Edward Chen

Experimental Investigation of Contact Resistance for Water Cooled Jacket for Electric Motors and Generators

The key to the successful implementation of water jacket frame cooling in high-power electric machines, such as permanent magnet, doubly fed induction, and synchronous generators, is the contact between the laminated stator core and the frame. For improved thermal design, it is important to quantify the contact thermal resistance between lamination and frame. This paper quantitatively presents the values of conventional stator lamination and frame interface resistance through experimental results. So far, no experimental investigation has been carried out to determine this resistance. The effects of several parameters, such as surface finish, shrink fit pressures, use of thermal grease, and phase change thermal interface material on thermal contact resistance, have been experimentally investigated. The obtained values of thermal contact resistance between laminations and frame can be applied for future thermal designs of electric machines to predict accurate thermal performance.

Direct drive HTS wind generator design for commercial applications

This paper describes the results of investigative studies performed for various design topologies of a direct drive HTS wind turbine generator. The investigation covers electrical, mechanical and thermal design with special considerations for design optimization for cost reduction and practical manufacturability for commercial applications. Detailed modeling and analyses are performed by taking into account the characteristic properties of the HTS and non-HTS materials. The investigations also use improved YBCO second generation (2G) HTS wire under development in a research program sponsored by the U.S. Department of Energy.

Noncontact High-Torque Magnetic Coupler for Superconducting Rotating Machines

We present the design of a noncontact high-torque magnetic coupler in the context of a high-speed (> 3600 r/min) fully superconducting rotating electric machine. The magnetic coupler is an essential component for machines where both stator and rotor are enclosed within a common cryostat. The magnetic coupler eliminates the need for rotating shaft vacuum seals, which would otherwise be needed if a conventional torque tube were used. The rotor is cooled by natural convection from the stator, similarly eliminating the need for the rotating cryogen transfer coupling used for conventional superconducting rotors. The magnetic coupler satisfies the need to transmit torque from the prime mover to the generator across a stationary cryostat boundary. We rely to an array of multiple radially spaced stages to limit axial extent and improve the torque rating of the design. We demonstrate that, while it is feasible to transmit several kilonewton meter of torque through a magnetic coupler for medium-size machines (> 10 MW), the magnetic coupler is nearly as complex as the rest of the machine. This option should be considered if known reliability issues with high-speed rotating vacuum seals and cryogen transfer couplings cannot be resolved.

Design concepts for a direct drive wind generator using new superconductors

Design concepts for a superconducting wind generator have been developed for offshore wind turbine applications. Electromagnetic, mechanical and thermal modeling and analyses are performed by taking into account the characteristic properties of the superconducting and non-superconducting materials. The investigations use new 4X improved YBCO (Yttrium Barium Copper Oxide) second generation (2G) high temperature superconducting (HTS) wire developed in a research program sponsored by the U.S. Department of Energy.

Design studies for a 10 MW direct drive superconducting wind generator

Design studies for a 10 MW superconducting wind generator have been performed for offshore wind turbine applications. Electromagnetic, mechanical and thermal analyses are performed by taking into account the characteristic properties of the superconducting and non-superconducting materials. The investigations use enhanced YBCO (Yttrium Barium Copper Oxide) second generation (2G) high temperature superconducting (HTS) wire under development in a research program sponsored by the U.S. Department of Energy.

High speed MW-rated induction motor drive system

Multi-physics design, simulation and analysis studies on an induction motor drive system rated 1 MW 15,000 RPM 4160 V are presented. Component level manufacturability and materials selection have been performed for the high speed application. Litz wire stator coils have been designed to reduce high frequency proximity losses. Prototype stator coils have been manufactured and tested. The various components of the system have been verified experimentally by bench tests. A novel power electronic drive using high power silicon carbide devices for the high speed application is developed. The complete motor and drive are now being manufactured for full load testing with the new dynamometer system at the eGrid Center of Clemson University.

Development of water jacket cooled motor and its applications in cement industry

Many researchers have shown a strong correlation between environmental protection and the life of electric motors. In harsh environments like those found in the cement industry, a motor needs adequate protection against airborne dust to operate at a safe temperature to prevent early winding insulation failure. Water jacket cooled motors are great candidates for such applications because of their superior heat transfer capability and protection against foreign particles. In addition, unlike traditional motors, water jacket cooled motors offer tremendous space savings because of the integrated heat exchanger within the motor frame, which leads to a compact motor with high power output/volume ratio. This can be attractive especially for cement plants with limited space or for replacing/upgrading motors inside existing infrastructures. This paper presents the design and tests of an 825 kW (1106 HP) water jacket cooled induction motor. Load tests were performed at different power ratings to characterize the thermal capability and the actual loss values of the machine. Lastly, applications for water jacket motors will be discussed to evaluate the feasibility of this technology in the cement industry.

Using plate heat exchanger (PHE) for totally enclosed air-to-air cooled (TEAAC) motor

Traditionally, totally enclosed air-to-air cooled (TEAAC) motors have used tubular heat exchangers as means to dissipate internal heat. Today, many tubular heat exchangers used in TEAAC are optimized to achieve high heat transfer rates but are ultimately limited by the air flow configuration inside the motor that uses one part counter flow and one part parallel flow. This leads to poor heat exchanger efficiency and significantly uneven temperature difference between the drive end (DE) and non-drive end (NDE) of the motor. A comparison test has been made between traditional tubular TEAAC and a plate heat exchanger (PHE) with a symmetric internal flow configuration. Unlike the asymmetric cooling of the tubular heat exchanger, the symmetric flow along with the two-step cross flow used in PHE provides an efficient and uniform cooling on DE and NDE. Until now, PHE has been largely used in heat recovery for heating ventilation and air conditioning (HVAC) and closed-circuit cooling in applications such as telecom cabinets and wind turbine generators. It offers a tremendous weight and size advantage due to its compactness. However, PHE may not be suitable for every application due to certain limitations of the technology. The paper will discuss the design, test comparison and the feasibility of this technology in motor applications.

Pulse Magnetization Studies on Partially Slit Second-Generation High-Temperature Superconductor Tape

Laboratory experiments were performed to study the second-generation (2G) YBCO high-temperature superconductor (HTS) partially slit tapes (PST) energized using pulse magnetization. The PST can be formed into a loop configuration without resistive splices. Following the decay of the pulsed magnetization transients, the currents flowing in the PSTs are persistent. This paper investigates the PSTs performance as affected by the changes in the pulse energy, presence of iron shielding, use of multi-PSTs, and different pulse charging techniques, at 77 K. One conclusion from the experiment is that the PSTs have the capability to activate, deactivate, and even reverse the magnetic fields by adjusting the polarity and magnitude of the pulse fields, in just a few milliseconds. This capability to quickly decrease the current in the 2G HTS tape can be used to protect the system in the case of a fault. In addition, the use of persistent tape eliminates resistive joints/splices, which can cause quench. This configuration also inherently protects the tape itself by limiting the current carrying capacity of the tape. These features have great potential to transform HTS 2G technology for high power motors, generators, and magnet applications.