Shorting switch and system to eliminate arcing faults in power distribution equipment

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is related to commonly assigned, concurrently filed:

U.S. patent application Ser. No. 10/172,208, filed Jun. 14, 2002, entitled “Shorting Switch And System To Eliminate Arcing Faults In Power Distribution Equipment;

U.S. patent application Ser. No. 10/172,826, filed Jun. 14, 2002, entitled “Shorting Switch And System To Eliminate Arcing Faults In Power Distribution Equipment”;

U.S. patent application Ser. No. 10/172,238, filed Jun. 14, 2002, entitled “Shorting Switch And System To Eliminate Arcing Faults In Power Distribution Equipment”;

U.S. patent application Ser. No. 10/172,622, filed Jun. 14, 2002, entitled “Bullet Assembly For A Vacuum Arc Interrupter”;

U.S. patent application Ser. No. 10/172,080, filed Jun. 14, 2002, entitled “Vacuum Arc Interrupter Having A Tapered Conducting Bullet Assembly”;

U.S. patent application Ser. No. 10/172,209, filed Jun. 14, 2002, entitled “Vacuum Arc Interrupter Actuated By A Gas Generated Driving Force”;

U.S. patent application Ser. No. 10/172,628, filed Jun. 14, 2002, entitled “Blade Tip For Puncturing Cupro-Nickel Seal Cup”; and

U.S. patent application Ser. No. 10/172,281, filed Jun. 14, 2002, entitled “Vacuum Arc Eliminator Having A Bullet Assembly Actuated By A Gas Generating Device”.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention is directed to shorting switches and, in particular, to shorting switches for eliminating arcing faults in low voltage power distribution equipment. The invention is also directed to shorting systems for eliminating arcing faults in power distribution equipment.

2. Background Information

There is the potential for an arcing fault to occur across the power bus of a motor control center (MCC), another medium voltage (MV) enclosure (e.g., a MV circuit breaker panel) and other industrial enclosures containing MV power distribution components. This is especially true when maintenance is performed on or about live power circuits. Frequently, a worker inadvertently shorts out the power bus, thereby creating an arcing fault inside the enclosure. The resulting arc blast creates an extreme hazard and could cause injury or even death. This problem is exacerbated by the fact that the enclosure doors are typically open for maintenance.

A high-speed shorting switch is needed for medium voltage as an alternative to arc proofing switchgear enclosures. Presently, manufacturers are developing more robust enclosures, which contain and direct the hot gases and flames out the top of the enclosure upon the occurrence of an internal arcing fault (e.g., a short across the bus bar, breaker, cable phase-to-phase or phase-to-ground). These faults can occur from a wide variety of sources, such as, for example, animals that crawl into the enclosure, tools left behind from maintenance crews, insulation failure, earthquakes, and other mechanical damage.

Rather than trying to contain and direct the blast, a new idea has been developed by others for eliminating the arcing fault altogether. This is done by shorting out the high-voltage bus either phase-to-phase or phase-to-ground. Known shorting switches use closing and holding techniques which are very expensive to buy and to maintain.

It is known to employ a high-speed shorting switch, placed between the power bus and ground, or from phase-to-phase, in order to limit or prevent equipment damage and personnel injury due to arc blasts. Such switches, which are large and costly, are located on the main power bus to shut down the entire power bus system when a fault occurs even if the fault is only on the load side of a branch circuit.

It is also known to employ various types of crowbar switches for this purpose. The switches short the line voltage on the power bus, eliminating the arc and preventing damage. The resulting short on the power bus causes an upstream circuit breaker to clear the fault.

Examples of medium voltage devices include a stored energy mechanism with vacuum interrupter contacts, and a mechanism to crush a conductor magnetically.

An example of a low voltage device is a stored energy air bag actuator, which drives a conductive member having a pin and a flange, in order to short two contacts. The first contact is in the form of a receptor for capturing the pin of the driven conductive member. The second contact has an opening, which allows the pin to pass therethrough, but which captures the flange of the driven member.

There is room for improvement in shorting switches and systems that respond to arcing faults and switch fast enough in order to protect workers and equipment from arc blasts associated with power distribution equipment.

