Abstract

During the beginning of the commercial operation of a natural gas power plant* in 2016, several units at a multi-unit station experienced problems. Event records showed excessive power oscillations in the subsynchronous range, at frequencies which corresponded to the machine’s torsional modes, and due to excessive oscillatory rotor acceleration and vibration events during operation, the operators manually tripped the units on several occasions.

There are several series-compensated lines in the immediate vicinity of the plant; however, a subsynchronous resonance analysis was not performed prior to putting the plant into operation, partly due to an expectation that the torsional modes of gas turbines make them less vulnerable to this phenomenon, as compared to steam turbines. This white paper presents an analytical model, based on the Electromagnetic Transients Program – Restructured Version (EMTP-RV), which is used to assess the potential for subsynchronous oscillations, and considers the potential contribution of this phenomenon to the damage of the rotors. The analysis in this paper investigates if the generators may experience subsynchronous resonance (SSR) events.

Sargent & Lundy offers services to determine the root cause of failures, faults, or malfunctions of transmission systems, including aspects such as SSR.

*Sargent & Lundy did not design the natural gas power plant analyzed in this white paper.

Authors: Juan Galvez, Michael Urbina, Douglas Mader, Jan Wisniewski