Title of Invention	"A NOZZLE OF IMPROVED THERMAL AND DIELECTRIC CAPABILITIES FOR SULPHUR HEXA-FLUORIDE (SF6) PUFFER INTERRUPTERS."
Abstract	This invention relates to a nozzle of improved thermal and dielectric capabilities for sulphur hexa-fluoride (SF6) puffer interrupters, said nozzle made of (PTFE) Polytetra fluoro ethylene and having a throat region (T) surrounding an inter-electrode gap (7) of said interrupter, characterized in that said throat region (T) is provided with liners comprising an insert (I, I') made from erosion resistant material capable of withstanding high arc temperatures.

Title of Invention

"A NOZZLE OF IMPROVED THERMAL AND DIELECTRIC CAPABILITIES FOR SULPHUR HEXA-FLUORIDE (SF6) PUFFER INTERRUPTERS."

Abstract

This invention relates to a nozzle of improved thermal and dielectric capabilities for sulphur hexa-fluoride (SF6) puffer interrupters, said nozzle made of (PTFE) Polytetra fluoro ethylene and having a throat region (T) surrounding an inter-electrode gap (7) of said interrupter, characterized in that said throat region (T) is provided with liners comprising an insert (I, I') made from erosion resistant material capable of withstanding high arc temperatures.

