Ralph H. Jansen

High Temperature Characterization of a Radial Magnetic Bearing for Turbomachinery

Open loop, experimental force and power measurements of a radial, redundant-axis, magnetic bearing at temperatures to 1000°F (538°C) and rotor speeds to 15,000 rpm along with theoretical temperature and force models are presented in this paper. The experimentally measured force produced by a single C-core circuit using 22A was 600 lb (2.67 kN) at room temperature and 380 lb (1.69 kN) at 538°C. These values were compared with force predictions based on a one-dimensional magnetic circuit analysis and a thermal analysis of gap growth as a function of temperature. The analysis showed that the reduction of force at high temperature is mostly due to an increase in radial gap due to test conditions, rather than to reduced core permeability. Tests under rotating conditions showed that rotor speed has a negligible effect on the bearings static force capacity. One C-core required approximately 340 W of power to generate 190 lb (845 N) of magnetic force at 538°C, however the magnetic air gap was much larger than at room temperature. The data presented are after bearing operation for eleven total hours at 538°C and six thermal cycles.

Single axis attitude control and DC bus regulation with two flywheels

A computer simulation of a flywheel energy storage single axis attitude control system is described. The simulation models hardware which will be experimentally tested in the future. This hardware consists of two counter rotating flywheels mounted to an airtable. The airtable allows one axis of rotational motion. An inertia DC bus coordinator is set forth that allows the two control problems, bus regulation and attitude control, to be separated. Simulation results are presented with a previously derived flywheel bus regulator (Kascak, 2001) and a simple PID attitude controller.

Fully Suspended, Five-Axis, Three-Magnetic- Bearing Dynamic Spin Rig With Forced Excitation

A significant advancement in the dynamic spin rig (DSR), i.e., the five-axis, three-magnetic-bearing DSR, is used to perform vibration tests of turbomachinery blades and components under rotating and non-rotating conditions in a vacuum. The rig has three magnetic bearings as its critical components: two heteropolar radial active magnetic bearings and a magnetic thrust bearing. The bearing configuration allows full vertical rotor magnetic suspension along with a feedforward control feature, which enables the excitation of various modes of vibration in the bladed disk test articles. The theoretical, mechanical, electrical, and electronic aspects of the rig are discussed. Also presented are the forced-excitation results of a fully levitated, rotating and non-rotating, unbladed rotor and a fully levitated, rotating and non-rotating, bladed rotor in which a pair of blades were arranged 180° apart from each other. These tests include the “bounce” mode excitation of the rotor in which the rotor was excited at the blade natural frequency of 144 Hz. The rotor natural mode frequency of 355 Hz was discerned from the plot of acceleration versus frequency. For non-rotating blades, a blade-tip excitation amplitude of approximately 100 g A−1 was achieved at the first-bending critical (≈144 Hz) and at the first-torsional and second-bending blade modes. A blade-tip displacement of 1.778×10−3m (70 mils) was achieved at the first-bending critical by exciting the blades at a forced-excitation phase angle of 90° relative to the vertical plane containing the blades while simultaneously rotating the shaft at 3000 rpm.

Demonstration of attitude control and bus regulation with flywheels

A flywheel energy storage device stores energy in a rotating mass. These devices can be used to perform the same function as traditional chemical batteries. In terms of the energy storage function, a flywheel system has significant advantages over chemical batteries: length of life, energy density, power density, and the capability of deep depth of discharge. Also, flywheels can be used to control the attitude of the spacecraft. This paper describes an experiment using two flywheels to simultaneously regulate a DC bus and provide single axis angle regulation on an air table. Models of the mechanical and electrical systems are developed, and simulations are run, then compared to experimental results. The correspondence of the simulations and experiments shows the sufficiency of the modeling of subsystems.

HIGH SPECIFIC POWER MOTORS IN LN2 AND LH2

A switched reluctance motor has been operated in liquid nitrogen (LN2) with a power density as high as that reported for any motor or generator. The high performance stems from the low resistivity of Cu at LN2 temperature and from the geometry of the windings, the combination of which permits steady-state rms current density up to 7000u2009A/cm2, about 10 times that possible in coils cooled by natural convection at room temperature. The Joule heating in the coils is conducted to the end turns for rejection to the LN2 bath. Minimal heat rejection occurs in the motor slots, preserving that region for conductor. In the end turns, the conductor layers are spaced to form a heat-exchanger-like structure that permits nucleate boiling over a large surface area. Although tests were performed in LN2 for convenience, this motor was designed as a prototype for use with liquid hydrogen (LH2) as the coolant. End-cooled coils would perform even better in LH2 because of further increases in copper electrical and thermal cond...

On the Dynamic Characterization for Flywheel Touchdown Bearing System Design

NASA Glenn Research Center has been developing efficient flywheel batteries for a variety of space power applications, which provide the advantages of higher energy density, longer life span, and lower maintenance over electrochemical batteries as a next-generation energy storage device. As a component of enhancing the reliability of a flywheel module, the touchdown bearing system plays a crucial role in case of the malfunction or failure of magnetic bearings. In this paper, a design for touchdown support system has been proposed, a mathematical model for characterizing the dynamic behavior for the touchdown bearing system developed and then the numerical analysis using key design parameters followed. Transient simulations for the flywheel 1G delevitation onto the touchdown bearings suggest a design guide for the touchdown system, which maximizes the minimum air gap at the magnetic bearings and minimizes the dynamic loading as well as allows a safe flywheel rotor landing.