Automatic overload protective system and operation method thereof

The invention provides an automatic overload protective system. The automatic overload protective system comprises a hydraulic pump, a reversing valve, a safety valve, a balance valve, a hydraulic motor, a brake, a winch and an oil tank. The oil tank, the hydraulic pump, the reversing valve and the hydraulic motor constitute an open circuit. The safety valve is arranged at an oil outlet of the hydraulic pump. The hydraulic motor drives the winch. The balance valve is arranged on an oil port, rising corresponding to the winch, of the hydraulic motor. The brake is arranged on the winch. A steelwire rope is wound around the winch, and a lifting tool is arranged on the winch. A tension sensor is arranged on the steel wire rope. The automatic overload protective system further comprises an automatic overload protective valve, an oil make-up source and a control oil source which are arranged between the hydraulic pump and the reversing valve. The automatic overload protective system provided by the invention can ef