Data centres |
NERC analysis of a large load loss incident and its data centre implications
NERC (North American Electric Reliability Corporation) has published a new incident review examining an event in the Eastern Interconnection of the USA in July 2024 that demonstrates the risks and challenges posed by the increasing integration of voltage-sensitive large loads, such as data centres and cryptocurrency mining facilities, into the US Bulk Electric System (BES). The review underscores the vulnerability of these loads to voltage disturbances, which could have significant reliability implications
During the July 2024 incident, a 230 kV transmission line fault led to customer-initiated simultaneous loss of approximately 1500 MW of voltage-sensitive load that was not anticipated by the BES operators. The electric grid has not historically experienced simultaneous load losses of this magnitude in response to a fault on the system, NERC notes. The grid has historically been planned to deal with large generation losses but not for such significant simultaneous load losses.
Simultaneous large load losses have two effects on the electric system, NERC says. First, frequency rises on the system as a result of the imbalance between load and generation. Second, voltage rises rapidly because less power is flowing through the system. In the July 2024 incident, the frequency did not rise to a level high enough to cause concern. The voltage also did not rise to levels that posed a reliability risk, but operators did have to take action to reduce the voltage to within normal operating levels. However, as the potential for this type of load loss increases, the risk of frequency and voltage issues also increases, NERC observes, and operators and planners should be aware of this reliability risk and ensure that these load losses do not reach intolerable levels.
Frequency 60.05
60.04 60.03 60.02 60.01 60.00 59.99 59.98 59.97
Frequency rises to 60.047
22 000 21 000 20 000 19 000 18 000 17 000 16 000 15 000 14 000 13 000
Approx. 1500 MW load lost
The load did not come back immediately
Instantaneous
Figure 1. System load (source: NERC)
The incident in more detail At 7 pm Eastern on 10 July 2024, a lightning arrestor failed on a 230 kV transmission line in the Eastern Interconnection, resulting in a lasting fault that eventually “locked out” the transmission line. The auto-reclosing control on the transmission line was configured for three auto-reclose attempts staggered at each end of the line. This configuration resulted in six successive system faults in an 82-second period. The protection system detected these faults and cleared them properly. The shortest fault duration was the
initial fault at 42 milliseconds, and the longest fault duration was 66 milliseconds. The voltage magnitudes during the fault ranged from 0.25 to 0.40 per unit in the load-loss.
Coincident with this six-fault disturbance, the same local area saw an approximate 1500 MW of load reduction. See Figure 1. None of this load was disconnected from the system by utility equipment; rather, the load was disconnected on the customer side by customer protection and controls. It was determined that the 1500 MW of load reduction was exclusively data centre type load. The area where the disturbance occurred has a high concentration of data centre loads. Frequency and voltage rose due to the load loss. See Figures 2 and 3. Frequency rose to a high of 60.047 Hz and settled back to 60.0 Hz in about 4 minutes. At the highest level, voltage rose to 1.07 per unit. Operators removed shunt capacitor banks in the local area to return voltages to normal operating values.
7/10/2024 6:45:00 PM 30.00 minutes Figure 2. Frequency at time of load loss (source: NERC) 26 | May 2025|
www.modernpowersystems.com 7/10/2024 7:15:00 PM
Causes of load reductions NERC had discussions with data centre owners/ operators to understand the specific cause of their load reductions. NERC determined that the data centres transferred their loads to their backup power systems in response to the disturbance. Data centre loads are sensitive to voltage disturbances. The data centre protections and controls are designed to avoid equipment outages in the event of voltage disturbances. In addition to the computer equipment at these facilities, cooling equipment is also critical
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7.11.2024 23:00
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