Rotary electromagnetic fault current limiter (FCL) is an emerging technology for limiting fault currents in the power network. The device consists of two movable air-core spherical reactor rings (i.e., inner and outer rings). The movable feature allows the reactor rings to rotate, and form a proper mutual positional displacement. This can limit the fault current since the effective inductance of the device is dependent to the mutual angular position of the reactor rings. Due to the unconventional structure, to this date, the design process has solely been based on finite element (FE) method. This paper aims to analytically validate the theory and the overall functionality of the device in both the steady state and transient regime. For this propose, the resistance and the inductance of the device are first computed at normal operating condition using the basic theory of engineering electromagnetics. Next, performance characteristics such as electromagnetic torque, rotational displacement of the reactors, effective inductance of the device, and the network current are calculated at the faulty condition. For verification purposes, analytical results are compared with via FE simulation and experimental test.

The authors deal with design and analysis of an air‐core electromagnetic fault current limiter (FCL) with rotary motion. The proposed device is characterised by a simple structure, fast operating speed and reversible operation. It consists of two movable concentric air core spherical reactor rings (i.e. inner and outer rings) with variable mutual angular displacement. At normal condition, reactors are approximately aligned, and subsequently, the effective inductance/impedance of the equipment and the respective voltage drop are low. At faulty conditions, the short circuit current exerts a repulsive rotary electromagnetic torque on the reactors, which results in a fast and steady increase of the reactors angular displacement. During this process, the effective inductance of the equipment rapidly rises up to a level that effectively limits the short circuit current. To determine the effectiveness of the proposed topology in limiting the network's fault current, the inductance profile of the proposed rotary FCL and the respective fault current characteristic are compared with similar case studies (a) with linear FCL and (b) without FCL. The analysis is carried out via a finite element (FE) and supported via analytical and theoretical discussion. Finally, a down‐scale prototype of the proposed FCL was built and tested to verify the functionality of the device in the lab environment.