Temperature sensor of thermal monitoring system for use in power distribution systems

A temperature sensor of a thermal monitoring system is provided for use in power distribution systems. The temperature sensor comprises ceramic printed circuit board (PCB) and a terminal. The ceramic PCB includes a temperature sensing element disposed on a side of the ceramic PCB. The terminal is configured to be fixed directly in contact with a measured point and is directly in touch with the ceramic PCB such that heat is conducted from the terminal, through the ceramic PCB and then to the temperature sensing element. The temperature sensing element is configured to generate an electrical signal in response to the heat such that the electrical signal is sent through a pair of lead wires to a controller for monitoring a temperature. The temperature sensor further comprises an epoxy to seal a portion of the terminal, the ceramic PCB in its entirety and a portion of the pair of lead wires to ensure a desired physical strength and a desired dielectric strength.

BACKGROUND

Aspects of the present invention generally relate to a temperature sensor of a thermal monitoring system for use in power distribution systems. The temperature sensor comprises a thermally conductive, electrically insulating ceramic material. The temperature sensor uses a direct contact to a measured joint and uses wired connections to transmit a signal.

2. Description of the Related Art

Abnormal situations, such as faulty installation and overloading, can cause substantial thermal rise in power distribution systems. Therefore, there is a need to have a continuous thermal monitoring system to monitor temperature rise in power connection joints, lugs and cables in various installation components. As an important part of the thermal monitoring system, a temperature sensor is needed. The temperature sensor needs to be easily installable, reliably sensing temperatures at a measured point, capable of withstanding the required system voltage and within a reasonable price range.

There are three kinds of sensor design concepts that have been implemented in the market. First kind of thermal monitoring systems use infrared (IR) sensors for temperature sensing. The infrared sensor is not in direct touch to the high voltage system, therefore eliminates concerns on electric breakdown. And such systems are generally more cost friendly. However, the measured joints need to be painted to certain colors, usually black, and the painting process is not user friendly. Also, the IR sensor can also pick up signals emitted by other than the measured joint, which can skew the measurement.

To avoid these drawbacks of IR sensors, second kind of thermal monitoring systems use a thermal sensor in a direct contact with the measure joint, and the sensing is done with thermocouples or components alike. To avoid electric breakdown due to the high system voltage, there have been two ways to transmit signals between the sensors and the control system. First is to use fiber optics to transmit the temperature signal back to the controller. While achieving the requirements, such sensor design can be costly to the end customers. Second is to use battery to send signal from temperature sensors through wireless connections. Such method requires battery powered thermal sensors to generate an active signal, and hence has the drawback of having to replace the battery for maintenance. It also has to ensure good wireless connections for reliable signal reading.

Third kind of thermal monitoring systems use RF powered temperature sensors. In such systems, one or more antennas are used to send RF signals to the sensors attached to the measured joints. At different temperatures, the sensors reflect the RF signal with different frequencies, but detecting the change in the reflected frequency, the temperature can be detected. Such systems are also costly and sensitive to the antenna-sensor arrangements.

Therefore, there is an ongoing need for a suitable temperature sensor of a thermal monitoring system for use in power distribution systems that is capable of providing a reliable temperature reading while being cost friendly.

SUMMARY

Briefly described, aspects of the present invention relate to a temperature sensor of a thermal monitoring system for use in power distribution systems that is capable of providing a reliable temperature reading while being cost friendly. The proposed sensor uses a direct contact to a measured joint, and uses wired connections to transmit a signal. Therefore, concerns on receiver arrangements (wireless, RF or IR) are eliminated. The temperature sensor comprises a thermally conductive, electrically insulating ceramic material. A ceramic printed circuit board (PCB) has a reasonable price point therefore utilizing such material significantly drives down the cost of the temperature sensor. The use of the ceramic PCB makes the temperature sensor more cost friendly when compared to fiber optics and all the other concepts.

