Protection of smart substation based on WLAN compliet with IEC 61850 using travelling wave analysis

IEC 61850 is an important industry standard for substation automation. It is a suite of protocols that provides interoperability between different devices from different vendors in a substation environment. Among many other features, it has a unified application interface, unified model and provides seamless data access within the substation. Furthermore, it integrates security and functions that contribute to in- creasing the system reliability. To this date IEC61850 based protection is primarily built on fiber-based high-speed Ethernet Local Area Network (LAN) because of its high bandwidth and noise im- munity. However, fiber-based Ethernet LAN is expensive and therefore may not be economically viable for medium voltage/low voltage (MV/LV) distribution network. In its place, Wireless Local Area Network (WLAN) technology can be adopted as a viable alternative to support distribution substation applications. Recent wireless network solutions such as IEEE802.11n offer sufficient data rates for high-speed ap- plications with low installation costs and speedy deployment. However, WLAN is not sufficient for remote control communications in distribution grids due to its lim- ited radio span of around 100m typically. Much more work is needed to assess WLAN for other substation applications such as control, monitoring, metering, pro- tection and automation, due to its limited bandwidth and coverage. In this thesis, wired and WLAN merging units (MUs) combined with breaker and protection and control (P&C) intelligent electronics devices (IEDs) have been mod- eled using the Opnet modeler in order to evaluate the performance of different ap- plications in the substation. ii After modeling of the MU and P&C IED according to the IEC 61850 stack, the per- formance of various smart distribution substation applications has been evaluated in terms of average and maximum message end-to-end delays and throughput. Although fiber optics offers very high data rate there is a limitation on its use for protection based on traveling waves. This is because the sampling frequency of trav- eling waves necessarily needs to be high to capture all the details of the transient waves. This is especially so when there are multiple MUs sharing the process bus. Hence, to achieve fast protection based on the transient signal detection that ema- nates from the fault location, it is necessary to redesign the MUs so that they can im- plement fast compression and feature extractions and also to re-factor the SV mes- sage. This thesis next proposes a novel pre-processing technique for high-sampling travel- ing waves using packing and compression or feature extraction. Packing and com- pression result in throughput and end-to-end delay improvement, while feature ex- traction gives improvement in protection and at the same time, reduces the required sampling frequency to the same level as in the traditional method. This proposed technique is shown to outperform traditional impedance-based techniques which suffer from low accuracy and are time consuming. In addition, distance protection IED based on traveling waves (PDTW) that is com- pliant with IEC 61850 has been designed, and it can be used for wide area protection instead of using the traditional phasor measurement unit. Different scenarios of pro- tection based on traditional and travelling waves have been tested and it was shown that WLAN can indeed be used for different protection applications. In addition, an analysis of the packet format of SV messages has been made. Essen- tially, there is as yet no particular format for WLAN that has been recommended for IEC 61850. Henceforth, a new WLAN packet format for different protections based on traditional and travelling waves have been designed after re-factoring the original SV packet format. The indoor and outdoor substation noise at 2.4 and 5.0 GHz bands respectively, was generated by way of the simulator to study its impact on the per- formance of WLAN, particularly on throughput and end-to-end delay. The simula- tion result shows that the end-to-end delay of sample value (SV) and generic object oriented substation event (GOOSE) message increased and WLAN throughput de- creased as signal-to-noise ratio (SNR) reduces, and the band of 5.0GHz is more sen- sitive to noise. Finally, in order to reduce traffic intensity on WLAN, the evaluation of Zigbee and 6LoWPAN working in co-existence with WLAN has also been done for different applications and in compliance with IEC 61850 protocols.

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