Transient Electricomechanical Analysis of Hydropower Generators Using Field and Circuit Models

Sammanfattning: The large-scale conversion of the electrical energy system to incorporate other renewable sources of power, concurrently with vast refurbishment of the present machinery, brings the Swedish hydropower industry face to face with new challenges. Introduction of new technical solutions in systems originally designed for a slightly different purpose implies that fundamental conceptions need to be questioned. To be able to question prevailing conceptions regarding the mutual electromechanical interaction between hydropower generators and the interconnected power system, more advanced mathematical models are required. The presented work consists of three successive parts. The first deals with the development and initial testing of a dynamical electromagnetic field model of a single hydropower generator feeding an infinite power-system bus. The model includes rotational dynamics as well as excitation control and are treated numerically by the finite element method. Transient time stepped simulations show that the model is suitable for studying the electromechanical dynamics of a hydropower generator and that the implementation of the excitation system have a decisive impact on its behaviour. The second part suggests a method for identification of the characteristic electrical parameters of the electromagnetic-field generator model for use in equivalent circuit models of the same machine. The method is based on time stepped simulations of four common standard test procedures and the obtained parameters are compared to measured data. It is shown that the suggested method is an expedient method to obtain most of the parameters. A few improvements are suggested to enhance the agreement even further. In the third part, the dynamical behaviour of the electromagnetic field model is compared to that of two equivalent circuit based models of the same system. One of the circuit models is a simplified version of the other and they are both parametrised with the parameters extracted from the field model in the second part. It is found that the field model exhibits significantly higher stiffness and damping properties than both the circuit models which raise questions regarding several popular applications of such models. Experimental work is planned for the continuation of the doctoral work to investigate these theories more closely.