BY JOHN SPERANZADIRECTOR OF APPLICATIONS AND TECHNICAL SERVICE, PROTON ENERGY

Water vapor and air: enemies of electric generatorsIn their quest to reduce costs and simplify operations, power generationfacilities face two formidable adversaries: water vapor and air. Both substances increase friction drag (windage loss) on the rotor windingswithin electric generators, reducing overall efficiency. And with today’sfuel costs at an all time high, windage losses can mean the differencebetween profits and losses.

In addition to increasing windage loss, water vapor contaminationinside a generator has been shown to reduce the life of its components,and high humidity can induce stress corrosion cracking on retainingrings. Water content of more than 500 ppmw in turbine oil createshigh dew points within generators that reduce generator efficiency andmay reduce a generator’s mean time between failures due to waterinduced electrical shorts.

The costs to a power generation plant for unplanned shutdowns andrepairs are significant. In addition to hard costs of parts and labor, agenerator repair of this type usually means an extended plant outageand significant lost revenues. The cost to a plant for stress corrosionrelated repairs is estimated at more than $1 million.

Managing water vapor and air within hydrogen coolantHow can power plant operators reduce the destructive presence of watervapor and air within their hydrogen-cooled generators? By displacingthese drag-inducing substances with a constant flow of dry hydrogengas, produced conveniently on the plant site from a hydrogen generator.

Hydrogen gas cooling is a primary tool in power generation plants’efforts to reduce the friction (windage) losses within generators fromwater vapor and air. Hydrogen’s high specific heat, high thermal con-ductivity and low density (14.4 times less dense than air and 8.9 timesless dense than water vapor) help keep wind resistance losses withingenerator rotors to a minimum.

Hydrogen is the coolant of choice for high speed generators includingcoal-fired, gas turbine and nuclear power plants, but it has to be pureand dry. Hydrogen that has a high water content loses its advantageouslow density and high thermal conductivity and becomes less effective as a coolant. For example, on an 800 MW generator, a two percentdecrease in hydrogen purity due to water contamination can cost a utilitymore than $300,000 in power sales per year.

Hydrogen coolant that has a high oxygen content can spark coronaactivity in a generator’s stator windings, which can in turn damage a generator’s high-voltage insulation system.

Hydrogen that’s delivered in cylinders or tubes may start out pure anddry, but it becomes increasingly impure and wet as it picks up moisturefrom the turbine oil and from air ingress. In turn, this moisture may be absorbed by the contaminants resident on the insulation, creating a conductive bridge between coils in the generator’s ventilation circuitthat can cause coil-to-coil shorts.

A generator’s gas cooled stator windings have high voltage copperexposed at each end of the stator bars. This design feature necessitateslong electrical creepage paths to prevent high voltage phase-to-phase orphase-to-ground faults. Operators of hydrogen cooled generators havefound that moisture degrades the electrical creepage strength of a surface.And when moisture migrates to the end turn area of a generator’s rotorwindings, it attacks the interturn insulation and results in shorted rotorend winding turns.

Hydrogen dryers and purity analyzers: costs vs. resultsBecause moisture in cooling gas can cause significant problems with a generator’s rotor winding insulation, plant operators must ensure that dewpoints in their hydrogen coolant stays as low as practical. To dry and ensure the purity of coolant hydrogen, power plants oftenemploy regenerative drying systems and purity analyzers. However,these methods carry associated cost and logistics issues, with potential negative side effects.

Drying systems are costly in terms of both capital expenditure andmaintenance. Furthermore, a dryer’s placement within the plant is critical to ensure effectiveness. Condensation of water in the dryers’purge exhaust drains should be closely monitored. Care must be takenthat desiccant materials from the dryer do not get into the generator.

Purity analyzers are good at detecting the percentage of air within thehydrogen gas. However, if the impurity is something other than air, the readings are less reliable. Readings can fluctuate based on ambienthumidity in the plant, the generator’s operational status, and where the drying system is located.

JANUARY 2005: A TECHNICAL UPDATE FROM PROTON ENERGY

Continuous hydrogen replacement techniqueoffers improved power plant electric generator efficiency and longevity

HOGEN hydrogen generators from Proton Energy offer dry, 99.999 percent pure hydrogen

TABLE A

Analysis Report – Atlantic Analytical LaboratorySample of H2 gas @ 225 psi generated by Proton’s HOGEN® hydrogen generator

Test Description/Units Result Report DetectionLimit (D.L.)

