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PAPER as used in the spiral laminated impregnated insulation of high-voltage power cables is available over wide ranges of density and thickness. There result important variations in the ordinary physical properties of the paper such as flexibility, tearing, tensile, and bending strength. Variations in the electrical properties of conductivity, dielectric constant, and breakdown strength also result. The peculiarly severe conditions imposed by the manufacture, transportation, installation, and operation of high-voltage cables have emphasized the importance that full attention be paid to all physical properties of the insulation, especially those relating to permanence of mechanical structure and of high insulating properties. Manufacturers of cables often utilize the several types of variation referred to in designing cable insulation to meet the particular requirements of cables for different types of service.

Nippon Synthetic Chemical Industry Co., Ltd. has developed a new form of binder, identified as a Gohsenol p-200, specifically designed for vinylon fibers.The effects of PVA powder as a bonding agent of vinylon paper have been mentioned in practice. The manufacture of vinylon paper on a pilot fourdrinier paper machine by using PVA powder as a bonding agent by the beater addition were studied.Physico-chemical properties of vinylon paper by using PVA powder is better than that of PVA fiber.PVA powder is convenient to handle and paper-making readily in the mill. For the most efficient results, care should be taken to select the preferred PVA powder for the specific need.

An important factor in the design of power cables is the type of screen used over conductor and insulation. Some designers have used aluminum metallized paper tape for many years, but others have preferred carbon black (CB) paper tapes. It was discovered a few years ago, however, that CB paper screens increased the power loss in the cable dielectric at high voltages and temperatures. From hundreds of tests on model and experimental cables this increase in dielectric loss in the cable is shown to result from an internal or mass effect and a surface effect. A small part of the loss increment occurs within the body or mass of the CB paper itself, but a much larger part represents a surface effect believed to be caused by emission of electrons from the paper. These effects are larger at the outer electrode of the model cables than at the conductor. The loss increment is influenced to only a small extent by changes in the amount and treatment of gas channel CB used in the CB paper. However, a reduction in power loss can be obtained by the use of a special CB paper in which a single sheet of paper is formed with CB on one side and insulating paper on the other.

We studied on the manufacture of wet strength paper by mixing water soluble melamine resin solution to sulphite pulp and Edgeworthia papyrifera sieb stuff.When wet strength Japanese paper is made, wallpaper, filter paper, umbrella paper, bag paper etc whick are difficult to tear in wet stage are produced. Melamine resin solutions were aged as follows

(Research Institute of Oji Paper Co., Ltd., Tokyo) New pulping methods of hard wood have been studied eagerly in Japan, because soft wood has become scarce by overfelling.Characteristics of hard wood pulp depend on the properties of the fiber, that is, short and slender shape and rich content of pentosan.Blending the hard wood pulp in various papers, the printability of the papers are improved and such properties as formation, smoothness, opacities rise.(1) Bleached kraft pulp of hard wood are used in fine paper, and owing to blending, the printability of the paper is improved considerably. But viscous printing ink sometimes takes away the vessels from paper surface during offset printing.(2) Semichemical pulp and chemi-ground pulp are used in news print and photogravure paper.Properties of chemi-ground pulp are similar to ground wood of soft wood, but lower opacity.(3) Ground wood of hard wood has high opacity, and is used in news print.

Extra high OF cables insulated by synthetic paper exclusively made of synthetic polymer were developed. It has been proved that the synthetic paper, given a structure similar to conventional paper, showed more favorable electric and physical characteristics and oil resistance, thus solving problems of extra high OF cables using films for insulation. This improvement is due to a structure having minute pores. This report develops considerations on this point. Trial OF cables with the synthetic paper for insulation were produced and tested on their characteristics; the measured results were satisfactory. Heating tests by loading power were conducted on its model samples. The test results showed that the synthetic paper is superior over the kraft paper as the insulator because of better heat resistance of its component polymers.

