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Development of a High Speed HTS Generator
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Transcript of Development of a High Speed HTS Generator
Seminar on
DevelopmentofaHighSpeedHTSGeneratorfor
AirborneApplications
ABSTRACT
General Electric, under contract with the Air Force Research Labs (AFRL), has
successfully developed and tested a high speed, multi‐megawatt superconducting
generator. The generator was built to demonstrate high temperature superconducting
(HTS) generator technology for application in a high power density Multi‐megawatt
Electric Power System (MEPS) for the Air Force. The demonstration tested the
generator under load conditions up to 1.3 MW at over 10,000 rpm. The new MEPS
generator achieved 97% efficiency including cryocooler losses. All test results indicate
that the generator has a significant margin over the test points and that its
performance is consistent with program specifications. This demonstration is the first
successful full‐load test of a superconducting generator for the Air Force. In this paper
we describe the development of the generator and present some key test results used
to validate the design. Extrapolation to a higher power density generator is also
discussed.
CONTENTS
1. INTRODUCTION
Major Program Successes
Remaining Challenges
2. HIGHSPEEDHTSGENERATOR
3. KEYFEATURES
4. TESTRESULTS
Open Circuit Tests
Short Circuit Tests
Load Tests
Zero‐Excitation Windage Tests
5. ECONOMICEVALUATION
Possible HTS Generator Benefits
Costs of the HTS Generator
Economic Assessment
Conclusions
6. CONCLUSION
I.INTRODUCTION
Several military and commercial applications need 1–5 MW capability in a portable high‐power‐
density electric power generation package. One approach is to use a high‐speed generator directly
coupled to a high‐speed gas turbine, with high frequency solid‐state power conversion.
Superconducting technology offers the highest entitlement for power density of the generator, but
several engineering challenges remain in making a reliable, light‐weight superconducting machine. To
address this need, a rugged, high speed, multi‐megawatt, HTS generator has been developed by GE
for the Air Force Research Lab (AFRL). The generator has been load tested up to 1.3 MW at GE’s high‐
speed machine test‐bed. The generator is based on the homopolar inductor alternator (HIA) topology
to obtain power densities greater than 8.8kW/kg in a robust construction suited for high‐speed
applications. This paper describes the generator construction and test results.
MajorProgramSuccesses
• Successfully built and tested a 1.5 MW demonstrator rotor in a conventional stator.
• Demonstrated that the concept of the warm iron rotor HTS generator was a practical
alternative to air core HTS machines.
• Demonstrated that an HTS coil could be suitably supported in the extreme environment of
a rotating electric machine.
• Demonstrated that while current Generation 1 BSSCO HTS wire may be suitable for
smaller or slower electric machines, practical high‐speed machines will require a wire
that is much stronger.
• Provided benchmark costs needed for HTS wire to be competitive in utility generators and
flagged the need for higher operating temperatures to reduce refrigeration costs
• Developed acceptable insulation systems for BSCCO wire
• Created a statistical database for the strain sensitivity of BSCCO tapes suitable for detailed
design of operating field coils
• Developed and verified the analytical tools needed to extend the design of an HTS generator
to ratings of 100 MVA and larger.
• Developed and tested a helium transfer coupling suitable for a 100 MVA HTS generator.
RemainingChallenges
GE observes that good progress is being made in a number of technologies that would improve
the prospects of HTS technology in the power industry. Nonetheless, there remain challenges
that must be overcome before an HTS generator displaces large conventional generators in utility
applications. They are directly related to the initial cost of the generator and include:
• HTS wire of any generation must become much less expensive than the current wire.
Benchmark prices of $5/kA-m are likely to be the maximum acceptable for large-scale
adoption of this technology.
• The technical performance of the wire should increase so that operation at temperatures of
50 – 70 K in magnetic fields of 1 – 2 tesla is possible.
• Increase the ability of the wire to withstand compressive, tensile, and cyclic strain by a factor
of four. This now appears to be occurring with the G2 (YBCO) tapes.
