Patent Publication Number: US-2023155333-A1

Title: Electrical Power Connector for Contacting an Elongated DC Power Distribution Busbar, and Method of Monitoring a Connection

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of the filing date under 35 U.S.C. § 119(a)-(d) of European Patent Application No. 21209013.8, filed on Nov. 18, 2021. 
     FIELD OF THE INVENTION 
     The present disclosure relates to an electrical power connector for contacting an elongated DC power distribution busbar and to a method of monitoring such a connection. 
     BACKGROUND 
     This disclosure generally relates to systems for distributing electrical power from a junction box to electrical devices via a busway or track, to which distribution sub-assemblies or power taps may be removably connected without shutting down the power supply. The busway or track includes multiple conductors, the busbars, to provide DC power. 
     Further, the Open Compute Project Foundation (OCP) was initiated in 2011 with a mission to apply the benefits of open source and open collaboration to hardware and rapidly increase the pace of innovation in, near and around data centers. As part of the OCP, DC power connectors are needed which are connecting to a busbar of a data center rack cabinet as part of a power supply. This connector has two poles, i.e. plus and minus, and is transmitting a current of e. g. 500 Ampere. For contacting an elongated flat busbar where the opposing surfaces are insulated against each other and can be connected to these opposing poles, the connector is a modified edge connector with spring contacts being pressed onto the busbar contact surface. The connectors are in particular used for power shelves, battery backup unit (BBU) shelves, IT trays/cubby shelves, or server sleds. 
     Because of the high current, the connector materials heat up. This temperature rise should normally stay within the required limits of the admissible maximum temperature of the respective application. 
     The proper function of the connector highly relies on the proper function of spring beams and that each of the multiple spring beams carry an even load. Vice versa, if one spring beam should have a malfunction, then the remaining spring beams will have to carry additional current load and therefore will heat up more. More heat will result in the risk that the spring properties of the remaining springs will soften and could cause higher contact resistance. This results again in more heat dissipation and could end up as a chain reaction with the result that the cabinet can catch fire. 
     SUMMARY 
     An electrical power connector includes a connector housing having a receptacle receiving an elongated DC power distribution busbar, a first spring contact element arranged at a first side of the receptacle and pressed with a contact area to a first surface of the elongated DC power distribution busbar, and a second spring contact element pressed to a second surface of the elongated DC power distribution busbar opposite the first surface. The second spring contact element is arranged at a second side of the receptacle opposite to the first side. The power connector includes a temperature sensing device arranged inside the connector housing and monitoring a temperature at the first spring contact element and/or the second spring contact element. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention may be understood by reference to the following description taken in conjunction with the accompanying figures, in which reference numerals identify features of the invention. 
         FIG.  1    is a perspective view of a power supply shelf for a data center; 
         FIG.  2    is a perspective view of the power supply shelf connected to a DC power busbar; 
         FIG.  3    is a perspective view of a cable harness with a power connector; 
         FIG.  4    is a perspective view of the power connector; 
         FIG.  5    is another perspective view of the power connector; 
         FIG.  6    is a perspective view of a spring contact element; 
         FIG.  7    is a perspective view of the power connector of  FIG.  4    without a housing; 
         FIG.  8    is a detail perspective view of the power connector of  FIG.  4    without the housing; 
         FIG.  9    is a schematic diagram of a temperature sensor; 
         FIG.  10    is a sectional perspective view of the power connector of  FIG.  4   ; 
         FIG.  11    is a sectional perspective view of an MID mounted temperature sensor; 
         FIG.  12    is a sectional perspective view of a temperature sensing device according to another embodiment with a housing; and 
         FIG.  13    is a detail perspective view of the temperature sensing device of  FIG.  12   . 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENT(S) 
     The accompanying drawings are incorporated into the specification and form a part of the specification to illustrate several embodiments of the present disclosure. These drawings, together with the description, serve to explain the principles of the disclosure. The drawings are merely for the purpose of illustrating examples of how the disclosure can be made and used, and are not to be construed as limiting the disclosure to only the illustrated and described embodiments. Furthermore, several aspects of the embodiments may form—individually or in different combinations—solutions according to the present disclosure. The following described embodiments thus can be considered either alone or in an arbitrary combination thereof. Further features and advantages will become apparent from the following more particular description of the various embodiments of the disclosure, as illustrated in the accompanying drawings, in which like references refer to like elements. 
