Leistungsdifferentialschutz für netzgeführte Stromrichter

For the line-commutated three-phase bridge, which forms the basic connection in most common three-phase power electronic applications, a power based differential protection scheme was developed. The electric power quantities were determined using space vector and zero sequence component of three-phase system. Based on the specified parameters the pickup and tripping criteria were defined and combined to form a protection tripping logic. The pickup and tripping thresholds have been obtained analytically from the typical operating ranges of the line-commutated converter.

The advantageous use of space vector and zero sequence components for the calculation of power electronic devices has been confirmed and extended in this thesis in relation to the converter protection. Consequently, the tripping criteria are gained by three different methods of measured data processing: space vector and zero sequence components, average and root mean square values. The equifrequency currents and voltages that contribute to the increase of active power are calculated as average values. The different frequency quantities are noticeable in distortion power and are derived from root mean square values. The evaluation of the circumference and the coordinates of the complex space vector was found as suitable for a fast and sensitive fault detection.

After the power quantities and tripping criteria were determined, other practical works are necessary to verify the analytical results. The common use of power electronic equipment, the increasing share of renewable energy sources to electricity production and expansion of DC systems on high and low voltage level emphasize the need and necessity for practical implementation of the power based differential protection. With no requirements regarding the form and frequency of the electrical quantities, the power based concept provides an alternative to the convential current based differential protection relays. In view of the progressive digitization and the development of power systems consisting of a mix of AC and DC systems with no predefined power flow pattern, the proposed protection scheme is a novel solution to the increased operational requirements of modern power systems.