Real-time Closed-Loop Test to Adaptive Protection in a Smart-Grid Context
On this seccion some of the intermidiate results obtained from this work are presented. For further details on the results you can consult the provisory version of the dissertation.
The figure presented below shows the network under study.
Figure 1 - Example of a Medium Voltage distribution network with Distributed Generation
When a fault is located outside the feeder including Distributed Generation, the Distributed Generation unit contributes to the fault and feeds a fault current ‘upstream’ towards the fault, which may trip the relay located at beginning of the Distributed Generation feeder. This means that the DG feeder will be unnecessary out of service. This situation is called sympathetic tripping.
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Results from the analytical study of sympathetic tripping:
Considering the occurrence of a three-phase fault at the end of line 2 the values of the short-circuit current and the contribution of the DG unit to the short-circuit are, respectively:
In the presence of a three-phase fault, the current seen by the protective relay R1 (see Figure 1) is greater than 2000 A, , and the current seen by the protective relays R2 (see Figure 1) is also greater than 2000 A, . This means both protective relays R1 and R2 see a current greater than the third level of detection of their phase overcurrent protection function. Thus, both feeder relays act for the same level of detection of the phase overcurrent protection function, sending a order to open the circuit breaker of both lines at the same time. Consequently, besides the faulty line (line 2), the healthy line (line 1 with DG) becomes unnecessarily out of service.
The adaptive protection scheme to enhance the availabilty of Distributed Generation and avoid sympathetic tripping, the provisory version of the dissertation should be consulted. To see the results from the closed-loop test which tested the adaptability of a commercial protective relay, the provisory version should also be consulted.