Electrical Systems

Replace beats repair for circuit breakers

Solid-state breakers increase reliability, cut costs at a nuclear plant.

By Doug Robling

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In 2002, facilities management at the Hope Creek Generating Station, Lower Alloways Creek, N.J., faced concerns about its aging low-voltage circuit breakers. The breakers at the 1,219 MW nuclear power plant had been in use since the facility opened in 1986.

“Hope Creek started to see an increasing trend of breakers failing to close on demand,” recalls Dave Davis, a former PSEG nuclear engineering specialist who worked in the plant’s engineering and maintenance departments before joining Nuclear Logistics Inc. (www.nuclearlogistics.com) in 2007 as northeast region site manager. “We were seeing these trends at the plant and also throughout the entire nuclear industry.”

The facility has two types of circuit breakers:

  • Non-safety related: These breakers operate equipment that isn’t essential to the plant’s operation, such as lighting or air-conditioning. Their function isn’t unlike similar breakers found in coal-fired power plants or common industrial manufacturing facilities.
  • Safety-related: Unique to nuclear plants, these breakers are relied upon to operate mission-critical equipment such as cooling-water pumps and the power equipment that safely shuts down the plant if a critical event occurs (which has never happened at the Hope Creek Generating Station). About 100 of the 260-plus breakers are safety-related, some of which are used as motor starters.
Installed in the same cabinets using an adapter cradle, the replacement AC switchgear is maintenance-free and offers remote-monitoring capabilities.
Installed in the same cabinets using an adapter cradle, the replacement AC switchgear is maintenance-free and offers remote-monitoring capabilities.

The breaker manufacturer recommended refurbishment every 20 years, which consists of disassembly, cleaning, inspection and replacement of lubricant, bearings and age-sensitive components. The work would have to be outsourced or would require an extraordinary amount of training and manpower to perform in-house.

Hope Creek owner PSEG Nuclear — a division of energy company Public Service Enterprise Group (PSEG) — commissioned the Electric Power Research Institute (EPRI) in 2002 to conduct a facility life cycle management plan, which included reliability evaluations of its circuit breakers and also underscored the eventual necessity of refurbishment or replacement. The alternative was removing the legacy breakers from their switchgear cubicles and replacing them with modern counterparts, along with an adapter cradle.

Facilities management worked with Nuclear Logistics to investigate both options. Though costs were comparable, replacement gradually emerged as more viable. For one thing, refurbishment would need to be completed again and perhaps multiple times in the future, which the replacement breakers didn’t require. “There were just a lot of long-term benefits with replacing the breakers,” David says, “So in 2003, we started to present to management a business case to replace the breakers at Hope Creek.”

That business case was first presented internally to Hope Creek plant management, then to PSEG Nuclear and finally PSEG corporate. With approvals in hand, work got underway in late 2005.

Hope Creek facilities management selected a Square D Masterpact NW replacement breaker designed by Square D Services from Schneider Electric (www.squared.com) and offered by Nuclear Logistics. The project got underway in 2005 with a scope of replacing more than 260 legacy breakers with Square D Masterpact NW counterparts, more than 200 of which are AC breakers featuring Square D Micrologic digital trip units; the rest are DC breakers with DC solid-state trip units.

“The decision primarily came down to a cost/benefit analysis,” says Greg Lichty, plant component specialist for circuit breakers and motors. “We’re installing a breaker that doesn’t require an overhaul. They’re lubricated with synthetic grease, which reduces the chances of grease hardening.” Grease hardening is one of the most common sources of circuit breaker failure in the nuclear industry.

Before the first legacy breaker could be removed from its switchgear bus, a significant amount of coordination was necessary to ensure the project progressed as smoothly as possible. This was performed by Nuclear Logistics, a supplier of equipment used in nuclear facilities, which handles qualification testing for any product used in a nuclear plant, including seismic testing. The company also prepares related documentation and conducts training of plant facilities management personnel.

“Some of the equipment we design and build ourselves, and a lot of the equipment we work with a partner — in this case, Square D Services — to supply a low-voltage replacement breaker,” says Craig Irish, Nuclear Logistics’ vice president of sales and marketing. “Our quality assurance program is in place at the Schneider Electric facility where the breakers are manufactured, with our quality-control inspectors witnessing certain critical points in manufacturing, and then doing final testing.”

An adapter cradle goes into the existing switchgear and houses the new breaker without any modification. Davis says, “Square D Services designed and fabricated the adapter cradle for the new breakers, which allow plant electricians to replace breakers safely with the plant on-line and without requiring a bus outage.”

The adapter cradle also increases safety for electricians, both during installation and future maintenance. When the breaker is racked out and removed from its cubicle, a shutter closes the primary disconnect so there is no exposure to a live bus. The Square D Masterpact NW breakers themselves feature an insulated case with no exposed metal parts on the front and sides that could act as conductors.

“The older technologies had a dead front on them, but they were metal and you could defeat the interlocks to get inside, whereas with the new breakers, you can’t,” Davis says.

The most crucial step was project execution — the physical task of removing a legacy breaker from its switchgear cubicle, and replacing it with an adapter cradle and the new breaker, along with a new exterior door. The replacement work is done by in-house electricians, who were trained by Square D Services and Nuclear Logistics, but the training was simplified by the fact that there was but one breaker type for electricians to master, greatly reducing the opportunity for mistakes.

“There was a lot of planning,” Lichty says. “What breakers can we do with the plant on-line, and what breakers do we have to do during an outage? Because of system complexity, we can’t just walk up and swap out the breaker. It has to be coordinated within the maintenance window. The operations department has to take the breaker out of service and turn it over to the maintenance department, which can be a coordination challenge. And that’s just one breaker.”

Lichty says plant electricians can receive, inspect, test and install a new breaker in one eight-hour shift, provided the replacement is present at the plant. But, “There are some breakers where the only time they can come out of service is during a refueling period,” Davis says.

The project is putting in place a common circuit breaker throughout the facility, saving time and cost because plant electricians don’t have to be trained on multiple types of breakers. Having common breakers also reduces spare parts inventory.

The digital trip units on the AC replacement breakers provide more intelligence to facilities management, from monitoring the load coming through a given breaker, to chronicling its trip history. They can even be used for power monitoring.

“We also have a more reliable breaker,” Lichty says. “Minimal maintenance is required, and in the case of corrective maintenance, you can replace any part on the breaker using a Phillips screwdriver or Allen wrench. Plus, there is a better allocation of human resources. Plant electricians can be doing things other than working on circuit breakers.”

Doug Robling, business development manager, Square D Services, Schneider Electric (www.squared.com) is an electrical engineer with more than 30 years of experience, including developing Square D Services’ offer to the utility market and meeting the requirements of nuclear plants.