On Constructing a LTE-based Experimental Network in Power Distribution Systems

Wei Wu, Yu Gong, Kunli Yang Information Center, Yunnan Power Grid Company,

Kunming, P.R. China, 650000 E-mail: wuwei.yptc@gmail.com

Abstract—With the development of power distribution system, it is necessary to provide a new communication infrastructure to support broad band and wireless access network in smart grids. In this paper, we propose an experimental access layer platform for power distribution network based on LTE technology. Some typical services such as concentrated meter reading, remote video surveillance, and system operation status monitoring are tested in the experimental system, which is deployed in Mengzi city, Yunnan province. The experimental results show that the proposed experimental system is robust and can satisfy the basic QoS requirements of the typical services in power distribution system.

Keywords-LTE, Smart Grids, Power Distribution Network, Experimental Network

I. INTRODUCTION Two-way seamless communication is the key aspect in

realizing the vision of smart grid [1-3] especially for power distribution network (PDN) at the distribution and end-user levels. With the increasing demands for automation and intelligence in PDN and its various service requirements, the transmission requirements are getting higher among the control center, substations and distribution terminals. Therefore, it is necessary to provide a new type of access technology to address these challenges, further to meet with the increasing communication requirements imposed by smart applications in smart grids.

There are several standardized wired and wireless communication technologies available for various smart grid applications. With the recent growth in wireless communication, it can offer standardized technologies for wide area, metropolitan area, local area, and personal area networks. Moreover, wireless technologies not only offer significant benefits over wired ones, such as low installation cost, rapid deployment, mobility, etc., but also are suitable for remote end applications. Many activities have been going on to explore specific applications of these technologies in smart grid environment [4-7].

Many studies in the literature focus on discussing the feasibility of various technical solutions. However, the evaluation of these technologies still needs to be studied further. In this paper, we proposed an access layer platform architecture in PDN based on LTE. An experimental test system is set up in Mengzi city, Yunnan province. Some typical services such as concentrated meter reading, remote video surveillance, and system operation status monitoring are then tested in the

experimental network. The experimental results show that this experimental system is robust and can satisfy the QoS demands of various services in smart grids.

The rest of this paper is organized as follows. Section 2 gives a brief introduction of LTE. Section 3 presents the experimental access layer platform in details. In Section 4, various services are tested on the experimental network, and the experimental results are also discussed. Finally, we conclude the paper in section 4.

II. INTRODUCTION OF LTE The present communication infrastructure of the power grid

in China shows that the backbone network is strong while the access network is weak. The PDN needs to be upgraded to facilitate the ever increasing services in smart grids.

Long Term Evolution (LTE) [8] is a 4G wireless broadband technology developed by the Third Generation Partnership Project (3GPP). It aims at providing a high data rate, low latency and optimized packet transmission wireless access system by exploiting OFDM (Orthogonal Frequency Division Multiplexing) and MIMO (Multiple Input Multiple Output) antenna technologies. Thus, LTE technology is expected to be a possible solution that can improve the performance of the access layer network in PDN. In this paper, we will propose an access layer framework in PDN based on LTE. An experimental system is then deployed to evaluate the feasibility of LTE technology in smart grids.

III. AN EXPERIMENTAL ACCESS LAYER PLATFORM BASED ON LTE IN SMART GRIDS

To construct a small-scale test-bed for LTE, we select Mengzi City in Yunnan Province as the target place. This is because the city’s PDN has a higher degree of automation, a relatively complete set of communications systems and power distribution terminal equipments. All these can satisfy the test requirements. The logical topology design of the experimental network is shown in Fig. 1. It is consisted of three parts, the application management system, wireless access layer and service aggregation layer.

A. Application management system of PDN The application management system (AMS) of the PDN

consists of several application servers, which is used for the storage, analysis, statistics, management of business data, as well as control functions. In the experimental network, the AMS is deployed in Mengzi power dispatch center, the Southern Power Grid Corporation Building. Five business

2013 8th International Conference on Communications and Networking in China (CHINACOM)

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servers, the electric meters reading service (AMRS) server, the DTU telemetry service (DTU-TS) server, the analog control service (ACS) server, the video surveillance service (VSS) and the system operation status monitoring server, are deployed. The AMRS server adapts GH-NC2000 system, and the DTU-TS server adapts GH-PDS2000, both of them are provided by

Jinhongwei Co. Ltd. The VSS server is also built using the video surveillance software provided by Jinhongwei Co. Ltd. The system operation status monitoring server controls the remote storage and displays real-time running information, such as traffic statistics of the base station, dynamic topology, received signal strength.

Figure 1.The logical topology design of the experimental network.

B. Wireless access layer The wireless access layer is the key of the experimental

platform, which is responsible for covering various application terminals in the PDN and link the business terminal with the management system. It collects the data from the business terminals through LTE and uploads the data to the application server located in the district dispatch center building. The structure of the wireless access layer is shown in Fig.1. Two LTE base stations and 4 LTE terminals are deployed to form two community-scaled networks. Each has one base station and two terminals. The frequency of LTE base station and LTE terminal is 2.6GHz, the maximum transmits power of the base station is 1w, the maximum transmit power of the terminal is 200mw (Note that, the LTE prototype devices are developed by

Institute of Computing Technology, Chinese Academy of Science ).

