Electric Machinery 电机学 英汉双语 刘慧娟 英文课件 Chapter5-Synchronous Machines新.ppt

* 5.6.2 Power-angle characteristics of synchronous generators When a synchronous generator which connected to a power grid under steady-state operation conditions with constant excitation and constant grid voltage (E0=constant, U=constant), the relationship Pe= f (? ) between the electromagnetic power Pe and the power angle δ is called the power-angle characteristic of the synchronous generator. Using the power-angle characteristic we can research the problems of active power and static stability when the generators and power grids are under paralleling operation conditions . * on the assumption that the armature resistance is ignored and the magnetic saturation is not considered: * Pe1 Pe Pe2 0° 45° 90° Pe δ 180° -180° generator motor * For the cylindrical rotor generator because of Xd = Xq= Xs ? =90? Pe δ * 5.6.3 Active power regulation and static stability Generators supply active and reactive power to power systems when synchronous generators are connected in parallel with systems 1. How to adjust the active and reactive power ? 1) Taking cylindrical generator as an example； 2) For simplicity, the magnetic saturation and armature resistance are ignored； 3) the power system is known as the infinite bus, the system voltage U =constant, frequency f = constant. * δ= 0 0 δ 900 power limit δ? 900 ? In order to increase the output active power of a generator, the input power supplied by the prime mover must be increased. 2. Static stability When a synchronous generator is running at a stable operation point in parallel with the grid, if some tiny disturbances from the grid or the prime mover are occurred, the operation point will be changed. If the disturbances disappear, the generator can revert to the original running state; this generator’s operation is called the static stability. If the disturbances disappear, the generator cannot revert to the original running state, this operation is called unstable. * Static stability the static stability