Device for disconnecting DC circuits

Abstract

A disconnect device 100 for a direct current (DC) circuit comprises a first end 102 having a first electrical connector 108, a second end 104 having a second electrical connector 110, and a conduit 10

Description

Field of the Invention

[01] The present disclosure relates to a device for disconnecting (or isolating) direct current ‘DC’ circuits. In particular, the disclosure is concerned with a thermal disconnector device which breaks a DC circuit in response to a dangerous build-up of heat (e.g., fire) in the device. Yet more specifically, the thermal disconnect device is intended for use as an improved connector between solar panels in an array of such panels. Background

[02] Solar panels are renewable energy sources that generate electricity from the sun’s rays. Arrays of panels are commonly interconnected in series, each panel typically generating between 17 V to 50 V each, with a string of panels often generating overall voltages up to 900 V per string, or up to 1500 V in special large arrays with high voltage panels.

[03] The most common connector used for connecting solar panels are MC4 connectors. However, such connectors are known to be the source of many faults in solar arrays. Faults with the connector may arise from such sources as environment factors (such as vermin or inclement weather) and poor installation (for example handling the connectors under load or cross mating the connectors). The result is that an electric arc can form across the connector which can melt and damage the connector and surrounding materials. In extreme cases, the electric arc can result in a fire which causes further faults (and arcs) in other connectors, escalating the problem.

[04] As many as 10 fires a month occur in the UK from solar panels, many of which are attributed in some way to the panel interconnectors. Although solar panels themselves are not overly combustible, the frames, mounting systems, cables and boxes used to fit them are often highly combustible. Therefore, fires can spread quickly and may produce dangerous toxic chemicals as these substances bum.

[05] Hence an improved technique for connecting solar panels is highly desirable. Summary

[06] The present invention is defined according to the independent claims. Additional features will be appreciated from the dependent claims and the description herein. Any embodiments which are described but which do not fall within the scope of the claims are to be interpreted merely as examples useful for a better understanding of the invention.

[07] The example embodiments have been provided with a view to addressing at least some of the difficulties that are encountered with current methods of connecting solar panels whether those difficulties have been specifically mentioned above or will otherwise be appreciated from the discussion herein.

[08] In one aspect of the invention there may be provided a device for disconnecting (i.e., breaking or isolating) a direct current ‘DC’ conduction pathway in an array of solar panels. The device comprises a first end, a second end, and a conduit therebetween. The first end comprises a first electrical connector and the second end comprises a second electrical connector which are preferably configured as opposite sides of a cooperating connector pair (i.e., one male end, one female end, e.g., opposite sides of an MC4 connector). A resilient conductive element is arranged within the conduit, with a first end of the element couplable to the first electrical connector by a first thermally breakable (electrically conducting) connection, and a second end of the element couplable to the second electrical connector by a second thermally breakable (electrically conducting) connection, thereby electrically coupling the first electrical connector to the second electrical connector. The device comprises a first configuration (or state) in which direct current ‘DC’ is conductible between the first electrical connector and the second electrical connector via the first thermally breakable connection, the second thermally breakable connection and the resilient conductive element, which is the configuration the device is in when in use and under normal operation to conduct current in a solar array. In the first configuration, the resilient conductive element may be held under tension through the conduit. Suitably the device also comprises a second configuration (or state) in which at least one of the first thermally breakable connections and / or the second thermally breakable connections has been broken due to heating at one (or both) ends of the device causing the thermally breakable connection to break; this can happen due to a fault in the (MC4) connector causing an electrical arc. In this way the electrical connection between the first electrical connector and the second electrical connector may be broken to prevent further current flow through the device. In the second configuration, the resilient conductive element may be relaxed (i.e., no longer under tension), so as to create a gap between the end of the element and the electrical connector to which the end was attached before the thermally breakable connection broke, thus particularly mitigating the possibility of an electric arc from a faulty connector causing further damage.

[09] In an example, the gap created between the respective end of the resilient conductive element and the first / second electrical connector may be about 50 mm, which is particularly suitable for operating voltages of about 900 volts (V).

[10] In an example, the thermally breakable connections may be a low temperature solder, with a melting (i.e., breaking) temperature of about 120°C.

[11] In an example, the conduit may be at least partially transparent so that the resilient conductive unit is visible within the conduit.

