Abstract :
To maintain the integrity of communication services and to protect the associated equipment, facilities and personnel, unique engineering considerations must be given to reducing unwanted potentials which might otherwise exist on a communication line in a power station environment. These potentials could be introduced on the network from Ground Potential Rise which can be caused by power fault conditions, induction, and lightning. Consequently, the electrical protection aspect becomes accentuated where reliable service is to be provided. Good reduction of Ground Potential Rise has been achieved by use of either Neutralizing or Isolating Transformers, or a combination of both. Neutralizing Transformers are connected in series with the communication line. Any potential difference impressed on the primary of the Neutralizing Transformer will induce on the secondaries, voltages in the opposite direction, and in this way, any potential rise appearing on the communication line is prevented; whereas the Isolating Transformer is in parallel with the line and isolates Ground Potential Rise. The main disadvantages in the use of Neutralizing Transformers for electrical protection lie with cost, bulk, and core saturation; while DC continuity is not available through Isolating Transformers. The new method presented here employs a “Relay Isolating Transformer” which has the same principle of operation as the Isolating Transformer, but, in addition, provides equivalent DC continuity through a relaying arrangement. Relay Isolating Transformers will maintain undistorted communication service into power stations during power fault conditions. The economical aspects are discussed; and a comparison is made between the costs of protection using the Neutralizing Transformer vs the costs of protection using the Relay Isolating Transformer.
