Temperature indicator for electrical equipment

A system for determining when an electrical contact or other component reaches a predetermined temperature. In operation, a trace material is dispersed into a surrounding environment (e.g., head space within a compartment above insulating oil), where the trace material is detected. A barrier may be ruptured or broken by temperature-induced gas pressure, or pierced by a spring-loaded member that is located within the same section that contains the trace material, and devices may be provided for moving the trace material through the foil barrier as the barrier is ruptured. The barrier may be opened solely by internal gas pressure. According to another embodiment, improved fail-safe operation may be achieved by providing a spring-loaded member and configuring the barrier to be ruptured by the pressure of the detectable gas material before the barrier is ruptured by the spring-loaded member.

BACKGROUND

The invention relates in general to electrical switches, load tap changers, circuit breakers, reclosers, and more particularly to electrical contacts and electrical switches utilizing the same.

Electrical switches that operate while under load (with current flowing) are susceptible to certain limits at which further use will result in equipment failure. For example, components that overheat during normal equipment operation will, at some point, reach a limit at which they must be replaced. This condition can have catastrophic consequences and has the potential for failure of valuable infrastructure assets and loss of life. The overheating of the electrical contacts causes failure of switches or deteriorated switch operation and otherwise generally reduces or limits the useful lives of the switches themselves.

The degree of deterioration from overheating is a function of the various conditions that exist during operation, such as the amount of current carried by the contacts, the voltage applied across the contacts, the maximum temperature experienced, along with the severity of service under which the contacts operate. In addition, overheating of electrical contacts can signal failure or malfunction of other switch components. Switches are also subject to overheating from a high resistive contact interface. Excessive heating of contacts or other switch components can dramatically change the electrical and mechanical characteristics of the contacts and the ability of the switch to properly operate. Further, it can cause carbon accumulation (coking), and failure of the switch through an inability to operate or a type of failure known as a “flash-over.”

As a result of the consequences described, utility companies spend hundreds of thousands of dollars annually and commit a considerable amount of human resources to monitor their high voltage electrical equipment for signs of abnormal conditions that indicate overheating is occurring and failure is possible or imminent.

There are four basic environments within which electrical contacts operate: (1) air; (2) inert gas; (3) oil; and (4) a vacuum. Electrical contacts are used for low, medium and high voltage equipment, including circuit breakers, transformer and regulator load tap changers, and reclosers. These contacts operate under oil, under pressurized gas (e.g., SF6), in an enclosure open to ambient air, or under vacuum. Electrical contacts that operate under oil or gas do so within a containment vessel or compartment, preventing easy access to the contacts. As such, regardless of the type of environment in which contacts and other components operate, they operate within some form of enclosure. Each of these environments presents challenges to the contact monitoring process.

Because overheating of electrical contacts cannot be eliminated, a user monitors the switch to detect when the switch experiences overheating to a predetermined critical point as prescribed by the utility or end user. Monitoring of the switch for overheating includes: sampling the surrounding oil, sampling the gasses in the headspace above the oil, or sampling the primary gas and performing dissolved gas analysis (DGA) through the use of gas chromatography; the use of infrared scanning of the external surfaces of the switch containment vessel or compartment, and the use of external temperature monitors to detect the temperature of the containment vessel or compartment.

A transformer has two sets of wire coils, known as the primary windings and the secondary windings. A voltage applied to the primary windings (also referred to herein as the “primary voltage”) will induce a voltage in the secondary windings (also referred to herein as the “secondary voltage”). The secondary voltage is typically higher or lower than the primary voltage, depending upon the numbers of turns, or coils, of wire in the primary and secondary windings of the transformer. A transformer with a greater number of coils in the secondary windings will produce a secondary voltage higher than the primary voltage. A transformer without taps, or access points, within the secondary windings will produce only one secondary voltage for each primary voltage.

Many examples of transformers have numerous taps within the secondary windings so a variety of secondary voltages may be selected from one transformer. A transformer which has taps in the secondary windings will allow several secondary voltages to be accessed, depending upon which tap is selected. One transformer may be used to both decrease and increase voltage, if it is tapped at points lower and higher in number than the number of turns in the primary windings. A “coil tap selector switch” or a “load tap changer” must be provided, however, to switch between the various secondary winding taps.

A “load tap changer” is a mechanical device that moves a moving electrical contact to different stationary tap contacts within the switch, depending on the voltage output required. Current practices, however, include the application of advanced diagnostic tools that in some cases have resulted in extending the maintenance interval with little or no regard to the number of operations.

Some of the methods used previously to monitor electrical equipment performance which attempted to overcome the effort and expense required by direct physical inspection include the following:

Dissolved Gas Analysis (DGA).

Dissolved gas analysis is used for monitoring the condition of electrical contacts that operate in an oil environment. The method includes extracting a sample of the oil surrounding the contacts and analyzing it using gas chromatography to determine the amounts and correlation of key gasses generated during operation. The resulting values, collectively, are indicative of various types of problems that may be occurring within the equipment. For example, the presence of acetylene dissolved in the oil is indicative of arcing, and its correlation to ethylene is a key consideration for detecting overheating and coking. This process, however, lacks the precision necessary to determine the point at which overheating reaches the temperature at which failure is possible or imminent, as the tests are performed intermittently and failures continue to occur as a result.

