RU2050610C1 - High-voltage current transformer - Google Patents

Abstract

FIELD: electrical engineering. SUBSTANCE: current transformer has case filled with insulating medium (sulfur hexafluoride or transformer oil). Case accommodates primary winding in the form of straight conductor and set of multiturn secondary windings embraced by toroidal electrostatic screen. Secondary-windings-and-screen assembly is placed on cylindrical insulating frame coaxial with primary winding conductor. Radial insulating spacers are installed between primary winding conductor and frame at its end, beyond maximum field strength area which is concentrated between secondary winding screen and primary winding conductor. EFFECT: improved reliability of transformer, reduced labour consumption for its assembly. 5 cl, 5 dwg

Description

 The invention relates to electrical engineering, in particular to the design of a measuring current transformer of high and ultra-high voltage with insulating filling.

 Known high-voltage outdoor current transformer [1] containing the primary winding in the form of a rectilinear conductor (rod or pipe), a multi-turn secondary winding wound on a toroidal magnetic circuit located on the primary winding and isolated from it by capacitor isolation, part of which is superimposed on the primary winding, and a part for the secondary winding with a magnetic circuit, a metal tank in which the windings are mounted, mounted on a support insulating column, the conclusions of the primary winding with porcelain passages GOVERNMENTAL insulators containing similar capacitor insulation and secured to the tank, and outputs a secondary winding extending in the insulating column. The transformer tank and insulating column are filled with oil or other insulating filler.

 The use of capacitor isolation between the primary and secondary windings of a transformer leads to the low reliability of the known transformer, since the insulation operates in a difficult thermal regime, heat removal from current-carrying parts and the magnetic circuit through it is difficult, which leads to frequent thermal breakdowns. In addition, foil lining between the layers of insulating material is difficult to perform without burrs and irregularities, which leads to the appearance of a local concentration of electric field strength and the appearance of partial discharges (PD) in such insulation and its breakdown. A disadvantage of the known transformer is also its large dimensions due to the significant axial dimensions of the high-voltage bushings of the primary winding, located in porcelain bushings, the size of which is determined by the need to provide the required electrical strength relative to the tank, which is under the potential, depending on the creepage distance along the surface of the porcelain bushings .

 Also known is a high-voltage outdoor current transformer [2] comprising a metal casing mounted on an insulating support column and filled with an insulating medium, in which the primary winding is in the form of a rectilinear conductor, the secondary windings on the toroidal magnetic circuits covered by a toroidal electrostatic screen, and the secondary winding distance system with a screen relative to the primary winding and the housing of insulating elements.

In such a transformer the secondary winding of the screen distanced about the primary winding and the housing by means of three insulating sleeves arranged in the radial direction along the outer perimeter of the toroidal an electrostatic shield at an angle ^120, which are mounted on the one hand to the cylindrical wall of the housing and on the other to the yoke, built into the secondary windings with a screen mounted on the same clamps. This design of a high-voltage current transformer eliminates the use of capacitor isolation between the windings, and thereby reduces the axial dimensions of the transformer along the high-voltage bushings of the primary winding, overall overall dimensions, improve heat transfer conditions, eliminate thermal breakdowns and the occurrence of PD due to poor-quality capacitor plates.

 However, the reliability of this current transformer is insufficient, and its design is difficult to manufacture. With this design of the transformer, the insulating sleeves simultaneously perform the functions of radial stretch marks, fixing the position of the massive component of the low-voltage secondary windings (with magnetic circuits and screen) relative to the primary winding and the housing having high potential. Under the influence of full voltage (operating and test) and high mechanical loads, the insulating sleeves and their fastening must satisfy, on the one hand, the requirements for ensuring the necessary electrical strength of the insulation system, and on the other hand, the requirements for mechanical strength and rigidity of fastening, including ensuring the lowest possible eccentricity a set of secondary windings with a screen relative to the conductor of the primary winding. The fulfillment of these requirements is associated with increased requirements for the characteristics of the material of the insulating sleeves and the quality of their performance, for the accuracy of their very laborious assembly with the housing and a set of secondary windings, with a complication of design, i.e. it is necessary to incorporate reinforced clamps around the perimeter of the secondary windings, increase the strength of the walls of the housing due to the thickness of the material used or additional stiffeners along with the device for fixing the bushings. In this case, the insulating sleeves distributed around the screen perimeter mechanically connect the elements insulated from each other, which creates the conditions for the occurrence of partial and surface discharges when the critical value of the field strength along the surface is exceeded. To prevent these phenomena, it is necessary to complicate the configuration of the insulating bushings or to additionally increase the insulating distance between the housing and the set of secondary windings with an electrostatic shield, given that the integrity of the screen at the attachment points of the bushings is violated and its effectiveness on the uniformity of the field around the perimeter is reduced. These circumstances make it difficult to achieve the required reliability of the current transformer, lead to the complication of its design and manufacturing technology, increase cost.

 In order to eliminate these shortcomings in the proposed high-voltage current transformer for outdoor installation, containing a metal housing mounted on an insulating support column and filled with an insulating medium, in which the primary winding is in the form of a rectilinear conductor, the secondary windings covered by a toroidal electrostatic screen, and the secondary winding spacing system with a screen relative to the primary winding and the housing of insulating elements, the insulating elements of the distance The secondary windings with the screen are made in the form of a frame coaxial with the primary winding conductor, on which the secondary windings with the screen are placed, and insulating spacers installed between the primary winding conductor and the frame at its ends outside the zone of maximum electrostatic field intensity concentrated between the secondary windings and the conductor primary winding. In this case, the insulating frame is made cylindrical, for example, in the form of a pipe segment of insulating material or of insulating rods located along the generatrices of the cylindrical surface. Insulating spacers providing the frame position coaxial with the primary winding conductor and the necessary insulation distance between the secondary winding screen and the primary winding, based on the characteristics of the insulating medium, can be made in a disk shape, as well as from radially located insulating rods that form, for example, crosses, fixed on the primary winding.