In accordance with one illustrative embodiment of the present invention, a temperature sensor of a thermal monitoring system is provided for use in power distribution systems. The temperature sensor comprises a ceramic printed circuit board (PCB) having a first side and a second side. The ceramic PCB includes a temperature sensing element disposed on the second side of the ceramic PCB. The temperature sensor further comprises a terminal having a first end and a second end. The first end of the terminal is configured to be fixed directly in contact with a measured point and the second end of the terminal is directly in touch with the first side of the ceramic PCB such that heat is conducted from the terminal, through the ceramic PCB and then to the temperature sensing element. The temperature sensing element is configured to generate an electrical signal in response to the heat. The temperature sensor further comprises a pair of lead wires. The electrical signal generated by the temperature sensing element is sent through the pair of lead wires to a controller for monitoring a temperature. The temperature sensor further comprises an epoxy to seal a portion of the terminal, the ceramic PCB in its entirety and a portion of the pair of lead wires to ensure a desired physical strength and a desired dielectric strength.

In accordance with one illustrative embodiment of the present invention, a thermal monitoring system for use in power distribution systems. The thermal monitoring system comprises a controller for temperature monitoring and a temperature sensor coupled to the controller. The temperature sensor comprises a ceramic printed circuit board (PCB) having a first side and a second side. The ceramic PCB includes a temperature sensing element disposed on the second side of the ceramic PCB. The temperature sensor further comprises a terminal having a first end and a second end. The first end of the terminal is configured to be fixed directly in contact with a measured point and the second end of the terminal is directly in touch with the first side of the ceramic PCB such that heat is conducted from the terminal, through the ceramic PCB and then to the temperature sensing element. The temperature sensing element is configured to generate an electrical signal in response to the heat. The temperature sensor further comprises a pair of lead wires. The electrical signal generated by the temperature sensing element is sent through the pair of lead wires to a controller for monitoring a temperature. The temperature sensor further comprises an epoxy to seal a portion of the terminal, the ceramic PCB in its entirety and a portion of the pair of lead wires to ensure a desired physical strength and a desired dielectric strength.

DETAILED DESCRIPTION

To facilitate an understanding of embodiments, principles, and features of the present invention, they are explained hereinafter with reference to implementation in illustrative embodiments. In particular, they are described in the context of a temperature sensor (with epoxy or plastic material) of the thermal monitoring system for use in the power distribution systems. The temperature sensor comprises a ceramic printed circuit board (PCB) made of a thermally conductive, electrically insulating ceramic material. The temperature sensor uses a direct contact to a measured joint and uses wired connections to transmit a signal. The temperature sensor provides a continuous thermal monitoring system to monitor a temperature rise in power connection joints, lugs and cables in various installation components. The temperature sensor is easily installable, reliably senses temperatures at a measured point, capable of withstanding any required system voltage and within a reasonable price range. Embodiments of the present invention, however, are not limited to use in the described devices or methods.

Consistent with one embodiment of the present invention,FIG. 1represents a representation of a temperature sensor (without epoxy or plastic material)5of a thermal monitoring system7for use in a power distribution system10in accordance with an exemplary embodiment of the present invention. The thermal monitoring system7comprises a controller12for temperature monitoring. The thermal monitoring system7comprises the temperature sensor5coupled to the controller12(although this generally is a correct illustration, our exact setup is that each sensor goes to a module, and a group of modules are connected to one controller). The temperature sensor5includes a ceramic printed circuit board (PCB)15having a first side17(1) and a second side17(2). The ceramic PCB15includes a temperature sensing element20disposed on the second side17(2) of the ceramic PCB15. The temperature sensor5includes a terminal22having a first end25(1) and a second end25(2). The first end25(1) of the terminal22is configured to be fixed directly in contact with a measured point27and the second end25(2) of the terminal22is directly in touch with the first side17(1) of the ceramic PCB15such that heat is conducted from the terminal22, through the ceramic PCB15and then to the temperature sensing element20.

For example, the ceramic PCB15may be made of a ceramic material that is an inorganic, non-metallic, often crystalline oxide, nitride or carbide material. Some elements, such as carbon or silicon, may be considered ceramics. Ceramic materials are brittle, hard, and strong in compression, weak in shearing and tension. The crystallinity of ceramic materials ranges from highly oriented to semi-crystalline, vitrified, and often completely amorphous (e.g., glasses). Most often, fired ceramics are either vitrified or semi-vitrified. Varying crystallinity and electron consumption in the ionic and covalent bonds cause most ceramic materials to be good thermal and electrical insulators. Ceramics generally can withstand very high temperatures, such as temperatures that range from 1,000° C. to 1,600° C. (1,800° F. to 3,000° F.). Glass is often not considered a ceramic because of its amorphous (non-crystalline) character. However, glassmaking involves several steps of the ceramic process and its mechanical properties are similar to ceramic materials. Crystalline ceramic materials are not amenable to a great range of processing. The glass is shaped when either fully molten, by casting, or when in a state of toffee-like viscosity, by methods such as blowing into a mold. If later heat treatments cause this glass to become partly crystalline, the resulting material is known as a glass-ceramic.