The effect of hemicellulose contents in pulp on beating rate and strength of paper made from it was studied.In this study two methods were used, one the adding method (adding isolated hemicellulose to the standard pulp) and the other the extracting method (removing hemicellulose stepwisely).In the former when the hemicellulose is isolated with drastic agents, chemical nature of hemicellulose is liable to change, so that it is impossible to say that the isolated hemicellulose will act in the same manner as it does in the original state. Therefore extracting method was employed in the present research.For the preparation of chlorite holocellulose, thin pieces of beech and aspen wood were treated with hot acidified sodium chlorite. These chlorite holocelluloses were treated with KOH solution under nitrogen gas, in order to minimize the oxidation of cellulose. For hemicellulose extraction, KOH solutions of various concentration (from 0.3 to 20%) were used in order to get a series of pulp in which the hemicellulose content was stepwisely arranged.The beating rate and the sheet strength of this series of pulp were examined. From the result of this study, it was concluded that there appeared to be the optimum hemicellulose content in pulp as for as the paper strength was concerned. Other observations were also made with regard to the result observed.

Coagulations of paper mill wastes were investigated by the use of polyelectrolytes. Nonionic polyacrylamide was the most effective for the purification of wastes. The suspension of pulp fiber was rather dispersed by the addition of anionic polyelectrolytes, such as sodium carboxymethyl cellulose, sodium alginate, and sodium polyacrylate. No remarkable effect of pH was seen for the coagulation of polyelectrolytes. The possibility to using polyelectrolytes for the purification of paper mill wastes was recognized in the case of the wastes suspending large fibrous colloid.

In this paper we reported on the problem of petroleum resin emulsion sizing which was chiefly treated for the application in beater sizing. As the results of application in beater sizing it is obtained that the amount is 0.252% on pulp weight, as compared with rosin size showed slowly sizing effect, and increased paper stiffness.The required amount of aluminum sulphate are sufficient 1%.

Effects of fiber length on mechanical strength, chemical strength, chemical properties and hygroscopic characteristics were investigated. Mechanical strength especially was measured inthe normal condition (R.H. 65%) and dry condition. The dry condition was obtained by the folloNN ing ways ; the paper sample was dried at 105°C for 3hr, and was impregnated with water-free oil.1) Tensile strength for fraction pulp decreases with increasing average fiber length, and in case of the same average fiber length, the tensile strength for whole pulp is higher than that for fraction pulp.2) Folding endurance and tearing resistance for fraction pulp increase with increasing average fiber length. There is a straight-line relationship between the average fiber length and tearing resistance of paper.3) Pentosan content of pulp decreases with increasing average fiber length, but DP of pulp increases.4) Moisture regain, dimensional change, water of monolayer absorption and internal surface area of paper decrease with increasing average fiber length, but crystallinites of paper fiber increase.

Blending of staple fiber of viscose rayon and straw pulp was dispersed in water and handmade paper for calligraphy was made. The Indian ink absorptive quality of straw paper is improved by the blending of viscose rayon fiber. The adhesive capability of straw pulp to rayon fiber in the paper making is so much that it works effective so far as about 50% component of rayon fiber in the stuff without any other adhesive agent. Bearing of fineness of the rayon fiber on the paper making properties was discussed.

Cernik, A. A., and Sayers, M. H. P. (1971). Brit. J. industr. Med., 28, 392-398. Determination of lead in capillary blood using a paper punched disc atomic absorption technique. Application to the supervision of lead workers. The presence of lead in blood is the most incontrovertible evidence of absorption but hitherto the need for venepuncture has limited its determination in the supervision of industrial workers. Micro-methods using atomic absorption spectrophotometry (AAS) have, however, made possible the development of a sufficiently reliable test using a drop of blood obtainable by ear prick for use in the field for screening purposes. A micro-sampling method by AAS is compared with a routine polarographic procedure (POL) using venous blood (corr. coeff. = 0·990). The pipetting of microlitres of blood can be eliminated by spotting the blood onto filter paper, allowing it to dry in air, and then using a punched-out standard disc of dried blood for analysis instead. Correlation of this method (PD) with the micro-sampling technique (AAS) is good (r=0·981). The PD method using capillary blood also correlates acceptably with the micromethod using venous blood (r = 0·913). A pilot field study using capillary blood estimated by the PD technique showed that with this method blood can be collected by ear prick in factories for monitoring workers in the lead industry, thus eliminating the need for routine venepuncture.

