| Hiroaki Yamada | Plant R&D Gr., Thermal Power Dept., |
| Kiyoshi Arayama | Power Plant Control Systems Engineering Dept., Information & Control Systems Div., Information & Telecommunication Systems, |
| Shigetoshi Okamatsu | Electrical Control Systems Engineering Dept., Information & Control Systems Div., Information & Telecommunication Systems, |
| Koichiro Nagata, Ph. D. | High Power Drive Systems Unit, Fifth Dept. of Systems Research, Hitachi Research Lab., |
Finding ways to save energy has become an increasingly urgent concern of the power industry. One strategy with enormous energy saving potential is to reduce the supply power of large auxiliary motors at power plants. Inverters have been used in the past for variable speed control over auxiliary motors, but the output voltage and capacity of conventional inverters are relatively small, so there has been little incentive to apply inverters to the larger scale auxiliary motors used by commercial thermal power plants. This motivated a joint research project between Electric Power Development Co., Ltd. and Hitachi, Ltd. to develop an 8,250-kVA highvoltage direct inverter that could be applied to high-voltage high-capacity large auxiliary motors. The direct inverter was connected to a 7,000-kW capacity induced draft fan motor at Electric Power Development Co., Ltd.'s Takehara Thermal Power Station No. 3 and subjected to extensive field trial testing. In pursuing the project we also developed a system configuration and control methods to ensure that the plant continues to operate stably even when disturbances occur from the power supply system, and the system demonstrated a high degree of reliability. It was found that substantial energy could be saved by using the inverter. For example, compared to a conventional configuration, motor power consumption could be reduced by as much as 70% when operating at an output capacity of 50% by using the inverter.
direct inverter, induced draft fan, energy saving, speed control, thermal power station
