During the past 10 years, several hundred miles of pipe type cable have been installed in urban areas to transmit electric energy at high voltage, usually 69 or 138 kilovolts. Figure 1 shows a view of three paper insulated cables in a 6-inch steel pipe. The pipe is coated with asphalt mastic for corrosion protection.
In order to provide fault current protection, the sections of pipe are welded together and the pipe is grounded to the station ground bus at both terminations.
For cathodic protection of the pipe, it is necessary to lower the potential of the pipe so that it becomes negative by a small voltage to the earth, station ground bus, water pipes and other grounded structures. This double requirement of grounding and maintaining a negative pipe potential has been met in the past by installing a large 2-volt lead acid storage cell in the grounding connection between...
