WO2017040303A1

WO2017040303A1 - Transformer, coil assembly and spacer

Info

Publication number: WO2017040303A1
Application number: PCT/US2016/049035
Authority: WO
Inventors: Rickie L. KINDER
Original assignee: Abb Schweiz Ag
Priority date: 2015-08-29
Filing date: 2016-08-26
Publication date: 2017-03-09

Abstract

A unique transformer includes a core and a coil assembly. The coil assembly includes a mold, a live part, a layer of grillage, a plurality of spacers and a resin layer. The grillage is disposed between the mold and the live part, and is formed by a plurality of intersecting ligaments that define a plurality of openings therebetween. The resin is disposed between the mold and the live part, and encapsulates the grillage and the spacers. The spacers are in engagement with the grillage, and disposed in the openings of the grillage. The spacers are constructed to space the mold apart from the live part, and to space the grillage apart from the mold and the live part.

Description

TRANSFORMER, COIL ASSEMBLY AND SPACER

Field of the Invention

The present application relates to transformers, and more particularly to a spacer for a transformer coil assembly.

Background

Transformers and transformer coil assemblies remain an area of interest. Some existing systems have various shortcomings, drawbacks and disadvantages relative to certain applications. For example, in some cast transformers, the spacers used to space the mold apart from the live part may not promote a uniform flow of insulating resin. Accordingly, there remains a need for further contributions in this area of technology.

Summary

Embodiments of the present invention include a unique transformer. The transformer includes a core and a coil assembly. The coil assembly includes a mold, a live part, a layer of grillage, a plurality of spacers and a resin layer. The grillage is disposed between the mold and the live part, and is formed by a plurality of intersecting ligaments that define a plurality of openings therebetween. The resin is disposed between the mold and the live part, and encapsulates the grillage and the spacers. The spacers are in engagement with the grillage, and disposed in the openings of the grillage. The spacers are constructed to space the mold apart from the live part, and to space the grillage apart from the mold and the live part.

Brief Description of the Drawings

The description herein makes reference to the accompanying drawings wherein like reference numerals refer to like parts throughout the several views, and wherein:

FIG. 1 schematically depicts some aspects of a transformer in accordance with a non-limiting example of an embodiment of the present invention.

FIG. 2 schematically depicts some aspects of a transformer in accordance with a non-limiting example of an embodiment of the present invention.

FIG. 3 illustrates some aspects of a transformer coil assembly in accordance with a non-limiting example of an embodiment of the present invention.

FIGS. 4A-4C illustrates some aspects of a spacer for a transformer coil in accordance with a non-limiting example of an embodiment of the present invention.

FIG. 5 depicts some aspects of an illustrative portion of grillage for a transformer coil assembly with spacers engaged therewith in accordance with a non-limiting example of an embodiment of the present invention.

Detailed Description

For purposes of promoting an understanding of the principles of the Transformer, Coil Assembly and Spacer disclosed herein, reference will now be made to the embodiments illustrated in the drawings, and specific language will be used to describe the same. It will nonetheless be understood that no limitation of the scope of the invention is intended by the illustration and description of certain embodiments of the invention. In addition, any alterations and/or modifications of the illustrated and/or described embodiment(s) are contemplated as being within the scope of the present invention. Further, any other applications of the principles of the invention, as illustrated and/or described herein, as would normally occur to one skilled in the art to which the invention pertains, are contemplated as being within the scope of the present invention.

Referring to the drawings, and in particular FIGS. 1 and 2, some aspects of a non-limiting example of an electrical power transformer 10 in accordance with an embodiment of the present invention are depicted. In one form, transformer 10 is three- phase transformer system having phase leg transformers 12, 14 and 16 disposed about respective legs 18, 20 and 22 of a transformer core 24. In other embodiments, transformer 10 may be a single-phase transformer or any other type of electrical power transformer. Each phase leg transformer, e.g., an example of which is phase leg transformer 14 as illustrated in FIG. 2, includes a low voltage (LV) transformer coil assembly 26 and a high voltage (HV) transformer coil assembly 28 disposed about the respective transformer leg, e.g., a cruciform core 20.