• Low cost, highly reliable refrigeration units should be developed.
II. HIGH SPEED HTS GENERATOR
Trade‐off studies based on electromagnetic, thermal, mechanical, cryogenic, and reliability
considerations have shown that the HTS homopolar inductor alternator is the preferred configuration
for a high‐speed superconducting machine. The generator comprises a stationary HTS field excitation
coil, a solid rotor forging, and an advanced but conventional stator, as shown in the schematic in Fig.
1. The armature consists of liquid‐cooled air‐gap windings placed within an advanced iron yoke with
laminations oriented in three‐dimensions to carry flux from one end of the machine to the other. The
stationary HTS field coil is placed around the ferromagnetic rotor forging and between two sets of
salient poles that are offset circumferentially by one pole pitch at either end. The HTS field coil
provides a magneto‐motive force (MMF) capability many orders of magnitude higher than a
traditional copper coil, enabling an ‘air gap’ armature winding with high flux density in the gap. The
HTS coil can either be within the armature winding or between the armature and the stator yoke.
Many advantages result from this design as described,
Fig.1 Schematic of homopolar inductor alternator with HTS field winding.
• The stationary field coil does not experience the large centrifugal forces that a rotating coil would
be subjected to. The coil can now be a simple solenoid around the rotor instead of a more
complicated racetrack coil, so the coil support can be much simpler. The thermal insulation between
the coil and ambient is also improved because of lack of centrifugal loads and reduced requirements
on the coil support.
• Without the large forces and resulting strains in the superconducting coil, more reliable HTS coils
can be produced based on BSCCO or YBCO coated conductor technology that operates at ~30 K or ~70
K, respectively, and at peak field of ~1 Tesla. Further, the reduced ampere‐turns required by this
machine design would enable considerable reduction in the utilization of superconductor compared
to air‐core machine designs.
Fig.2.HomopolarinductoralternatorwithHTSfieldwinding.
• 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. Instead, the coil can be cooled by one of the established,
more reliable ways of cooling, including conduction cooling. The vacuum or foam insulation, as
required for good thermal insulation, will be stationary and therefore highly reliable. Other parts of
the insulation scheme can also be made more reliable without the large ‘g’ forces.
• There is no need for a ‘slip‐ring’ assembly to transfer current to the coil from a stationary exciter.
The voltage across the coil is then more predictable and makes it easier to detect quench and protect
the coil with a reliable protection circuit.
• There is no need to consider rotating brushless exciters. Fig. 2 shows a CAD model of a prototype
design. The cryocoolers and cryogen re‐condenser unit are mounted on top of the generator in a
simple, robust assembly. Table I summarizes the key design parameters of the generator derived from
program specifications. A 1 MW demonstrator generator was built to validate key features of this
new generator type. The generator has been successfully load tested.
Results are summarized in the following sections
III. KEY FEATURES
Fig. 3 shows a picture of the demonstrator generator in the high‐speed test bed. The power
density of the HTS homopolar inductor alternator design is not as high as that of fully air‐core designs
because it relies primarily on the iron‐core rotor and stator yoke to carry the flux, and there is
significantly more leakage flux in the inter polar space that needs to be carried through the iron rotor
and stator components. The power density, however, improves significantly with the high flux density
of the air‐gap armature winding and rotor speed, but moderately with the number of poles, while the
stationary field excitation HTS coil is utilized more efficiently than in any other machine design
because it ex‐ cites all pole pairs in parallel. As a result, the field ampere‐turns remain constant as the
number of poles is increased to enhance the machine power density.
The low full‐load ampere‐turn requirement of the stationary HTS coil greatly simplifies the
development of this coil. The coil can be designed with BSCCO or YBCO coated conductor, and our 1
MW demonstrator used BSCCO that operates at current of 150 A at ~30 K and peak field of ~1T. The
HTS coil is cooled by gravity‐fed boiling liquid neon through a cooling tube heat exchanger in contact
with the coil outside surface, and the return boil off neon is re‐condensed by a single GM cryocooler.
