Arrester disconnector assembly having a capacitor and a resistor

FIELD OF THE INVENTION

The present invention relates to a disconnector assembly for an arrester. The arrester is isolated upon arrester failure. More particularly, the present invention relates to a pair of electrical terminals coupled by a capacitor assembly, a spark gap and an explosive cartridge. The capacitor assembly includes a capacitor and resistor connected electrically in series, and is electrically parallel to the spark gap.

BACKGROUND OF THE INVENTION

100021 Lighting or surge arresters are typically connected to power lines to carry electrical surge currents to ground, thereby preventing damage to lines and equipment connected to the arresters. Arresters offer high resistance to normal voltage across power lines, but offer very low resistance to surge currents produced by sudden high voltage conditions caused by, for example, lighting strikes, switching surge currents or temporary overvoltages. After the surge, the voltage drops and the arrester normally returns to a high resistance state. However, upon arrester malfunction or failure, the high resistance state is not resumed, and the arrester continues to provide an electrical path from the power line to ground. Ultimately, the line will fail due to a short circuit condition or breakdown of the distribution transformers, and the arrester will require replacement.

To avoid line lockout, disconnector assemblies are commonly used in conjunction with arresters to separate a malfunctioning arrester from the circuit and to provide a visual indication of arrester failure. Conventional disconnector assemblies have an explosive charge to destroy the circuit path and physically separate the electrical terminals. Examples of such disconnector assemblies are disclosed in U.S. Pat. No. 5,952,910 to Krause and U.S. Pat. Nos. 5,057,810 and 5,113,167 to Raudabaugh, as well as U.S. Pat. No. 5,434,550 to Putt, U.S. Pat. No. 4,471,402 to Cunningham and U.S. Pat. No. 4,609,902 to Lenk, the subject matter of each of which are hereby incorporated by reference.

Traditionally, polymer-housed distribution class arresters are assembled with a ground end insulating bracket that physically supports the arrester, as well as isolating the ground end of the arrester from the system ground in the event of arrester service failure. A ground lead connector, or isolator, connects the ground end of the isolator to the system neutral or ground wire.

In normal service conditions, the arrester grading current flows through the ground lead isolator. If the arrester fails, the arrester 60 Hz fault current flows through the failed arrester and through the ground lead disconnector, which causes the ground lead disconnector to operate. The disconnector disconnects from ground, thereby effectively isolating the failed arrester from ground. Separating the arrester from ground allows the utility to provide uninterrupted service to its customers. This also facilitates identifying the failed arrester so that it may be replaced with a new arrester.

Existing disconnectors typically have a grading component in parallel with a sparkgap. The grading component and sparkgap are located close to a detonating device, such as an unprimed cartridge. The grading component conducts the arrester grading current under normal service conditions. If arrester failure occurs, the arrester grading current increases from a few milliamperes to amperes or thousands of amperes, depending on the utility system grounding at the arrester location. This high current flow causes voltage to develop across the disconnector grading component. When voltage reaches a predetermined level, the parallel sparkgap sparks over, thereby causing heat build-up on the cartridge. The cartridge then detonates and separates the ground lead connection.

Typically, the grading component is a low voltage precision resistor, a high power resistor, or a semi-conductive polymer material. However, these grading components tend to fail during prolonged temporary overvoltage situations. Failure of the grading components can prevent disconnectors from properly detonating. A need exists for a disconnector providing a more reliable cartridge detonation.

Furthermore, existing grading components are often significantly damaged during durability testing, which results in deterioration of the electrical integrity of the disconnector. A deteriorated grading component may result in a degraded time-current deterioration characteristic. A need exists for a grading component that is not significantly deteriorated by durability testing.

A need exists for an improved disconnector assembly for an arrester.

SUMMARY OF THE INVENTION

Accordingly, it is a primary objective of the present invention to provide an improved disconnector assembly.

A further objective of the present invention is to provide a disconnector assembly for an arrester that provides a more reliable cartridge detonation.

A still further objective of the present invention is to provide a disconnector assembly for an arrester having a grading component that is not significantly deteriorated by durability testing.