In one form, each of LV transformer coil assembly 26 and HV transformer coil assembly 28 is independently produced, e.g., as single unitary structures, after which LV transformer coil assembly 26 is installed over and disposed about cruciform core 20, and HV transformer coil assembly 28 is installed over and disposed about LV transformer coil assembly 26. In some embodiments, a radial gap between LV transformer coil assembly 26 and HV transformer coil assembly 28 may be supplied with cooling air for cooling LV transformer coil assembly 26 and HV transformer coil assembly 28. In one form, each of LV transformer coil assembly 26 and HV transformer coil assembly 28 is a dry-type cast coil. In other embodiments, either or both of LV transformer coil assembly 26 and HV transformer coil assembly 28 may take other forms.

In some embodiments, LV transformer coil assembly 26 and HV transformer coil assembly 28 may be included in a multi-coil assembly, wherein the LV and HV live parts, that is, the electrically and magnetically active conductor windings/coils of the transformer, are part of the same coil assembly, e.g., cast together to yield a single unitary structure. In some such embodiments, cooling channels may be disposed between the live parts of the multi-coil assembly, e.g., between the LV windings and the HV windings. In various embodiments, the transformer coil assemblies may or may not include cooling channels therein, depending upon the needs of the particular application. In various embodiments, transformer 10 may include a greater or lesser number of coil assemblies or of live parts in each coil assembly at each leg, e.g., may also include a medium voltage (MV) coil or other intermediate voltage coils. In addition, one or more of the coil assemblies or live parts may be a tap coil. Also, in some embodiments, transformer 10 may include a greater or lesser number of legs. Referring to FIG. 3, 4A-4C and 5, some aspects of a non-limiting example of a transformer coil assembly 30 in accordance with an embodiment of the present invention are depicted. Transformer coil assembly 30 may be, for example, an LV coil assembly or HV coil assembly for any of phase leg transformers 12, 14 and 16, or may be another coil assembly, e.g., an MV coil assembly, a tap coil assembly or any other transformer coil assembly. Transformer coil assembly 30 includes an inner mold 32, grillage 34, a plurality of spacers 36, a resin layer 38, a live part or winding 40, grillage 42, a plurality of spacers 44, a resin layer 46 and an outer mold 48.

Transformer coil assembly 30 is a dry-type cast coil assembly, in which a resin, e.g., an insulating resin, is poured into a cavity defined by inner mold 32 and outer mold 48 during manufacturing of coil assembly 30. In some embodiments, the resin may be mixed with a curative prior to the pouring process, or may otherwise include a curative. In some embodiments, an accelerator may be used to accelerate crosslinking reactions between the resin and the curative, e.g., in order to promote shorter cure time and press time.

Disposed within the cavity are grillage 34, spacers 36, live part 40, grillage 42 and spacers 44. The resin poured during the casting process encapsulates grillage 34, spacers 36, live part 40, grillage 42 and spacers 44. In some embodiments, the casting process takes place in a vacuum, e.g., in order to minimize the viscosity of the resin and/or in order to promote reduction or elimination of interstices and gaps or spaces between inner mold 32, grillage 34, spacers 36 and live part 40; those between live part 40, grillage 42, spacers 44 and outer mold 48; and those within or about live part 40. The resin is cured after the pour, e.g., in an oven, binding inner mold 32, grillage 34, spacers 36, resin layer 38, live part 40, grillage 42, spacers 44, resin layer 46 and outer mold 48 together, yielding transformer coil assembly 30 in the form of a single unitary structure bound together by the resin. The resin poured during the casting process yields resin layers 38 and 46. In one form, the resin is an insulating resin. The resin may be, for example, an epoxy resin, e.g., a thermosetting epoxy resin, or a polyester resin. The resin may be filled or unfilled. An example of a suitable epoxy resin is disclosed in U.S. Pat. No. 6,852,415, which is assigned to ABB Research Ltd. and is incorporated herein by reference.

Inner mold 32 is an inner wall structure of transformer coil 30. In one form, inner mold 32 is a cylinder. In other embodiments, inner mold 32 may take other geometric forms. In one form, inner mold 32 is metallic. In other embodiments, inner mold 32 may be formed of one or more nonmetallic materials in addition to or in place of a metallic material. In one form, inner mold 32 is both a mold and a mandrel for winding a conductor thereabout to form windings or live part 40. In other embodiments, inner mold 32 may not be a mandrel. In some embodiments, inner mold 32 may be another structure, such as one or more cooling ducts, or an inner winding or live part for another coil in a multi-coil assembly or other structure.