Vacuum is used to thermally insulate the coil, with a total heat load of 40 W. This refrigerator load
requires a single‐stage GM cold head with 75 W capacities at 25 K, but two cold heads may be
preferable for increased reliability and serviceability.
TABLE I
DESIGN PARAMETERS OF AN AFRL HIGH‐SPEED HTS HIA
The air gap armature winding design utilizes bars which are wound with compacted Litz copper
wire turns and cooled by ordinary water or a dielectric fluid flowing inside alumina ceramic cooling
tubes. Each bar is wet wound in a precision mold with thermally conductive epoxy and cured. The
bars are then assembled and adhesively bonded to the ceramic cooling tubes and G10 cylindrical
inner and outer shells using thermally conductive epoxy. The G10 shells on the ID and OD of the
armature bars serve as ground wall insulation. The armature winding assembly is bonded to the
stator yoke to form a rigid structure capable to withstand fault torques, vibration, and shock loads.
Fig.3. 1 MW generator in test.
The rotor shaft is sealed with Ferro fluid seals inboard of the bearings to enable a vacuum of a few
torr to be maintained within the active rotor chamber. This is necessary to reduce windage losses in
such a high‐speed machine. Especially for a salient pole rotor such as we have employed, the rotor
windage losses at 10,000 rpm would be too high to sustain without ma‐ chine damage, and active
cooling would have been difficult and heavy.
The yoke within the stator consists of laminated blocks of iron‐cobalt alloy to enable both lower
eddy current losses from the high frequency operation and high magnetic saturation for the high
field developed by the field coil. These blocks are also laminated in different directions to build up
the total yoke in order to facilitate the transport of flux from the rotor pole radially, axially, and
circumferentially, through the armature windings, to reach the opposite pole, which is offset
circumferentially from the first pole.
Provisions were made for balancing the solid rotor, first at high (full) speed in a balance pit and in
vacuum as needed be‐ fore assembly. Further balancing of the main rotor mass was un‐ necessary,
but balance provisions were made for other portions of the overall drive train after assembly of the
machine into the test facility
The generator was fully instrumented for testing: vibration, thermal, electrical. An IR camera with
IR window in the stator was employed to read the rotor temperature during operation. Power input
to the generator was measured with a torque meter and tachometer at the drive end, and electrical
output was mea‐ sure with voltage, current, and phase readings of the output.
A major reason for building and testing our HIA generator has been to verify the models and
analysis we employed in de‐ sign. Because of high nonlinearity of the generator and the complex
three‐dimensional nature of the flux paths, effects that are considered higher order in conventional
machines dominate and characterize the performance of the HTS HIA. Of 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 of the machine and optimize the
detailed design. Substantial differences in the flux distribution between the linear and non‐linear
cases, especially the leakage and bucking flux, meant that all analyses had to be performed with
detailed non‐linear models. For the conceptual analysis, isotropic properties are used throughout,
ignoring the effect of laminations. Eddy currents are not considered directly.
Analysis was performed in two ways:
1) Static 3D model with imposed armature currents, and field excitation;
2) Time‐stepping 3D transient model with coupled external circuit.
Power factor and terminal voltage for rated armature currents as a function of field current and
load angle are obtained from the magneto‐static analysis. The results are a strong function of
saturation. The linear models give vastly different results because of significantly different flux
distributions and the effect of the ‘bucking flux’. The results extracted from the magneto‐static runs
are then confirmed with the time stepping model.
The static and time‐stepping models gave initial confirmation of the electromagnetic performance
of the preliminary design of the HTS HIA. The saturation levels need to be monitored closely to
optimize machine weight. Finite element modeling with coupled external circuit helps identify areas
to focus on for optimization. The model also provides the capability to analyze transient conditions
associated with load duty cycle, fault conditions, etc.
