Maintenance-free supply transformer 20 kV. Toroidal transformer for low and high voltage supply. High voltage toroidal transformers. High voltage transformer for space telescope. Surge voltage proof high voltage isolating transformer. High voltage transformer 30 kV. High potential isolating transformer up to 80 kV potential difference. High voltage isolating transformers, potted under vacuum, up to 3 kV, separation up to 35 kVDC. High potential isolating transformer, customer solution.
Three-phase high potential isolating transformer up to kV separation. This primary winding can be of either a single flat turn, a coil of heavy-duty wire wrapped around the core or just a conductor or bus bar placed through a central hole.
Get Started for Free Download App. Answer Detailed Solution Below Option 1 : positive when the secondary winding voltage reversed leads the primary winding voltage. Phase angle error: The error between the secondary terminal voltage which is exactly in phase opposition with the primary terminal voltage.
It will be positive when the secondary winding voltage reversed leads the primary winding voltage. It will be negative when the secondary winding voltage reversed lags the primary winding voltage. The ratio error is important when measurements of voltage are to be made and the phase angle error is important while measurement of power.
This error depends upon the resistance, reactance of the winding and no-load current of the transformer. Potential Transformer MCQ Question 5: Resistance potential divider generally not used in voltage controlled circuits due to, Non-linearity with variation Lack of insulation Distortion in waveform High power losses Low sensitiviy.
Concept: A voltage divider also known as a potential divider is a passive linear circuit that produces an output voltage V out that is a fraction of its input voltage V in. The output voltage can be found by using voltage division rule.
Potential Transformer MCQ Question 7: In the case of a potential transformer PT , the phase angle error is positive when the secondary winding voltage reversed leads the primary winding voltage negative when the secondary winding voltage reversed leads the primary winding voltage always positive always negative.
Induction Regulator: The induction regulator is a special type of potential transformer with primary winding mounted on a cylindrical core that may be turned on its axis. The inner member 54, however, has no opening or folded ends. The inner and outer members 54 and 50, respectively, are concentrically located and held in place by spacing members 56 and 58, which may be corrugated pressboard strips fastened to said inner and outer members by cementing, or other suitable means.
Spacing members 6t and 52 are similar to spacing members 56 and 58, except members 69 and 62 are short pieces or strips so that dielectric fluid may flow freely along the length of the static shield 42B. Rounding means 64 and 66, located on both ends of the tubular assembly, partially between the inner and outer tubular members 54 and 5t respectively, may be formed of materials such as rope or metal tubing. If metal tubing is used it may function as the sensing por tion of a capillary thermometer mounted on top of bushing 32, thus allowing the high voltage coil temperature to be monitored visually.
The static shield 42B is completed by disposing a shielding member around the entire static ring assembly. More specifically, a conducting or semiconducting tape is so disposed as to cover the entire assembly, inside as well as out. In particular, the shielding member 7 0 covers the rounded ends of the static ring formed by members 64 and The shielding member portion 76b of static ring 42B is formed by tightly winding a flexible conducting material having a layer of electrically insulating material secured thereto, such as; crepe paper backedmetallic foil in the form of tape, around and through the static shield 42B.
The circumferential ends of the lower portion of the inner shield 42 are preferably overlapped, but with a gap which is filled with solid insulation 40 to prevent a short circuited turn around the magnetic core Referring again to FIGS. The upper and lower portions 42A and , respectively, of the inner shielding member 42 are electrically connected to one another to form a continuous conducting path throughout the shielding member 42 which will limit the potential difference between the different portions thereof to a negligible value so that there is no interruption in the shielding effect between the upper and lower portions of the shielding member The upper end of the inner shielding member 42 is electrically connected to the terminal 21 by the flexible conducting lead 80 in order that the shielding member 42 provides a substantially equipotential surface around the high voltage winding 12 and high voltage lead 22, which is at substantially the same potential as the outermost layer of the high voltage winding 12, to thereby sub stantially eliminate any potential stress to which any fluid dielectric inside said shielding member is subjected.
It should be noted that the fluid dielectric uses the upper and lower portions of the inner shield 42 as ducts or channels. Fluid flow is accomplished by the counterfiow method, wherein heated fluid rises up through the insulating member 31 and cooler fluid flows down said insulating member. It is to be understood that although a separate lead 22 is shown connected from the high volt-age coil 12 to terminal 21, the high voltage coil 12 could just as effectively be connected to the metallic portion of the inner shield at the lower end of insulating member Then, the only connection to terminal 21 would be a flexible lead fill from the metallic shield at the upper end of insulating member 30 to terminal The shield around insulating member 30 may effectively be utilized as the high voltage lead because of the small currents involved.
The outer shielding member 90 is formed by winding around and through the central opening of the high voltage winding 12 a flexible conducting material having a layer of insulation secured thereto for mechanical purposes, after the solid insulation 40 has been assembled around the high voltage winding 12 and by winding the same type of flexible sheet material snugly and tightly around the outer surface of a solid insulation after the latter insulation has been assembled around the lead The outer shield 90 may be formed of materials such as aluminum foil backed crepe paper or carbon backed crepe paper.
When carbon backed crepe paper is used, its higher resistivity makes it possible to allow the shield to form a complete circuit around the core leg that carries the high and low voltage coils 12 and When metal backed crepe paper is used, it is necessary to include a gap in the shielding, in order to prevent a short circuited turn around the magnetic core Carbon backed crepe paper has other advantages over metal backed crepe paper, in that wrinkles and sharp edges are not as detrimetal when using carbon backed paper as opposed to metallic type shields.
