US 3508096 A
Description (OCR text may contain errors)
Aprll 21, 1970 UMKYULL ET AL 3,508,096 ARRANGEMENT FOR PREVENTING GLOW DISCHARGES Q BETWEEN INSULATED CONDUCTORS IN GENERATOR END TURNS Filed Nov. 25, 1968 3mm Ulrich ku LL RoLa Incl 50H u Ler- A M' U,J-QA%ME FAQ United States Patent Filed Nov. 25, 1968, Ser. No. 778,424 Claims priority, application Switzerland, Dec. 5, 1967, 17,035/ 67 Int. 'Cl. H0211 3/40 US. Cl. 310-196 4 Claims ABSTRACT OF THE DISCLOSURE An arrangement for preventing glow discharges between two insulated electrical conductors having diflFerent potentials, particularly at the end turn portions of windings of high voltage rotary electrical machines, utilizes conductive layers embedded in the insulation of the two conductors where they approach one another in the end turn area and these conductive layers are electrically interconnected. Semiconductor layers are also embedded in the insulation and surround the winding conductors as well as the contact the conductive layers, and semiconductor layers are also applied to the exterior surfaces of the insulation. Intermediate supporting and spacing elements of semiconductive material reinforced with glass fiber are provided in the air gap between conductors.
responding to the line or rated voltage of the machine.
During a voltage test, the full test voltage occurs at these points. Since, however, the distance between the conductors at the end turns of the winding cannot be appreciably increased for constructional reasons, it is possible that already at the normal operating voltage discharges can occur in the air or gas gaps at the phase separation points which under certain circumstances can be very undesirable. With conventional constructions this is often avoided by filling the space between the phases at the separation points with a semiconductive mass, whereby in most cases the filling material also serves as a mechanical supporting element.
By filling the space between the end turn parts of the coils with such a mass, which generally consists of a material for instance glass fibre, which is saturated with a semiconductive varnish, it is possible to obtain a very small conductor spacing but such a filling is not very durable. This is due to the fact that it is impossible to produce a filling of this kind which is free of cavities and furthermore as a result of the shrinkage which occurs when the filling masses hardens, vibrations result between the conductor insulation and the filling so that the latter becomes brittle and fine cracks occur. The gradual destruction of the filling mass due to glow discharges is bound to affect its mechanical strength, so
that it can no longer also act as a supporting element.
As a result of the continuously increasing size of modern machines with correspondingly higher voltage ratings, it has become necessary to provide a device which prevents glow discharges between two insulated conductors of dilferent voltage potential, particularly with rotating machines having a high rated voltage. In accordance with the invention this is achieved by providing an electrically conductive layer in the critical region at least on the opposite sides of the conductors, this layer being located within the conductor insulation, the surface of which is covered on all sides with semiconductive glow discharge protection layers, the conductive layers being connected together electrically and-at least their edges being covered with an additional semiconductive coating.
A constructional example of the invention is explained by means of the accompanying drawings wherein:
FIGURE 1 shows the phase separation point of two bar conductors in the end turn part of a generator winding in longitudinal section, and
FIGURE 2 shows the same bar conductors in a crosssectional view taken along the line AA of FIGURE 1.
With reference now to the drawings, at least the opposite broad sides of the end turn part of two neighboring conductor bars 1 are provided at the phase separation point with conductive layers 2 which are most expediently in the form of a coating of varnish. These layers 2 below the surface of the conductor insulation 4 extend in the longitudinal direction up to the points where the bars begin to diverge, that is to say the layers in this example lie in the critical region between both bends in the end turn part of the winding where the parallel bars come very near to each other. The edges of the layers 2 are covered on all sides with a semiconductive coating 3 which in the critical region also surrounds the bar inside the insulation. The conductive layers 2 as well the semiconductive layers 3 are produced when the usual insulation layer 4 is applied to the conductor, for instance by means of coatings or the insertion of suitable thin foils, whereupon a semiconductive layer 5 which acts as a protection against glow discharges is also applied to the outside of this insulation.
The conductive layers 2 are connected together bymeans of electrically conductive contact strips 6 and an intermediate supporting element 7 located in the gas gap. This supporting element 7 which for instance consists of a semiconductive synthetic material reinforced with glass fibre also serves as a spacer for the bars. Since the capacity between the conductive layers 2 and the conductor copper of both bars 1 is approximately equal, the voltage of the layers 2 and of the intermediate part of the insulation and the gas gap is reduced to half the voltage between the conductors of both bars 1. The layer of insulation 4 on the outer side which is provided with a semiconductive protective layer 5 serves solely to control the voltage build-up at the edges of the layers on the surface of the bars so as to prevent the occurrence of glow discharges.
With the arrangement described above, a suitable voltage control enables the gas gaps at the phase separation points to be completely relieved of all electrical stresses because these are now transferred to the conductor insulation which can withstand glow discharges. In this way it is possible to obtain minimum spacing between the conductors at the phase separation points and also an improvement as regards fiow discharges during voltage tests. The supports for the coil end turns have a constant mechanical strength and operational safety is increased. Finally, cooling is also improved because the gas gaps are no longer filled with a semiconductive mass.
1. An arrangement for preventing glow discharges between two insulated electrical conductors having different potentials, and particularly at the end turn portions of windings of high voltage rotary electrical machines comprising conductive layers embedded in the insulation of the two conductors where they approach one another in the end turn area, means interconnecting said conductive layers, semiconductive glow discharge protecti ve layers also embedded in the insulation and surrounding said conductors at the location of said conduc-r tive layers, and semiconductor layers surrounding the insulations on said conductors.
2. The invention as defined in claim 1 wherein said means interconnecting said conductive layers includes conductive strips which pass through the insulation of the conductors.
3. The invention as defined in claim 1 wherein said means interconnecting said conductive. layers is comprised of conductive strips which pass through the insulation of the conductors, and an electrically conductive supporting element located between the conductors.
4. The invention as defined in claim 3 wherein said electrically conductive supporting element between said conductors is comprised of glass fiber reinforced semiconductor synthetic material.
References Cited UNITED STATES PATENTS WARREN E. RAY, Primary Examiner