The measurement of substation ground resistance and its use in determining protection for metallic communication circuits

The increased use of metallic communication circuits in electric substations requires that adequate protection be provided for personnel and equipment during fault conditions. The design of such protection requires a knowledge of the behavior of ground systems, ground rise calculations, and communication techniques. This paper discusses the problem in three parts: I. A development of the characteristics of and measurement techniques for groundbeds and a discussion of how interconnections affect the measurement problem. A new measurement technique is developed which is capable of accurately measuring the resistive part of the grounding impedance of interconnected groundbeds. II. A discussion of the proper use of fault study and ground resistance information for the calculation of ground potential rise. III. A description of the metallic communication circuit protection techniques used by Northern States Power Company.