Shunt reactors are a key component of power systems, providing critical voltage regulation in bus-, line-, and transformer-connected applications. Reactor faults, particularly when undetected and uncleared, can cause major damage to the grid. RTDS Technologies is proud to have been involved with a recent paper, A Fresh Look at Practical Shunt Reactor Protection, which presents and demonstrates a new approach to turn-to-turn reactor fault protection. The paper was presented at the 49th Annual Western Protective Relay Conference in October 2022, in with co-authors from Schweitzer Engineering Laboratories, Avista Utilities, and Trench Limited.

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The paper presents a new protection scheme and accompanying settings guidelines for turn reactor fault protection, based on directional sequence overcurrent elements. The authors consider the unique properties and behaviour of air core reactors in determining how they should be protected – in particular, their lowered protection sensitivity, caused by lower magnetic flux coupling between faulted and healthy turns.


The resulting innovative protection approach, which provides optimal protection for phase-to-phase, phase-to-ground, and turn faults for different reactor applications, is demonstrated to clear turn faults within a few cycles with sensitivities in the 0.1-0.2% range. The paper also provides instrument transformer selection criteria, settings guidelines to ensure protection security during reactor energization, and a novel scheme for ensuring security during line de-energization. Security and dependability of the presented protection schemes was demonstrated by real-time simulations involving a new faulted shunt reactor model for the RTDS Simulator.

Iron-core (left) and air-core (right) options for the faulted reactor component in RSCAD

Available in RSCAD 5.003 or higher, the single-phase faulted shunt reactor model can short 1% to 98% of reactor turns. Users can place up to two fault points and can model phase, ground, and turn faults. Both air- and iron-core reactors can be modelled, and reactor core types determine the inductance matrix for the set of mutually coupled inductors. Real field events reflecting reactor turn faults from a utility were also used for demonstration.

Component configuration menu for an iron-core faulted reactor in RSCAD


The RTDS Simulator’s RSCAD software, and its highly detailed and trusted power system models, is a comprehensive and efficient way to demonstrate the effectiveness of novel protection schemes like this one. The new techniques have been applied successfully in the field at a utility with extra high-voltage air-core reactor banks.