The paper deals with mica-loaded kraft paper developed with the aim of applying it to the extra-high-voltage oil-filled (OF) cable and pipe-type OF cable and an outline of an experimental 275-kV OF cable containing mica-loaded kraft paper.

Studies were made on the measuring method of the dust concentration in the gas flow using a dust sampler of a flat paper filter type. The results of these investigation showed the dust concentration can be obtained only by measuring the rate of increase of the pressure drops per unit time on both side of the beds of filter paper, and needless to weigh the sampled dust in each case, but the value of specific resistance of the dust must be obtained beforehand by means of the preliminary experiment. So, the dust concentration C is expressed by the following formula. [numerical formula] where P^*(m) : the rate of increase of the pressure drops per unit time through the filter paper (dP/dt mmAq/min). η : dust collection efficiency of the filter paper (almost 100 %). μ : coefficient of viscosity of the flowing gas (kg s/m2). u : mean velocity of the flowing gas through the filter paper (m/s). α : specific resistance of the dust (m/kg).

A study with filter paper strips partially impregnated with the precipitating agent with or without colloid as the fixing agent reveals that in the case of spotted strips run in aqueous alcoholic mixture as the solvent, uniform bands of the precipitate are formed. In these cases, chromatographic observations such as measurement of ‘S’ and ‘Rf’ values is possible. Rhythmic structures can also be obtained with these strips when the reactant solution is used as the solvent. In the absence of colloids rhythmic structures are obtained at a high concentration and the bands obtained have to be washed and repeatedly dipped in hot water in order to clear the structure of rings present underneath. In the presence of colloid, rhythmic vertical bands are obtained at a much lower concentration and the clear interspaces are visible even without washing. Thus an independent method for obtaining rhythmic structures on filter paper with a technique very similar to chromatography has been developed.

Synthetic Pulp, are fibrillatable and water dispersible and of a shape and size distribution similar to conventional wood pulp.Synthetic pulp can be used with natural cellulose pulps on conventional paper machine without special equipment requirements or handling problems.The synthetic pulp paper is characterized by heat sealability, dimensional stability, high brightness and opacifying ability.On the contrary, the more the ratio of synthetic-blends increases, the more paper strength decreases.The hat body paper and the converting quality test was accomplished by using synthetic pulp made from blends of polypropylene and polyethylene (Gosei-pulp produced by the Nippon Goseikagaku Co.) The most remarkable features of the hat for the summer are flexible and tough and have given excellent elastic recovery.The physical properties of these one ply paper and drycreped paper are shown in Table 1-4 and Fig. 2-4.Synthetic pulp for the summer hat will be used approximately 100 tons from October of 1972 till 1973 in Japan.

The graft polymerization of acrylamide onto filter paper preirradiated in air with electrons from a 200-keV accelerator has been shown to lead to weight increases of up to 210%. The degree of grafting depends on the radiation dose, the moisture content of the paper, and the time interval between irradiation and grafting, but is independent of the radiation dose rate. The degree of grafting increases with the monomer concentration of the reaction medium, and increases as the grafting temperature is reduced. Irradiations in the presence of O2 or N2 and the effect of ferrous ions in the grafting solution indicated that peroxides derived from cellulose do not contribute significantly to the initiation reactions up to 60°C. The results are consistent with the degree of grafting depending primarily on the concentration of trapped radicals present in the paper at the time of copolymerization. The cellulose in the grafted material was degraded and the grafted acrylamide was isolated and its molecular weight measured and compared with a calculated value. The moisture regain characteristics of the grafted material are reported.

A rapid polymerization method for in situ synthesis of polyethylene in a typical paper matrix of cellulose fibers is described. The unique properties of this double matrix, polyethylene in cellulose, are the result of performing the polymerization in a nonsolvent such that simultaneous polymerization and crystallization takes place yielding a nascent morphology. The morphology has been studied by scanning electron microscopy and was found to be different from what is usually obtained for melt crystallized polyolefins. Optical microscopy shows the polyethylene to be present as a complementary matrix with respect to the basic fiber construct. Mechanical, optical, and other properties of encapsulated filter paper have been measured using standard TAPPI tests. The results show a general improvement in physical properties for a range of “add ons” from 0 to 27%. Wet-strength and opacity undergo major changes.

