The rotor is designed to withstand cyclic duty and rapid loading.Radial ventilation provides even cooling. Low vibration levels areachieved by dynamic balancing and machine design.

2-Pole Turbine GeneratorsRotor Construction

WARRANTY

Rotor Forging and MachiningThe rotor forging is a special alloy steelcontaining nickel, chromium, molybdenum,and vanadium. It has the physicalproperties required to withstand thestresses encountered over a wide rangeof temperature and load conditions. Theforging material is produced from anelectric furnace vacuum degassed ingot.All forgings are heat treated after theforging operation and stress relieved afterrough machining. To control quality, achemical analysis is made of each heatcycle, and radial test samples are takenfrom the rotor body to indicate the physicalproperties. Longitudinal tensile and impacttest specimens are taken from the extramaterial at the end of the forging. Theholes from which the radial samples weretaken are tapped and plugged with steel,and are positioned to be at the centers ofthe poles. The forging manufacturerperforms an impact test to determine thelow temperature ductility of the steel. Inaddition, ultrasonic tests and magneticparticle tests are made to assure that theforging is sound.

Field Coils• Rotor coils are made of silver-bearing strap copper for greater creep resistance. The coil is accurately formed to precisely fit in the rotor slot with minimum distortion. Ventilating slots are punched in the straight portion of the coils to allow for radial discharge of cooling air.

• The rotor body coil slot is lined with a Nomex insulating cell formed to the exact shape of the slot. The slot cell ground insulation level is checked before the coils are installed.

• Each field coil is suspended over a pole and inserted, turn-by-turn, into the slots. Individual turns are insulated with Nomex which is coated with a B-state resin. The coils are pressed to a specified size, then heated to cure the resin and bond the turns. Aluminum alloy slot wedges are inserted to hold the winding firmly in place.

• A teflon coated strip is placed on top of the coils to help in providing a controlled slip plane for coil expansion and contraction that occurs during start/stop and loading cycles.

2-Pole Turbine GeneratorsRotor Construction

Rotor Forging and MachiningThe rotor forging is a special alloy steel containing nickel, chromium, molybdenum, and vanadium. It has the physical properties required to withstand the stresses encountered over a wide range of temperature and load conditions. The forging material is produced from an electric furnace vacuum degassed ingot. All forgings are heat treated after the forging operation and stress relieved after rough machining. To control quality, a chemical analysis is made of each heat cycle, and radial test samples are taken from the rotor body to indicate the physical properties. Longitudinal tensile and impact test specimens are taken from the extra material at the end of the forging. The holes from which the radial samples were taken are tapped and plugged with steel, and are positioned to be at the centers of the poles. The forging manufacturer performs an impact test to determine the low temperature ductility of the steel. In addition, ultrasonic tests and magnetic particle tests are made to assure that the forging is sound.

Field Coils• Rotor coils are made of silver-bearing

strap copper for greater creep resistance. The coil is accurately formed to precisely fit in the rotor slot with minimum distortion. Ventilating slots are punched in the straight portion of the coils to allow for radial discharge of cooling air.

• The rotor body coil slot is lined with a Nomex insulating cell formed to the exact shape of the slot. The slot cell ground insulation level is checked before the coils are installed.

• Each field coil is suspended over a pole and inserted, turn-by-turn, into the slots. Individual turns are insulated with Nomex which is coated with a B-state resin. The coils are pressed to a specified size, then heated to cure the resin and bond the turns. Aluminum alloy slot wedges are inserted to hold the winding firmly in place.

• A teflon coated strip is placed on top of the coils to help in providing a controlled slip plane for coil expansion and contraction that occurs during start/stop and loading cycles.

The rotor is designed to withstand cyclic duty and rapid loading. Radial ventilation provides even cooling. Low vibration levels are achieved by dynamic balancing and machine design.

Rotor SlotsSlots for field windings are step milled over the entire length of the rotor body. They are milled in a pattern to give the 2-pole configuration and also to provide liberal area for field copper. Step milling minimizes stress level at the roots of the teeth, one of the most critical parts of the rotor. Grooves for slot wedges are accurately machined into the slot walls. Slots for rotor ventilation are positioned directly under the rotor coil slots and are reduced width extensions of the regular milled coil slots.

Rotor slots for field winding.Machining radial slots in rotor forging.

