Research of the application of the Low Power Wide Area Network in power grid

Low Power Wide Area Network (LPWAN) technologies developed rapidly in recent years, but these technologies have not make large-scale applications in different application scenarios of power grid. LoRa is a mainstream LPWAN technology. This paper makes a comparison test of the signal coverage of LoRa and other traditional wireless communication technologies in typical signal environment of power grid. Based on the test results, this paper gives an application suggestion of LoRa in power grid services, which can guide the planning and construction of the LPWAN in power grid.


Introduction
Low Power Wide Area Network (LPWAN) is an IoT(Internet of Things) technology which developed rapidly in recent years. LPWAN has the characteristics of long coverage distance, low power consumption and low operation and maintenance costs [1]. LPWAN technologies have not made large-scale applications in different application scenarios of power grid. Among several LPWAN technologies which have similar communication performance, LoRa is a mainstream technology using public spectrum resources [2]. This paper will test the signal coverage of LoRa and other wireless communication in typical signal environment of power grid to verify availability of the application of LPWAN in power grid.

Test scheme
Traditional wireless communication networks in power grid include 2G/3G/4G public cellular networks rented from the telecom operators, 1800MHz and 230MHz private TD-LTE network [3].
The comparison test in this paper deploys the LoRa gateway equipment and the base station of the 1800MHz private TD-LTE network [4] in the same location. The locations of the base station can be on the roof of the office buildings or transformer substations which are the property of the power grid enterprises. This test selects several typical signal test points which cover the common electric environments where the measurement automation terminals and distribution automation terminals are deployed. This comparison test uses signal testing instrument to test and record the signal strength, packet loss probability and other performance parameters of LoRA, 1800MHz private TD-LTE network and public cellular networks in every signal test point.

Specifications of the LoRa equipment in the test
The LoRa equipments in the test include LoRa gateway [5], LoRa communication module and LoRa signal tester.

LoRa gateway.
The LoRa gateway can receive the data packets from the LoRa communication modules in its coverage area and forward them to application servers of power grid. The working frequency of the gateway is 470MHz~510MHz and the maximum sensitivity is -140dBm. The gateway has 9 configurable channels(The bandwidth of 8 channels of them is 125kHz, The communication speed of these 8 chanels is adaptive and these 8 chanels support the spreading factor SF7~SF12.One of the 9 configurable channels is a high-speed channel with 250 kHz /500 kHz bandwidth). The maximum power output of the gateway is 25dBm, in this test the output is configured in 17dBm and the radio central frequency is 476.5MHz. The access message length is 23 bytes and the normal message length is13 bytes. The frame rate mode is configured into low speed mode. The roof height of the building where the LoRa gateway is deployed is 50 meters and the antenna height of the gateway is 3 meters.

LoRa module.
The LoRa communication modules can acquire the data packets from different service terminals of power grid and send them to the LoRa gateways.The LoRa module supports LoRaWAN Class-A/C protocol. The radio frequency of the LoRa module is set to 476.1MHz, 476.5MHz, 478.2MHz, and 478.8MHz, and the bandwidth is 125 kHz. The spreading factor of the LoRa module is set to SF12 (the maximum sensitivity is -140dBm at SF=12) and the encoding rate is set to 4/5.

LoRa signal tester.
The LoRa signal tester can test uplink data packet loss rate, downlink data packet loss rate, and the signal quality (RSSI and SNR) of the gateway sending packets.   Table 1shows the receiving sensitivity of LoRa in different spreading factors and bandwidths from the experimental data. In different environments, the test results of the LoRa in 4 test points are shown in Table 2. The results prove that In 4 test points with building sheltering, the LoRa network can make normal communication.   Table 3. The test results show that 1800MHz private TD-LTE network has worse performance in signal receiving in building sheltered electric environment. The construction of the indoor distribution systems of telecom operators can effectively improve the signal coverage of the public cellular networks in some test points. But in some sheltered electric environment without indoor distribution