Industrial Wireless Technologies and their Applications for Protection Automation & Monitoring

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

Industrial wireless technology can provide power utilities with industrial grade reliability, security and performance. Industrial wireless devices are built with various substation-hardened standards, such as IEEE 1613 and IEC 61850-3, with the devices able to withstand electrostatic discharge (ESD) and electromagnetic field (EMF) radiation, as well as mechanical vibrations and extreme temperatures which are commonly encountered in grid applications.

Wireless networks are equipped with encryption technologies like IPSec VPNs and APNs with key rotation used to enable an end-to-end encrypted IP tunnel through which data can flow securely between utility assets. Similar to a private network, a public wireless network allows RADIUS, authorization, authentication and accounting services.

As shown in Figure 1 for Industrial and Distribution Protection and Automation, appropriate wireless technology can be selected and deployed to meet data latency and throughput requirements. This article focuses on three basic wireless technologies:

1.   Cellular

2.   Licensed

3.   Unlicensed

 

Cellular

Cellular systems operate on different licensed frequency spectrums that can be purchased/leased from governments for various applications. Existing 3G (3rd Generation) / 4G (4th Generation) cellular technology operates on the licensed spectrum ranges of 824-894 MHz / 1720-1900 MHz / 2500 MHz. Data transmission rates of this technology are 60-240Kbps for 3G and can be greater than 20Mbps for 4G, while distance coverage is dependent upon the availability of cellular service tower installations, which facilitate non-interrupted data flow. This results in a point-to-point architecture that can receive data from serial or Ethernet interfaces and transmit data on a second interface over the cellular network, enabling normally wired components to become wireless.

As cellular network technology has evolved, key performance characteristics have improved considerably. 4G is the present standard for cellular technology, with each generation improving the throughput, coverage, hand-off, link quality, and latency of the network. Since network coverage is from the service provider, range tends to be less important to users than with other wireless implementations. Table 1 shows the key 4G cellular performance parameters.

The advantage of cellular technology is that the existing established infrastructure covers a wide area, and with recent growth in 3G / 4G cellular technology, the data rate and Quality of Service (QoS) are improving rapidly.

Licensed Spectrum

This type of wireless technology requires a license from the government to operate in a given geographic area. In the United States, the government entity that grants licenses is the FCC (Federal Communications Commission). Different countries have different frequency bands available for licensed wireless operation. In North America, traditionally, there are frequency channels in portions of the 200, 400, and 900 MHz spectrum. Since these channels are spaced quite close together, this spectrum is often referred to as “licensed narrowband.” In the US, a commonly used narrowband frequency band is the 900 MHz Multiple Address Systems Band.

 Licensed Narrowband Channels are typically 12.5 kHz, 25.0 kHz, or 50.0 kHz wide, which offers data throughputs based on the modulation technique used (e.g. QPSK/QAM offer data throughput 2 to 6 times greater than FSK), in addition to advanced networking and security features.

The benefits of operating an industrial wireless network on a licensed wireless channel are:

  • No interference from other systems. Since permission to operate requires a license, no one else is operating equipment on the same frequency. This means that all bandwidth on the channel can be utilized privately
  • Greater transmit power. Since governments typically permit one licensed operator in a geographic area, the transmitter rules often allow for relatively high transmitter power. For example, 5-10 Watts is common. This is larger than for unlicensed bands, (Wi-Fi, Bluetooth, etc.) and means that the radio signals can propagate further

The high transmit power and good receiver sensitivities that accompany narrowband signals results in narrowband wireless signals that can propagate long distances and penetrate obstructions well. Because of that, licensed narrowband networks have typically been constructed in a point-to-multipoint fashion (hub-and-spoke) with the Master Station (Access Point) installed with its antenna at a great height, allowing these networks to be very large geographically.

For example, remote radios located 50 miles in all directions communicating with one master station is a common network model. In these types of systems, with remote locations that are hard to reach and located at a distance, it is important for the radio equipment to be rugged, reliable, and offer advanced diagnostics. Licensed wireless systems are often deployed with the remote devices communicating solely with the master station. Since the remote devices are at fixed locations, directional antennas can further improve the signal quality and allow for even more distant radio connections.

These directional antennas (which offer more signal gain than omnidirectional antennas) are typically mounted on poles and aimed at the master station. Geographically large wireless networks can be very economical solutions for monitoring remote power substations or industrial facilities. A network with a 50-mile radius, for example, covers 7800 total square miles. Contrast that to a typical 0.5 miles radius cellular system with a coverage area of 0.78 square miles - the licensed narrowband system is 10,000 times larger in this example. Now assume 400 to 500 remote devices can be monitored from this single master station. Since licensed wireless solutions are interference-free, the wireless channel can be dedicated to delivering data packets. Licensed narrowband systems, therefore, can provide very low latency even though their data throughput is also very low. For example, small-packet one-way latencies of under 15 ms are common. Figure 3 shows how a wireless network that supports different data speeds for different signal conditions (automatically), can more effectively use the radio spectrum and allow the network to support multiple applicatio

Unlicensed Spectrum

No license is required to operate in unlicensed frequency bands, so long as the equipment is approved for use. These unlicensed wireless bands are officially referred to as "industrial, scientific and medical (ISM)" radio bands. Worldwide, there are many different unlicensed bands, with common frequency bands located at 2.4 GHz and 5.8 GHz. In North America, Central America, and South America, another popular band is the 902-928 MHz ISM band. (Figure4).

