Industrial Wireless Technologies and their Applications for Protection Automation & Monitoring

Authors: Palak Parikh, Justin Smith, and Michael Pilon, GE Grid Solutions

Comparison of Wireless Solutions

As we’ve seen above, the diverse set of spectrum rules (frequency, power, bandwidth) used by governments across the globe contributes to the variety and adding to this diversity is the fact that not every wireless use-case is the same. Designers need to trade off bandwidth for range and transmit power for energy savings. The result is a varied combination of key performance metrics that results in many different wireless standards and pseudo-standards. In Table 4 we summarize some of the most popular technologies.

By using standard networking and security methods, wireless equipment can be used in a hybrid manner to provide connectivity to all devices and locations you require. As we show in Figure 5, often the best way to pick the best solution is to NOT select a single wireless technology…use a combination or hybrid solution.

Wireless Applications 

DER Islanding/Transfer trip Application:  Depending on the grid code, some utilities require islanding of Distributed Energy Resources (DERs) from the distribution feeder upon detection of a feeder fault. Figure 6 illustrates using a transfer trip over wireless / radio between the wind farm site and utility’s substation feeder IED. The transfer trip scheme can also assure islanding of all DERs before tripping of the feeder, such that DERs do not operate in an unsafe mode, i.e. without ground reference. Point-to-multipoint wireless communication can be used for multiple DER locations with coverage up to 48 km away with a repeater site in between if required. The remote transfer trip signal is tested to be received by the DER sites within 10 to 30 ms.

Wireless technology uses frequency hopping spread-spectrum radios that operate in the unlicensed spectrum between 902 and 928 MHz. The radios hop between 128 channels with a bandwidth of 130 kHz, with this frequency hopping technique making the radios extremely resistant to interference. Frequency hopping also establishes a high level of security because data transmission occurs on a variety of frequencies in a random pattern. In addition, wireless technology uses a 32-bit CRC algorithm to further ensure reliability of data.

A robust system, maximizing range and performance is achieved by mounting the wireless antenna at a height above surrounding terrain and obstructions (Figure 6).

Line Monitoring:  Typically, line monitoring devices are mounted at strategic points in the overhead network. These line sensors measure current and calculate both amplitude and phase of the RMS value, and have built-in communications such as a 2.4 GHz radio (100 ft /30m range). The sensors have the capability to pick up fault currents and report this current data back via radio to the Sensor Network Gateway (SNG).

The SNG links a network of sensors together, sending commands to the sensors and receiving data in response. This data can consist of current values, fault event current data, or other related information such as temperature. The SNG links back to the Data Acquisition Communicator (DAC) unit, via backhaul communication over a cellular network.

The DAC Unit is generally mounted in the substation and its function is to record the activity of the sensor network. The DAC also links the sensor network to the system software controls.

Line Monitoring illustrates the benefits of using multiple wireless technologies within one system. 2.4 GHz radio bands support higher throughput for shorter ranges with low latency in the range of 2 ms, making it the most suitable option for transmitting data from sensors to the SNG. With the recent growth of cellular technology, the data rate and improved QoS make it an ideal choice to transfer the data from the SNG to the DAC.

Utilities can use the existing cellular communication infrastructure to some extent to support this application. Cellular networks provide latency in the range of 50-100 ms, with the network owned and operated by a service provider, minimizing network maintenance (Figure 8).

 

Distribution Automation (DA) Applications: Major distribution applications such as Fault Detection, Isolation and Restoration (FDIR) and Coordinated Volt-VAR Control (CVVC) can also be achieved using robust wireless communications, as illustrated in Figure 7.

Next generation smart distribution is already proposed in the PACW magazine article “Emerging Trends in Smart Distribution Networks: Distributed Intelligence with Centralized Management” published in June 2018.

A Single IED platform across distribution network applications (including substation feeder relay, recloser controller, switch controller, capacitor bank controller, and voltage regulator control) can be applied with IEC 61850 GOOSE using robust wireless technologies.

High performance 900 MHz unlicensed technology can transport IEC 61850 GOOSE Ethernet frames natively, allowing for data rates of up to 1.25 Mbps with a latency tunable to as low as 5 ms. In addition, advanced QoS functionality allows for the prioritization of egress traffic based on Layer 2- Layer 4 classifications. In this fashion, critical applications are assigned to the priority queue and are switched first to meet application requirements.

Stateful firewalling as well as RF and IPSec encryption enables network operators to meet NERC CIP/EPCIP and other stringent cyber security requirements by encrypting communication links and protecting network assets and users against intrusion (Figure 7).

IED Configuration and Personal Safety:  It is well established that only qualified personnel can work on energized switchgear, and appropriate PPE is needed to be within the defined arc flash boundaries. Often, protective relays are installed in the same cubicle section as the breaker. It is always a good practice to connect to the relays remotely through the network, but in cases where it is not possible, users have no alternative except to use the front port of the relay to connect the computer. To avoid any exposure to arc flash, wireless communication with the relay can be integrated so that users can be much further away from the relay and yet can communicate and retrieve data.

Such wireless communication with the relay can be done through Wi-Fi, eliminating the need for personnel to be in front of the relay. Figure 9 shows the prohibited boundary and use of wireless communication for increased safety. As shown in the figure, the IED Configuration Tool (ICT) used from the laptop at a safe distance can directly transfer CID files into the breaker/switchgear cabinet, as well as retrieve records, and show simulated relay HMI screen (including LEDs, screens, PBs status and control). (Figure 9).

Remote Monitoring & Metering:  With the wide use of mobile phones, cellular coverage is becoming available even in very remote locations. Supervisory Control and Data Acquisition (SCADA) from remote locations can now be achieved over cellular communications between the substation Remote Terminal Unit (RTU) and SCADA server.

Figure 10 shows the application of cellular technology for a SCADA interface with the remote distribution substation site. Remote site DER or unmanned distribution substations can be monitored using one, or a combination of wireless technologies.

Summary

Recent advancements in industrial wireless technology are applied to various power applications where a wired network is difficult to deploy or has less feasibility e.g. low installation cost, mobility/portability, remote location coverage, rapid installation, etc. Robust industrial wireless technologies or a combination of technologies can deliver reliable, secure and cost-effective solutions for protection, automation and monitoring applications.

Cyber security requirements are achieved over both licensed/private and unlicensed/public wireless technology options. Suitable wireless technology should be selected based on criteria such as bandwidth, range, data latency, and regional frequency spectrum availability.

Industrial wireless has already been applied for DER transfer trip, line/feeder fault location, distribution automation, P&C IED configuration, and remote DER or substation monitoring.

Relion advanced protection & control.
BeijingSifang June 2016