The physical properties of a ceramic substance of the ceramic PCB15are a direct result of its crystalline structure and chemical composition. Solid state chemistry reveals the fundamental connection between microstructure and properties such as localized density variations, grain size distribution, type of porosity and second-phase content, which can all be correlated with ceramic properties such as mechanical strength a by the Hall-Petch equation, hardness, toughness, dielectric constant, and the optical properties exhibited by transparent materials. Mechanical properties are important in structural and building materials as well as textile fabrics. They include many properties used to describe the strength of materials such as: elasticity/plasticity, tensile strength, compressive strength, shear strength, fracture toughness & ductility (low in brittle materials), and indentation hardness. Some ceramics are semiconductors. Most of these are transition metal oxides that are II-VI semiconductors, such as zinc oxide. For example, the ceramic PCB15may be made of a ceramic material that has a high dielectric strength and a high thermal conductivity.

In operation, the temperature sensing element20is configured to generate an electrical signal30in response to the heat. The temperature sensor5further includes a pair of lead wires32(1-2). The electrical signal30generated by the temperature sensing element20is sent through the pair of lead wires32(1-2) to the controller12for monitoring a temperature35. The terminal22comprises a material with high thermal conductivity. The terminal22is configured to conduct the heat from the measured point27to the temperature sensing element20and the terminal22provides a means to connect the temperature sensor5to the measured point27. The terminal22may be a ring lug which is configured to be bolted onto the measured point27. The terminal22may be a cylindrical tube which is configured to be attached to cables with wire ties.

The temperature sensor5further includes an epoxy (not shown) to seal a portion of the terminal22, the ceramic PCB15in its entirety and a portion of the pair of lead wires32(1-2) to ensure a desired physical strength and a desired dielectric strength. The epoxy is either an insulating epoxy or a plastic material. The epoxy serves as a mechanical stress relief when the temperature sensor5is being handled.

The ceramic PCB15provides a dielectric insulation between the terminal22being a high voltage part and the temperature sensing element20being a low voltage part. The ceramic PCB15provides heat conduction from the terminal22to the temperature sensing element20. The ceramic PCB15comprises a material with high thermal conductivity. For example, the material with high thermal conductivity may be aluminum nitride.

To ensure good heat conduction both the terminal22and the temperature sensing element20are directly soldered to the ceramic PCB15. A heat conducting grease (not shown) may be disposed in between the terminal22and the ceramic PCB15and in between the temperature sensing element20and the ceramic PCB15. In one embodiment, the temperature sensing element20may be a sensing chip, such as TI LMT01.

The temperature sensing element20may be a thermocouple. This thermocouple may be an electrical device consisting of two dissimilar electrical conductors forming electrical junctions at differing temperatures. Such thermocouple produces a temperature-dependent voltage as a result of the thermoelectric effect, and this voltage can be interpreted to measure temperature. The thermocouple may be self powered and require no external form of excitation. When different metals are joined at the ends and there is a temperature difference between the joints, a magnetic field is observed. The magnetic field is due to a thermo-electric current. The voltage generated at a single junction of two different types of wire is what is of interest as this can be used to measure temperature at very high and low temperatures. The magnitude of the voltage depends on the types of wire being used. Generally, the voltage is in the microvolt range and care must be taken to obtain a usable measurement from a very little current flow. In the standard configuration for thermocouple usage, the desired temperature Tsenseis obtained using three inputs—the characteristic function E(T) of the thermocouple, the measured voltage V, and the reference junctions' temperature Tref. The solution to the equation E(Tsense)=V+E(Tref) yields Tsense. The measured voltage V can be used to calculate temperature Tsenseprovided that temperature Trefis known. To obtain the desire measurement of Tsense, it is not sufficient to just measure V. The temperature at the reference junctions Trefmust be already known. Thermocouples as measurement devices are characterized by a precise E(T) curve, independent of any other details. Characteristic functions for thermocouples that reach intermediate temperatures, as covered by nickel-alloy thermocouple types E, J, K, M, N, T.

