How is the Arc Suppression Blanket used to Create Safety Systems?
How is the Arc Suppression Blanket utilized to Create Safety Systems?
An important consequence of the testing of the Arc Suppression Blanket was the revelation that the proper attachment of the blanket was as important to the function of protecting the worker as was the ability of the blanket to perform. Therefore, the function of a Utilities Work Methods and Practices task forces are an important adjunct to insuring that the blanket performance is optimally effective in suppressing the effects of arc flash and blast.
1. The Pressure Wave creates a vacuum and draws the blanket inwards
2. The Thermal Explosion pushes the blanket outward
3. The Energy is channeled away from the worker
The Blanket
The following methods have been derived from testing done over the last several years and in conjunction with several Investor-Owned Utilities. Each method stemmed from this fundamental concept: “Channel Energy Never Challenge It.”
The "J" Method
The “J” installation is so named because upon placement of the blanket in front of the racks and splices the bottom of the blanket is tucked back toward the vault wall. The top is arrayed in a “D” shape with the middle of the blanket bowed out so that the completed arrangement looks much like a sail. The potential arc blast is not allowed under the blanket and its energy is channeled up and out of the manhole. |
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The Wrapped or Clamshell Method
This installation method is used primarily when there are energized cables below the de-energized cable that is to be worked on. The wrap method is a loose wrap of a large blanket around the splice and tied loosely at the ends of the blanket to the cable. A regular blanket is then used to create a “Clamshell” over the wrapped blanket and is anchored top and bottom to the vault wall with the open end of the “C” shape pointed to the vault wall. The intent is to channel the energy sideways away from the worker and since one of the blankets is lying directly on the splice a second blanket system is arrayed as a precaution. Workers have the most trouble properly applying this method and extra attention should be used to inspect this application. |
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The Suspension Wall Method
This method was invented and tested by Progress Energy and is a devise made of steel piping that is assembled in the vault and attached to screw jacks. The jacks are tightened exerting pressure on the ends and thus holding the structure in place. A blanket is attached to these stanchions creating a barrier wall. It can be used against the vault wall or away from it. Creating a clean and secure surface for the pressure pads is a challenge but in testing at the Kinetrics Lab in Ontario Canada it has performed well in the test vault including the management of 40KA /10 Cycle shots. However, in some applications it has proven to be diffi cult to get the piping pieces into the manhole or vault.
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The Weave Method
This method was developed with Detroit Edison and assumed that the attachment points for the blanket would be behind the splices, which are located on racks. In the testing we used the Suspension Wall Device up against the vault wall and fi tted it around the splices. Of the three spices the middle was de-energized while the top and bottom were energized. The blanket is attached at the top in the same manner as the “J” Method and then woven behind the dead circuit and then back into the front of the rack and draped down the rest of the racks and splices. At the bottom the blanket is folded back toward the vault wall and secured. This has proven to be the most trouble free and user friendly method. |
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Because of the complexity and arrangement of the wiring and splicing, the variety of vault and manhole sizes and confi gurations, the composition of the vaults walls and hardware and the stresses exerted on them from the environment no one methodology outlined can be used solely.
Each vault will have its own sets of advantages and limitations as to which technique would be most useful but the goal with arranging the blankets is to “Channel Energy Never Challenge It.” |
The Vault
There are many variables found in a Power Utilities work environment. Splices and live cables can be positioned in many different locations, the racking systems are different and the sizing and construction of the vault can vary widely. These obvious simple facts are important because these variables have a direct infl uence on how the Arc Suppression Blanket is used and therefore on the total performance capability of creating a protected work area.
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The use of a blanket based protection system does provide the versatility and the strength necessary to signifi cantly suppress, redirect and or divert the forces present in an arching fault. The arraignment and proper anchoring of these blankets are an important element in the overall function of this system. Professional assessment and proper work methods and practices by the user is required. |
Arc Suppression Blanket - References