Boost Converters as a Means to Reduce Capital Costs

In a telephone office, one of the main objectives is to maintain the load voltage above a minimum value for the required duration of a power outage. Often a mixture of old and new equipment with different minimum voltages complicates the situation. Also, the equipment is sometimes located far from the battery plant, resulting in large and costly distribution cable. In the past, end cell battery plants were utilized to solve this problem. However, reliability, maintenance, and performance problems discourage their use for new installations. This paper investigates alternate approaches to solving the problem by means of boost converters in new and existing plants. Like end cells, boost converters insert up to several volts in series with the distribution cable. Unlike end cells, the converters need not produce sudden changes in the load voltage. Also, the converters can be located outside the battery room. Therefore, the plant engineer can treat only those loads which require a boosted voltage. Equations are developed by the author which allow an evaluation of the capital cost savings possible with a converter plant. This is done by determining the optimum combination of battery plant and cable size, both with and without converters. The techniques are then expanded to include the costs of energy, money, and other related items. Sample cases are utilized to illustrate the use of these methods, and a computer program is included in the appendix to facilitate the use of the equations.