Development of an IoT-Based Differential Protection System for Power Transformers: A Case Study of New Enma Substation, Aden, Yemen

Abstract

Differential protection is the primary and fastest protection scheme for power transformers; however, its failure may lead to severe thermal and mechanical damage to the transformer. Conventional backup protections such as overcurrent and earth fault relays suffer from intentional time delays, while deploying multiple commercial differential relays significantly increases protection and circuit breaker costs. This paper presents a parallel and independent IoT-based differential protection scheme that operates alongside the main transformer protection to provide a fast supplementary protection layer in the event of main differential protection failure, thereby enhancing transformer protection reliability without replacing the existing protection system. The proposed scheme utilizes RMS current measurements from both high-voltage and low-voltage sides. These measurements are acquired through industrial current transducers and processed locally using an industrial IoT platform. A percentage differential algorithm is implemented without harmonic restraint, where magnetizing inrush maloperation is avoided through breaker-status-dependent enabling logic. The protection decision is executed locally and transmitted through a hardwired tripping path via an auxiliary relay, ensuring protection-grade operation independent of supervisory, communication, or Internet-based services. The proposed protection scheme is carried out on a 33/11 kV, 20 MVA power transformer and validated using six-phase secondary current injection tests. Practical experimental validation and continuous field operation confirm that the proposed scheme reliably detects internal faults, remains stable during transformer energization and external fault conditions, and provides a practical, low-cost supplementary differential protection solution suitable for real substation applications. The proposed architecture is readily adaptable to transformers with different voltage ratings and power capacities, making it a practical and scalable supplementary protection solution for modern digital substations.