Patent Application
20160290035
This invention relates to covers for protecting against arc flash hazards in a manhole.
An arc flash is an explosive electrical event highly hazardous to persons in its vicinity. An arc flash may result from failure of power cables. When a power cable fails, electric current flowing through the cable may leave its intended path and flow through the air, causing energy to be released. The energy released is an arc flash. At high voltages, large amounts of energy are released, potentially producing an arc flash with powerful explosions, extremely high temperatures, flames, fumes, blinding light, loud noise, and pressure waves. Persons exposed to such an arc flash could suffer serious injury. It is necessary, therefore, for personnel working within the vicinity of high voltage power cables to be adequately protected from arc flashes that may result from failure of those cables.
Manholes provide access to subterranean high voltage power cables by connecting underground vaults housing power cables to a street level. A vault opening provides access into vault from the manhole. Persons working in the manhole (for example, personnel making repairs to the manhole frame or cover) may be exposed to arc flash events from power cables in the vault through the vault opening. The risk of arc flash events is especially high when the power cables are in poor or deteriorating condition. Thus, personnel require protection from arc flash events when working in a manhole.
Several methods are available for protecting personnel in manholes from arc flash hazard. The methods include de-energizing power cables in the vault, modifying the design or configuration of power cables to minimize arc flash occurrences, inspecting and fixing any cables in poor condition, or covering the vault opening leading to the manhole. However, these methods may be cumbersome, costly, or difficult to implement. De-energizing power cables results in changes in electrical configurations making operations more difficult to manage. Modifying the design or configuration of power cables in the vault is typically not feasible. Although cables in poor or deteriorating condition may be fixed, repair of the cables must be arranged before work in the manhole begins, causing possible delays in repairs to the manhole. Also, the condition of the cables must be inspected first before any repairs to the cables are made, adding to the delay.
Covering the vault opening may therefore provide the most practical option for protecting personnel working in manholes from arc flash hazard. However, the cover must operate as an effective shield against arc flash events in the vault, yet also be easily removable to allow access to the vault when manhole repairs are complete.
It is therefore a challenge to protect personnel working manholes from arc flash hazards and for manhole repairs to be completed safely and efficiently regardless of the manhole or cable condition. It is clear that advantages may be obtained by using a cover which is easily placed and removed and which effectively shields personnel from any arc flash events in the vault.
The invention concerns a cover. In an example embodiment, the cover comprises a frame having first and second sides oppositely disposed from one another. The frame defines a perimeter. The example cover may comprise first and second lifting lugs attached to the frame.
A first plate is attached to the first side of the frame. A portion of the first plate extends outwardly from the perimeter and forms an engagement surface surrounding the frame. The first plate may comprise a glass in a polymer base.
The example cover may further comprise a second plate attached to the second side of the frame. The second plate may be substantially parallel to the first plate. The example cover may further comprise at least one lifting lug attached to the second plate. The second plate may comprise a glass in a polymer base. The frame may further comprise one or more connecting members positioned between the first and second plates, forming a central space between the plates.
The example cover may further comprise a gasket attached to the engagement surface of the first plate. The gasket substantially surrounds the frame. The gasket may comprise a flexible resilient tube. The gasket may further comprise a sleeve surrounding the tube.
The invention further comprises a method of shielding a subject from an arc flash. An example method comprises positioning a cover within an opening to a vault having an interior space. Positioning the cover within the opening may further comprise lowering of the cover to the opening, tilting the cover, and inserting the cover into the opening.
A portion of the interior surface of the vault forms a peripheral surface surrounding the opening. The cover comprises a first plate attached to a frame defining a perimeter. A portion of the first plate extends outwardly from the perimeter and forms an engagement surface surrounding the frame. The example method also comprises drawing the cover so as to bring the engagement surface proximate to and in facing relation to the peripheral surface surrounding the opening. The example method may further comprise engaging a gasket attached to the engagement surface of the cover with the peripheral surface surrounding the cover so as to form a seal. The example method may further comprise securing the engaged cover in place so as to maintain the seal.
The cover 10 comprises a frame 14 having a first side 16 and a second side 18 oppositely disposed from one another. The frame 14 defines a perimeter 20. A first plate 22 is attached to the first side 16 of the frame 14. A portion of the first plate 22 extends outwardly from the perimeter 20 and forms an engagement surface 24 surrounding the frame 14. The cover 10 further comprises a second plate 26. The second plate 26 is attached to the second side 18 of the frame 14 and is substantially parallel to and spaced apart in relation to the first plate 22. The frame 14 further comprises one or more connecting members 28 positioned between the first 22 and second plates 26 and forming a central space 30 between the plates 22 and 26. Advantageously, the frame 14 is formed from aluminum.
The cover 10 may further comprise lifting lugs 40 to allow convenient positioning, maneuvering, and securing of the cover 10. The lifting lugs 40 may be attached to the frame 14 or the second plate 26. As shown in
For the cover 10 to effectively shield against an arc flash, the plates 22 and 26 attached to the frame 14 are formed from materials providing sufficient electrical insulation and flame and heat resistance. Such materials may include plastics, including thermosetting phenol formaldehyde resins such as polyoxybenzyl methylene glycol anhydride (Bakelite™). The materials may also include composite materials comprising glass and plastic, such as glass fibers in a polymer resin base. The glass fibers may be woven into a mat or in random configuration. The plates 22 and 26 may also be formed of laminate material. Advantageously, the plates 22 and 26 are laminate sheets of GPO-3, a random, non-woven mat of glass fibers held together by a polyester resin binder.
To protect against arc flash, the cover 10 is temporarily installed to an opening 12 leading to a vault 42 housing power cables. When installed, the cover 10 protects the manhole 13 located above the vault 42 against exposure from arc flash events that may occur in the vault 42 from failing power cables. As shown starting with
The cover 10 may be positioned within the opening 12 by lowering the cover 10 to the opening 12 then tilting the cover 10 to insert the cover 10 into the opening 12 (
To close the opening 12, the cover 10 is drawn to the opening 12, which draws the engagement surface 24 towards the peripheral surface 46 (
When the cover 10 is drawn to the opening 12, the engagement surface 24 is brought in proximity to and in facing relation to the peripheral surface 46, allowing the gasket 32 to engage with the peripheral surface 46.
For the gasket 32 to effectively form a seal 34, the gasket 32 is formed of flexible resilient materials such as rubber to allow the gasket 32 to deform when compressed. For example, the gasket 32 may comprise a flexible resilient tube 36. Advantageously, the flexible resilient tube 36 is a rubber hose. The flexible resilient tube 36 may be further enclosed in a sleeve 38. Advantageously, the sleeve 38 is formed of leather or a similar tough, abrasive material to make the gasket 32 durable and resistant to damage from repeated use.
Once the cover 10 is engaged and a seal 34 is formed, the cover 10 is then secured in place to maintain the seal 34. The cover 10 may be secured by positioning a fixture (such as a fixed bar 50) above the engaged cover 10 and strapping the cover 10 to the fixture.
Covers according to the invention and methods of operating the cover are expected to provide effective protection against arc flash events for personnel working in a manhole. They are expected to provide a safe, cost-effective, and efficient way for manhole repairs to be completed without regard to conditions of cables beneath the manhole.