[12] In an example, the resilient conductive element comprises a tension spring, which may comprise phosphor bronze or an equivalent copper alloy. As an example, the cable from which the spring is formed may be made from tinned copper spring platted wire. Suitably the spring may act as both resilient means and electrically conductive means and is particularly appropriate for 900 V (or thereabouts) systems. In another example, the conductive element of the resilient conductor may be separate to the resilient element (e.g., the device may comprise a separate conductive cable attached to the spring), which is more appropriate for systems greater than 900 V.

[13] In one example, the conduit may comprise an electrically insulating fluid, such as an oil with high dielectric strength. Preferably, the oil is translucent such that the spring is visible when arranged / displayed within the conduit. In this example the required gap to prevent arcing may be made significantly shorter, for example in the rage of about 15mm to 50mm.

[14] In one example, the device further comprises a first insulating layer and a second insulating layer disposed within the conduit proximate to the first end and the second end of the device respectively. In an example, the first / second insulator are formed from rubber. The insulator layers may each comprise an aperture through which the first / second end of the resilient conductive element may pass. In the second configuration, the end of the resilient conductive element may be pulled through the respective layer.

[15] In one example, each end of the resilient conductive element may be provided with a visual aid, or marker, which is suitably visible within the conduit.

[16] In a related aspect of the invention, there is provided a solar panel array comprising a set of solar panels interconnected in series and a set of disconnect devices connecting sequential panels in the set. For example, the set comprises a first solar panel and a second solar panel, and the set of disconnect devices comprises a first device arranged to electrically connect the first panel to the second panel.

[17] As used herein, unless otherwise expressly specified, all numbers such as those expressing values, ranges, amounts or percentages may be read as if prefaced by the word “about”, even if the term does not expressly appear. The term “about”, or “substantially”, when used herein means +1- 5% of the stated value. Also, any numerical range recited herein is intended to include all sub-ranges subsumed therein, and the terms “from” and “to” a pair of values are intended to indicate such values are included in the range. Singular encompasses plural and vice versa. Additionally, although the present invention has been described in terms of “comprising”, the processes, materials, and coating compositions detailed herein may also be described as “consisting essentially of’ or “consisting of’. Brief Description of the Drawings

[18] For a better understanding of the present disclosure reference will now be made by way of example only to the accompanying drawings, in which:

[19] Fig. 1 shows a solar panel array;

[20] Fig. 2 shows an example DC disconnect device in a first configuration;

[21] Fig. 3 shows an example resilient conductor;

[22] Fig. 4 shows the example DC disconnect device of Fig. 1 in a second configuration; and

[23] Fig. 5 shows another example DC disconnect device. Detailed Description

[24] At least some of the following example embodiments provide an apparatus for disconnecting a direct current ‘DC’ circuit. The example device is simple to fit and compatible with existing connectors used with solar panels. Many other advantages and improvements will be evident from the discussion herein.

[25] Figure 1 shows an example of a solar array 10. The array comprises a set, or string, of solar panels 12 interconnected in series; that is, a direct current (DC) flows from one end of the string of panels 12 to the other. In this example, the set 12 comprises a first panel 12a and a second panel 12b, representing two constituent parts of a plurality of such panels forming the string of panels 12. It will be appreciated that the string of panels 12 may comprise many tens of such panels. Each panel may generate a voltage, for example in the range of about 17 V to about 50 V, with the set / string of panels 12 comprising an overall voltage between 600 V and 1500 V, preferably about 900 V (and of course voltages in the ranges between about 600 V and about 900 V, and between about 900 V and about 1500 V).

[26] The solar array also comprises a disconnect device 100. The disconnect device 100 is provided to join electrical cabling 14a, 14b, connecting to the first and the second panel 12a, 12b, respectively. That is, the first panel 12a and the second panel 12b are connected via a first disconnect device 100. In particular, where the panels 12a and 12b are configured to couple via MC4 connectors (i.e., the end of the cables 14a, 14b are a mating pair of MC4 connectors), then the disconnect device 100 is suitably adapted to cooperate with those MC4 connectors (by e.g., comprising its own MC4 connector ends).

[27] Suitably, scaling to a string of multiple panels 12, a disconnect device 100 may be provided to connect adjacent (i.e., sequential) panels in the string 12. Put another way, if a string of panels 12 comprises N panels, then the array 10 may comprise N-1 disconnect devices 100, each device 100 being provided to electrically connect sequential panels 12a, 12b, etc. In another example, if the string of panels 12 comprises N panels, the system 10 may comprise N+1 disconnect devices 100, the two extra devices 100 in this example being provided at each end of the string of panels 12.

