Sequence Impedances criterion for loss of main detection of embedded generation

Numbers of large and medium size embedded generators, which are working as paralleled with the main in distribution system, are increasing rapidly. Since the existing generation, transmission and distribution systems are planed based on Centralized Generation with no considering of embedded generators, some adverse consequences and problems are initiated in power system control and protection. One major issue is the protection of generator against loss of main (LOM) or islanding conditions. A proficient diagnosis system should discriminate LOM from normal occurrences such as switching, load variations or other common faults and it should detect LOM very quickly. In this paper, embedded generations and consequent dilemmas in distribution systems are investigated and by categorizing the LOM diagnosis methods, a comparison and discussion are presented. Furthermore, a system comprising an embedded generation unit and a typical distribution network are simulated. Wide range possible occurrences are examined and several LOM detection criteria such as frequency, voltage and power variations of embedded generation unit in the distribution network are studied. A new method based on sequence Impedances of the possibly existing synchronous generator in the distribution network is developed that presents an improved diagnosis system performance. The MATLAB/SIMULINK based system simulation shows the validity of the proposed method.