Summary of Distributed Resources Impact on Power Delivery Systems

Because traditional electric power distribution systems have been designed assuming the primary substation is the sole source of power and short-circuit capacity, DR interconnection results in operating situations that do not occur in a conventional system. This paper discusses several system issues which may be encountered as DR penetrates into distribution systems. The voltage issues covered are the DR impact on system voltage, interaction of DR and capacitor operations, and interaction of DR and voltage regulator and LTC operations. Protection issues include fuse coordination, feeding faults after utility protection opens, impact of DR on interrupting rating of devices, faults on adjacent feeders, fault detection, ground source impacts, single phase interruption on three phase line, recloser coordination and conductor burndown. Loss of power grid is also discussed, including vulnerability and overvoltages due to islanding and coordination with reclosing. Also covered separately are system restoration and network issues.

I. Introduction

Electric power distribution systems have traditionally been designed assuming that the primary substation is the sole source of power and short-circuit capacity. Distributed resources invalidate this assumption by placing power sources onto the distribution system. As a result, DR interconnection results in operating situations that do not occur in a conventional system without generation directly connected at the distribution level. Careful engineering can effectively eliminate the potentially adverse impacts that DR penetration could impress on the electric delivery system, such as exposing system and customer equipment to potential damage, decrease in power quality, decrease in reliability, extended time to restoration after outage, and potential risks to public and worker safety.