With a hydroelectric generating capacity of 1100 megawatts, the 8-generator Muddy Run Pumped Storage Facility in southeastern Pennsylvania helps the mid-Atlantic power grid meet peak demands. The local Amish families won’t use a single watt produced by the plant, but the rest of us —— millions of electricity users —— take it for granted that our air conditioners, televisions, and other appliances will work when we turn them on.

Built in 1966, the plant is undergoing a major generator switchgear upgrade that is phased over several years to minimize the impact on output capacity.

The Muddy Run plant boosts its output by drawing down its reservoir in peak periods and replenishing it off-peak. Four earthen dams form an 887-acre lake that holds up to 1.5 billion cubic feet (11.4 billion gallons) of water by containing the waters of the Muddy Run and a few other small tributaries that traverse Pennsylvania Dutch farmland on their way to the Susquehanna River.

On the other side of the dams, at the river’s edge, sits the power plant. In the daytime, water from the reservoir falls 343 feet through four intake shafts, each 25 feet in diameter, and is shunted through eight tunnels to the turbines. Late at night and on weekends, when the demand for electricity is low, the turbines are reversed to pump water up to the reservoir from the river 400 feet below. Twenty hours of full-load operation causes the surface of the reservoir to drop 50 feet.

The owner of the facility, Exelon Power, is a division of Exelon Generation Company, which is a subsidiary of Exelon Corporation, a Chicago-based energy giant with more than $19 billion in annual revenues. Exelon’s ability to boost its output as needed —— especially on hot summer days in the late afternoon and early evening when people typically get home from work and turn up their air conditioners —— is critical to meeting the region’s dynamic peak electricity demands.

“The reservoir is like a giant battery,” explains Charles Tuttle Jr., the plant’s senior electrical engineer who is supervising the upgrade.

By design, Muddy Run is not far (upstream and across the river) from the Peach Bottom Atomic Power Station —— two nuclear reactors operated and partly owned by Exelon Generation. The nuclear plant runs all the time, so Muddy Run makes use of the excess power generated by the reactors at night to double its output the next day as needed.

In service for about 40 years, the Muddy Run generator units, each of which includes a generator circuit breaker and a set of complicated switchgear, require two days of maintenance after every 500 operations (on/off cycles). Since the number of operations depends on the demand for electricity, there are days in the spring and fall when demand is low and some of the units are idle. But demand is higher in the winter and higher still in the summer, when it is not unusual for every unit to run at least twice a day. The facility’s eight 140-megawatt generators have already been replaced, but the aging switchgear is becoming expensive to maintain.

“The old switchgear is at the end of its life,” says Tuttle. “It is obsolete, and has become very labor-intensive for us.”

The first of the eight replacement high-current switchgear units was commissioned in April 2007. Five more units have been commissioned since then, and the upgrade plan calls for the last two to be installed next spring (2010).

Exelon’s multi-year contract for the eight sets of generator switchgear is with ABB Inc., the world’s largest manufacturer of high-voltage equipment. At the heart of each replacement unit is ABB’s state-of-the-art SF6 high-current generator circuit breaker, manufactured in Switzerland. For the rest of the gear —— a veritable 3-D maze of high-voltage switches, control systems, and hundreds of feet of copper cable and buswork —— ABB turns to its Boston-based supplier, Phoenix Electric Corporation.

Phoenix Electric designed and is building the massive stacked switchgear cubicles (6 per generator) that house ABB’s circuit breakers as well as the new Phoenix gear. Each of the eight 6-cubicle units is approximately 18½’ high x 20’ x 7½’ and weighs about 15 tons. Each unit is rated for 6,000 amps continuous duty at 15,000 volts and is capable of interrupting 100,000 amps short-circuit —— among the highest-rated equipment of its kind in the world. When each unit is completed, it is shipped from Phoenix’s Massachusetts assembly plant to Pennsylvania in three sections strapped to semitrailer flatbed trucks.

Phoenix Electric has no “off-the-shelf” products; all of the company’s work is custom. The design/development phase, in which Exelon, ABB, and Phoenix engineers worked together, took thousands of hours of design, calculations and testing to ensure the new equipment would interface properly with the ABB breakers as well as the generators.

“These are the largest units we have ever built, and they are rated 20% higher than the units they replace,” notes Stephen Simo, Vice President of Phoenix Electric. “The complexity of what Exelon needed, combined with the challenge of fitting more powerful switchgear into the limited available space, was a true engineering challenge. This project represents the culmination of all our capabilities.”

To speed and simplify the design of the units, Phoenix engineers made use of new 3D software. They knew there was no room to spare; the new, higher-capacity cubicles had to be the same size as the old ones. The software made it easier for the engineers to visualize not only the components, but the spacing between them.

Positioning the components precisely within each cubicle was key to fitting them all in. Pertinent codes specified clearances or flame-retardant dielectric insulation between certain components.

“Exelon put a lot of trust in us,” says Simo. “There was no way we were going to let them down.”

The design for each cubicle also had to ensure that its bus connections would line up perfectly with those of adjacent cubicles. After the assembly and individual testing of each cubicle, Phoenix tested and measured each bus connection between each individual cubicle section to verify proper alignments.

Last but not least, Phoenix had to design the packaging for the cubicles, which had to withstand the vibrations of a 10-hour truck ride to Pennsylvania.

William Conley Jr., P.E., director of contracts for ABB Inc., had worked with Simo before on several projects. In fact, ABB and Phoenix Electric have enjoyed a 30-year partnership. Recently the two men collaborated on a project for the U.S. Army Corps of Engineers involving 109 generator circuit-breaker retrofits (each with customized Phoenix switchgear) for 11 hydroelectric dams in the Pacific Northwest. But the new units for Muddy Run are more than three times larger than any in that project.

“We knew Phoenix had the expertise and capability to produce high-quality product on time,” says Conley, who is based in North Carolina. “We’ve always had a good relationship with them, and we also know they provide great customer support. It has been a strong team effort.”

“This project has been an ambitious and successful collaboration, resulting in a much higher level of reliability and a reduction of maintenance costs to our customer,” notes Ed Sharp, ABB’s product development manager for North American switchgear retrofits.

“The folks at Phoenix Electric have done everything we asked them to do and more,” says Tuttle. “Their design worked out wonderfully. At the first installation, everything fit together. At the end of the day it all had to work, and it did.”

“We’re quite pleased with the way things are going —— the entire process to this point has been very smooth,” adds Tuttle, who looks forward to completing the long upgrade project. Tuttle anticipates the new switchgear units will last another 40 years, but Conley thinks they may actually last longer. All of the original Muddy Run circuit breakers are General Electric air-blast models. Conley points out that because the new ABB SF6 breakers make use of a newer, more reliable gas-insulation technology, they are rated for 40,000 on/off cycles with minimal maintenance —— more than 54 years of service at two cycles per day.

So, while they may ride peacefully in horse-drawn buggies along River Road atop the main dam on a hot summer evening, the Amish will probably never use any of the power produced by the facility. But, for those of us who are accustomed to a more energy-dependent lifestyle, thanks in part to the Muddy Run plant, the power will be there when we need it.