Arcs in boundary layer flow

Measurements of the electric field generated in an arc, when it is driven by high-speed flow onto the edge of a plate whose surface lies parallel with the flow, are found to be in good agreement with previous theoretical calculations. Conventional and streak photographs confirm the boundary layer configuration assumed in the theory. The same theoretical and experimental approach has been extended to include the case of an array of plates, as might occur in some types of air-blast circuit breaker. Here the applicability of the theory is more open to question, but, in fact, quite reasonable agreement is obtained between theory and experiment. The various hydrodynamic forces tend to increase the width of the arc, while the heat loss effects tend to reduce this quantity. In practice, it is found that, over a range of values of current between 30 and 300 A, the width-to-thickness ratio remains in the range of two to three.