As DERs rise, watch out for islands in your grid
I’ve attended several utility industry webinars over the past year and one thing I’ve noticed is the growing prominence of distributed energy resources (DERs) in the generation portfolios of many companies. As utilities aim to align with government climate policies, meet their own carbon objectives and satisfy customer demand for green energy, more of them are either developing their own DER capacity or acquiring it from independent power producers. That’s made DER interconnection with the main grid a hot topic of discussion.
Doing it right requires special measures to avoid what’s called “islanding” — but with the right prevention scheme and the right communications network, utilities can indeed provide safe, resilient, high-quality, interconnections.
What’s driving DER growth?
DERs are small-scale power-generation resources (typically 1 kW to 10 MW) located close to end users and connected to a local distribution system. They include renewables such as solar, wind and biomass power, as well as technologies such as energy storage systems — all of which are important to achieving net-zero and carbon-neutral mandates.
To decarbonize their electric grids, countries around the world are actively encouraging the use of small-scale renewables through tariffs and other policy tools. In the United States, where electricity generation accounts for more than 25 percent of greenhouse gas emissions, the Federal Energy Regulatory Commission (FERC) approved Order 2222 in September 2020. FERC 2222 breaks down the barriers to entry for DER aggregators, allowing them to compete in all regional wholesale electric markets across the country. It empowers new energy technologies to come online and participate on a level playing field, which will encourage even further innovation across the energy industry.
The challenges of interconnecting DERs
Some utilities are moving faster than others in response to these trends. Iberdrola is one example of a utility that has gone “all in” on DERs, with recent acquisitions making it the third-largest renewable energy operator in the United States. But whether a utility is a pioneer like Iberdrola or a cautious adopter, they’re all facing challenges as they interconnect more DERs with their grids.
Most electric grids were designed and built decades ago, without consideration for today’s bidirectional flow of energy between substations and DERs. On top of that, renewables are non-deterministic by nature: their power output varies depending on environmental conditions. Utilities need continuous, intensive oversight of DER infeed conditions, such as voltage and frequency, at the interconnection point with the grid (also called the point of common coupling) to inform power balancing and help ensure grid stability and safety.
Without this oversight, if there is a fault in a feeder circuit that is energized by both a substation and DER, utilities could experience unintentional islanding — where a customer is cut off from the main grid but still getting power from the DER. While the main grid can usually absorb and mitigate any fluctuations in reliability or stability present in DERs, in an islanding situation, there’s risk of out-of-range voltages and frequencies. This can lead to poor-quality power for customers, damage customer equipment and, most importantly, put the safety of maintenance crews at risk.
As shown below, when a fault is detected, the adjacent recloser and substation circuit breaker open to de-energize the circuit, with only the DER energizing the homes and businesses along section 12. This creates an electrical island.
Solving the islanding challenge with DTT and a converged FAN
Direct transfer trip (DTT) is one way to protect against islanding — a modification of its original purpose, which was high-speed tripping of generator and substation circuit breakers. After a fault is detected, DTT sends a trip command to the downstream switch telling it to open along with the circuit breaker and recloser. That stops the DER from energizing the feeder.
Because trip commands have to be delivered quickly and reliably — in less than two seconds — to prevent any damage to the grid, the quality, resiliency and security of the communications channel carrying those commands is critically important.
At Nokia, we believe a converged field area network (FAN) is the solution to making DTT better and solving the DER interconnect challenge. A converged FAN combines an IP/MPLS field router with a private LTE network. That allows it to wirelessly bring a broad range of capabilities to utility poles, low-voltage substation and DER sites, grid-connected intelligent electronic devices (such as reclosers and line switches), and more.
Specifically, it is the key delivering the essential attributes needed not just for DTT but all other grid communications: end-to-end multi-fault network resiliency, deterministic quality of service for assured data delivery, any-to-any multi-point connectivity for more efficient machine-to-machine communications, and robust cyber security defenses.
Download our new white paper for the technical details on how a converged FAN delivers these capabilities for DTT-based DER islanding protection — and provides the communications foundation that will further power utilities’ green energy journeys.