The foregoing objects are basically attained by providing a disconnector assembly for an arrester. A non-conductive housing has first and second opposite ends separated by an internal chamber. A first electrical terminal is connected at the first end. A second electrical terminal is connected at the second end. A capacitor assembly engages and extends between the first and second terminals in the internal chamber. A sparkgap is electrically parallel to the capacitor assembly between the first and second terminals. A cartridge with an explosive charge is positioned in the internal chamber, the cartridge being electrically parallel to the capacitor and electrically in series with the spark gap.

In another embodiment, the foregoing objects are basically attained by providing a disconnector assembly for an arrester. A non-conductive housing has first and second opposite ends separated by an internal chamber. A first electrical terminal is connected at the first end. A second electrical terminal is connected at the second end. A capacitor assembly engages and extends between the first and second terminals in the internal chamber. The capacitor assembly includes a capacitor and a resistor electrically connected in series. A sparkgap is electrically parallel to the capacitor assembly between the first and second terminals. A cartridge with an explosive charge is positioned in the internal chamber, the cartridge being electrically parallel to the capacitor assembly and electrically in series with the sparkgap. The capacitance characteristic of the capacitor allows the capacitor to withstand prolonged temporary overvoltage conditions that cause linear resistors to fail, thereby providing a more reliable disconnector assembly.

Other objects, advantages and salient features of the invention will become apparent from the following detailed description, which, taken in conjunction with the annexed drawings, discloses preferred embodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

Referring now to the drawings that form a part of the original disclosure:

FIG. 1

is a side elevational view in partial cross section of a disconnector assembly according to the present invention;

FIG. 2

is a bottom plan view in cross section taken along line

2

—

2

of

FIG. 1

of the present invention;

FIG. 3

is a schematic electrical diagram according to a first embodiment of the present invention showing the capacitor assembly connected electrically parallel the spark gap;

FIG. 4

is a schematic electrical diagram according to a second embodiment of the present invention showing the capacitor connected electrically parallel the spark gap;

FIG. 5

is an elevational view of the capacitor assembly taken in cross section along a plane through the longitudinal axis of the capacitor assembly of the present invention; and

FIG. 6

is a bottom plan view of the capacitor assembly of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

As shown in

FIGS. 1-5

, the present invention relates to a disconnector assembly

10

for an arrester

13

. A non-conductive housing

21

has first and second opposite ends

91

and

93

separated by an internal chamber

27

. A first electrical terminal

12

is connected at the first end

91

. A second electrical terminal

41

is connected at the second end

93

. A capacitor assembly

95

engages and extends between the first and second terminals

12

and

41

in the internal chamber

27

. The capacitor assembly includes a capacitor

31

and a resistor

81

electrically connected in series. A cartridge

51

with an explosive charge is positioned in the internal chamber

27

. The cartridge is electrically parallel to the capacitor

31

. A spring spacer

53

receives the cartridge

51

. The spring spacer

53

is adjacent the first terminal

12

and spaced from the second terminal

41

.

Referring initially to

FIGS. 1 and 2

, a disconnector assembly

11

, according to the present invention, comprises a first, upper electrical terminal

12

electrically connected to arrester

13

, and a second, lower electrical terminal, or stud,

41

electrically connected to ground

17

. Arrester

13

is electrically connected to power line

15

, which is representative of a power system. Terminals

12

and

41

are mechanically and electrically coupled to each other.

Arrester

13

is conventional, and thus, is not described in detail. The arrester may be formed according to U.S. Pat. No. 4,656,555 to Raudabaugh, the subject matter of which is hereby incorporated by reference.

Terminals

12

and

41

are mechanically connected to one another by a bracket

21

. Bracket

21

may be formed of any suitably strong insulating material, such as a non-conductive plastic. Preferably, the bracket is made of a glass filled polyester material. As noted above, the bracket

21

has a base

23

and a wall

25

extending substantially perpendicularly from base

23

, with wall

25

defining an internal cavity

27

extending between surface

22

of base

23

and surface

28

of wall

25

. The upper end of cavity

27

is connected to bracket surface

26

by cylindrical upper bore

30

. The lower end of cavity

27

is connected to surface

28

of wall

25

by a stepped lower chamber

32

. The transverse diameter of lower chamber

32

is greater than the transverse diameter of internal cavity

27

.

