The contribution to distribution network short-circuit current level from the connection of distributed generation

Electrical power production from distributed generation (DG) is playing an increasing role in the supply of electricity in liberalised electricity markets. Currently DG is attracting both distribution utilities and electricity users, as it can provide meaningful advantages to both. The increasing demand on the distribution network (DN) imposed by new DG such as renewable sources and Combined Heat Power (CHP) will impact on the operation of the DN in a number of areas including short-circuit (SC) current and voltage levels. In general, all new DG causes some increase in fault levels. An increase in CHP generation, that would be most likely to occur in urban DN, would lead to an increase in fault level issues as urban networks tend to have the lowest fault level headroom. The aim of this paper is to use the methodology of the latest edition of the IEC 60909 standard to calculate the maximum fault level in a DN with DG connected at MV/LV level. The application of the methodology is demonstrated using fictitious networks resembling typical DN configuration applied in commercial buildings where continuity of power supply is very important. A discussion is also included on potential measures available to reduce the fault level.