In a conventional power plant, thermal or potential energy is converted to mechanical energy, which in turn must be converted to electrical energy. A steam, gas or water turbine is used to drive a rotating shaft, which in turn drives a generator, producing electricity at a relatively low voltage (typically in the range 15kV-24kV). This low voltage must be transformed to a higher voltage using a generator step-up transformer, otherwise the transmission conductors would be too large in cross-section to be practical, and the voltage drop (typically 10kV on typical transmission line) would mean that little or no power could actually be transmitted.