SUMMARY OF THE INVENTION

These needs and others are met by the present invention, which provides a shorting switch and system for eliminating arcing faults in power distribution equipment. The shorting switch includes a vacuum switch having fixed and movable contact assemblies, a driven member, and a mount mounting the driven member for linear movement along a path substantially parallel to a longitudinal axis of the movable contact assembly. The driven member is coupled to the movable contact assembly to move the movable contact assembly between open and closed circuit positions with the linear movement of the driven member. A spring member has a compressed state and a released state, which moves the driven member and the movable contact assembly to the closed circuit position. A release mechanism holds and releases the driven member and the spring member. First and second terminals are respectively electrically interconnected with the fixed contact assembly and the movable contact assembly.

As one aspect of the invention, a shorting switch for eliminating arcing faults in power distribution equipment comprises: a vacuum switch comprising a vacuum envelope containing a fixed contact assembly and a movable contact assembly movable along a longitudinal axis between a closed circuit position in electrical contact with the fixed contact assembly and an open circuit position spaced apart from the fixed contact assembly; a driven member; a mount mounting the driven member for linear movement along a path substantially parallel to the longitudinal axis of the movable contact assembly, the driven member coupled to the movable contact assembly to move the movable contact assembly between the open circuit position and the closed circuit position with the linear movement of the driven member; a spring member having a compressed state and a released state, which moves the driven member and the movable contact assembly to the closed circuit position; a release member having an opening therein, the release member coupled to the driven member and normally maintaining the spring member in the compressed state; a charge disposed in the opening of the release member, the charge being actuated to fracture the release member and release the spring member to the released state; and first and second terminals respectively electrically interconnected with the fixed contact assembly and the movable contact assembly.

The spring member may be a compression spring having a first end and a second end. The release member may be a release bolt having a first end and a second end. The mount may comprise a bushing having a longitudinal opening and a longitudinal tube having a closed end and an open end, the longitudinal tube housing the compression spring, the release bolt and the charge. The first end of the compression spring may engage the closed end of the longitudinal tube. The first end of the release bolt may be coupled to the closed end of the longitudinal tube. The first end of the driven member may be coupled to the second end of the release bolt. The bushing may rest in the open end of the longitudinal tube, the driven member may rest in the longitudinal opening of the bushing, and the second end of the compression spring may bias the driven member to move the movable contact assembly to the closed circuit position after actuation of the charge.

The charge may be an electrically activated, chemical charge. The charge may be activated to provide a shock wave to fracture the release member. The release member may be a release bolt having a body and a breakline disposed thereon to locate and control fracture of the release bolt responsive to the shock wave. The breakline may have a predetermined depth in the body of the release bolt. The spring member may have a predetermined compression force, with the release bolt being structured to maintain at least the compression force until after the charge is activated.

As another aspect of the invention, a shorting system for eliminating arcing faults in power distribution equipment comprises: a vacuum switch comprising a vacuum envelope containing a fixed contact assembly and a movable contact assembly movable along a longitudinal axis between a closed circuit position in electrical contact with the fixed contact assembly and an open circuit position spaced apart from the fixed contact assembly; a driven member; a mount mounting the driven member for linear movement along a path substantially parallel to the longitudinal axis of the movable contact assembly, the driven member coupled to the movable contact assembly to move the movable contact assembly between the open circuit position and the closed circuit position with the linear movement of the driven member; a spring member having a compressed state and a released state, which moves the driven member and the movable contact assembly to the closed circuit position; a release member having an opening therein, the release member coupled to the driven member and normally maintaining the spring member in the compressed state; a charge disposed in the opening of the release member, the charge being actuated to fracture the release member and release the spring member to the released state; first and second terminals respectively electrically interconnected with the fixed contact assembly and the movable contact assembly; and means for detecting an arcing fault and responsively activating the charge disposed in the opening of the release member, wherein the activated charge fractures the release member, which releases the spring member, which drives the driven member to move the movable contact assembly to the closed circuit position to eliminate the arcing fault.

The charge may include an electrical input, the means for detecting an arcing fault and responsively activating the charge may comprise means for detecting the arcing fault and responsively outputting a trigger signal, and means for detecting the trigger signal and responsively outputting an activation signal to the electrical input of the charge.

