Em resumo, o estudo mais citado/conhecido pelo Departamento de Energia dos EUA sobre este tópico concluiu que a adoção mais rápida de veículos elétricos exigirá um pouco mais de investimento nas redes elétricas locais, mas muito menos do que as pessoas pensam, e também indicou que a utilização inteligente da energia elétrica pode ajudar a economizar 30% desse investimento. No estudo que abrange cinco estados, os autores estimaram aproximadamente $2,3 bilhões de custo com carregamento não gerenciado e $1,6 bilhões com os gerenciados em despesas de distribuição de 2027 a 2032. Isso equivale a cerca de 3% de todo o dinheiro gasto pelas empresas de utilidade nesses estados para distribuição no período dado.
A pesquisa não é uma regulamentação nem significa que cada uma das estações de carregamento tenha que instalar um novo transformador. O estudo fornece um modelo detalhado de distribuição de carga elétrica e expansão de equipamentos necessários para esse propósito. Este documento abrange todos os aspectos principais que se deve considerar ao estimar se os pontos de carregamento e as subestações precisam de atualizações como parte do programa de carregamento de veículos elétricos do DOE.
Quanto à independência, a Subian Electric é uma empresa de manufatura especializada na produção de transformadores e subestações. Não há conexão entre nós e o Departamento de Energia e todos os resultados da pesquisa do DOE não podem ser interpretados como endosse de qualquer empresa ou seus produtos, incluindo os nossos.
O que o Relatório de Atualização de Distribuição de Carregamento de Veículos Elétricos do DOE realmente encontrou
Quem realizou o estudo e o que ele modelou
O relatório do Estudo de Impacto da Eletrificação do Transporte em Múltiplos Estados, comumente abreviado como TEIS, foi lançado no mês de março de 2024 e produzido pelo Laboratório Nacional de Energia Renovável, Laboratório Nacional Lawrence Berkeley e a empresa de análise de rede Kevala com assistência do DOE. Os pesquisadores modelaram a demanda de eletricidade em nível de parcela nas redes de distribuição na Califórnia, Illinois, Nova York, Oklahoma e Pensilvânia, escolhidas devido às suas várias combinações de espaços urbanos e rurais, designs de redes, tecnologias de transporte de carga e políticas relacionadas a veículos elétricos.
Os autores compararam duas situações futuras para o ano de 2027 e outra situação bastante semelhante no ano de 2032. Ou seja, no cenário de Ação, o esquema de eletrificação de veículos avança através de uma das opções de conformidade com os requisitos federais de emissões de veículos considerados em 2023 para ter 55 milhões de veículos elétricos instalados até 2032. O cenário Sem Ação resulta em instalações menos eficazes de veículos, ou seja, 41 milhões de veículos. Nos cinco estados analisados, os números totais de veículos são 20 milhões e 16 milhões, respectivamente, o que implica uma diferença de 3,9 milhões. Ambos os cenários foram desenvolvidos com tecnologia de carregamento não gerenciado, o que significa que os veículos recebem eletricidade em carga total logo após serem conectados.
Os Números Principais
Todos os valores abaixo são incrementais, significando a diferença entre os cenários de Ação e Sem Ação, e estão em dólares de 2023.
| Descoberta | Resultado de cinco estados |
|---|---|
| Investimento incremental em rede de distribuição, carregamento não gerenciado (2027–2032) | Cerca de $2,3 bilhões |
| Investimento incremental em rede de distribuição, carregamento gerenciado | Cerca de $1,6 bilhões (30 por cento menor) |
| Participação do investimento anual atual em distribuição nos cinco estados | Cerca de 3 por cento |
| Ativos de rede incrementais, carregamento não gerenciado | 8 subestações de distribuição, 125 alimentadores e 30.000 transformadores de serviço |
| Redução nas necessidades de ativos com carregamento gerenciado | Subestações cerca de 50 por cento, alimentadores cerca de 40 por cento, transformadores de serviço cerca de 30 por cento |
| Portos de carregamento incrementais necessários até 2032 | 2,3 milhões, dos quais 97 por cento são portos AC |
| Investimento combinado em carregamento e rede | $12,0 bilhões, dos quais $9,7 bilhões são equipamentos de carregamento e $2,3 bilhões são atualizações de rede |
| Benefício líquido vitalício para o consumidor dos veículos incrementais | $33 bilhões, mais de 2,5 vezes o investimento em infraestrutura |
Existem dois pontos mais sutis que podem não ser facilmente apreciados. O primeiro é representado pela situação estudada no relatório com campos de subestações, bancos de transformadores e transformadores de serviço finalizando as operações de construção em 2027 para fechar a lacuna de demanda de 2032 e que as atualizações dos alimentadores ainda estão em progresso em 2032. Assim, pode-se ver que os alimentadores permanecem como a questão aqui. O segundo ponto importante é que o custo aumentou em graus semelhantes mesmo em estados muito diferentes: no cenário não gerenciado, o custo da distribuição de energia aumentará em 3,3-4,3 por cento até 2032.
