Since the main objects of power sys

Since the main objects of power system component protection are generators and transformer groups, this chapter will start with these two components to study the short-circuit calculation of power system component protection. Firstly, the structural characteristics of the generator and its equivalent circuit diagram during normal operation and fault operation are introduced. The process of using the symmetrical component method to solve the port parameters under several common external short-circuit conditions of the generator is analyzed. At the same time, for the common internal short circuit faults of the generator, the fault equivalent circuit model is established, and the electromagnetic equations of the stator circuit, rotor damping circuit, and excitation circuit are listed to solve the electromagnetic transient before and after the generator failure. Then, the single-equal value circuits of the two-winding transformer and the three-winding transformer are analyzed respectively, and the positive and negative sequence equivalent model and the zero sequence equivalent model are established, and the nodal admittance matrix is ​​formed which is convenient for software calculation and application.According to the different types of prime movers used to drive, synchronous generators can be divided into steam turbine generators and hydraulic generators. Steam turbines usually adopt hidden pole structure, and hydraulic turbines are generally salient pole type. Generators are generally composed of stators, rotors, machine covers, bearings and other components. The stator windings generally use double-layer three-phase symmetrical windings, while the rotor varies greatly depending on the type of generator: the rotor of a turbogenerator is generally two Due to the high speed, the rotor diameter is limited by the centrifugal force and cannot be made too large, so the diameter is smaller, the length is longer, and the cooling system is more complicated; while the large hydro-generators are usually vertical structures, which are compared with steam turbines. , Its speed is low, the number of poles is large, it requires large rotational inertia, so it is characterized by large diameter and short length. Due to space limitations, this article mainly analyzes hydroelectric generators.The first section of generator fault analysisA generator symmetrical fault analysis.As a salient-pole synchronous motor, the hydro-generator has the characteristics of air gap and uneven magnetic resistance. For the convenience of analysis, the armature fundamental magnetomotive force Fa is usually decomposed into The vertical axis armature reaction magnetomotive force Fad and the horizontal axis armature reaction magnetomotive force Faq acting on the vertical axis are the double reaction method. When the saturation of the magnetic circuit is not remembered, the principle of superposition can be used to establish the direct-axis armature reaction electromotive force and the quadrature-axis armature reaction electromotive force in the stator windings [26-29]. Using this method, the terminal voltage and terminal current of the stator winding are respectively decomposed. When the motor is in a steady state, the electric potential formula of the stator winding of the synchronous motor is: