"Power System Automation" original

Time overview

From February 8 to 20, 2021, Texas, USA (referred to as Texas) experienced a power outage caused by extreme cold weather, which is also the fourth power outage caused by extreme cold in the United States in 10 years. In the accident, a total of 1,045 generator sets in Texas and the central and southern United States suffered from failure/reduced power operation/unable to start; the most serious accident occurred from 7:00 a.m. on February 15th to 1:00 p.m. on February 17th, with an average total of 3,400 The 10,000-kilowatt unit was unable to work normally due to various faults, which was about half of the peak load in winter; the accident also caused a total of 23.418 million kilowatts of load to be shut down, which was the largest manual shutdown event in the history of the United States.

In this accident, more than 4.5 million Texas residents experienced power outages, and some residents even suffered continuous power outages in extreme cold for up to 4 days. At least 210 people were killed due to hypothermia and carbon monoxide poisoning. In addition, according to statistics from the Dallas Federal Reserve Bank, the direct/indirect economic loss of Texas caused by the power outage amounted to 80 billion to 130 billion US dollars, and the total output value of Texas in February 2021 fell by nearly 50% compared with January.

Looking back at the entire incident, as early as February 8 and 9, the Electric Reliability Council of Texas (ERCOT), Southwest Power Pool (SPP) and Midcontinent Independent System Operator (Midcontinent Independent System Operator) System Operator, MISO) received an early warning of an approaching cold wave, a large-scale load increase and generator outages hit, but ERCOT still had enough units to provide power supply at that time. On the night of February 14, the temperature further decreased, and the peak load of ERCOT system reached 69.87 million kilowatts. The continuous surge in load and the large-scale outage of generator sets caused the frequency of the entire power system to continue to drop. At 12:18 a.m. on February 15, the system frequency had dropped below the normal line. Therefore, ERCOT was started at 1:20 a.m. Two rounds of 1 million kilowatt loads have been shut down, but the frequency is still decreasing. In the worst case, there is only 9 minutes left for ERCOT to deal with the low frequency problem. Otherwise, the 17 million kilowatt unit may be triggered due to the low frequency. downtime and cause a system blackout. It can be seen that ERCOT's large-scale load rotation was also helpless at that time.

February 14-20 Actual Load/Projected Load/Curated Load Curves in Texas, USA (Source: ERCOT)

To make matters worse, SPP and MISO adjacent to ERCOT are also facing power supply shortages due to extremely cold weather, and the transmission lines between each other are also affected by the weather and suffer frequent failures, so that ERCOT can only receive slightly more power from the adjacent grid at most. 1 million kilowatts of electricity, it is difficult to effectively alleviate the power supply crisis.

Schematic diagram of the connection line between Texas and neighboring regional power grids (Source: ERCOT)

Analysis of the core cause of the accident

The "Report" issued by FERC clearly pointed out that the main reason for the large-scale power outage caused by the extreme cold weather in the central and southern United States is the unplanned outage, reduced power operation and failure to start the power generation side caused by extreme low temperature and freezing rain weather. Fault. Among the faults caused by extreme cold weather counted in the "Report", 44% of the faults were directly caused by extreme low temperature and freezing rain, and 31% of the faults were closely related to the fuel of the generator set. In addition, 21% are low temperature-related internal mechanical system and electrical system faults, such as embrittlement of system components at low temperature; only 2% of the faults are grid-side faults related to power transmission and distribution systems. 

Number of equipment failures caused by extremely cold weather during the accident (by failure cause) 

The fault on the power generation side directly caused by extreme low temperature and freezing rain is the primary cause of the accident. For example, the freezing of fan blades may lead to unplanned shutdown or reduced power operation of wind turbines, the freezing of pressure water column in the control and signal devices of power plants may cause malfunction of the devices, and the freezing of internal liquids such as water supply systems, ventilation systems, and lubrication systems in power plants It may cause the device not to work properly, etc.    