O que o Relatório Não Diz
É tão importante interpretar esses números corretamente quanto citá-los com precisão. A pesquisa foi focada apenas em subestações, alimentadores, transformadores e linhas de distribuição. Portanto, os custos de geração e transmissão não foram contabilizados. Os cinco estados criam uma boa compreensão, mas não representam todas as circunstâncias em todas as concessionárias. A modelagem incluiu apenas carregamento residencial e de frotas, enquanto ignorava outras cargas não-EV nos mesmos circuitos, os autores chamam as economias de conservadoras. O estudo não aloca encargos de rede para usuários de EV ou outros clientes que utilizam a mesma capacidade.
Como o Estudo Decidiu Quando um Transformador, Alimentador ou Subestação Precisa de uma Atualização
A informação que tem máxima aplicação para engenheiros no relatório é baseada não no custo que é mencionado no título, mas na forma como tal custo foi calculado. A Kevala foi capaz de calcular a carga de pico horária em cada nível da rede e definir algumas regras claras mostrando quando um equipamento está sobrecarregado e o que pode ser usado como substituto.
| Nível da rede | Teste de sobrecarga utilizado no estudo | Correção modelada |
|---|---|---|
| Subestação de distribuição | Carga de pico acima de 100 por cento da capacidade | Adicionar um banco de transformadores de 30 MW a subestações abaixo de 100 MW, ou um banco de 35 por cento da capacidade para as maiores; se ainda sobrecarregado, construir uma nova subestação, tipicamente de 60 MW |
| Alimentador | Carga de pico acima de 100 por cento da capacidade térmica | Primeiro transfira a carga para alimentadores vizinhos onde possível; caso contrário, adicione um novo alimentador de cerca de 11 MW (até 15 kV), 24 MW (16 a 25 kV) ou 30 MW (26 a 35 kV) |
| Transformadores de serviço | Pico agregado de todos os transformadores de serviço em um alimentador acima de 125 por cento de sua classificação combinada, excluindo carregamento rápido em CC | Adicione transformadores de serviço de 50 kW para cobrir a carga extra |
| Locais de carregamento rápido em CC | Cada local com carregamento rápido em CC | Um transformador de serviço trifásico dedicado dimensionado a partir da potência do carregador, contagem de portas e um fator de diversidade |
O artigo de pesquisa também detalhou os custos dos componentes. Para a Califórnia 2032, o custo médio publicado para construir novas subestações foi de cerca de $30 milhões, $10 milhões para a construção de um novo banco de transformadores de subestação, cerca de $611.000 para a construção de um novo alimentador, aproximadamente $20.000 para um transformador de serviço do tipo convencional e $50.000 para um transformador de serviço dedicado a um centro de carregamento rápido. Embora esses sejam custos esperados, eles dão uma ideia de quão rapidamente os custos estão aumentando. O tempo segue o mesmo padrão. Referindo-se a outras pesquisas, o relatório afirma que um projeto de carregamento com duração de 3 a 10 meses pode ganhar um ano se precisar atualizar seu alimentador e até 4 anos para uma atualização de subestação.
Os Efeitos do Carregamento de VE em Cada Camada da Rede de Distribuição Elétrica
The electrical distribution network has three distinct levels and EV charging creates different forms of disruption in each one. The most valuable information for planning purposes is to know which of these levels is the bottleneck, as responses differ for each of them.