Synthetic pulp for papermaking may be manufactured by beating the fibers of polyvinylalcohol (the PVA) mixed-spun with starch or the fibers of polyolefins mixed-spun with PVA polymer. Various papermaking tests were carried out with this synthetic pulp to obtain the following results. 1) The more the PVA or starch content in the fiber, the more easily can it be fibrillated and the better are the dispersibility and other properties for papermaking. 2) The PVA fibers, if pre-mixed with starch on spinning, can be made into paper by beating without mixing any other material such as wood pulp, wether the fibers have been subjected to only heat treatment or to both the heat treatment and formalization in their manufacturing process. The fibers heat-treated only may also be used as a bonding material. 3) If the beaten PVA fibers, heat-treated, are formalized to eliminate interfiber bonds, then the strength of the paper made will depend on only the tangle of the fibers and it can be estimated at a quarter of the whole strength of the same paper but not formalized. 4) Polyolefins can be converted into another synthetic pulp by means of flash-or mixed-spinning. This pulp can be made into synthetic paper, being mixed with wood pulp.5) Hydrophilic synthetic pulp may be obtained by beating the thicker fibers that are produced by mixed-spinning the three polymers : polypropylene, polyethylene and polyvinylalcohol. Such synthetic pulp can be made into paper either by itself or by mixing wood pulp in any proportion, which will be, if calendered, not inferior at all in strength to the conventional paper of wood pulp

The collection efficiency of Whatman 41 filter paper has been determined using submicron test aerosols of monodispersed polystyrene latex. Measurements were made over a velocity range of 12 to 195 fpm, using aerosols with diameters of 0.088, 0.188, 0.264, 0.365, and 0.557 mu . For sizes less than 0.557 mu , well-developed efficiency minima occur in the velocity range of 20 to 30 fpm. In no case was the efficiency found to be below 70%. At 195 fpm, the efficiency was essentially size-independent. (auth)

The effects of unplasticized and plasticized synthetic resin coating on the bursting strength (BS) of papers were studied.The commercial kraft papers were coated with two kinds of commercial vinyl latices (PVC latex and PVC-polyvinyldene chloride latex) of various cone. under various drying conditions.When the coated papers are dried below the film-forming temp. Tf of latices (M. Fujii and Y. Otsuka ; Chem. of High Polym., Japan, 12, 93 (1955) and see Report I), the BS of the papers are smaller than the BS of untreated paper, but the curing effect is great. Too much plasticizer content decreases the BS, in spite of good film are formed.The authors have discussed the experimental results from the Tf of the latices and the strength of resin mass, and have succeeded to show the important nature of Tf of latices for the paper coating (see Report I, II, III and IV).

The penetration of particles through IPC 1478, Whatman 41, and Type 5G filter papers has been measured by using monodispersed polystyrene latex aerosols at ambient temperature and pressure. The aerosols were 0.264, 0.365, 0.557, 0.796, and 1.099 microns in diameter and consisted of more than 85% single particles. Initial electronic charge on the test aerosols was reduced with a radiation source to an average elemental electronic charge per particle of 0 to 3. Penetration was measured through filters at air velocities from 0.1 to 100 cm/sec. Well-defined velocities for maximum penetration for each particle size were found for the three filter papers. Particle sizes for maximum penetration were also found for IPC 1478 and Type 5G papers as a function of air velocity.

Filter mats for filtersticks, filter tubes, andGooch crucibles are easily prepared with the use of filter papers made of glass fibers or fibers of vitreous silica. The reliability of such filter mats for the purpose of quantitative micro analysis has been tested with silica fiber paper which is somewhat more difficult to use, but permits high ignition temperatures.