     The present disclosure will now be further explained referring to the Figures, and firstly referring to  FIG.  1   .  FIG.  1    shows a perspective view of an exemplary power supply shelf  100  for a data center. The power supply shelf  100  may for instance be compatible to the open compute project (OCP). The power supply shelf  100  comprises a metal casing  102  with a cover  106  protecting the electronic components mounted on the power supply shelf  100 . The electronic components may, for instance, comprise AC/DC converters for providing a DC power from an AC source. The AC input power is connected to the power supply shelf  100  via input connectors  108 . The DC power is output via an electrical power connector  104  for contacting an elongated DC power distribution busbar. 
     Various electronic components, e. g. AC/DC converters, are connected to the input connectors  108  via input cables. Furthermore, a plurality of output cables  114  connected to the electronic components are attached to the power connector  104 . The power connector  104  has a receptacle  105  which in a mounted state partly encompasses the DC power distribution busbar to contact it in the manner of an edge connector. 
       FIG.  2    illustrates schematically the connection between the power supply shelf  100  and a DC power distribution busbar  116 . It should be noted that for reasons of simplifying the drawing, the input connectors  108  are not shown in  FIG.  3   . The elongated DC power distribution busbar  116  and the connector  104  have a common longitudinal axis  118 . The busbar  116  has a first electrically conductive surface  120  and a second electrically conductive surface  122 . The first electrically conductive surface  120  and the second electrically conductive surface  122  are arranged on opposing sides of the busbar  116 . Thus, the first electrically conductive surface  120  and the second electrically conductive surface  122  can be connected to a positive and a negative pole of the DC power, respectively. 
     The connector  104  grips the busbar  116  similar to a card edge connector. As will become more apparent from the following Figures, the connector  104  according to one example has spring contacts arranged opposite to each other so that the first electrically conductive surface  120  and the second electrically conductive surface  122  are electrically contacted by the electrical power connector  104 . 
       FIG.  3    schematically depicts an example of an electrical power connector  104  with a set of cables  114  attached thereto. However, it is clear that the electrical power connector  104  may also be designed to be connected to a flexible foil or to the conductive leads of a printed circuit board (PCB) for being connected the electronic components of the power supply shelf. 
     The electrical power connector  104  has an electrically insulating housing  124 , shown in  FIGS.  3  and  4   , which is for instance fabricated from a plastic material. Screw connectors  126  fix the electrical power connector  104  at the casing  102  of the power supply shelf  100 . As will become more apparent from the following Figures, the electrical power connector  104  comprises two rows of spring contact elements  128 , each row of spring contact elements  128  being configured to electrically contact one pole of the busbar  116 . 
     Turning now to  FIGS.  4  and  5   , these Figures show the electrical power connector  104  in more detail. The electrical power connector  104  comprises a row of equidistantly arranged first spring contact elements  128 A and, opposite to the first spring contact elements  128 A, a symmetrical row of equidistantly arranged second spring contact elements  128 B. This construction allows for an evenly distributed contact force applied to the busbar and thus an evenly distributed current density. These spring contact elements are protected by a spring contact housing  139 . The spring contact housings  139  are integrally formed with the remaining connector housing  124 . Openings  136  are arranged at lateral mounting flanges  138  so that the connector  104  can be screwed to the power supply shelf  100 . 
     When attached to the busbar  116  of  FIG.  2   , the first spring contact elements  128 A contact the side of the busbar which represents the plus pole, while the second spring contact elements  128 B contact the opposing side of the busbar which represents the minus pole. 
       FIG.  6    shows the plurality of spring contact elements  128 A which are for instance integrally formed with a contact plate  110 A. The contact plate  110 A and the spring contact elements  128 B are, in an embodiment, formed as a stamped and bent metal part. The contact plate  110 A is connected to the output cables of one polarity (e. g. the positive polarity as shown in  FIG.  5   . Although not shown in the drawings, the opposing spring contact elements  128 B of the electrical power connector  104  are formed mirror-symmetrically and are integrally fabricated with a contact plate to be connected to the output cables of the opposing polarity (here the negative polarity). 
