WO2001075908A1

WO2001075908A1 - Dry type semi-conductor cable distribution transformer

Info

Publication number: WO2001075908A1
Application number: PCT/US2001/010766
Authority: WO
Inventors: Thomas J. Lanoue; Benjamin Weber; Helmut Boehme
Original assignee: Abb Power T & D Company Inc.
Priority date: 2000-04-03
Filing date: 2001-04-03
Publication date: 2001-10-11

Abstract

A dry type cable distribution transformer (20) is disclosed of the type having a two winding (24, 26) dry type transformer (20) with a standard core frame (22) but uses insulated cable (30) (unshielded or shielded) for the LV winding (24) and semi-conductor coated (42), insulated round wire (44) for the HV winding (26).

Description

DRY TYPE SEMI-CONDUCTOR CABLE DISTRIBUTION TRANSFORMER

Background of the Invention

This invention relates to a dry type distribution transformer and more particularly to a dry type semi-conductor cable distribution transformer. Heretofore dry type distribution transformers were manufactured with conventionally insulated unshielded conductor, which require large electrical spaces to be used in the design. Since the spaces are open to contamination and environmental changes over time, the reliability of the insulation system is reduced. It would be desirable to provide a dry type distribution transformer wherein the normally required sizable clearances and spacings between the windings can be substantially reduced.

Summary of the Invention

It is an object of the present invention to provide a dry type cable distribution transformer having the conventional two windings with a standard core frame but utilizes, insulated cable (unshielded or shielded) for the LV(low voltage) winding and semi-conductor coated, insulated round wire, for the HV (high voltage) winding. In accordance with one aspect of the invention there is provided a dry type distribution transformer having a core, a low voltage winding directly on the core, the low voltage winding including insulated cable conductor and a high voltage winding on the low voltage winding, the high voltage winding including semi-conductor coated insulated round wire. In another aspect of the invention there is provide a dry type distribution transformer including a core and a low voltage winding directly on the core, the low voltage winding comprising insulated cable conductor. The transformer also includes a high voltage winding on the low voltage winding, the high voltage winding mcluding a round central conductor and a cable insulation system consisting of at least two coaxial layers, namely an inner semi-conductive layer having a non- conductive insulation layer thereon. In another aspect of the invention, the cable insulation system includes three coaxial layers, namely an inner semi-conductive, and outer semi-conductive layer and an intermediate non-conductive insulation layer. In a further aspect of the invention there is provided a method of making a dry type cable distribution transformer having low voltage and high voltage windings on a core frame. The method includes the steps of winding an insulated cable on the core to provide a low voltage winding and winding a semi-conductor coated insulated round wire on the low voltage winding to provide a high voltage winding. In one aspect of the method of the invention the insulated cable in the low voltage winding is shielded. In another aspect of the method of the invention the semi-conductor coated insulated, round wire for the high voltage winding is shielded.

For further objects and advantages of the invention reference may be had to the following drawings taken in conjunction with the accompanying description.

Brief Description of the Drawings: Fig. 1 is a schematic view of a conventional dry type distribution transformer.

Fig. 2 is a schematic view of a dry type semi-conductor cable distribution transformer according to the present invention.

Fig 3 is a fractional view of Fig. 2 on enlarged scale. Fig. 4 is a cross-sectional view of insulated non-shielded cable having an inner semi-conductor shield.

Fig. 5 is a cross-sectional view of a shielded cable having inner and outer semi-conductor shields. Detailed Description of the Preferred Embodiment

Referring to Fig. 1 there is illustrated a dry type distribution transformer of the conventional type. The transformer 10 includes a core 12 . Each leg of the core is provided with a LN (low voltage) winding 14 and an HN (high voltage) winding 16. These windings use non-electrically shielded conductors. Thus full electrical voltage exists between adjacent windings and grounded parts. Thus a conventional dry type distribution transformer requires sizable clearances and spacing between the windings. As the operating voltages increase, the spacings must become larger. For example, the HV to LV winding space for a 125 kN BIL design requires a minimum of 72 mm spacing between windings, and the spacing for the HN winding to the core requires a minimum of 150 mm.