Rotor SlotsSlots for field windings are step milled overthe entire length of the rotor body. Theyare milled in a pattern to give the 2-poleconfiguration and also to provide liberalarea for field copper. Step millingminimizes stress level at the roots of theteeth, one of the most critical parts of therotor. Grooves for slot wedges areaccurately machined into the slot walls.Slots for rotor ventilation are positioneddirectly under the rotor coil slots and arereduced width extensions of the regularmilled coil slots.

2-Pole Turbine GeneratorsRotor Construction

Rotor Forging and MachiningThe rotor forging is a special alloy steel containing nickel, chromium, molybdenum, and vanadium. It has the physical properties required to withstand the stresses encountered over a wide range of temperature and load conditions. The forging material is produced from an electric furnace vacuum degassed ingot. All forgings are heat treated after the forging operation and stress relieved after rough machining. To control quality, a chemical analysis is made of each heat cycle, and radial test samples are taken from the rotor body to indicate the physical properties. Longitudinal tensile and impact test specimens are taken from the extra material at the end of the forging. The holes from which the radial samples were taken are tapped and plugged with steel, and are positioned to be at the centers of the poles. The forging manufacturer performs an impact test to determine the low temperature ductility of the steel. In addition, ultrasonic tests and magnetic particle tests are made to assure that the forging is sound.

Field Coils• Rotor coils are made of silver-bearing

strap copper for greater creep resistance. The coil is accurately formed to precisely fit in the rotor slot with minimum distortion. Ventilating slots are punched in the straight portion of the coils to allow for radial discharge of cooling air.

• The rotor body coil slot is lined with a Nomex insulating cell formed to the exact shape of the slot. The slot cell ground insulation level is checked before the coils are installed.

• Each field coil is suspended over a pole and inserted, turn-by-turn, into the slots. Individual turns are insulated with Nomex which is coated with a B-state resin. The coils are pressed to a specified size, then heated to cure the resin and bond the turns. Aluminum alloy slot wedges are inserted to hold the winding firmly in place.

• A teflon coated strip is placed on top of the coils to help in providing a controlled slip plane for coil expansion and contraction that occurs during start/stop and loading cycles.

The rotor is designed to withstand cyclic duty and rapid loading. Radial ventilation provides even cooling. Low vibration levels are achieved by dynamic balancing and machine design.

Rotor SlotsSlots for field windings are step milled over the entire length of the rotor body. They are milled in a pattern to give the 2-pole configuration and also to provide liberal area for field copper. Step milling minimizes stress level at the roots of the teeth, one of the most critical parts of the rotor. Grooves for slot wedges are accurately machined into the slot walls. Slots for rotor ventilation are positioned directly under the rotor coil slots and are reduced width extensions of the regular milled coil slots.

Rotor slots for field winding.Machining radial slots in rotor forging.

Retaining RingsRetaining rings support the rotor coil endturns against the centrifugal forcesencountered during high-speed operation.They are made from forgings that meetrigid specifications and are resistant tostress corrosion cracking. Compliance withthese specifications is assured by tests forphysical properties made on prolongationsallowed at the end of the forging.Ultrasonic tests are conducted to assuresoundness of the forging. Any forgingfound to be defective is rejected. Circularsteel plates are shrunk into the outer endof the retaining ring to add section and toreduce distortion. The retaining rings areshrunk on a machined fit on the rotorbody. This fit is calculated to provide firmcentering of the ring on the rotor bodyeven under overspeed conditions.

Circumferential keys at the rotor body lockthe rings in place. In effect, the retainingrings nest the end turns inside a shelf orextension of the rotor body and preventdisplacement and consequentialunbalance. Since the retainers do notdepend on the shaft for support, shaftdeflections cannot transmit forces thatcause such displacements and unbalance.The field coil end turns are cooled byair passing circumferentially and axiallybetween the coils and dischargingthrough radial slots in the rotor windingsand wedges.

Electric Machinery800 Central Avenue NEMinneapolis, Minnesota 55413United StatesTel: +1 612 378 8000Fax: +1 612 378 8051www.electricmachinery.com

© Electric Machinery 2011. Publication NA.10005.gb.11-09.01. Electric Machinery, the Electric Machinery logo and any version thereof are trademarks and service marks of Electric Machinery.The other names mentioned, registered or not, are the property of their respective companies.