Grillage 34 and grillage 42 are operative to add strength to respective resin layers 38 and 46. Grillage 34 and grillage 42 are similar in form, and hence the description herein made with respect to grillage 34 applies equally to grillage 42. Grillage 34 is a screen formed by a plurality of intersecting ligaments 50. The intersecting ligaments 50 define a plurality of openings 52. In one form, openings 52 are square. In other embodiments, openings 52 may be one or more of rectangular, polygonal, triangular or any desired geometric shape. In one form, a single circumferential layer of grillage 34 surrounds inner mold 32 (or, for grillage 42, live part 40). In other embodiments, a greater number of layers may be employed. In still other embodiments, or only portions of a layer may be employed, e.g., portions spaced apart circumferentially about inner mold 32 (or, for grillage 42, live part 40).

In one form, ligaments 50 are formed of glass fibers, and are woven into a grid that forms openings 52. In one form, the glass fibers are e-glass fibers (electrical grade glass fibers). In various embodiments, one or more of various fiber materials may be employed to form ligaments 50, for example, polyphenylene sulfide (PPS), polyamides (nylon), polyvinyl chloride (PVC), flouropolymers (PTFE). In various other embodiments, other materials, fibrous or otherwise, may be employed. In some embodiments, ligaments 50 may be impregnated with a varnish, or a resin, such as the same resin used to form resin layers 38 and 46, which may lend stiffness to the grillage. In other embodiments, ligaments 50 may be impregnated with another material.

Live part 40 is the electrically active portion of transformer coil assembly 30. In one form, live part 40 is a winding. In various embodiments, live part 40 may be formed of conductor foil, a strip conductor (e.g., wherein live part 40 is a plurality of disc windings) or of wire. The conductor material may be, for example, copper or aluminum. Live part 40 may include taps (not shown) for providing access to the conductor, i.e., for electrical connection to the winding. In the illustrated embodiment, live part 40 may be an LV coil or an HV coil. In other embodiments, live part 40 may be an MV coil, a coil with taps or may be another form of coil. In one form, live part 40 is cylindrical. In other embodiments, live part 40 may have another geometric shape. Live part 40 is wound around spacers 36, which are supported radially by inner mold 32.

Outer mold 48 is an outer wall structure of transformer coil 30. In one form, outer mold 48 is a cylinder. In other embodiments, outer mold 48 may take other geometric forms. In one form, outer mold 48 is metallic. In other embodiments, outer mold 48 may be formed of one or more nonmetallic materials in addition to or in place of a metallic material. In some embodiments, outer mold 48 may be another structure, such as one or more cooling ducts, or an outer winding or live part for another coil in a multi-coil assembly or other structure.

Spacers 36, 44 are disposed in selected openings of respective grillage 34, 42. Spacers 36 and spacers 44 are constructed to space the respective mold 32 and mold 48 apart from live part 40. In addition, spacers 36, 44 are constructed to space ligaments 50 apart from the mold 32, 48 and live part 40 and hence space grillage 34, 42 apart from mold 32, 48 and from live part 40, e.g., to suspend grillage 34, 42 between mold 32, 48 and live part 40 so that grillage 34, 42 is disposed inside resin layer 38, 46, thereby strengthening resin layer 38, 46. In one form, spacers 36 and 44 are formed of the same resin used to form resin layer 38 and 46. In other embodiments, one or both of spacers 36 and 44 may be formed of a different material than respective resin layers 38 and 46.

Spacers 36 and spacers 44 are similar in form, and hence the following description made with respect to spacers 36 applies equally to spacers 44. Spacers 36 include a body 54. Formed in body 54 is a groove 56 extending around the periphery of body 54. Groove 56 may be subdivided into a plurality of groove portions, e.g., groove portions 58, 60, 62 and 64, that is, a groove portion disposed on each of one or more sides or ends or faces of body 54. Some embodiments may not include a groove extending around the entire periphery of body 54, but rather, may include only one or more groove portions, e.g., groove portions 58 and 60. Groove 56 or portions thereof subdivide body 54 into a hub 66 and lobes 68 and 70 adjacent thereto and disposed oppositely to each other.

