structure was placed in a lucite tank filled with commercial quality insulating oil. Photographs of the discharges were made through the walls of the tank by means of a slit and mirror arrangement. The Kraft board insulation used in these tests was first impregnated with oil under vacuum, and transferred to the testing tank just before tests were begun.

The thought has been expressed that the manufacturer and user of insulating materials, who may use electrical resistance measured in accordance with ASTM D-257(1) as one means of evaluation and control, may not be familiar with the d-c tests that these materials are subjected to after assembly into insulation systems in apparatus. One of the purposes of this paper is to review d-c tests as they are used in the field to evaluate the condition of the insulation in power apparatus. It is largely in power equipment such as rotating machinery, switch-gear, cable and transformers that such field tests can be economically justified (2).

Machine taped coils insulated with a Resin Rich B Stage glass backed mica paper tape have now been in production for a number of years. This process allows all the main wall insulation to be applied and consolidated in one application to all types of coils without any vacuum treatment. The system can be used at Class F temperatures. No voltage restriction has been made and the production processes have been developed for use up to 30 kV.

Following the very successful application of extruded polyethylene insulation to coaxial submarine telephone cables, the first high voltage power transmission circuit using this insulation under water was energized in 1968 at Cook Inlet, Alaska. The accumulated experience with 138 kV solid dielectric submarine cables now amounts to nearly 30 circuit-mile-years without a single electrical underwater fault. The major advantages of this new form of cable are simplicity in construction, easier installation, and lower electrical capacitance and thermal impedance. The critical length of a 138 KV cable with 2000 MCM conductor is 150-200 miles, depending on sediment thermal resistivity. Extruded polyethylene insulation, therefore, makes it possible to transmit ac power over long distances under water.

Applications for higher service temperature rigid thermosetting electrical insulation for rotating machinery are increasing each year. Higher service temperatures allow a reduction in size, weight and, frequency, cost of electrical apparatus. The limitations in maximizing service temperature have traditionally been the thermal endurance and cost of the electrical insulation.

During the past 8 years, mica has lost ground in its usage growth as compared to the total electrical insulation market. However, this loss has not been to materials that have superior electrical insulating properties but rather in applications which did not need the properties of mica. There is no product on the market that has the voltage endurance and corona resistance of mica. Combine these properties with the high temperatures and capability and superior dielectric strength of mica and for real heavy duty applications mica is the preferred insulation.

The life of electrical insulation in water is limited by steam (24 psig) which shows three orders of magnitude reduction in life as determined by AIEE #57. Power equipment in water must be temperature controlled to avoid the steam condition. This means larger volume of equipment, lower power densities and lower temperature rise above the ambient. If this is not done by the designer then the operator is forced to downrate the equipment to preserve useful life. To overcome this limitation in size one must develop steam resistant electrical insulation in order to be able to operate at higher temperatures. Techniques to seal the system to exclude water are not satisfactory because small amounts of water passing through barriers or internally generated in the system, may be the equivalent of operating the electrical equipment in 100% steam if temperature is not controlled.

The references presented in this chapter are concerned with the electrical properties of organic film or fiber insulation. The literature search was based largely on Chemical Abstracts and Science Abstracts. Other sources of relevant information included the 1964 Conference on Electrical Insulation, NAS-NRC; Conference of Dielectric and Insulating Materials (London: IEE, 1964); and the magazine Insulation which provided both original articles and abstracts of the European literature.

Ten years ago the standard resin for Class H insulation was silicone. The volume of electrical equipment made for this thermal class was small, disproportionately small considering the engineering involved in the insulation. Accordingly, such insulation was expensive. Expanded use of high temperature insulation was contingent on attainment of lower cost, both in materials and process.

As indicated previously, use of the term "Class F" has become increasingly prevalent. Many users of electrical insulation are intensely interested and are inquiring about the availability of such materials. They want to design equipment in the 155°C range, but must have materials which can retain their properties sufficiently and adequately to insulate their motors, transformers, and other electrical equipment.

The subject of this session relates to Electrical Insulation Systems and it is to such systems or more particularly to one such system that I wish to direct attention.

Summary form only given, as follows. This paper is divided into two sections. Section I describes the results of approximately six million transistor hours of operation on various types of transistors from four different manufacturers. The data was taken on two different transistor systems containing digital type circuitry and on a set of transistor flip-flop circuits operated under semi-controlled conditions. The types of transistor failures that have occurred will be listed and the general aging trend will be discussed. This section will be accompanied with slides showing some of the circuitry. Based on the above life data along with the experience gained in operating transistor systems, Section II will cite certain conclusions leading to the design of reliable switching-type circuits. In particular a design procedure is demonstrated in the form of a clamped-level multivibrator. This section will show how initial discrepancies in transistor parameters are taken into account along with long term drifts in 'B' and 'Ico.' Aside from the fundamental design practices involved, the multivibrator circuit is chosen because it is relatively difficult to obtain the functional equivalent of a vacuum tube multivibrator due to transistor idiosyncrasies. These idiosyncrasies include low input impedance and hence slow circuit response because of the large coupling capacitors necessary for even small delays. The paper will be concluded with comments regarding clamped vs. unclamped logic and large system operation.