Between cavity

27

and lower chamber

32

, the bracket has a radially extending lower annular shoulder

34

. An upper shoulder

36

extends radially at the interface of cavity

27

and upper bore

30

.

Upper electrical terminal

12

is of conventional construction, and has a head portion

38

located within cavity

27

and abutting upper shoulder

36

. An externally threaded shank portion

40

of terminal

12

extends from the head portion through upper bore

30

, such that the shank portion is at least partially exposed exteriorly of bracket

21

for coupling to arrester

13

. In this manner, head portion surface

42

engages upper shoulder

36

, while head portion surface

44

is exposed in cavity

27

.

An isolator assembly

11

is disposed in cavity

27

. The isolator assembly may include a capacitor

31

, a cartridge

51

, and a spring spacer

53

. The spring spacer

53

abuts surface

44

of terminal head portion

38

. Spring spacer

53

provides a biasing force to maintain electrical or physical contact of the isolator assembly components within cavity

27

, and facilitates electrically connecting upper terminal

12

to lower terminal (stud)

41

. Tab

55

extends downwardly from the spring spacer

53

into the cavity

27

and receives cartridge

51

.

Capacitor

31

is mounted in cavity

27

and extends between the spring spacer

53

and upper surface

47

of cap

46

, thereby providing an electrical connection between the upper and lower terminals

12

and

41

through conductive cap

46

.

FIG. 4

shows an electrical diagram of the isolator assembly

11

having a capacitor

31

between the arrester

13

and ground

17

. Preferably, the capacitor is formed of a high voltage material, such as ceramic. Preferably, the capacitor

31

is encased in an insulative sleeve or ceramic collar

71

to protect the capacitor from carbon contamination during a gap sparkover that causes the cartridge

51

to discharge.

The capacitance of the high-voltage capacitor

31

eliminates failure during periods of prolonged overvoltage conditions, which was a problem with the resistors. Failure of the resistors prevents proper detonation of the cartridge after an arrester has been exposed to a prolonged temporary overvoltage condition. Since the high-voltage capacitor

31

does not fail during the arrester overvoltage event it provides a more reliable cartridge detonation, thereby eliminating the nuisance associated with system lockouts experienced by utilities and their customers. The high-voltage capacitor

31

provides improved temporary overvoltage capabilities for the arrester during system overvoltage conditions than was available with resistors used alone in isolators, thereby eliminating capacitor failure and non-detonation of the cartridge. Thus, the high-voltage capacitor

31

improves temporary overvoltage capability for the arrester

13

under system overvoltage conditions.

The electrical and mechanical integrity of the high-voltage capacitor

31

, in conjunction with the good dielectric integrity of the ceramic collar or insulative sleeve

71

, prevents significant deterioration when the serially connected arrester is exposed to durability testing. Durability testing, such as

100

kA lightning impulse duty, does not significantly deteriorate the electrical integrity of the isolator assembly

11

having a high-voltage capacitor

31

. Isolators using a resistor alone may be significantly damaged by this type of duty, resulting in deterioration of the electrical integrity of the disconnector assembly. Such damage includes a degraded time-current detonation characteristic, which results in an unreliable cartridge detonation.

The isolator assembly

11

having the high-voltage capacitor

31

detonates at a lower current level, typically around a few hundred milliamperes, than existing isolator assemblies using resistors, since the high-voltage capacitor has a high impedance. The high impedance allows sparkover of the sparkgap when the arrester

13

has only partially failed or fails in a high-impedance grounded or delta system configuration, thereby providing a more reliable cartridge

51

detonation and a more reliable isolator assembly

11

.

In another preferred embodiment, a capacitor assembly has a capacitor

31

connected electrically in series with a resistor

81

, as shown in

FIGS. 3 and 5

, to provide the electrical path between the arrester

13

and the ground

17

. The resistor

81

improves the capability of the capacitor to withstand high frequency oscillations associated with the gap sparkover

75

, thereby minimizing the probability of damaging the capacitor. Preferably, both the capacitor

31

and resistor

81

are housed in an insulative sleeve

71

to protect the capacitor from carbon contamination during a gap sparkover occurring during arrester operations, as shown in FIG.