Full Text	FIELD OF THE INVENTION The present invention relates to a nozzle of improved thermal and dielectric capabilities for sulphur hexa-fluoride(SF&) puffer interrupters. BACKGROUND OF THE INVENTION Sulphur hexa-fluoride (SF6) has successfully replaced oil as an efficient power interruption medium, in high voltage circuit breakers. When two current carrying contacts are separated in an alternating current (AC) interrupter, an arc is drawn between the electrodes. This arc helps commuting the current till its natural current-zero. The shape and size of the arc column is controlled by the magnitude of the current and the cooling offered by the gas flowing over the arc. The gas flow and the flow pattern are regulated by an insulated nozzle surrounding the gap between the two electrodes. The gas mass is delivered in this zone using an internal compression arrangement, using a cylinder and piston combination linked to the moving system. Conventionally, PTFE (polytetra fluoro ethylene) nozzles are used for single pressure (puffer) SF6 interrupters in medium and high voltage AC circuit breakers. During the interruption process,high energy intense arc is formed between the separating contacts. Since the nozzle is positioned in the vicinity of this intense arc, the heat of the arc and the hot gas cause evaporation of the PTFE material in the throat and nearby region of the nozzle suffer which heavy erosion with each arcing/interruption. This causes change in the nozzle throat and the throat size increases gradually with the number of interruptions performed by the interrupter. This affects the designed performance and may ultimately lead to failure of the interrupter. The evaporated material together with arc material mixing with the cooling gas may contaninate the host insulating medium during the process of interruption. This contaminated gas exhibits lower dielectric strength and may lead to dielectric failures during the process of interruption. The PTFE nozzles being made of soft structured material, the hot metallic and non-metallic particles of the arc and the eroded material may get embedded on the surface of the nozzle exposed to the arc. The embedded particles degrade the tracking characteristics of the nozzle resulting in failures. SUMMARY OF THE INVENTION Thus the main object of the present invention is to enhance the thermal and dielectric ratings of SF- puffer interrupters by reducing nozzle erosion and generation of erosion products. Another object of the invention is to retain the nozzle size, thereby improving the reliability of current interruption for increased number of operations. These and other objects of the present invention are achieved by controlling the contaminants,principally, the ablation/erosion from the soft nozzle and containing the nozzle distortion and retaining the dielectric strength of the insulating medium of SF& gas. This control is achieved by providing an insert of high temperature resistant material as liners in the throat region of the nozzle; the high temperature resistant material exhibiting insignificant erosion at high arc temperatures. The low throat region of the nozzle can be of high-alumina ceramic (Al2O3)- For better thermal shock-withstanding capability and for ease of stacking, circular coin like disc laminates are used. The disc shaped alumina laminates are sized to suit the throat dimension of the nozzle and assigned interrupter fault rating . For best results a radial depth of at least 8 to 10 mm are used. Laminates in axial thickness varying between 4 mm and 8 mm give best results and a minimum of three laminates are used per nozzle. For low current capacitive or inductive switching applications stacks of disc laminates with stepped formation are advantageously used. The formation enhances tracking length and exhibits higher tracking resistance. Thus the present invention provides a nozzle of improved thermal and dielectric capabilities for sulpur hexa-fluoride (SFg) puffer interrupters,said nozzle made of PTFE and having a throat region surrounding an inter-electrode gap of said interrupter, characterized in that said throat region is provided with liners comprising inserts made of erosion resistant material capable of withstanding high arc temperatures. BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS Figures l(a), l(b) and l(c) shows the interrupter in cross-section in a closed, partially open and open states. Figure 2(a) shows the prior art nozzle. Figure 2(b) shows the nozzle of the present invention. Figure 3(a) shows the disc laminate. Figure 3(b) shows the insert or the disc laminates stack of the present invention. Figure 4(a) shows the stepped disc laminate. Figure 4(b) shows the insert, made of stepped disc laminate stack. DETAILED DESCRIPTION OF THE DRAWINGS The invention will now be described in detail by way of examples, with reference to the accompanying drawings. Figures l(a),l(b) and l(c) show an interrupter in cross-section. Three positions of the interrupter 'closed ', 'partially open1 an 'open1 are shown. In the 'closed' position the main moving contact 2 is shown in contact with the main fixed contact 1. In this position the moving arcing contact 4 is also shown engaged to the fixed arcing contact 3. When the arcing contacts 3 and 4 are separated, as shown in figure l(b) (partially open position), an arc is drawn between the contacts, the shape and size of the arc is determined by *the magnitude of current and the cooling offered by the SF6 gas flowing over the arc. The flow of SF6 gas and the flow pattern is regulated by an insulated PTFE nozzle 5. Nozzle 5 is so arranged that its throat region T surrounds the inter electrode gap 7 of the interrupter. As shown in Figure 2(b), the throat region T of the nozzle 5 is provided with liners comprising an insert I. Insert I is made from erosion resistant material which can withstand high arc temperatures. High alumina ceramic (Al2O3) is used for making the insert I. The insert I comprises a stack of at least three disc laminates D which are made in the shape of circular coin like shape for better thermal shock withstanding capacity and for ease of stacking. The size of the disc laminate D will depend on the dimension of throat T of the nozzles 5 and the assigned interrupter fault rating. For best results the disc laminates D should have a minimum radial depth of 8-10 mm and axial thickness varying between 4 mm and 8 mm. With the use of such inserts as lining for the throat region T of the nozzle 5, the nozzle size can be retained by minimizing erosion which ultimately results in reduction of contamination. Thereby, for the interrupter, increased dielectric rating and consistency in performance ever after prolonged/repetitive arcing are achieved. Figures 4(a) and 4(b) show a stepped disc laminate D' and a stack thereof respectively, which can be used as an insert I' for higher tracking resistance for special switching applications like low current capacitive or inductive switching applications. The above description of the invention should be considered as illustrative and not restrictive. The invention may be embodied in other specific forms by one skilled in the art, without departing from the spirit or essential characteristics thereof. WE CLAIM; 1. A nozzle of improved thermal and dielectric capabilities for sulphur hexa-fluoride (SF6) puffer interrupters, said nozzle made of PTFE and having a throat region (T) surrounding an inter-electrode gap (7) of said interrupter, characterized in that said throat region (T) is provided with liners comprising an insert (I,I') made from erosion resistant material capable of withstanding high arc temperatures. 2. The nozzle as claimed in claim 1 wherein said insert (I,I')is made from high-alumina ceramic (Al2O3). 3. The nozzle as claimed in the preceding claims wherein said insert comprises a stack (I,I') of circular coin like disc laminates (D,D'). 4. The nozzle as claimed in the preceding claims wherein said disc laminates (D,D') are sized to suit the dimension of said nozzle throat (T). 5. The nozzle as claimed in the preceding claims, wherein said disc laminates (D,D') have a radial depth of at least 8 to 10 mm. 6. The nozzle as claimed in the preceding claims wherein said disc laminates (D,D') have an axial thickness between 4 mm and 8 mm. 7. The nozzle as claimed in the preceding claims wherein said insert comprises a stack (I,!1) of at least three disc laminates (D,D'). 8. The nozzle as claimed in claim 3 wherein said stack (I') of disc laminates comprises stepped formation disc laminates (D')for higher tracking resistance in low current application. 9. A nozzle of improved thermal and dielectric capabilities for sulphur hexa-fluoride (SF6) puffer interrupters, substantially as herein described and illustrated in the accompanying drawings.

