We’ve come a long way since the first waterwheel in 200 BC. Renewable energy sources now make up about 30% of the world’s generated power and are set to more than double as governments and utilities aim to meet their net-zero emission targets by 2050.
That’s a tall order, especially for utilities with an aging infrastructure and little spare cash to pay for modernization. Still, the demand for integrating renewables, also known as distributed energy resources (DERs), requires utilities to rethink the electric grid.
To start, utilities must consider better communication between control centers, substations, and feeder circuits, as well as speed and intelligence. Field area networks (FANs) will play a significant role in connecting intelligent electronic devices (IEDs) in substations and on feeder circuits, with application and management systems to monitor, control, and protect the grid. Let’s take a look at the implications of driving more DERs through the grid, and how a secure and converged FAN provides real, tangible benefits for utility operators.
DERs are electric power sources, including generation and storage facilities, on the distribution system. Typically small-scale (between 1 kW and 10 MW), sources include solar, wind, and biomass, as well as battery facilities, and they are normally located close to end-users.
While countries around the world are actively encouraging the use of such small-scale renewables with tariffs and other policy tools, most electric grids were not designed for DERs. Therefore, the grid can expect to experience challenges ranging from balancing energy supply and demand to voltage and frequency fluctuations.
This will only worsen with the pressure to interconnect the blossoming micro- and nano-grid industry established to serve discrete footprints, and the growth in bi-directional electricity flows from the so-called “prosumers”—those who both consume and produce energy with such sources as rooftop solar panels (Figure 1), electric vehicles, and home batteries.
The complexity is further compounded by the unpredictability of weather, which causes DER generation variability. This is one of the biggest worries for a grid that demands continuous, intensive oversight of DER infeed conditions, such as voltage and frequency, at the interconnection point with the grid to maintain electricity balancing and help ensure grid stability and safety.
The Island Effect
That’s a lot for the grid to chew on, but there is also the hard reality of rules. Plugging any kind of DER into the grid without conforming to the local utility’s regulations is a bad idea.
For example, in a traditional one-way grid, when a fault occurs, remedial actions are usually taken upstream through the operation of reclosers or fuses. Adding DERs at the downstream end can cause issues such as DER islanding, which will in turn require remedial action to be taken locally.
Imagine a scenario where an array of solar panels is attached at the downstream end of the circuit to a traditional substation that is providing power to a neighborhood feeder circuit (Figure 2). If the distribution automation system detects a fault incident in Section 11, it will send trip commands to open circuit breaker (CB1) and recloser (R1) to isolate the fault. Then, if the solar array inverter does not detect island formation, it would still feed power through the point of common coupling (PCC) and into circuits downstream from the recloser. This creates an electrical island—a hazard for the line crews dispatched to deal with the fault, as well as for the local electrical equipment on that section of the feeder, which can experience out-of-range voltage and frequency.
Direct transfer trip (DTT) is one way to protect against this islanding. Originally designed for high-speed tripping of generator and substation circuit breakers, in this situation, after a fault is detected, DTT sends a trip command to the downstream switch S1 telling it to open along with the circuit breaker and recloser—stopping the DER from energizing the feeder.
This is where a converged field area network (FAN) can make a real difference. These trip commands must be delivered in fewer than two seconds to prevent any damage to the grid. That means the quality, resiliency, and security of the communications channel carrying those commands is critically important.
A converged FAN combines an IP/MPLS field router with a private LTE network, which allows the network to wirelessly bring a broad range of distribution automation applications to utility poles, low-voltage substations, DER sites, grid-connected intelligent electronic devices (such as reclosers and line switches), and more. Specifically, the converged FAN not only delivers the essential attributes needed for DTT but also all the other grid communications, including end-to-end multi-fault network resiliency, deterministic quality of service for assured data delivery, any-to-any multi-point connectivity for improved machine-to-machine communications, and cybersecurity defenses.
Benefits of an ADMS
Advanced distribution management systems (ADMSs) are being deployed by many utilities to improve the resiliency and reliability of distribution systems. Fault location, isolation, and service restoration (FLISR) is a critical ADMS application that is growing more prevalent. In fact, a U.S. Department of Energy study found that FLISR reduces the number of customers interrupted (CI) by 55% and customer minutes of interruption (CMI) by 53%.
With traditional FLISR applications, reliable communications are essential. A line sensor, such as a supervisory control and data acquisition (SCADA) remote terminal unit or an advanced metering infrastructure (AMI), sends a message to the FLISR controller to indicate a service interruption. Working together, the distribution and outage management systems can locate the fault, determine line switches, or have circuit breakers isolate the section. When able, power is re-routed to downstream users through an alternative substation, limiting the effect of the outage to only the users on the isolated sub-circuit.
With the addition of DERs, this scenario becomes more complicated. The DERs can also contribute to faults—meaning there are multiple locations to isolate, which is more than older FLISR systems can manage. This is where the significance of an ADMS really comes into play.
By knowing the DERs’ exact configuration, one can use the ADMS software to model the more complex system to correctly carry out the restorative actions. Centralized ADMS FLISR applications require significant bandwidth to handle multi-way communications with IEDs in the substation and on feeder circuits to collect data and send instructions once the fault(s) are located and appropriate actions determined. A converged FAN can support flexible any-to-any communications to meet this complex need.
FLISR is also relevant in helping more quickly detect downed power lines, which are being implicated in some of the worst forest fires of this century. Ignitions occur when distribution and transmission network components fail. This often happens because of high-strain conditions, often associated with winds, or electrical contact and arcing.
Detecting and de-energizing falling conductors before they hit the ground is key to mitigating wildfires. A converged FAN, leveraging IP/MPLS and private LTE/5G, can also carry real-time synchrophasor data for the distribution automation controller to detect and de-energize fallen power lines. In fewer than two seconds, a snapped line can be detected and isolated while in mid-air before it sparks on the ground, significantly mitigating the threat of widespread destruction and injury or death.
Moving Forward from Here
The robustness of the grid becomes even more mission-critical with the electrification of the public, residential, transportation, and industrial infrastructure, especially as climate change, which is producing more high winds, flooding, and fires, poses a threat to continued grid operation. DERs’ renewable energy will be a vital way that utilities can provide carbon-neutral energy generation, but they impose new issues for distribution management that can be solved with the help of converged FANs, which bring together the best of IP/MPLS, optical fiber, and private LTE networks.
The argument for a converged FAN is compelling. It not only supports smart grid applications—it will significantly reduce operating expenses by consolidating multiple legacy FANs into one. At a time when cybersecurity is a clear concern for utility executives, the converged FAN also offers strong symmetric key encryption to protect against cyber threats. As renewables take on greater and greater importance, converged FANs offer an integral communication platform for grid modernization strategies to meet net zero, maximize grid reliability, ensure public safety, and more.
—Dominique Verhulst is Global Head of Utilities at Nokia.