Laboratory Investigation of Using Wi-Fi Protocol for ... - IEEE Xplore

IEEE International Conference on Smart Grid Engineering (SGE’12) UOIT, Oshawa, ON, Canada, 27-29 August, 2012

Factors Affecting on the Next Generation Protection on Smart Grid based on Wi-Fi Wireless Technology M M Eissa (SIEEE)

K. M. Abdel-Latif

Department of Electrical Machine and Power Engineering Faculty of Engineering-Helwan University at Helwan – Egypt, Email: [email protected] Abstract- Protecting the distribution grid in a smart and cost-effective way can be a major challenge when faced with the complexity of expanding network topologies. Wireless communication based relays is the next generation suitable protection for smart grid. A new laboratory transmission line protection scheme using Wireless Fidelity (Wi-Fi) communication protocol for data sharing between the two relays located at the ends of the transmission line is presented in this paper. Various factors that can affect data transmission through the wireless communication network are studied. The D-Link DWL-G700AP Access Points are used. They have the ability to transfer files with a maximum wireless signal rate of up to 54Mbps. Index Terms- D-Link DWL-G700AP Access Point cards, Prototype physical Transmission line, Digital Relaying, Wireless communication, Wi-Fi protocol. 1.

INTRODUCTION

The smart grid promises a more efficient way of supplying and consuming energy. In essence, the smart grid is a data communications network integrated with the power grid that enables power grid operators to collect and analyze data about power generation, transmission, distribution, and consumption-all in near real time. Smart grid communication technology provides predictive information and recommendations to utilities, their suppliers, and their customers on how best to manage power and protect the grid. The communication facilities also allow engineers to exchange operation, test and maintenance information with the neighboring utilities, and access real-time and historical relay information [1]. Use conventional logic processor to apply directional comparison protection to complex distribution network in a smart grid is not proper. The logic processor must have programmable logic to receive, process, and transmit relay internal bits over a communications channel. Figure 1(a) shows the directional comparison scheme for many terminals. This scheme is applicable to lines having more than three terminals. The logic processor, installed at Terminal 3 in this example, communicates with relays at Terminal 1 and Terminal 2 via digital radio or fiber-optic channels. The processor also communicates locally with the Terminal 3 relay via fiber or copper wires. The wireless networks are now becoming a popular choice for new network algorithms. The wireless communication network allows the exchange of information among the protection relays. The exchange of information among the relays assists the protective relays to take the correct decision [2]. In applying differential protection on transmission lines, the pilot wire is considered as the main method for exchanging the current signals between the relays at the two ends of the line. The length of the line that can be protected by the pilot wire differential protection is limited by the effect of resistance and capacitance of the pilot wire. Moreover the relay function may be lost due to line disconnection. The wire link also needs additional protection [2-6]. Wireless technologies are one of many types of media that could meet many Smart Grid requirements by enabling access where other media are too costly or otherwise not workable. Wireless can be used in field environments across the smart grid including generation plants, transmission systems, substations, distribution systems, and customer premises communications. Smart grid is a concept for transforming the electric power grid by using advanced communications, automated controls, and other forms of information technology. This concept, or vision, integrates energy infrastructure, processes, devices, information, and markets into a coordinated and collaborative process which allows electricity to be generated, distributed, and consumed more effectively and efficiently [8]. A high performance, reliable and secure communication network is one of the fundamental building blocks to the introduction of smart grid applications. Applying the wireless technology in transmission line protection satisfies the following features:  Synchronized measurements.

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IEEE International Conference on Smart Grid Engineering (SGE’12) UOIT, Oshawa, ON, Canada, 27-29 August, 2012      

Decision is not stand alone based. Information exchange with the neighbors. Relays behave adaptively according to any change in system parameters. Wireless communication (no need for pilot wires). Lower cost compared to leased lines. Response time, less than one half-cycle, is fast.