As another aspect of the invention, a shorting switch for eliminating arcing faults in power distribution equipment comprises: a vacuum switch comprising a vacuum envelope containing a fixed contact assembly and a movable contact assembly movable along a longitudinal axis between a closed circuit position in electrical contact with the fixed contact assembly and an open circuit position spaced apart from the fixed contact assembly; a driven member having a longitudinal opening with a circumferential groove therein; a mount mounting the driven member for linear movement along a path substantially parallel to the longitudinal axis of the movable contact assembly, the driven member coupled to the movable contact assembly to move the movable contact assembly between the open circuit position and the closed circuit position with the linear movement of the driven member; a spring member having a compressed state and a released state, which moves the driven member and the movable contact assembly to the closed circuit position; a ball-lock member having a plurality of ball bearings and a push rod with a circumferential groove therein, the ball bearings engaging the circumferential groove of the longitudinal opening of the driven member to hold the spring member in the compressed state and to hold the movable contact assembly in the open circuit position; means for driving the push rod of the ball-lock member into the longitudinal opening of the release member to cause the ball bearings to engage the circumferential groove of the push rod of the ball-lock member and to release the driven member, in order to move the movable contact assembly to the closed circuit position; and first and second terminals respectively electrically connected to the fixed contact assembly and the movable contact assembly.

The means for driving the push rod may be a solenoid having a plunger, which drives the push rod of the ball-lock member into the longitudinal opening of the release member when the solenoid is actuated.

As another aspect of the invention, a shorting system for eliminating arcing faults in power distribution equipment comprises: a housing; a vacuum switch comprising a vacuum envelope containing a fixed contact assembly and a movable contact assembly movable along a longitudinal axis between a closed circuit position in electrical contact with the fixed contact assembly and an open circuit position spaced apart from the fixed contact assembly; a driven member; a mount mounting the driven member in the housing for linear movement along a path substantially parallel to the longitudinal axis of the movable contact assembly, the driven member coupled to the movable contact assembly to move the movable contact assembly between the open circuit position and the closed circuit position with the linear movement of the driven member; a spring member having a compressed state and a released state, which moves the driven member and the movable contact assembly to the closed circuit position; a latch member, which normally latches the driven member to hold the spring member in the compressed state and to hold the movable contact assembly in the open circuit position, the latch member releasing the driven member to move the movable contact assembly to the closed circuit position, with the latch member having an end, which engages the driven member, and a pivot in the housing; means for detecting an arcing fault and responsively unlatching the end of the latch member to release the driven member to move the movable contact assembly to the closed circuit position; and first and second terminals respectively electrically interconnected with the fixed contact assembly and the movable contact assembly.

The end of the latch member may be a first end, and the latch member may also have a second end. The means for unlatching the latch member to release the driven member may be a solenoid having a plunger, which moves the second end of the latch member to pivot the latch member about the pivot and to cause the first end of the latch member to release the driven member.

BRIEF DESCRIPTION OF THE DRAWINGS

A full understanding of the invention can be gained from the following description of the preferred embodiments when read in conjunction with the accompanying drawings in which:

FIG. 1

is an exploded front elevation view of a single phase, spring-loaded, high-speed vacuum shorting switch employing a single vacuum interrupter (VI) in accordance with the present invention.

FIG. 2

is a plan view of the release bolt of

FIG. 1

, which is employed to hold the spring compressed, shown as being fractured after the charge is activated.

FIG. 3

is a plot of breaking torque versus breakline depth for the release bolt of FIG.

1

.

FIG. 4

is a front elevation view of a three-phase, spring-loaded, high-speed vacuum shorting switch employing three of the shorting switches of FIG.

1

.

FIG. 5A

is a schematic diagram of an arcing fault sensor suitable for use with the shorting switch of FIG.

1

.

FIG. 5B

is a schematic diagram of another arcing fault sensor suitable for use with the shorting switch of FIG.

1

.

FIG. 5C

is a schematic diagram of a modified form of the arcing fault sensor of FIG.

5

B.

FIG. 6

is a block diagram of a shorting system including the shorting switch of FIG.

1

.

FIG. 7A

is a plot of bus voltage and current over five cycles at 500V and 38 kA for a shorting switch similar to the shorting switch of FIG.

1

.

FIG. 7B

is a plot of bus voltage and current over 27 cycles at 500V and 38 kA for a shorting switch similar to the shorting switch of FIG.

1

.

FIG. 7C

is a plot of bus voltage and current over 27 cycles at 500V and 38 kA for a shorting switch similar to the shorting switch of

FIGS. 7A and 7B

except that symmetrical length movable and stationary VI electrical stems are employed.

FIG. 8

is a block diagram in schematic form of the detection circuit of FIG.

6

.