Also, the higher resistance of carbon has a potential grading effect because the displacement current due to stress concentration causes a voltage drop along the semiconducting layer. This phenomenon is well known and utilized in condenser bushings and windings of high voltage generators. It is also known that due to so called surface activity, an insulation with a semiconducting electrode, such as carbon, in the highest stressed boundary has higher dielectric strength than a system with metallic electrodes only.
The outer shielding member forms a continuous conducting surface or electrode having a cylindrical configuration around the high voltage winding 12 and a generally hollow cylindrical shape around the lower portion of lead The outer shielding member 90 is maintained at ground or zero potential by electrically connecting said shielding member by a flexible conducting lead as indicated at 94 in FIG. The outer shilding member 90 is disposed in substantially concentric relation with the inner shielding member 42, and similar to the latter shielding member, the outer shielding member 90 forms a continuous, substantially equipotential surface around the outer surface of the solid insulation 40 and the outer surface of the lower portion of the solid insulation The flexible shielding material from which the outer shielding member 98 is formed permits said shielding member to closely follow the contour or outer surface of the solid insulation 40 and prevents the occurrence or voids or pockets which would otherwise be filled with the associated fluid dielec trio and which would be subject to possible insulation failure or breakdown.
In order to reduce the radial stresses on the static shield 42B and the high voltage coil 12, and produce a favorable voltage distribution longitudinally along the bushing 32, an intermediate shielding member 20, having upper and lower portions 20A and , respectively, is disposed to substantially surround the high voltage winding 12 and the lower portion of the lead In addition to surrounding the high voltage coil 12, the intermediate shield 24 interposes the high voltage coil 12, dividing said high voltage coil into two portions or sections, 12A and It is to be noted that the outer surface of the lower portion of intermediate shield 20 is embedded in the solid insulation The inner surface of said lower portion of intermediate shielding member 26 interposes and separates the high voltage winding 12 into inner and outer portions designed as 12B and 12A, respectively.
The upper portion 20A of intermediate shielding member 20 is embedded in the solid insulation which surrounds lead The upper and lower portions 20A and 21B of the intermediate shielding member 20 may be formed in a manner similar to the outer shielding member 90, as previously described, by winding a flexible conducting or semiconducting material having a layer of insulation secured thereto, such as crepe paper with metallic foil or carbon attached to it, in the form of a tape or sheet, around and innterposing the high voltage winding 12, after approximately half the solid insulation 40 has been assembled around the high voltage winding and around the lower portion of the lead 22 after approximately half the solid insulation has been assembled around said lead.
The intermediate shielding member includes a gap if a metallic shield is used in order to prevent a short circuited turn around the magnetic core As previously explained, no gap is necessary if a semiconducting shield, such as carbon, is used. The upper and lower portions and 26B, respectively, of the intermediate shielding member 20 are electrically connected with one another or former from the same flexible conducting material to provide a continuous, substantially equipotential surface around the high voltage winding 12 and the lower portion of lead Similar to the outer shielding member 2 0, the intermediate shielding member 2f forms a generally cylindrical electrode surface around the high voltage winding 12 and also a generally cylindrical electrode surface around the lower portion of lead 22 in substantially concentric or parallel relation with the inner shielding member 42 and the outer shielding member The intermediate shielding member interposes the high v oltage coil 12 at some intermediate point, dividing said high voltage coil into portions 12A and The potential of the intermediate shielding member 2t is fixed to a suitable value by connecting said intermediate shielding member to that point in the high voltage coil 12 having the desired inductively fixed alternating potential.
The potential of the intermediate shield is fixed to a value between the potential applied to the transformer primary terminal 26 and ground or zero potential, with the value usually being between 34 and 70 percent of the applied potential. Locating the intermediate shield 20 in this manner, interposing and dividing the high voltage coil 12 into two portions 12A and 12B, reduces appreciably the maximum voltage gradients on the static shield 42B by moving the intermediate shielding member 20 radially away from the location where the corresponding equipotential surface would be located in the absence of said intermediate shield.
By reducing the critical voltage gradients on the static shield , the intermediate shielding member 28 makes possible a marked reduction in major insulation and improves the corona characteristics of the transformer ill. Also, the reduction in insulation makes heat transfer less of a problem and more efficient cooling is obtained, even when using a smaller volume of fiuid dielectric.
A further advantage of the intermediate shielding member 20, as will be explained in greater detail hereinafter, is the more favorable voltage distribution obtained longitudinally along the bushing This more linear voltage distribution along the bushing 32 also contributes to a reduction in the amount of fluid dielectric and major insulation required.
While the easiest manner of fixing the voltage of the intermediate shield 20 to the desired value is to actually make a physical connection from the appropriate portion of the high voltage coil 12 to the intermediate shielding member Zil, it will be appreciated that the desired potential at the intermediate shielding member 20 could also be obtained without any physical connections.
The desired potential at the intermediate shielding member 20 could be obtained by proper arrangement of the shielding members 2 6, 42 and lit with respect to each other and with respect to the grounded portions of transformer ill. Once current is flowing through a transformer, the voltage distribution is determined inductively or by magnetic coupling and may be designed to be substantially uniform.
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