Nitrogen (ppm vv/by MS) nd 4

Oxygen (ppm v/v by MS) nd 4

Carbon Dioxide (ppm v/v by MS) nd 4

Argon (ppm v/v by MS) nd 4

Helium (ppm v/v by MS) nd 10

Hydrogen (% v/v by MS) 99.9+ 0.1

Total hydrocarbons (ppm v/v as CH4) — 0.1

Water Vapor (ppm v/v by EDP) nd 0.5

D.L. = report detection limit. nd = indicates the concentration is less than the reportdetection limit. — = test not performed. % = percent. ppm = parts per million. ppb= parts per billion. v/v = volume analyte/volume sample. w/w = weightanalyte/weight sample. Unit conversions: 1 ppm v/v = 0.0001% v/v.

Delivered hydrogen vs. continuous hydrogen replacement from a hydrogen generatorMany power generation industry veterans now advocate use of continuoushydrogen replacement techniques to keep generators free of moisture,oxygen, and other contaminants that can prematurely degrade equipment.However, power plants have been reluctant to employ a continuoushydrogen replacement method of maintaining purity for two reasons.The high cost of delivered hydrogen is one barrier. An effective purgemethod will require using a larger amount of hydrogen gas that a plantis currently using. A second obstacle is plant operators’ safety concernsabout leaving a large volume of pressurized hydrogen from tanks or cylinders “on line” and unattended.

TABLE B

How it works

TABLE C

Power plants can increase operating efficiencies by producing hydrogenon site to continually replenish hydrogen coolant within their generators.

Mirant Mid-Atlantic’s success storyThe first HOGEN 40 hydrogen generator in the Mirant Corporation’sMid-Atlantic system was placed in service for testing on Unit 1 of itsDickerson, Maryland plant on February 17. On February 17, the dewpoint of the hydrogen coolant in the low-pressure generator measured37°F. On March 4, the dew point was down to about 30.8°F. By May18, the dew point was between 12 and 15°F. Presently the dew pointremains between 12°F and 15°F.

Onsite generation = no guesswork with hydrogen dryness and purityA cost-effective approach to ensure hydrogen purity and dryness forlowest windage loss is to generate it at your facility by a clean, safemethod such as Proton Exchange Membrane (PEM) electrolysis.

Proton Energy recently contracted with Atlantic Analytical Laboratoryto analyze hydrogen gas produced by one of its HOGEN® hydrogengenerators through PEM electrolysis. More than 50 trace elements werequantified in the sample. Water vapor, oxygen, total hydrocarbons, helium,argon, carbon dioxide and nitrogen each registered below the laboratory’sdetection limits. Hydrogen generated by the HOGEN hydrogen gener-ator consistently reported a dewpoint of -85°F.

Proton Energy has solved these two obstacles with its onsite generators.Proton’s HOGEN hydrogen generation systems not only make hydrogenon demand, but also have the ability to monitor demand and alertplant operators. For example, if a seal fails within the turbine generator,hydrogen demand will increase rapidly and dramatically. Monitorswithin the HOGEN hydrogen generator will sense the increaseddemand, and display the increased usage to the operator giving themtime to take the appropriate actions to safeguard their facility.

TABLE D

Dew point of hydrogen coolant in Mirant Mid-Atlantic’s Dickerson Unit 1low-pressure generator after installation of Proton’s HOGEN 40 onsitehydrogen generator.

According to Lawrence A. Dusold, senior consultant with Dickersoncontractor Cetrom Inc., the plant’s original intent was to reduce thehydrogen dew point by upgrading the existing dryers. During theirinvestigation, Dickerson’s management learned that a HOGEN 40hydrogen generator could provide dry hydrogen in excess of their rateof consumption, allowing the plant to continually purge the generatorwith pure, dry hydrogen. The installed cost of a single HOGEN 40hydrogen generator, which can provide hydrogen to both the plant’shigh and low pressure generators, is a fraction of the cost of the twodriers that would have been installed.