     The spring contact elements  128  are each formed as resilient, unilaterally cut free spring arms with a contact region  112  for contacting the busbar  116  at the free end. The contact plate  110  with the spring contact elements  128  may, for instance, be fabricated from copper or steel. This construction allows a particularly easy connecting and disconnecting to/from the busbar  116  and is safe in that the spring forces are monitored via the temperature sensing devices  130 . The opposing end of the spring arm has a connecting region at its fixed end which is connectable to a component to be provided with DC power. This may for instance be a crimp connection, a solder connection, a press-fit connection, a welded connection, or a plug connection. Any suitable form of a stable electrical connection can be used for contacting the spring contact elements  128  at their contact region  112 . 
     Furthermore, as illustrated in  FIG.  7   , where the housing  124  is not shown, the connector  104  comprises secondary springs  132  and a retaining bracket  134  for pressing the spring contact elements  128  towards the busbar  116 . 
     It could be shown that it is essential for a failure free and safe operation that the spring forces of the first and second spring contact elements  128 A,  128 B are constant and remain essentially identical for all the spring contact elements  128 . The same is valid for the spring characteristics of the secondary springs  132  and the retaining bracket  134 . If the spring characteristics deteriorate due to a temperature rise, the spring forces lessen and the electrical resistance at the contact between the spring contact element  128  and the busbar surface increases. This increase in electrical resistance damages the spring contact element even more and a compounding effect resulting in the connector housing catching fire may occur. By attaching a temperature sensing device close to the secondary spring element  132 , an overheating of this component as well as a decline of the spring force can be detected at an early stage. 
     In order to be aware of any rise in temperature which gives an early indication of an impending failure, the present disclosure proposes to arrange a temperature sensing device inside the connector housing  124 . As can be seen from  FIG.  7   , for instance a temperature sensor, e. g. a thermocouple,  130  may be arranged in close vicinity with at least one of the rows of first and second spring contact elements  128 A,  128 B. Importantly, the temperature sensor  130  registers a rise in temperature at a very early stage of a deterioration of the electrical contact. The temperature sensor  130  may be in close vicinity, for example directly opposite, to a contact area in which the first spring contact element  128 A contacts the first surface  120  of busbar  116 . 
     The output signal of the thermocouple  130  can be used to generate a warning signal long before the danger of a compounding reaction arises. Providing the temperature sensing device  130  inside the housing  124  and as close as possible to the spring contacts  128 A,  128 B allows to detect a beginning failure condition before an irreversibly critical situation has been reached. In other words, a potential loss of the material characteristics of the spring contact can be detected in an early stage. 
     Temperature sensors essentially comprise an outer protective housing that is in contact with a medium to be monitored, and a temperature sensitive element which is arranged inside the protective housing and transduces the sensed temperature into the electrical output signal. In order to achieve fast response time and an accurate measurement, it is essential that a particularly good thermally conductive connection is provided between the temperature sensitive element and the outside medium, so that the temperature at the site of the temperature sensitive element mirrors the temperature outside the protective housing as exactly as possible. Any suitable type of temperature sensing element can be used in a temperature sensing device  130 . For instance, said temperature sensing element comprises a resistive temperature detector (RTD), a thermistor, or a silicon-based temperature sensor. 
     In particular, silicon IC sensors which use single-crystal silicon permit on-chip fabrication of IC (integrated circuit) enhancements. However, the use of IC processes also restricts the operation of silicon-based temperature sensors to an upper limit of about 150° C. Two types of silicon sensors are in general use: spreading resistance based on bulk charge conduction and pn-junction voltage difference. Further, thermistors are based on ceramic-oxide compositions are manufactured to exhibit NTC or PTC (negative, or positive, temperature coefficient) resistance characteristics, where resistance of the sensors decrease, or increase, several orders of magnitude as temperature is increased. NTC sensors offer many advantages for temperature measurement, e.g. small size, durable stability, high accuracy, and precision. In so-called RTD (Resistive Temperature Detector) high-temperature sensors, a platinum-film sensing element is printed and then embedded inside an alumina-ceramic layered structure. The resistance of the platinum element linearly increases as temperature is increased. 
     A thermoelement sensor consists of two unequal metals, joined to each other at one end. The temperature is measured at this branching. The two metals generate a small voltage, which can be measured and evaluated by a control system. The unequal metals are insulated individually, and with the help of a jacket a tight bifilar configuration is maintained. Thermoelement sensors have the advantage of a wide operating temperature range, largely constant sensitivity over their entire range, and availability in suitable miniaturized sizes. 