Infrared monitoring may be used in an air, inert gas, vacuum, or oil environment. The method includes the use of an infrared camera to monitor the external temperature of high voltage equipment. Temperature and resistance are directly related. As resistance to current flow through electrical equipment increases, the temperature of the oil also increases. The infrared camera measures in a general sense the temperature increases and alerts the user accordingly. However, this system is inexact because it cannot monitor the temperature of contacts or other components separately from other neighboring components within the enclosure. As a result, the utility does not know what components will require replacement when the switch is opened for repair.

Temperature Differential Monitoring.

Temperature Differential Monitoring consists of temperature sensors applied directly to the outside surfaces of both the switch compartment and the outside of the main transformer tank. Temperature sensors attach to instrumentation that measures and logs the temperature in real time. Most utility companies schedule internal inspection when the temperature differential between the switch compartment and the main transformer tank reaches 10° C.

The above diagnostic methods have proven to be useful in a general sense for identifying overheating and coking. These methods, however, do not have the ability to distinguish the point at which the contacts have overheated to their limit of service life or that failure of the switch is possible or imminent. In addition, typical sampling intervals present the possibility that oil analysis could not detect an upset condition prior to failure. Peak efficiency can only be achieved where a method exists that provides continuous monitoring for the detection of overheating of electrical contacts and when they have reached a prescribed temperature.

Accordingly, there exists in the industry a need to provide a temperature indicator for electrical contacts that can be used to provide an indication of overheating and provide an alarm or notification to users that a certain critical temperature has been reached.

SUMMARY

The aforementioned problems, and other problems, are reduced, according to exemplary embodiments, by a plurality of temperature indicators that are designed to activate by exposing and detecting trace materials when the critical temperature of components is reached.

In an exemplary embodiment, a temperature indicator is provided for an electrical contact to indicate the heating of the electrical contact operating in, but not limited to, oil, inert gas (e.g., SF6), air, and vacuum environments. The temperature indicator containing a trace material is attached to or within a surface of the electrical contact or other component. The temperature indicator consists of a tubular shaped body with a spring-loaded pointed penetrator held into the compressed position using a metallic solder composition with a melting point (i.e., liquidus temperature) corresponding to the temperature at which the utility has prescribed. When the contact or component reaches the temperature corresponding to the melting point of the metallic solder, the solder reaches liquidus temperature and releases the penetrator. At that point, the compressed spring is released and activates ejecting the penetrator into the container of the trace material. The trace material is then dispersed into the oil and through vaporization, the gas space above the dielectric oil, or, for electrical contacts that operate within a gas environment, into the gas.

In an exemplary embodiment, nanocrystals are provided for use as a trace material implant of a temperature indicator, installed in an electrical contact. And, the use of different nanocrystals that emit light frequencies that are readily distinguishable from that of the surrounding oil makes them desirable to be used as a trace material.

In another exemplary embodiment, multiple temperature indicators with different retaining solders and/or trace materials are installed in electrical contacts in different areas of the switch to detect different temperatures of the electrical contacts. For example, multiple temperature indicators with different trace material implants are installed in an electrical contact to detect one or more temperatures.

A temperature indicator constructed in accordance with the present invention may, if desired, include provisions to ensure that no particulate is released into the surrounding insulating medium. A screen to prevent such release of particulates may be especially useful in connection with a device that is used within high-voltage electrical equipment, as released particulates could cause failure of the equipment and serious injury or potentially even death of maintenance personnel.

According to one aspect of the invention, a piercing shaft is used as an activator, for example to activate release of trace material into a surrounding medium by piercing, puncturing or rupturing a foil seal or diaphragm. The force generator for activating the piercing shaft (or other suitable device) may be a compressed spring. According to other aspects of the invention, however, the spring may be in tension and creates the activation by releasing such tension. According to other aspects of the invention, the force generator may be compression or Belleville (e.g., cone-shaped or undulating) washers. According to other aspects of the invention, one or more additional devices may be employed to multiply the force of the force generator.

According to another aspect of the invention, multiple chambers may be provided for combining chemicals for desired reactions to generate a final trace material for detection.

According to another aspect of the invention, the mechanical force created by the force generation device may be used for activation of switching devices, including mechanical, electronic or optical, sealed or unsealed; energizing or de-energizing voltage and/or current, operations, or other flow or electronic control devices.

According to another aspect of the invention, fusible material may be employed, and the fusible material is not limited to solder. Materials may be added to the fusible material, and organic firing materials or fusible alloys may be employed toward the intended purpose of the device.

According to another aspect of the invention, trace materials may be provided in a plurality of chambers that are activated at different activation temperatures. Each chamber may be provided with its own fusible material pool. Alternatively, the plural chambers may share a common pool of fusible material with other devices.

According to another aspect of the invention, an activation rod is used to rupture or pierce a foil opening, membrane, or other container closure.

According to another aspect of the invention, trace material may be evacuated from a storage region by a piston and cylinder device. The device may be configured to maximize the release of the trace material during activation, and thereby ensure reliable detection of the trace material in the surrounding environment (insulating oil or other material).

According to another aspect of the invention, material that is released during activation may be detected within the insulating oil, the headspace or gas-space above the oil, or within sulfur hexafluoride (SF6) or air.

According to another aspect of the invention, the force generator (e.g., the compressed spring) and the fusible alloy (e.g., the solder) may be located at junctures for activating multiple devices.

