Evaluation of Harmonic Distortion In Distribution Networks Under Transformer N-1 Security Criterion

A major goal for electricity distribution utilities is to provide electrical energy with a high reliability and power quality level. To achieve this goal, a common practice in distribution feeders is assigning transformer rated power to two parallel transformers, so that one of them can work if the other fails or is under maintenance. Security criterion N − 1 typically consists on verifying that the adequate security and power quality conditions are fulfilled when one transformer is not available. In this paper, a probabilistic methodology is proposed to verify if harmonic distortion limits are complied in such cases. Then, the methodology is applied to a case study where the criterion is tested in different transformers of a low voltage urban distribution network with approximately 8100 customers connected. The results show that, in certain cases when the transformer rated power is drastically reduced to half by a contingency, harmonic distortion can be a constraint more critical and restrictive than fundamental voltage drops.