US20210027936A1

US20210027936A1 - Transformer Apparatus

Info

Publication number: US20210027936A1
Application number: US16/936,563
Authority: US
Inventors: Nikolay Tal; Tzachi Glovinsky
Original assignee: SolarEdge Technologies Ltd
Current assignee: SolarEdge Technologies Ltd
Priority date: 2019-07-23
Filing date: 2020-07-23
Publication date: 2021-01-28
Also published as: US20210039723A1; CN112289566A; JP2021019206A; EP3770931A1; US11688545B2

Abstract

Systems, apparatuses, and methods are described for a transformer designed for supporting two or more sets of windings referenced to different voltage levels. Use of semiconductive shields may direct electrical fields caused by the different voltage levels to have a first amplitude in a first region of the transformer and a second amplitude in a second region of the transformer, and may enable efficient and cost-effective use of insulating materials and transformer design.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a non-provisional of and claims priority to U.S. Provisional Patent Application No. 62/877,687, filed Jul. 23, 2019, which is hereby incorporated by reference in its entirety.

BACKGROUND

A transformer is an electronic device that includes at least two sets of windings, sometimes known as primary and secondary sets of windings. A transformer provides galvanic isolation between the first and second sets of windings. In some cases, where the number of windings in the first set of windings is different from the number of windings in the second set of windings, the transformer provides voltage conversion. It is desirable to reduce an electric field present between the two sets of windings in order to reduce electric stress experienced by an insulating medium insulating the windings. It is also desirable to reduce a quantity of encapsulation material used to facilitate effective cooling of the transformer.

SUMMARY

The following summary presents a simplified summary of certain features. The summary is not an extensive overview and is not intended to identify key or critical elements.
Systems, apparatuses, and methods are described for a transformer than includes at least two sets of windings, and at least two semiconductive shields configured and disposed to cause a first electrical field between the two semiconductive shields, a second electrical field between a first of the semiconductive shields and a first set of windings, and a third electrical field between a second of the semiconductive shields and a second set of windings. According to features of the disclosure herein, the second and third electrical fields may be smaller than the first electrical field. Enhancing the first electrical field with respect to the second and third electrical fields may enable disposing the sets of windings using reduced insulation, and may increase cooling efficiency of transformer elements.
These and other features and advantages are described in greater detail below.

BRIEF DESCRIPTION OF THE DRAWINGS

Some features are shown by way of example, and not by limitation, in the accompanying drawings. In the drawings, like numerals reference similar elements.

FIG. 1 shows a transformer in accordance with the disclosure herein.

FIG. 2 shows additional details of a transformer in accordance with the disclosure herein.

FIG. 3 shows additional details of a transformer in accordance with the disclosure herein.

FIG. 4 shows additional details of a transformer in accordance with the disclosure herein, according to a profile view, and including electric field indications.