[28] The disconnect device 100 is provided to break the path of electric current between two sequential panels 12 under certain conditions, so as to prevent an unsafe build-up of electric charge and therefore fire. In particular, the disconnect device 100 is provided to mitigate the problem of MC4 connector faults leading to an electric arc which can cause, inter alia, fires in the solar array 10. More specifically, the disconnect device 100 comprises a first state, or configuration, in which the device 100 allows current flow between panels 12a and 12b, and a second state, or configuration, in which current cannot flow from panel 12a to panel 12b (i.e., the current flow is stopped, and arcing is prevented), as is explained in further detail below. Suitably, the disconnect device 100 may also be termed a DC isolator, as it breaks the circuit of the panel string 12 and thereby isolates one or more panels of the array 10.

[29] More generally, Fig. 1 can be thought of as demonstrating any DC circuit in which 12a and 12b represent two resistive units connected in series via the disconnect device 100. Suitably, instead of MC4 connectors, cabling 14 may comprise any suitable pair of mating connectors. That is, cable 14a may comprise a primary electrical connector, and cable 14b may comprise a correspondingly configured secondary electrical connector. For example, the primary electrical connector may comprise a male coupling part and the secondary electrical connector may comprise a female coupling part, or vice-versa, with the male coupling being receivable within the female coupling.

[30] Figure 2 shows an example of the device 100 in the first configuration. The device 100 comprises a first end 102, a second end 104, and a conduit 106 therebetween joining the first end 102 to the second end 104.

[31] The first end 102 comprises a first electrical connector 108 and the second end 104 comprises a second electrical connector 110. Here the first and second connectors 108,110 may form a mating pair of connectors. That is, the first connector 108 may be a male / primary connector and the second connector 110 may be a female / secondary connector. Suitably, consistent with the above, the first and the second connectors 108,110 may be corresponding parts of an MC4 connector. In other examples, not shown, the first and the second connectors 108, 110 may be the same, with corresponding mating opposites provided on the ends of the cable 14.

[32] The conduit 106 may be configured as a substantially hollow tube, the ends of which are sealed by the first and second connectors 108, 110, and may be formed from an electrically insulative material such as PVC (polyvinyl chloride), polycarbonate, PMMA (polymethyl methacrylate) or an equivalent clear acrylic material; here the tube is cylindrical, although it will be appreciated that other shapes are also possible. In a preferred example, the conduit is transparent so that the inside of the tube is visible. In some examples (not shown), only the conduit 106 proximate to each of the ends 102, 104 may be transparent, with a central region being at least partially opaque.

[33] The device 100 comprises a resilient conductive element 112 housed within the conduit 106. That is the element 112 is arranged within the hollow tube of the conduit 106. The resilient conductive element 112 is provided to electrically connect the first connector 108 and the second connector 110. The resilient conductive element 112 is suitably electrically conductive in order to facilitate the flow of electricity from one end 102, 104 to the other end 104, 102 through the device 100 (dependant on the direct of current flow of course). Here resilient includes the conductive element having a structure that may be extended and relaxed. In particular, when the element 112 is extended then the element 112 may be held in tension, and when the element 112 is relaxed (i.e., tension is released) the element may compress; i.e.,the element 112 in the relaxed state may be shorter than its state when under tension.

[34] In one example, the resilient conductive element 112 comprises a single component which is jointly electrically conductive and resilient. For example, the resilient conductive unit may be a tension spring. The spring may be formed of suitable size and material to carry at least 900V, so that it is suitable for use in a solar array 10. In a preferred example, the spring may be formed from phosphor bronze or an equivalent copper alloy.

[35] Figure 3 shows another example of the resilient conductive element 112, whereby the resilient conductive element 112 comprises a separate resilient component 114 and conductive component 116. In both cases, the resilient component 114 may be a spring as substantially just described, while the conductive component 116 may be a wire conductor (i.e., electrical cable) configured to carry suitable current, voltage, etc, for solar installations. Figure 3A shows an example of the conductor 116 passing through the centre of the spring 114, while Figure 3B shows an example of the conductor 116 being on the outside of the spring 114. In both cases the conductor 116 is attached to the spring 114, so that when the spring 114 is extended or compressed (i.e., relaxed), the conductor 116 is similarly extended or compressed in correspondence with the spring 114. This arrangement is particularly suitable in large solar installations where a jointly electrically conductive and resilient element 112 may not be suitable due to voltage drop.

[36] Returning to Fig. 2, the device 100 comprises a first thermally breakable connection 118 by which the resilient conductive element 112 is electrically coupled (at one end) to the first electrical connector 108, and a second thermally breakable connection 120 by which the resilient conductive element is electrically coupled (at the other end) to the second electrical connector 110.

