Study of Low Frequency AC Transmission for Wind Turbine Applications

Abstract

This paper presents our continuing investigations in low frequency AC (LFAC) operation for wind turbine applications. It is intuitive to see that when the operating frequency of a power system is lowered, the transmission reactance is reduced significantly. This results in a great reduction of the reactive power amount on the transmission line. In addition, the low frequency operation can mitigate the capacitive line charging, known as the Ferranti effect, in an overhead line transmission system and thus prevent over voltage rising issues. These benefits of low frequency operation are mathematically demonstrated through a two-bus power system. More importantly, the transformer behaviors under different operating frequencies are investigated. A detail transformer model for a 2.0 MW wind turbine application is modeled and simulated in Ansys Maxwell 3D. The simulation show that the core losses, i.e. hysteresis and eddy current losses, of a transformer under low frequency operation is smaller than that in a 60 Hz operation. However, the flux density inside the transformer core is higher under low frequency operation compared to that in a 60 Hz operation, and thus the transformer design should be careful for low frequency operation.