Among the benefits that the plant is experiencing, Dusold said thatcontinually purging Dickerson’s generators with pure, dry hydrogenproduced by a HOGEN unit has reduced both the plant’s dependenceon hydrogen cylinders and the demurrage cost of keeping these cylinderson site. Futhermore, hydrogen from the HOGEN generator is purerthan the hydrogen supply from cylinders.

The Dickerson plant employs General Electric hydrogen cooled synchronous type ATB 4-pole, 3-phase 60-cycle generators, rated at115,000 kilovolt-amperes at 1800 rpm and 13.8 kilovolts. They aredesigned for a power factor of 0.85, 30 psig hydrogen cooling pressureand armature amperage of 4811 amps. GE’s guidelines for this generatorproject a 1/2 percent increase in kilovolt-amperes output for each 1 psiincrease in hydrogen pressure within the generator.

Dickerson’s generators typically operate on cycling load rather than con-tinuous full load. Dusold projects that the stability increase in hydrogenpressure within Dickerson’s electric generators since introducing theHOGEN systems can produce an additional 900 kilowatts of additionalgeneration. As an example, based on an estimated 5000 operating hoursannually and an average electricity selling price of $.05kW/h, an additional$225,000 in revenue can be realized from each of the three generators.When when full load demands occur, Local Market Pricing (LMP)policies allow Dickerson to further increase revenue from operating the generators at maximum capacity.

“We are very happy with the performance of our HOGEN 40 hydrogengenerators,” said Michael Bennett, maintenance group leader at theDickerson plant. “With these units, both dew point and purity have

About the authorJohn Speranza is Director of Applications and Technical Service atWallingford, Conn.-based Proton Energy, which manufactures HOGENon-site hydrogen generators for a diverse range of industrial andenergy applications. John has more than 15 years experience in thedesign and development of Proton Exchange Membrane (PEM) basedproducts for industrial and energy uses. He leads a group of engineersresponsible for providing Proton’s commercial customers with hydrogensupply solutions that are best suited for their specific application.

ReferencesAlbright, J.D. and Albright D.R., Generatortech, Inc. “Generator Field WindingShorted Turns: Moisture Effects”. Presented at EPRI™ Steam Turbine GeneratortechWorkshop and Vendor Exposition, Nashville, Tenn., August 25-27, 2003.

Borkey, Ed (general manager, Fluid Energy); Reynolds, Tom (electrical engineer,Progress Energy). “Water Contamination in Hydrogen-Cooled Generators Lurks as Serious Operational Threat”. Power Engineering, August 2003.

Vandervort, Christian L. and Kudlacik, Edward L. GE Power Systems, SchenectadyNY: GE Generator Technology Update, April 2003

GE Power Systems’ Generator Products Overview, October 2003.

changed positively from our pre-installation values. Operationally, theyhave proven to meet the needs of our generators, enabling us to reducethe storage, transport and manual operations required of cylinders.”

Mirant-Zeeland improves operational efficiency withHOGEN H Series generatorThe company’s Zeeland, Michigan plant is benefiting from theirHOGEN H Series’ hydrogen generator’s reliability along with savingson delivered hydrogen and more productive use of plant personnel’stime. Mirant-Zeeland’s generators require about 70 scf/hour of purehydrogen gas, about 4-6 cylinders per day. Before installing Proton’s HSeries hydrogen generator in March, the plant paid $30,000-$36,000per year for hydrogen cylinder deliveries. After seven months’ testing ofa pre-production HOGEN H Series system to cool three of their electricgenerators, Mirant’s Zeeland power plant has purchased a productionunit which will give them extra capacity for growth.

About Proton’s HOGEN hydrogen generatorsProton’s HOGEN H Series and HOGEN 20/40 hydrogen generators,which are now installed at more than 20 power generation facilities inthe U.S. and Europe, offer reduction of windage loss, longevity, andoperational efficiency compared with delivered hydrogen. HOGEN HSeries and 20/40 generators produce 99.999 percent pure hydrogen gasat up to 218 psig (15 bar) without use of a compressor. Seven capacitiesare available, from 76 to 228 scfh. The H Series generator can be easilyupgraded in the field for additional capacity. The H Series generator'senclosure and ventilation systems are weatherproofed for outdoorinstallation. Built under Proton's ISO 9001:2000 quality system, theunits are Nationally Recognized Testing Laboratory (NRTL) approvedfor use within U.S. and Canada, and CE approved for use within theEuropean Union.