A special insulating paper, developed for use in EHV power cable, is described. Generally speaking, where the insulating paper is made of the same pulp, the thinner the paper, the higher the impulse breakdown strength, and the lower the power factor. In view of this fact, a special insulating paper (combination paper), with a high-impulse breakdown strength, low power factor, and great mechanical strength has been developed by making thin insulating paper and cementing a plurality of sheets together with a suitable adhesive. 275-kV, 1 ×1200 mm2 oil-filled cable and 275-kV, 3 ×1400 mm2 pipe-type oil-filled cable using this combination insulating paper have been proved to possess excellent properties, such as shown in Table IV and Fig. 10, respectively, and the special characteristics of the insulating paper are fully displayed in the finished cable. The motive for the development of the combination paper, its theoretical background, and the properties of the insulating paper and of the cable using that insulating paper are reported.

Sizing is achieved by adding Petroleum Resin first to the pulp in beater and then, when it is well mixed with about 20% of precipitated calcium carbonate in the pulp, aluminium sulphate (“ alum ”). It will be observed the perfect of sizing on the tissue paper, or the test result of K.B.B Sizing test by sugar solution is indicated about 50 seconds, Stockigt method was 5 seconds. (40g/m2) Influences affected by the fluorescent whitening agent to the sizing effect were investigated.

Electron microscopic studies were carried out with regard to the effects of the filling, the internal sizing and the surface sizing on the surface fine structures of uncoated papers. Results were summerized as follows : (1) Direct carbon reprica technique was found to be available especially for observing filler distribution on uocoated paper surfaces. (2) By observing commercial uncoated paper surfaces by the transmission and scanning electron microscopy, it was found that the wire side showed a greater filler loss than the top side. (3) The two sideness of filler retention was found to depend on the methods of sheet formation. In hand made sheet, the wire side had higher filler retention than the top side. On the paper made by the miniature fourdrinier paper machine, the two sideness of filler retention was almost eliminated. On the paper made by the commercial fourdrinier paper machine, the filler retention of the wire side was conspicuously lower than the top side. (4) Two sideness of the filler retention of commercial papers was found to be increased as the filler content increased. (5) In the surface sizing, surface of the fibers were found to be covered with an amorphous film of a sizing agent in proportion to the degree of sizing.

Recently the fibers other than wood fibers have come to utilize as the paper making raw material worldly.The non-wood fiber resources for pulping is considered as useable economically for industrialization.In this report, several vegetable fibers are studied except the wood fibers as the natural resourees for pepar making pulp.

The frequency of occurrence of defects in electrical insulation can be shown to follow the Poisson law of probability. One of the more important defects in thin paper insulation is conducting particles. In this paper expressions are derived for the probable breakdown voltage as a function of conducting particle occurrence. It is shown by statistical evidence that large conducting particles exist in the insulating paper and bridge one or more layers of paper in the finished capacitor through chance reorientation caused by manufacturing processes and operation. The degree and frequency of reorientation of particles with a typical grade of paper is determined experimentally, and the probable insulation thickness and consequent voltage strength of various size capacitors is calculated. A method of determining the optimum voltage strength of this insulation is illustrated. It is concluded that conducting particles are a predominant factor in determining the voltage strength of present day capacitors and that one of the greatest opportunities for improvement lies in the reduction of the conducting particle content in the paper.

This paper describes the characteristics and properties of a new insulation system currently used to manufacture high-voltage bushings at voltage ratings of 15 through 69 kV for transformers and switchgear apparatus. The system is compared with other forms of insulation such as phenolic-paper, oil-paper, mineral-filled epoxy, and electrical porcelain. Its application in high-voltage condenser bushings is also discussed. With this new insulation, epoxy resin is used to totally impregnate an electrical grade of kraft paper resulting in a resin-rich (approximately 70 percent) material having unusual properties. Its predominant characteristic is the complete absence of voids resulting in high-corona-inception voltages and high-dielectric strength. It also has excellent physical properties which, coupled with a flexible manufacturing process. open up numerous new design possibilities in high-voltage engineering.