IV. TEST RESULTS
A series of standard machine tests were performed on the generator to validate performance and
obtained data to use in scale‐up studies. Results and findings are summarized here. Throughout the
tests, and continuously for several months, the HTS coil temperatures were steadily maintained with
the closed cycle neon refrigeration.
A. Open Circuit Tests
The purpose of this test was to demonstrate the ability of the machine to generate the desired
voltage at the terminals and to obtain the no‐load saturation curve from test to verify the
electromagnetic design of the magnetic circuit. The test simultaneously challenged the ability of:
• The superconducting field coil to provide the ampere‐turns of MMF to create flux in the
generator.
• The HTS cryogenic refrigerator to cool the winding including any ac losses penetrating the
flux shield.
• The rotor permeability and air core flux paths to link the stator winding and provide useful
voltage.
• The cooling circuits to handle any localized heating effects due to the magnetic field.
Open circuit testing up to 300 V line‐line rms was performed at 10500 rpm. This voltage would
scale to 357 V at 12500 rpm, and 428 V at 15000 rpm, limited by rotor saturation. Fig. 4
shows the open circuit saturation curve from test compared to the predicted curve from the EM
models. The test results com‐ pare well with prediction up to and beyond the rated voltage.
Voltage imbalance between the different phases was less than ±1%.
At these flux levels, the flux density in the stator yoke is significantly below designed values,
resulting in low core losses as shown below. Fig. 5 compares predicted core losses with
measured losses.
B. Short Circuit Tests
The purpose of this test was to determine the short‐circuit characteristics of the generator
under armature current loading without power loading, with all the terminals of the generator
shorted together. Power input to the shaft under this condition is for overcoming friction and
windage, the joule heating losses of the current flowing in the generator armature, and a small
level of core losses.
Fig.4. Open circuit saturation curve
Synchronous impedance tests up to armature line currents of 1450 A rms were performed.
Fig. 6 shows the short circuit characteristic of the generator obtained from testing
compared to model predictions. The results are within a few percent of expected values.
Imbalance between the two three phase sets was about 3% even without the use of trim
inductors to balance the leakage reactance of the different phases. The maximum
imbalance among all the phases was ±9%.
Fig. 5. Core losses during open circuit test compared to prediction
In conventional synchronous machines, the electrical losses are dominated by the ohmic
losses in the copper windings during short circuit runs and core losses in the open circuit
runs. Traditionally, loss data from steady state heat runs under ‘zero‐excitation’, open
circuit, and short circuit are used to segregate losses in the different components using
this assumption. In the MEPS HIA generator, significant ac losses in the armature winding
during open circuit conditions and significant core losses during the short circuit runs,
coupled with varying cryostat losses, make this procedure inaccurate.
Fig. 6. Short circuit characteristics.
Fig. 7. Copper losses during SC test compared to prediction. An alternate procedure to segregate losses is analysis of heat rejection in the different
cooling systems within the generator. The HIA generator has been designed to have
dedicated cooling for most of its major loss centers, including armature straight sections,
end sections, iron core, and cryostat, with little heat transfer between these sub‐systems.
Flow and coolant temperature rise from these cooling circuits have been used to obtain
the loss breakdown reported here. Any error in this data is due to the actual flow and
temperature measurements and cross‐talk between the different subsystems. These are
assumed to be minimal.
Fig. 8. Efficiency of SC generator observed during load test.
Fig. 9. Phase voltages during 1 MW load test.
Fig. 7 compares copper armature loss obtained from short circuit tests with calculated
losses. The results are in general agreement and confirm that the armature has the
capability to work at the rated current of 2309 A rms. The cryogenic systems operated
without any problems during these runs.
One explanation for the lower measured losses at higher current levels is that at these
levels the copper windings are hotter than the yoke, resulting in heat transfer from the
windings in to the yoke and out through the yoke cooling. This would also explain the
reversed effect at the lower current levels.
