System, apparatus, and method for reducing inrush current in a three-phase transformer

摘要

A system for reducing inrush current in a three phase utility transformer upon energization of the transformer by an applied three phase voltage utilizes a pre-flux circuit for establishing residual flux levels in the core segments of the primary windings of the transformer which are near the prospective flux levels established in the core segments by the applied voltage. The pre-flux circuit includes a pre-fluxing capacitor which, after being charged to a predetermined voltage level, is discharged serially through two of the primary windings to establish the predetermined flux levels in the core segments of the two windings, and a reduced flux level in the core segment of the remaining primary winding. The transformer is energized at the instant of positively-referenced peak phase voltage to the third primary winding such that prospective and residual flux approach a near-equal level in all three core segments and inrush current is reduced. The method may be applied to the secondary or tertiary windings instead of the primary windings. Additionally, an alternative method allows application of the pre-fluxing circuit to a delta-connected set of transformer windings.

主权项

1. A pre-fluxing system for a three-phase transformer to reduce inrush current in the three-phase transformer having first A, B and C phase windings, second A, B and C phase windings, and a magnetic core having A, B and C segments associated with the first and second A, B and C phase windings, respectively, comprising:
a three-phase line circuit including a three-phase line breaker for applying line voltage to the three-phase transformer; a pre-fluxing capacitor; a direct current source for charging the pre-fluxing capacitor; a charging circuit for connecting the direct current source to the pre-fluxing capacitor and charging the pre-fluxing capacitor to a predetermined voltage level; a pre-fluxing circuit for connecting the pre-fluxing capacitor to two first windings of the first A, B, and C phase windings; and a control circuit for controlling a closing of the three-phase line circuit to apply line voltage to the three-phase transformer coincident with a positively-referenced voltage peak of a phase associated with a pre-determined winding.