A fast persistent switch for microSMES

The economics of microSMES for a potential customer are adversely affected by the costs associated with cooling both the magnet cryostat and the power electronics in the system. One way to reduce these loads, and hence the cost, is to operate the magnet in persistent mode while waiting for a power interruption to occur. The reason this has not been implemented to date is because conventional persistent switches cannot be opened fast enough to respond to transients on an incoming power line. The Technology Development Laboratory of the Houston Advanced Research Center has successfully developed a persistent switch with opening times from fifty microseconds to two milliseconds, depending on the triggering mechanism. This switch provides enough resistance to be appropriate for microSMES applications. The paper describes a design and test results for a persistent switch appropriate for a one megawatt, fifteen ampere microSMES application. With this switch, a microSMES cryostat can be equipped with power leads rated for transient operation, with a greatly reduced heat leak. Cooling requirements for the power electronics are similarly reduced.