According to another aspect of the present invention, a device is provided for responding to the temperature of an electrical component. The device has a first section containing a detectable material (such as one that includes a tracer), a cover (such as a foil barrier) for maintaining the detectable material within the first section, and a spring-biased member for opening the cover. The spring-biased member may be located within the first section, and a temperature-responsive fusible material (such as solder) may be used to retain and release the spring-biased member, to thereby open (preferably rupture with a sharp end) the cover to release the detectable material from the first section, in response to the electrical component reaching a predetermined temperature.

The spring for biasing the spring-biased member toward the cover may be, among other things, a coil compression spring, a coil tension spring, or Belleville washers. According to other aspects of the invention, other resilient members may be employed instead of or in addition to such springs and washers.

According to another aspect of the invention, a first section contains a detectable material, a cover maintains the detectable material within the first section, a spring-biased member is configured to open the cover, and a temperature-responsive fusible material is provided for releasing the spring-biased member to open the cover and thereby release the detectable material from the first section. A piston may be arranged to move toward the cover, with the spring-biased member, to move the detectable material toward the cover, to apply pressure to the detectable material, to thereby enhance the extent to which the detectable material is dispersed into insulating oil or another insulating medium. According to one aspect of the invention, the piston is located between the spring and the cover.

The present invention also relates to a method of and system for releasing a detectable gas material into an insulating medium, where the gas material can be detected, in response to the rising temperature of an electrical component. A foil barrier may be used to maintain the detectable gas material within a first section, and, if desired, a spring-biased member may be configured to rupture the barrier, while a fusible material maintains the member in a first non-deployed position. According to another aspect of the invention, the system may be operated without the spring-biased member. If desired, the barrier may be ruptured solely by temperature-induced gas pressure, and the system may have no movable parts other than the pressure-rupturable barrier.

In operation, the temperature of the detectable gas material increases due to the rising temperature of the electrical component, so that the correspondingly increasing vapour pressure of the detectable gas material causes the foil barrier to rupture. The foil barrier employed in this method may be redundantly configured to be ruptured by the spring-biased member or the pressurized detectable material, whichever is deployed first, to ensure fail-safe dispersion of the detectable gas material into the insulating oil or other surrounding medium. According to another embodiment, a foil seal containing the detectable gas material is ruptured solely by gas pressure generated within the detectable gas material, such that the foil seal ruptures and the detectable gas material is released in response to the temperature of the electrical component.

The foregoing has outlined rather broadly certain features and technical advantages so that the detailed description that follows may be better understood. Additional features and advantages of the illustrated embodiments of the invention will be described hereinafter. It should be appreciated by those in the art that the embodiments may be readily used as a basis for modifying or designing other structures for carrying out the same purposes of the present invention. It should also be realized by those in the art that such equivalent constructions do not depart from the spirit and scope of the invention as set forth in the claims.

DETAILED DESCRIPTION

Referring now to the drawings, where like elements are designated by like reference numerals, there is shown inFIG. 1an electrical contact10constructed in accordance with a preferred embodiment of the invention. Although heating of electrical contacts can be attributed to a variety of circumstances, in most instances such heating is a result of high current loading, and infrequent operation, or both. For these reasons, it is needed that a reliable device and method be provided that will allow the utility to react to heating events in a timely manner. With reference now toFIGS. 1-4in conjunction, the electrical contact10is preferably made of copper, although other electrically conductive materials may be used. The electrical contact10is used in a reversing switch such as that for coil tap selectors or load tap changers used on high voltage transformers or step voltage regulators. One or more reversing switch electrical contacts are provided for each phase of the load tap changer. A second part of the electrical contact10(not illustrated) is used to make contact with the neutral, raise, and lower contacts, depending on the voltage required by the user. The reversing switch of which the electrical contact10is a part often switches between raise and lower contacts. The electrical contact10may be provided with one or more mounting holes11for mounting to the conductive contact support.

The electrical contact10has one or more threaded holes, or bores disposed in the surface. A threaded hole or bore12is formed in the electrical contact10such that it is threaded or sized to provide for an interference fit to ensure secure engagement contact with an internal surface of the hole12. The hole12may also be contained within an extended surface boss13attached to the contact surface by brazing, riveting or other desired means known to one skilled in the art that will provide engagement contact and heat transfer. To allow for ease of manufacture, the hole12is preferably, though not necessarily, cylindrically shaped as a result of drilling, although other shapes may be used. The hole12contains a bottom30which may be flat, tapered or conical, depending on the method used to form the hole12. After the hole12is created, a temperature indicator14is threaded, pressed or otherwise inserted into the hole12and maintained in engagement position by the threading or interference fit. The temperature indicator14has therein a container, or ampoule16which contains a trace material15.

The temperature indicator14includes a copper barrel17, a high temperature compression spring18, a penetrator19, a penetrator retention solder20, an insulating ring21, a container22(an ampoule may be located within the container22), the trace material15, and a top cover23. According to one aspect of the preferred embodiments, the container22is provided with a foil-covered opening disposed directly above the penetrator19. As the foil-covered opening of the container22is pierced by the penetrator19, the trace material15comes into communication with and is dispersed into the environment surrounding the electrical contact10. When the presence of the trace material15is detected, as described below, in the environment in which the electrical contact10is operated, it signifies that inspection and corrective action is, or might be, required.

