Research On Fault Condition Monitoring Of Centrifugal Pump Mechanical Seal Based On Sensorless Technology

Centrifugal pump is a kind of fluid conveying equipment,which is widely used in aerospace,petrochemical,nuclear power plants and other fields.Mechanical seal is the core component to prevent fluid leakage.Once the mechanical seal is damaged,it will cause the internal fluid leakage of the centrifugal pump,resulting in the decline of the working efficiency of the centrifugal pump and the increase of energy consumption.When the mechanical seal is seriously damaged,it may even lead to casualties.Therefore,timely monitoring the mechanical seal status of centrifugal pump is the key to ensure the safe operation of centrifugal pump unit.Traditional monitoring methods need to install sensors to collect relevant state parameters of centrifugal pump mechanical seal,such as vibration signal,pressure pulsation and acoustic wave.However,the traditional monitoring methods have many shortcomings,such as high cost of sensors and instruments,unfriendly installation to the external structure of equipment,poor monitoring anti-interference ability and so on.In order to solve the above problems,this paper proposes a mechanical seal fault condition monitoring method based on sensorless technology,which uses the time-frequency domain characteristics to process the stator current signal of the driving motor to realize the condition monitoring and fault identification of the mechanical seal system of centrifugal pump.This method is friendly to the external structure of the monitoring object,cost-effective,and reliable diagnosis results,which makes up for the shortcomings of traditional monitoring methods.Therefore,this paper takes the mechanical seal of centrifugal pump as the research object,adopts the methods of theoretical analysis,numerical simulation and design test research,analyzes the mechanism of the sensorless technology to realize the monitoring of the mechanical seal fault state,puts forward the method of sensorless technology to monitor the mechanical seal state,and obtains the corresponding signal characteristic information of the mechanical seal fault state of centrifugal pump,Finally,the fault diagnosis of mechanical seal of centrifugal pump based on sensorless technology is realized.The main innovations and research contents of this paper are as follows:(1)In view of the frequent occurrence of mechanical seal failure in centrifugal pump,and the traditional monitoring methods have the problems of damaging the pump body and poor anti-interference ability,this paper proposes a method to realize the condition monitoring of the mechanical seal of centrifugal pump based on sensorless technology.The theoretical analysis of the normal state and fault state of the mechanical seal shows that the mechanical seal failure will destroy the dynamic balance of the rotor shafting.The hydraulic load torque fluctuates.In this paper,through the establishment of three-phase asynchronous motor model,it is found that the fluctuation signal of hydraulic load torque can transmit the mechanical seal fault characteristic information to the drive motor.Because the characteristic frequency of mechanical seal fault will be presented in the current spectrum in the form of sideband,and then affect the current signal.When the fault degree of mechanical seal increases,the fluctuation range of load torque becomes larger,and the motor current changes significantly.(2)Aiming at the problem of dynamic characteristics change after mechanical seal failure,this paper established a three-dimensional model of mechanical seal for numerical simulation,mainly studied the mechanical seal under different degrees of end extrusion failure,and obtained the dynamic characteristics,liquid film pressure and sealing performance parameters of mechanical seal under different degrees of failure.In this paper,the corresponding rotor shafting model is established in workbench.With the help of finite element analysis technology,the transient hydraulic load torque excitation is loaded on the impeller side of the rotor shafting,and the torque response diagram of the motor side of the shafting is obtained.By means of simulation,it shows that the torque of rotor shafting can respond to the hydraulic load torque under different faults,and further proves the feasibility of mechanical seal condition monitoring based on sensorless technology.(3)Aiming at the problem that the fault condition monitoring method of mechanical seal of centrifugal pump is complex,and the applicability of the current fault monitoring method of mechanical seal is not strong,this paper designs the test scheme according to the fault monitoring requirements of mechanical seal of centrifugal pump,and carries out the external characteristic test,cavitation characteristic test and vibration characteristic test of mechanical seal under different fault degrees.Through the above tests,the stator current signal and vibration signal of the driving motor of the mechanical seal of the centrifugal pump under different fault degrees were measured.The influence of mechanical seal failure on the running state and cavitation characteristics of centrifugal pump was analyzed.The test results show that the failure of mechanical seal will lead to the decline of the head and efficiency of centrifugal pump,and the decline range of the head coefficient of centrifugal pump is the largest under the condition of small flow Q=40m~3/h and large flow Q=60m~3/h.(4)In order to solve the problem that the current signal analysis method is difficult to identify the degree of mechanical seal fault,this paper realizes the mechanism of centrifugal pump mechanical seal condition monitoring based on sensorless technology,and establishes the method of mechanical seal fault diagnosis based on stator current signal Pulse factor index and power spectrum index are used to identify different degrees of mechanical seal faults of centrifugal pump.The test results show that when the centrifugal pump is in the high efficiency operation area(Q=40m~3/h～Q=45m~3/h),the current pulse factor index can effectively identify the fault state of the mechanical seal.The root mean square index of current can identify the characteristics of mechanical seal failure,but when the centrifugal pump is in the small flow condition,the root mean square index of current can not distinguish the light fault from the serious fault.The power spectrum index of stator current can effectively identify the fault degree of mechanical seal.According to the characteristic frequency amplitude of current signal,it shows the rule that mechanical seal in normal state is less than mechanical seal in light fault and less than mechanical seal in serious fault.