IEC 61850 Process-Bus Based
In IEC 61850 environment, each Intelligent Electronic Device (IED) is able to access more measured signals, is able to be quickly informed of the status of various devices in the substation and to send various signals such as trip, block or informative to other IEDs. These features provide a unique opportunity for a new generation of bus protection relays. This article introduces Directional Comparison Bus Protection Unit (DCBPU) based on IEC61850 process-bus and provides the hardware implementation and test results of DCBPU in a laboratory environment.
Bus protection in conventional high voltage systems is based on biased current differential principle. The reality devices are very expensive, limited to several numbers of feeders and require the consideration of different conditions such as CT saturation for external faults.
One of the key challenges of conventional bus protection relays for big buses is to acquire current signals from numerous CTs in one box. Because of the heat capacity, size and processing limitations, it is almost impossible to realize a relay with more than six to eight three phase current inputs. For protection of buses with several feeders, several IEDs forming a distributed bus protection system having a master and slaves are employed to distribute processing and heat and expand the required size.
In a 61850 process-bus environment, all the current and even voltage measurements from multiple feeders can be transmitted from merging units to a single IED through communication where the bus protection relay algorithm is implemented. In this case, both the problems of heat capacity and size limitations can be overcome. However, distributed data processing and communication within one relay is required to provide fast protection for big buses with numerous feeders.
In addition, by employing both voltage and current signals, it is possible to use Directional Comparison Bus Protection (DCBP) instead of biased differential technique. This technique is based on fault direction for each circuit connected to the protected bus. Therefore, compared to biased current differential protection, it is inherently immune to CT mismatch and saturation. More
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