DETAILED DESCRIPTION

The accompanying drawings, which form a part hereof, show examples of the disclosure. It is to be understood that the examples shown in the drawings and/or discussed herein are non-exclusive and that there are other examples of how the disclosure may be practiced.
Reference is now made to FIG. 1, which shows a transformer 100 as described herein below. The transformer 100 comprises core 110, and is encompassed by case 120. Case 120 may be made of, for example, resin, and may be disposed to protect internal components of transformer 100 (e.g., from dust, humidity, etc.) and, as shown in FIG. 1, may obstruct an external view of the additional internal components, that are shown and discussed in further detail below. Core 110 may be made of ferromagnetic material or ferromagnetic compound, and may be designed to cause magnetic flux induced by windings of transformer 100 (not depicted in FIG. 1) to flow primarily through core 110.
Transformer 100 may be placed in a grounded conducting case, or casing (e.g., a box, not depicted) or a grounded conducting frame, to increase safety and reduce electrical field leakage from transformer 100.
Reference is now made to FIG. 2, which shows additional elements of transformer 100 that are obscured by case 120 as depicted in FIG. 1. In addition to core 110, transformer 100 comprises first windings 210 a and 210 b, first inner shield lid 211 a, second inner shield lid 211 b, first outer shield lid 212 a, second outer shield lid 212 b, first bobbin 213 a and second bobbin 213 b. Transformer 100 may include additional components that are concealed in FIG. 2 by first windings 210 a and 210 b, and will be described below.
In the illustrative design shown in FIG. 2, core 110 is of rectangular shape, having two legs, and two shorter members connecting parallel legs to form a full magnetic path. According to some features, core 110 may also include an air gap. First windings 210 a and 210 b are each wound around one of the parallel legs.
Windings 210 a and 210 b are shown each having a single winding of conductive material, the conductive material substantially filling the entire space between first outer shield lid 212 a and second outer shield lid 212 b. According to features of the disclosure herein, each of windings 210 a and 210 b may comprise more than one winding (e.g., several, tens, hundreds of thousands of windings), and may fill the entire space or part of the space between first outer shield lid 212 a and second outer shield lid 212 b. Windings 210 a and 210 b may be formed using single-strand wire, or multi-strand wire (e.g., Litz wire). Winding 210 a may be wound around a first leg of core 110 (with intermediate elements disposed between winding 210 a and the first leg of core 110, as described herein), and winding 210 b may be wound around a second leg of core 110 (with intermediate elements disposed between winding 210 b and the second leg of core 110, as described herein).
Each of first windings 210 a and 210 b may feature two or more terminals or taps (not explicitly depicted) for connecting to voltage terminals external to the transformer. For example, first winding 210 a and first winding 210 b may each have two voltage terminals, and may each be connected to a varying [e.g., an alternating current (AC)] voltage having an amplitude of several volts, tens of volts, hundreds of volts or thousands of volts. First windings 210 a and 210 b may be magnetically coupled to one another via core 110, and may also be magnetically coupled to secondary windings (depicted herein in FIG. 3).
First inner shield lid 211 a and second inner shield lid 211 b may be formed using semiconductive material, for example, semiconductive plastic, isolating plastic with a semiconductive coating, or other semiconductive materials. First inner shield lid 211 a and second inner shield lid 211 b may be connected to one another by first and second inner shield legs (not shown in FIG. 2) to form an inner semiconductive shield having two semiconductive shield legs encompassing the first and second legs of core 110. Similarly, first outer shield lid 212 a and second outer shield lid 212 b may be connected to one another by first and second outer shield legs (not shown in FIG. 2) to form an outer semiconductive shield having two semiconductive shield legs encompassing the first and second legs of core 110. The inner semiconductive shield may be manufactured (e.g., cast) as a single component (e.g., a single mold may be used for manufacturing the inner semiconductive shield, the mold forming the shapes of first inner shield lid 211 a, second inner shield lid 211 b, and the first and second inner shield legs), or may be formed combining separately-manufactured elements [e.g., first inner shield lid 211 a and second inner shield lid 211 b may be manufactured (e.g., cast) separately, and may be connected, during construction of transformer 100, to the first and second inner shield legs]. Similarly, the outer semiconductive shield may be manufactured (e.g., cast) as a single component or may be formed combining separately-manufactured elements. The inner and outer shields may be shaped to form Rogowski profiles, or other profiles designed to increase uniformity in an electrical field between the inner and outer shields and to suppress field enhancement at the shield edges.
FIG. 2 also shows surfaces of first inner bobbin 213 a and second inner bobbin 213 b. First inner bobbin 213 a and second inner bobbin 213 b may encompass the first and second legs of core 110, respectively, and may be provided to support mounting of windings (not depicted in FIG. 2) magnetically coupled to (and galvanically isolated from) windings 210 a and 210 b. According to features of the disclosure herein, first inner bobbin 213 a and second inner bobbin 213 b might not be used, and additional windings may be disposed directly around the first and second legs of core 110.
