Active System Grounding With a Novel Distribution Transformer Design

• Main Author: Michael D. Everton
• Format: Article
• Language: English
• Published: IEEE 2020-01-01
• Series: IEEE Open Access Journal of Power and Energy
• Subjects: Ground fault; grounding methods; transient overvoltage; transformer design; protective relaying; distribution supply reliability
• Online Access: https://ieeexplore.ieee.org/document/9097241/

A novel Wye-wye transformer design for active system grounding, is described in this paper. Proposed as a solution to improve the ground fault performance in distribution line networks, the zero-sequence flux developed in the magnetic core of a transformer is on a ground fault harvested by coils wound around three limbs, or extra limb(s) in a Wye-wye transformer. Built with three limbs, and no tertiary winding, the flux developed in the core on a ground fault is forced to return through air, which has a high reluctance, but with four or more limbs, the flux circulates in the transformer magnetic core, which has a low reluctance. Connected to one or more single-phase windings, the transformer neutral current is on a ground fault actively altered by fixed and switched load impedances. In theory, a ground fault arc is with a low current and delay in recovery voltage self-extinguishing, and no interruption in supply is required, but sustained, must be isolated. Proposed in this paper, for an active load switched grounding method, the neutral current on a sustained ground fault is increased to enable plain overcurrent and fuse protection to operate without the need of sensitive directional relay protection.