RU2088024C1 - Rod of stator winding for high-voltage electric machine - Google Patents

Abstract

FIELD: electric engineering, in particular, generators which output 24 kW and more. SUBSTANCE: rod has slot and front parts and contains copper conductors which are located in temperature-hardening insulation, low-resistance semiconductor cover which is deposited over insulation in slot part of rod, pieces of layer of front corona-quenching cover. Said pieces contact low- resistance cover and partly overlap it. In addition device has protection insulation layer which is applied over pieces of layer of front corona-quenching cover. Said insulation layer contacts low- resistance slot cover using additional low-resistance jacket which is made from cups of glass fiber fabric which is preliminary treated with low-resistance temperature-hardening binder. Said cups in region of entrance of copper conductors to insulation are fixed in regions of mutual overlap of slot and front covers which are located in first of covers. Said cups in region of slot part are turned over layer of additional protection insulation so that cup edge is shifted towards rod ends with respect to region of mutual overlap in first layer. EFFECT: increased reliability of cover and insulation due increased temperature and mechanical stability, decreased wearing of most loaded part of cover. 2 dwg

Description

 The present invention relates to turbine generators, mainly performed on a voltage of 24 kV and above.

 A known design of the rods of the high voltage winding, equipped with protection against sliding discharges. So in US patent N 3210461 describes a single-stage enamel coating applied to the insulation of the rod, the electrical properties of which are set by micropowder of silicon carbide (SiC) with the addition of carbon black or graphite. Such coatings reliably work only at a normal voltage of about 10 kV. At higher voltages, a longer coating length is required, which increases the current load, and already at voltages of more than 15 kV the thermal stability of the coating, on which burnouts (carbonized tracks) appear during the tests, is noticeably reduced.

 A more complex construction of a two-stage coating applied to the rod is known (US Pat. No. 4,207,482), the first stage being 50-100 mm long, made of a layer with lower electrical resistance than the second stage. At the same time, to increase thermal stability at high operating and test voltages, the first stage is reinforced by applying a layer of asbestos tape or asbolavsan tape, which transmits a greater current without damage.

 Such a coating turns out to be fully functional up to a voltage of less than 24 kV, but the use of asbestos materials is currently almost universally prohibited for environmental reasons and, in addition, these materials have increased hygroscopicity, which can lead to a loss of the regulatory properties of the coating, i.e. reduce its stability.

 Closest to the claimed and selected for the prototype, is the design of the two-layer coating described in US patent N 3975653 (published 08/17/1976, volume 949, N 3). This coating is intended for use in machines U ≥ 24 kV, where the test insulation voltage of the rods can reach 80 kV or more.

 The increase in thermal stability in this design is achieved by applying to both steps of the first coating layer located on the core insulation of the rod, an additional (protective) insulation layer with a thickness of 0.2 to 0.5 of the thickness of the main insulation. On top of this protective layer, a second layer of a two-stage coating is applied, almost identical to the first, but offset from it towards the ends of the rod by the length of the shielding part of the grounded electrode. Due to the introduction of an additional insulation layer and a second coating layer, currents and heat load are redistributed between these two layers, which determines an increase in thermal stability at high voltages.

The disadvantages of this design are:
electrical contact between low-impedance steps located in different layers of the coating is carried out using an enamel layer, the current-carrying capacity of which is relatively small. With thermal damage to this contact layer, the distribution of currents between the layers is completely disrupted and the advantages of this design are lost;
with the inevitable vibrations of the rods, abrasion of the contact enamel layer rather quickly or even peeling and chipping it off the surface of additional insulation is possible;
baking an additional layer of insulation leads to the inevitable hit of a part of the binder on the already mentioned contact enamel, as a result of which, as established experimentally, its resistance increases, and thermal stability, respectively, decreases.

 It is important to note that the deterioration of the thermal stability of the contact can lead to visually undetectable defects leading to a subsequent breakdown of the insulation.

 The objective of the proposed invention is to increase the reliability of the coating of the rod in machines with a rated voltage of ≥ 24 kV by increasing thermal and mechanical stability, as well as the durability of the most current-loaded coating area.

