At every stage of IR Window design
At the heart of the Fluke CV Series ClirVu® Infrared Window design was the need to survive a 63 kA arc blast test. Achieving that was no small challenge. It required scrupulous testing and review of the design at every stage from prototyping to final product.
After designing the windows on the computer, the design team produced a specially formulated plastic prototype from the 3D CAD design. "That initial prototype allowed us to evaluate a lot of things that we couldn't evaluate on the computer screen image," says Gary Gunell, Mechanical Engineer at Fluke. "That initial prototype gave us a chance to see the basic form and function of the window and hinged cover."
Once that initial prototype proved the design was viable, the design team created functional machined aluminum prototypes to evaluate the robustness of the windows. "We did extensive testing of the machined prototypes to make sure they could withstand all the potential blast forces," says Gunell. "That preliminary testing was critical. We were going to spend a lot of time and money on tooling the final product that would be sent to the test labs and we wanted to ensure with a high probability that the final design would pass the certification tests without the need for costly redesigns and delays."
The functional prototype testing generated a few tweaks to the product design before tooling and assembling the final product from zinc die cast parts with the ClirVu window crystal. The initial run of CV Series windows was sent out to Underwriters Labs, TUV, and KEMA Powertest labs, achieving positive test results at all levels. The windows also achieved an IP67 rating, meaning they are impervious to fine dust and can withstand submersion in up to three meters of water for up to an hour without moisture penetration.
The big test
In November 2013 it was time for the CV Series Windows to meet their biggest challenge - the 63 kA arc blast test at KEMA labs. "The equipment is the size of a small conference room, encased in heavy-gauge double-clad metal," says Gunell. "They have heavy-duty hinges on the door latch, and the doors are secured by half-inch bolts spaced every three or four inches."Four Fluke CV Series IR windows were installed at various locations on the medium voltage switchgear under test.
Observers were sequestered 100 feet away from the blast site, in a safe building equipped with bullet proof glass windows. The explosion, the equivalent of three sticks of dynamite, was triggered inside the switchgear. The blast produced 30 cycles of arc flash at 63kA in only a half-second interval, and when it was over, the Fluke CV Series IR Windows remained intact. The blast test report confirmed that no projectiles or hot gases were emitted through the IR window and no external indicators were ignited.
"Surviving the 63 kA arc blast test makes the Fluke CV Series the first glass IR window to be successfully tested on medium-voltage metal-clad switchgear," says Gunell. "But it also makes the CV Series a great choice for lower voltage equipment, which accounts for most applications around the world. In those applications it delivers the same high blast resistance as well along with the installation and inspection time savings."