To get an optimal wireless coverage, we made site coverage test on several alternative locations, such as the 10kV ring network switch cabinets (No.1~No.6) at Ginkgo Branch Road, Mengzi Substation, the No.5 switch cabinet at Pinghu Branch Road, Xiangxi residential community, Zizhu residential community, distribution dispatch center building and Mengzi dispatch center building. The final choice is marked on Fig.2, which also presents two separated community cells.

In Fig.2a, the LTE base station is deployed on the distribution dispatch center, the corresponding access devices are deployed in the two 10kV ring network switch cabinets (No.5 and No.6) at Ginkgo Branch Road, respectively. The

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distribution dispatch center is with a height of 45m, the surrounding environment is a typical urban block. The straight-line distance between the LTE base station and the access devices is about 270m, and there are more than five building shelters in the middle area. The inter-communication between the base station and the access devices utilizes signal reflections with the all directional antennas, whose directional antenna gain is 10.6dBi, and horizontal coverage angle is 40 degrees.

In Fig.2b, the LTE base station is deployed on the Mengzi dispatch center, the corresponding access devices are placed in Zizhu Community, and Xiangxi Community, respectively. This deployment environment is a typical residential block, there does not exist a straight visible transmission channels. Therefore, the inter-community in this cell is via the directional antenna with the same parameter setting as the cell 1.

In our experimental network, all the business data are firstly gathered via the LTE wireless access layer, then submitted to the application management systems of PDN by wire lines.

Figure 2.The deployment of LTE access layer.

C. Service aggregation layer Service aggregation layer is in charge of information

collection and aggregation from a variety of distribution businesses terminals. In order to fully test the distribution network business, we set four typical services, the electric meters reading, the DTU telemetry, the analog control, and the video surveillance in the experimental platform.

1) The automaticmeters reading service (AMRS): it completes reading information from electric meters in a concentrate manner at a residual community. This type of data is strongly concurrent, but with a lower real-time requirement. All electric meters reading services are deployed in the Zizhu residential community and the Xiangxi residential community, respectively. Among them, the Zizhu community is equipped with one concentrator unit, six collector units, and the data is acquired by power line carrier (PLC). The Xiangxi community is divided into two areas, which has two data acquisition methods-ZigBee and broadband PLC. Nine Zigbee collectors, one Zigbee concentrator, 19 PLC collectors, and two PLC concentrators are installed in the communication cabinets of the Xiangxi community. Zigbee concentrators and PLC collectors are deployed in the area I, and the PLC concentrators are deployed both in the area I and II.

2) The DTU telemetry service (DTU-TS): It collects various analogy variables, switching variables and status variables from the DTUs, and uploads these variables to the

DTU telemetry server through wireless access layer. Compared with the electric-meters-reading service, the DTU telemetry service has a higher real-time and accuracy requirement on transmission. In the experimental platform, the DTU telemetry operations are deployed in two 10kV ring-network switch cabinets (No.5 and No.6) at Ginkgo Branch Road.

3) The analog control service (ACS): when the analog control service is running, the control host sends commands order by order to the host; the host checks the received commands. If the commands are correct, then it performs related actions, and counts the number of correct message, otherwise, it only counts the number of wrong message. The analogy control service requires a higher reliability of the transmission system. In the experimental platform, the hosts are deployed in a 10kV ring-network switch cabinet (No.5) at Ginkgo Branch Road.

4) The video surveillance service(VSS): this kind of service is for remote transmission of the realtime operational status of distribution equipment, to help judging equipment operating status, and further supporting equipment error diagnosis and recovery. The services require the underline system to provide a high-bandwidth transmission capacity. To test this service, an integrated camera is deployed in Xiangxi Coummunity, Zizhu Community, and the two 10kV ring-network switch cabinets at Ginkgo Branch Road, respectively. The cameras monitor and return video streams in real-time.

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The detailed information about the service equipment deployment is shown in Table I.

TABLE I. THE DEPLOYMENT OF THE SERVICE EQUIPMENT

Service Type

Deployment Place

AMRS DTU-TS ACS VSS

Equipment Number Equipment Number Equipment Number Equipment Number 10kV switch cabinet (No.5) at Ginkgo Branch Road

N/a DTU 1 Simulation host 1 camera 1

10kV switch cabinet (No.6) at Ginkgo Branch Road

N/a DTU 1 N/a camera 1

Zizhu Renjia Residential Community

PLC Concentrator 1 N/a N/a camera 1 PLC Collector 6

Xiangxi Lanan Residential Community

ZigBee Concentrator 1

N/a N/a camera 1 ZigBee Collector 6 PLC Concentrator 2 PLC Collector 19

Notices：N/a indicates no deployment

D. The characteristics of the experimental platform The experimental PDN access layer platform based on LTE

technology provides some specific merits which can satisfy the requirements of high-level applications.

