Sponsored by Eaton.

Medium-voltage control plays an important role in industrial processes. It involves the safe and efficient flow of electricity when starting and stopping large motors, typically operating between 2,400 and 7,200 volts. And with great power comes great responsibility.

Arc faults — rare but catastrophic electrical failures — pose a serious safety threat. These faults occur when electricity strays from its intended path, generating intense heat that melts copper components within the equipment. The molten copper rapidly vaporizes, expanding up to 67,000 times its original volume and creating a superheated pressure wave. This pressure, contained within a metal enclosure, transforms the equipment into a potential pressure bomb. As a result, the force can deform the structure and even blow doors open to release hot exhaust in a violent burst.

“On a small scale, it’s like when you plug something into an electrical socket and see a little spark between the plug and the outlet,” says Ian Andrup, product manager at Eaton. “That’s electricity jumping through the air. Obviously, that’s much smaller because it’s happening in your house at 120 V. This is at 4,000 V, so it’s much more severe when electricity goes somewhere it shouldn’t.”

Given the potential for risk to personnel working in such settings, the need for arc-resistant (AR) motor control is paramount in medium-voltage systems. Traditional methods rely on external ducts to direct the explosion away from equipment and vent it outside the building. The ducts lead to a designated exhaust area, typically 12×12 feet, where people are not allowed to be present (i.e., it can’t be a parking lot or picnic area). While effective, these external exhaust systems come with their own challenges.

“One of the limitations is that you may not know where you’re installing that electrical equipment,” says Andrup. “Oftentimes, it may be an electrical room in the center of a building. That means you have to create exhaust ducts that potentially route hundreds of feet to get outside.”

Even in systems housed within a dedicated enclosure called an IPA where there isn’t as much distance for the exhaust to travel, engineers must account for the added complexity and cost of installing ductwork. Like HVAC systems, exhaust ducts require the assembly, sealing and inspection of mounting brackets. Weatherproofing must be installed at a downward slope to avoid water traveling backwards through the ducts toward electrical equipment. And there’s always the possibility of birds and rodents crawling into electrical equipment from outside.

“You also have to fence off an area so nobody is standing right under the exhaust,” adds Mike Kellis, applications engineering manager at Eaton. “We’ve had instances where there wasn’t space available outside the IPA. In those cases, they had to route the exhaust ducts out the back of the building, turn them up, and then back over the roof to exhaust above the building. That kind of setup gets fairly complex.”

Eaton’s Ampgard ductless AR motor control offers a streamlined alternative to conventional exhaust duct systems by incorporating arc-absorbing technology directly within the equipment.

“That entire layer of complexity that you would normally have to plan around is completely removed,” says Andrup. “As long as you have space to place the electrical equipment, you can drag and drop it without having to coordinate attaching exhaust ducts at all. You’re no longer tied to installing them, drilling holes in the wall, or creating an exhaust zone.”

So how does the Ampgard ductless AR motor control work? When an arc fault occurs, fuse barriers first channel the exhaust toward the rear arc chamber at the back of the equipment. “We’re the only ones that put the fuses behind the barrier,” says Kellis. “We feel that provides an extra level of protection because it forces the highest pressures to the rear of the compartment — typically where workers are not located.”

(Image: Eaton.)

From there, the exhaust travels up into the plenum, which houses ceramic arc absorbers that reduce the temperature and pressure of the blast. These absorbers also remove any shrapnel or particles, and exhausts the remaining byproducts out the top of the gear.

Beyond arc absorption, the system incorporates several structural and electrical safeguards. Strengthened front doors and reinforced latches ensure the enclosure remains sealed under high-pressure conditions. The enclosure itself is constructed with extremely thick steel. The main bus is insulated, and a compartmentalized isolation switch helps minimize the risk of arc faults occurring in the first place.

The Ampgard ductless AR is especially helpful for facilities where it is difficult to implement traditional exhaust systems. “There was a building where there was nowhere to install ducts — it was in a basement, so there was no way to get outside the building,” says Andrup. “They had to build the exhaust area inside the building and barrier it off. Now, you have 100 square feet of your building that’s entirely unusable. You pay for footprint. The Ampgard ductless AR is a more accessible solution.”

In addition to its features, the Ampgard ductless AR is certified to IEEE C37.20.7-2017, the industry standard for arc-resistant equipment. Eaton has tested and qualified the system to the latest revision of this standard, ensuring it maintains the highest possible level of protection for a worker standing in front of the equipment.

“The standard is very stringent, very difficult to meet, and has a lot of test criteria,” says Andrup. “It’s also a very expensive standard to certify to since you have to send equipment for testing. That sets the standard for safety, and then we go beyond that by making this solution easier and more affordable. We’re currently the only competitor that can meet the standard and do it without exhaust ducts.”

Ampgard ductless AR motor control is well-suited for industries where large motors are frequently utilized. Oil and gas facilities are a key application, as they rely on numerous high-horsepower motors and adhere to strict safety standards. Mining projects similarly benefit from the system’s arc-resistant design to protect workers and personnel maintaining and using electrical equipment. Water treatment plants — especially in large metropolitan areas — can also leverage the technology to eliminate the need for complex exhaust systems in their medium-voltage control operations.

To learn more, visit Eaton.com.

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