       FIG.  8    illustrates a detail of  FIG.  7   . It should be noted that, in this Figure, the harness of output cables  114  is only represented in a simplified schematic manner. As shown in  FIG.  8   , the thermocouple  130  may have a two-pole wiring  140  which can be connected to a control unit arranged inside the power supply shelf. The control unit may evaluate the output signal of the temperature sensor  130  and compare it to a pre-defined threshold value of a maximum admissible temperature. Additionally or alternatively, also a time dependent temperature profile can be monitored in order to anticipate a potential risk of spring force degradation. In  FIG.  8    a thermocouple  130  is shown which exemplarily may be used as a temperature sensing device according to the present disclosure. 
     As an alternative, also a thermistor may be used as the temperature sensor.  FIG.  9    exemplarily illustrates a micro thermistor probe  130 . Such micro thermistor probes are advantageous in that they provide a rapid temperature response and can be mounted where space is limited. These miniature thermistors are potted in a polyimide tube with a thermally conductive epoxy. The sensing element comprises an NTC sensor, i. e. a sensor with negative temperature coefficient resistance characteristics, where resistance of the sensor decreases several orders of magnitude as temperature increases. 
     Of course, any other suitable temperature sensing means may also be used as the temperature sensor  130 . The temperature sensing device  130 , in various embodiments, may comprise at least one temperature sensing element formed by a positive temperature coefficient, PTC, thermistor, and/or a negative temperature coefficient, NTC, thermistor, and/or a non-linear thermal resistor, and/or a pyroelectric sensor, and/or a bimetallic sensor. 
     In order to monitor a plurality of spring contact elements more closely and thus enhance the operational safety of the power connector, the temperature sensing device  130  may comprise two or more temperature sensing elements. In an embodiment, these temperature sensing elements are arranged distanced apart along a longitudinal axis which in operation extends along the longitudinal axis of the busbar  116 . 
     In order to provide a smart connector comprising some degree of intelligence, the temperature sensing device  130  is formed as an integrated component comprising an analog-digital-converter for generating a digital output signal. 
     As an alternative to using a transducer element that outputs a signal indicative of a temperature, the temperature sensing device  130  may comprise a current sensing unit for monitoring a current value at the at least one first and/or second spring contact element  128 A,  128 B and an evaluation unit which is operable to calculate the temperature from the sensed current value. 
     As the main current flows generate magnetic fields, it is possible to place one or more coil like sensors at the contact areas to measure the power of the magnetic fields, if a field gets weaker in a certain area it would indicate that current goes down because of higher contact resistance—this indicates a energy loss by heat dissipation. Of course, any other magnetic field sensor may also be used, e. g. a Hall-effect sensor. 
     According to a further advantageous example, the temperature sensing device  130  comprises a separately housed sensor unit which is arranged to be in direct mechanical contact with the at least one first and/or second spring contact element  128 A,  128 B. This allows the use of prefabricated components and even a retrofitting of existing connectors. An advantage of using such separately housed components can be seen in the fact that already existing connectors  104  may be retrofitted with a temperature sensing device. 
     However, also an integrated solution based on an MID component may advantageously be used. As mentioned above, MID is the abbreviation of the term “molded interconnect device” and comprises a three-dimensional circuit carrier which is injection molded from a modified polymeric material. This modification may allow laser activation of circuit tracks on the surface of the circuit carrier. The activated areas become metallized in a chemical metallization bath in order to build conductive tracks which are thus extending into the third dimension. Apart from laser direct structuring (LDS) techniques (additive as well as subtractive) also a two-shot injection molding, hot embossing, and insert molding can be used for fabricating a three dimensional substrate that may be employed for assembling a temperature sensing unit according to the present disclosure. Advantageously, the connector housing may at least partly be formed as a molded interconnect device, having a plurality of conductive leads, wherein the temperature sensing means is mounted at the connector housing and is connected to the conductive leads. 
     If an LDS printed conductor path or any other 2D or 3D conductor printing process according to MID and/or LDS technology is applied to one of the inner half of the insulation body of the connector housing, then a digital sensor temperature sensor can be applied directly in the area of the contact springs and no wiring will be needed to connect a sensor in that area. Applying such sensor gives additional benefits as the digital sensor can be also packed as a system-on-chip (SOC) with an integrated microcontroller. Therefore, the sensor advantageously may be programmed to give a signal output which indicates an error. Such a smart connector may be operable to perform self-diagnosis and may also be part of a decentralized monitoring and safety system. 
