Switching Problems in Crowbar and Power Crowbar Systems
Comparing different schemes of energy storage such as capacitive storage, inductive storage, inertial storage and battery, it can easily be shown that for the submillisecond range the capacitive storage is advantageous because of its high power density and its low cost per MW. From an examination of the cost for the various capacitor banks at Garching it follows that its costs rise with the square root of the rise time(1)(2). Considering also commercial low–cost, high–density capacitors, we find the costs converging at 10 DPf/joule for a risetime of approximately 0.5 msec. A reliable crowbar–switch is essential for an economically reasonable employment of a capacitive storage to generate a quasi–stationary magnetic field with a short rise time. Switching problems are crucial for any storage system of that type. Besides starting switches — which have been extensively described in literature — we will restrict ourselves to compare and discuss the various crowbar switches. which have been developed at Garching(3)(4)(5). First to mention is the ferrite decoupled spark gap developed early in 1963 and extensively incorporated in many experiments. Because the current taken over is somewhat delayed in this switch we initiated in 1968 the development of power crowbar spark gaps with simultaneous break down. We will discuss this feature in detail and present experimental results. Lately it was found that the laser-triggered power crowbar spark gap is very promising. Experimental results with spark gaps with pressurized argon show that the power of presently available laser is sufficient even to switch big systems. This is also true with a view of the rather simple and powerful CO2 laser. From the resistance-current characteristics of the different crowbar switches it follows that — for long current ptilses — in addition to the fast switching spark gaps one has to employ also low resistive mechanical closing switches. We will report on the development of a free from thumbing and therefore high load mechanical closing switch(6).