Ice Testing and Its Influence Upon Switch Design

Requirements for disconnecting switches to operate when ice-coated demand special attention to details of design and to methods of testing the performance of a given design. In order for an ice test to provide a true criterion of the performance of a design, the icing program must be preceded by a wetting period above freezing temperatures, the simulated rain must be uniform over the test area, and the volume of water must be in balance with the ambient temperature in order to permit continuous wetting of the surfaces upon which ice is forming. Operation tests should be made at 20 degrees Fahrenheit and adequate time should be allowed after ending the spraying to equalize the masses of ice and metal at this temperature. Based upon the observed results of almost 100 individual ice tests, it is found that rounded contours, generous clearances, dry sealed bearings, small radii of all rotating members, sealed and enclosed hinge contacts, high-pressure line contacts, optimum clearance at linkage points, and absence of compression points are all required to maximize the ability of a disconnecting switch to be operated when coated with ice.