Research On The Security Of The Shafting Torsional Vibration Of The Feedwater Pump With Frequency Control

With the advancement of energy conservation and emission reduction policies in China, the thermal power industry energy conservation has been the main issue of the electric power enterprises. In large coal-fired power plants, the auxiliaries are the biggest house supply users. In recent years, the frequency conversion renovations of high power auxiliaries are more and more popular in the power plant. However, at the same time of reducing energy consumption, frequency conversion renovations have also brought some unexpected accidents. Such as the abnormal vibrations, and power grid harmonics. It even can cause damage to the auxiliary equipments.As is known to all, energy consumption of motor-driven feedwater pump is quite large. So, it is the main object of inverter in power-saving retrofitting. In this paper, The security of the shaft system is studied from the aspect of torsional vibration.Firstly, a multi-stage lumped mass model of gear-rotor system is established; and the transfer matrix method is used to solve the model of the natural frequencies and mode shapes. Meanwhile, a finite element model of the system is also established to get the inherent characteristics, in order to ensure the accuracy of the multi-stage lumped mass modal. Then, the reasons of torsional vibration in VVVF(Variable Voltage Variable Frequency) system are studied, mainly for output harmonic characteristics of VVVF and the three-phase unbalanced supply. And electromagnetic torque fluctuations sre simulated by Matlab/Simulink. At last, a combined algorithm of Newmark-β and Riccati Matrix Transfer Method is used to calculate the dynamic response of the shaft system. The security and life loss of the shaft system are calculating by Local Stress-strain Method and Rain-flow Method.