Power up grid operations with wireless connectivity

[ad_1]

This second blog in our series on wireless for smart networks explores the critical role of substations in power transmission.

Wireless technology enhances substation control with its flexibility—in latency, performance, and ecosystem economies of scale—and is central to the modernization of the energy grid. LTE and 5G provide an upgrade to the patchwork of communication systems interconnecting elements of the power grid today and provides viable options as the power grid is modernized from time-division multiplexing (TDM) to resilient, reliable, multi-functional packet-based infrastructure.

To set the stage for the role of wireless in grid modernization, let’s first understand a simplified view of the major functional aspects to the power grid described in Figure 1.

  • Generation of electricity occurs at the power plants, where coal, gas, wind, solar and nuclear energy are transformed into electricity in the power grid.
  • Transmission substations ensure that generated power is efficiently distributed through substations, by working with multiple sources of power generation.
  • Distribution substations get the electricity into our industries, offices and homes.

Transmission substations control the input of the power into the distribution grid. This control could be through isolation, or switching of power generation sources using breakers, switches and relays. Distribution substations ensure continuity and reliability of power towards industrial, commercial and residential consumption by switching in power sources based on demand and fault detection/isolation.



Components in the power grid: Power plant, step-up transformer, tower, transmission substation, home, transformers, and distribution substation

Figure 1: The Power Grid

To understand the applicability of 4G and 5G to the power grid, let’s now look at some of the voltage levels addressed by substations in different parts of the power grid. The higher the power/voltage, the more critical the latency requirements are for direct control of substation equipment. 

Using North American voltage classes as an example, power is usually generated at about 69kV at the power generation stations. Transmission substations, located closer to power stations, step this up to 138kV–768kV to minimize transmission losses over long distances, and for interconnection towards other power grids. Closer to the consumers, distribution substations step the transmission down to 26–69kV to cater to three classes of consumers (industrial—11kV–69 kV; commercial—4kV –11kV; residential—120V–240V). 

Transmission substations implement the vital function of active voltage and reactive power management of power generation resources. Multiple transmission power lines converge at these substations to interconnect a few generation locations and multiple distribution locations. 

  • Distribution substations implement consumption-focused functions related to demand response in order to address a continuously varying consumer load.
  • Distributed energy management is implemented to balance power generation feeds across both traditional and sustainable resource power grids to avoid overloading the distribution grid on a sunny or windy day. Other aspects handled by the distribution grid include management of the Electric Vehicle (EV) charging infrastructure and automation functions supporting Advanced Metering Infrastructure (AMI) and building and home automation.

Devices like isolators, circuit breakers, and reclosers are used as part of the continued balancing act between availability of power on the generation grid and consumption on the distribution grid.

  • Isolators are used to disconnect power sources when availability exceeds consumption, or to connect additional generation sources when consumption exceeds switched power.  
  • Circuit breakers and relays protect the infrastructure by disconnecting the overloaded transmission line to protect the grid from damage. 
  • Reclosers temporarily isolate paths at distribution substations, caused by weather or conditions like falling trees or branches.  The reclosers test the integrity of the isolated line after a short time period, and resume distribution if, for example, the fallen tree branch is no longer causing a danger on the line.

Devices operating at high voltages in substations need to operate quickly to minimize the danger of sending high voltage on a compromised transmission line. Mesh networks are often custom-built based on the use cases above, and lack the consistency, flexibility in latency offered by a single multipurpose private LTE network.

Enhancing connectivity to substations:

Communication and wide area networks today are used for the following important functions in the power grid:

  • Grid management and telemetry: These systems are designed for centralized control and SCADA. The round-trip latency for centralized control is relatively relaxed (50–100ms), and well within the capabilities of the 20–80ms latencies available on LTE networks. A private LTE network provides the flexibility to carry multiple classes of traffic like voice and control simultaneously, with the necessary priority and pre-emption of traffic. 
  • Teleprotection: This is a power grid protection concept for monitoring the condition of the grid, isolating faults and preventing damage to critical parts of the power grid. It involves direct control of the devices described above that carry high voltages and requires round-trip latency of the order of 10–20 ms to allow for instantaneous fault isolation. This can be achieved with dedicated 4G wireless transport like microwave today, or with 5G NR bearers using high-band spectrum.

In Figure 2, centralized Human Machine Interface (HMI) functions implement the grid management and telemetry, while the remote substation implements many of the teleprotection functions.



LTE replaces slower-speed broadband lines as performance needs increase at substations.

Figure 2: LTE replaces slower-speed broadband lines as performance needs increase at substations.

Wireless networks—For grid management and use case convergence

With the understanding of the distinction between transmission substations and distribution substations, it’s easier to appreciate the advantages of wireless private networks for management of power utilities based on the substation use case.

Transmission substations could be located in remote areas—where the hydroelectric, nuclear or coal/gas power generation is located—far away from the control centers. Long-haul wireless provides connectivity between the transmission substation and the established wide area network that monitors the power grid. Wireless technologies like long-haul microwave can be used instead of expensive fiber upgrades or can replace low-speed links with higher-performance interconnections of transmission and distribution substations. The latency and performance offered by long-haul wireless is an important first step towards grid transport modernization. 

Distribution substations could be closer to population centers—closer to the consumption. A private LTE network would add capabilities of wireless 4G or 5G solutions to enhance or expand existing data connections and offerings. Wireless would also add a layer of reliability to the operational communication needed to monitor and control the substation, as many of these devices are already reliant on a backup public wireless network, which would now be replaced by a better-designed, predictive private wireless network.

Looking at the same set of substations from a performance standpoint, use cases such as smart video monitoring require a ramp up in performance characteristics, with either an expansion of existing transport capabilities towards a remote monitoring center with expensive fiber, or more flexible expansion with Citizens Broadband Radio Service (CBRS) PAL-based private wireless.

The same private wireless system enabling scaling of superior performance also allows for integration of employee devices with private enterprise features. When the sensors and substation IEDs, remote terminal units (RTUs) and relay systems migrate towards wireless, we will see integration of grid management and corporate communication into the same mobile devices. This decreases operational complexity at utilities, bringing the IT and OT worlds closer together. 

Extending the reach of substation equipment for teleprotection



Components of a teleprotection system

Figure 3: Components of a teleprotection system

Going back to the short introduction above on voltage levels, we see a wide variation at different points of the power grid—generated 69kV stepped up to transmitted 768kV down to distributed 11kV/4kV/120V. Teleprotection depends on a responsiveness of 5–10ms one-way from the network to protection equipment and switching gear like isolators, relays, switches and reclosers. The associated mission-critical resilience and reliability should be an integral part of the private wireless network. 

Local functionality is usually deployed at individual substations to address these latencies, with the associated lead times for action after fault isolation. With the right combination of wireless 4G/5G low latency solutions coupled with Artificial Intelligence/Machine Learning (AI/ML) solutions, we can extend the reach of teleprotection beyond the local substation to more central locations.

In the short term, while utilities are driven by an LTE-device ecosystem and spectrum assets, microwave connectivity can be used to extend this millisecond responsivity outside the substation. The use of AI/ML applied to system behavior at the substations will allow for proactive fault isolation. In the longer term, development of the device ecosystem for wireless technologies like 5G NR and higher band spectrum would allow for remote control of mission-critical switching infrastructure with 5–10ms latency. This will allow for scaling and centralizing of mission-critical substations control from more central…

[ad_2]

Read More:Power up grid operations with wireless connectivity