Full Text

FIELD OF THE INVENTION
The present invention relates to a nozzle of improved thermal
and dielectric capabilities for sulphur hexa-fluoride(SF&) puffer
interrupters.
BACKGROUND OF THE INVENTION
Sulphur hexa-fluoride (SF6) has successfully replaced oil
as an efficient power interruption medium, in high voltage
circuit breakers.
When two current carrying contacts are separated in an
alternating current (AC) interrupter, an arc is drawn between
the electrodes. This arc helps commuting the current till its
natural current-zero. The shape and size of the arc column is
controlled by the magnitude of the current and the cooling
offered by the gas flowing over the arc.
The gas flow and the flow pattern are regulated by an insulated
nozzle surrounding the gap between the two electrodes.
The gas mass is delivered in this zone using an internal
compression arrangement, using a cylinder and piston combination
linked to the moving system. Conventionally, PTFE (polytetra
fluoro ethylene) nozzles are used for single pressure (puffer)
SF6 interrupters in medium and high voltage AC circuit breakers.
During the interruption process,high energy intense arc is formed between the separating contacts. Since the nozzle is positioned in the vicinity of this intense arc, the heat of the arc and the hot gas cause evaporation of the PTFE material in the throat and nearby region of the nozzle suffer which heavy erosion with each arcing/interruption. This causes change in the nozzle throat and the throat size increases gradually with the number of interruptions performed by the interrupter. This affects the designed performance and may ultimately lead to failure of the interrupter.
The evaporated material together with arc material mixing with the cooling gas may contaninate the host insulating medium during the process of interruption. This contaminated gas exhibits lower dielectric strength and may lead to dielectric failures during the process of interruption.
The PTFE nozzles being made of soft structured material, the hot metallic and non-metallic particles of the arc and the eroded material may get embedded on the surface of the nozzle exposed to the arc. The embedded particles degrade the tracking characteristics of the nozzle resulting in failures. SUMMARY OF THE INVENTION
Thus the main object of the present invention is to enhance the thermal and dielectric ratings of SF- puffer interrupters by reducing nozzle erosion and generation of erosion products. Another object of the invention is to retain the nozzle size, thereby improving the reliability of current interruption for increased number of operations.
These and other objects of the present invention are achieved by controlling the contaminants,principally, the ablation/erosion from the soft nozzle and containing the nozzle distortion and retaining the dielectric strength of the insulating medium of SF& gas.
This control is achieved by providing an insert of high temperature resistant material as liners in the throat region of the nozzle; the high temperature resistant material exhibiting insignificant erosion at high arc temperatures.
The low throat region of the nozzle can be of high-alumina ceramic (Al2O3)-
For better thermal shock-withstanding capability and for ease of stacking, circular coin like disc laminates are used. The disc shaped alumina laminates are sized to suit the throat dimension of the nozzle and assigned interrupter fault rating . For best results a radial depth of at least 8 to 10 mm are used. Laminates in axial thickness varying between 4 mm and 8 mm give best results and a minimum of three laminates are used per nozzle.
For low current capacitive or inductive switching applications stacks of disc laminates with stepped formation are advantageously used. The formation enhances tracking length and exhibits higher tracking resistance.
Thus the present invention provides a nozzle of improved thermal and dielectric capabilities for sulpur hexa-fluoride (SFg) puffer interrupters,said nozzle made of PTFE and having a throat region surrounding an inter-electrode gap of said interrupter, characterized in that said throat region is provided with liners comprising inserts made of erosion resistant material capable of withstanding high arc temperatures. BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Figures l(a), l(b) and l(c) shows the interrupter in cross-section in a closed, partially open and open states.
Figure 2(a) shows the prior art nozzle.
Figure 2(b) shows the nozzle of the present invention. Figure 3(a) shows the disc laminate.
Figure 3(b) shows the insert or the disc laminates stack of
the present invention.
Figure 4(a) shows the stepped disc laminate.
Figure 4(b) shows the insert, made of stepped disc laminate stack.
DETAILED DESCRIPTION OF THE DRAWINGS
The invention will now be described in detail by way of examples,
with reference to the accompanying drawings.
Figures l(a),l(b) and l(c) show an interrupter in cross-section. Three positions of the interrupter 'closed ', 'partially open1 an 'open1 are shown. In the 'closed' position the main moving contact 2 is shown in contact with the main fixed contact 1. In this position the moving arcing contact 4 is also shown engaged to the fixed arcing contact 3.
When the arcing contacts 3 and 4 are separated, as shown in figure l(b) (partially open position), an arc is drawn between
the contacts, the shape and size of the arc is determined by
*the magnitude of current and the cooling offered by the SF6 gas flowing over the arc. The flow of SF6 gas and the flow pattern is regulated by an insulated PTFE nozzle 5. Nozzle 5 is so arranged that its throat region T surrounds the inter electrode gap 7 of the interrupter.
As shown in Figure 2(b), the throat region T of the nozzle 5 is provided with liners comprising an insert I. Insert I is made from erosion resistant material which can withstand high arc temperatures. High alumina ceramic (Al2O3) is used for making the insert I.
The insert I comprises a stack of at least three disc laminates D which are made in the shape of circular coin like shape for better thermal shock withstanding capacity and for ease of stacking. The size of the disc laminate D will depend on the dimension of throat T of the nozzles 5 and the assigned interrupter fault rating. For best results the disc laminates D should have a minimum radial depth of 8-10 mm and axial thickness varying between 4 mm and 8 mm.
With the use of such inserts as lining for the throat region T of the nozzle 5, the nozzle size can be retained by minimizing erosion which ultimately results in reduction of contamination. Thereby, for the interrupter, increased dielectric rating and consistency in performance ever after prolonged/repetitive arcing are achieved.
Figures 4(a) and 4(b) show a stepped disc laminate D' and a stack thereof respectively, which can be used as an insert I' for higher tracking resistance for special switching applications like low current capacitive or inductive switching applications. The above description of the invention should be considered as illustrative and not restrictive. The invention may be embodied in other specific forms by one skilled in the art, without departing from the spirit or essential characteristics thereof.

