With a hydroelectric generating capacity of 1,100 MW, the 8-generator Muddy Run Pumped Storage Facility in southeastern Pennsylvania helps the mid-Atlantic power grid meet peak demands.
Built in 1966, the plant is undergoing a major generator switchgear upgrade that is phased through the next several years to minimize its 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 the way to the Susquehanna River.
On the other side of the dams, at the river's edge, sits the power plant. During the day, water from the reservoir falls 343' through four intake shafts, each 25' in diameter, and is shunted through 8 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
The facility owner, Exelon Power, is a division of Exelon Generation Company and 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 is critical to meeting the region's dynamic peak electricity demands.
"The reservoir is like a giant battery," said 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 include 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. All 8 of the facility's 140 MW generators have already been replaced, but the aging switchgear is becoming expensive to maintain.
"The old switchgear is at the end of its life," Tuttle said. "It is obsolete, and has become very labor-intensive for us."
The first of the 8 replacement high-current switchgear units was commissioned in April 2007. Two more units were commissioned in the spring of 2008, and all three of the new units are performing well. The upgrade plan calls for three more units to be installed this past spring (2009) and the last two in the spring of 2010.
Exelon's multi-year contract for the 8 sets of generator switchgear is with ABB Inc., a 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 mix of high-voltage switches, control systems and hundreds of feet of copper cable and buswork, ABB uses 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 6-cubicle units is approximately 18½' high x 20' x 7½' and weighs about 15 tons, with 8 units total. 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.
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