Poly (vinyl acetate) emulsion was incorporated to paper by (1) beater addition and (2) saturation. The addition of (poly vinyl acetate) solution to paper was also accomplished by (3) saturation. Measurements of percentage resin retentions of the modified sheets (gms. of resin retained per 100 gms pulp) obtained from the pulps of various degrees of beating by three different procedures (1, 2, 3) were made efficiently. The surface structures of the untreated as well as various PVAc resin treated sheets were examined by optical and electron microscopes. The effect of beating on the fibres and the sheets was studied. The differences in the surface structures of the modified sheets owing to the difference in the method of resin treatment and the quantity of resin retained to the sheets and the mechanism of polymer deposition were discussed. In the case of both emulsion and solution saturation it was found that the percentage of resin retention was decreased with the increase in the degree of beating but increased with the increase in the solid, content in the emulsion and solution respectively. On the other hand the beater added sheets showed an increase in the percentage of retention both with the increase in the degree of beating as well as the resin-pulp ratio The percentage of resin pick up (gms. of resin picked up per 100 gms of resin used) by the beater added sheets was found to increase remarkably with the increase in the degree of beating and showed a considerable increment with the increase in the resin-pulp ratio particularly those from the beaten pulp. The measurement of percentage of pick up gave some information to the study of the mechanism of polymer deposition on fibre by beater addition procedure.

Effects of mono-valent cations on dielectric properties of oil-impregnated paper were studied by the same method as that of un-impregnated paper.(1) In the range of this work, effects of mono-valent cations on the dielectric loss at low temperature (about 20°C) is not observed.(2) It is obvious that the order of cations which influences badly on the dielectric properties of oil-impregnated paper is same as that of un-impregnated paper. The order is as follows;(3) In order to compare the dielectric loss of oil-impregnated paper with that of un-impregnated paper, a value of tan δt/tanδu is obtained. Those values of the paper treated with NH4-salts are by far larger than those of the paper treated with other three electrolytes.

Direct exposure to the sun-light for 100200 hrs causes Japanese-paper to turn yellow, and also causes unbleached paper to increase in whiteness.This is considered to be caused by oxidation of fibrins or impurities. We can find this by the fact that copper value will he fairly increased.

The relationship between physical properties of paper, especially stiffness and/ or rigidity, and printabiltiy was investigated.The samples studied were 32 fine papers which were manufactured on a midget Fourdrinier paper machine according to the experimental design previously planned, including several factors which were considered to affect the physical properties of paper.The printing experiments were carried out on a M-3 type laboratory printing press, using four plates comprising a solid and half-tones.As the first step of this study, a numerical expression of printability was investigated. Result was obtained that reproducibility which was tentatively designated to the value obtaining from the following equation had highly significant correlationship to the printability (order, ranked by a functional examination).Reproducibility=WPG/WOG (1-α/100) WPG : Brightness of printed surfaceWOG : Brightness of original paperBoth measured by the Hunter Multi-PurposeReflectmeter, using green filter.χ : Area of half-tones of used plateAt the second step, inquiries were carried out into the correlationship between printability and physical properties of paper including stiffness and/or rigidity, smoothness, compressibility, oil absorbency etc. In this case, reproducibility was used as a printability value.Further, relations between reproducibility, coefficient of ink transfer and printed opacity and printing conditions were analysed.Furthermore, the correlations in some combinations among five physical properties comprising Youngs' modulus, compressibility and stiffness of three types, such as Clark (softness, rigidity and stiffness), Olsen and Gurley, were made clear.Following conclusions were obtained.1. In the scope of these experiments, there was no correlation between stiffness of paper and printability.2. Other physical properties which correlated to printability were only the properties indicating smoothness of paper.3. Reproducibility related merely to the properties of ink used, i.e., tack and film thickness on the plate.4. Although coefficient of ink transfer have been affected by the type and tack of ink, film thickness and printing speed, printed opacity referred not to printing speed. Further, it was made clear that in these two properties there was a reverse tendency in each other.5. In five physical properties of paper concerning stiffness or the like, it was indicated that highly significant correlations have been found in seven combinations, for example, in the case of Gurley stiffness vs. Clark stiffness plot, 0.9065 was obtained as the correlation coefficient, Olsen stiffness vs. compressibility, -0.7283.