FIGS. 9A-9C

are a block diagram in schematic form of the activation circuit of FIG.

6

.

FIG. 10

is a cross-sectional view of a single phase, spring-loaded, high-speed vacuum shorting switch employing a single vacuum interrupter (VI) and a ball-lock mechanism in accordance with another embodiment of the present invention

FIG. 11A

shows the ball-lock mechanism of

FIG. 10

with the VI contacts open, the solenoid plunger stationary, and the ball-lock not released.

FIG. 11B

shows the ball-lock mechanism of

FIG. 10

with the VI contacts open, the solenoid plunger striking the ball-lock push rod, and the ball bearings sliding on the push rod shaft.

FIG. 11C

shows the ball-lock mechanism of

FIG. 10

with the VI contacts open, the solenoid plunger pushing the ball-lock push rod, and the ball bearings rolling down the circumferential groove of the push rod shaft.

FIG. 11D

shows the ball-lock mechanism of

FIG. 10

with the VI contacts closing, the solenoid plunger stopping, and the ball-lock push rod shaft releasing the spring.

FIG. 12

is block diagram of a single phase, high-speed vacuum shorting switch employing a mechanical latch release mechanism, a solenoid, and a single vacuum interrupter (VI) in accordance with another embodiment of the present invention.

FIG. 13

is a schematic diagram of a circuit for driving the solenoids of

FIGS. 10 and 12

.

FIGS. 14A-14C

are plots of solenoid gap, plunger force and solenoid coil current for analyzing the motion of the solenoid of FIG.

12

.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to

FIG. 1

, a single phase, spring-loaded, high-speed vacuum shorting switch

2

eliminates arcing faults in power distribution equipment (not shown). The shorting switch

2

includes a single vacuum switch, such as a conventional vacuum interrupter (VI)

4

(e.g., a 3″ VI bottle made by Eaton/Cutler-Hammer). As is well known, the vacuum interrupter

4

includes a vacuum envelope or sealed vacuum chamber (e.g., vacuum bottle

6

) containing a fixed contact assembly

8

and a movable contact assembly

10

movable along a longitudinal axis between a closed circuit position (not shown) in electrical contact with the fixed contact assembly

8

and an open circuit position (as shown in

FIG. 1

) spaced apart from the fixed contact assembly

8

.

The fixed contact assembly

8

includes a fixed contact

12

sealed within the sealed vacuum bottle

6

and an electrical conductor

14

connected to the fixed contact at one end thereof. The electrical conductor

14

sealably penetrates the sealed vacuum bottle

6

and terminates at a first terminal

16

at the other end of the fixed contact assembly

8

. The movable contact assembly

10

includes a moveable contact

18

sealed within the sealed vacuum bottle

6

and moveable between a first position (as shown in FIG.

1

), out of electrical communication with the fixed contact

12

, and a second position (not shown), in electrical communication with the fixed contact

12

. The movable contact assembly

10

further includes a movable electrical stem

20

connected to the moveable contact

18

at one end thereof. The movable electrical stem

20

sealably penetrates the sealed vacuum bottle

6

and terminates at a second terminal

22

at the other end of the moveable contact assembly

10

. Preferably, the second terminal

22

is a copper stem including a plurality of threads

24

.

Although a conventional VI

4

is shown, the shield (not shown) and the contacts

12

,

18

may be removed (e.g., as a cost reduction), the length of the movable electrical stem

20

may be adjusted (e.g., shortened), and the length of the fixed or stationary stem or terminal

16

may be adjusted (e.g., lengthened) in order to provide a wide range of lengths (e.g., asymmetrical lengths).

Other modifications to the conventional VI

4

may be made to further reduce the moving mass and/or the cost of the shorting switch

2

. For example, reducing the mass will reduce the time to close. This may involve making a relatively short movable electrical stem

20

, lengthening the stationary or fixed terminal

16

, removing the contacts

12

,

18

, removing the shield (not shown), and/or employing a reduced diameter of the terminals

16

,

22

(e.g., about ⅝″ diameter).

A driven member such as, for example, an aluminum adapter shaft

26

having a threaded longitudinal opening

28

is threadably coupled at one end to the threads

24

of the movable electrical stem

20

. The aluminum adapter shaft

26

is also threadably coupled at its other end to the threads

30

of a release member, such as release bolt

32

.