Failures of the Service Transformer
The service transformer refers to the unit mounted at either the top of a pole or resting on the ground. Its main responsibility is to transform voltage from a medium level to a low one that can be used by customers of a given community including homes or car stations. The service transformer usually serves several customers, up to about a dozen, and hence becomes the first one to encounter the issue of clustered charging stations. The transformer is based on the need to meet the demands of all residents of a community living in homes; but this solves little in case several stations of 7-11 kW power pull the trigger at the same time.
Feeder Thermal Constraints
A feeder is the medium-rated voltage circuit which usually has 12.47 KV, 13.2 KV or 24.9 KV in North America and 10, 11, 20 or 33 KV in other countries. It can run out of capacity either when its load reaches the thermal limit or when the level of voltage on the load side changes dramatically. The triggers typically include fast charging hubs, truck depots and other places of charging where one charging station consumes more power than a whole area of residential buildings.
Substation Capacity Limitations
A substation consists of two or four transformer banks. Substation operations are the least likely to be undermined by extensive home charging; however, this is one of the most expensive and time-consuming processes of upgrades.
How EV Charging Load Differs by Site Type
The same amount of energy can be easy or hard for the grid to deliver depending on how concentrated it is and when it arrives. The TEIS appendix estimates the distribution upgrade cost attributable to each type of charger, which gives a useful sense of scale.
| Site type | Typical charger power | First pressure point | Modeled grid upgrade cost per charger, 2032, unmanaged / managed |
|---|---|---|---|
| Single-family home, Level 2 | 7 to 11 kW | Shared street transformer | About $1,500 / $1,300 |
| Workplace, Level 2 | 7 to 19 kW | Building or site transformer | About $5,000 / $5,200 |
| Public fast charging, light-duty, 150 kW | 150 kW | Dedicated site transformer, sometimes the feeder | About $29,700 / $27,400 |
| Public fast charging, light-duty, 250 kW | 250 kW | Dedicated site transformer and feeder | About $48,700 / $44,200 |
| Truck depot, 150 kW DC | 150 kW | Feeder and sometimes substation | About $47,100 / $38,000 |
| Public heavy-duty charging, 1.5 MW | 1.5 MW | Feeder and substation | About $256,600 / $187,400 |
Two notable trends emerge. The price per charger increases substantially with power, and managed charging has the highest advantage when vehicles remain parked for long periods of time, such as depots, while making almost no impact at workplaces with a steady load throughout the day. This confirms the study’s major finding that the greatest savings to the grid derive from residential spaces and fleet depots where charging can be scheduled without inconveniencing the driver.
How to Size a Distribution Transformer for DC Fast Charging
Many projects either oversize their transformer or undersize it. Oversizing occurs when the nameplate ratings for every charger are summed to calculate the size leading to wastage of capital, while ignoring losses and the coincidence of chargers sizing results in undersizing. Proper sizing of DC fast charging transformers occurs between these two extremes since it relies on clearly defined assumptions.
Charger Nameplate vs Real Grid Demand
Normally a charger will be rated for DC output. But since the grid must supply that output along with conversion losses, the AC input must be greater in value than the DC rating. In addition, not all chargers deliver their full power at any time as vehicles come at different levels of charge and charging power is reduced when the battery is filled. A lot of the sites also have a system-level limit and share power among the dispensers.
Diversity Factors Used in the DOE Study
The TEIS team sized each fast-charging site’s dedicated transformer by multiplying charger power and port count by a diversity factor that depends on charger size, vehicle class and the number of ports. For light-duty sites, the factors were:
| Charger power per port | Up to 3 ports | 4 to 8 ports | More than 8 ports |
|---|---|---|---|
| 50 kW | 1.0 | 1.0 | 1.0 |
| 150 kW | 1.0 | 1.0 | 0.5 |
| 350 kW | 1.0 | 0.75 | 0.5 |
| 500 kW | 1.0 | 0.75 | 0.5 |
It was assumed that small sites would operate at full capacity, while diversity only came into play on larger sites with high-capacity charger installations. The considerations are only assumptions in modeling, but they are a good verification tool to validate one’s own calculations. In the USA, article 625 of NEC puts EV chargers into the category of continuous loads and that affects the rating of both customer-side conductors and protective devices.
