Maintaining the reach of protective devices in distribution system with penetration of distributed generation

Abstract

Protection schemes of distribution system are designed conventionally for radial feeder structure with one source supplying. The presence of distributed generation as the second source causes the protection schemes to be confused in operations. This paper evaluates the reach of protective relays after distributed generation has been installed into the system. All types of faults are analyzed with the consideration of system grounding methods and connection transformer which connects distributed generation to power system. Then, an approach is proposed to maintain the protected areas of protective devices.

Maximization of distributed generation by considering system operating limits and protection reach reduction as constraints

“…If its reactance is sized properly, the corresponding transformer can provide an effectively grounded source. However, the ground overcurrent function (GOF) of DG relay should be maintained to enable the ability of detecting ground faults on the utility side [6]. Thus, a careful analysis on the proper size of grounding reactance along with the increase of DG size is performed in the following sections.…”

“…the utility substation. Adding a new source such as DG can decrease the fault current flowing from the substation through utility relays, causing their sensitivity to degrade [6]. When the fault current is overdecreased and less than the relay pick-up value, the required protected area becomes smaller and electric elements in the unprotected section of the system may be damaged.…”