GB1590320A - Arc detention - Google Patents

Description

(54) IMPROVEMENTS IN OR RELATING TO ARC DETECTION (71) We, THE MARCONI COM PANY LIMITED, a British Company, of Marconi House, New Street, Chelmsford, Essex, CMl 1PL, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to arc detection and in particular to the detection of arcs within enclosed cavities such as waveguides and similar components.

It is often required to detect the presence of arcing within enclosed cavities. Often this is rendered difficult, however, without unduly interfering with the electrical characteristics of the enclosed cavity.

One object of the present invention is to provide an improved arc detection arrangement in which the above difficulty is mitigated.

According to this invention an arc detection arrangement comprises a wall forming part of, or adapted to form part of, the wall of an enclosed cavity in which arcing may occur and wherein said first mentioned wall is provided with a pin hole and light responsive means is provided to obtain a view of the interior of said cavity device through said pin hole.

The expression "pin hole" is used in a manner similar to that in which it is used in the camera field when reference is made to a "pin hole" camera. The size of the pin hole should be sufficiently small as to provide a satisfactory depth of view and at the same time avoid serious electrical disturbance of the cavity. The smaller the hole the less will be the light transferred to the light responsive device in the event of arcing and therefore preferably said light responsive device is a photo-multiplier tube.

When applied to waveguides typically the arrangement will consist of a waveguide bend section with said pin hole extending through the outer apex of said bend and a photomultiplier tube mounted in a screened enclosure carried by said bend section.

Particularly where said enclosed cavity is or is to be pressurized, evacuated or gas filled, said pin hole may be sealed with transparent material, for example glass, quartz or plastics material.

The invention is illustrated in and further described with reference to the drawing accompanying the provisonal specification which is a cross-section through one arc detection arrangement in accordance with the present invention.

Referring to the drawing, 1 and 1' represent two portions of a waveguide run in which arcing may be expected to occur along the length of the portion 1. Between the portions 1 and 1' is introduced a waveguide bend 2, which has a pin hole 3 provided through its wall at the outer apex of the bend. Forming part of the wall of the waveguide bend 2 is a screened enclosure 4 in which is mounted a photomultiplier tube 5 positioned to receive light through the pin hole 3 originating from arcing along the length of the waveguide portion 1. The electrical output connections for the photomultiplier tube 5 are represented at 6. The cross-sectional dimensions of the pin hole 3 are sufficiently small as to provide a considerable depth of view along the length of the waveguide portion 1. This makes use of the optical effects of a pin hole providing as it does (theoretically) an infinite depth of focus.

It will be noted that the surface within the waveguide bend 2 is little effected by the presence of the pin hole which has been found to have little effect upon the VSWR (voltage standing wave ratio). In addition, photomultiplier tubes tend to have a high order of stability with temperature, which, coupled with the position of the multiplier tube, tends to avoid many of the drift problems associated with semiconductor photodiodes or photoresistor circuits positioned within the waveguide itself.

Due to the very small cross-sectional dimensions of the required hole the invention is suitable for application to waveguide sizes down to the millimetre range of frequencies, without serious deterioration of performance. In addition, the small crosssectional dimensions of the hole tend to prevent r.f. leakage through the hole and hence the photomultiplier tube has satisfactory protection from such fields.

Whilst as illustrated the invention is shown and applied to a waveguide clearly the invention has application to a wide range of enclosed cavity devices in which arcing is required to be detected.

In cases where the cavity device is to be evacuated, pressurised or gas filled, the pin hole 3 would be sealed with light transmissive material such as glass, quartz or plastics material as appropriate. The sealant should be chosen having regard to the predominant wavelength of the light emission of any possible arcing, the most appropriate physical constants of transmission for this wavelength being chosen to obtain optimum sensitivity.

Even where the cavity device is not to be pressurised, evacuated or gas filled, the pin hole 3 may be sealed with light transmissive material as aforesaid.

WHAT WE CLAIM IS: 1. An arc detection arrangement comprising a wall forming part of, or adapted to form part of, the wall of an enclosed cavity in which arcing may occur and wherein said first mentioned wall is provided with a pin hole and light responsive means is provided to obtain a view of the interior of said cavity device through said pin hole.

2. An arrangement as claimed in claim is 1 and wherein said light responsive device is a photomultiplier tube.

3. An arrangement as claimed in claim 1 or 2 and consisting of a waveguide bend section with said pin hole extending through the outer apex of said bend and a photomultiplier tube mounted in a screened enclosure carried by said bend section.

4. An arrangement as claimed in any of the above claims and wherein said pin hole is sealed with light transmissive material.

5. An arc detection arrangement substantially as herein described with reference to the drawing accompanying the Provisional specification.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (5)

**WARNING** start of CLMS field may overlap end of DESC **. tube, tends to avoid many of the drift problems associated with semiconductor photodiodes or photoresistor circuits positioned within the waveguide itself. Due to the very small cross-sectional dimensions of the required hole the invention is suitable for application to waveguide sizes down to the millimetre range of frequencies, without serious deterioration of performance. In addition, the small crosssectional dimensions of the hole tend to prevent r.f. leakage through the hole and hence the photomultiplier tube has satisfactory protection from such fields. Whilst as illustrated the invention is shown and applied to a waveguide clearly the invention has application to a wide range of enclosed cavity devices in which arcing is required to be detected. In cases where the cavity device is to be evacuated, pressurised or gas filled, the pin hole 3 would be sealed with light transmissive material such as glass, quartz or plastics material as appropriate. The sealant should be chosen having regard to the predominant wavelength of the light emission of any possible arcing, the most appropriate physical constants of transmission for this wavelength being chosen to obtain optimum sensitivity. Even where the cavity device is not to be pressurised, evacuated or gas filled, the pin hole 3 may be sealed with light transmissive material as aforesaid. WHAT WE CLAIM IS:

1. An arc detection arrangement comprising a wall forming part of, or adapted to form part of, the wall of an enclosed cavity in which arcing may occur and wherein said first mentioned wall is provided with a pin hole and light responsive means is provided to obtain a view of the interior of said cavity device through said pin hole.

2. An arrangement as claimed in claim is 1 and wherein said light responsive device is a photomultiplier tube.

3. An arrangement as claimed in claim 1 or 2 and consisting of a waveguide bend section with said pin hole extending through the outer apex of said bend and a photomultiplier tube mounted in a screened enclosure carried by said bend section.

4. An arrangement as claimed in any of the above claims and wherein said pin hole is sealed with light transmissive material.

5. An arc detection arrangement substantially as herein described with reference to the drawing accompanying the Provisional specification.