Worked Example: Eight 180 kW DC Fast Chargers
Consider a public hub with eight 180 kW DC chargers. Assume a 70 percent coincidence factor enforced by the site’s load management, 95 percent charger efficiency, a 0.98 input power factor and a 15 percent design margin for growth and auxiliary loads such as lighting, cooling and payment systems.
| Passo | Cálculo | Resultado |
|---|---|---|
| Coincident DC output | 8 × 180 kW × 0.70 | 1,008 kW |
| AC input power | 1,008 kW ÷ 0.95 | About 1,061 kW |
| Potência aparente | 1,061 kW ÷ 0.98 | About 1,083 kVA |
| With 15 percent margin | 1,083 kVA × 1.15 | About 1,245 kVA |
| Next standard size, IEC practice | Round up | 1,250 kVA |
| Next standard size, North American three-phase pad-mount | Common ANSI ratings step from 1,000 to 1,500 kVA | 1,500 kVA |
The factor of coincidence determines the parameters of the project more than anything else. If the site is run at the loading of 50%, the value will be about 889 kVA, which would require the supply of 1,000 kVA of capacity, regardless of the system. In the case of running the site under load at 100% and without load management, the required capacity is about 1,779 kVA, which would call for 2,000 kVA. This influence is the reason why load management should be determined first, rather than done after ordering the transformer. Remember that this example is just an example, not a design – real project includes the measurement of harmonics of the chargers’ power electronics, transformer impedance, and levels of short-circuit currents, ambient temperature, and electric utility regulations.
When Is a Feeder Upgrade Needed Instead of a Bigger Transformer?
A larger transformer can be useful at a site but it will not solve issues concerning an already overloaded feeder. This is a point that often confuses people as the developer owns the transformer while the utility has the control over the feeder.
An upgrade to the electrical system for electric vehicle charging will be necessary if the following three issues occur: the new load increases the electric load that the feeder can carry; voltage levels at the end of the circuit are beyond the legal limits; or according to the utility’s hosting capacity study or interconnection study, the circuit cannot accommodate the new load without any negative effect on other consumers. As for the approach taken by the Department of Energy that pioneered the idea, the utility’s representatives focused on shifting loads to the feeder that has enough capacity before they even think about building the new circuits.
Thus, one of the lessons for developers is inescapable: work on feeders usually requires more time and costs more in comparison to switching transformers, and sometimes even means that new digging or overhead work needs to be carried out on a site. There is also an idea to get in touch with the utility in advance to check on the loading capacity before making a decision to make a purchase.
Is it Possible for Managed Charging and Battery Storage To Delay Grid Improvements?
Yes, usually, and that is the main finding from the study carried out by the Department of Energy. Managed charging is meant to transfer or redistribute loads from other power sources so that existing infrastructure is able to handle the loads required. Research has indicated that managed charging can allow for a reduction in the peak electric load due to electric vehicles by about thirty percent and contribute to the need for construction of new substations, feeders, and transformers by about fifty percent, forty percent, and thirty percent respectively.
Time-of-Use Pricing and Dynamic Load Management
The most basic approach is the so-called time-of-use pricing, which means that users are incentivized to charge vehicles after the peak period in the evening. More advanced approaches allow for dynamic load management, which permits power management in real time by limiting the load in terms of performance of various charging points. In this instance, modified software can allow for effective use of transformers by distributing workload over time and limiting the total load on transformers.
Flexible Connection to the Grid
An upcoming method is the so-called flexible connection to the grid (first introduced in a paper published in 2024 by the Office of Electrical Power of the Department of Energy). This approach permits connections to charging stations before construction of facilities is completed, based on the condition that electrical charge of the facilities is reduced in fixed situations of overload. Several Californian and some northeastern states have piloted this approach and connected the electrical loading for public charging on the charging vehicle stations.
