Patent Description:
Electrical systems of various types, e.g., circuit breaker systems, remain an area of interest. Some existing systems have various shortcomings, drawbacks and disadvantages relative to certain applications. For example, in some SF6 insulated circuit breaker systems, low ambient temperatures may precipitate a lockout state of the circuit breaker too quickly. Accordingly, there remains a need for further contributions in this area of technology.

<CIT> relates to a gas-insulated switch comprising SF6 and a heater for heating the tank, according to the preamble of claim <NUM>.

<CIT> relates to a heat insulator unit for puffer type and arc assisted type circuit breakers which utilize gas.

<CIT> relates to an electric power gas circuit breaker with a heater.

<CIT> relates to engine warming-up apparatus for a vehicle to warm up an internal combustion engine.

<CIT> relates to circuit-breaker modules with SF6 gas for arc-extinction and insulation.

The invention relates to a insulated circuit breaker system with the features of claim <NUM>. Further embodiments, forms, features, aspects, benefits, and advantages of the present application shall become apparent from the description and figures provided herewith.

For the purposes of promoting an understanding of the principles of the invention, reference will now be made to the embodiments illustrated in the drawings and specific language will be used to describe the same. Any alterations and further modifications in the described embodiments, and any further applications of the principles of the invention as described herein are contemplated as would normally occur to one skilled in the art to which the invention relates.

Referring to <FIG>, some aspects of a non-limiting example of a sulfur hexafluoride (SF6) insulated circuit breaker system <NUM> in accordance with an embodiment of the present invention are schematically illustrated. In one form, circuit breaker system <NUM> employs an SF6 dielectric gas puffer system to force pressurized SF6 between the circuit breaker contacts during circuit interruption (opening of the contacts). In other embodiments, circuit breaker system <NUM> may employ any suitable SF6 arc quenching system, e.g., circuit breaker system <NUM> may be a self-blast system. Circuit breaker system <NUM> includes a circuit breaker <NUM> having conductors <NUM> and <NUM>; contacts <NUM> and <NUM> and a system <NUM> for operating contacts <NUM> and <NUM>; a tank <NUM> constructed as a reservoir to hold a quantity of SF6; a density monitor <NUM> including a temperature sensor <NUM> and a pressure sensor <NUM>; and a thermal energy storage system <NUM>.

Contacts <NUM> and <NUM> are operated by system <NUM> to selectively make and break electrical current paths to respectively allow and interrupt current flow through conductors <NUM> and <NUM>. Contacts <NUM> and <NUM> are insulated by SF6 from tank <NUM> for arc quenching. In one form, contacts <NUM> are double motion contacts. In other embodiments, single motion contacts may be employed. Tank <NUM> is constructed to store SF6, and to act as a reservoir for the SF6. In the illustrated embodiment, contacts <NUM> and <NUM> are disposed within tank <NUM>. In other embodiments, contacts <NUM> and <NUM> may be located outside of tank <NUM>, and may be supplied with SF6 from tank <NUM>.

Density monitor <NUM> is operative to determine and monitor the density of the SF6 gas in tank <NUM>. Under normal conditions, SF6 functions as an electrical insulator, an interrupting media to quench arcing, and a mechanical damper for contacts <NUM> and <NUM> in circuit breaker <NUM>. The SF6 is stored in tank <NUM> under pressure at typical temperatures, e.g., room temperature. Under some conditions of low temperature, e.g., from -<NUM> to -<NUM> or lower, the SF6 gas in tank <NUM> can experience liquefaction, wherein some of the SF6 gas becomes a liquid. Liquefaction of some of the SF6 gas reduces the density of the gaseous SF6 in the tank that is used for quench arcing, e.g., during the opening of contacts <NUM> and <NUM>. In one form, density monitor <NUM> employs using temperature sensor <NUM> and a pressure sensor <NUM> to determine the density of the SF6 gas in tank <NUM>.

