The electric grid needs to adapt to meet the forthcoming Electric Vehicle load.

 

The demand for electricity has been stable for years, or even decreasing with our electronic equipment getting more efficient. However, with the advent of Electric Vehicles, Electric Heat Pumps, Large Data Centers, the demand for electricity will surge in the years ahead, and our power grid today is not ready to meet this increasing demand. Typical Electric Vehicles charging at homes are done at 5kW-10kW, these essentially double the size of the electric load for a home.

The challenge for the electric utilities to be able to meet this doubling of electric load due to electric vehicles. The electric utilities are also challenged in ways the utility cannot practically go ahead and double the capacity of the power grid without having significant increases in the electric rates. Below discusses the strategies for utilities to enable electric vehicles.

Planning- Electric utilties needs to innovate its grid forecasting and planning process to granulary indentify where the electric vehicles are being connected to the grid. A nible utility will be able to identify where exactly where the grid is already constrained and areas where the electric vehicles will likely happen, for example- high way exits, hotes, parking lots, specific neighborhoods. Knowing where, when, and how many the electric vehicles are being connecting to the grid is important first step for the utility.

Time of Use Rates- The utility then can offer tools that offer smart charging to incentivize specific behaviors to alletiave grid constraints. These includes options such as offering Time of Use rates, Managed Charing, Demand Charges and other flexible charging.

 

Image Credit: ESIG

Each of these options have their strengths and weaknesses. While a Time of Use rate can solicit a strong response from the customers, in a sceneiro of mutiple EVs in the system where are all programmed to charge at the time of use rate starts on, then this stacks all of the EV load at the same time that can be larger than what the grid can provide. A better solution is to stagger the EV load during the offpeak time.

Image Credit: ESIG

Managed Charging- Managed charging options provides a nimble approach than time of use rate where the utility can provide incentives to charge at a specific time. These could be provided on a staggered time such that all the EVs don’t start charging at the same time.  

 

Automated Load Management- In an advanced scenario, the utility or the third party can provide a dynamic charging, the grid capacity is shared dynamically with the EVs such that each EVs are charged but the total capacity does not exceed the utility’s existing capacity. They can sense which EVs need more charge or prioritize specific vehicles based on need or other profile.

 

Building  new infrastructure- The flexible charging options only work successfully to the existing limit of the infrastructure. There is also decreasing marginal gain from each additional vehicles that are added with flexible charging. After a level, the utility will need to go ahead of size the systems larger with planning that more EVs will coming online in the future.

 

The integration of Electric Vehicles into the grid presents significant challenges. By adopting innovative planning techniques, implementing smart charging strategies, and investing in infrastructure, utilities can manage the increased demand effectively, and support the electrification of transportation that has been a long time coming. 

Detecting and Managing Energized Downed Conductors

Detecting energized downed conductors in utility distribution systems remains an challenge problem. When there is downed energized conductor, in many cases, the electric utility is not aware of the issue until it is reported. Meanwhile these downed energized conductor poses serious safety hazard causing electrocution when contact with humans or in some cases can result in an wildfire. The challenge in detecting energized downed conductors lies in the fact that when a wire is down, it does not draw much current creating a high impedance fault which usually does not trigger imbedded protection systems. Storms and car accidents are common causes of downed wires as shown in image below.

Image Credit:Downed Wire Safety (Unitil)

The amount of current drawn in a downed conductor depends on the soil type. Grounded downed conductors typically carry 10-20A, which is below the typical fuse rating of 80A, preventing the fuse from being activated. Normal relays are not effective in detecting such low impedance faults.

The existing prevent use of single phase reclosers also add to this issue, because the recloser, only sees a fault, but will now know that the conductor has broken and thereby the recloser will continue activate  to try to clear the circuit and continue to energize the line. 

There are new technologies that are being developed to address this issue. Advanced relays, AMI meters, and algorithms that analyze current signatures are being currently being explored. One such algorithm called "arc sense" examines cycle-to-cycle variations to detect these impedance faults.

