Timo Keil

Advanced Coordination Method for Overcurrent Protection Relays Using Nonstandard Tripping Characteristics

This paper describes an advanced coordination method for an optimized protection time grading based on a new nonstandard tripping characteristic for overcurrent protection relays. The intention is the highest possible reduction of tripping times for a selective fault clearing in distribution networks protected by overcurrent relays without communication links. The new nonstandard tripping characteristic will be described from its basic idea to its constraints of the optimization problem. The optimization is solved by the method of Lagrange generalized with the Karush-Kuhn-Tucker conditions and is aimed at selective fault tripping with shorter tripping times as standard characteristics and conventional coordination methods. Overcurrent relay coordination becomes a mathematical optimization task. A comparison with the standard characteristics and conventional coordination methods shows a notable advancement regarding their average and maximum tripping times which can be achieved using this new method.

Dynamic influences on protection systems in distribution networks with distributed generation

This paper deals with the protection system in distribution networks with distributed generation. It describes the dynamic influences of synchronous generators on the direction determination of protection relays during network disturbances. Therefore the dynamic behaviour of the measured electrical quantities during network disturbances is derived. A relay-model is implemented to study the behaviour of protection relays. The results show that the direction determination may see reverse faults in forward direction, following unwanted tripping, during the period of acceleration of synchronous generators.

Coaction of protection and distribution management systems in case of islanded distribution networks

This paper describes how an adjusted coaction of protection and distribution management systems in future distribution networks can help to improve security of supply. A high penetration with distributed energy resources is considered, challenges for network operation are discussed and protection concepts for both interconnected and islanded operation are developed.

Advanced planning methods maintaining reliability and power quality in networks with increased distributed generation

Distributed generation (DG) is finding its way into the worldwide distribution networks very rapidly. As the existing networks were not created for this new structure of electricity production, the preservation of a reliable network operation and a high level of power quality is a big challenge for all network operators. In a study conducted by the University of Erlangen and the Erlanger Stadtwerke AG (public utility company of Erlangen), this problem was investigated using an existing distribution network. In this paper the study and its results are presented. Different future scenarios of network configurations with increased DG will be shown. On the basis of calculations for each scenario regarding load and voltage profile, short-circuit currents and (n-1)-aspects the effect of DG on the distribution network will be pointed out. Using these results methods will be presented that guarantee a secure operation in those scenarios. In addition, necessary investment costs are registered in this paper.

Influence of ion current on current transfomers of AC systems in near vicinity of DC systems

Equipping one support structure with DC and AC systems in parallel can increase the transport capacity of existing transmission corridors. The constant electric field of the DC system induces a constant DC component into the AC systems in near vicinity. All magnetic equipment including an iron core is in danger to saturate. Especially current transformers (CTs) for protection issues can be influenced in the way that the time-to-saturation is reduced. Therefore, maybe the protection relays are affected adversely and the selectivity is harmed. This paper evaluates this major impact by determining the transient dimensioning factor and the time-to-saturation in presence of a constant DC component in the fault current and remanent flux. The influence on the transient dimensioning factor is marginal and can be almost neglected. But for metering cores it could be a problem and should be tested because of the different excitation curves.