The "Report" pointed out that these power generation equipment susceptible to cold weather should be classified as key equipment, identified by the power generation side in advance and prepared for winter to ensure their normal operation.

In extremely cold weather, the failure of the power generation side caused by the fuel problem of the unit is the second important cause of the accident. In this part of the failure, the failure of the natural gas-fueled unit accounted for 87%, and the failure caused by other fuels accounted for only 13%. On the one hand, the extreme low temperature and freezing rain caused the wellhead of the natural gas well to freeze, and the road transportation conditions also deteriorated, and the maintenance of natural gas facilities could not be carried out normally. Production has dropped sharply; on the other hand, the power supply of natural gas facilities is also facing severe shortages due to power plant failures and load rotations caused by extreme cold weather, which further limits the production of natural gas. The "Report" pointed out that a major negligence when starting the load wheel stop is precisely that natural gas facilities are not used as a key load to ensure its power supply, resulting in a "positive feedback" type of transmission effect. The large number of power generation side failures caused by unit fuel problems are inseparable from the fact that the installed capacity of gas turbines in the south central and Texas regions accounts for more than half of the installed capacity and the tight coupling between electricity and gas energy sources (electricity-gas interdependence) is inseparable.

It is worth noting that the entire accident analysis report did not talk too much about the improper disposal of the three ISOs such as ERCOT, SPP, and MISO. On the contrary, the "Report" clearly stated that during the accident, the three ISOs "were able to sense the real-time status of the power grid efficiently at all times and took appropriate measures to ensure the reliability of the power supply of the power grid".

Implications for China's power and energy industry

1. Continue to strengthen research on the energy Internet. One of the characteristics of the Energy Internet is the deep integration between different energy forms. The power outage accident in Texas revealed that the coupling degree between the two important infrastructures, the power system and the natural gas system, is increasingly deepening, and it is urgent to study the deep interaction mechanism between the two. At the beginning of this year, the National Development and Reform Commission issued the guidance to promote the development of multi-energy complementary. China is currently carrying out extensive basic research, commercial demonstration and engineering application of the integrated energy system, which is in line with this theme.  

Multi-energy complementarity can not only improve the economy of the system under steady-state operation, but also effectively improve the safety of the system under extreme weather conditions.

2. Appropriately increase energy reserves such as natural gas. If ERCOT does not take load rotation shutdown measures, Texas may lead to a larger-scale power outage accident, and once a large power outage occurs, some black-start units will not be able to effectively perform the black-start function due to the lack of natural gas fuel, and the consequences will become more serious. This provides inspiration for the planning and operation of the power system, that is, it is necessary to moderately increase fuel reserves such as natural gas, especially for the fuel reserves of black-start units. At the same time, the configuration of long-term energy storage facilities, such as seasonal energy storage, hydrogen energy storage, etc., should be appropriately increased to cope with the risk of long-term capacity shortage and insufficient power in extreme weather.

3. Give full play to the value of cross-regional power grids. Also located in the central and southern regions of the United States, the two regional power grids, SPP and MISO, have strong tie-line connections with other regional power grids and sufficient power exchange. In this extremely cold weather, the power system was affected. Lighter; while ERCOT was hit hard. One of the important reasons is that ERCOT has only a little over 1 million kilowatts of DC tie lines connected to the external network. One positive and one negative case, the role and value of the cross-regional power grid is self-evident. It is reported that Texas is currently constructing a southern interconnection transmission project, which aims to strengthen the electrical connection between ERCOT and SERC.

Finely assess the power and electricity balance. The power outages in Texas reflect the shortcomings of dispatch agencies in assessing the adjustable power capacity of generator sets. The "Report" pointed out that when evaluating the adjustable power capacity of generators, it is necessary to consider historical weather adaptability, fuel constraints, environmental constraints and the performance of fuel contracts, so that dispatching agencies can more accurately grasp the development of power and power balance. situation. This provides inspiration for China's power supply security work. It is not only necessary to grasp the fuel inventory situation, but also to accurately grasp the future performance of the fuel contract, and take precautions to consider risks. 

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