At first, a study has made of the effect of moisture content on the electrical resistance of the sample, but it has been found that the electrical resistance was effected not only by the variations in the fiber furnish, but the electrical resistance of the stock, from which the sample was made of.Next, a study has made on the methods of measuring the dielectric constant of the sample. We used two condencers. One of them was a paper-condencer. which is made of the sample inserted between two plates. The other was a air-condencer, which is made of two plates, and the distance of them was a function of the sample thickness.When we compare with these two condencers by the cross coil meter, we get the dielectric constant of the sample, which has no relation with the thickness variation of the sample.Measurements were made to ditermine the effect on the dielectric constant-moisturecharacteristic of variations in fiber furnish, thickness, density, etc. It was found that. the effect of these variations needs calibration curve for each sheet.The accuracy of this meter is 0.1% when we use a caribration curve which based on the bulk of the sheet.

A new procedure for the analysis of air-borne lead, based on chromatography, is described. Samples collected on filter paper tape are treated with hydrochloric acid-butanol reagent to prepare the chromatogram. Spraying with a dithizone reagent develops the color. The system is applicable to other metals.

The repeated-impulse testing like the drop testing was discussed in these studies.The principle of the repeated-impulse testing was that a weight was dropped from a constant height and the energy of it was given the tested paper repeatedly.The relation between the repeated-impulse testing and the mechanical properties of paper was also discussed.The materials tested in these studies were kraft paper and high stretchable paper.The results were as follows.(1) The machine direction of kraft paper was brittle, but it was not fatigued soon or immediately.(2) The toughness of virgin paper was related to the results of the repeated-impulse testing in most cases.(3) However, for evaluation of the service strength of bag paper, it was not sufficient that only the toughnes was measured.It should be necessary that the decrease rate of toughness during the repeated-impulse testing must he measured additionally.

Pressure pulses of 8.2 × 107 dyn cm-2, each lasting for about 0.01 sec, were applied to paper, and the scattered light from it was measured simultaneously in order to study the response of pores in paper under dynamic conditions. During the compression phase the deformation in pore surface, i.e. the loss in fibre-air interface, is found to be linearly related to the square root of pressure, and the minimum pressure required to compress a paper to the non-porous state is estimated to be around 5 × 108 dyn cm-2, depending on the type of paper. The decompression curve, however, always follows a different path; thus, a cycle of compression and decompression shows large hysteresis. An approximate calculation is made of the energy loss per cycle, and this shows the associated temperature rise to be less than 1 degc. The delayed recovery from compression is large compared with the elastic recovery, but the permanent set is very small. Both the resistance of pores to compression and the energy loss per unit volume seem to be related to the paper density.

In order to clarify the vacuum drying and impregnation process of lapped insulation paper layer, permeability of i) cylindrical model insulation layers made of lapped paper tapes, and of ii) piled annular paper sheets along their inter-surfaces, is measured. The results are ; (1) Permeability of measured insulation layer per 1 tape, is 23 times larger than that of the original paper sheet, owing to flow passing the inter-surface and gaps between tapes. So it also increases by drying due to shrinkage of paper thickness.(2) Permeability of the inter-surface of measured annular sheets per 1cm × 1 cm is comparable with that of the paper sheet itself per 1 cm2, but widely changes with pressing stress. (3) Permeability of paper lapped layer can be calculated from permeability of the sheets and of the inter-surface.(4) These informations are useful in analyzing a drying or impregnation process of paper insulation layer.

About 2 years ago a series of researches was started to study the causes of dielectric loss, chemical deterioration, and electrical failure of oil impregnated paper insulation. Miniature technique has been developed so that at moderate cost specimens can be assembled in glass under accurately controlled conditions, subjected to high voltage life tests, tested periodically for electrical properties and finally examined minutely for changes in electrical, physical, and chemical properties. The results obtained in the first part of this program are presented herewith. Hypotheses now held regarding the effects of variations in several different factors on the life of oil impregnated paper insulation are discussed, and a description of the techniques developed for preparing and testing specimens is given. Illustrative examples are given of the results obtained to date from the correlation of life tests with microscopic physical and chemical examination.