 In FIG. 1 shows a current transformer with a partial longitudinal section; figure 2 current transformer, side view, with a partial cross section; figure 3-5 shows embodiments of the insulating frame and struts.

 The measuring high-voltage current transformer comprises a cylindrical metal housing 1 filled with SF6 gas or other insulating medium (for example, transformer oil). The primary winding 2 and a set of multi-turn secondary windings 3, wound on toroidal magnetic circuits (not shown), which is covered by a toroidal electrostatic screen 4, are placed in the housing. The single-turn primary winding is made in the form of a rectilinear conductor (rod or pipe), one end of which is facing outwardly fixed in the end cover 5 of the housing and has the same potential with the housing, and the other in its opposite end wall by means of an insulating sleeve 6.

 The distance winding system of the secondary windings with the surrounding toroidal shield relative to the primary winding and the housing, which are fully energized for the necessary, based on the characteristics of the insulating medium, insulating distances includes a cylindrical frame 7 of insulating material, coaxial with the primary winding conductor, and insulating spacers 8. Secondary windings with a screen are placed on an insulating frame. The frame can be made in the form of a continuous cylinder 9 (Figs. 3, 5) of a piece of pipe made of insulating material or formed of insulating rods 10 (Fig. 4) located along the generatrices of a cylindrical surface and spaced along the inner perimeter of the toroidal screen of the secondary windings.

 Insulating spacers are installed at the ends of the frame between it and the primary winding conductor, fixing their coaxial location, and can be made in the form of disks 11 (Figs. 3, 4) or from radially located insulating rods 12 (Fig. 5), forming fixed to the primary winding crosses. Moreover, the length of the insulating frame along the primary winding conductor is such that its ends extend beyond the size of the electrostatic screen on both sides so that the insulating spacers located at the ends of the frame are removed from the zone of maximum electrostatic field strength concentrated between the primary winding conductor and the secondary winding screen . Therefore, they are not exposed to the full potential difference between the screen and the primary winding. The size of the spacers in the radial direction is determined by the required insulating distance between the screen of the secondary windings and the primary winding.

 The metal casing is mounted on an insulating support column 13, which is hermetically connected with both the casing and the base 14 (base). The junction of the metal casing and the insulating column is protected by an electrostatic shield 15. Taps 16 of the secondary windings pass inside a cylindrical electrostatic shield 17.

 The proposed high-voltage current transformer in comparison with the known (prototype) has a higher reliability, less complicated and less time-consuming to manufacture.

 The device of the distance system in it provides obtaining in zones of maximum tension between the insulated parts: the screen of the secondary windings, the primary winding and the screen of the secondary windings of the housing (in the places of their closest convergence) fields with significantly less heterogeneity (than the prototype) due to the fact that in these zones there are no solid insulation elements connecting insulated surfaces under various potentials.

 The outer and inner surfaces of the cylindrical frame located between the primary winding and the screen of the secondary windings are located along equipotential lines of the electric field in the zone where the electric field is already small and the frame is under the influence of an insignificant potential difference. Insulating spacers are also exposed to only part of the total (working or test) voltage between the insulated parts of the transformer. In addition, their removal from the zones of maximum field strength, along with a sufficient extension of the ends of the frame, provides much lower field strengths along the surfaces of the insulating elements of the distance system. Under these conditions, there is no need for significant complications of their shape (to reduce the surface field strength) and cheaper insulation materials can be used for them.

 The design of the electrostatic screen of the secondary windings is simplified, and increasing the uniformity of the electrostatic field between the screen and the housing also increases reliability or reduces the size of the insulation gap. There is no need to incorporate reinforced clamps into the set of secondary windings and equip special attachment points for fastening elements of the distance system on secondary windings with a screen and on the housing.

 When placing massive secondary windings with a screen on the surface of a rigid cylindrical frame (in the place of attachment at three points), resting on the ends of the insulating spacers mounted on the rectilinear conductor of the primary winding, more stable and reliable fixation of their position and mutual alignment with the primary winding and the housing are achieved . At the same time, the assembly of the transformer is simplified.

Claims (5)

 1. A HIGH-VOLTAGE CURRENT TRANSFORMER of an outdoor installation, comprising a metal housing mounted on an insulating support column, filled with an insulating medium, in which a primary winding in the form of a rectilinear conductor, secondary windings covered by a toroidal electrostatic screen, and a secondary winding distance system with a screen relative to the primary winding are placed and housings made of insulating elements, characterized in that the insulating elements of the distance system of the secondary windings with the screen are The primary winding and the housing are made in the form of a frame coaxial with the primary winding conductor, on which the secondary windings with a screen are placed, and insulating spacers installed between the primary winding conductor and the frame at its ends outside the zone of maximum electrostatic field strength concentrated between the secondary windings and conductor of the primary winding.  2. The transformer according to claim 1, characterized in that the frame is cylindrical, for example, in the form of a pipe segment of insulating material.  3. The transformer according to claim 1, characterized in that the frame is made of insulating rods located along the generatrices of the cylindrical surface.  4. The transformer according to paragraphs. 1 to 3, characterized in that the insulating spacers are made disk-shaped.  5. The transformer according to paragraphs. 1 to 3, characterized in that the spacers are made of radially arranged insulating rods.

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