Appendix H: Inductor and Magnet Hazards
This section describes
inductors and magnets that can store more than 100J of energy or that
operate at 50V or more. The following are some hazards peculiar to inductors
- The ability of an
inductor to release stored energy at a much higher voltage than that
used to charge it.
- Stray magnetic fields
that attract magnetic materials.
- Time-varying stray
fields that induce eddy currents in conductive material, thereby causing
heating and mechanical stress.
- Time-varying magnetic
fields that may induce unwanted voltages at inductor or magnet terminals.
- Automatic Discharge. Use freewheeling diodes, varistors, thyrites, or other automatic shorting
devices to provide a current path when excitation is interrupted.
- Connections. Pay particular attention to connections in the current path of inductive
circuits. Poor connections may cause destructive arcing.
- Cooling. Many inductors and magnets are liquid-cooled. The unit should be protected
by thermal interlocks on the outlet of each parallel coolant path, and
a flow interlock should be included for each device.
- Eddy Currents. Units with pulsed or varying fields must have a minimum of eddy-current
circuits. If large eddy-current circuits are unavoidable, they should
be mechanically secure and able to safely dissipate any heat produced.
- Grounding. Ground the frames and cores of magnets, transformers, and inductors.
- Rotating Electrical
Machinery. Beware of the hazards of residual voltages that exist
until rotating electrical equipment comes to a full stop.
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