5

. The capacitor assembly

95

has the capacitor

31

housed between the resistor

81

and a terminal

97

. The resistor

81

has a conductive surface

82

and the terminal

97

has a conductive surface

98

(

FIG. 6

) to provide an electrical connection from the upper terminal

12

through the capacitor assembly

95

to the lower terminal

41

. The insulating sleeve

71

may have an RTV type material oriented in the interface between the sleeve and the resistor

81

, capacitor

31

and terminal

97

to enhance the dielectric integrity of the interface.

Cartridge

51

with an explosive charge is mounted in cavity

27

adjacent capacitor

31

. Cartridge

51

is elongated along a cartridge axis that is substantially perpendicular to the longitudinal axis of terminals

12

and

41

and of bracket cavity

27

. Cartridge

51

receives the spring spacer tab

55

between its head

61

and body

62

, as shown in

FIG. 1

, to secure the cartridge in cavity

27

proximal the spring spacer

53

.

Second terminal, or lower terminal,

41

is a conventional stud. The second terminal

41

has a head portion, or cap,

46

and a threaded shank portion

64

. Head portion

46

has an upper surface

47

facing into cavity

27

and abutting the housing lower shoulder

34

. Terminal

41

is maintained in position in housing

21

by engagement of its head portion

46

with housing lower shoulder

34

and by a suitable adhesive

56

, such as an epoxy.

An adhesive

56

between the shoulder

48

of head portion

46

and the wall

25

secures the second terminal within the housing

22

. Any suitable adhesive may be used, but preferably the adhesive is a thick epoxy that has a fast curing time in air to avoid contaminating the disconnector assembly during the manufacturing process.

A gasket

57

is positioned between the upper surface of the shoulder

48

of the head portion

47

and the lower shoulder

34

of the cavity

27

. The gasket further ensures adhesive

56

docs not enter cavity

27

, thereby possibly damaging any of the components of the disconnector assembly.

As illustrated in

FIG. 1

, a spark gap

75

, shown schematically in

FIGS. 3 and 4

, is provided between the head

61

of the cartridge

61

and the upper surface

27

of the lower terminal

41

. The spark gap

75

is connected electrically in parallel to the capacitor

31

between the first and second terminals

12

and

41

, as shown in FIG.

4

. In another embodiment shown in

FIG. 3

, the spark gap

75

is connected electrically in parallel to the capacitor assembly

95

. The cartridge

51

is connected electrically in series with the spark gap

75

, as shown in

FIGS. 3 and 4

, so that when the gap sparks over during arrester failure the cartridge detonates, thereby isolating the arrester

13

from ground

17

.

Assembly and Disassembly

A fully assembled disconnector assembly

11

is shown in

FIGS. 1 and 2

. Upper electrical terminal

12

is inserted through bore

30

to connect bracket

21

to an arrester

13

. The isolator assembly

11

is then simply dropped into cavity

27

over terminal

12

. Cavity

27

is then sealed by securing gasket

57

and lower terminal stud

41

to wall

25

of bracket

21

with adhesive

56

. Disconnector assembly

11

is then completed by allowing the adhesive

56

to cure, thereby sealing the isolator assembly

11

in cavity

27

.

During normal non-fault operation of the arrester

13

, little or no current passes through isolator assembly

11

due to the high resistance of the arrester. When subjected to lighting or surge currents, the arrester discharges high pulse currents which travel through arrester

13

and isolator assembly

11

. Within the isolator assembly, the current will arc over between the spring spacer

55

of the cartridge

51

and upper surface

47

of the lower terminal

41

and to ground

17

.

When the arrester is properly functioning, the gaps spark over for high current, short duration pulses which last less than 100 milliseconds for lightening and less than several milliseconds for switching currents. For such short sparkovers, insufficient energy is generated to activate or denote the cartridge. However, if the lightening arrester fails to withstand the voltages, the arcs are generated over a sufficiently extended period to activate the unprimed cartridge, causing an explosion that separates the terminals

12

and

41

mechanically from one another. The force of the exploded charge forces at least one of the terminals, usually lower terminal

41

, from the housing

21

. This action electrically disconnects arrester

13

from the system, and provides a visual indication of the need for arrester replacement.

While advantageous embodiments have been chosen to illustrate the invention, it will be understood by those skilled in the art that various changes and modifications may be made therein without departing from the scope of the invention as defined in the appended claims.