1) The flat network architecture decreases deployment cost, and enhances efficiency: Power distribution network system has a complex structure with huge mount of equipments. It is hard to build a general-purpose wireless access platform. A hetergenous wireless access system will cause huge management cost, and is difficult to locate the error location when failure happens. Using the LTE technology, we can construct a simple network management via its flat structure, which is accord with the requirements in building a PDN communication platform.

2) High system capacity: As the power distribution network evolves into the smart grid, the increasingly various business urges a higher demand on the capacity of the access layer system. By introducing the LTE technology, we can achieve a 100Mbps downlink transmission rate and a 50Mbps uplink transfer rate [6, 8], whcih is enough for various high data rate business in smart grids.

3) High reliability and low latency of data transfer: LTE technology enhance the reliability of the data transfer by introducing HARQ and ARQ in data processing. This ensures the reliable transmission of electricity distribution businesses. At the same time, a simplified protocol architecture is designed to ensure the one-way data transmission delay less than 5ms, which meets the business data transfer requirements in the power grid whose end-to-end delay is generally limited under a threshold of 15ms.

IV. EXPERIMENTAL RESULTS After the deployment of the experimental platform, we fully

tested the above-mentioned services for a month over the communication platform.

TABLE II. A PART OF THE TEST RECORD OF DTU TELEMETRY SERVICE

Signal Name

Serial Number Coefficent DTU

Display DDC

Display Correctness

10kV switch cabinet (No.5) at Ginkgo Branch Road Ua1 1 0.001 10.155 10.22 √ Ub1 3 0.001 0.001 0 √ Uc1 5 0.001 0.001 0 √ Ia11 7 0.001 0.006 0.01 √ Ib11 9 0.001 0.005 0 √ Ic11 11 0.001 0.005 0 √ Ia12 13 0.001 0.003 0 √ Ib12 15 0.001 0.003 0 √ Ic12 17 0.001 0.004 0 √ Ia13 19 0.001 0.004 0 √ Ib13 21 0.001 0.002 0 √ Ic13 23 0.001 0.002 0 √ Ua2 25 0.001 10.154 10.23 √

10kV switch cabinet (No.6) at Ginkgo Branch Road Ua1 1 0.001 10.151 10.22 √ Ub1 3 0.001 0.001 0 √ Uc1 5 0.001 0.001 0 √ Ia11 7 0.001 0.005 0 √ Ib11 9 0.001 0.004 0 √ Ic11 11 0.001 0.004 0 √ Ia12 13 0.001 0.002 0 √ Ib12 15 0.001 0.002 0 √ Ic12 17 0.001 0.003 0 √ Ia13 19 0.001 0.003 0 √ Ib13 21 0.001 0.002 0 √ Ic13 23 0.001 0.002 0 √ Ua2 25 0.001 10.157 10.22 √

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For the AMRS, it has successfully completed data acquisition from 431 meters, among which 117 meters are in Zizhu community, 88 Zigbee-connected meters and 226 PLC-connected meters are in Xiangxi community. No data transferring error occurred during the test.

For the DTU-TS, the experimental platform can fully meet the specific needs, and make the telemetry variables keep integrity. The relative error of measured values and actual values is less than 1.5%, according to the reading values from the local monitoring and scheduling side. Part of DTU-TS test records is shown in Table II, where DDC means the district dispatch center.

For the ACS, we design a repeated test for a long time. The statistical results show that packet loss rate less than 2%, and the outcome can meet the telemetry requirements in power distribution network. The test results of ACS are shown in Table III.

TABLE III. THE TEST RESULTS OF ACS

Parameters Values No. Control Signals 21,600

No. Successfully Sent Control Signals 21,211 No. Lost Control Signals 389

Packet Receive Rate 98.19% Packet Loss Rate 1.8%

For the VSS, we tested the clarity and smoothness of video stream. During the test, the video surveillance system is stable. The video quality can reach a high resolution (larger than 420 TV lines) and a smoothing frame rate (larger than 25 frames per second). The test results of VSS are shown in Table IV.

TABLE IV. THE TEST RESULTS OF VSS

Camera Place Test Case Effectiveness Clarity Smoothness 10kV switch cabinet (No.5)

at Ginkgo Branch Road ≥420TV ＞25fps √

10kV switch cabinet (No.6) at Ginkgo Branch Road ≥420TV ＞25fps √

Zizhu Community-1 ≥420TV ＞25fps √ Zizhu Community-2 ≥420TV ＞25fps √

In addition, while running the test, the monitoring system correctly shows the real-time network status. The difference between the traffic statistics from the monitoring side and that of the business server is less than 0.2 %. The received signal

strengths are exactly the same as that of the base station. The real-time displayed network topology is consistent with the actual network topology.

V. CONCLUSIONS AND FUTURE WORKS In this paper, we established an experimental access layer

platform for power distribution network based on LTE technology. The system topology and the deployment of the experimental network are described in details. Some typical applications in PDN, such as the automatic meter reading, telemetry, analogy control and video surveillance are deployed and tested in the test bed. The experimental results show that the proposed access layer system can meet the increasing communication requirements in smart grids. In the next step, the platform will be deployed in large scale and a comprehensive assessment of the system will be carried out.

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