# Shafting Torsional Vibration Analysis of 1000 MW Unit under Electrical Short-Circuit Fault
## 6 Conclusions  
Taking a 1000 MW turbo-generator unit as the research object, a system model of a 1000 MW turbo-generator unit based on MATLAB/SIMULINK is built. The ode23 tb algorithm is used to simulate and analyze the faults of two-phase and three-phase short-circuits at generator terminals, and two-phase and three-phase short-circuits at the grid side through the synchronous generator module and the multi-mass steam turbine module based on flux linkage equation. The transient electromagnetic impact torque and short-circuit current fluctuation under four fault conditions are extracted and analyzed; the simulation results are close to the actual behavior of the system, providing a database for subsequent research and a reference for fault diagnosis for practical engineering.  
1. In terms of the transient electromagnetic torque impact value, the two-phase short-circuit fault of the generator terminals was the largest, the three-phase short-circuit fault of the grid side was the smallest, and the electromagnetic torque impact value of the generator terminals under fault was greater than that of the grid side. The transient electromagnetic impact torque caused by a two-phase short-circuit at the same fault point was greater than that caused by a three-phase short-circuit;
2. The transient impulse current under three-phase short-circuit at any fault point is greater than that under two-phase short-circuit. The impact current of a grid-side short-circuit fault is much larger than the generator terminals' short-circuit fault. The speed fluctuation between rotors and the fluctuation difference caused by the three-phase short-circuit on the grid side are the largest;
3. Four kinds of fault with transient electromagnetic force alternating frequencies, excluding the natural frequency of the unit shaft torsional vibration, will not give rise to short-circuit fault time domain shaft torsional resonance. However, the potential impact of the residual small fluctuation of torque in the rotor system after the fault is removed needs further analysis.  
Figure 12: Speed deviation of steam turbine and generator under different short-circuit faults.  
**Author Contributions:** Conceptualization, H.P. and T.Z.; methodology, H.P. and Y.W.; software, Y.W.; validation, H.P.; formal analysis, Y.W.; investigation, H.P. and T.Z.; resources, H.P.; data curation, Y.W.; writing--original draft preparation, H.P.; writing--review and editing, Y.W.; visualization, Z.P. and Y.F.; supervision, T.Z.; project administration, Z.P. and T.Z.; funding acquisition, H.P. and T.Z. All authors have read and agreed to the published version of the manuscript.  
**Funding:** This research was funded the National Natural Science Foundation of China, grant number 51805076, U1708255 and 51775093, National Science and Technology Major Project of China, grant number J2019-I-0008-0008, and the Fundamental Research Funds for the Central Universities of China, grant number N2105013; China Postdoctoral Science Foundation, grant number 2019M661125, Doctorate Start Foundation of Liaoning Provincial, grant number 20180540077, Scientific Research Funding Project of Liaoning Education Department, grant number J1-2003, Science and Technology Program of Shenyang, grant number 20-206-4-16, Science and Technology Innovation Team Support Program of Shenyang middle-aged and young people, grant number RC190342.  
**Institutional Review Board Statement:** Not applicable.  
**Informed Consent Statement:** Not applicable.  
**Data Availability Statement:** Data sharing not applicable.  
**Conflicts of Interest:** The authors declared no conflict of interest.