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The physical parameters of the guard gap between the guard and the guarded electrodes of the three electrode system generally used for dielectric loss measurements can be modelled by a simple T-network. Theoretical analysis shows that under certain conditions these parameters can cause great errors or even make the apparent dissipation factor negative, when measured with a Schering bridge. The sharp...
The flashover in a non-uniform field air gap is influenced by the presence of an insulating screen in the gap. In the presence of a solid insulating barrier, the flashover voltage of a point-plate gap is substantially raised. The paper examines the influence of the position of a barrier on the flashover voltage of point-plate gap. Measurement was made using positive and negative d.c. and 60 Hz alternating...
The temperature index of micaceous insulation is influenced by that of the bonding resin used therein, the thermal degradation processes being synonimous. Systems using epoxy novolac and cycloaliphatic offer rigid insulation and pose discharge problems.; Their temperature index has been improved by adopting better backing materials. However, epoxies become brittle during ageing at 210/230°C because...
When not detected visually, the iron damage can be identified by performing a "loop test" when the unit is scheduled for rewinding. However, in most of the cases the decision to restack the core is taken after the rotor is out, thus usually extending the duration of the outage. We, at Hydro-Quebec, are interested in finding a method enabling us to assess the state of the iron prior to removal...
In a previous paper, a model pole was described. The method of determining the Arrhenius Equation for this model was detailed. The equation was given for two different pole insulation systems. The maximum accumulated running time for a standby diesel-generator in nuclear service amounts to 8768 hours at a design hot spot of 130°C. Proof of qualified life requires the model to withstand an earthquake...
Electrical termination is a critical issue in a large-scale accelerated-testing program with model extruded cables because economic forces dictate that the termination be low in cost and easily assembled. The termination must also be at least equal to the cable insulation in resisting the high stresses of accelerated testing. Achieving this result is difficult since the testing program included the...
This paper describes the results of an investigation designed to evaluate the long-term compatibility of tracer gases with HPOF cable insulation in view of selecting one or several gases for the detection of leaks in underground cable networks. Accelerated aging was done on cable models with He, CF4, SF6, c-C4F8 and N2 gases dissolved in the oil. The aging was performed at 120°C with a voltage stress...
Sections of EPR and XLPE insulated electric power cables were oven aged at 175°C for a period of eight weeks. After 2, 4 and 8 weeks of aging, pieces of each cable were removed and samples were prepared for measurements of D.C. resistivity, dielectric constant, dielectric loss and A.C. breakdown strength. In each measurement, ASTM procedures, respectively D257, D150 and D149, were followed. All measurements...
Bond strength is one of the most important properties of an impregnating material. This property can be measured by a number of test methods. The main question needing to be answered is which method provides the most accurate values in the most reasonable amount of test time. This paper is a reevaluation of three methods which have moved into the foreground as being the best methods for testing this...
Towards 1840, R. Davidson built a small car driven by an electromotor (Figure 1). Only three years later a six tons vehicle built by him reached a velocity of four miles per hour. The batteries allowed to cover a distance of 1½ miles.
Growth in the application of the Vacuum Pressure Impregnation treatment of form wound motors has stimulated extensive research in the development of tapes receptive to such processing. Criteria which must be achieved in the design of these unique mica based tapes include low binder content, compatibility with the wide variety of industrially available impregnants, exhibiting good electrical properties,...
During the 1981 E/EIC Conference, Suflex introduced a new product, namely, Acryflex VPI sleeving, which could be used by manufacturers of motors as well as motor re-builders as an alternative to the commonly used manually assembled multiple wall ("telescoped") sleeving combinations for form-wound coil lead insulation. This paper will serve to report the results of further testing which has...
Insulation material suppliers are witnessing a rapid growth of interest for both repair and manufacture of high voltage (>6900) rotating apparatus. Although these machines have been produced for several years the new interest is growing for several reasons, among them: 1. High voltage machines have now been operating long enough to begin needing repair and overhaul. 2. Rewind upgrading of earlier...
Solvent varnishes have been used on electrical equipment with excellent results for many years. They combine low cost, easy handling and excellent electrical and thermal aging properties. The growth of regulatory institutions during the first half of the 1970's and legislation concerning the toxicity and safety of organic solvents led manufacturers to search for alternate materials. Two systems, quite...
The use of highly filled, thixotropic, single-component, solventless, Bisphenol A/Lewis Acid cured epoxy resin is one of the most desirable compounds for use as the bonding and insulating resin system for wet winding rotating field coils and generator coils. There are five properties that are of prime importance in this type of resin system.
Catalyzed storage stability tests have been carried out with a series of vacuum pressure impregnation epoxy-anhydride solventless impregnants. The changes in viscosity with storage time were recorded for several of these resins. Replenishment storage tests, in which a 20% addition of fresh material was added every two weeks, were also carried out. The data obtained indicate that under the most severe...
Resin bonded glass yarn banding tapes are wound around the surface of the ends of the slot section of heavy duty direct current motor armatures to function mechanically as restraining bands. They secure the armature from the effects of the large centrifugal forces which the rotation of the armatures of large D.C. equipment such as traction motors produces.
PPMM® Pelletized Polyester Molding Material is a breakthrough in plastics materials technology. This paper describes the properties and end-use applications of a series of new generation free flowing, solid, pelletized, glass fiber reinforced, highly reactive thermoset polyester molding materials. The PPMM molding material is a highly filled, multi-resin composition that combines the most desirable...
Wire taping as means of applying insulation to conductors has been around for many years; however, a great deal of this process is still art. The objectives of this paper are to survey the wire wrapping process in detail and attempt to reduce some wire taping art to a science. A mathematical model of the process will be presented which can be utilized to determine head speeds, taping angles, and optimum...
Almost without exception, magnet wire is wound into coils for its actual application. Magnet wire, therefore, might be better called winding wire and its windability or softness is an important factor in the efficient production of high quality coils of all types used in motors and various kinds of apparatus. On the other hand, once the coil is in place, after having been suitably treated, for instance...
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