The electrical grid is an interconnected network designed to produce and deliver electricity to consumers. It consists of generating stations,  high voltage transmission lines that deliver electricity to sub-stations, and distribution lines that  deliver power to homes, schools and business.

MISO's Responsibilities 

MISO is a Regional Transmission Organization (RTO) responsible for doing three things:

1. Managing the generation and transmission of electricity across high-voltage lines located within its region
2. Facilitating the buying and selling of electricity within its region
3. Planning the MISO region grid of tomorrow

MISO's role as a grid operator is similar to an air traffic controller. Air traffic controllers manage the movement of planes from point A to point B safely and reliably 24/7/365. They don't own the planes, they don't own the runways, they don't own the terminals. They simply manage themovement of planes.

Instead of planes, MISO operators manage the movement of  electricity from where it is generated, across the high-voltage lines, to your local utilities.  MISO does not own the generators, the transmission towers, or the transmission lines. Our members do.

MISO's responsibility is to ensure the right amount of electricity is generated and transmitted to our member utilities safely and reliably 24/7/365. It is the utilities responsibility to deliver the power to their customers.

Learn more about MISO and the Electric Industry on our Industry Foundations page.

MISO communicates and partners with its members every day to ensure power is flowing and the lights stay on. During abnormal conditions, such as severe weather impacting the grid, MISO operators may need to rely on a set of emergency procedures or "tools" to keep power flowing and protect the bulk electric system. Implementing emergency procedures enables operators to access resources not available under normal grid conditions. These resources include, but are not limited to, reserve and/or emergency generation, importing emergency power, and working with member utilities to reduce power usage. When electricity supply can longer meet demand, the only step available to avoid wide-spread outages, and to protect the system from long-term damage, is to temporarily interrupt power to consumers. This step, known in the electric industry as load shed, is a last resort option and is rarely used.

When it appears electricity supply will be "tight," MISO notifies member operators of what we are seeing, what we expect to see, and what actions operators need to take. MISO posts these notifications on its website at the bottom of the home page. They can also be viewed on the MISO app.

The Grid Conditions gauge on the homepage shows current grid conditions based on available capacity (supply). Movement of the needle from “Green” is triggered by a control room market capacity related notification. The yellow wedge represents alert and warning notifications. The orange and red wedges represent Energy Emergency Alerts.   

MISO’s emergency operating procedures establish requirements and instructions for members during supply and transmission shortages. Load shed is the last-resort action necessary to maintain grid reliability during system emergencies. MISO and its members play critical and distinct roles in executing load shed events. 

What is load shed, and why is it necessary? 

Load shed prevents widespread, long-duration power disruptions and catastrophic electrical equipment damage. This is a consistent practice among all grid operators and is codified in the NERC standards. It is the final step in our emergency procedures, deployed only after all other options are exhausted. It prioritizes electricity for demand that can be served using available generation and transmission while initiating outages for unserved demand. 

Emergency procedures, including load shed, are necessary in real-time when forward planning and market procurement mechanisms fail to meet demand. If supply and demand are not balanced within about 30 minutes, grid frequency destabilizes, activating protection schemes that trigger automatic generation and transmission shutdowns to prevent extensive blackouts. The grid’s stability relies on maintaining a constant 60Hz frequency, directly tied to the supply-demand balance.  

When would MISO shed load?

Load shed is initiated during critical emergencies, such as severe weather events, unexpected generation or transmission losses, or system constraints that create significant imbalances between energy supply and demand or transmission constraints. These scenarios could include generation shortfalls or transmission issues that cannot be resolved through standard congestion management processes. Most MISO-directed load shed events have been during extreme winter weather events or hurricanes.   

In a supply shortage, also known as a capacity emergency, a load shed reduces the electricity demand to restore balance across MISO’s footprint or specific sub-areas affected by transmission limitations. A load shed reduces the electricity demand in a sub-area for transmission emergencies to avoid overloading transmission facilities. Instances of MISO-directed load shed are at the end of this memo. 

What is MISO’s role in load shed events? 

MISO is responsible for directing load shed actions by communicating required demand reductions to each Local Balancing Authority or Transmission Operator, monitoring implementation, and coordinating additional steps to prevent uncontrolled blackouts. Load shed amounts are calculated, allocated among affected entities, and communicated for prompt execution. MISO provides the amount of load to shed, and the Local Balancing Authority or Transmission Operator determines which specific loads will be interrupted to meet that instruction.    

MISO actively communicates with all members and neighboring regions to manage risks associated with generation and transmission challenges, using tools such as conservative operations, congestion management and maximum generation warnings.  

What is the role of MISO’s Local Balancing Authorities and Transmission Operators in load shed events? 

MISO’s Local Balancing Authorities and Transmission Operators are responsible for identifying the load to be shed, executing the load shed instructions immediately upon receipt, and maintaining the load reductions until MISO terminates the instruction. They are expected to have automated or manual processes in place, coordinate with their transmission and distribution teams to avoid outages for critical infrastructure (e.g., hospitals and natural gas), and manage customer impact, such as rotating blackouts, when following MISO’s directives. 

How does MISO ensure its preparedness for executing load shed events? 

MISO prepares for load shed events through regular drills and exercises to ensure readiness to issue a load shed instruction and membership preparedness to execute that instruction. MISO discusses load shed scenarios during our annual hurricane, power system restoration, market capacity, and cold weather drills. Additionally, MISO holds monthly load shed drills with member operations personnel to ensure that load shed systems are functional and that members can respond quickly to MISO’s instructions. These exercises help identify areas for improvement in communication and execution, fostering a proactive approach to managing potential emergencies. 

MISO, as a Regional Transmission Organization, has a specific role to play, and specific "tools" it may rely upon, when it comes to power restoration. 

Power Restoration Role and Responsibilities

MISO’s primary role during a power grid restoration in its region is to serve as a facilitator during the restoration process: coordinating, exchanging information, and maintaining stability.

MISO is responsible for the collection and exchange of information, as well as communication and coordination with the impacted entities.  Additionally, MISO is responsible for working with our impacted members to coordinate getting the power flowing again across the grid while maintaining stability so as to prevent a re-collapse of the system.

MISO also coordinates with its neighbors to ensure stability throughout the restoration process.

Restoration "Tools" or Procedures

MISO operators can rely on a number of emergency procedures to ensure grid stability and reliability during restoration. These "tools" can include sending emergency notifications and declarations to member operators in the MISO region. Some of the notification and declarations that could be issued include:

• Transmission Advisory
  • This communication tool is used for situational awareness. The message informs members that, based on projected system conditions, there may a transmission issue that will require specific actions to be taken in order to ensure reliability.
• Local Transmission Emergency
• This declaration identifies a specific entity or entities and provides instructions for mitigating a transmission emergency for a specific area of the grid
• Transmission System Emergency
• This declaration provides instructions for mitigating operating emergencies on the Transmission System that have the potential to exceed a pre-defined system operating limit that could lead to instability or outages.