Feeder voltage regulator application

PROPER VOLTAGE LIMITS have been established by the joint Edison Electric Institute-National Electrical Manufacturers Association committee on preferred voltage ratings for a-c systems and equipment. Many regulatory commissions have established voltage limits for power utilities operating within their jurisdiction. To stay within these established limits the design voltage drop from the primary at the first transformer (“feed point”) to the customer entrance on the most distant service from the last transformer should be within 9 per cent or 11 volts on the 120-volt base. Experience and the results of studies in economic distribution system design have indicated definite apportionment of voltage drops beyond the feed point to various individual components, namely, primary, transformer, secondary, and service. It is considered that proper compensator setting on the voltage regulator to assure an optimum utilization voltage of approximately 118 volts will require a full load voltage level at the feed point or primary of the first transformer of 125 volts. The light load voltage level at the primary of the first transformer will be approximately 121 volts. Thus a 4-volt variation in voltage between light load and full load must be supplied by the regulator for this portion of a distribution system.