Summary form only given, as follows. The complementary pair family of circuits can yield great economy in digital computer design, as has been shown in the preceding paper. One member of this family is attractive, because of its simplicity, in those situations where the ultimate in speed and load handling capacity is not required. If it were possible to allow saturation in the transistors, a very simple bistable element would result. In general, ·this is not permissible, for the degradation of performance is too severe. By application of a new principle, which has been called by the author that of "Controlled Saturation," one of the transistors may be allowed to saturate without undue performance deterioration. Then the other transistor may be prevented from saturating at a cost of only a single resistor. The paper first describes the process of Controlled Saturation, and then shows the synthesis of a practical trigger circuit employing it.

This paper will discuss a monolithic operational amplifier which utilizes an improved feedforward technique to compress the feedforward pole-zero pair and yield an experimentally-observed total unity gain acquisition time (slewing plus settling) of 600 ns to 0.01% with a 10-V input step, without compromise of the dc performance parameters or the use of complex compatible processing.

Design criteria and techniques used to minimize the interference levels between the communication and signal channels for control of rapid transit vehicles and other working systems (such as propulsion, power system, auxiliaries, etc.) or the environment, are analyzed in this paper. The particular system under consideration utilizes a higher frequency band to allow a wide separation from signal to noise, but below 10 KHz and at low power level so that it does not require special license to operate. In addition, the use of Frequency Shift Keying (FSK) and the well known features of signal capture as developed in F.M. Systems are used to further increase the Electro-magnetic Compatibility (EMC) of the overall system. The automatic train control (ATC) engineer must always design his equipment to interface with the outside world, but under some circumstances he may be able to influence the design of other subsystems to meet his particular requirements. For that reason it is extremely important that the ATC and propulsion or power engineers work hand in hand to achieve the electro-magnetic compatibility required in today's systems. An example of such activity is presented to illustrate the extreme importance of designing a transportation system as an integral part of its environment, versus the design of individual subsystems which do not have well defined interfaces. The techniques presented in this paper have been successfully implemented in various transit systems which are presently in operation.

This paper presents a technique for identifying unknown parameters for a dynamic equivalent of a portion of an electric power system from on-line measurements made in another portion of the system. The resulting model is suitable for use in a standard transient stability program such as those used by system analysts for evaluating the security of a proposed or existing system. The method is based on stochastic system identification using the maximum likelihood technique and relies on natural system fluctuation. This paper describes the mathematical development of a maximum likelihood identifier for a dynamic model of a power system. The resulting identification program was tested using a simulated power system tuned to match measurements made on a real system.

This paper will discuss a nonvolatile 2048-bit MNOS block-oriented RAM array with a serial clear/write or read/cycle data rate of over 2 MHz with less than 400-mW power dissipation.

This paper presents a survey of active microwave semiconductor devices with emphasis on devices made from Gallium Arsenide which is presently the material with the greatest scope and promise. Thanks to the three properties of high mobility, low threshold field and the existence of semi-insulating substrate GaAs is now preferably used as the starting material for avalanche (IMPATT) diodes, transferred electron (Gunn) diodes and field effect transistors. The GaAs IMPATT diode is presently the hottest performer in the frequency range up to X-band, whereas at higher frequencies the double-drift Si IMPATT diode still has the honor of maximum power and efficiency. Although exhibiting lower power and efficiency the Gunn diode has certain advantages such as low noise, low bias voltage, needs less critical tuning and bias circuitry and has a simpler structure. During recent years the GaAs field effect transistor has been developed to the fastest three terminal semiconductor device with outstanding noise performance. The paper outlines the basic device physics, terminal characteristics and reports the newest results.

This paper is somewhat tutorial in nature although the results shown here are derived from the thermal analysis of a specific microwave power transistor. Computer-aided thermal simulation techniques are used to derive heat transfer characteristics and to estimate the operating temperature of the device for a time varying sequence of power pulses. The technique and results are discussed to point out important thermal effects that occur and are common to most semiconductor devices. Points of interest include the temperature distribution both on and within the chip, effects of temperature dependent material properties, the effect of adding a heat spreader under the chip, and finally, the meaning and significance of the effective thermal time constant for the junction, the chip, the carrier and other parts of the electronic package. Some effects of unwitting temperature measurement by experimental techniques are also indicated where appropriate. These results form somewhat of a sequel to an earlier paper, which discussed similar results for other semiconductor devices.1 The main difference of this device compared with those in the earlier paper is that the effective junction time constant is much shorter since it is only on the order of 50 ms. As a result, junction temperature excursions become quite large even for power pulses of only several microseconds duration.