C. Load Tests
The generator was connected to the resistive load bank, ramped up to 10,500 rpm, and
the excitation level stepped up gradually till the generator output was 1.3 MW (limited by
the test facility). The terminal voltage was 266 V‐rms line to line, and line current was
1460 A‐rms at the maximum power level. Power factor was 0.985. The generator
efficiency computed from the generator output versus the input power plus the rated
power of the cryocooler compressor is shown in Fig. 8. The efficiency is about 97% at 1
MW, and approaches 98% (the designed value) as the power is increased towards the
designed rating of 4 MW.
Steady state heat runs under load were performed up to 1.05 MW. Loss data and
temperatures were consistent with those obtained from the no load runs. Voltage and
current imbalances were within 2%, and waveforms are as expected and are showed in
Figs. 9 and 10.
Fig. 10. Line currents during 1 MW load test
Minimal windage and pole face heating was observed during the load tests.
Fig. 11. Atmospheric windage results to 10,000 RPM.
D. Zero-Excitation Windage Tests
Windage tests were performed at five speeds with degraded vacuum in the air gap.
Thermal steady‐state was achieved at the lower speeds and transient tests were
performed at higher speeds due to high rotor and stator temperatures not allowing steady
state to be obtained. The torque is measured by the torque meter, and the computed
power loss is plotted in Fig. 11.
A power curve of the form ‘torque = (constant)*(speed)n‘ is fitted through the data. The
exponent for windage torque is found as n~1.44, and since ‘windage power loss
=(torque)*(speed)’, its exponent of speed is (n+1)~ 1.44. This is consistent with our
expectation that windage power loss has n ~ 2–3 for losses between concentric cylinders
with no axial flow. A maximum power loss of 40 kW is measured for a speed of 10,000 rpm
in 1 atmosphere pressure, and this shows the need for low pressure for high‐speed
operation.
Also shown in Fig. 11 are plots representing the predictions from two different rotating
cylinder loss models. Each of these models assumes a perfectly cylindrical surface spinning
in a thin annular space. The geometry of the MEPS rotor is very different from this, with
four salient poles on each end and a lower diameter mid‐section. The approach here was
to use the relationship between the salient pole depth to rotor radius ratio and a smooth
cylinder windage multiplying factor, developed by Vrancik. In the case of our rotor, the
calculated smooth cylinder windage value determined by the aforementioned windage
models, were multiplied by a factor of 5. While the majority of the windage losses occur
due to the cylindrical surface, the predictions in Fig. 11 include adding the effects of the
two side “disks” that represent the ends of the cylinder. The disk losses (associated with
heating due to the air friction on the sides of the spinning cylinder) were calculated using
the same model, applicable to a solid circular disk. For the purposes of this calculation, the
outer diameter of the salient pole was used as the disk diameter.
The data clearly fall within the regime of both windage models, fitting the model of Ran
slightly better, especially at the higher speed range. The curve fit also follows the two
windage model curves reasonably well, but it is clear that the rate of increase near the
higher speeds is not the same as the windage models.
Several windage tests were performed at the lowest pressures attainable in the
machine, ~375–533 Pa. Three of the tests were open circuit heat runs, two were full load
tests, and one was a zero excitation test. None were run as an actual windage test, but we
were able to take measurements before the field excitation was applied, thus enabling a
windage + friction test point at the speed of the particular electrical test. The windage and
friction
The windage and friction measurement includes bearing and Ferro‐fluidic seal losses. To
determine the windage contribution, they must be subtracted because, unlike the 1 atm
windage tests, they are not negligible. The Ferro‐fluidic seal losses were measured by
measuring their removal by the Ferro‐fluidic seal water cooling circuit, and the estimated
bearing losses were estimated by scaling from the manufacturer’s stated losses. The losses
were quite constant across all the tests. To obtain the windage loss, the bearing and Ferro‐
fluidic seal losses are subtracted from the windage and friction measurement. While there
is some scatter in the data, it shows the windage to be about 1.5 kW.