A suitable mount

34

, which includes a bushing

36

(e.g., nylon) and a spring cover tube

38

, mounts the adapter shaft

26

for linear movement along a path substantially parallel to the longitudinal axis of the movable contact assembly

10

. The adapter shaft

26

is coupled to the movable contact assembly

10

to move the same between the open and closed circuit positions of the vacuum interrupter

4

with the linear movement of such shaft.

A spring member, such as compression spring

40

, has a compressed state (as shown in

FIG. 1

) and a released state (not shown), which moves the adapter shaft

26

and the movable contact assembly

10

to the closed circuit position. The release bolt

32

, which is coupled to the shaft

26

, normally maintains the compression spring

40

in the compressed state. The two ends of the compression spring

40

are disposed between a pair of washers

42

,

44

(e.g., steel). The head

46

of the adapter shaft

26

normally engages the washer

42

and the head

48

of the release bolt

32

engages the washer

44

.

The longitudinal tube

38

has a closed end

50

and an open end

52

with a flange portion

53

(e.g., steel). An opening

54

in the end

50

threadably receives and is closed by a threaded retainer bolt

56

(e.g., steel), which is threadably coupled to a threaded portion

57

of a longitudinal opening

58

of the release bolt

32

, thereby coupling the head

48

of the release bolt

32

to the closed end

50

of the longitudinal tube

38

. The lower (with respect to

FIG. 1

) end of the compression spring

40

engages the washer

44

(and, thus, the head

48

of the release bolt

32

at the closed end

50

of the longitudinal tube

38

).

Disposed within the release bolt opening

58

is a suitable charge, such as an electrically activated, chemical charge

60

. The charge

60

is actuated to fracture the release bolt

32

and release the compression spring

40

to the released state. The longitudinal tube

38

houses the compression spring

40

, the release bolt

32

and the charge

60

, which is, of course, advantageous during the activation of such charge.

The bushing

36

includes an upper portion

62

and a lower portion

64

(e.g., with respect to FIG.

1

). The upper portion

62

rests on the flange portion

53

of the longitudinal tube

38

and the lower portion

64

rests in the open end

52

of such tube. A longitudinal opening

66

passes through the upper and lower portions

62

,

64

of the bushing

36

. As shown in

FIG. 4

, the adapter shaft

26

rests in the longitudinal opening

66

of the bushing

36

.

The opening

58

of the release bolt

32

provides a longitudinal cavity

68

(shown in

FIG. 4

) along the longitudinal axis of such release bolt. The charge

60

activated to provide a shock wave to fracture the release bolt

32

. Preferably, as shown in

FIGS. 2 and 4

, the body

70

of the release bolt

32

has a breakline

72

disposed thereon to locate and control fracture of the release bolt

32

responsive to the shock wave. The breakline

72

has a predetermined depth in the release bolt body

70

, and the compression spring

40

has a predetermined compression force, with the release bolt

32

being structured to maintain at least the compression force until after the charge

60

is activated.

The release bolt

32

normally compresses the compression spring

40

. After activation of the charge

60

inside the release bolt

32

, such bolt fractures at or about the breakline

72

(as shown in FIG.

2

), thereby releasing the compression spring

40

. In turn, the upper end (with respect to

FIG. 1

) of the spring

40

biases the washer

42

and the adapter shaft

26

to move the movable contact assembly

10

to the closed circuit position after actuation of the charge

60

.

The exemplary charge

60

is a small electrically activated, chemical charge, such as model number RP-501 made by Reynolds Industries Systems, Inc. RISI). The RP-501 is a standard, end lighting, exploding bridge wire (EBW) detonator for use in general purpose applications (e.g., it is capable of detonating compressed TNT and COMP C-4). Although an exemplary detonator charge is employed, any suitable charge may be employed to fracture any suitable release member.

The release bolt

32

is employed to hold open the separable contacts

12

,

18

and to compress the spring

40

as shown in FIG.

1

. Upon activation of the charge

60

inside the bolt

32

, such bolt preferably fractures at a predetermined location, such as the breakline

72

, thereby releasing the energy of the compression spring

40

. The exemplary spring

40

closes and holds the contacts

12

,

18

closed with about 512 lbs. of force. This holding force prevents such contacts from reopening and vaporizing, while maintaining a suitably low contact resistance. For example, it is believed that at least about 300 lbs. of force is desired to hold the contacts

12

,

18

closed at a rated current of about 38 kA

RMS

symmetrical.