The trace material15is preferably composed of, but not limited to, 19.1 oPDCH (1.2 perfluorodimethylcyclohexane), 19.2 PDCB (1,2 & 1,3 perfluorodimethylcyclobutanemagnesium), or nanocrystals. Detection of the dispersion of the trace material15within the oil or gas space above the oil, gas, air, or vacuum environment surrounding the electrical contact10can be accomplished using existing spectrophotometric chromatography techniques or using electrochemical transducers. These techniques of detecting the trace material15may be employed remotely, in a manner similar to DGA testing, in which the contents of the enclosure surrounding the electrical contact10are periodically sampled and tested by any of the foregoing or other equivalent techniques for the presence of the trace material15.

Alternatively, numerous portable and online methods may be used including sampling of the gasses in the gas space above the oil or the use of electrochemical transducers mounted within the enclosure in substantially continuous contact with the contents of the enclosure, allowing either a remotely or locally-situated detector operatively connected to the transducers to signal detection of the presence of the trace material15. One skilled in the art will recognize that other detection techniques are available and may be developed and can be used for detection of the trace material.

Detection of the presence of the trace material15indicates that the electrical contact10has reached the pre-set temperature dictated by sublimation of the penetrator retention solder20. Additional and alternative temperatures may be selected if desired, by the selection of a different penetrator retention solder with higher or lower melting or liquidus temperature. Additional or fewer holes12could also be provided, or the electrical contact10may include pairs of holes12. The penetrator retention solder20is preferably composed of a tin-lead or bismuth-indium based composition and formulated or selected such that substantially all of the fusible material contained in the copper barrel17transforms from a solid to the liquid phase at a selected temperature to release the spring-loaded penetrator19, to pierce the foil-covered opening of the trace material container22comprising the trace material15and to be detected.

The electrical contact10is, therefore, preferably contained in oil, to allow ready diffusion of the trace material15from the electrical contact10. Once released from the trace material container22, the trace material15diffuses into the immediately surrounding oil environment. It also vaporizes into the gas space above the oil. Other operating environments may be used upon selection of the proper trace materials and detection techniques. When the presence of the trace material15is detected by the detector appropriate with the environment in which the electrical contact10is operated, or in the gas space above the oil, replacement of the contacts or inspection of the switch within which the electrical contact10operates is indicated.

In accordance with one embodiment of the invention, the copper barrel17is partially filled with the penetrator retention solder20having a melting point of 242° C. Detection of the presence of trace material15from the temperature indicator14would thus indicate that the electrical contact10had reached the predetermined temperature of 242° C. in operation. Additional and alternative temperatures may be predetermined, if desired, by the selection of different penetrator retention solders with higher or lower melting points. Additional or fewer holes12may also be provided. The trace materials15may also be placed into containers which are attached to the electrical contact10.

Turning now toFIG. 4, the temperature indicator14is shown in a side view and as a cutaway along line4A-4A and depicts released trace material15from the trace material container22upon penetration of the foil covered opening by the penetrator19. As described above, the penetrator19activates with a spring-released force and pierces the foil-covered opening of the trace material container22only after the penetrator retention solder20has melted upon reaching its melting point, thus releasing retention of the penetrator19and causing the trace material15to be dispersed into the existing environment through the pierced foil-covered opening of the trace material container22.

It will be apparent to one of ordinary skill in the art that the temperature indicator14described with reference toFIGS. 1-4could be used in other components in order to detect heating.

FIG. 5illustrates a nanocrystal molecule50for a trace material that may be used in accordance with some exemplary embodiments of the present invention. The molecule50relates to “core/shell” nanocrystals, which consist of a core52of cadmium selenide (CdSi) and a shell54of zinc sulfide (ZnS). According to one embodiment of the invention, the nanocrystal may be a man-made semiconductor crystalline material seven nanometers in diameter. Since the diameter of each nanocrystal is less than ten nanometers, the nanocrystals are referred to as quantum dots. What makes nanocrystals particularly desirable as one kind of trace material implant is their ability to emit light of varying frequencies, as determined by size, that are readily distinguishable from that of the surrounding oil.

The nanocrystals50are encapsulated in a transparent cross-linked polymer coating that is impervious to acid and dissolved gases in the oil. The coating may also have paramagnetic properties that will allow removal of the nanocrystals50after breaching using electromagnetic filtration. This allows the nanocrystals50to be concentrated for detection and subsequently removed from the oil after breaching.

FIG. 6Aillustrates three emission spectrums of oil with three different nanocrystal concentrations when the excitation wavelength of the contained nanocrystals is 380 nm. More specifically, it shows an emission spectrum60of oil with a nanocrystal concentration at 100 mg/L, an emission spectrum62of oil with a nanocrystal concentration at 200 mg/L, and an emission spectrum64of oil with a nanocrystal concentration at 100 mg/L, while the excitation wavelength of the contained nanocrystals is 380 nm. According toFIG. 6A, as the optical density increases, the oil absorbs the excitation wavelength of 380 nm which prevents the contained nanocrystals from receiving the light they need to fluoresce.

