K. Sivasubramaniam

GE Global Research, Niskayuna, New York, United States

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Publications (16)14.39 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: General Electric proposes to apply transformational technology in the form of low-temperature superconductivity to the design of direct-drive wind turbine generators of the 10-MW power level and greater. Generally, optimal steady state 4 K cryogenic cooling of a large thermal mass (> 10 000 kg) and its dimensions (> 4 m diameter and 2.5 m length) with minimum levelized cost of energy is difficult to achieve. A cooling strategy has been found that turns this size disadvantage to ones favor, and furthermore enables the design scalability of the field winding cooling assembly towards 15 to 20 MW. In this design study, we show that size and efficiency are not mutually exclusive and that it is indeed possible to minimize cryogenic complexity and reduce cost. The cryogenic push-button closed loop circulating system is invisible within the nacelle of a wind turbine and requires no handling of cryogenic liquids. Besides the occasional cryocooler service requirement, the proposed solution is maintenance-free in all operating states and allows the system health to be monitored remotely. The design solutions proposed could potentially make large superconducting generators a reality for off-shore wind turbine deployment.
    IEEE Transactions on Applied Superconductivity 06/2013; 23(3):5200804-5200804. · 1.20 Impact Factor
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    ABSTRACT: The experimental results of a cryo-free high-field magnet system for a novel magnetizer are presented. The magnet for the application is a superconducting racetrack coil of 0.7 m length using low AC-loss ${\rm Nb}_{3}{\rm Sn}$ wire from Luvata. The coil selection, reaction, epoxy selection, winding trials and vacuum impregnation are reported in a previous paper. Here the experimental testing of the prototype is presented. The magnet was cooled down with a 4 K GM cryocooler to its operating temperature and ramped. The behavior during cooldown, ramping and training are presented, demonstrating the viable operation of this low-cost engineering prototype.
    IEEE Transactions on Applied Superconductivity 01/2012; 22(3):9500905-9500905. · 1.20 Impact Factor
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    ABSTRACT: We present the engineering and design aspects of a cryo-free 10 T high-field magnet system for a completely new type of superconducting application. Design criteria and specifications for the racetrack shaped conduction-cooled magnet and the cryostat are discussed and disclosed.
    IEEE Transactions on Applied Superconductivity 07/2011; · 1.20 Impact Factor
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    ABSTRACT: General Electric, under contract with the Air Force Research Labs (AFRL), has successfully developed and tested a high speed, multimegawatt superconducting generator. The generator was built to demonstrate high temperature superconducting (HTS) generator technology for application in a high power density Multimegawatt 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.
    IEEE Transactions on Applied Superconductivity 07/2009; · 1.20 Impact Factor
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    ABSTRACT: Superconducting devices operating within a power system are expected to go through transient overload conditions during which the superconducting coil has to carry currents above the rated values. Designing the coil to remain superconducting through any possible fault scenario can be cost prohibitive, necessitating operation beyond the critical current for short periods. In order to set operating limits and design adequate protection systems for superconducting devices connected to a power system, the region of safe operation of these devices has to be described with general capability curves. Existing standards that define limits for these over-current situations are based on copper winding experience that do not apply to devices with superconducting components because of the highly nonlinear interaction between magnetic fields, operating temperature, and current density in the superconductor, and the rapidly varying material properties at cryogenic temperatures. In this paper, the behavior of superconducting coils during over-currents is discussed and a simplified capability curve is described to help standardize device capabilities. These curves are necessary to aid power system designers in appropriately designing the system and associated protection systems.
    IEEE Transactions on Applied Superconductivity 10/2008; · 1.20 Impact Factor
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    ABSTRACT: General electric, under contract with the Air Force Research Labs (AFRL), has successfully developed and tested a high speed, multimegawatt superconducting generator. The generator was built to demonstrate high temperature superconducting (HTS) generator technology for application in a high power density multimegawatt 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. Here we report key features of the generator and test results.
    Power and Energy Society General Meeting - Conversion and Delivery of Electrical Energy in the 21st Century, 2008 IEEE; 08/2008
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    ABSTRACT: This paper describes a high power density high-temperature superconducting (HTS) electric machine topology that is scalable for marine propulsion and power generation. The design, currently being pursued for airborne applications, is based on homopolar inductor alternator (HIA) technology, which is new within HTS applications. The basic machine design configuration of the HTS HIA is based on a stationary HTS field excitation coil, a solid rotor, and an advanced but conventional stator comprising liquid-cooled air-gap armature winding and an advanced iron core. High power density is obtained by the enhanced magneto-motive force capability of the HTS coil, the increased airgap flux density and armature current loading, and the high tip velocity of the rotor. Preliminary scaled up designs look attractive for three marine applications: propulsion drive, primary ship power generation, and power generation modules. The generators are driven directly by the turbines without the additional complexity of a clutch and gear system. A conceptual design study of a 36-MW 3600-r/min generator, a 4-MW 7000-r/min auxiliary generator, and a 36-MW 120-r/min and 4-MW 132-r/min propulsion motor are summarized.
    IEEE Transactions on Applied Superconductivity 04/2008; · 1.20 Impact Factor
  • M.R. Shah, A.M. EL-Refaie, K. Sivasubramaniam
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    ABSTRACT: Permanent magnet (PM) synchronous machines are becoming increasingly popular for a wide range of applications. This is mainly due to the significant advantages they provide in terms of power density and efficiency. One of the key challenges of using PM machines is fault-tolerance issue as the machine cannot be simply de-excited. This becomes even more important in safety-critical applications. The most severe and probable type of fault is the turn-to-turn fault. This paper provides a thorough analysis of turn-to-turn faults in surface PM machines with multi-layer fractional-slot concentrated windings. Different winding arrangements, and different slot/pole combinations are analyzed.
