Coil Failure Research Articles

Comparison of Naturally and Artificially Aged Solenoid Valves in Accident Simulations

A qualification research program conducted on naturally and artificially aged solenoid valves revealed no significapt differences in performance during seismic tests, but some differences during main-steam- line-break/loss-of-coolant-accident (MSLB/LOCA) simulation. Although the naturally aged valves were subjected to less severe aging than the artificially aged valves, they failed earlier than the artificially aged valves in the MSLB/LOCA test. Only a valve with metal seats performed satisfactorily throughout the program. All other valves tested experienced failure or diminished functional capability as a consequence of degradation of the EPDM components (seals, seats, diaphragms). Degradation manifested itself in the form of severe compressive set, embrittlement, and adherence of tacky material to bounding metal parts. There were also two coil failures. This paper analyzes the causes of degradation and recommends ways of improving the qualification method.

The Cochlear Implant

The cochlear implant offers an alternative to selected profoundly deaf patients in whom conventional treatments or prostheses have been unsuccessful. Substantial benefits have been obtained by patients, with apparently minimal risk. There have been no serious surgical complications and only a few postoperative problems, which were remedied satisfactorily. The device has continued to function in patients over a period of years, and in cases of internal coil failure it has been removed and replaced. Replacement devices seem to function as well as the patient's first device. There has been no evidence of any decrement in performance after years of electrical stimulation or any measurable adverse effects. The cochlear implant is now widely available and should be considered an option to be offered to appropriate patients.

Mechanical forces in superconducting windings of toroidal magnet systems

A new computer code is briefly described which can be advantageously applied to superconducting toroidal systems with complicated coil shapes. The guiding idea is to use the same geometry for the current elements and the stress model. Furthermore, a short review shows that more work is necessary for elucidating the influence of mechanical stress on the critical current density of the superconductors and on the physical properties of the non-superconducting stabilizing material. Values for the centripetal force acting on each torus coil can be easily calculated when the "1/r approximation" for the magnetic flux density is assumed. The influence of the magnetic flux leaking out between the coils is discussed and it is shown that for tori with large numbers of coils (say, 32 to 64) and with not too large aspect ratios (say, 1.5 to 2) the above mentioned approximation for the calculation of the centripetal forces yields values which are only a few percent too large. Finally, the consequence of a coil failure in a toroidal magnet is discussed under the assumption that each superconducting coil operates in persistent mode. Due to the re-arrangement of the currents and of the magnet fields, centripetal forces and perpendicular force components result whose asymptotically reached values are appreciably larger than the static values calculated for a torus with one coil missing.

Improved construction of Rogowski coils for measurement of plasma currents

A method of constructing Rogowski coils is described which eliminates coil failure due to insulation faults.

Improvements in the Zero Gradient Synchrotron (ZGS) Main Magnet Coil Protection

Two main coil failures in a one-year period initiated a review of on-line protective circuitry. Two existing circuits, which would limit damage, were made more reliable. Four new circuits were added to monitor coil condition and protect against voltage transients.

Insulation temperature standards for industrial-control coils

FOR many years, American Standard C19 (Underwriters Laboratories, Inc. issue of 1938 and National Electrical Manufacturers' Association industrial-control standards publication 40–59, April 1940) for industrial-control apparatus has specified an allowable temperature rise for industrial-control coils with class-A insulation of 85 degrees centigrade by resistance. Although this is 25 degrees centigrade higher than the value of 60 degrees centigrade rise by resistance established for rotating machinery with class-A insulation, service experience with control coils has been thoroughly satisfactory. It is estimated from field experience that not more than five per cent of all coil failures have been caused by temperature, despite the frequent use of above-normal voltages. The author believes, therefore, that the present control standard has proved to be conservative with respect to temperature-rise limits.

Insulation Temperature Standards for Industrial-Control Coils

FOR many years, American Standard C19 (Underwriters Laboratories, Inc. issue of 1938 and National Electrical Manufacturers' Association industrial-control standards publication 40–59, April 1940) for industrial-control apparatus has specified an allowable temperature rise for industrial-control coils with class-A insulation of 85 degrees centigrade by resistance. Although this is 25 degrees centigrade higher than the value of 60 degrees centigrade rise by resistance established for rotating machinery with class-A insulation, service experience with control coils has been thoroughly satisfactory. It is estimated from field experience that not more than five per cent of all coil failures have been caused by temperature, despite the frequent use of above-normal voltages. The author believes, therefore, that the present control standard has proved to be conservative with respect to temperature-rise limits.