As shown in

FIG. 4

, the charge

60

includes an electrical input, such as a pair of conductors

74

, which pass through the opening

58

of the release bolt

32

and through an opening

76

of the bolt

56

. The charge

60

is suitably activated by an electrical signal on the conductors

74

to provide a shock wave to fracture the release bolt

32

.

In the exemplary embodiment, the bolt body

70

has a 0.5-inch diameter and the bolt cavity

68

has a 0.295-inch diameter. The exemplary bolt

32

is 4.5 inches in length, with the cavity

68

being 2.0 inches deep from the bolt head

48

, and the breakline

72

being 1.9 inches deep from the bolt head

48

. The exemplary breakline

72

is employed to locate and control the fracture zone when the shock wave, created from the charge

60

, fractures the metal release bolt

32

.

The first and second terminals

16

,

22

, which are respectively electrically interconnected with the fixed contact assembly

8

and the movable contact assembly

10

, are adapted for electrical connection to first and second power lines

78

,

80

, respectively. For example, the first power line

78

may be a copper power bus (e.g., a single phase; one phase of a three-phase power bus) and the second power line

80

may be a copper ground bus. Although a ground bus is shown, a neutral bus or a different phase may be employed.

As shown in

FIG. 1

, the vacuum interrupter

4

has a pair of mounting studs

82

,

84

(e.g., steel), which pass through respective openings

86

,

88

of the second power line

80

and through respective openings

90

,

91

of a bushing

96

and which are secured thereto by suitable fasteners

92

. The second terminal

22

of the vacuum interrupter

4

passes through a suitably sized opening

94

of the second power line

80

and through an opening

95

of the bushing

96

(e.g., nylon). The bushing

96

is secured with respect to the second terminal

22

by a nut

98

(e.g., brass). The nut

98

is suitable attached (e.g., welded; brazed) to a flexible shunt

99

(e.g., a copper laminate), which is suitable electrically connected to the second power line

80

by a pair of fasteners

100

(e.g., brass) at opposite ends of the shunt

99

. As discussed above, the second terminal

22

is coupled to the adapter shaft

26

for movement therewith and is electrically connected to the second power line

80

by the flexible shunt

99

. The flexible shunt

99

is movable between and is preferably insulated by the upper and lower nylon bushings

96

,

36

.

FIG. 3

shows the result obtained from testing the torque required to fracture a ½″ diameter bolt with a 0.295″ diameter hole for the charge. A breakline (e.g.,

72

of

FIGS. 2 and 4

) is employed to locate and control the fracture zone when the shock wave, created from the charge

60

, fractures the metal. The vertical line (MT) represents the minimum torque on the release bolt

32

suitable to fully compress the compression spring

40

. The plot shows the maximum depth of the breakline

72

while still maintaining a spring force of about 1200 pounds plus a suitable safety factor. The exemplary release bolt

32

is “grade 5” and can safely withstand a tensile stress of about 120,000 PSI without fracturing. An optimum breakline depth of about 0.025 inch or 0.03 inch is preferably employed to reliably fracture the exemplary bolt

32

with the exemplary charge

60

and still allow the spring

40

to be compressed solid and held with a suitable safety margin.

FIG. 4

shows a three-phase, spring-loaded, high-speed vacuum shorting switch

101

employing three of the shorting switches

2

of FIG.

1

. For example, the three first terminals

16

of the three shorting switches

2

may be respectively electrically connected with three corresponding power busses (e.g., phases A, B and C). The three second terminals

22

of the three shorting switches

2

may be electrically connected to a common ground bus (not shown) by the common flexible shunt

99

′. The three-phase shorting switch

101

may employ, for example, a conventional molded housing

102

without an operating mechanism.

The closing times of the shorting switches

2

of

FIG. 1

depend upon the amount of mass being moved and on the force applied by the compression springs

40

. For example, the exemplary shorting switches

2

,

101

are capable of being activated in the presence of an arcing fault in medium voltage switchgear and are able to maintain contact closure under medium voltage operating circuit parameters (e.g., 15 kV

RMS

at 38 kA

RMS

).

One form of an arcing fault sensor unit suitable for use with the shorting switches

2

,

101

is shown in FIG.

5

A. The sensor unit

103

includes the first photovoltaic device

104

including at least one, or a plurality of series connected photovoltaic cells

105

, and a first filter

107

which filters light incident upon the photovoltaic cells

105

. This first filter

107

has a passband centered on the characteristic wavelength, e.g., 521.820 nm, of the arcing material.