(a)

(b) Figure 1: The conventional and future protection technology for multi-terminal lines in smart grid. To protect smart grid with the technology of wireless, the current signals are exchanged using Wi-Fi protocol through wireless communication network. The protection system for multi-terminal lines consists of the IED relays (Intelligent Electronic Devices), the relays make the final decision based on the shared information (current signals) sent through a wireless communication network, Figure 1(b). 2. OVERALL STRUCTURE OF THE SYSTEM MODEL The main parts of the model used to test the proposed technique for protecting the transmission line are shown in Figure 2. A single machine connected to a constant voltage bus was physically modeled. A software program has been developed. The software program for the digital relay at both ends of the transmission line is applied using LABVIEW package [9]. A three-phase synchronous micro- separately excited DC machine is employed to model the generating stations. The transmission line is modeled by a lumped element physical model. The purpose of the Data Acquisition Card (DAC) is to convert the analog data into a form usable by a digital processor. The data acquisition card is characterized by 14-bit input resolution and the sampling rate is 48 kHz. Three input channels for three phase currents are used with a sampling frequency of 10 kHz for each channel. Figure 2 shows the data acquisition card interfaced with the PCs. The D-Link DWL-G700AP Access Point has the ability to transfer files with a maximum wireless signal rate of up to 54Mbps. Figure 3 shows the wireless access point. The DWL-G700AP is Wi-Fi IEEE 802.11g compliant, meaning that it can connect and interoperate with other 802.11g compatible wireless client devices.

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IEEE International Conference on Smart Grid Engineering (SGE’12) UOIT, Oshawa, ON, Canada, 27-29 August, 2012 The Wireless Bridge D-Link DWL-810+ is a high-speed wireless networking product capable of transfer rates up to 22Mbps. The D-Link Air plus DWL-810+ Ethernet-to-Wireless Bridge is a device that can be implemented in a variety of ways to provide wireless access by converting an Ethernet connection.

Figure 2: Model for main parts of the protection system. 3. MODEL OPERATION The windows XP version is used as operating system in both computers. The network and sharing center built in function in windows XP is used to setup a wireless network between both computers. After this step the receiving end computer appeared as an hard disk drive on sending end computer and vice versa. Now the software program on both computers read the current signals using DAC and stores this data in both computers. The DACs are interfaced at the two ends of the transmission lines. After reading the data, they are sent through two wireless access points using the Wi-Fi protocol. In the study the DWL-G700AP Wi-Fi IEEE 802.11g is used. The lab View program controls the capacity of data files.

Figure 3: Hardware devices used in the laboratory model. The protection scheme is based on measuring the current signals only at two ends of the transmission line. The power system configuration is shown in Figure 2. The suggested technique can be explained through an analysis of three key components.  Synchronization Element.  Differential Element.  Decision Element. The differential element calculates the sum of the sampled current signals during ¼ cycle using (1). k



i a ,b,c ( k )   i1a ,b,c ( j )  i2a ,b,c ( j )



(1)

j 1

where:

Δi j

is the sum of ¼ cycle instantaneous current samples for phase a, b and c. is the index.

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IEEE International Conference on Smart Grid Engineering (SGE’12) UOIT, Oshawa, ON, Canada, 27-29 August, 2012 k

i1 i2

is the number of samples during ¼ cycle which equal 50 samples. Generator Bus end current. City Bus end current.

For normal operation and external faults: In this case, exchanging the measured current with the neighboring relays will help Relay-1 to take an accurate decision because in this case the Relay-1 will depend on the locally measured current signals and the current signals exchanged with Relay-3. a , b, c i a , b, c  i pre

(2)

For internal faults:

i a , b, c

>

a, b, c i pre

(3)

