Dielectric Strength of Water in Relation to Use in Circuit Interrupters

This paper describes the behavior of water as a dielectric, in particular with reference to its use in water circuit breakers. Water is generally considered to have the properties of an electrical conductor rather than those of an insulator. There are, however, a few applications where the dielectric rather than the conductive properties of water are of importance, as, for example, in its use as the interrupting liquid in circuit breakers. Here the water between electrodes must withstand full circuit voltage during the closing operation until the electrodes are in metallic contact, and also in the opening operation following extinction of the arc, until some auxiliary switch in series can open. Since there appears to be very little published information available on the subject, further knowledge of the behavior of water as a dielectric seemed to be of considerable interest and importance. To secure this information, a study of the subject was undertaken, the results of which will be reported in this paper. Experimental data are presented which indicate that electric breakdown between electrodes immersed in water is, in general, determined by the temperature rise produced by the leakage current in the water. Breakdown appears to occur when steam generation begins. Calculation of time to cause temperature rises to 100 degrees centigrade in the water agree closely with observed time between applied voltage and breakdown.