Research On The Operation Characteristics And System Fault For Powerformer

Powerformer, a new concept of high-voltage synchronous generator, has aroused extensive attention both at home and abroad. Its innovations are stator windings using XLPE (cross-linked polyethylene), this innovational structure enable it to generate high voltage and connect to the power grid directly, and omits the impact voltage protectors, the generator breakers, bus bars, and the step-up transformers. The power plants equipped with Powerformers have advantages of low cost, high efficiency and low maintenance etc as a whole.Firstly, the developing background and study state at home and abroad are introduced in this paper, and the significance of research on operation characteristics and system fault for Powerformer is analyzed in detail.Then, a mathematical model of operation characteristics for generator is built through electric machines and electromagnetic field theory in this paper, and the method of solving the two-dimension electromagnetic field with FEM is given. To satisfy the demand of calculation of operation characteristics, the electromagnetic field with finite element method and external circuit of generator are coupled to calculate the operation curves for Powerformer under different conditions, including no-load characteristic, short-circuit characteristic, regulation characteristic and external characteristic. And direct-axis synchronous reactance x dand short-circuit ratio SCR are calculated through no-load characteristic and short-circuit characteristic. Comparing with the experimental results, it is proved that the simulation results are right, which provides some references for the practical application of Powerformer.At the same time, dynamic performances for Powerformer are analyzed, the mathematical model of dynamic performance for Powerformer is built, and simulation model based on Simulnk is built. Two-phase short circuit and three phase short circuit on no load conditions of Powerformer are simulated, and after that the variable curves of stator current, rotor current and electromagnetic torque are derived.Finally, the physical processes for Powerformer system is analyzed respectively when the line breaks down because of one phase to ground fault, phase to phase fault, two phases to ground fault and three phase to ground fault. The electric drawings and equivalent circuits are plotted when Powerformer runs in normal state and fault state, after that, the expressions of power are deduced based on the equivalent circuits when Powerformer system runs in fault state, and impact of excitation regulator is taken into account when Powerformer runs in the foregoing fault states. And the circuit fault limit removal times of generator faults for Powerformer system are presented with simulation analysis and comparative study.