Lobes 68 and 70 of body 54 have an overall dimension 72 greater than a dimension 74 of openings 52 of the grillage. Although illustrated as being vertically disposed, in other embodiments, dimension 74 may extend in any direction. Groove portions 58 and 60 define therebetween a dimension 76 of hub 66 that corresponds substantially to dimension 74 of openings 52. That is, as described herein, spacers 36 are installed into select openings of grillage 34 and engage ligaments 50. Dimension 76 corresponds substantially to dimension 74 insofar as dimension 76 may be somewhat greater or lesser than dimension 74, e.g., not so much greater as would damage the ligaments upon installation of the spacer, and not so much lesser that the spacer would readily fall out of the grillage after it was installed. Groove 56 is constructed to receive and capture ligaments 50, and to retain ligaments 50 in proximity to hub 66 and retain spacer 36 in opening 52. For example, spacer 36 may be so retained owing to dimension 72 of lobes 68 and 70 being greater than dimension 74; and owing to dimension 76 not being lesser than dimension 74 to such an extent as would allow the translation of spacer 36 (e.g., in the vertical direction in FIG. 5) to a degree where the outer extents of one or both of lobes 68, 70 fail to overlap the corresponding ligament 50.

Body 54 and groove 56 are constructed to space ligaments 50, and hence in some embodiments the grillage, apart from the respective mold 32 and 48 and live part 40. For example, lobes 68 and 70 have dimensions 78 and 80, which define the distance by which the ligaments captured in the respective groove portions are spaced apart from mold 32, 48 and live part 40. Body 54 spaces live part 40 apart from respective inner mold 32 and outer mold 48. It will be understood that in some embodiments, spacers of the same size may be employed as spacers 36 and 44, and that in other embodiments, spacers 36 may be a different size than spacers 44.

Body 54 has a thickness 82 that defines the degree to which mold 32, 48 is spaced apart from live part 40, forming a gap between mold 32, 48 and live part 40. For cylindrical coils, thickness 82 is measured in the radial direction, e.g., from the perspective of FIG. 3. For non-cylindrical coils, thickness 82 may be a thickness measured in a direction from a center plane or other direction perpendicular to a corresponding face of the mold and live part.

Lobes 68 and 70 of body 54 are constructed to have less than a surface area contact with adjacent components mold 32, 48 and live part 40, that is, other than any incidental surface area contact that may result from any deformation of spacers 36, 44, molds 32, 48 or live part 40. In particular lobes 68 and 70 of body 54 include curved surfaces 84 and 86 for contact with respective molds 32, 48 and live part 40. Curved surfaces 84, 86 have a radius of curvature different than the radius of curvature of molds 32, 48 and live part 40, thereby preventing surface area contact with molds 32, 48 and live part 40. In one form, surfaces 84 and 86 are cylindrical, yielding line contact with respective molds 32, 48 and live part 40. In other embodiments, other curved surfaces may be employed to yield less than surface area contact between spacers 36, 44 and respective molds 32, 48 and live part 40. By creating less than surface area contact, e.g., line contact between spacers 36, 44 and respective molds 32, 48 and live part 40, in some embodiments the resin may flow more uniformly and completely around spacers 36, 44 in the gap between molds 32, 48 and live part 40. This may reduce or eliminate voids or air gaps between spacers 36, 44 and molds 32, 48 and live part 40, which may provide a more uniform dielectric characteristic and mechanical strength in some embodiments than if surface area contact between spacers 36, 44 and molds 32, 48 and live part 40 occurred.

Spacers 36, 44 may be installed into grillage 34, 42 by inserting each spacer 36, 44 diagonally into an opening 52, e.g., as illustrated in opening 52A, and then rotating the spacer 36, 44 into engagement with ligaments 52, as illustrated in opening 52B. Spacers 36, 44 may be installed in selected openings 50, e.g., to achieve a desired stagger pattern. The stagger pattern may be selected to promote the flow of resin into the gap between molds 32, 48 and live part 40. In some embodiments, spacer 36, 44 may be translated to a desired position within an opening 52, e.g., as illustrated in opening 52C, which may allow, e.g., more variation in stagger patters. In some embodiments, one or more other groove portions, e.g., groove portion 64, may envelope an additional ligament 50, e.g., as illustrated in opening 52C. Embodiments of the present invention include a transformer, comprising: a core; a coil assembly disposed about the core, wherein the coil assembly includes: a mold; a live part; a layer of grillage disposed between the mold and the live part, the grillage being formed of a plurality of intersecting ligaments, the ligaments defining a plurality of openings therebetween; a plurality of spacers in engagement with the grillage, each spacer being disposed in an opening of the plurality of openings; each spacer being constructed to space the mold apart from the live part, and each spacer being constructed to space the grillage apart from the mold and from the live part; and a resin layer disposed between the mold and the live part and encapsulating the grillage and the spacers.