FIG. 6Billustrates three emission spectrums for three different nanocrystal concentrations when the excitation wavelength of the nanocrystals is 518 nm. More specifically, it shows an emission spectrum70of oil with a nanocrystal concentration at 100 mg/L, an emission spectrum72of oil with a nanocrystal concentration at 200 mg/L, and an emission spectrum74of oil with a nanocrystal concentration at 100 mg/L, while the excitation wavelength of the contained nanocrystals is 518 nm. As shown inFIG. 6B, an excitation light source of wavelength 518 nm is able to pierce the optical density of the oil even when the nanocrystal concentration is 100 mg/L. Using the nanocrystals of excitation wavelength 518 nm as trace materials allows them to be detected at lower concentrations, and the lower nanocrystal concentrations equate to a lower cost for the end product.

There are many materials (e.g. perfluorocarbon chemicals, etc.) that may be used as a trace material. As a result, the preferred embodiments of the invention are able to use different materials for multiple temperature indications in an electrical contact to indicate different temperatures of the electrical contact. For example, multiple temperature indicators with different trace materials may be installed in an electrical contact to identify the detections of one or more temperatures, such as a slightly overheated temperature of 100° C., an intermediate temperature of 242° C. and higher temperatures of 350° C. and 450° C.

FIGS. 7A and 7Bare a perspective view of an electrical contact80with two installed temperature indicators, and a partial cross-sectional view. A temperature indicator82may contain one kind of trace material86and another temperature indicator84may contain another kind of trace material88. Both indicators82,86are installed in the electrical contact80. The first temperature indicator82is filled with a penetrator retention solder90having a melting point at temperature T1, while the second temperature indicator84is filled with another penetrator retention solder92having a melting point at temperature T2. The temperature indicators are installed to indicate two different temperatures T1, T2for the electrical contact80. The detection of trace material86indicates the electrical contact80reaches the temperature T1, and the detection of trace material88indicates the electrical contact80reaches the temperature T2. In this way, multiple temperatures are detected for an electrical contact. This is desirable as temperature T1provides an indication that the electrical contact has reached a temperature above normal.

As indicated earlier, one of the reasons reversing switch contacts overheat is due to infrequent operation. Many utility companies have schedules to operate the reversing switch “through neutral” to “wipe” or break-up surface oxides that develop over time due to infrequent operation. The temperature T1could be an indicator that the switch needs to be operated to restore its rated current capacity. It would follow that the utility would be aware the load tap changer had the occurrence of slightly elevated temperature and would thus observe more closely its operation. It would also provide the opportunity to order replacement parts in preparation for an inspection that would be triggered by the activation of the temperature indicator indicating that temperature T2had been reached. At temperature T2, failure of the switch would be considered possible or imminent. A utility may use this information to operate its own laboratory-based dissolved gas analysis (DGA) diagnostics program.

Second Embodiment

Referring now toFIG. 8, there is a shown a load tap changer case100that contains, among other things, an electrical contact102, a temperature indicator104, insulating oil106, and a sampling/monitoring device108. The electrical contact102and the temperature indicator104may be immersed in the insulating oil106. In operation, when the electrical contact102reaches a predetermined temperature, the temperature indicator104releases a trace material15into the insulating oil106. The trace material15enters the headspace107, because of its volatility, and is detected by the monitoring device108, and causes the monitoring device108to issue a corresponding warning, an enunciation of an alarm, a notice or other signal to an operator (not shown). According to one aspect of this disclosure, the monitoring device108may be located outside of the headspace107, and is connected to the headspace107by a suitable tube (not illustrated) (e.g., ¼-inch stainless steel tube). In alternative embodiments, the electrical contact102and the temperature indicator104may be replaced or supplemented by the electrical contacts10,80and the temperature indicators14,82,84shown inFIGS. 1 and 7A. In other embodiments, the insulating oil106may be replaced or supplemented by another insulating liquid, a gas, including but not limited to sulfur hexafluoride (SF6), or a vacuum.

As illustrated inFIG. 9, the temperature indicator104has a cylinder case110, a pierce container112, a solder container114, a piercing rod116, and a spring retainer118. The cylinder case110has a cylindrical main section120that is open at one end122and closed at the other end124. Between the main section120and the closed end124, there is a cylindrical connection section126with outer and inner threads128,130. The respective outer and inner diameters of the connection section126are smaller than those of the main section120. The outer threads128may be used to threadedly connect the temperature indicator104to a threaded opening in the electrical contact102(FIG. 8). In other embodiments, the outer surface of the connection section126may be non-threaded, and the connection section126may be press-fit into or welded or otherwise connected or adhered to the electrical contact102. A shoulder132is located between the main section120and the connection section126. The shoulder132may be in contact with a surface of the electrical contact102when the temperature indicator104is connected to the electrical contact102. The temperature indicator104may be formed of heat-transmissive copper, another metal or other heat-transmissive materials.

The pierce container112(FIG. 10) has a cylindrical main section140(FIG. 9) and a cylindrical connection section142. The main section140has an axially-open front end144and radially-directed fluid-flow openings146. The open front end144and the openings146provide fluid communication between (1) a cylindrical space148located within the main section140of the pierce container and (2) an annular space150located between the main section140of the pierce container and the main section120of the cylinder case110. In theFIG. 10configuration, the trace material15is located within the cylindrical space148and the annular space150. The connection portion142has a closed end152and a threaded outer surface154(FIG. 10). The connection portion142may be threadedly connected to the inner threads130of the larger connection section126. Castellated indents156may be engaged by a tool (not shown) to threadedly turn the pierce container112into the inner threads130, such that a shoulder158of the pierce container112fits tightly against the shoulder132of the cylindrical main section120.