[37] Suitably, in this first configuration of Fig. 2, direct current ‘DC’ is conductible between the first electrical connector 108 and the second electrical connector 110 via the first thermally breakable connection 118, the second thermally breakable connection 120, and the resilient conductive element 112.

[38] The first and the second thermally breakable connections 118,120 are configured so that they are conductive within a specific temperature range; if the thermally breakable connections 118,120 increase in temperature above their designed temperature range then they break. Suitably, the thermally breakable connections 118, 120 may comprise a low temperature solder. Here low temperature solder may be a solder with a melting point of at least 80 degrees centigrade (°C), which is above normal operating temperature for most solar array components, which may be in the region of 75 °C. Preferably, however, the solder may have a melting point of at least 120 °C in order to allow for increases in operational temperature above the norm.

[39] Figure 4 shows an example of the device 100 in its second configuration, in which at least one of the first 118 and / or the second 120 thermally breakable connection is broken (e.g., due to the solder melting), so that direct current is not conductible between the first electrical connector 108 and the second electrical connector 110. In this example the first thermally breakable connection 118 is shown as broken. Suitably, where the device is used as a coupling in a solar array 10, breakage of the thermally breakable connection 118, 120 means there is no electrical connection between the first solar panel 12a and the second solar panel 12b. Put another way, current flow between the string of solar panels 12 in the array 10 will be disconnected.

[40] Suitably, in the second configuration, the resilient conductive element 112 is no longer electrically coupled to the first and / or the second connector 108, 110. Rather, the resilient conductor 112, which was under tension in the first configuration, relaxes to a compressed form so as to create a gap 122 between the end of the resilient conductive element (here a first end 124) and the electrical connector to which that end was coupled (here 108). The size of the resilient conductive element 112 in its relaxed state is chosen so that the gap 122 is sufficiently large enough that current is unable to arc across the gap 122. Put another way, the gap 122 provides enough distance to inhibit electrical discharge.

[41] Suitably, a size of the resilient conductor 112 (e.g., tension spring), its resilient properties, and the size of the gap 122, are interrelated such that the device 100 may be adaptably designed based on the intended usage of the device 100 - i.e., based on the voltage that the device 100 is expected to carry. For example, where the voltage in use may be taken to be about 900V, the resilient conductor 112 may be configured to compress and cause a gap 122 of at least 50 mm. Where the usage voltage may be about 1000V, the resilient conductor 112 may be configured to yield a gap 122 of at least 60 mm. Where the usage voltage may be about 500V, the resilient conductor 112 may be configured to yield a gap 122 of at least 26 mm. It will be appreciated that other sized gaps 122 may be generated. For example, in addition to the gap sizes above, the resilient conductor 112 may be configured to generate gap 122 sizes of at least 18 mm, at least 20 mm, at least 42 mm, and at least 90 mm, with corresponding impact on the voltage at which the device 100 may be rated for,

[42] During installation of a solar array 10, many tens of panels may require coupling together via the example device 100. Likewise, maintenance of an array 10 may require checking many tens, or even hundreds, of such devices 100. Suitably, in order to provide a quick check that a device is expected to be operational, a visual aid, or marker, 126, may be provided at each end of the resilient conductive element 112, with the marker 126 being visible due to transparency of the conduit 106.

[43] Figure 5 shows another example disconnect device 100, which comprises all the features just discussed, but in which the conduit 106 comprises an electrically insulating fluid 128. The fluid may be an insulating oil, more specifically a contactor electrical insulating oil as used in high voltage switch gear, which is preferably translucent (so that the conductive element 112 and any marker 126 thereon is visible). In this example, the size of the gap 122 may be made smaller, so that the disconnect device 100 may be also made correspondingly shorter (at least along its major axis). Suitably, in this example, when in the second (broken) configuration the gap 122 may be in the range of about 15 mm to about 50 mm.

[44] Also, in this example the device 100 may comprise a first insulator 130 and a second insulator 132 arranged within the conduit 106, respectively, toward the first end 102 and the second end 104 of the device 100. Suitably, the first and the second insulators 130, 132 may comprise (or be entirely formed from) an electrically insulating material such as rubber, PVC (polyvinyl chloride) or contactor oil. In particular, in the present example the first and the second insulator 130,132 may be rubber rings. Suitably, in the first configuration. Each end of the resilient conductive element 112 extends through a suitable aperture in the first / second insulator 130,132; the first end 124 of the element 112 through the first insulator 130, and the other (second) end of the element 112 through the second insulator 132. In the second configuration, relaxation of the resilient conductive element 112 causes the relevant end of the element 112 to be pulled through the insulator 130, 132, thereby further reducing the potential for arcing between the (faulty) electrical connector 108, 110 and the element 112.