In a refinement, each spacer includes a body with two groove portions therein; the body having an overall dimension greater than a dimension of the opening; the groove portions defining a dimension therebetween substantially corresponding to the dimension of the opening.

In another refinement, each spacer includes a body with two groove portions therein, each groove portion being constructed to receive and capture a ligament therein and to retain the spacer within the opening.

In yet another refinement, the body and the groove portions are constructed to space the captured ligaments apart from the mold and from the live part.

In still another refinement, the spacer includes a body having a thickness defining a gap between the mold and the live part. In yet still another refinement, the spacer includes a body constructed to have a line contact with the mold and/or the live part.

In a further refinement, the spacer includes a body having curved surface constructed to have a line contact with the mold and/or the live part.

In a yet further refinement, the spacer is formed of a resin material.

Embodiments of the present invention include a transformer coil assembly, comprising: a mold; a live part; a layer of grillage disposed between the mold and the live part, the grillage being formed by a plurality of intersecting ligaments, the ligaments defining a plurality of openings therebetween; a plurality of spacers disposed in engagement with some of the ligaments and spacing the mold apart from the live part, wherein the spacers are constructed to suspend the grillage between the mold and the live part, and wherein each spacer is disposed in an opening of the plurality of openings; and a resin layer disposed between the mold and the live part and encapsulating the grillage and the spacers, wherein each spacer includes a body constructed to space the mold apart from the live part, the body including a hub having a dimension substantially corresponding to a dimension of the opening, and including a first lobe adjacent to the hub and having an overall dimension greater than the dimension of the opening.

In a refinement, each spacer further includes a second lobe disposed opposite to the first lobe and adjacent to the hub, wherein the second lobe has an overall dimension greater than the dimension of the opening; and wherein the first and second lobes are constructed to capture the ligaments therebetween and retain the spacer in the opening. In another refinement, the first and/or the second lobe is constructed to contact the mold and/or the live part with less than a surface area contact.

In yet another refinement, the first and/or the second lobe is constructed to have a line contact with the mold and/or the live part.

In still another refinement, the mold is cylindrical.

In yet still another refinement, the live part is cylindrical.

In a further refinement, the live part includes a plurality of disc windings.

Embodiments of the present invention include a spacer for a transformer coil assembly, comprising: a body constructed to space a mold of the transformer coil assembly apart from a live part of the transformer coil assembly, the body including a hub having a dimension substantially corresponding to a dimension of an opening between ligaments of a grillage of the transformer coil assembly; and the body including a first lobe disposed adjacent to the hub and having an overall dimension greater than the dimension of the opening.

In a refinement, the spacer further comprises a second lobe disposed opposite to the first lobe and adjacent to the hub, wherein the second lobe has an overall dimension greater than the dimension of the opening; and wherein the first and second lobes are constructed to capture the ligaments therebetween and retain the ligaments in proximity to the hub. In another refinement, the first lobe and/or the second lobe is constructed to engage the mold and/or the live part with less than a surface area contact.

In yet another refinement, the first lobe and/or the second lobe is constructed to have a line contact with the mold and/or the live part.

In yet still another refinement, the spacer is constructed to suspend the grillage between the live part and the mold.

While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiment(s), but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims, which scope is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures as permitted under the law. Furthermore it should be understood that while the use of the word preferable, preferably, or preferred in the description above indicates that feature so described may be more desirable, it nonetheless may not be necessary and any embodiment lacking the same may be contemplated as within the scope of the invention, that scope being defined by the claims that follow. In reading the claims it is intended that when words such as "a," "an," "at least one" and "at least a portion" are used, there is no intention to limit the claim to only one item unless specifically stated to the contrary in the claim. Further, when the language "at least a portion" and/or "a portion" is used the item may include a portion and/or the entire item unless specifically stated to the contrary.