Density monitor <NUM> is operative to indicate a state associated with the density of the SF6 gas in tank <NUM>, which varies with the temperature of the SF6 gas in tank <NUM>. If the SF6 gas in tank <NUM> has sufficient density for normal arc quenching operation without undue damage to contacts <NUM>, density monitor <NUM> outputs a signal indicating a nominal state. If the SF6 gas density is lower than a first predetermined density level, density monitor <NUM> outputs a signal indicating an alarm state, e.g., to indicate to the operator of circuit breaker system <NUM> that service is required, e.g., to supply heat to tank <NUM>, although in some cases the alarm state may also be used to indicate the need to replenish the supply of SF6 in tank <NUM> or take other measures to increase the density of the SF6 in tank <NUM>. If the SF6 gas density drops to a second predetermined density level below that associated with the alarm state, density monitor <NUM> outputs a signal representing a lockout state. In one form, the lockout state occurs when the SF6 temperature is -<NUM>, i.e., the lockout temperature of the SF6 is -<NUM>. In other embodiments, other temperatures may be used to designate a lockout state. The density levels associated with the nominal state, the alarm state and the lockout state may vary with the needs of the particular application, and are known to those skilled in the art. In some embodiments, when in the lockout state, circuit breaker system <NUM> allows a single occurrence of a circuit interruption, i.e., allows contacts <NUM> and <NUM> to be opened a single time, but does not allow contacts <NUM> and <NUM> to be closed or subsequently closed, or does not allow charging of springs, pistons or other devices used to close contacts <NUM> and <NUM> until reset of the lockout state. In some embodiments, once in the lockout state, circuit breaker system <NUM> does not allow either opening or closing of contacts <NUM> and <NUM> until reset of the lockout state.

Thermal energy storage system <NUM> includes a thermal capacitor <NUM>. The thermal energy storage system also includes a heater <NUM> and insulation <NUM>. The circuit breaker system <NUM> includes a heater disposed on the tank <NUM>, and may include insulation disposed about tank <NUM>, in addition to or in place of heater <NUM> and insulation <NUM>. Thermal capacitor <NUM> is in conductive engagement with tank <NUM>, and operative to store heat energy. In one form, thermal capacitor <NUM> is bolted to bosses on tank <NUM> (not shown), In other embodiments, thermal capacitor <NUM> may be attached to tank <NUM> using straps, clamps or other fastening systems or devices, or in some embodiments may be integral with tank <NUM>. Thermal capacitor <NUM> is constructed to conduct the stored heat energy to the SF6 in tank <NUM>, via conduction through the walls of tank <NUM>. Thermal capacitor <NUM> is operative to increase the thermal mass of circuit breaker system <NUM>, and to increase the thermal time constant of circuit breaker system <NUM>. In one form, thermal capacitor <NUM> is metallic. In other embodiments, thermal capacitor <NUM> may be nonmetallic. In one form, thermal capacitor <NUM> is an aluminum casting. In other embodiments, other materials and/or methods of forming thermal capacitor <NUM> may be employed, e.g., thermal capacitor <NUM> may be a weldment.

Heater <NUM> is coupled to thermal capacitor <NUM>. Heater <NUM> is operative to supply heat to thermal capacitor <NUM>, and to supply heat to the SF6 disposed in tank <NUM>, e.g., via thermal capacitor <NUM>, in order to achieve and maintain the SF6 gas in tank <NUM> at or above a desired temperature or density value suitable for quenching arcs between contacts <NUM> and <NUM>. In one form, heater <NUM> is a plurality of cartridge heater elements (cartridge heaters), e.g., coupled to thermal capacitor <NUM>. In other embodiments, heater <NUM> may be strip heater elements (strip heaters) or any suitable type of heater(s) coupled to thermal capacitor <NUM>. In some embodiments, heater <NUM> may be disposed inside thermal capacitor <NUM>, or may be disposed between thermal capacitor <NUM> and tank <NUM>. Insulation <NUM> is disposed about thermal capacitor <NUM>, e.g., preferably at least to the extent necessary to cover heater <NUM>. Some embodiments may not include insulation <NUM>. In some embodiments, insulation <NUM> may extend all the way around the outer portions of thermal capacitor <NUM>, except where thermal capacitor <NUM> is in contact with tank <NUM>. Insulation <NUM> may be, for example, an insulation blanket wrapped partially around thermal capacitor <NUM>.

Referring to <FIG> and <FIG>, some aspects of non-limiting examples of tank <NUM> and thermal capacitor <NUM> in accordance with some embodiments of the present invention are illustrated. The thermal capacitor <NUM> is constructed to partially wrap around tank <NUM>, e.g., to increase heat conduction between tank <NUM> and thermal capacitor <NUM>. In some embodiments, thermal energy storage system <NUM> includes a heat conduction medium or conductive medium <NUM>. Conductive medium <NUM> is configured to increase heat conduction from tank <NUM> to thermal capacitor <NUM> and the SF6 stored in tank <NUM>. In one form, conductive medium <NUM> is disposed between thermal capacitor <NUM> and tank <NUM>. In some embodiments, conductive medium <NUM> may extend into thermal capacitor <NUM> and/or tank <NUM>. In one form, conductive medium <NUM> is a thermal grease. In other embodiments, conductive medium <NUM> may be a thermal paste, a thermal compound or any material, structure or device that is operative to conduct heat between thermal capacitor <NUM> and tank <NUM>, or between thermal capacitor <NUM> and the SF6 stored in tank <NUM>.