 The specified technical result is achieved by the fact that in the stator winding rod of a high-voltage electric machine having a groove and a frontal part and containing copper conductors enclosed in thermosetting insulation, a low-resistance semiconducting coating deposited on top of the specified insulation in the groove part of the rod; being in electrical contact with this coating and partially overlapping sections of the frontal extinguishing coating, as well as sections of additional insulation superimposed on top of the first layer of the frontal coating and a second layer of frontal coronary extinguishing coating located on top of the sections, introduced into electrical contact with the low-resistance groove coating using an additional low-resistance coating layer, the specified low-resistance coating layer is made in the form of cuffs made of fiberglass, previously impregnated with low-resistance thermor with an active binder, these cuffs are fixed at one end in the areas of mutual overlapping of the groove and the frontal coverings, and the other is turned onto a layer of additional protective insulation so that the contact zone of the steps in the second coating layer is shifted relative to the same zone in the first layer towards the exit from the insulation copper conductors.

 The novelty of the claimed design lies in the fact that the rod is equipped with two additional cuffs made of fiberglass, previously impregnated with a low-resistance thermosetting binder, each of these cuffs being located simultaneously in two layers of the crown-absorbing coating, forming a heat-resistant and low-wear contact zone.

The claimed design has significant differences, since the interaction of new features (the presence of additional cuffs from a fiberglass with low electrical resistance, located simultaneously in two coating layers and setting the required shift of the contact zones) with the known tells it the following new properties:
the thermal stability and permissible current load of the contact layer are increased;
increases the wear resistance and mechanical strength of the specified contact layer;
deterioration of the initial properties of the coating during baking of additional insulation is prevented;
it is possible to use test voltages of the order of 80 kV, which ensures a higher level of reliability of the entire winding at rated voltages ≥ 24 kV.

 In FIG. 1 shows a longitudinal section of a portion of a rod coated with the claimed design.

 In FIG. 2 shows the installation and fixation of the cuff in the first and second coating layers.

Copper conductors 1 are enclosed in the main insulation 2. On top of the insulation 2 in the groove part of the rod is applied a low-impedance semi-conductive coating 3 made of varnish containing graphite or soot. The surface resistivity of this varnish is
ρ _s1 = 10 ³ ... 10 ⁴ Ohms.

Partially overlapping this varnish (zone 4), a more high-resistance frontal quenching extinguishing coating was applied 5 (in the first layer) and 6 in the second. It is made of enamel based on silicon carbide (SiC) micropowder, has a nonlinear current-voltage characteristic with an initial value of ρ _s2 = 10 ⁹ Ohms at E 1 kV / cm.

 In section 4 (contact zone), a cuff 7 of a fiberglass impregnated with a previously low-resistance thermosetting binder (prepolymer of the EUD-288 brand with the addition of 3.5 parts by weight of graphite) was fixed.

After protective additional insulation 8 is applied, part of the cuff 7 (sections 9 in Fig. 2) is turned in the direction of arrow 10 onto it and baked together with it so that its right edge (Fig. 1) extends beyond the left by the value L (length of the shield electrode) ) The value of L depends on the ratio of the thicknesses of the insulating layers (d ₁ , d _{2 of} their dielectric permittivities (ε ₁ , ε ₂ ) and a number of other factors. The value of L is experimentally optimized to reduce the heating of the coating. For the most typical variant of the ratio, these are: U _n 27 kV; d ₁ 6.5 mm; d ₂ 1.3 mm; ε _r1 = 5; ε _r2 = 5.5; L 20.25 mm.

As follows from FIG. 2, the total length of the pre-cut cuff 7 is determined by the formula:
L 2 • L _k + d ₂ + L where:
l _{k the} length of the contact zone 4 (usually 10.15 mm).

 As follows from FIG. 2, the cuff 7 is made with some overlap. This ensures a high barrier efficiency, which is the cuff for the excess binder coming out during pressure testing from additional insulation. For commonly used sizes, an overlap of 15.20 mm is sufficient.

Claims (1)

 The stator winding rod of a high-voltage electric machine, having a groove and frontal parts, containing copper conductors enclosed in thermosetting insulation, a low-resistance semi-conductive coating deposited on top of the specified insulation in the groove of the rod, in electrical contact with this coating and partially overlapping the first layer of the frontal extinguishing coverings, additional protective insulation applied on top of the frontal extinguishing coating, and located on top of additional protective insulation the second layer of the frontal extinguishing coating, in electrical contact with the low-resistance semiconductor coating using an additional low-resistance coating layer, characterized in that said low-resistance coating layer is made in the form of cuffs made of fiberglass impregnated with a low-resistance thermosetting binder, these cuffs on the output side of the insulation of copper conductors fixed on the zones of mutual overlap of the groove low resistance semi-conductive coating and the first layer of the frontal quenching blanket, and from the groove part, they are turned to additional protective insulation so that the edge of the cuff is shifted towards the ends of the rod relative to the zone of mutual overlap.

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