JPS5698808A - Three phase transformer - Google Patents

Abstract

PURPOSE:To prevent the overcurrent by setting a primary and a secondary main and auxiliary windings at a leg of a three phase iron core and connecting the auxiliary winding of other phase to the main winding in series, thereby fixing an impedance between the primary and the secondary windings at a given relation. CONSTITUTION:A three phase transformer 92 is provided in parallel with an established transformer 91 which is operating connecting an A and B system, and a circuit breaker 93 is provided. When the impedance between the primary and the secondary windings of the established transformer 91 is Xr, the current, I=(XT/ XT+X)IA flows to the transformer 92, in case of an accident. Accordingly, according to The venin's theorem, if VO is a potential difference between the points a and b before the establishment of the high voltage transformer 92, and XO is an impedance of the power system between the points a and b when the whole power source of the power system is removed at the time of an accident before the establishment, the current, I=VO(VO/XO+X) flows to the transformer in case of the accident. Accordingly, by forming X>=VO/I-XO of impedance, a small sized and economical transformer can be obtained at ordinary time withholding the overcurrent at a given high impedance at the time of accident.