Abstract
We present a numerical methodology to estimate the transient fault currents and to simulate the remote sensing of transient fault information embedded in the magnetic field emissions caused by inter-turn shorts in 60 Hz air-core reactors, thru a magneto quasi-static (MQS) field approximation in the method of Finite-Difference Time-Domain (FDTD) in 2-dimensional (2D) space. The MQS 2D FDTD fields of reactor in normal operation are scaled by correlation against an equivalent circuit model that is derived from application of basic physics principles to parameters of the 3D air-core reactor. The proposed multi-scale quasi-static modeling methodology, based on the reduced c modification, provides fine-feature access down to the single-wire level and can efficiently estimate the transient fault fields and currents due to turn-to-turn short in a reactor with core height in several meters, core diameter in meters, wire diameter in millimeters, and number of turns in the thousands, at 60 Hz; this is accomplished by using computational resources of a typical laptop computer within seconds or minutes , as opposed to days that would be otherwise required without the reduced c modification.
Highlights
The air-core reactor [2] is primarily used as a current limiting device across power networks around the world
Given the goal of this work is to present a computational electromagnetic (CEM) modeling methodology for numerical estimation of the transient fault currents and remote-sensing transient fault events due to inter-winding shorts in air-core reactors, further details of formulation and implementation of magneto quasi-static (MQS) equations in 2D Finite-Difference Time-Domain (FDTD) fall outside the scope of the present paper; those details may be submitted as a separate publication in the future
CORRELATION OF FDTD MODEL AGAINST EQUIVALENT CIRCUIT MODEL, THRU NUMERICAL EXPERIMENTS IN SIMULATION With the MQS 2D FDTD simulation model scaled to the equivalent circuit solution, we perform five numerical experiments in which we plot Vcoil(t) vs. time t across variations in rw, NT, rc, Nwl, and d to validate the MQS 2D FDTD model by correlation against the equivalent circuit model
Summary
The air-core reactor [2] is primarily used as a current limiting device across power networks around the world. To achieve the same level of inductance in lieu of a magnetic core (such as ironcore), an air-core reactor needs many more wire turns than its magnetic-core counterpart. Iron core reactors are filled with dielectric oil, while air-core reactors are seeing increased use in environmentally sensitive areas. Turn-to-turn faults involving a small number of turns are difficult to detect in air-core reactors, due to the limited voltage drop per turn.
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