Sigre 2015. — 8 с.
Siemens AG, Germany, [email protected]Transformers are very important protective objects in the electric energy system. Therefore dif-ferent protection principles as well as devices are used in the applications. From the engineering point of view the design of transformers have an influence on protection concepts. For an efficient control of the power flow phase shift transformers are installed in the energy system. These types of transformers have specific requirements on the design of the differential protection. The paper addresses different aspects in the field of transformer protection. It starts with a general discussion regarding basic design of the protection schemes and presents a concept which is used in Germany.
A further focus of the paper is the differential protection. From the practical experiences over some decades two main points are discussed. The first point is the inrush detection. Due to the different magnetic conditions as well as magnetic characteristics of a transformer an overfunction of 2nd har-monic principle is possible. In the new design an additional principle - the analysis of the current wave form analysis (CWA method) - operates in parallel. The second point is the stability during external faults. The transient performance of the current transformers plays an important role. The required transient performance factor (Ktd) is related to the used algorithm. Due to a new method of the CT sat-uration detection the factor can be reduced.
An application for an autotransformer scheme with the new design of a modular hard- and software structure will be discussed. Two different differential protection functions are active in parallel in the IED. A phase to earth fault can be detected phase selective in an autotransformer bank design.
A new application area in the differential protection is the phase shift as well as special transformer application. In this field the classical design of differential protection cannot be used. That means the conventional correction of a phase shift in steps of 30 degrees. A flexible angle adaption is necessary. This allows the numerical technology due to a universal design of the transformation matrix for phase-shift correction. The basic changes in differential protection for this kind of application are presented and the differences between the typical applications are shown.
