无用功 Idle Work ; goose chase

做无用功 lipstick on a pig ; Flogging a dead horse

无功补偿用电力电容器 no-load compensating power capacitor

无功备用 Reactive power reserves

通常的无用功 unnecessary amount of work

浪费时间做无用功 Reinvent the wheel

美丽的东西最终无用功 Beautiful things end in futility

别再做无用之功 Don't beat a dead horse