Reference is now made to FIG. 3, which depicts an “exploded” view of various elements of transformer 100. For simplicity and brevity, elements encompassing second leg L2 of core 110 are depicted. It is understood that optionally, similar or identical elements may encompass first leg L1 of core 110, in accordance with FIG. 2. Dotted lines terminated by arrows indicate order of layering: an arrow pointing at a first element, with a dotted line extending from the arrow to a second element, indicates that the second element may be disposed around (e.g., may partially or completely encompass) the first element.
Inner bobbin 213 b may encompass second leg L2. A first surface s1 of inner bobbin 213 b may fit around a first corresponding slot slot/of first inner shield lid 211 a (as shown in FIG. 2), and a second surface s2 of inner bobbin 213 b may fit through a corresponding slot (not depicted in FIG. 3) of second inner shield lid 211 b.
Windings 310 may be wound around inner bobbin 213 b. According to another implementation of transformer 100 of the disclosure herein, inner bobbin 213 b might not be used, and instead, windings 310 may be wound directly around second leg L2. Windings 310 may be constructed similarly to or the same as windings 210 a and 210 b, but may feature a different number of windings compared to windings 210 a and 210 b. Windings 310 may feature two or more voltage taps (e.g., voltage terminals) to be connected to voltage terminals of a power circuit (e.g., a full-bridge of transistors or diodes, or a different type of power electronics circuit). Shield leg 311 may be disposed around (e.g., may encompass) windings 310. Shield leg 311 may be attached to (e.g., manufactured together with, or later connected to) first shield lid 211 a and second inner shield lids 211 b, for forming an inner shield disposed around (e.g., encompassing) windings 310, and “shielding” windings 310 from strong electrical fields. The inner shield (e.g., one of first inner shield lid 211 a and second inner shield lid 211 b, and/or shield leg 311) may be connected to a first voltage tap of windings 310, and may be referenced to the same electrical potential as the first voltage tap of windings 310.
Shield leg 312 may be disposed around (e.g., may encompass) shield leg 311. Shield leg 312 may be attached to (e.g., manufactured together with, or later connected to) first and second outer shield lids 212 a and 212 b, for forming an outer shield disposed around (e.g., encompassing) shield leg 311. Insulating material (not explicitly depicted) may be injected between shield leg 311 and shield leg 312, between inner shield lid 211 a and outer shield lid 212 a, and between inner shield lid 211 b and outer shield lid 212 b. Shield leg 312, and outer shield lids 212 a and 212 b may be made of semiconductive material the same as or similar to shield lid 311, and inner shield lids 211 a and 211 b.
Windings 210 b may be wound around shield leg 312. Windings 210 b may feature two or more voltage taps (e.g., voltage terminals), with a first one of the voltage taps electrically connected to the outer shield (e.g., one of first and second outer shield lids 212 a, 212 b and/or shield leg 312) and referencing the outer shield to the same electrical potential as the first one of the voltage taps of windings 210 b.
Windings 210 b may be referenced (e.g., by direct electrical connection) to a first electrical potential, and windings 310 may be referenced to a second electrical potential that is different from the first electrical potential. For example, windings 310 may be referenced to ground, and windings 210 b may be referenced (e.g., electrically connected) to a potential that is 100V, 1000V, 10 kV, 20 kV, 50 kV, 100 kV, or even higher. Windings 310 may be referenced to a varying potential reference point. For example, windings 310 may be referenced voltage reference point varying (e.g., sinusoidally or as a square-wave) between, for example, −1 kV and +1 kV, −10 kV and +10 kV, −20 kV and +20 kV, −100 kV and +100 kV, or a varying (e.g., sinusoidal) potential having an amplitude above 100 kV or even above 1 MV.
As a result of windings 210 b and 310 being referenced to different potential levels, a voltage drop may exist between windings 210 b and 310. In accordance with the numerical examples above, the voltage drop may be large—for example, tens, hundreds or thousands of kilovolts. By electrically connecting windings 210 b to the outer shield and electrically connecting windings 310 to the inner shield, the voltage drop may exist between the inner shield and the outer shield. By designing the inner shield to be disposed around (e.g., encompass) the inner windings and by designing the outer shield to be disposed around (e.g., encompass) the inner shield, windings 210 b and windings 310 may be “shielded” and separated from one another by the shields. This may enable reducing the insulation around the wires used for the windings to a rating that may be far less than the potential difference between windings 210 b and windings 310. For example, windings 210 b may have a voltage drop of up to 1000V between two taps on windings 210 b. Similarly, windings 310 may have a voltage drop of up to 1000V between two taps on windings 310. Windings 210 b may be referenced to 20 kV, and windings 310 may be referenced to ground (0V). Without shielding, insulation of wires used for windings 310 and 210 b would be rated to withstand over 20 kV. Using inner and outer shields, as disclosed herein, may enable reducing the wire insulation to 100V, and disposing insulating material rated to withstand 20 kV between the inner shield and the outer shield, which may provide cost savings and/or may enable more efficient cooling of transformer elements such as core 110, windings 210 b and windings 310 b, as the transformer elements are not covered by large quantities of insulating material.