The windage and friction measurement includes bearing and Ferro‐fluidic seal losses. To
determine the windage contribution, they must be subtracted because, unlike the 1 atm
windage tests, they are not negligible. The Ferro‐fluidic seal losses were measured by
measuring their removal by the Ferro‐fluidic seal water cooling circuit, and the estimated
bearing losses were estimated by scaling from the manufacturer’s stated losses. The losses
were quite constant across all the tests. To obtain the windage loss, the bearing and Ferro‐
fluidic seal losses are subtracted from the windage and friction measurement. While there
is some scatter in the data, it shows the windage to be about 1.5 kW.
V. ECONOMIC EVALUATION
The economic judgments associated with any technology program are always done
in the context of the organization making the judgment. That context includes:
• A view of the external market (in this case, the power generation market)
• Estimates about the progress on technology
• Financial considerations (cost of money, etc.)
As such, different organizations may arrive at different conclusions for a given
technology opportunity. That is likely to be the case for HTS generators.
GE’s economic evaluation of the HTS generator is based on proprietary information
that cannot be disclosed. However, general comments and high‐level considerations of
benefits vs. cost can illustrate how the evaluation was made.
PossibleHTSGeneratorBenefits
The benefits of any HTS generator in a power generation application may
include
• The value of avoided losses.
• Any possible reduction in the capital cost of the generator because of the HTS
rotor.
• Potential revenue because of enhanced reactive power capacity (VARS)
• Incremental improvements in generator reliability
• Improved power plant stability
Avoided losses can represent either fuel not burned or incremental sales of electricity
and that choice is at the discretion of the power plant operator. The value will depend
greatly on the cost of fuel, the number of operating hours per year, and the market
price for electricity.
Studies done within this program and elsewhere confirm that reductions in the
overall generator cost are possible if a generator were initially designed with an HTS
rotor. Most of those savings are related to an improved use of ventilation that allows
for an overall higher power density.
The opportunity for revenue from enhanced reactive capability appears to be
highly situational. In some instances, reactive power capacity may have a well‐defined
value. However, there is no generally accepted means to establish that value for the
general case, nor a means to compensate a power plant owner for any additional
reactive power capacity in the HTS generator.
It is quite possible the HTS rotor will offer reliability benefits to the generator owner simply
because the rotor would experience far fewer thermal excursions over its lifetime. That lessened
thermal duty may translate into a delayed rotor rewind after 20 – 25 years. However, that
improved reliability must be considered in the context of a more complex generator. The
transfer coupling and the cryocooler are additional components in the power train that
represent instances of single point failures. Redundant cryocoolers could be included but at an
additional cost. Nonetheless, the transfer of coolant onto the rotor would remain a weak point.
Improvements in power plant stability have been cited as driving forces for superconducting
generators in some countries. However, as with the reactive power capacity, this benefit is
certainly situational and cannot support a general business case for this technology.
Costs of the HTS Generator
The additional costs of the HTS generator in a utility application include
• A possible higher capital cost
• An increase in maintenance costs
GE’s investigation into the cost structure for the HTS generator shows that the higher cost for
the generator is driven by three major factors:
• The cost of the HTS wire,
• The cost to support the HTS coil during operation, and
• The cost of the cryocooler.
Table 6‐1 shows the comparative cost of the 100 MVA HTS generator as a percentage of the cost
of the conventional generator assuming an HTS wire cost of $25/kA‐m. The HTS coil, the
refrigeration, and the mechanical support represent an extra 70% cost beyond the same
functional components in the conventional generator. These estimates are based on GE’s
judgment of “mature” product costs given the present technology.
Regardless of the cost of the generator, the HTS generator in the power plant represents an on‐
going cost to the plant operator. Maintenance personnel will have to be assigned (part‐time)
to monitor the equipment and perform periodic maintenance of the refrigeration system.
This cost will be assumed to be $20,000/year.