In theFIG. 9configuration, a foil seal170prevents the trace material15from reaching the circular open end122of the temperature indicator104. The foil seal170may be held in place by opposed washers172,174. At least one of the washers172is immovably fastened to the cylindrical interior surface176of the cylindrical case110. The foil seal170and the washers172,174are structurally strong enough to provide a gas-tight seal, such that no trace material15reaches the insulating oil106so long as the temperature indicator104is in theFIG. 9configuration. The foil seal170may be pierced, punctured and/or ruptured by a sharp end178of the piercing rod116, as shown inFIG. 10. Before deployment, the sharp end178is immersed in the trace material15, and separated from the oil106.

According to another aspect of the invention, the foil seal170may be ruptured by the pressure of the trace material15when the trace material15reaches a predetermined temperature. That is, the foil seal170itself may be ruptured by the pressure of the trace material15before the foil seal170is contacted by the sharp end178of the piercing rod116. The heat-related pressure of the trace material15applies increasing force to the foil seal170from left to right, as viewed inFIG. 9, as the temperature of the trace material15increases. The foil seal may have the reverse-conical cross-sectional configuration illustrated inFIG. 18, discussed in more detail below. When employed in theFIG. 9device, the concave side of the partially-spherical section of theFIG. 18foil seal would face toward the piercing rod116.

In theFIG. 9configuration, the distal end180of the piercing rod116contacts the rear inner surface of the solder container114, and the open end of the solder container114is closed by the spring retainer118. The spring retainer118is axially symmetrical about the center line of the piercing rod116, and has an annular insert portion182(FIG. 10) that fits into the circular open end of the solder container114. The piercing rod116is slidably positioned within a central opening184of the spring retainer118. Thus, the piercing rod116is centered by the inner, cylindrical surface of the spring retainer opening184, and the spring retainer118is centered by the inner, cylindrical surface of the solder container114. In theFIG. 10configuration, a shoulder186(FIG. 10) of the spring retainer118abuts the axial front end188of the solder container114(or a front surface of the main shoulder132).

The solder container114is filled entirely or at least partially with hardened solder190, and a compressed coil spring192is immersed within the solder190. The rear end of the spring192contacts the rear surface of the solder container114. The front end of the spring192contacts the rear surface of the insert portion182of the spring retainer118. In theFIG. 9configuration, the solder190is below its melting point and therefore prevents the spring192from expanding in the axial direction of the temperature indicator104. If desired, the piercing rod116may have a necked-down section194for mechanical inter-engagement with the hardened solder190.

As mentioned above, the cylinder case110, the pierce container112, and the solder container114may be formed of copper or some other heat-transmissive material. Consequently, when the electrical contact102(FIG. 8) reaches a predetermined temperature, the heat reaches the solder190though the threaded connections128,130,154, such that the solder190is at nearly the same predetermined temperature. When the solder190reaches its melting temperature, the spring192expands axially to the position shown inFIG. 10, where the sharp end178of the piercing rod116punctures the diaphragm170, such that the trace material15enters the insulating oil106through the open end122of the temperature indicator104.

In operation, as the spring192begins to expand axially, the front end of the spring192moves the spring retainer118through an initial travel distance D1, without moving the piercing rod116. The spring retainer118slides over the piercing rod116during the movement of the retainer118through the initial travel distance Di(FIG. 9). Subsequently, the front surface of the spring retainer118engages a rear surface of a collar200. Once such engagement occurs, further axial expansion of the coil spring192causes (through forces applied to the retainer118and the collar200) the piercing rod116to reach theFIG. 10configuration. Permitting the spring retainer118to move the initial travel distance Dibefore movement-inducing engagement with the piercing rod116yields a more robust motion of the sharp end178of the piercing rod116through the foil seal170.

By the time the retainer118reaches the collar200, the spring192has essentially been released from the solder190, such that the full decompression force of the spring192can be applied toward movement of the piercing rod116. In addition, the extra movement (by the amount Di) of the retainer118contributes to the agitation of the trace material15as it comes into contact with the oil106, to thereby increase the extent to which the trace material15is rapidly mingled into the oil106and moved toward the headspace107.

If desired, the sharp end178of the piercing rod116may have three or more broadhead units202with triangular open spaces204to ensure effective fluid communication through the ruptured foil seal170. The piercing of the foil seal170may be sufficiently robust to ensure that substantial open spaces are provided for fluid communication into the insulating oil106, yet not so forceful as to propel the piercing rod116completely out of the temperature indicator104. Preferably, when the solder190is melted, the piercing rod116ends up in the position shown inFIG. 10.

Third Embodiment

Another axially-symmetric temperature indicator300(FIG. 11) may be employed instead of or in addition to the temperature indicator104. The temperature indicator300has a pierce container302, a spring retainer/guide304, a foil seal170, and a piercing rod308for piercing the foil seal170. The pierce container302has a cylindrical main section306that is open at one end and closed at the other end. The diameter of the main section306is greater than that of the end section. The spring retainer/guide304is immovably press-fit into the closed end of the cylindrical main section306.

