In the continental United States between 1970 and today, underfrequency relaying schemes have actuated to stabilize the electric power grid less than once every ten years, and have generally prevented wide area blackouts. Although the risk of a wide area blackout caused by insufficient energy production is very low, the consequences are huge. The Northeast blackout of 2003 cost over $5 billion in losses and recovery, and led to the perception that electric utilities are not as adept during a crisis as other industries.
This event also led to a change in regulations and the establishment of the North American Electric Reliability Corporation (NERC) as an industry monitoring corporation. However, even with these changes in place, more must be done to prevent wide area blackouts in the future.
With the increased use of dispersed renewable energy sources, the widespread acceptance of electric vehicles (EVs), and the introduction of smart appliances, innovative and imaginative dynamic frequency controls are needed to maintain the level of performance seen over the last 50 years. EVs provide an opportunity to support the grid during underfrequency events. Let’s take a closer look at the impacts of frequency excursions and an innovative method to prevent wide area blackouts.
Over and Under Frequency Can Lead to System Collapse
In North America, the electric power grid operates at 60 Hertz. Occasionally, frequency rises to 60.02 Hz or dips to 59.98 Hz, but almost all the time, the system operates at 60 Hz. The expected range of operation and expected actions are illustrated in Figure 1.
If frequency rises to 66 Hz, overspeed trips actuate to shut down diesel generators, turbine generators, and other rotating energy sources. This prevents damage to mechanical elements caused by very high centrifugal forces as turbines spin above their rotational speed of 1800 RPM or 3600 RPM.
Generally, electric motors are not equipped with overfrequency protection as electric motors are compact enough to withstand centrifugal forces created by overspeed.
If frequency drops to 59.4 Hz, the first level of underfrequency load shedding occurs. At this frequency, all motors, generators, and transformers continue to operate normally. However, at this point there is concern that the amount of energy consumed is greater than the amount of energy produced, and so the next event will lead to system collapse.
Generally, 10% of system load is shed when frequency drops to 59.4 Hz. An additional 10% is shed when frequency drops to 58.8 Hz and 58.2 Hz. Even at 57 Hz, all motors, generators, and transformers continue to operate normally. In the present practice, underfrequency load shedding is an inconvenience to residences and a financial impact to businesses and factories in the load shed area.
However, if frequency drops below 57 Hz, the turbines that spin the electromagnets used to produce electric energy can be damaged by turbine blade resonance. Therefore, turbine generators are tripped offline when frequency drops to 57 Hz and the electric system collapses.
Electric Vehicles Can Provide Grid Support
As more distributed renewable energy sources are installed, electric vehicles replace combustion powered vehicles, and smart appliances become commonplace, the dynamics of the power system will change. This will present more opportunities to manage frequency excursions.
EV batteries and chargers provide an opportunity for dynamic frequency control. When 10,000,000 EVs are in use, the demand for electric power will increase by approximately 5,000 MW to 20,000 MW from today’s demand. The actual increase varies with miles driven, charger parameters, etc.
Equipping EV battery chargers with frequency sensitive controllers can restore the balance between energy consumed and energy produced. To do this, battery chargers can automatically enter standby mode during minor underfrequency excursions. Chargers can also automatically enter grid support mode during severe underfrequency excursions. For these functions to work, EV batteries must be connected to the chargers to provide the energy needed to support the grid. The 10,000,000 EV batteries can provide an instantaneous boost in energy production from 10,000 MW to 40,000 MW. This philosophical change in operations is shown in Figure 2.
Electric Vehicle Owner Incentives
To create a transparent system, EV owners will know when the grid is using EV energy storage systems to supplement frequency stabilization. They will be notified via their EV app when battery chargers are in standby for 15 minutes when minor underfrequency events occur, or in discharge mode for 30 minutes when severe underfrequency events occur.
Electric utilities should require that all energy storage devices such as EV batteries include automatic frequency monitoring and support. To incentivize EV owners to participate in a frequency stabilization program, electric utilities should:
Provide payments of $5 per month to every EV owner who joins the frequency stabilization program.
Pay EV owners $5 for every frequency stabilization actuation that lasts up to 15 minutes.
With these incentives in place, as well as required frequency monitoring and support in all EV batteries, EVs can easily provide grid support to prevent wide area blackouts when frequency excursions occur. This will significantly reduce the risk of electric system collapse as we embrace a future with more distributed renewable energy sources and increased demand on the power grid.