Table 5-1 - Cost of 100 MVA HTS Generator Compared to Conventional Generator
Base Generator Cost
HTS Generator Cost
Field Coil (*) 11% 34%
Refrigeration --- 21
Rotor Forging & Coil Support 9 35
Other Rotor 12 19
Stator & Final Assembly 59 58
Exciter 9 9
Total Generator Cost 100% 176%
* For $25/kA-m HTS wire
Economic Assessment
Given the potential benefits of higher efficiency and the prospect of significantly greater
generator costs, one can bound the overall economic viability of the HTS generator.
Table 5‐2 shows a simple model of the value of the avoided losses. It assumes the
improved losses shown in Table 5‐2 (265 kW) and considers both a base‐loaded generator
operating 8000 hours per year and a unit operated only 3000 hours per year (quite typical of
smaller air‐cooled generators). Furthermore, the table considers the cost of HTS wire over a range
from $150/kA‐m to $5/kA‐m. The present value of the losses is based on incremental electricity
sales at $35/MW‐hr over a 15 year period at 15% cost of money.
Table 5‐3 addresses the benefits for a 575 MVA hydrogen‐cooled generator.
One simple question: “Does the more efficient HTS generator return enough capital to pay for
its HTS wire?” Table 5‐2 shows that, for the most part, the 100 MVA generator does not. The
only exceptions are for a cyclic‐loaded unit with very inexpensive wire ($5/kA‐m) or a base‐
loaded unit with wire at $25/kA‐m or less. In contrast, Table 5‐3 shows that the efficiency
benefit of the larger generator is sufficient to cover the wire cost in most cases.
This assessment shows that high operating hours and inexpensive HTS wire are necessary for the
HTS generator to be economically viable. However, they are not sufficient. As Table 5‐1
showed, the cost of the refrigeration and coil support remain expensive components in the rotor
assembly. Improvements in refrigeration and wire characteristics (higher operating temperatures
and strain capacity) are needed.
Table 5-2 - Benefits of Efficiency Savings on a 100 MVA Generator
Base Load
Cyclic Operation
Loss Savings kW 265 265
Operating Hours hrs/yr 8000 3000
Incremental Electricity Sales $1,000/yr 74 28
Annual Maintenance $1,000/yr 20 20
Net Benefit $1,000/yr 54 8
Present Value of Benefit $1,000 317 46
HTS Wire Price $/kA-m 150 25 5 150 25 5
Covers the HTS Wire Cost? NO YES YES NO NO YES
T bl 5 3 B fit f Effi i S i 575 MVA G t
Base Load
Cyclic Operation
Loss Savings kW 2000 2000
Operating Hours hrs/yr 8000 3000
Incremental Electricity Sales $1,000/yr 560 210
Annual Maintenance $1,000/yr 20 20
Net Benefit $1,000/yr 540 190
Present Value of Benefit $1,000 3158 1111
HTS Wire Price $/kA-m 150 25 5 150 25 5
Covers the HTS Wire Cost? YES YES YES NO YES YES
Conclusions
GE has concluded that given the current HTS technology and the cost of the HTS wire, the cost
disadvantage of a 100 MVA HTS generator, combined with its relatively infrequent operation,
more than offsets any efficiency benefits.
Larger generators with ratings greater than 500 MW may be suitable candidates for the HTS
technology. They offer greater efficiency benefits and are more likely to be operated as base‐
loaded units. Furthermore, some cost trends scale more slowly than the rating, so factors that
are significant for small generators may be less significant in larger generators.
VI. CONCLUSION
An HTS HIA high-speed generator was designed, built, and tested. It produced 1.3 MW of electrical
power under resistive load in a dynamometer test cell at a speed exceeding 10,000 rpm and with a
closed cycle neon cryogenic HTS cooling system. This satisfied all specifications of the Air Force
contract. Generator operating characteristics were measured and compared to design predictions,
leading to the conclusion that the design methods are adequate for a non-linear HIA machine. In
addition, valuable data on windage losses of the salient-pole rotor at high speeds and low air
pressures, for which no precise models exist, were gathered.
BIBLIOGRAPHY
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Luongo, IEEE Transactions, Applied Superconductivity
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