In one form, thermal capacitor <NUM> is hollow. In other embodiments, thermal capacitor <NUM> may be solid. In one form, thermal capacitor <NUM> includes a heat storage material <NUM> disposed within thermal capacitor <NUM>. In one form, heat storage material <NUM> is operative to supply latent heat to the SF6, e.g., via tank <NUM>. In other embodiments, heat storage material <NUM> may not be operative to supply latent heat to the SF6. In one form, heat storage material <NUM> is a paraffin wax. In other embodiments, other materials may be employed. The paraffin wax of the present embodiment has a melting point of <NUM>. In other embodiments, paraffin waxes having other melting points may be employed. When the paraffin wax solidifies, it's volume decreases by approximately <NUM>%. During production, thermal capacitor <NUM> is filled with the paraffin wax in a liquid form. Upon solidification, the pressure inside thermal capacitor <NUM> reduces, e.g., to sub atmospheric. In some embodiments, the pressure inside thermal capacitor <NUM> may be a near or partial vacuum upon solidification of the paraffin wax. In some embodiments, risers or other geometric features of thermal capacitor <NUM> may be employed to form air pockets, so that the pressure swings inside thermal capacitor <NUM> stemming from the paraffin wax phase changes are reduced, thereby reducing cyclic stresses in thermal capacitor <NUM>. In some embodiments, vents, breathers, or other features/devices/systems may be employed to maintain a desirable pressure or pressure range within thermal capacitor <NUM> without regard to the paraffin wax phase changes.

In certain regions, the requirements for circuit breaker systems such as circuit breaker system <NUM> include that at ambient temperatures of -<NUM>, upon the failure of the heaters or the power supply to the heaters, the circuit breaker system must continue to function for at least two (<NUM>) hours prior to entering the lockout state. Accordingly, thermal storage system <NUM> and thermal capacitor <NUM> are configured to store enough heat energy to prevent a lockout state of the circuit breaker system due to liquefaction of the SF6 in -<NUM> ambient temperature conditions for at least two (<NUM>) hours.

In an experiment, an embodiment of circuit breaker system <NUM> with thermal energy storage system <NUM> exposed to -<NUM> ambient temperature conditions went from a starting point at <NUM> paraffin wax temperature and -<NUM> SF6 temperature to a lockout SF6 temperature of -<NUM> in approximately <NUM> hours. The experiment commenced with the shutting off power to heater <NUM>. During the experiment, the temperature of the SF6 decreased from the initial value of -<NUM> as the paraffin wax temperature decreased, and then stabilized at a temperature above lockout temperature during the phase change of the paraffin wax from liquid to solid at a wax temperature of <NUM> as the latent heat of fusion was supplied to the SF6 from the paraffin wax. After solidification of the wax, the SF6 temperature then continued to decrease as the wax temperature decreased, until reaching lockout temperature approximately <NUM> hours after the start of the test. The thermal capacitor <NUM> used in the test held approximately <NUM> of paraffin wax. The paraffin wax returned 201J/g of heat during the phase change. The same circuit breaker system minus thermal energy storage system <NUM> took less than one hour to go from a -<NUM> temperature to a lockout SF6 temperature of -<NUM> in ambient temperature conditions of -<NUM>. Thus, it is seen that the addition of thermal energy storage system <NUM> substantially increased the thermal mass and thermal time constant of the circuit breaker system, thereby improving the ability of the circuit breaker system to maintain operation above an SF6 lockout temperature in low ambient temperature conditions. By causing the SF6 to cool more slowly, more time is available for the operator of the circuit breaker system to take measures to prevent the circuit breaker system from reaching the lockout state.

Claim 1:
A sulfur hexafluoride (SF6) insulated circuit breaker system (<NUM>), comprising:
a tank (<NUM>) constructed to hold a quantity of SF6;
a circuit breaker (<NUM>) having contacts (<NUM>, <NUM>) insulated by the SF6;
a heater (<NUM>) operative to supply heat to heat the SF6;
a thermal capacitor (<NUM>) in conductive engagement with the tank (<NUM>),
characterized in that the thermal capacitor (<NUM>) is operative to store heat energy and constructed to conduct the heat energy to the SF6 in the tank (<NUM>) via conduction through the walls of the tank (<NUM>), wherein the thermal capacitor (<NUM>) is at least partially wrap around the tank (<NUM>) and is attached to the tank (<NUM>) using a fastening system.