[45] In summary, exemplary embodiments of an improved DC disconnect device 100 have been described. Additionally, the described exemplary embodiments are convenient to manufacture and straightforward to use. The example device 100 may be manufactured industrially. An industrial application of the example embodiments will be clear from the discussion herein.

[46] Various combinations of optional features have been described herein, and it will be appreciated that described features may be combined in any suitable combination. In particular, the features of any one example embodiment may be combined with features of any other embodiment, as appropriate, except where such combinations are mutually exclusive. Throughout this specification, the term “comprising” or “comprises” means including the component(s) specified but not to the exclusion of the presence of others.

[47] Although preferred embodiment(s) of the present invention have been shown and described, it will be appreciated by those skilled in the art that changes may be made without departing from the scope of the invention as defined in the claims.

[48] Each feature disclosed in this specification may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.

[49] Attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference.

[50] The invention is not restricted to the details of the foregoing embodiment(s). The invention extends to any novel one, or any novel combination, of the features disclosed in this specification, or to any novel one, or any novel combination, of the steps of any method or process so disclosed.

Claims

1. A disconnect device for a direct current ‘DC’ circuit, comprising:a first end, a second end, and a conduit therebetween;the first end comprising a first electrical connector and the second end comprising a second electrical connector;a resilient conductive element arranged within the conduit; anda first thermally breakable connection and a second thermally breakable connection for electrically connecting a first end and a second end of the resilient conductive element to, respectively, the first electrical connector and the second electrical connector;wherein the apparatus comprises a first configuration in which direct current ‘DC’ is conductible between the first electrical connector and the second electrical connector via the first thermally breakable connection, the second thermally breakable connection, and the resilient conductive element; anda second configuration in which at least one of the first and / or the second thermally breakable connection is broken so that the direct current is not conductible between the first electrical connector and the second electrical connector.

2. The device of claim 1, wherein:in the first configuration the resilient conductive element is configured in tension; andin the second configuration, the resilient conductive unit is relaxed so as to generate a gap between at least one of the first and the second end of the resilient conductive unit and the respective first or second electrical connectorto which the end was connected.

3. The device of claim 1 or 2, wherein the gap is at least about 50mm.

4. The device of any preceding claim, wherein the first electrical connector is a male connector, and the second electrical connector is a female connector.

5. The device of claim 4, wherein the first electrical connector and the second electrical connector comprise at least one part of an MC4 connector.

6. The device of any preceding claim, wherein the first thermally breakable connection and the second thermally breakable connection are a low temperature solder.

7. The device of claim 6, wherein the low temperature solder has a breaking point of at least 120°C.

8. The device of any preceding claim, wherein the conduit is at least partially transparent.

9. The device of any preceding claim, wherein the resilient conductive element comprises atension spring.

10. The device of claim 9, wherein the spring comprises phosphor bronze or copper alloy.

11. The device of any preceding claim, wherein the resilient conductive element comprises a resilient element separate to a conductive element.

12. The device of any preceding claim, wherein the conduit comprises an electrically insulatingfluid.

13. The device of claim 12, wherein the electrically insulating fluid comprises oil.

14. The device of claim 13, wherein the oil is translucent.

15. The device of claims 12 to 14, wherein the gap is in the range of about 15 mm toabout 50 mm.

16. The device of any preceding claim, further comprising a first electrical insulator and a second electrical insulator arranged within the conduit, wherein the first end of the resilient conductor extends through the first electrical insulator, and the second end of the resilient conductor extends through the second electrical insulator.

17. The device of claim 16, wherein the first and the second electrical insulators comprise rubber, PVC (polyvinyl chloride) or contactor oil.

18. The device of any preceding claim, wherein the resilient conducting element comprises a visual indicator at each end.

19. A solar array comprising a set of solar panels interconnected in series and a set of disconnect devices according to any previous claim,wherein the set of solar panels comprises a first panel and a second panel, the set of disconnect devices comprises a first disconnect device, and the first panel and the second panel are connected via the first disconnect device.

20. The solar array of claim 19, wherein the set of solar panels are configured to generate an output voltage of at least about 900V.14

Images