Enclosure Requirements to Protect Personnel from Spinning Rotor Frailures at the Power Electronics and Electric Machinery Research Center
- ORNL
Performance evaluation of electric motors is a major function of the Power Electronics and Electric Machinery Research Center (PEEMRC). Normally these motors have a fixed wire-wound stator and a rotating rotor, which may have conductors embedded in a ferromagnetic core (induction motors), magnets mounted on the surface of the ferromagnetic core with a thin metal or composite cylinder or ring to hold them in place, or magnets embedded in the ferromagnetic core. Most of the work currently involves the last two permanent magnet (PM) configurations. Although the stator of a radial-gap motor can absorb energy from many of the fragments ejected from the rotor during operation, the stator of an axial-gap motor is not positioned to provide significant protection. The housing of each motor can also absorb some of the energy. The most conservative approach, however, is to assume that all fragments from the rotor must be contained by a protective enclosure. An ideal enclosure is transparent. Manufacturers of such plastics as Lexan, Tuffak, and Cyrolon sell different variations of transparent enclosure material. Lexan is a polycarbonate sheet. Lexgard{reg_sign} is a penetration resistant material made by layering polycarbonate material between pieces of ordinary glass. A fragment striking a sheet of enclosure material will pierce the surface layer, but the layered polycarbonate-glass material is able to absorb the fragment's energy before it completes penetration. Tuffak{reg_sign} is Lexan polycarbonate. Cyrolon{reg_sign} bullet resistant material is acrylic sheet. The ability of the enclosure to stop a fragment depends on its thickness as well as the penetration capability of the fragment; for example, a lead fragment has much less penetrating capability than a steel fragment. Enclosure thicknesses are commercially available to provide several levels of protection. These levels depend on the momentum of the fragments and have been evaluated for some common types of ammunition. This summary quantifies four typical worst-case fragments which have maximum translational kinetic energy when ejected from a rotating annulus. (1) The first fragment is released from a rotating annular titanium ring. (2) The second fragment is a magnet released from the Oak Ridge National Laboratory's (ORNL's) 30-kW axial-gap PM motor. Analysis of the second fragment which is like a segment of half-angle, {alpha}, from a thin annular ring is similar to that of the titanium ring segment except that the angle is 10{sup o} instead of 133{sup o}. (3) The third fragment is a magnet from the radial-gap 6-kW fractional-slot surface-mounted PM (SPM) motor with concentrated windings. Analysis of the third fragment is similar to the analysis of the second fragment. (4) The fourth fragment is a 133{sup o} segment of an entire rotor which assumes that the laminates and magnets in the rotor fail as a single fragment, truly a worst case assumption.
- Research Organization:
- Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Power Electronics and Electric Machinery Research Facility
- Sponsoring Organization:
- USDOE Office of Energy Efficiency and Renewable Energy (EERE)
- DOE Contract Number:
- DE-AC05-00OR22725
- OSTI ID:
- 932617
- Report Number(s):
- ORNL/TM-2007/040; VT0302000; CEVT022; TRN: US200814%%737
- Country of Publication:
- United States
- Language:
- English
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