    Electrical Machines, 2008. ICEM 2008. 18th International Conference on; 01/2008
  • K. Sivasubramaniam, E.T. Laskaris, J.W. Bray
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    ABSTRACT: We present a conceptual design study to develop high power density high temperature superconducting (HTS) machines for two navy applications: primary ship propulsion power generation and drive, and power generation modules (PGM). The objective of the study was to evaluate the design of a 36 MW, 3600 rpm generator, a 36 MW, 120 rpm propulsion motor, and a 4 MW, 7000 rpm power generation module. The generators are to be driven directly by the turbines without the benefit of clutch or gear. Several design concepts were evaluated, including iron core rotors and homopolar inductor alternator topologies. Engineering trade-offs make the re-introduction of ferromagnetic iron attractive for a number of reasons. High power density is obtained by the increased airgap flux density and armature loading, and, for high speed applications, the high tip velocity of the rotor.
    Power Engineering Society General Meeting, 2007. IEEE; 07/2007
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    ABSTRACT: When a synchronous generator connected to the power grid experiences a fault, it is required to stay on line, ride through the fault, and be able to carry full rated field current when the fault is cleared. The peak current during these events could be 2 times higher than the normal operating current. This may cause an HTS rotor coil to go into normal state and generate Joule heating. If the fault event is short enough and the heat dumped can be carried away by the cooling system, the coil may recover to the superconducting state at the end of the fault. Otherwise, the coil may thermally run away, or dasiaquenchpsila. To investigate the quench behavior of the HTS rotor coil of the 100 MVA generator at GE Global Research Center, a 1.5 MVA prototype coil was developed and tested to quench under different conditions. The experiment design, set up, tests and test results are presented in this paper.
    IEEE Transactions on Applied Superconductivity 07/2007; · 1.20 Impact Factor
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    ABSTRACT: High-temperature superconducting (HTS) coils are generally stable against transient thermal disturbances. Protection against spontaneous quenches is not a main design issue for an HTS coil. However, HTS coils used in many electric devices such as motors, generators, transformers, and current limiters will operate under over-current fault conditions, which may result in a coil quench and thermal runaway. Those electric devices should be able to ride through some grid fault conditions and remain functional. This requires a certain over-current capability of the HTS coils. This paper discusses the over-current requirements from grid faults and the thermal transient responses of a BSCCO coil. It presents the analysis results of the coil subjected to over-current pulses at different operating conditions. The study also investigates the thermal runaway current and its relationship with the over-current pulse
    IEEE Transactions on Applied Superconductivity 01/2007; · 1.20 Impact Factor
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    ABSTRACT: Open MRI magnets are generally designed with ferromagnetic poles to contain and shape the magnetic flux and to reduce conductor cost. Permanent magnet MR magnets have blocks of PM and bulk ferromagnetic materials on or close to the pole face. These electrically conducting regions are sources of eddy currents that affect the image quality because of their relatively long time constants and close proximity to the imaging volume. The impact on image quality can be minimized by appropriate segmentation and/or lamination of these components. Detailed eddy current diffusion models are necessary to quantify the field distortion and time constants of the resulting field to perform design studies. The three dimensional frequency or time domain models required to accurately predict effects of eddy currents due to gradient fields are not computationally economical. This paper describes modeling of a PM imaging system using simplified 2D models with appropriate assumptions to evaluate the impact of these eddy currents. Experimental validation of some of the results with a prototype magnet is provided
    IEEE Transactions on Applied Superconductivity 07/2006; · 1.20 Impact Factor
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    ABSTRACT: As part of the DOE-SPI funded project a commercial HTS utility-size generator is being developed based on GE's iron core superconducting generator technology. The iron core concept has significant advantages over air core designs. The rotor consists of a cold superconducting field coil and coil supports and a warm iron core, which takes the torque and transmits to the shafts. Heat load due to AC losses in the cold mass of the rotor are a key design constraint. Analyses have been performed both at the component and system levels. AC loss tests have been conducted on an HTS generator. This paper presents and discusses the analytical and test results.
    IEEE Transactions on Applied Superconductivity 07/2005; · 1.20 Impact Factor
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    ABSTRACT: HTS wires, which may be used in many devices such as magnets and rotating machines, may be subjected to mechanical strains from electromagnetic, thermal and centripetal forces. In some applications these strains will be repeated several thousand times during the lifetime of the device. We have measured critical current degradation due to repeated strain cycles for both compressive and tensile strains. Results for BSCCO-2223 HTS conductor samples are presented for strain values up to 0.5% and cycle numbers up to and beyond 10<sup>4</sup>.
    IEEE Transactions on Applied Superconductivity 07/2005; · 1.20 Impact Factor
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    ABSTRACT: A 1.5‐MVA high temperature superconducting ( HTS ) generator of novel design has been designed, built and successfully tested by the General Electric Company. The 1.5‐ MVA generator has served as the engineering prototype for a much larger 100‐MVA beta unit now under design.
    AIP Conference Proceedings. 06/2004; 710(1):849-858.
  • K. Sivasubramaniam, E.T. Laskaris, D. Ryan
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    ABSTRACT: This paper investigates the suitability of MgB<sub>2</sub> tapes clad in a high magnetic permeability iron sheath for use in practical multi-turn superconducting coils. The flux-density in the MgB<sub>2</sub> portion of a single filamentary tape under various configurations is analyzed and its effect on the critical current capability is evaluated. The magnetic field is computed numerically using the finite element (FE) method. The FE model used for the analysis is described along with the assumptions made. The results indicate that the iron-clad MgB<sub>2</sub> tapes are undesirable for SC coils in many practical applications from a steady state performance stand point.
    IEEE Transactions on Applied Superconductivity 07/2003; · 1.20 Impact Factor