The cylindrical piercing rod308has necked-down portions310and a sharp, forward end178. A disk-shaped piston312is located between the two ends of the piercing rod308. The piston312may be an integral part of the piercing rod308, and has a peripheral diameter that is approximately equal to the inner diameter314of the main section306. In theFIGS. 11 and 12sealed configuration, the rear end of the piercing rod308is encased in hardened solder190. At the same time, a coil spring316is compressed between a front surface of a shoulder of the pierce container302and the rear surface of the piston312. The spring316is not in contact with the hardened solder190. In the hardened condition190, the piercing rod308is prevented from moving toward the foil barrier170, because the solder190cannot move the fixed guide304.

The open end of the pierce container302may be covered by a vented cap318. The vented cap318has openings320, such that insulating oil106is located within and may flow through the vented cap318. Suitable mating threads322may be used to connect the cap318to the open end of the pierce container302. The vented cap318may be surrounded by a suitable muffler (not illustrated). The muffler may be used to muffle the sudden release of pressure and thereby prevent a shock wave from blowing or breaking carbon loose in the vicinity of the device300.

The main elements128,302of the temperature indicator300may be made of copper or some other suitable heat-transferring material. Thus, when the electrical contact102(FIG. 8) reaches a predetermined temperature, the solder190located within the rear end of the container302has almost the same temperature. When the solder190melts, the piercing rod308is caused to move toward the foil seal170under the force of the decompressing spring316. The spring316may be formed of a high-temperature-resistant nickel-alloy (e.g., Inconel material) coil. As the compression of the spring316is released, the forward end of the spring316pushes the piston312toward the foil barrier170. During the axial movement, the piercing rod308is centered by the guide/centering element304.

In theFIGS. 11 and 12configuration, trace material15is located within the container302, to the left of the foil seal170as viewed inFIG. 12. In theFIGS. 11 and 12configuration, the foil barrier170separates the oil106from the trace material15. As the piercing rod308moves to theFIG. 13deployed configuration, the pressure of the trace material15is increased by the reduction in volume caused by the piston312moving toward the foil barrier170. Consequently, when the sharp end178ruptures the foil seal170, the trace material15is released into the muffler area associated with the vented cap318and is thereby forcibly mingled with the insulating oil106, providing an immediate dispersion, and thereby a prompt and sure indication of the trace material15to the detector108(FIG. 8).

Fourth Embodiment

The temperature indicator400shown inFIGS. 14-16may be employed instead of or in addition to the temperature indicators shown inFIGS. 1, 8, 9 and 11. The temperature indicator400has a cylindrical, two-piece ampoule402, a cylindrical main case404(made of copper or other suitably heat-transmissive material), a disk-shaped foil seal170for retaining trace material15in the ampoule402, and a cylindrical piercing rod406for rupturing the foil seal170when the temperature indicator400is at or above a predetermined temperature. A compressed coil spring408is provided for moving the piercing rod406from the sealed configuration shown inFIGS. 14 and 15, to a deployed configuration, where a sharp end178(FIG. 16) of the piercing rod406is located partially or entirely within the ampoule402, having pierced through the foil seal170.

The ampoule402has a ring-like inner shoulder410for supporting the foil seal170. A washer174is provided on the other side of the foil seal170. The two cylindrical pieces412,414of the ampoule402are threaded together (416) to form a sealed, gas-tight compartment for the trace material15. The first piece412, which is tube-shaped, is threaded (418) to the otherwise open end of the main section404. The second piece414is cap-shaped and is threaded (419) onto the other end of the first piece412. In operation, insulating oil106is located within a compartment420adjacent to the foil seal170, and the sharp end178of the piercing rod406is located within the same compartment420. Radially-directed openings422are provided through the cylindrical wall of the main piece404to permit the insulating oil106to flow into the device400to immerse the sharp end178of the piercing rod406.

The piercing rod406has a collar424for centering the rod406within the cylindrical portion of the main section404. In the illustrated embodiment, the collar424is an integral (one-piece) part of the piercing rod406. The present invention is not limited, however, to what is shown in the drawings. The collar424, for example, may be mechanically connected to the piercing rod406by threads or other devices or instrumentalities, not shown.

In the sealed configuration, hardened solder190is located within the temperature indicator400to the left (as viewed inFIG. 15) of the collar42. The hardened solder may be mechanically inter-engaged with a necked-down portion426of the piercing rod406. When the solder190is melted by heat transmitted into the device400from electrical equipment102, the necked-down portion426pulls through the liquefied solder190under the resilient biasing force of the compressed spring408. As the spring408is thereby permitted to decompress, the front end of the spring408drives the sharp end178through the foil barrier170, rupturing the foil barrier170, and moves the sharp end178into the ampoule402.

By occupying a significant volume of the ampoule402, a cone-shaped portion428of the sharp end178of the piercing rod406volumetrically displaces the trace material15from the ampoule402and forcibly causes the trace material15to mingle with the insulating oil106. At the same time, the heat-induced pressure of the trace material15contributes to the forcible way in which the trace material15is comingled with the oil106. If the piercing rod406fails to rupture the foil barrier170at the predetermined temperature, the pressure of the trace material15itself may cause the foil seal170to rupture (from right to left as viewed inFIG. 15) so that the trace material15is reliably dispersed into the insulating oil106to be sensed by the detector108(FIG. 8). The foil seal may have the reverse-conical shaped configuration illustrated inFIG. 18, discussed in more detail below. When employed in theFIG. 15device, the concave side of the partially-spherical section of theFIG. 18foil seal would face away from the piercing rod406.