Referring to Figs. 2 and 3 there is illustrated a dry type semi-conductor cable distribution transformer 20 according to the present invention. The transformer 20 includes a core 22 having an LV winding 24 wound directly on the legs of core 20 with insulated cable conductor and an HV winding 26 of semi-conductor insulated cable wound directly on the LV winding at the same work station and in the same process. The insulated cable for the LV winding may be shielded or non-shielded. An example of the non-shielded type cable is illustrated in Fig. 4 where the cable 30 comprises an electrical conductor 32 which may be made of copper or aluminum having an inner semi-conductor shield 34 and an outer dielectric insulation coating 36. An example of a shielded cable 40 is illustrated in Fig. 5. The shielded cable 40 has a cable insulation system consisting of three coaxial layers namely, an inner semi- conductive layer 42 on the conductor 44, an outer semi-conductive layer 46 and an intermediate non-conductive insulation layer 48. The HV winding 26 for the transformer 20 shown in Figs. 2 and 3 is wound from semi-conductive insulated cable similar to the cable 30 illustrated in Fig. 4. The non-conductive layers 36 and 48 are a polymeric dielectric material such as a polyolefin or blend of rubbers, commonly used in cable manufacture. The semi-conductive layers 34 in Fig. 4 and 42 and 46 in Fig 5 may also be made of the same material but are made semi-conductive by the incorporation of conductive fillers, such as carbon black, graphite etc. An example of such materials is disclosed in U.S. Patent No. 4,687,882. In one embodiment of the invention the inner conductors 32 and 44 had an outside diameter of about 3.0 mm. The inner semi-conductive shields 34 in Fig. 4 and 42 in Fig. 5 had a thickness of about 0.2 mm. The non-conductive layer of insulation 36 in Fig. 4 and 48 in Fig 5 had a thickness of about 1.4 mm. The outer semi-conductive shield 46 in Fig 5 had a thickness of about 0.25 mm.

The term "shielded" as used herein refers to the outer semi-conductive coating on the insulation of the cable. The term "unshielded" as used herein refers to cable that has no outer semi-conductive coating on the insulation. Both shielded and unshielded cable may have inner semi-conductive coatings on the conductors.

Generally, the LV winding will have only insulated cable with no semi-conductive coating on the inside or outside. However, in some applications the LV winding may be shielded or unshielded.

The primary concept in the present invention is the application of high voltage, semi-conductive cable technology to the manufacturing of distribution transformer LV and HV windings. This unique invention greatly simplifies the transformer manufacturing process. The concept involves winding the LV winding directly on the core leg with insulated cable conductor and then winding the HV winding with semi-conductive insulated cable all at the same work station and in the same process. The main advantage of using insulated shielded semi-conductive cable is that the voltage stresses are contained within the cable; thus the clearances or spacings between the windings and grounded parts can be reduced to mechanical construction spaces. Therefore the entire core window opening can be used for the windings.

As pointed out above in connection with Fig. 1 the prior art uses non- electrically-shielded conductors. Thus full electrical voltages exist between adjacent windings and grounded parts. Therefore the prior art requires sizable clearances and spacings between the windings. As the operating voltages increase, the spacings must get larger. As pointed out above, by way of example, the HV to LV winding space for a 125 kV BIL design requires a minimum of 72 mm spacing between windings, but a cable winding designed according to Figs. 2 and 3 of the present invention requires only mechanical building allowances of 10 mm. The same applies to the spacing of the HV winding to the core, which reduces from 150 mm to 20 mm. Thus the present invention provides the electrical power industry with a new type dry distribution transformer design concept that is applicable to both dry and liquid transformer applications.

While a preferred embodiment of the invention has been described and illustrated, it is to be understood that further modifications may be made without departing from the spirit and scope of the invention as set forth in the appended claims.

Claims

What is claimed is:

1. A dry type distribution transformer comprising: a core, a low voltage winding directly on said core, said low voltage winding comprising insulated cable conductor, and a high voltage winding on said low voltage winding, said high voltage winding comprising semi-conductor coated insulated round wire.

2. A dry type distribution transformer according to claim 1 wherein said low voltage winding comprises unshielded insulated cable conductor.

3. A dry type distribution transformer according to claim 1 wherein said high voltage winding comprises semi-conductor shielded, semi-conductor coated insulated round wire.

4. A dry type distribution transformer comprising: a core, a low voltage winding directly on said core, said low voltage winding comprising insulated cable conductor, and a high voltage winding on said low voltage winding, said high voltage winding comprising a round central conductor and a cable insulation system consisting of at least two coaxial layers, namely an inner semi-conductive layer having a non-conductive insulation layer thereon.

5. A dry type distribution transformer according to claim 4 wherein said cable insulation system comprises three coaxial layers, namely an inner semi- conductive layer, an outer semi-conductive layer and an intermediate non-conductive insulation layer.

6. A dry type distribution transformer according to claim 5 wherein said intermediate layer is a polymeric dielectric insulation material.

7. A dry type distribution transformer according to claim 6 wherein said inner and outer semi-conductive layers are made of a polymeric dielectric material having incorporated therein a conductive filler.

8. A method of making a dry type cable distribution transformer having low voltage and high voltage windings on a core frame, comprising the steps of: winding an insulated cable on the core to provide a low voltage winding and winding a semi-conductor coated, insulated round wire on the low voltage winding to provide a high voltage winding.

9. A method according to claim 8 wherein said insulated cable in said low voltage winding has an inner semi-conductive coating.

10. A method according to claim 9 wherein said insulated cable in said low voltage winding is unshielded.

11. The method according to claims 8 or 9 wherein said semiconductor coated, insulated, round wire for the high voltage winding is shielded.