Topologically Protected Loop Flows in High Voltage AC Power Grids

TL;DR

This paper draws an analogy between circulating power flows in high voltage AC power grids and supercurrents in superconducting rings, demonstrating their topological protection, creation mechanisms, and behavior under dissipation.

Contribution

It introduces the concept of topologically protected circulating power flows in AC grids, inspired by superconductivity, and analyzes their creation, stability, and dissipation characteristics.

Findings

Circulating power flows are topologically protected and persist despite dissipation.

Three mechanisms can generate circulating flows: loss of stability, line tripping, and reclosing.

Circulating flows are quantized, similar to superfluid vortices.

Abstract

Geographical features such as mountain ranges or big lakes and inland seas often result in large closed loops in high voltage AC power grids. Sizable circulating power flows have been recorded around such loops, which take up transmission line capacity and dissipate but do not deliver electric power. Power flows in high voltage AC transmission grids are dominantly governed by voltage angle differences between connected buses, much in the same way as Josephson currents depend on phase differences between tunnel-coupled superconductors. From this previously overlooked similarity we argue here that circulating power flows in AC power grids are analogous to supercurrents flowing in superconducting rings and in rings of Josephson junctions. We investigate how circulating power flows can be created and how they behave in the presence of ohmic dissipation. We show how changing operating conditions may generate them, how significantly more power is ohmically dissipated in their presence and how they are topologically protected, even in the presence of dissipation, so that they persist when operating conditions are returned to their original values. We identify three mechanisms for creating circulating power flows, (i) by loss of stability of the equilibrium state carrying no circulating loop flow, (ii) by tripping of a line traversing a large loop in the network and (iii) by reclosing a loop that tripped or was open earlier. Because voltage angles are uniquely defined, circulating power flows can take on only discrete values, much in the same way as circulation around vortices is quantized in superfluids.