The ceramic PCB15serves two purposes. First, it provides dielectric insulation between the high voltage part (the terminal22) and the low voltage part (temperature sensing element20). Second, it provides heat conduction from the terminal22to the sensing element20. Ceramic in general has a wide range of thermal conductivities. To achieve good heat conduction, a material with high thermal conductivity, such as aluminum nitride, should be used. Also to ensure good heat conduction, both the terminal22and the temperature sensing element20are directly soldered to the ceramic PCB15. If solder is not used, a heat conducting grease or alike may be used in between components. The temperature sensing element20can be either a thermocouple or other type of the temperature sensor. The electrical signal30generated by the temperature sensing element20is then transmitted through the pair of lead wires32(1-2) to the controller12for temperature monitoring.

Referring toFIG. 2, it illustrates a representation of a temperature sensor200(with epoxy or plastic material) of the thermal monitoring system7for use in the power distribution system10in accordance with an exemplary embodiment of the present invention. The temperature sensor5further includes an epoxy217to seal a portion of the terminal22, the ceramic PCB15in its entirety and a portion of the pair of lead wires32(1-2) to ensure a desired physical strength and a desired dielectric strength. The epoxy217is either an insulating epoxy used for sealing or a plastic material in that sealing is done through an injection molding process. The epoxy217serves as a mechanical stress relief when the temperature sensor5is being handled. The temperature sensor200further comprises a plastic housing220disposed around the epoxy217.

Turning now toFIG. 3, it illustrates a top view of a ring lug design300of the terminal22for bolt-on applications in accordance with an exemplary embodiment of the present invention. A portion of the ring lug design300of the terminal22that is inside the epoxy217has a holding slot305which is filled with epoxy such that when the terminal22is pulled the holding slot305directly acts on the epoxy217instead of relying on a surface bond in order to ensure a force is not acted on a PCB joint.

FIG. 4illustrates a side view of the ring lug design300of the terminal22ofFIG. 3in accordance with an exemplary embodiment of the present invention. The ring lug design300may comprise a ring400and a stem405extending away from the ring400. The ring400and the stem405may be made of a metal or a metal alloy such as copper or aluminum. The ring lug design300may comprise a bend410in between the ring400and the stem405such that the ring400and the stem405may not be at a same level. In particular, the ring400will be at a lower level415(1) than a level415(2) of the stem405when the temperature sensor5or200is laid flat on a surface.

As seen inFIG. 5, it illustrates a top view of a tube design500of the terminal22for wire tie applications in accordance with an exemplary embodiment of the present invention. A portion of the tube design500of the terminal22that is inside the epoxy217has a holding slot505which is filled with epoxy. The tube design500may comprise a pair of wings510(1-2) and a stem515extending away from the pair of wings510(1-2). The pair of wings510(1-2) and the stem515may be made of a metal or a metal alloy such as copper or aluminum. The tube design500may comprise a bend520(seeFIG. 6) in between the pair of wings510(1-2) and the stem515such that the pair of wings510(1-2) and the stem515may not be at a same level. In particular, the pair of wings510(1-2) will be at a lower level that the stem515when the temperature sensor5or200is laid flat on a surface.

As shown inFIG. 6, it illustrates a side view of the tube design500of the terminal22ofFIG. 5in accordance with an exemplary embodiment of the present invention. The terminal22serves two purposes. First, it conducts heat from the measured point27to the temperature sensing element20, and hence should be made of material with high thermal conductivity, such as copper. Second, it provides a means to connect the temperature sensor5to the measured point27. In one configuration, as shown inFIG. 3, the terminal22is a ring lug, which can be bolted onto the measured joint27. In another configuration, as shown inFIG. 5, the terminal22is a cylindrical tube, which can be attached to cables with wire ties.

InFIG. 7, it illustrates a front view of the tube design500of the terminal ofFIG. 5in accordance with an exemplary embodiment of the present invention. In the tube design500the pair of wings510(1-2) form a cylindrical tube which can be attached to cables with wire ties.

