Engaging with Large Loads

 

Since 2022, many large electronic-based loads have connected to the ERCOT Interconnection. ERCOT has observed that much of this load exhibits voltage-sensitive behavior and will immediately reduce consumption under moderate voltage disturbances. This has the potential to adversely affect reliability, so ERCOT has been actively monitoring load behavior and considering grid code changes to maintain reliability.

To date, approximately 6,300 MW of large load has been approved to energize through the ERCOT Large Load Interconnection process. ERCOT has worked with utilities to confirm the type of load at these facilities, and the majority consists of cryptocurrency and traditional data centers. The ERCOT Large Load Integration team has monitored and tracked the peak consumption of these operational loads and continues to approve additional loads to be connected to the system once the required studies and interconnection requirements are completed. The table below summarizes the aggregate of peak observed load, approved to energize load, and additional approved load in MWs for cryptocurrency and data center facilities in ERCOT.

Large Load Events

ERCOT Operations began seeing events in the fall of 2022 in which these loads were immediately reducing consumption during system faults. Due to the expected increase of large electronic-based loads within the coming years, ERCOT Operations decided to start identifying and tracking events in which the aggregate of large electronic-based loads reduced consumption by at least 100 MW during a system fault. The chart below shows events from November 2023 to the present that meet this criterion. Twenty-four events were identified, ranging from 102 MW to 432 MW of total reduction, and events included anywhere from one to eight loads that reduced during the fault. System frequency typically increased to the range of 60.02 to 60.04 Hz and recovered within two minutes.

The light-colored portion at the top of the bar for each event represents the total pre-disturbance consumption of all loads that reduced consumption during the fault. The darker lower portion of each bar represents the reduction seen of the affected loads. ERCOT observed a large variance in the percentage reduction of the affected loads during the different events. Potential factors contributing to these large variations could be how low the voltage fell at a given load or varying protection schemes within the facilities. Some events shown in the darker blue bars include a portion of consequential loss in which the load was disconnected from the system as a result of fault clearing and not because of failure to ride through a voltage disturbance.

Understanding Large Load Events

All of the loads involved in the events above were cryptocurrency facilities. ERCOT has not identified an event in which a large traditional data center reduced consumption due to a voltage disturbance at the transmission bus during a system fault. Since large loads are not registered as Market Participants, ERCOT has limited means to perform thorough event analysis for these types of events. From the limited information ERCOT has received through its Request for Information process, when voltage at the transmission bus of a cryptocurrency facility drops below a certain level, typically below the 0.75 per unit range, data mining servers or compute-intensive systems may stop processing or turn off the computing elements of the data mining servers. This is due to voltage at the power supply dropping, and, therefore, being unable to provide stable power during these conditions. This is a notable difference relative to the performance of traditional data centers, which typically maintain their processing during grid voltage disturbances by temporarily switching the load over to UPS systems or backup generation during more severe disturbances. It is unknown to ERCOT whether traditional data centers have been riding through fault events or whether ERCOT has just not identified an event in which a data center transfers its load abruptly over to UPS or backup generation during a voltage disturbance.

Due to the amount of large electronic-based load projected to energize in upcoming years, ERCOT is concerned that these events may become larger in magnitude and begin impacting system frequency and voltage stability. The impacts of events thus far have been minimal, but the potential of thousands of megawatts of load instantly dropping or switching to backup generation during normally cleared system faults could pose significant risks to system reliability. ERCOT is currently performing studies to identify the level of instant load loss the system can withstand before seeing adverse effects of large frequency spikes and overvoltage. In addition, ERCOT has reduced System Operating Limits due to the potential of sudden load loss immediately causing a system violation. System Operating Limits are implemented to prevent voltage instability, uncontrolled separation, or cascading outages by limiting the pre-contingency power flow on a defined interface, usually consisting of multiple transmission lines. Sudden and unexpected loss of load behind an interface can immediately increase the power flow on an interface above the pre-defined limit and, therefore, limits must be lowered, which effectively curtails generation behind the interface.

Mitigating Large Load Events

ERCOT continues to investigate ways to limit the magnitude of the events as more and more large electronic loads connect to the system. To do so, ERCOT must first thoroughly understand the ride-through capabilities of different types of large electronic loads and have these characteristics properly modeled for more accurate studies. ERCOT is working with multiple industry groups, such as the North American Electric Reliability Corporation (NERC) Large Load Task Force and the ESIG Large Load Task Force, as well as engaging with utilities and large load facility owners to understand facility and equipment capabilities and identify the best ride-through, modeling, and study practices. The knowledge gained with these efforts may be implemented in grid codes to reduce the potential for larger events and mitigate associated reliability risks. One ongoing effort is to study specific areas with high concentrations of large electronic loads to understand the potential load loss and determine whether improved ride-through capabilities can be implemented for future projects.

In summary, ERCOT and the industry as a whole have a lot of work ahead to identify and mitigate potential reliability risks associated with large amounts of voltage-sensitive load being connected to the bulk power system. ERCOT is seeing significant loss-of-load events on a regular basis and a potential for larger events to occur in the near future. As more large electronic loads connect to the system, it is essential that the two industries collaborate and identify best practices for limiting the overall loss of load during normal system faults. If ride-through capabilities are not implemented in certain areas, it may necessitate limiting the amount of large electronic load that can reliably connect in these areas.

 

Patrick Gravois
Lead Operations Engineer
Grid Analysis, Operations Planning
Electric Reliability Council of Texas (ERCOT)