其理由是桶焊机除了需要产生缝焊的实际功率之外，还需要大量的无效功率。

The reason is that Drum welding machines require a large amount of 'reactive power' in addition to the 'true power' required to make the weld.

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此无效功率产生的磁场对诸如运行的焊接变压器和电机的感应电器设备来说是重要的。

This reactive power generates the magnetic fields which are essential for inductive electrical equipment such as the welding transformer and electric motors to operate.

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这种手术成功率高，但需要开胸操作，所以往往只适合于那些其他治疗无效的患者。

The procedure has a high success rate, but because it requires open-heart surgery, it's usually reserved for people who don't respond to other treatments.

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