Dead tank circuit breaker with surge arrester connected across the bushing tops of each pole

Surge arrester structure is provided for a dead tank circuit breaker. The circuit breaker has a pole assembly with a first electrical terminal in a first bushing, and a second electrical terminal in a second bushing. The first terminal is electrically connected to a stationary contact and the second terminal is electrically connected to a movable contact. The surge arrester structure includes a surge arrester having first and second opposing ends. A first conductor structure electrically and mechanically connects the first end of the surge arrester with an end of the first terminal. A second conductor structure electrically and mechanically connects the second end of the surge arrester with an end of the second terminal. The surge arrester is electrically connected parallel with respect to the stationary and movable contacts so that the surge arrester can limit transient over voltages occurring across the contacts when the contacts are open.

FIELD

The invention relates to high voltage, dead tank circuit breakers and, more particularly, a surge arrester connected across the tops of each pole in horizontal or vertical configurations.

BACKGROUND

Circuit breakers are commonly found in substations and are operable to selectively open and close electrical connections. Typical dead tank circuit breakers have pole assemblies that include first and second electrical conductors in associated bushings. As is known in the art, electrical power lines are coupled to first and second electrical conductors, and the circuit breaker selectively opens or closes the electrical connection there-between.

Surge arresters are typically used in the industry for lightning impulse protection wherein they are connected line-to-ground closer to the equipment being protected on a separate pedestal. The surge arrester application is very common as transmission line protection connected from overhead line to ground for lightning protection.

Reactor de-energizing is a severe switching duty for any high voltage circuit breaker. The reactors are used for compensation purposes and are switched almost daily. Reactor de-energizing can cause over voltages and re-ignitions and thus a thermal/dielectric failure of an interrupter. Re-ignitions have the potential to be catastrophic to the breaker if current starts flowing again.

There is a need to provide a surge arrester structure that is electrically and physically connected across the circuit breaker contacts for overvoltage protection on special switching applications such as reactor switching applications.

SUMMARY

An object of the invention is to fulfill the need referred to above. In accordance with the principles of the embodiments, this objective is obtained by providing surge arrester structure for a dead tank circuit breaker. The circuit breaker has a pole assembly with a first electrical terminal carried in a first bushing, and a second electrical terminal carried in a second bushing. The first electrical terminal is electrically connected to a stationary contact which is immovably secured within the pole assembly and the second electrical terminal is electrically connected to a movable contact that is slidable within the pole assembly. The surge arrester structure includes a surge arrester having first and second opposing ends. A first conductor structure is constructed and arranged to electrically and mechanically connect the first end of the surge arrester with an end of the first electrical terminal. A second conductor structure is constructed and arranged to electrically and mechanically connect the second end of the surge arrester with an end of the second electrical terminal. The surge arrester is electrically connected parallel with respect to the stationary and movable contacts so that the surge arrester can limit transient over voltages occurring across the contacts when the contacts are open.

In accordance with another aspect of a disclosed embodiment, a method limits transient over voltages occurring across first and second contacts of a circuit breaker when the contacts are open. The method provides a circuit breaker with at least one pole assembly, with a first electrical terminal carried in a first bushing, and a second electrical terminal carried in a second bushing. The first electrical terminal is electrically connected to the first contact and the second electrical terminal is electrically connected to the second contact. A first end of a surge arrester is electrically and mechanically connected with an end of the first electrical terminal. A second end of the surge arrester is electrically and mechanically connected with an end of the second electrical terminal to thereby electrically connect the surge arrester parallel with respect to the contacts so that the surge arrester can limit transient over voltages occurring across the contacts when the contacts are open.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

With reference toFIG. 1, a high-voltage, dead-tank circuit breaker is shown, generally indicated at10. Circuit breaker10is preferably a three phase circuit breaker and thus includes three pole assemblies12a,12band12c. Each pole assembly12includes a first electrical terminal14carried in a first bushing16and a second electrical terminal18carried in a second bushing20. The bushings16and20extend generally vertically. Electrical power lines are coupled to the first and second electrical terminals14and18, and the circuit breaker10selectively opens or closes the electrical connection there-between. It can be appreciated that the number of pole assemblies12can be selected for the desired application and need not be limited to three.

With reference toFIG. 2, a simplified view of an interior of a pole assembly12is shown, wherein first electrical terminal14is electrically connected to a stationary contact22which is immovably secured within pole assembly12. Second electrical terminal18is electrically connected to a movable contact24which is carried within pole assembly12in a manner allowing longitudinal movement therein. Thus, in a first position, the movable contact24may be positioned to break the electrical connection between first the electrical terminal14and second electrical terminal18. In a second position, the movable contact24may be brought into contact with stationary contact22to electrically connect the first electrical terminal14and the second electrical terminal18. The interior space of pole assemblies12are sealed and generally adapted to minimize arcing between stationary contact22and movable contact24. The interior volume of pole assembly12may be filled with dielectric material that preferably includes SF6, dry air, dry nitrogen, CO2or oil. Alternatively, a vacuum-type interrupter could be employed within the tank volume surrounded by dielectric materials mentioned.

