Improved Voltage Stability Boundary Monitoring by Accounting for Variations in Thevenin Voltage Magnitude

Abstract

This paper identifies weakness of existing method for voltage stability assessment and proposes new approach for determining point of maximum deliverable power to a given load that accounts for the variations in the Thevenin voltage magnitude. The approach uses Thevenin equivalents seen from nodes of constant voltage magnitude and load nodes in order to determine a distance to instability. A simple five-bus system together with IEEE 14 bus system were used in order to perform dynamic simulation in PSS/E. The simulation data were used to create synthetic Phasor Measurement Unit (PMU) snapshots, which served as input to the proposed approach. The new approach is demonstrated on the two test systems, where improved accuracy in determining the point of maximum deliverable power is demonstrated. The results show that the point of maximum deliverable power to the load occurs well before the Thevenin impedance matching criteria.

Voltage stability assessment accounting for non‐linearity of Thévenin voltages

“…Generator G 1 represents a manually excited machine that operates with a constant mechanical input power of P inj = 14.6 MW and G 2 represents an infinite machine. The OLTC-transformer parameters can be found in [16]. The load is represented at the high-voltage side of the OLTC-transformer.…”

“…In [16] an approach is proposed for determining the maximum deliverable power to a load by including the non-linearity of the Thévenin voltage magnitude as the load impedance magnitude changes for a fixed load angle. The approach has been further improved and the steps are shown in Algorithm 2 (see Fig.…”

“…This paper introduces a voltage stability assessment method based on Thévenin equivalents, which takes into account the nonlinear changes in the Thévenin voltage magnitude seen from a load. In previous work [16], the weaknesses of existing Thévenin based methods were investigated, where it was shown that the assumption of a constant Thévenin voltage magnitude with respect to load changes is not reliable. It was shown that the point of voltage instability occurs well before the boundary where the magnitude of the load impedance equals the magnitude of the Thévenin impedance.…”