An Armature-Stator Contact Resistance Model for Explosively Driven Helical Magnetic Flux Compression Generators

• Main Authors: Kiuttu, G.F., Chase, J.B.
• Format: Conference Proceeding
• Language: English
• Subjects: Circuits; Coils; Contact resistance; Helium; Inductance; Laboratories; Magnetic flux; Stators; Switches; Wire
• ISSN: 2158-4915; 2158-4923
• DOI: 10.1109/PPC.2005.300682

Although helical magnetic flux compression generators (HFCGs) have been in use for more than four decades, no one has been able to satisfactorily model their behavior. To bring computed currents into agreement with experimental values, tuning factors or anomalous flux loss factors are used. Such factors are not universal, and they must be adjusted for each generator design, or for different operational parameters (e.g., seed current or load inductance) for a given design. Many HFCG modeling codes have been reported over the years with various types of these empirical factors. One of the recognized issues for HFCGs is magnetic flux loss near the moving contact point between expanding armature and helical stator coil winding. In our new model, we have analytically estimated the rate of magnetic field diffusion in the vicinity of the contact point. When converted to a flux loss rate, we find that it usually scales nonlinearly with the instantaneous current, and that the resulting effective resistance is proportional to the square root of the current. This result applies even at relatively small operating currents. Whereas the usual HFCG resistances drop as the generator length decreases, the contact resistance generally increases throughout operation. While small initially, we find that it usually dominates late in time and ultimately limits the gain of most generators. In this paper, we present the derivation of the contact resistance model and show its effectiveness in estimating current gain for simple HFCG designs using a simple spreadsheet program. The model has also been implemented in the 11/2-D FCG-model code, CAGEN, and an accompanying paper presents CAGEN results for a wide range of HFCGs, benchmarking the new model. The formulation for our model is universal; i.e., there are no adjustable factors, and it has generally enabled calculation of HFCG currents to within 20% of experimentally reported values.