Advantages of Sub-1 GHz Connectivity for Grid Asset Monitoring, Protection and Control

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Advantages of Sub-1 GHz Connectivity for Grid Asset Monitoring, Protection and Control [Copy link]

The evolution of the power grid requires the addition of wireless connectivity to existing wired connections for asset monitoring and control. The main factors for increasing wireless connectivity include:

• Adopt a decentralized microgrid model with distributed energy resources used together with traditional power generation, transmission and distribution.
• There is an increasing demand for health and status monitoring of remote distribution and automation assets, and the health and status monitoring of primary equipment is supervised to optimize power management; resource allocation; fault location, isolation and service restoration ( FLISR ). Grid remote monitoring helps achieve efficient operation of the grid, reduce the number and duration of power outages, and minimize losses.

Data analysis of grid assets can help operators quickly identify faults while also enabling predictive maintenance of critical equipment, which is almost non-existent today. Deciding which specific wireless technology to adopt, such as Sub- 1 GHz , Bluetooth Low Energy , Wi-Fi , or a multi-standard protocol, depends on factors such as data, bandwidth, distance between nodes, number of connections required, available power, and required response time.

In grid assets, nodes located in remote areas such as fault indicators need to be connected to a data collector, as shown in Figure 1 , for automatic data exchange with a centralized system. In such applications, wireless communications such as sub- 1 GHz are chosen because of its wide range (tens of meters to kilometers) and very low power consumption (tens of microamps average). Sub- 1 GHz is also an easy-to-configure, low-cost technology when adding multiple nodes in the field, using a common collector to obtain data on demand from remote devices.

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Figure 1 : Connecting a fault indicator to a data collector using sub- 1 GHz

Adding sub- 1 GHz connectivity involves two-way communication with data collectors in a star network. Nodes are configured to have faster response times to communicate fault information, conveying fault information including location with minimal delay, thereby providing faster recovery or self-healing capabilities.

Sub- 1 GHz offers these advantages over other wireless connectivity solutions, including 2.4 GHz Bluetooth low energy communications :

• The communication range is longer due to the use of lower transmission frequencies and data rates, since the receiver sensitivity is a function of the data rate. As a general rule of thumb, reducing the data rate by a factor of four doubles the communication range.
• Low-frequency (longer wavelength) radio frequency ( RF ) waves are able to penetrate obstacles, which makes sub- 1 GHz work well in a variety of environments.
• The low duty cycle allowed in sub- 1 GHz RF regulations reduces interference.

One of the common grid terminal devices using sub- 1 GHz connections is the fault current indicator ( FCI ) for medium and high voltage transmission. The FCI is powered by harvesting power from the load current. It can be used to harvest currents in the range of tens of microamperes. The biggest challenge in integrating connections with FCIs is whether it can work properly when there is no load current to harvest power. In addition, the requirement to operate under a wide range of environmental conditions (such as line of sight, obstacles, etc.) also limits the use of traditional capacitors or certain batteries. Therefore, it is crucial for RF communication to simplify data transmission to reduce current consumption, which is achieved by optimizing the communication mode between the node and the collector.

There are two modes for managing data transmission ( TX ) and reception ( RX ): beacon mode and non-beacon mode. In non-beacon mode, the sensor node is always in receive mode because there is no defined time when the data collector can communicate with it, which translates into higher current consumption (about 5 mA ). In addition to optimizing the transmission power level based on the distance between the nodes, beacon mode communication (see Figure 2 ) is most suitable because it can implement duty cycle cycling between wake-up mode and sleep mode on the sensor node to help save power when the transceiver is turned off.

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Figure 2 : Beacon mode communication

Beacon mode involves broadcasting a beacon from the data collector at fixed intervals, which all sensor nodes can receive. It synchronizes the communication between individual sensor nodes and the collector. The sensor node wakes up only when it receives a beacon, and deciphering the beacon provides information to the sensor if the collector wants to send or receive data before the next beacon. This process allows the sensor to switch to sleep mode during the transition, which is ideal for fault indicators.

TI reference design for adding connectivity to FCI

Designers face many hardware and firmware challenges when integrating sub- 1 GHz connectivity into FCI .

Integration of low power RF involves:

• Network settings.
• Use beacon mode for both sending and receiving.
• Data exchange including configuration and over-the-air firmware upgrades.
• Fault identification and data communication.

How to minimize power consumption between the fault indicator and the data collector by:

• Current consumption data is currently provided for the U.S. ( 915-MHz ), ETSI ( 868-MHz ), and Chinese ( 433-MHz ) bands.
• RX current is less than 6 mA and TX current is less than 16 mA (at +10 dBm ).
• Ability to achieve average current consumption of less than 20 μA with a 5 s beacon interval ( fault indicator configured in RX mode) in a star network .

This reference design uses TI 's SimpleLink Sub- 1 GHz devices for connecting multiple nodes over short distances, and the 15.4 stack built on the SimpleLink microcontroller platform . It provides a single development environment with code portability to multiple connection protocols. It is a ready-to-use, easy-to-update low-power connection solution that helps solve the challenges associated with node firmware development.

Sub- 1 GHz is a simple, easy-to-use and install, cost-optimized way to add wireless connectivity to existing grid assets, making legacy assets more reliable and providing faster fault response.

Are you working on any form of grid connection? What challenges do you face? Let us know your views in the comments.