Insulating material between the inner and outer shields may be the same as the material used for manufacturing case 120, and may be injected during the formation of case 120. For example, a mold having the shape of case 120 may be placed around the elements of transformer 100 as depicted in FIG. 2, and insulating material (e.g. resin epoxy, silicon, polyurethane) may be injected into the mold, both creating case 120 and filling in a gap between the inner and outer shields. The injection may be, for example, vacuum potting, automatic pressure gelation, or other suitable methods of injection.
Bobbin 213 b, windings 310, shield leg 311, shield leg 312 and windings 310 b have been described with respect to leg L2 of core 110. Similar or identical elements (e.g., windings 210 a of FIG. 2, corresponding to windings 210 b; or bobbin 213 a of FIG. 2, corresponding to bobbin 213 b) may be disposed around leg L1 of core 110, to increase efficient use of core 110. For brevity, those elements have not been shown explicitly with respect to FIG. 3, but they are included in the scope of the disclosure herein.
Reference is now made to FIG. 4, which shows an X-Y cross-section of transformer 100, according to the X-Y-Z axes of FIG. 1, in accordance with the disclosure herein. For increased clarity, some reference numbers are shown more than once and indicate different parts of a single element that, due to the cross-section view, does not appear to be contiguous. Arrows indicating electrical field directions and magnitudes as obtained from an electrical simulation are also shown. Dark arrows indicate a weak field, and arrows having a lighter color indicate a stronger field. Windings 310 b correspond to windings 310 of FIG. 3, disposed over leg L2 of core 110. Windings 310 a are similar to windings 310 b, and are disposed over leg L1 of core 110. Shield leg 311 b corresponds to shield leg 311 of FIG. 3, disposed over leg L2 of core 110; and shield leg 311 a corresponds to another shield leg similar to shield leg 311 of FIG. 3, disposed over leg L1 of core 110. Shield leg 312 b corresponds to shield leg 312 of FIG. 3, disposed over leg L2 of core 110; and shield leg 312 a corresponds to another shield leg similar to shield leg 312 of FIG. 3, disposed over leg L1 of core 110.
The simulation included connecting a first square wave voltage generator producing a square wave varying between −700V and +700V to two terminals of windings 210 a (in the simulation, there are no additional voltage taps), a second square wave voltage generator substantially in-phase with the first square wave voltage generators, and producing a square wave varying between −700V and +700V to two terminals of windings 210 b. Windings 310 have 20% more turns than windings 210 a and 210 b, resulting in a square wave varying between −840V and +840V across windings 310 a and across windings 310 b. Windings 210 a and 210 b are referenced (in this example, directly connected to a potential of about 0V), and windings 310 a and 310 b are referenced to a voltage of about 10 kV. The simulation included placing transformer 100 in a grounded, conducting case (e.g., a box) having conducting sides spaced approximately 60 mm from the outer edges of transformer 100.
Area A as depicted in FIG. 4 refers to the space outside of transformer 100 (i.e., outside case 120). Area B is the area within casing 120 that is not between the semiconductive shields. Area C is the area between the semiconductive shields (e.g., between a shield leg 311 and shield leg 312, or between a shield lid 211 a and shield lid 212 a, or between a shield lid 211 b and shield lid 212 b. As shown by the field arrows, in area A, the electric field is of small magnitude, and flows outwards from transformer case 120 towards the conductive casing used in the simulation. In area B, the field is also weak, and flows in a somewhat “curved” (due to an “edge effect” present at edges of charged plates) direction from shield lid 212 a to shield lid 211 a, and from shield lid 212 b to shield lid 211 b. In area C, between the two shields, the electric field is strong (as indicated by light-colored arrows), and “flows” from the inner shield (formed by shield lids 211 a and 211 b, and shield legs 311 a and 311 b) to the outer shield (formed by shield lids 212 a and 212 b, and shield legs 312 a and 312 b.
Although examples are described above, features and/or steps of those examples may be combined, divided, omitted, rearranged, revised, and/or augmented in any desired manner. Various alterations, modifications, and improvements will readily occur to those skilled in the art. For example, legs L1 and L2 of core 110 may have round or oval cross-sections, rather than a rectangular cross-section; and shield legs 311 and 312 may have round or rectangular cross sections instead of an oval cross-section. As another example, core 110 may include a third leg, and each leg may feature more than two sets of windings and/or more than two shields. Such alterations, modifications, and improvements are intended to be part of this description, though not expressly stated herein, and are intended to be within the spirit and scope of the disclosure. Accordingly, the foregoing description is by way of example only, and is not limiting.