Battery Storage for Peak Shaving
A battery energy storage system is put into use at the charging station where it receives charging exposure from the grid at a slow pace when traffic is low and vice-versa where it actually discharges when activity is heavy. This enables the station to offer more power than the grid itself allows. Energy storage is useful in the locations where peak periods are short and predictable. A battery energy storage system adds its own components like a power conversion unit, devices for protection, etc. Our guide to the subestação compacta de armazenamento de energia explains how the PCS, transformer and medium-voltage switchgear fit together in these projects.
When Hardware Upgrades Are Still Unavoidable
Management has limitations. If a facility has a set energy requirement each night, scheduling may help reduce the peak load but won’t lower the total consumption. Charging a battery is not possible if the load already exceeds the supply capacity since the battery can’t recharge. There is limited flexibility for a DC fast charging station that needs to serve any vehicles arriving at that time. Results from the US Department of Energy show that managed charging is not effective. In Oklahoma, where the demand peaks in the morning, postponing charging at night did not ease the situation. In this case, installing a well-sized transformer at the charging location or doing some work on the feeder is the only practical solution.
Choosing the Equipment: Pad-Mounted, Dry-Type or Prefabricated Substation
Pad-Mounted Transformers for Public Charging Sites
In the majority of outdoor charging locations, three-phase pad-mounted transformers are used as standard equipment. Such transformers are mounted on a concrete slab and have a protected enclosure so they can be put near the charging points. Important settings for selection include input voltage, loop or radial power supply, connection configuration, resistance, and effectiveness. Subian Electric manufactures three-phase pad-mounted transformers configured to each project’s network voltage and standard.
Dry-Type Transformers for Indoor and Parking Structures
In instances where invigilators are installed within the underground parking areas, underground garages, or buildings, the fire safety regulations would generally prefer isolation transformers. Hence, the most common option would be cast resin dry type transformers that do not need an oil tank at all and need minimal servicing. Subian’s transformadores tipo seco includes epoxy-resin cast units for these installations.
Prefabricated Substations for Large Charging Hubs
Medium-voltage switchgear, one or several transformers and a low-voltage board are usually required at large hubs and bus stations where charging is combined with solar and storage. A prefabricated substation manufactured in a plant provides everything in one tested enclosure and saves a lot of time when working on the site.Our compact substation guide covers how these units are specified. Subian’s subestação pré-fabricada série YB integrates the three sections in one unit, and for 33 kV networks the company also builds 33 kV compact substations.
IEEE C57 vs IEC 60076 and IEC 62271-202
The two main families of standards should not be mixed, because voltages, ratings and test levels differ.
| Item | North American utility projects | International projects |
|---|---|---|
| Padrão de transformadores | IEEE C57 series, including IEEE C57.12.34 for three-phase pad-mounted units | Série IEC 60076 |
| Prefabricated substation standard | Utility and customer specifications | IEC 62271-202 |
| Typical distribution voltages | 12.47, 13.2, 24.9 and 34.5 kV | 10, 11, 20, 22 and 33 kV |
| Frequência | 60 Hz | 50 Hz in most markets, 60 Hz in some |
| Common three-phase ratings around 1 MVA | 750, 1,000, 1,500 kVA | 800, 1,000, 1,250, 1,600 kVA |
| Approval route | Utility specification and approved vendor list | Type test reports and utility or consultant approval |
Subian Electric builds mainly to IEC standards for projects in Asia, Africa, the Middle East and Latin America. North American requirements can be engineered on a project basis, but voltage, insulation level, configuration and utility acceptance must be confirmed at the start of every enquiry.
What Drives Upgrade Costs and Lead Times?
There is a huge variation in implementation costs of charging sites, from very low in cases of present spare capacity to many millions if the expansion of a substation is required. Major factors in the overall costs of charging site implementation are transformer and switchgear itself; installation costs incurred, which usually exceed hardware costs; costs related to utility make-ready and interconnection; and completion of various reinforcement works. It is important to note that the charging cost estimations are based on TEIS documents, which do not take into account utility-side improvements or on-site storage, which is significant, according to the authors.
The person who pays the bill depends on the ownership boundary. Utility practices vary: the utility bears the costs and owns the equipment before the revenue meter (with transformer sometimes included), while the developer pays for everything behind it in some cases. In some other cases, customer is making the purchase of the needed transformer himself. The earlier the boundaries of the costs responsible for the parties at the project are checked, the fewer chances for budget surprises.