WARRANTY

Rotor FansSteel axial flow fans are fabricated, testedand balanced. The fans are keyed andshrunk on the rotor body outboard of theretainer rings.

Balance And VibrationPrecautions are taken throughout thedesign and manufacturing operations toensure precise balance and minimizevibration. For example, account is takenof the fact that the stiffness of the usual2-pole rotor varies as the rotor turns.When the poles are positioned vertically,the rotor is more resistant to bendingand deflection than when the poles arehorizontal. As the rotor turns, the positionof these planes of stiffness changes twiceeach revolution, tending to cause 7,200vibrations per minute at 3,600 rpm (120per second). On larger ratings, to reducethe magnitude of the double frequencyvibrations, transverse slots are milled intoeach pole face at intervals along the rotorbody to equalize the rigidity of the rotor inthese two planes.

Similarly, the critical speed of the rotoris controlled to avoid possible excitationof bearing oil whip and consequentialvibration. This is accomplished by graduallystepping down the shaft diameter fromthe rotor body so as to provide optimumshaft stiffness.

The rotor is balanced in three places in ahigh speed balancing facility. An overspeedrun is made with the rotor assembled inthe generator.

Brushless ExcitationAn axial hole is drilled in to the shaft at theexciter end and is used to carry DC powerfrom the exciter, under the bearing journal,to the main field winding.

www.converteam.com

Converteam Electric Machinery800 Central Avenue NEMinneapolis, Minnesota 55413United StatesTel: +1 612 378 8000Fax: +1 612 378 8051

North America Headquarters:Converteam Inc.Pittsburgh, PennsylvaniaTel: +1 412 967 0765

France Tel: +33 1 77 31 20 00Germany Tel: +49 30 76 22 0UK Tel: +44 1788 563563Brazil Tel: +55 31 3330 5800China Tel: +86 21 6442 1666India Tel: +91 44 2440 0900Russia Tel: +7 495 225 1916

Retaining RingsRetaining rings support the rotor coil end turns against the centrifugal forces encountered during high-speed operation. They are made from forgings that meet rigid specifications and are resistant to stress corrosion cracking. Compliance with these specifications is assured by tests for physical properties made on prolongations allowed at the end of the forging. Ultrasonic tests are conducted to assure soundness of the forging. Any forging found to be defective is rejected. Circular steel plates are shrunk into the outer end of the retaining ring to add section and to reduce distortion. The retaining rings are shrunk on a machined fit on the rotor body. This fit is calculated to provide firm centering of the ring on the rotor body even under overspeed conditions. Circumferential keys at the rotor body lock the rings in place. In effect, the retaining rings nest the end turns inside a shelf or extension of the rotor body and prevent displacement and consequential unbalance. Since the retainers do not depend on the shaft for support, shaft deflections cannot transmit forces that cause such displacements and unbalance.

The field coil end turns are cooled by air passing circumferentially and axially between the coils and discharging through radial slots in the rotor windings and wedges.

Rotor FansSteel axial flow fans are fabricated, tested and balanced. The fans are keyed and shrunk on the rotor body outboard of the retainer rings.

Balance And VibrationPrecautions are taken throughout the design and manufacturing operations to ensure precise balance and minimize vibration. For example, account is taken of the fact that the stiffness of the usual 2-pole rotor varies as the rotor turns. When the poles are positioned vertically, the rotor is more resistant to bending and deflection than when the poles are horizontal. As the rotor turns, the position of these planes of stiffness changes twice each revolution, tending to cause 7,200 vibrations per minute at 3,600 rpm (120 per second). On larger ratings, to reduce the magnitude of the double frequency vibrations, transverse slots are milled into each pole face at intervals along the rotor body to equalize the rigidity of the rotor in these two planes.

Similarly, the critical speed of the rotor is controlled to avoid possible excitation of bearing oil whip and consequential vibration. This is accomplished by gradually stepping down the shaft diameter from the rotor body so as to provide optimum shaft stiffness.

The rotor is balanced in three places in a high speed balancing facility. An overspeed run is made with the rotor assembled in the generator.

Brushless ExcitationAn axial hole is drilled in to the shaft at the exciter end and is used to carry DC power from the exciter, under the bearing journal, to the main field winding.

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Rotor end turn area.Rotor winding process.Rotor retaining rings.