WE CLAIM;
1. A nozzle of improved thermal and dielectric capabilities for sulphur hexa-fluoride (SF6) puffer interrupters, said nozzle made of PTFE and having a throat region (T) surrounding an inter-electrode gap (7) of said interrupter, characterized in that said throat region (T) is provided with liners comprising an insert (I,I') made from erosion resistant material capable of withstanding high arc temperatures.
2. The nozzle as claimed in claim 1 wherein said insert
(I,I')is made from high-alumina ceramic (Al2O3).
3. The nozzle as claimed in the preceding claims wherein
said insert comprises a stack (I,I') of circular coin like disc
laminates (D,D').
4. The nozzle as claimed in the preceding claims wherein
said disc laminates (D,D') are sized to suit the dimension of
said nozzle throat (T).
5. The nozzle as claimed in the preceding claims, wherein
said disc laminates (D,D') have a radial depth of at least 8
to 10 mm.
6. The nozzle as claimed in the preceding claims wherein said disc laminates (D,D') have an axial thickness between 4 mm and 8 mm.
7. The nozzle as claimed in the preceding claims wherein
said insert comprises a stack (I,!1) of at least three disc
laminates (D,D').
8. The nozzle as claimed in claim 3 wherein said stack
(I') of disc laminates comprises stepped formation disc laminates
(D')for higher tracking resistance in low current application.
9. A nozzle of improved thermal and dielectric capabilities
for sulphur hexa-fluoride (SF6) puffer interrupters,

substantially as herein described and illustrated in the accompanying drawings.

Documents:

780-del-2003-abstract.pdf

780-del-2003-claims.pdf

780-del-2003-correspondence-others.pdf

780-del-2003-correspondence-po.pdf

780-del-2003-description (complete).pdf

780-del-2003-drawings.pdf

780-del-2003-form-1.pdf

780-del-2003-form-19.pdf

780-del-2003-form-2.pdf

780-del-2003-form-3.pdf

780-del-2003-gpa.pdf

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Patent Number

227361

Indian Patent Application Number

780/DEL/2003

PG Journal Number

04/2009

Publication Date

23-Jan-2009

Grant Date

07-Jan-2009

Date of Filing

05-Jun-2003

Name of Patentee

BHARAT HEAVY ELECTRICALS LTD

Applicant Address

BHEL HOUSE, SIRI FORT, NEW DELHI-110 049, INDIA.

Inventors:

#	Inventor's Name	Inventor's Address
1	JAIN HARI SHANKAR	C/O. BHARAT HEAVY ELECTRICALS LIMITED, (A GOVERNMENT OF INDIA UNDERTAKING), CORPORATE RESEARCH & DEVELOPMENT, VIKASNAGAR, HYDERABAD 500 093 A.P. INDIA.
2	SUBRAMANYAM VINAY KUMAR	C/O. BHARAT HEAVY ELECTRICALS LIMITED, (A GOVERNMENT OF INDIA UNDERTAKING), CORPORATE RESEARCH & DEVELOPMENT, VIKASNAGAR, HYDERABAD 500 093 A.P. INDIA.

PCT International Classification Number

B05B 3/00

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1			NA