The benefits of operating an industrial wireless network on an unlicensed channel are:

  • No licenses & No cost. Because no license is required, a user can operate a network as per the application requirements
  • Bandwidth. Unlicensed frequency bands typically offer large amounts of bandwidth (>20 MHz). Licensed wireless channels are typically narrow bandwidth (narrowband) or require a considerable investment to purchase (cellular)

The downside to unlicensed / ISM operation is that the user may have to share this large bandwidth with several other simultaneous users

While indoor Wi-Fi networks can provide multi-megabit per second throughputs, long range 900 MHz ISM systems typically provide less than 1 Mbps. For example, a 900 MHz ISM band system with proper antennas and antenna height can provide 250 kbps (shared) to 100 devices located within 5 miles of the access point. In the unlicensed bands there are many different types of equipment with a wide variety of performance. Since industrial and distribution protection applications most often involve connecting end devices to networks, we will look at two use cases: short range/high throughput over Wi-Fi, and long range/medium throughput over 900 MHz radio.

Wi-Fi:  Unlicensed wireless networks are often privately owned and operated within the 2.4 GHz and 5.8 GHz bands. The large bandwidth and GHz carrier frequencies mean that these networks are well suited for indoor operation requiring high data throughput.

With their lower transmit power and higher frequencies (high frequencies propagate less distance), unlicensed networks tend to be short-range (300 meters or less) with a medium number of nodes per network (10-50 devices).

As Wi-Fi has matured it has become much more secure and trusted for industrial applications. As such, it has become a popular way to achieve short range and high throughput connectivity; Wi-Fi is often updated and upgraded with improvements to speed and QoS. For most current industrial use cases, IEEE 802.11 g/n are the most popular. (Table 2).

Long Range 900 MHz:  With greater transmit power and lower carrier frequencies (lower frequencies propagate a greater distance), the 900 MHz ISM band is often used for outdoor/long-range applications. While still used for indoor applications as well, large networks of 900 MHz ISM equipment for monitoring distant assets is common. These networks tend to be built in a similar fashion to licensed wireless systems: point-to-multipoint topology, access point antennas mounted high on a tower, remote directional antennas, and large numbers of remote devices (100-200).

Wireless equipment used in the unlicensed band is designed to share the air waves with other equipment. It is important to realize that while the equipment will tolerate interference, performance "mileage" varies depending on how many other networks are operating nearby, with range, throughput, and latency all affected by congested ISM bands.

For industrial outdoor use-cases, the 900 MHz unlicensed band provides a good combination of throughput, range, and robustness. The greater transmit power, lower carrier frequency, and lower bandwidth results in equipment in this band providing reliable long-range communications. The best equipment for this band features frequency hopping, robust receiver design, and several modulation choices - all allowing for reliable communications in this shared spectrum. Since the unlicensed band is characterized by proprietary solutions, performance varies depending on the technology used. Below we show typical performance for equipment designed for outdoor / long-range use (Table 3).

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.

Biographies

Palak Parikh has been with GE Grid Solutions as a product R&D application engineer for the past 6 years. She pursued her PhD at the University of Western Ontario, Canada and her Master’s and Bachelor’s degrees in Electrical Engineering in India.  Palak has proven expertise in Distribution Automation, Power System Protection, & Microgrid Solutions. She has authored more than 25 international journal and conference papers and is a member of the IEEE Smart Distribution Committee.

Justin Smith is a Principal Engineer/Architect with GE Industrial Communications (GE MDS). He has 22 years of experience in wireless product design and development. He has led teams creating both hardware and software through product requirements, technical specification, development, test, and transition to manufacturing. Justin holds a BSEE and MSEE with a concentration in communications and signal processing. His current focus areas include Internet of Things (IOT) and industrial applications running on edge devices.

Michael Pilon is the Senior R&D Engineering Manager for Distribution and Industrial programs at General Electric. He has been with General Electric since 1997. In his 20-year career at GE, he held several positions in product engineering and program management starting from hardware design to entire industrial R&D program management. His responsibilities included electronic hardware design, EMC/EMI compliance, product reliability testing and enhancements, IEC 61850 product interoperability, and managing the product development teams. From voice of customer to product manufacturing, he has been involved in every phase of the product development cycle. Michael holds an Honors Diploma in Electrical Engineering.

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