Overhaul at Ludington4 January 2012
Following earlier turbine overhauls, all six units are being refurbished and upgraded at Ludington pumped storage plant, beside Lake Michigan, reports Patrick Reynolds
With plans to seek relicensing for one of the world’s biggest pumped storage plants some way off, in 2019, the co-owners of the 1872MW Ludington station, Michigan, have had a project in development for a major overhaul of the equipment and facility before the deadline.
The joint owners, Consumers Energy (51%) and DTE Energy/Detroit Edison (49%), have been planning the refurbishment and upgrade project for the facility, on the east shore of Lake Michigan, for the last six years. The majority of the US$800M project calls for works on the six pump-turbines units to achieve greater operational reliability, increased efficiency and a capacity upgrade for generation to 2172MW.
Earlier this year, Toshiba was awarded a US$500M contract to undertake the key equipment works for the project. The company is currently pushing ahead with design engineering in Japan and the project schedule calls for installation of new equipment onsite to commence in mid-2013 – some 40 years after Ludington was commissioned.
Afterwards, the contract will proceed at a rate of replacing one unit per year being changed over to complete the project after six years. With all units needed in operation in the middle of each year, the window for changeover of equipment onsite falls in winter, which typically does not give the easiest of working conditions in the high northern latitude.
Consumers Energy says, related to the size of the equipment, the main challenges are expected to be around matters of site logistics – the ‘harsh winter environment’, because ‘the units are planned to be available during the normal, high-utilisation summer months’.
Consumers Power and Detroit Edison formed the Michigan Electric Power Coordination Center in the 1960s, and in 1966 they agreed to jointly own and build the Ludington pumped storage project. Construction began in 1969 near the town of Ludington, Michigan.
The plant’s surface powerhouse holds six 312MW pump-turbines. The main contractor for the plant was Ebasco Engineering Co., which also provided the balance of plant while Hitachi handled the pump-turbine units. The facility was completed in 1973 and ranked then as the largest pumped storage scheme in the world.
The pumped storage plant moves water between Lake Michigan and a 4km (2.5 miles) long by 1.6km (1 mile) wide, asphalt- and concrete-lined upper reservoir. The scheme has net generation head of 100.4m (362ft) and can deliver 1960MW of pumping capacity to return the water 113.5m (372.5ft) to the upper lake, which has a minimum elevation of El. 175.3m (El. 575ft). The dyke encircling the reservoir is 9.6km (6 miles) long with an average height of 31.4m (103 ft).
In its opening year, the plant was awarded the Outstanding Engineering Achievement by the American Society of Civil Engineers (ASCE), and in 1987, upon Michigan’s 150th anniversary, was named one of the state’s top 10 engineering achievements.
The reservoir is 33.5m (110ft) deep with approximately the top 60% used for pumped storage operations. Consumers Energy says the reservoir has more than 15GWh of generation storage, and the plant operates with approximately 70% cycle efficiency. It adds: “With all six units operating, the plant can operate at maximum capacity for about nine hours.”
The need for the overhaul of the six units became apparent in the mid-1980s, says Consumers Energy. The problems were focused on leakage at the wicket gate bottom bushing seal, and increased cavitation at the runners.
A series of refurbishment works were undertaken before the major programme now underway. The first major overhaul was completed in 1987, the most recent in 1996. The works addressed the problems of cavitation, gate leakage and the wicket gate bushings. There was also increased concern over cracking at the runner crown plates and problems with the thrust bearings.
Each of the turbines has been overhauled. Unit 4 is the pump-turbine with the longest service time since its last overhaul. Although it was recommended that there be only 12-15 years between overhauls on the pump-turbines, for Unit 4 it has been almost a quarter century since it underwent a full refurbishment.
“So, it is planned to be the first unit in our upcoming six-year overhaul and efficiency upgrade project,” says Consumers Energy.
For the motor-generators, the majority of the units were rewound at a rate of one per year from 1998 to 2003. The block of work on the five units – Units 2-6 – followed five years on from the first to be rewound – Unit 1.
Refurbishment & Upgrade
Five years ago, following the earlier overhauls of the units, a condition assessment and life extension examination for the entire plant was carried out by Devine Tarbell. The relicensing deadline of 2019 may have been some years off but, given the size of the facility and the scale of the improvement task needed, loomed on the commercial horizon.
In a statement in February, upon the announcement of the contract award to Toshiba, Detroit Edison’s president said: “This kind of long-term investment would not have been possible without the comprehensive energy legislation adopted by the state legislature in 2008.”
For the plant, the owners are looking for greater flow rates in pumping mode to fill the upper reservoir faster during periods of lowest off-peak power at night and so reduce operational costs; the upgrade would reduce by two hours to 9.5 hours the time taken to fill the pond. The owners are also seeking greater flow rates in generating mode to produce more power from the same water.
They also want increased unit flexibility, such as ability to run in pumping mode at higher upper reservoir elevations, and so be able to help the owners and grid secure lower cost renewable energy generation of various kinds, says Consumers Energy. In the February statement, it was also noted: ‘The Ludington plant addresses a key challenge of wind energy, which is produced intermittently and cannot be stored, with the exception of special facilities’ like the pumped storage plant.
To achieve the gains, the latest refurbishment work is pursuing increased efficiency in the pump-turbines units, more capacity in the motor-generators in which the stator cores have deteriorated, and more capacity also for the balance of electrical plant. The improvements are to be achieved by obtaining new stainless steel runners for the pump-turbines, and new stators, cores and winding for the motor-generators.
In addition, by contracting to deliver increased plant reliability, Consumers Energy notes that the new equipment is designed to last until the next overhaul in 30 years, and the co-owners’ contract with Toshiba includes performance guarantees.
The refurbishment project will see the six pump turbines replaced, each with Francis runners of approximately 8.4m (27.5ft) diameter and weighing about 260 tonnes. Each unit is to be upgraded by 50MW, or 16%, to 362MW.
Design engineering for the refurbishment of all six units is being undertaken in Japan by Toshiba’s Keihin Product Operations unit. Toshiba said most the equipment will be manufactured by its Toshiba Hydro Power (Hanzhou) Co., Ltd, subsidiary in China.
Consumers Energy says that work on site will take about eight months to overhaul each unit in turn outside of the peak summer demand season.
Other works included in the major refurbishment programme include the US$8 million contract award to Grand River Construction in the middle of the year, a large portion of which – for a seawall, retaining wall and deep piles foundations for two fabrication shops – is being fulfilled by local subcontractor Hardman Construction.
The works are important to preparations to receive shipments of the turbine and generator equipment, says Consumers Energy.
|Ludington Pumped Storage Plant|
Location: Mason County, Michigan