| 摘要 |
PURPOSE:To eliminate the need of negative phase relay by making PWB and CPU for three-phase three-wire system compatible with a three-phase four-wire system of different voltage. CONSTITUTION:The voltage state is detected between phases S and N and between phases R and N of a power supply and a decision is made whether the phases of power supply are normal or not. If the phase is abnormal, power supply to a compressor 1 is interrupted thus eliminating the need of negative relay for a three-phase four-wire system and realizing reduction in space. Since the CPU 4 control software and PWB 3 for three-phase three-wire system can be commonly used, significant cost reduction is achieved. |