An important technical challenge to address is the high dielectric strength needed. To ensure that, a part of the terminal22, the whole ceramic PCB15and a part of the pair of lead wires32(1-2) are sealed in an insulating epoxy. The epoxy217chosen has a high dielectric strength to create enough isolation between the low voltage parts inside and the high voltage part outside. The insulating epoxy can also serve as mechanical stress relief when the temperature sensor5,200is being handled. An example is shown inFIG. 3. The portion of the terminal22that is inside the epoxy217has the holding slot305, which is filled with epoxy, instead of being flat. Therefore, when the terminal22is pulled, the holding slot305can directly act on the epoxy217, instead of relying on a surface bond, and can ensure the force is not acted on the PCB joint. Similar concepts can also be used on the lead wire side, although not shown here. Epoxy can be chosen to have high bonding force with the wire insulation, or middle components, such as crimps or terminals, can be used to isolate the joint on the ceramic PCB15. If further strength is needed, the plastic housing220can be used around the epoxy.

Products such as panel boards, switchboards, switchgears, bus bar systems etc are integrated with energy monitoring products. A Branch Circuit Thermal Monitoring System provides an expanded avenue within an ecosystem with monitoring capabilities. By embedding the thermal monitoring system7within panel boards, switchboards, switchgears, bus bar systems one enhances product offering from a customer's perspective. The temperature sensor5is an important component of the thermal monitoring system7and is crucial to the Branch Circuit Thermal Monitoring System.

While a thermocouple-based temperature sensor is described here a range of one or more other types of temperature sensors are also contemplated by the present invention. For example, other types of temperature sensors may be implemented based on one or more features presented above without deviating from the spirit of the present invention. Thermistors are thermally sensitive resistors whose prime function is to exhibit a large, predictable and precise change in electrical resistance when subjected to a corresponding change in body temperature. Resistance thermometers, also called resistance temperature detectors (RTDs), are sensors used to measure temperature. A silicon band-gap temperature sensor is an extremely common form of temperature sensor (thermometer) used in electronic equipment.

The techniques described herein can be particularly useful for a thermal monitoring system for use in power distribution systems. While particular embodiments are described in terms of the thermal monitoring system embedded within panel boards, switchboards, switchgears, bus bar systems, the techniques described herein are not limited to the power distribution systems but can also be used with other systems—digital or analog, circuits or devices.

The ceramic PCB15may be a metal core printed circuit board (MCPCB). Ceramic printed circuit boards are a type of metal core PCB. One of the main reasons why one would avoid other PCBs vs. a ceramic circuit board or other MCPCB board has to do with heat transfer. Metal cores like aluminum nitride and beryllium oxide are extremely thermally conductive. Other metal core PCB materials in addition aluminum and beryllium can include copper and steel alloy. Steel alloys provide a stiffness that one will not get with copper and aluminum, but are not as effective at heat transfer. Copper has the best ability to transfer and dissipate heat as part of printed circuit boards, but it is somewhat expensive—so one can opt for aluminum as a cheaper but still highly effective heat-dissipating alternative. The most cost-effective solution will be metal core printed circuit boards with an aluminum base. One gets good rigidity and thermal conductivity at a more reasonable price. The reason metal core PCBs are so much more effective at dissipating heat than fr4 boards is due to their thermal conductivity dielectric material, which serves as a thermal bridge from the IC components to the metal plate, automatically conducting heat through the core to a heat sink. Metal core printed circuit boards are available as single-layer PCBs, single-layer Chip-on-Board PCBs, double-layer PCBs, double-sided PCBs, and multi-layer PCBs.

Additionally, any examples or illustrations given herein are not to be regarded in any way as restrictions on, limits to, or express definitions of, any term or terms with which they are utilized. Instead, these examples or illustrations are to be regarded as being described with respect to one particular embodiment and as illustrative only. Those of ordinary skill in the art will appreciate that any term or terms with which these examples or illustrations are utilized will encompass other embodiments which may or may not be given therewith or elsewhere in the specification and all such embodiments are intended to be included within the scope of that term or terms.

Respective appearances of the phrases “in one embodiment,” “in an embodiment,” or “in a specific embodiment” or similar terminology in various places throughout this specification are not necessarily referring to the same embodiment. Furthermore, the particular features, structures, or characteristics of any particular embodiment may be combined in any suitable manner with one or more other embodiments. It is to be understood that other variations and modifications of the embodiments described and illustrated herein are possible in light of the teachings herein and are to be considered as part of the spirit and scope of the invention.