Measurement of harmonic currents in a very large turbogenerator

Very large turbogenerators are connected to extra high voltage grids (transmission grids). Transmission grids used to be free from harmonic sources. Harmonic sources are more frequent in subtransmission and distribution grids. However, as large wind farms and high speed trains are being connected to transmission grids, harmonic currents from them are more likely to disturb large turbogenerators.

Harmonic currents can affect large turbogenerators in different ways: overheating, pulsating torques, vibrations and fatigue. Among them, we recall the 100 Hz issue (in 50 Hz grids). Turbine-masses torsional oscillations are in the subsynchronous frequency range whereas turbine-blade oscillations are around 100 Hz. The industry is concerned about the possible excitation of turbine-blade oscillations by external harmonic current sources.

This paper reports measurements of harmonic current components in a very large turbogenerator of a nuclear power generating station in the period from 27 May through 3 June 2014. The measurement setting is described. Not only individual harmonic components are detailed but the total harmonic distortion and spectrum are also provided. The measured values are compared with the limits imposed by standards.