“pre” refers to the values in the previous cycle. The final decision is also exchanged between the two relays to help the relay make an accurate decision. 5. CASE STUDY Effect of failure in the communication network In this case the relay at the generator bus does not receive any current signals from the other end due to a failure in the communication network. The current signals at the generator end are also measured during a single line to ground fault on phases A, solidly ground, 100km from the generator bus as shown in Figure 4(a, b & c). The deviation signals for phases A, B and C for the line are shown in Figure 4(d). The deviation signals of all phases are less than the threshold value and the relay does not detect the internal fault and no trip signal is produced, Figure 4(e). Another case study is also tested due to three phase short circuit fault. The current signals measured at the generator end during an internal three phase short circuit fault at 100km from the generator bus. The deviation signals for phases A, B and C at Generator Bus are calculated. The deviation signals for phases A, B and C are greater than the threshold value. This means that the fault is internal. When the relay starts to exchange the decision with the other relay to assure that the fault is internal it cannot do so due to the failure in the communication network. In this case the relay produce a tripping signal based on the available information. One of the advantages of the new proposed technique is the facility to exchange the measured current signals between relays. As shown in Figure 5, Relay-1 can exchange the measured current signals with Relay-2, Relay-3 and Relay-4. This facility will help the relays to take an accurate decision in the case of a failure in some communication channels. For illustration, focus on the Relay-1. The operation of Relay-1 is based on the relay applying the protection algorithm described above on the locally measured current signals and the current signals received from Relay-2 through the wireless communication network. When the communication channel between Relay-1 and Relay-2 fails, Relay-1 may not detect the fault. CONCLUSIONS A laboratory model using Wireless Fidelity (Wi-Fi) communication protocol for data sharing between two relays located at ends of the transmission line is demonstrated. The protection algorithm applied in relays at each end of the line is based on current signals measured at the two ends of the transmission lines. The data is exchanged through the wireless communication network. The relay algorithm detects and classifies all internal faults within one half-cycle of the fundamental frequency after the fault inception.

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IEEE International Conference on Smart Grid Engineering (SGE’12) UOIT, Oshawa, ON, Canada, 27-29 August, 2012 The paper introduced new application for system protection using wireless communication protocol. The experimental results encourage wide applications for protecting complex topology of power system and smart grids. REFERENCES [1] X. R. Wang, K. M. Hopkinson, J. S. Thorp, R. Giovanini, K. Birman and D. Coury, "Developing an agent-based backup protection system for transmission networks," Power Systems and Communications Infrastructures for the Future, Beijing, September 2002. [2] M. Monjaras, J. M. Jaramillo, and I. Munoz, "Protection Scheme for a Three-Terminal 115 kV Line Using Directional Comparison Relays," Proceedings of the 19th IEEE Mexico Section Summer Meeting on Power and Industrial Applications, Acapulco, Gro. Mexico, July 2006. [3] S. H. Horowitz, England, 1992.

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[4] Ilia Voloh and Ray Johnson, GE Multilin, “Applying digital line current differential relays over pilot wires”, Protective Relay Engineers, 2005 58th Annual Conference, April 2005, pp. 287-290. [5] Murty Yalla, Mark Adamiak, A. Apostolov, J. Beatty, S. Borlase, J. Bright, J. Burger, S. Dickson, G. Gresco, W. Hartman, J. Hohn, D. Holstein, A. Kazemi, G. Michael, C. Sufana, J. Tengdin, M. Thompson, and E. Udren, “Application of a Peer-to-Peer communication for protective relaying”, IEEE Trans. on Power Delivery, Vol.17, No.2, April 2002,pp.446-451. [6] M Yamaura, J Inagaki, K. Igarashi, I Shuto, K Fiashisako, C Shilomi, N lnoue “Development of digital current differential relay built-in sampling synchronization function” at K (Korea), IEE Annual Conference on Power Systems and Apparatus, 1988-11. [7] K. M. Abdel-Latif, M. M. Eissa, , A. S. Ali, O. P. Malik and M. E. Masoud , “Laboratory Investigation of Using Wi-Fi Protocol for Transmission Line Differential Protection l”, IEEE Trans. on Power Delivery, Vol.24, No.3, July 2009, pp.1087-1094. [8] Michigan, Department of Labor and Economic Growth, "21st Century Energy Plan," Alternative Technologies Workgroup, Meeting Handout 1, July 27, 2006, _www.dleg.state. mi.us/mpsc/electric/capacity/energyplan/alttech/smartgrid_draftreportoutlinejul19_2006.pdf_. [9] Gary W. Johnson and Richard Jennings, “LAB VIEW Graphical programming”, McGraw-Hill, 2006. [10] M. Gilany, "A microprocessor-based relay for parallel transmission line," Ph.D. Dissertation, Dept. of Electrical and Computer Eng., University of Calgary, Canada, 1992. [11] IEEE Std. 802.11, Wireless LAN Medium Access Control and Physical Layer Specifications: Further Higher Data Rate Extension in the 2.4 GHz Band.

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Figure 4: Generator bus relay performance during three phases solidly grounded fault at 100 km from Generator side with a failure in the communication network.

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Figure 5: Exchanging measured data between neighbor relays.

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