With reference toFIGS. 3 and 4, surge arrester structure is shown, generally indicated at26, in accordance with an embodiment, mounted generally horizontally between the top portions of terminals14and18of respective bushings16and20. Thus, the surge arrester structure26is electrically and mechanically connected across the circuit breaker contacts22and24. Although a surge arrester structure26is shown only for one pole12a, it can be appreciated that a surge arrester structure26can be provided for each pole12a,12band12cof the circuit breaker10, in the manner similar to that shown inFIG. 3.

The surge arrester structure26includes a silicone-housed surge arrester28having first and second opposing ends30and32, respectively. First end30is electrically and mechanically connected to the terminal14via a first conductor structure, generally indicated at34, and the second end32is electrically and mechanically connected to the terminal18via second conductor structure, generally indicated at36. Each of the conductor structures34and36includes a generally horizontally disposed line terminal37and joined therewith, a generally vertically disposed line terminal38to provide the electrical and mechanical connection between the end30,32of the arrester28and the terminal14,18, respectively. Thus, the surge arrester28is mounted generally horizontally between the bushings16and20.

The surge arrester28includes conventional metal oxide disks (not shown) housed therein and acknowledged for their high energy capability, excellent low level protective characteristics and long life. A conventional grading ring40is coupled at each end of30,32of the arrester28.

As noted above, the surge arrester structure26connects electrically across the circuit breaker contacts22and24. The surge arrester structure26is bypassed when the circuit breaker10is closed. The fast acting surge arrester structure26protects the circuit breaker10during the open operation or de-energization by clamping the overvoltage exceeding its protective level appearing across the circuit breaker10. The surge arrester structure26is thus a protective device which protects the internal dielectrics of a high-voltage apparatus against the strain of impermissible overvoltage surges. The surge arrester structure26thus protects from surges that occur due to switching operations such as a reactor switching application.

With reference toFIG. 5, another embodiment of surge arrester structure is shown, generally indicated at26′ preferably for use above 345 kV applications. In this embodiment, the surge arrester structure26′ is mounted generally vertically between the bushings16and20. The surge arrester structure26′ includes a silicone-housed surge arrester28′ having first and second opposing ends42and44, respectively. First end42is electrically connected to the top or end of terminal18via a conductor structure46. The second end44is electrically connected to the top or end of terminal14via a conductor structure48, preferably with a fusible breakaway connection. The conductor structures46,48can be electrical wires. The surge arrester28′ mounts vertically on a station post insulator50and a stand-alone pedestal52that are preferably also mounted vertically. Similar to the surge arrester structure26ofFIG. 3, the surge arrester structure26′ connects electrically across the circuit breaker contacts22and24and thus functions in a manner similar to that described above.

An optional surge arrester counter54, such as EXCOUNT from ABB, is mounted to the surge arrester28′ and counts the number of discharges. The counter54also records the amplitude of the surges, together with their date and time, and measures the total leakage current and (optionally) resistive current through the arrester28′. The measurements are stored in the EXCOUNT sensor, and can be collected when convenient with the aid of a hand-held cordless transceiver (not shown).

Conventional surge arresters are not electrically/physically connected across the circuit breaker for overvoltage protection on special switching applications such as reactor switching applications. The conventional surge arresters are typically being used in the industry for lightning impulse protection wherein they are connected line-to-ground closer to the equipment being protected on a separate pedestal. The embodiments disclosed herein are used to limit transient over voltages appearing across the circuit breaker open contacts caused by severe switching duties such as the reactor being de-energized. The surge arrester structure26,26′ connects parallel and external to the circuit breaker at bushing top terminals14,18. By electrically connecting the surge arrester structure26parallel to the circuit breaker contacts, the voltage appearing across circuit breaker open contacts22and24will be clamped. The voltage clamping will be decided by the protective level of the surge arrester structure26,26′.

The surge arrester structure26,26′ can be installed on existing circuit breakers externally without compromising dielectric ratings of the breaker. The surge arrester structure26connected directly to the circuit breaker bushing top terminals14,18will not require separate foundation for surge arrester installation. The surge arrester structure26,26′ that is mounted very close to the circuit breaker contacts is very effective for fast rising transient over voltages.

The surge arrester structure26,26′ prevents the over voltage going across the interrupter open contacts, therefore reducing the probability of internal flashovers after reactor is de-energized. The voltage stress level on the internal grading capacitors is also reduced due to parallel connection of surge arrester structure26,26′ in case of multi-break interrupter chamber.