Research On The Inter-turn Fault Protection For Stator Windings Of Generators

Generator is an important component of the modern power system. Its operation has direct impact on the operation of power grids and the safe and economical power supply to the users. It plays a vital role in the whole system for security and stability. The failure of timely fault clearing will cause great economic losses. A lot of statistical data and research indicate that inter-turn short-circuit exists in stator windings of generators The inter-turn fault protection for stator windings of generators is an important and effective measure to ensure the safe operation of the generator.This thesis discussed several research methods of the generator with internal armature windings fault The symmetrical component method is the traditional means to study asymmetrical operation of generators. Phase coordinates method takes the phase winding as a whole, multi-loop method considers the generator is composed of a number of circuits. These methods have advantages and disadvantages. A suitable method is chosen according to the demand.On the basis of analyzing the internal fault of the generator stator windings, this thesis researches a variety of the inter-turn fault protections for stator windings of generators, such as the single element transverse differential protection, the incomplete longitudinal differential protection, the negative sequence directional protection against fault component and the longitudinal residual voltage protection. Then analyze the reasonable allocation of the main protections which can greatly improve the reliability of operating units.The recorded data and the research show that there exist a lot of inter-harmonics when inter-turn short circuit happens in the stator. As these inter-turn fault protections for stator windings of generators are built on the principle of reflecting the sine fundamental wave or some integral harmonics, so the existence of inter-harmonics influences the properties of the protection.In view of these issues, the thesis studies deeply on the digital filters, such as the Fourier algorithm, FIR band-pass filter and IIR narrow-band filter. It proposes the improved filtering method: low-pass filtering method based on the frequency shifting principle on the basis of these methods. This method can filters the inter-harmonics well as applying to analyzing the recorded data of normal operation or short-circuit condition. The amplitude of the fundamental wave will be very smooth and accurate after applying the improved filtering method to the longitudinal residual voltage protection of the generator. It not only eliminates the third-harmonics, but also decreases the impact of inter-harmonics. At the same time, the maximum value of the fundamental amplitude is also reduced which improves the reliability of the protection.