Operation of a medium voltage distribution network with a large penetration of distributed generation

The paper presents the study of the behaviour of a real MV public distribution network in a mid-size in Italy, characterized by a very large amount of distributed generation (DG), reaching 100% of supplied network load. A parametric steady-state analysis of operating regimes was carried out, considering different load and DG scenarios (maximum and minimum load, maximum and minimum DG). The deterministic study did not evidence any operational problem, such as overloads and violation of voltage constraints. Occasional voltage violations (high MV voltages at full DG output) are easily overcome by tap-changer operation on the HV/MV transformers. Although feeder voltage profiles are actually improved by DG, a drastic power factor reduction is found at the utility supply points, as well as the possible active power flow inversion, entailing contractual and regulatory issues. Extensive short-circuit studies were also carried out, showing that DG fault contribution in the studied network is far from negligible, but does not dictate changes of either circuit breaker rating or overcurrent relaying coordination.