     The present invention results in the higher integration of temperature diagnostics for a busbar/card edge style connector by placing temperature sensing devices  130  directly at the contact spring, using conventional wired sensor components or MID/LDS technologies for the wiring. Of course, also a wireless communication interface can be provided for outputting the error signal. 
       FIG.  10    shows a sectional view of the electrical power connector  104 . According to a further advantageous example of the present disclosure, the temperature sensing device may also be integrated into the housing material, e. g. directly into at least one of the spring contact housings  139 . 
     A first example is shown in  FIG.  11   , where the spring contact elements  128  and the output cable  114  are removed to show the inner surface  146  of the connector housing  124 . As schematically illustrated, a lead pattern  144  is arranged on the inner surface of the connector housing  124 . A, for example, digital temperature sensor  142 , an integrated component, may be soldered to the electrically conductive lead pattern  144 . The digital temperature sensor  142  is exemplarily depicted as a surface mount device (SMD) digital sensor. Alternatively, a discrete voltage temperature sensor  143  may also be used. 
     The advantage of this arrangement can be seen in providing a connector where the temperature detection as well as a basic signal evaluation can be performed directly at the site to be monitored. The safety and robustness of the electrical power connector can thus be enhanced. 
     According to a further example of the present disclosure, the inner surface  146  of the connector housing  124  may directly provide the substrate for a temperature sensor. For instance, as schematically shown in  FIGS.  12  and  13   , lead patterns  144  forming one or more temperature sensors may be deposited directly onto the inner surface  146  of the spring contact housing  139 . 
       FIG.  13    shows an example of such a temperature sensor  130  formed by a pattern  144  of resistive leads on the inner surface  146  of the spring contact housing  139 . The resistive leads may for instance form a platinum resistance sensor. Alternatively, coil style sensors which measure the magnetic field strength may be used for indirectly measuring the temperature. 
     This extremely high level of integration allows for a minimal space requirement, a reduced component complexity and enhanced fabrication efficiency, and at the same time provides high accuracy and operational safety of the temperature monitoring process. 
     A method according to an embodiment of monitoring a connection between at least one electronic component to a DC power distribution busbar  116 , using such an electrical power connector  104 , comprises the following steps: 
     connecting the electrical power connector  104  to the elongated DC power distribution busbar  116 , so that the at least one first spring contact element  128 A contacts a first pole  120  of said DC power distribution busbar and the at least one second spring contact element  128 B contacts a second pole  122  of said DC power distribution busbar, 
     connecting the temperature sensing device  130  to a control unit which reads an output signal of the temperature sensing device  130  and generates a warning signal if the output signal is indicative of an abnormal operational state. 
     Such a warning (or alarm) signal allows the system to react to the abnormal state in an early state, so that no catastrophic event such as a fire results. For instance, the output signal of the temperature sensing device  130  may be compared to a predefined temperature threshold value, and the warning signal is generated if the output signal exceeds the threshold value. In order to create an early warning system, this threshold can be chosen to be much lower than the actual admissible maximum temperature of the connector components. 
     As mentioned above, an alternative method of determining the temperature at the spring contact elements  128  involves determining the current density at the at least one first and/or second spring contact element  128 A,  128 B and calculating the respective temperature therefrom. Such a temperature measurement without a dedicated sensor by monitoring e. g. the current through the device and using of connector specific algorithms to calculate the critical thermal energy reduces the required space and enhances the accuracy of the monitoring. 
     Coil style sensors which measure the magnetic field strength are used for indirectly measuring the temperature. Of course, any other magnetic field sensor may also be used, e. g. a Hall-effect sensor. 
     Furthermore, advantageously the control unit is arranged inside the electrical power connector, and the warning signal is a shutdown signal which disconnects the at least one electronic component from the DC power distribution busbar. Thus, a particularly fast reaction to a potential failure and fire hazard can be achieved. 
     The present disclosure adds a temperature sensing device, such as the thermistor  130 , in the area of the spring contact elements  128 . Customers can, for instance, implement the data provided from the thermistor  130  into a permanent diagnostics routine which can be linked to an alarm system. In case of failure, the alarm system which could for example switch off the  500  A load from the connector and by doing this may avoid fire hazard. For an even more precise thermal diagnostic there may be also applied two or more thermistors  130 , so that default parameter changes (like an increase of the ambient temperature) could be excluded from the control diagnostics. Thus, an individual thermistor showing alarming parameters can be identified. In other words, a predictive maintenance of the connector can be achieved, enhancing the safety of the connector in operation.