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Actual defects, as well as areas of low resistance to the penetration of moisture, can be detected on coated insulating materials; and the spreading of these areas can be recorded by a modification of the electrographic printing method.
During the dissection of cable from an experimental installation of 120-kv, high-pressure, gas-filled cable, “dry” spots of an unfamiliar appearance were noted in the individual tapes of the oil-impregnated paper insulation. These “dry” spots were generally of small diameter and appeared in clusters, in the aggregate giving the paper surface a “peppered” appearance. When viewed by reflected light,...
Standard methods of locating faults in insulated cables are very well-known, particularly the use of the loop tests, Murray Loop and Varley Loop, etc., also comparative capacity tests for opens and comparative inductance tests for shorts. The above methods are very common, and wherever the faulty cable is paralleled by a good cable, such methods are the most accurate where tests are made from the...
Some time ago a survey of the electric power companies showed that the dielectric strength measurement was the one test most relied upon to determine whether insulating oils were satisfactory for initial service and for continued service in both oil cooled electric equipment and electric switch gear. Its popularity as a service test is probably due in part to being simple to perform and in part to...
Three of the alkali halides (LiF, NaCl and KBr) have been used' as integrating crystal detectors for X and cathode rays with energies up to 3 million volts. The dosage measurements were based on the photoelectric and optical absorption characteristics of crystals colored by X-ray and cathode ray bombardment. Doses ranging from 20 to 105 roentgens were measured photoelectrically with the crystal arrangement...
The electrical conductivity of silicate glasses has been examined very thoroughly by many workers and is fairly well understood, Low temperature conductivity is the result of monovalent cations, Na+, and in some instances H+ migrating through an otherwise rigid framework of SiO4 tetrahedra.
The dielectric constants of pure samples of four normal long-chain bromides and four normal long-chain alcohols were measured as a function of temperature at 0.25, 0.5,5.0, 50 and, in one case, at 525 kc. to obtain information on the relationship between the molecular structure of solids and their dielectric properties. Long-chain molecules present the interesting possibility of rotation about the...
The present method employs the very commonplace phenomenon of timing a parallel combination of inductance and capacitance to resonance. In Fig. 1 a constant voltage E is applied to the L C tuning circuit and C is varied until the current I is a minimum. This residual current is a measure of the total loss of the tank circuit. This loss may be indicated by a figure in mhos conductance, that is the...
The cell, shown in Fig. 1, consists primarily of two quartz tubes, upon which are fastened metal electrodes. One quartz tube is mounted on a movable carriage rolling on invar rods which serve as ways. The other tube is rigidly mounted on the bed. A large metal cylinder encloses the electrodes, forming a resonant cavity, which may be modified for use at lower frequencies by switching in one of a series...
Power factor measurements by resonant circuit techniques are limited by losses in the resonant circuit. Essentially the methods in use measure the loss, or Q of the circuit under the two conditions: (a) dielectric sample in the circuit and (b) sample out. Sample losses are obtained by the difference of the two measurements, and in the case of polystyrene and similar low loss dielectrics at radio frequencies...
When capacitor paper is subjected to electrical stress, large variations in durability are noted from lot to lot. These variations cannot, except in rare cases, be correlated with the usual chemical and physical tests made on such paper. We have indications that the variable characteristics of most significance in regard to durability are probably physical and structural in nature. The mercury electrode...
To meet its own needs and those of other Government agencies, and to fulfill its normal function of providing standards, the National Bureau of Standards is in the process of obtaining facilities for making precision dielectric measurements in the 10 kc to 300 Mc frequency range. The work described in this paper is that of the High-Frequency Standards Section of the Bureau's Central Radio Propagation...
In industrial high frequency dielectric heating, heating cycles involving rates of temperature increase up to three hundred or four hundred degrees (F) per minute are common. It is important to know the values of the dielectric properties of the substance heated over the whole range of the heating cycle. Conventional methods of measurement, such as ASTM shunted susceptance, are not available as they...
The transmission of electrical impuleses from a pick-up device to an amplifier is usually accomplished through a microphone cable, which has metallic braid shielding to eliminate spurious impulses. While this has been satisfactory in short lengths, the use of longer lengths has shown that pick-up of mechanical vibration or shock introduces serious problems where faithful transmission of the desired...
The dielectric constant of certain polar wax-like capacitor impregnants can be significantly increased in the solid state by melting these materials and then allowing them to solidify in an electric field® The field must be maintained until the wax has solidified completely. This increase is permanent so far as is now known provided the wax is not remelted, If the wax is again melted and allowed to...
Dielectrics having compositions in the system 3CaO:TiO2-BaTiO3-TiO2 were matured (less than 0.1 percent absorption) at 1260° to 1500°C. Data are given for the compositions, heat treatments, absorption, shrinkage, and for K, the dielectric constant, and Q, the reciprocal of the power factor at 25°C and frequencies of 50, 1000, and 20,000 kc/s, and at 3,000 mc/s when K is not greater than 50. Values...
The purpose of this study was to obtain information on the initial ionization in a hydrocarbon by electronic bombardment. Paraffin wax, because of its low d-c conductivity, was chosen. A thin layer of paraffin wax, prepared in a stainless steel cell, was subjected to a d-c voltage until the charging current disappeared. A radioactive source was then placed on top of the sample without disturbing the...
It is well known in the case of ferromagnetic metals that permeability falls with increasing frequency because the domains begin to lag in their orientation. Above this range of the Barkhausen noise a further steep decrease takes place between about 108 and 1010 cycles/sec. until the permeability is practically reduced to that of free space. The cause for this second decline has been sought in eddy...
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