In this paper,a set of differential equations with nonlinear-periodic coefficients isderived for coupling of the mechanical and electric vibrations of the generating sets,by usinga new method. By using a orthogenal transformation matrix,the set of current equation withperiodic coefficents are transferred to the equation with constant coefficient. The relationshipon angular displacement of the generator rotor and torsional vibration are obtained by usingthe conservation with moment of momentum. Therefor... In this paper,a set of differential equations with nonlinear-periodic coefficients isderived for coupling of the mechanical and electric vibrations of the generating sets,by usinga new method. By using a orthogenal transformation matrix,the set of current equation withperiodic coefficents are transferred to the equation with constant coefficient. The relationshipon angular displacement of the generator rotor and torsional vibration are obtained by usingthe conservation with moment of momentum. Therefor a system of differential equations cou-pled with the mechanical and electric with nonlinear constent coefficient are obtained. By us-ing that mathematical model we studied the problem for torsional vibration of shaft system ofgenerator under the condition of three phase short-circuit suddenly. Some resuIts which haveimportant applications worth in enginering are obtained. |