Impacts

The influx of EVs will exacerbate existing issues and create new burdens for utilities of all sizes across the country. EVs heavily impact circuit efficiency and maintenance due to heavy phase unbalance and immense coincident load. The longevity of grid equipment will be compromised and outage consequences will worsen as electrification accelerates. On the other hand, increased grid equipment capacity, enhanced demand response and revitalized standards could mitigate the majority of these risks.

Current Phase Unbalance

EV charging loads on the end‑of‑the‑line single‑phase laterals can lead to extreme phase unbalances in the absence of proper planning for these loads.

In Figure 1, the system is perfectly balanced in the base case, with the same load on A, B and C. Phase A receives distributed generation, decreasing current demand. Enough generation can cause reverse power flow on this phase. Phase C receives EV load, increasing current demand. As a result, the current unbalance is exacerbated by the combination of new load and generation rather than either alone.

In cases of extreme phase unbalance, we encounter two issues:

• Protection coordination strategies generally assume voltage unbalance of less than 3%. Unbalanced phases lead to fuse preloading, which results in miscoordination of fuses with other protection devices. Additionally, line‑to‑line single phase loads do not generate the ground fault current necessary to trip the ground relay.
• Three‑phase motors and variable speed drives are designed to operate most efficiently on a balanced three‑phase system. As the system becomes unbalanced, motor operation and efficiency suffer. A voltage unbalance of 5% causes temperature increases in excess of 25%.

An analysis of data from a mid‑sized investor‑owned utility in the United States shows poorly balanced circuits in a sample area have 12% phase unbalance at the service transformer on a summer night without EV charging. As EV load increases on these circuits, phase unbalance can increase to above 250%. When measured at the meter under no‑load conditions, a circuit should maintain a voltage unbalance of less than 3% (current unbalance of about 15%), according to American National Standards Institute (ANSI) 84.1‑2020.

Coincident Peak Load

Across the U.S., EV adoption as of 2021 stood at less than 1%, with market share hovering around 2%. Conservative estimates project that the market share should increase to 12% and 29% by 2025 and 2030, respectively. These levels of market share translate to adoption levels of approximately 2.4% in 2025 and 7.5% in 2030. Honda plans to stop selling gasoline‑powered vehicles entirely by 2040. At adoption levels as low as 5%, the peak demand on a circuit can increase 20%. At 20% EV adoption, the peak demand on a distribution circuit can easily double, as typical charging times align with peak summer air conditioning usage and increased electric heating during the winter.

Evening charging is not the only concern. EVs can charge at any time of day. These vehicles can charge in business parking lots, parking garages and at work during the daytime, leading to very clustered intermittent demand. At night, passenger vehicles charge at residential homes on single‑phase lateral lines. Similarly, parking garages and transport depots will have multiple chargers in a concentrated area. To reach 1 MW of load, a parking garage would only need 70 Level 2 AC chargers.

EV charger ratings are increasing every year. At first, AC Level 1 charging had approximately 1.5 kW of demand. However, the 2020 Tesla Gen 3 Wall Connector is now capable of 11.5 kW. In addition, Ford and GM have announced production of electrified SUVs by 2024, and the home charger could be upgraded to 19.2 kW.

Overloading a typical suburban residential transformer is a highly plausible scenario. In this case, four residences with two‑car garages are assumed to have 7 kVA of average baseload served by a 50 kVA transformer. Just three electric sport utility vehicles (SUVs) could place an extra 60 kVA on the transformer already carrying 28 kVA baseload, bringing the transformer to 88 kVA (176% loading). In a worst‑case scenario, each home purchases two electric SUVs, resulting in an overloading of approximately 376%. When field crews replace this transformer, it won’t be long before they need to return. On the example circuit in Figure 3, at 30% EV adoption, 85% of transformers were loaded to 120% or greater (71 overhead transformers and 35 pad‑mounted transformers). Based on pricing from Figure 4, replacing the overloaded transformers on this circuit would be expected to cost between $2.4 million and $3.2 million. That’s just the price tag at 30% EV adoption.

The 25 kVA transformer is the most common in the U.S. Since a single transformer feeds multiple homes, more than six electric vehicles could charge on a transformer. Considering transformer problems arise with two vehicles to a transformer, and even one per transformer causes issues at a distribution level, several measures will be required to prepare for EVs.

How to Prepare for It?

EVs represent significant challenges and opportunities. 1898 & Co. uses a strategic methodology combining demographic and business data, geographic information systems and circuit models to study potential impacts and create a tailored plan to minimize the cost of adoption and decrease operations and maintenance costs.

Understanding Customers and Increasing Engagement

Such planning includes utilizing communications to gain insights, boost efficiency and develop forecasts:

• Establish meter analytics to identify unregistered EVs and increase customer engagement to forecast EV adoption throughout your service territory.
• Equip customers with easy‑to‑use info on how to charge during off‑peak hours and reduce their energy bill.
• Develop two‑way communication between charging infrastructure and utility control centers. Two‑way communication enables a world of demand response and forecasting options.

Planning and Engineering Solutions

Making the most of existing assets and looking ahead to upcoming needs is a foundation. Also key is implementing updates that can make a difference now and in the future:

• Raise circuit voltages to decrease current unbalance and to serve the added EV load.
• Assess engineering standards for low‑cost improvements that will avoid future maintenance or reinstallation and reduce upgrade costs. For instance, building a single‑phase 15‑kV lateral line with spacing for 35‑kV and poles designed to handle three phases only adds about 10% to the project’s cost. These measures also reduce the need to replace poles and conductor spacing in the future.
• Align utility‑installed distributed generation with coincident load to determine when it can help with demand response.
• Standardize EV risk assessment studies to create custom risk portfolios by circuit.
• Develop resiliency frameworks to assess high‑value resiliency improvement projects. EV risk mitigation happens through this process, which also benefits the overall health of the distribution system.

Due to the very long life cycle of distribution and substation assets (40–80 years), thoughtful standards and business practices are required to prepare for and mitigate the effects of EVs and avoid costly reactive system upgrades.

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