Balancing Characteristics of Zero-Phase Current Transformers for Reliable Residual Current Detection

Zero-phase current transformers are key sensing components in GFCIs, RCDs and EV-charging safety systems. Ideally, equal incoming and outgoing currents produce no secondary output. In practice, core imperfections, uneven windings, asymmetric conductor placement and electromagnetic interference create residual voltage. This can impair trip sensitivity and stability, particularly in low-current protection.

The presentation examines residual output, practical measurement methods using conductor or transformer rotation, and design measures to reduce it. Topics include laminated-core selection, winding uniformity, primary-conductor geometry and magnetic shielding. Attendees will learn how sensor design, production and verification support reliable residual-current detection.