Nowadays, time matters as much as money. Demand growing from sources of renewables, data centers, and electrification can lead to expansion of transformers’ lead time in different markets. Therefore, if a project is waiting for the permits to start the process of equipment ordering, it may wait for a considerable period of time. Hence, it is better to choose standard ratings, to make sure the specifications check is done, and to involve more than one qualified manufacturer.
EV Charging Distribution Transformer RFQ Checklist
Whether you are buying a single pad-mounted unit or a complete substation, sending the same clear brief to every supplier makes quotations comparable.
| Categoria | What to specify |
|---|---|
| Classificações | Primary and secondary voltage, frequency, rated kVA with the load calculation and coincidence assumption behind it |
| Electrical design | Vector group, impedance, basic insulation level, tap range, harmonic loading from chargers |
| Configuração | Loop or radial feed, dead-front or live-front, primary protection, LV outgoing feeders |
| Efficiency and construction | Loss limits under local regulations, insulating fluid or dry-type construction |
| Site conditions | Ambient temperature, altitude, corrosion and flood risk, enclosure protection |
| Standards and documents | IEEE C57 or IEC 60076, routine test reports, type test evidence, drawings |
| Comercial | Delivery time, packing, warranty, commissioning support |
Perguntas Frequentes
What does the DOE EV charging distribution transformer and feeder upgrades report say?
The Multi-State Transportation Electrification Impact Study published in 2024 projected that an additional $2.3 billion distribution investment was required across five states from the year 2027 to the year 2032 with the adoption of unmanaged charging that included 8 substations, 125 feeders and 30,000 service transformers. The amount required to invest in the distribution with managed charging decreased to around $1.6 billion.
Does EV charging always require a transformer upgrade?
No. In most cases, the connections to the home and small sites remain the same. Upgrades may occur where multiple chargers share a single service transformer, where a site implements high-power DC fast charging, or where a fleet depot has numerous vehicles in one location.
What size transformer does a DC fast charging station need?
Charging capacity is determined by the number of chargers, coincidence factor, efficiency as well as power factor. In the example mentioned above, eight 180 kW chargers which have a coincidence of 70 percent require about 1,245 kVA, which amounts to 1,250 kVA as per IEC standard and 1,500 kVA according to standard North American specifications.
Can managed charging avoid a feeder upgrade?
There are times when it happens. The research conducted by DOE proved the reduction of the feeder requirements by approximately 40 percent. Changing or limiting loads helps contain peaks of the load within the feeder’s limits. With versatile connections, some installations can connect before the upgrade is finished, however, an installation with energy demand exceeding the level must be upgraded.
Can battery storage replace a transformer upgrade?
Battery storage can cover short, predictable peaks and let a site deliver more charging power than its connection allows. It cannot replace an upgrade when the site’s average load is already close to or above its grid connection.
Are DOE transformer efficiency standards the same topic?
No. The TEIS document is a grid planning report. The Department of Energy is responsible for the implementation of minimum efficiency standards for distribution transformers sold in the United States through rules issued in 2024 to come into force in 2029. Each is relevant to buyers, however, they are not the same.
Referências
- U.S. Department of Energy: Multi-State Transportation Electrification Impact Study (2024)
- National Renewable Energy Laboratory: Transportation Electrification Impact Study results
- U.S. Department of Energy Office of Electricity: Flexible DER and EV Connections (2024)
- Alternative Fuels Data Center: Procurement and Installation for EV Charging Infrastructure
- Transformador de distribuição, Wikipedia
The DOE research makes one point clear: grids can support large-scale EV charging, provided the right equipment is planned in the right place and load is managed sensibly. When your charging hub, fleet depot or parking project needs a transformer or substation, Jiangsu Subian Electric Power Equipment Co., Ltd. designs and builds pad-mounted and dry-type transformers, prefabricated substations and new energy substations for charging and storage projects, configured to your network voltage and standard. For private-label or distributor supply, see our programa OEM e ODM. Send your charger list, network voltage and site conditions through our página de contato, and our engineers will reply with a sizing check, drawings and a factory quotation.