Hitachi, Ltd. has completed development of an air-cooled turbine generator — named GH1550A — that achieves the world's highest efficiency and low noise, and we have already shipped units Nos. 1 to 5 to our customers. The GH1550A achieves the world's highest-level performance among air-cooled generators; namely, efficiency of 98.75% at 60 Hz and PF of 0.85 or 98.77% at 50 Hz and PF of 0.80, and a noise level of 74 dBA for a single generator body during 50-Hz operation or 77 dBA during 60-Hz operation. To attain this performance, network ventilation analysis and stator-core electromagnetic analysis were used, and loss was extensively reduced. Furthermore, a noise-reduction configuration for optimizing sound insulation — based on results from various noise tests — was developed and applied to the GH1550A. In addition, analysis techniques such as rotor-vibrational analysis, temperature analysis, and localized stress analysis were used, and performance and reliability of the generator were improved. The GH1550A was confirmed to satisfy design specifications such as efficiency, noise, temperature rise, and rotor vibration.