Claims

Claims What is claimed is:

1 . A transformer, comprising:

a core;

a coil assembly disposed about the core, wherein the coil assembly includes: a mold;

a live part;

a layer of grillage disposed between the mold and the live part, the grillage being formed of a plurality of intersecting ligaments, the ligaments defining a plurality of openings therebetween;

a plurality of spacers in engagement with the grillage, each spacer being disposed in an opening of the plurality of openings; each spacer being constructed to space the mold apart from the live part, and each spacer being constructed to space the grillage apart from the mold and from the live part; and a resin layer disposed between the mold and the live part and encapsulating the grillage and the spacers.

2. The transformer of claim 1 , wherein each spacer includes a body with two groove portions therein; the body having an overall dimension greater than a dimension of the opening; the groove portions defining a dimension therebetween substantially corresponding to the dimension of the opening.

3. The transformer of claim 1 , wherein each spacer includes a body with two groove portions therein, each groove portion being constructed to receive and capture a ligament therein and to retain the spacer within the opening.

4. The transformer of claim 3, wherein the body and the groove portions are constructed to space the captured ligaments apart from the mold and from the live part.

5. The transformer of claim 1 , wherein the spacer includes a body having a thickness defining a gap between the mold and the live part.

6. The transformer of claim 1 , wherein the spacer includes a body constructed to have a line contact with the mold and/or the live part.

7. The transformer of claim 1 , wherein the spacer includes a body having curved surface constructed to have a line contact with the mold and/or the live part.

8. The transformer of claim 7, wherein the spacer is formed of a resin material.

9. A transformer coil assembly, comprising:

a mold;

a live part; a layer of grillage disposed between the mold and the live part, the grillage being formed by a plurality of intersecting ligaments, the ligaments defining a plurality of openings therebetween;

a plurality of spacers disposed in engagement with some of the ligaments and spacing the mold apart from the live part, wherein the spacers are constructed to suspend the grillage between the mold and the live part, and wherein each spacer is disposed in an opening of the plurality of openings; and

a resin layer disposed between the mold and the live part and encapsulating the grillage and the spacers,

wherein each spacer includes a body constructed to space the mold apart from the live part, the body including a hub having a dimension substantially corresponding to a dimension of the opening, and including a first lobe adjacent to the hub and having an overall dimension greater than the dimension of the opening.

10. The transformer coil assembly of claim 9, wherein each spacer further includes a second lobe disposed opposite to the first lobe and adjacent to the hub, wherein the second lobe has an overall dimension greater than the dimension of the opening; and wherein the first and second lobes are constructed to capture the ligaments therebetween and retain the spacer in the opening.

1 1 . The transformer coil assembly of claim 10, wherein the first and/or the second lobe is constructed to contact the mold and/or the live part with less than a surface area contact.

12. The transformer coil assembly of claim 10, wherein the first and/or the second lobe is constructed to have a line contact with the mold and/or the live part.

13. The transformer coil assembly of claim 10, wherein the mold is cylindrical.

14. The transformer coil assembly of claim 10, wherein the live part is cylindrical.

15. The transformer coil assembly of claim 14, wherein the live part includes a plurality of disc windings.

16. A spacer for a transformer coil assembly, comprising:

a body constructed to space a mold of the transformer coil assembly apart from a live part of the transformer coil assembly, the body including a hub having a dimension substantially corresponding to a dimension of an opening between ligaments of a grillage of the transformer coil assembly; and the body including a first lobe disposed adjacent to the hub and having an overall dimension greater than the dimension of the opening.

17. The spacer of claim 16, further comprising a second lobe disposed opposite to the first lobe and adjacent to the hub, wherein the second lobe has an overall dimension greater than the dimension of the opening; and wherein the first and second lobes are constructed to capture the ligaments therebetween and retain the ligaments in proximity to the hub.

18. The spacer of claim 17, wherein the first lobe and/or the second lobe is constructed to engage the mold and/or the live part with less than a surface area contact.

19. The spacer of claim 17, wherein the first lobe and/or the second lobe is constructed to have a line contact with the mold and/or the live part.

20. The spacer of claim 16, wherein the spacer is constructed to suspend the grillage between the live part and the mold.