The sensor

103

includes a second photovoltaic device

109

, which also includes one or more series connected photovoltaic cells

111

, and a second filter

113

which filters light incident upon the photovoltaic cells

111

and has a passband that does not include the characteristic wavelength of the arcing material, e.g., centered on about 600 nm in the exemplary system.

The first photovoltaic device

104

generates a sensed light electrical signal in response to the filtered incident light, and similarly, the second photovoltaic device

109

generates a background light electrical signal with an amplitude dependent upon the irradiance of light in the passband of the second filter

113

. An electric circuit

115

, having a first branch

115

1

connecting the first photovoltaic cells

104

in series and a second branch

115

2

similarly connecting the second photovoltaic cells

111

in series, connects these two electrical signals in opposition to a light-emitting device such as a light-emitting diode (LED)

117

. When arcing is present, the sensed light electrical signal generated by the first photovoltaic device

104

exceeds the background light electrical signal generated by the second photovoltaic device

109

by a threshold amount sufficient to turn on the LED

117

. While in the absence of arcing, the first photovoltaic device

104

will generate a sensed light electrical signal due to some irradiance in the passband of the first filter

107

, it will be insufficient to overcome the reverse bias effect of the background light signal generated by the second photovoltaic device

109

on the LED

117

. In fact, where the background light is fluorescent, from an incandescent bulb or a flashlight all of which have very low irradiance in the passband of the first filter

107

, but significant irradiance in the passband of the second filter

113

, the background light electrical signal will significantly exceed the sensed light electrical signal and strongly reverse bias the LED

117

. The filters

107

and

113

can be interference filters, although lower cost bandpass filters could also be utilized.

An alternate embodiment of the sensor unit

103

′ shown in

FIG. 5B

adds a bias generator

119

in the form of one or more additional photovoltaic cells

121

connected in series with the first photovoltaic device

104

in the first branch

115

1

of the electrical circuit

115

. This puts a forward bias on the LED

117

so that fewer or smaller filtered photovoltaic cells

105

and

111

can be used. This also reduces the size and therefore the cost of the filters

107

and

113

. As the additional photovoltaic cells

121

are not provided with filters, the total cost of the sensor is reduced. The embodiment of

FIG. 5B

can be modified as shown in

FIG. 5C

to place the bias generating cells

121

of the sensor

103

″ in series with both filtered photovoltaic cells

105

and

111

, but still provide the same effect of forward biasing the LED

117

.

Through their utilization of photovoltaic cells

105

,

111

and

121

, the sensors

103

and

103

′ of

FIGS. 5A-5C

are self-energized.

FIG. 6

shows a shorting system

140

including one or more shorting switches

2

of

FIG. 1

(only one switch (SW)

2

is shown in FIG.

6

). The shorting system

140

eliminates an arcing fault

142

in medium voltage power distribution equipment

144

(e.g., switchgear). The shorting system

140

also includes a detection and activation circuit

146

for detecting the arcing fault

142

and responsively activating the shorting switch charge (C)

60

, in order that the activated charge

60

results in the elimination of the arcing fault as discussed above in connection with

FIGS. 1-3

. The circuit

146

includes a detection (OD) circuit

148

for detecting the arcing fault

142

and responsively outputting one or more trigger signals

150

, and an activation circuit (ACT)

152

for detecting the one or more trigger signals

150

and responsively outputting the activation signal

154

to the electrical inputs

155

of the charges

60

. The detection circuit

148

utilizes photovoltaic cells in a sensor unit, such as one of the sensor units

103

,

103

′,

103

″ of

FIGS. 5A-5C

.

FIGS. 7A-7C

are test waveforms showing that a shorting switch similar to the shorting switch

2

of

FIG. 1

is capable of operating within a suitable time (e.g., without limitation, less than about 4 ms) and can hold closed at about 38 kA

RMS

fault current for a duration of about 0.5 second. The conventional molded housing

102

of

FIG. 4

makes for convenient mounting to the bus bar (e.g.,

78

of

FIG. 1

) of the switchgear (e.g.,

144

of

FIG. 6

) without any additional mold costs.

FIGS. 7A and 7B

show plots of bus voltage and current over five cycles and 27 cycles, respectively, at 500V and 38 kA. In the test of

FIG. 7A

, the window in a molded case circuit breaker (not shown) used to generate arc light for testing purposes was clear (clean).

