Study of 1000‐kV network protection

Abstract

AbstractElectric power systems in Japan are developing due to economic growth. Especially, recent demand for electrical power in metropolitan areas has increased by more than 250 percent since 1973 when the 50‐kV system was first used. Increasing power demands will continue in the future. To satisfy this demand, utilities developed new transmission lines to make networks substantial with stable and efficient operation of the power system. However, this countermeasure causes extremely large fault currents at the substations where large power sources are concentrated. Problems such as large fault currents beyond interrupting the capacity of a circuit breaker or electromagnetic interference have become more severe. To solve these difficulties, Tokyo Electric Power Company is going to develop 1000‐kV networks. These increase the capacity of transmitted power and suppress the fault current level by splitting the 500‐kV system into several parts. Considering the associated difficulties of 1000‐kV networks (such as increasing capacitive current on transmission line), prolonged dc time constants due to large diameter conductors and other electrical characteristics of 1000‐kV networks, we examine the applications of a reliable protection system. The results are summarized as follows: 1) To adopt multiple phase autoreclosing with highspeed grounding switches to suppress secondary arcing on faulted phases. 2) To adopt air‐core type CT for 1000‐kV busbar protection as a countermeasure against CT saturation. 3) To adopt the current comparison scheme to realize sensitive protection for paralleled transformer bank. A new protection system will be field‐tested in 1995.