Claims

1. An apparatus comprising:

a transformer comprising:

a core comprising at least a first core leg,

first windings disposed around the first core leg,

a first semiconductive shield disposed around the first windings,

a second semiconductive shield disposed around the first semiconductive shield,

second windings disposed around the second semiconductive shield.

2. The apparatus of claim 1, further comprising a first bobbin disposed around the first core leg, wherein the first windings are wound around the first bobbin.

3. The apparatus of claim 1, wherein the first windings comprise at least two voltage taps, and a first voltage tap of the first windings is electrically connected to the first semiconductive shield.

4. The apparatus of claim 1, wherein the second windings comprise at least two voltage taps, and a first voltage tap of the second windings is electrically connected to the second semiconductive shield.

5. The apparatus of claim 1, wherein the first windings comprise at least two voltage taps,

wherein a first voltage tap of the first windings is electrically connected to the first semiconductive shield,

the second windings comprise at least two voltage taps, wherein a first voltage tap of the second windings is electrically connected to the second semiconductive shield,

wherein the first voltage tap of the first windings is connected to a first reference electrical potential, and the first voltage tap of the second windings is connected to a second reference electrical potential.

6. The apparatus of claim 5, wherein a voltage difference between the first reference electrical potential and the second reference electrical potential is above 100V.

7. The apparatus of claim 5, wherein a voltage difference between the first reference electrical potential and the second reference electrical potential varies sinusoidally.

The apparatus of claim 7, wherein a voltage difference between the first reference electrical potential and the second reference electrical potential varies according to a sine wave having an amplitude of 10 kV or higher.

8. The apparatus of claim 5, wherein the first reference electrical potential is electrical ground.

9. The apparatus of claim 15, wherein the second reference electrical potential is electrical ground.

10. The apparatus of claim 1, wherein the core comprises a second core leg, the transformer further comprising:

third windings disposed around the second core leg,

a third semiconductive shield disposed around the third windings,

a fourth semiconductive shield disposed around the third semiconductive shield,

fourth windings disposed around the fourth semiconductive shield.

11. The apparatus of claim 10, wherein the first windings and the third windings are connected to a first electrical potential, and the second windings and the fourth windings are connected to a second electrical potential.

12. The apparatus of claim 1, further comprising a conductive case, wherein the transformer is placed in the conductive case.

13. The apparatus of claim 12, wherein the conductive case is grounded.

14. The method of claim 11, further comprising insulating material disposed between the first semiconductive shield and the second semiconductive shield.

15. A method comprising:

winding a first winding around a first leg of a magnetic core,

disposing a first cylindrical shield around the first winding,

disposing a second cylindrical shield around the first shield,

disposing a second winding around the second shield,

electrically connecting the first winding to the first shield, and

electrically connecting the second winding to the second shield.

16. The method of claim 15, further comprising injecting insulating material between the first shield and the second shield.

17. The method of claim 15, further comprising encompassing the magnetic core, the first and second windings and the first and second shields in a case.

18. The method of claim 15, wherein the case is a resin epoxy case.

19. The method of claim 15, further comprising voltage terminals of the first winding to a voltage source.

20. The method of claim 15, further comprising voltage terminals of the second winding to a voltage source.

21. The method of claim 15, further comprising connecting the first winding to a first electrical potential, and connecting the second winding to a second electrical potential that is different form the first electrical potential.