Impact of distributed generation on distribution protection and power quality

Abstract

The impact of distributed generation (DG) on voltage sags in a distribution network depends on the design of the protection system and the coordination between the different protective devices. DG changes the radial nature of distribution systems and affects the performance of the protection system. This paper summarizes the impact of conventional synchronous machine-based DG on the present protection practices for distribution systems, analyzes the effect of small generation units on voltage sags, and discusses the different alternatives for distribution and DG intertie protection design.

Modeling Protective Devices for Distribution Systems With Distributed Generation Using an Emtp-Type Tool

“…DG can have a positive impact on the performance of a distribution system; however, small embedded generation units alter the power flow direction and can lead to miscoordination of protective devices [8,17], [29]. This paper has presented the main features of protective device models implemented in an EMTP-type tool to analyze the impact that small distributed generators embedded in a distribution utility grid can have on the performance of the protection system.…”

“…For a simplified analysis of the impact that the connection of embedded generators can have on the coordination of distribution protective devices see reference [29]. Figure 15 shows the characteristics of the overcurrent relays that control circuit breakers B1 and B2.…”

“…Note the different shapes of the overcurrent sensed by each circuit breaker; the current through B2 exhibits the typical waveshape of the short-circuit current caused by a fault not far from a synchronous generator. Several solutions have been proposed for this case, see for instance [25] and [29]. Since this can be seen as a miscoordination between overcurrent relays, one solution is to select faster time-current characteristics for the overcurrent relay of the faulted feeder, see Figure 17.…”

“…Figure 23 shows the results obtained with this case when there is not distributed generation. When a generator is connected to the system and the point of common coupling is between the recloser and the fuse, as in Figure 14, the current through both devices in front of a fault located at point B will be different, since the current through the recloser will decrease and the current through the fuse will increase with respect to the values without generation [29]. This may cause a miscoordination between both devices, and the fuse could open first, even if the fault is temporary.…”

Investigation on voltage sags caused by DG anti-islanding protection

“…In addition, there have been efforts to identify the impacts of DG on the intensity and duration of voltage sags caused by short circuits in distribution networks [10]- [14]. Such impacts can either be positive [10], [11] or negative [12], and depend on several aspects, such as the DG position, the coordination between DG and network protection, and DG controllers' characteristics [13], [14]. On the other hand, little effort has been dedicated to study voltage dips caused by sudden DG disconnection.…”