Other technologies that work with Advanced Metering Infrastructure (AMI) can help identify voltage losses, which are then reported to the recloser through an Outage Management System (OMS). In cases where SCADA indicates the recloser is closed but the OMS reports an outage, it indicates a live downed wire.

To effectively track downed conductors, utilities require AMI, outage visualization, and SCADA on the distribution system. However, not all devices provide outage notifications, and many utilities struggle to accurately track the number of downed conductors. For most utilities, it is challenging to track downed conductors. In most case, the utilities don’t have a special code restoration code to track downed conductors.

To address these challenges, it is crucial to track downed conductors, understand their location and cause, and implement detection technologies. Overall, detecting and managing energized downed conductors requires a combination of technological advancements, regulatory attention, and proactive measures to ensure the safety and reliability of utility distribution systems.

Grid Forming Inverters is key to enable 100% Renewable Grid

  

Given the existential threat[1] of climate change, our electric grid needs to shift away from carbon fuel resources to a renewable power resource. Traditional hydrocarbon based generation systems are based on rotational kinetic energy that are synchronized with the frequency of the power grid. This synchronous provide rotational inertial energy to the power grid that can withstand small voltage or frequency fluctuation in the power grid providing a foundational characteristic of a stable power grid. Replacing these Synchronous generation system with renewable energy systems such as PV, wind, or storage that are Inverter Based Resources (IBRs) reduces the rotational inertia in the system thereby reducing the ability of the power grid to stabilize.

Traditional IBRs are “Grid Following (GFL) Inverters” depend of the grid frequency to synchronize it output. These GFL IBRs output current  that is synchronized to grid. On the otherhand the Grid Forming (GFM) Inverters can make its own voltage waveform which helps to maintain system voltage. GFM IBRs can provide very fast responses to the disturbances in the power frequency to help maintain the frequency of the power grid thus providing increased inertia to the grid. These GFMs can also provide blackstart capabilities to the grid.

As the grid becomes more saturated with IBRs, there is need to include more GFMs IBRs. A new metric – “voltage forming ratio”- quantifies the how saturated the power grid with IBRs. This ratio is calculated by dividing the Output of Inverter Based Resources (IBR) by Total Generation capacity. There is a liner decrease in stability of the system with penetration of GFL IBRs, however to keep the grid stable, the GFL should be a serious concern around 60 percent penetration. These depends on the system characteristics, types of disturbances, and the location of the grid. GFM can increase stability of grid in all these scenarios of high penetration of IBRs.

The GFM IBRs are an emerging technology that has yet to see mass adoption. While GFM IBRs have demonstrated their potential they are challenges of standardization before they replace GFL IBRs. The capabilities and the functionality have not been standardized. The vendors and manufacturers need to work on the interoperability in order to increase adoption of GFMs.

To work on this issues of interoperability, group of industry, government, and researchers have created a group UNIFI (https://unificonsortium.org) that is seeking to address the challenges of integrating GFM IBRs in the grid. By developing uniform specifications and technical requirements to cover GFMs for all IBR applications, it will address the challenges of interconnection, integration and interoperability of these systems.

The proposed specifications for GFMs can be divided into two categories- 1) Requirements during Normal Grid conditions, and 2) Requirements Outside of Normal Conditions. Under normal conditions, the GFMs can change its output based on the grid conditions and dispatch energy, but also provide damping to the voltage to stabilize frequency and thereby increasing the strength of the grid. During operations outside of normal conditions, the GFMs can provide ride through by injecting current during and after a voltage sag to aid in voltage recovery. During asymmetrical faults, the GFMs can maintain a balanced internal voltage. In case of the abnormal frequency, the GFMs can aid in the frequency recovery and stability. Other features can include islanding, black start, regulating harmonics and others.

As these capabilities are standardized, then it will make it easy for the GFM IBRs to have mass commercialization thus enabling the transition to 100% renewable energy to power our grid.

---

[1] https://www.un.org/sg/en/content/sg/statement/2018-09-10/secretary-generals-remarks-climate-change-delivered