For the test of

FIG. 7B

, the window of the sensor unit is blocked to prevent arc light from reaching the detector, which is aimed at the arc-viewing window. A circuit breaker (not shown) arcs phase-to-phase on the line side and the sensor unit detects this. The sensor did not respond to the arc through the window in the circuit breaker since the light was blocked. But, since the breaker arced phase-to-phase, externally, the arc light was subsequently detected, albeit at a later time (4.4 ms total response time versus 3.20 ms). In response, the shorting switch

2

responsively quenches the arcing fault, thereby saving the circuit breaker.

FIG. 7C

shows a plot of bus voltage and current over 27 cycles at 500V and 38 kA on a shorting switch, similar to the shorting switch for

FIGS. 7A and 7B

, except that symmetric length movable and stationary electrical stems are employed in the vacuum interrupter. In this test, the window of the sensor unit is darkened. The sensor response time is longer (0.82 ms versus 0.60 ms) and the total response time is less than the response time for

FIGS. 7A and 7B

since a smaller moving mass is employed.

Table 1 summarizes the shorting system operating times for the examples of

FIGS. 7A-7C

.

TABLE 1

Total

Sensor

Switch

Operating

Time (ms)

Time (ms)

Time (ms)

Arc Source

0.60

2.60

3.20

Clean window

1.58

2.84

4.42

Window black, phase-phase

0.82

2.06

2.88

Dark window

The exemplary spring-loaded vacuum shorting switch

2

successfully operates within about 3.2 ms (FIG.

7

A), including sensing time, and holds closed for 27 cycles at 38 kA

RMS

(FIGS.

7

B and

7

C). As shown by Table 1, the shorting switches, switch, after triggering, between about 2.06 ms and about 2.84 ms and each one remains closed for the duration of the fault current.

Referring to

FIG. 8

, the detection circuit

148

is shown. In the exemplary embodiment, the medium voltage power distribution equipment

144

of

FIG. 7

includes two circuit breaker cells

156

,

157

, two upper cable cells

158

,

159

, and two lower cable cells

160

,

161

, although the invention is applicable to a wide range of medium voltage power distribution equipment having any count (e.g., one or more) of cells in which an arcing fault may occur. As another example, U.S. Pat. No. 6,229,680, which is incorporated by reference herein, discloses a switchgear cabinet having a forward compartment, a middle compartment and a rear compartment. The forward compartment is divided vertically into three cells in which are housed electrical switching apparatus such as circuit breakers.

The detection circuit

148

includes six photovoltaic sensors

162

,

164

,

166

,

168

,

170

,

172

adapted to detect arcing faults in the cells

156

,

158

,

160

,

157

,

159

,

161

, and output optical trigger signals

174

,

176

,

178

,

180

,

182

,

184

, respectively. These photovoltaic sensors

162

,

164

,

166

,

168

,

170

,

172

are self-powered from arc light and have an output

186

(as shown with sensor

162

) with the respective optical trigger signals

174

,

176

,

178

,

180

,

182

,

184

, which are responsive to the arc light. In the exemplary embodiment, suitable photovoltaic sensors are shown in

FIGS. 5A-5C

, although any suitable sensor for detecting any characteristic of an arcing fault may be employed. In the exemplary embodiment, the detection circuit

148

is employed for each switchgear enclosure (not shown), with three photovoltaic sensors for each circuit breaker cell.

The detection circuit

148

further includes a suitable optical multiplexer

188

having a plurality of fiber optic inputs

190

,

192

,

194

,

196

,

198

,

200

and a fiber optic output

202

. A plurality of suitable fiber optic cables

204

,

206

,

208

,

210

,

212

,

214

are connected between the outputs

186

of the photovoltaic sensors

162

,

164

,

166

,

168

,

170

,

172

and the inputs

190

,

192

,

194

,

196

,

198

,

200

, respectively, of the optical multiplexer

188

. The fiber optic cables (as shown with cable

210

) include a first connector

216

attached to the corresponding photovoltaic sensor output (as shown with the output

186

of sensor

168

) and a second connector

218

attached to the corresponding optical multiplexer input (as shown with input

196

).

The output

202

of the optical multiplexer

188

outputs an optical trigger signal

220

to another fiber optic cable

222

, which includes a first connector

224

attached to the multiplexer output

202

. The other end (as shown in

FIG. 9A