1033 / 2019-05-18 00:39:02

Assessment of Data Flow Control Methods and their Performance on IEC61850 based Digital Substation

IEC61850,Substation automation system,FIFO,PQ,WFQ

IEC 61850 standards have been published for the communications in substation automation system (SAS). The Standards can provide the interoperability between multi-vendor IEDs. This can bring benefits and advantages to the electric utilities and industries. The standards define the object-oriented data models and services and communication protocols that allow the information and data exchange between IEDs via Ethernet networks. For instance, the Generic Object Oriented Substation Event (GOOSE) messages have been used for such as tripping switchgear, alarms, interlocking and others in the protection and control schemes of a substation. Since the tripping signals are required as quick as possible therefore the GOOSE messages are time-critical. However, there are many other types of messages, such as MMS or FTP sharing the SAS communication network, various network loads can increase the network latency and network congestion during the abnormal events, these will affect the performance of the time-critical messages and the unexpected delay of the time-critical messages will affect the protection and control scheme. Thus, it is important to manage the data flow within the SAS communication network. To address these issues, a number of data traffic control methods have been considered to control and improve the data flow performance within SAS communication networks. For example, VLAN separation and multicast filtering techniques have been used to manage the multicast data traffic. Packet scheduling technique has also been considered in the IEDs itself to reduce the GOOSE messages delay. However, the impact of unexpected delay (due to abnormal events or faults) on the time-critical messages within the substation communication network still needs to be explored.
This paper presents the Priority Queuing (PQ) control method application to National Gird Architecture of Secondary System Substation (AS3) based IEC 61850-based SAS communication network. The time critical data flow performance during different scenarios are evaluated and compared with other data flow control methods. The substation communication network with the priority data control method is modelled and implemented using the OPNET simulation tool. The performance of Priority Queuing (PQ) control method has been evaluated and compared with other two data control methods: First-in-first-out (FIFO) and Weight-Fair Queuing (WFQ). After simulation, the results show that the PQ control methods can reduce the impact of unexpected delay for the time critical messages on the performance of protection and control functions during the abnormal conditions. However, FIFO is not able to handle the various polling rate of the MMS reports, GOOSE trip during the abnormal condition. Although, the WFQ can also ensure the time delay of GOOSE message to meet the requirement of 3 ms, but it is not as good as PQ since it has to provide sufficient bandwidth for the non-critical messages MMS and FTP.