Fifth Embodiment

The temperature indicator500shown inFIGS. 17 and 18may be employed instead of, or in addition to, the temperature indicators shown inFIGS. 1, 8, 9, 11 and 15. The device500has many elements in common with the device300shown inFIG. 13. The elements that are the same in the two embodiments are designated in the drawings by common reference numerals and are not described further herein. There are at least two differences between theFIG. 13device300and theFIG. 17device500, as follows: First, the latter device500does not have a spring-retainer guide304, a piercing rod308, or a coil spring316. Second, theFIG. 17device500has a container302′ that is shorter (measured in the left-to-right direction ofFIGS. 13 and 17) than the pierce container302. TheFIG. 17device500can be shorter (more compact) than theFIG. 13device300, and still provide the same volume for containing the detectable gas material15, because the container302′ does not have to accommodate a spring-retainer guide304, a piercing rod308, or a coil spring316.

The indicator500has a rupture disc502that is axially symmetric about an axis504that extends lengthwise through the indicator500. The disc502has an annular flange506that is secured by adhesive, welding or some other suitable connection device to one or more washers172. A frusto-conical section508extends from the flange506into the container302′ (where the trace material15is stored). A compression-loaded, partially-spherical section510extends from and is located annularly within the frusto-conical section508. According to the illustrated embodiment, the flange506, the frusto-conical section508, and the partially-spherical section510are formed from a single, thin sheet of metal. The cross-sectional configuration of the disc502,506,508,510, as illustrated inFIGS. 17 and 18, is reverse conical, like that of a broad letter “w.”

In operation, the vapour pressure of the trace material15within the container302′ increases as the temperature of the trace material15increases. The vapour pressure applies a force toward the concave side of the partially-spherical section510. At a predetermined design temperature, the force applied by the vapour pressure causes the partially-spherical section510to snap away from the frusto-conical section508at a circular score line512. In the illustrated embodiment, there is no other device or mechanical component that contributes to the desired rupturing of the disc502. When the break (rupture) occurs at the score line512, the trace material15is rapidly dispersed into the oil that surrounds the indicator500, in the direction of arrows514. Most of the debris that is created by the rupture will be too big to pass through openings320, and therefore will be retained within the indicator500. If desired, or if needed to prevent contamination of the insulating oil, smaller debris may be retained by a finer screen (not illustrated) that may be located or wrapped around the device500. However, an advantage of theFIGS. 17 and 18indicator500is that the disc502can be configured to burst cleanly, without generating any significant or substantial amount of debris, and the device500does not require fusible material which could contaminate the insulating oil, by becoming dissolved or entrained within the oil, while the fusible material is melted.

There is a need in the commercial, utility electrical industry for new methods and technologies to extend service intervals and monitor equipment conditions to avert catastrophic failures, reduce maintenance costs, and increase the reliability of load tap changers. Indeed, it has been estimated that half of all legacy load tap changer outages are related to electrical contacts. The typical causes for load tap changer failures include overheating, coking, contact wear, or problems within the mechanism. Failures due to overheating and coking may be dramatically reduced or averted by monitoring the temperature of reversing switch contacts. Temperature indicators with chemical tracers constructed in accordance with the present invention can overcome the problems of the prior art to a large extent. The indicators104,300,400,500can be used by utility companies to detect overheating of electrical contacts102before coking begins to form and failure is imminent.

According to one aspect of the present invention, a solder with a uniform melting temperature, the “set temperature,” holds a piercing pin116,308,406in place. When the temperature of the device104,300,400reaches the melting point of the solder190, the solder melts, the pin is released, and the pin pierces a foil-sealed (170) compartment containing one or more highly detectible chemical tracers15. According to another embodiment, the integrity of the foil-sealed container is compromised only by pressure that is generated within the container302′ itself. When the container is ruptured or otherwise compromised, the released tracer15is then detected by dissolved gas analysis or some other suitable monitor.

Perfluorocarbon may be the most sensitive of all non-radioactive tracer technologies and concentrations in parts per quadrillion (1 in 10−15) can be routinely measured. An amount of perfluorocarbon detectible by dissolved gas analysis may remain in load tap changer oil for at least twenty-four months unless removed by vacuum degassing.

According to one aspect of the invention, a gas sampling pump circulates a sample of the headspace gas107(FIG. 8) through the monitor108for the detection of acetylene, ethylene and the chemical tracer. A display (not shown) may be used to display the date, time, sample temperature, and gas concentrations of acetylene (Gas 1; C2H2) and ethylene (Gas 2; C2H4). The ratio of C2H4/C2H2is labeled as the Thermal Index. The detection of the chemical tracer may be digitally designated (either “yes” or “no”). The monitor108may have an internal microprocessor and a flash memory card for recording data. Communications may be customized to include various protocols. The system of which the detector108is a part is preferably sealed, electrically shielded, and can be used as either a dedicated on-line monitor or as a portable detector.

A suitable gas-monitor (not illustrated) may be much less expensive and less complicated than an on-line DGA monitor. The three-gas monitor also may be easier to install, and does not require any supporting infrastructure. An added benefit is that the three-gas monitor may be used to sample the headspace107above the insulating oil106, eliminating issues related to penetrations of the wall of the tank100. The system may be preferred for utilities who want to comply with smart grid mandates but without the complexity of an on-line dissolved gas analysis monitor.