VIPIN PRoll No. 42

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Military and commercial applications need 1–5 MW capability in a portable high-power-density electric power generation package

Superconducting technology offers the highest entitlement for power density of the generator

HTS generator has been developed by GE for the Air Force Research Lab (AFRL).

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The generator comprises Stationary HTS field excitation coil Solid rotor forging Advanced but conventional stator Armature

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The stationary field coil does not experience the large centrifugal forces that a rotating coil would be subjected to.

More reliable HTS coils can be produced based on BSCCO or YBCO coated conductor technology

The cryostat of the coil is stationary. There is no need for a transfer coupling to introduce a cooling medium into the rotating cooling circuit

There is no need for a ‘slip-ring’ assembly to transfer current to the coil from a stationary exciter

There is no need to consider rotating brushless exciters

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The power density of the HTS homopolar inductor alternator design is not as high as that of fully air-core designs

The low full-load ampere-turn requirement of the stationary HTS coil greatly simplifies the development of this coil.

Vacuum is used to thermally insulate the coil Total heat load of 40 W. This refrigerator load requires a single-

stage GM cold head with 75 W capacity at 25K

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The HTS coil is cooled by gravity-fed boiling liquid neon

Return boil off neon is re-condensed by a single GM cryocooler.

Vacuum is used to thermally insulate the coil,

Total heat load =40 W. Requires a single stage GM cold

head with 75 W at 25K

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The air gap armature winding design utilizes bars which are wound with compacted Litz copper wire turns

Each bar is wet wound in a precision mold with thermally conductive epoxy and cured

The bars are assembled and bonded to the ceramic cooling tubes and G10 cylindrical inner and outer

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It is sealed with Ferro fluid seals inboard of the bearings to enable a vacuum of a few torr

This is necessary to reduce windage losses in a high-speed machine(>10000rpm speed)

The yoke within the stator consists of laminated blocks of iron-cobalt

These blocks are also laminated in different directions Flux from the rotor pole transport radially, axially, and circumferentially,

through the armature windings

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generator was fully instrumented for testing: vibration, thermal, electrical.

An IR camera with IR window is employed to read the rotor temperature

Power input measured with torque meter and tachometer

Electrical output was mea-sure with voltage, current, and phase readings of the output

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Verify the models and analysis we employed in design Special concern are the leakage paths, fringing fields, ac losses,

ampere-turn requirement, and core losses

A full 3D electromagnetic model has been built to understand the behavior and optimize the detailed design

Eddy currents are not considered directly Analysis was performed in two ways:

Static 3D model with imposed armature currents, and field excitation

Time-stepping 3D transient model with coupled external circuit

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Demonstrate the ability of Machine generate the desired voltage at the terminals coil to provide the ampere-turns of MMF cryogenic refrigerator to cool the winding The cooling circuits to handle any localized heating effects Air core flux paths to link the stator winding and provide useful voltage

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To determine the short-circuit characteristics Power input is for overcoming friction and windage, the joule

heating losses In conventional synchronous machines ohmic losses dominant

in short circuit runs and core losses in the open circuit runs In MEPS HIA significant ac losses in open circuit and core

losses in short circuit runs test

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The generator connected to resistive load bank Ramped up to 10,500 rpm Excitation level stepped up till the generator output was 1.3 MW

Terminal voltage

Line current

Power factor

Efficiency

266 V 1460A 0.985 97%

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Windage tests were performed at five speeds with degraded vacuum in the air gap

Thermal steady state was achieved at the lower speeds

transient tests were performed at higher speeds

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Superconducting Wind Generation

Conventional Gearbox

5 MW~ 410 tons

Conventional Gearless

6 MW~ 500 tons

HTS Gearless

8 MW~ 480 tons

Superconducting generators: half the size and weight

double the output for same land area

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The predictability of wave power makesit an attractive renewable energy source.Devices which use permanent magnetgenerators (PMG) (direct conversion) orhydraulic systems (indirect conversion)typically have to restrict power capturein heavy seas.

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