Whether caused by an attack on power grid infrastructure, a design deficiency, or human error, wide area blackouts are a threat to electric power grid reliability. They lead to disruption of everything that requires electric power to function, from industrial manufacturing to residential air conditioning and wireless internet.
The risk of wide area blackouts is a critical issue that can be addressed with risk assessments and enhancements to the existing electric power grid. But what exactly is a wide area blackout and why are they cause for concern?
In this new series, I will address these and other questions on the topic of wide area blackouts, as well as upgrades to the electric power grid that can minimize the risk. First, let’s explore what a wide area blackout is, how they occur, and why they are cause for concern.
Wide Area Blackouts Defined
A wide area blackout occurs when part of the electric power transmission system collapses, interrupting the flow of electric power to 250,000 customers or more. This is equivalent to shutting off electric power at 20 large neighborhood substations, leaving all the surrounding neighborhoods without power for several hours to days.
Several well-known wide area blackouts have occurred, including the Northeast blackout of 1965, Northeast blackout of 2003, and the Pacific southwest blackout of 2011. During these historic blackouts, power grid collapse resulted in simultaneous loss of electric power across several states.
The blackouts in 1965, 2003, and 2011 were caused by human error (lack of attention to detail). The northeast blackout of 1965 occurred when circuit breakers connected to five 230 KV transmission lines opened in 2 seconds. The Northeast blackout of 2003 occurred when a 345 KV transmission line sagged into trees while the power grid was experiencing low voltage. The Pacific southwest blackout of 2011 occurred when a 500 KV air break switch was opened at the wrong time.
More recently, the United Kingdom blackout of 2019 occurred when two large generators tripped offline nearly simultaneously. This blackout was caused by a design deficiency.
Luckily, each of these blackouts required minimal repairs and power was restored in less than 24 hours. However, this may not be the case for future wide area blackouts.
What Causes Wide Area Blackouts
Wide area blackouts are caused by mismatches between energy production and energy consumption. During normal system operation, energy produced is equal to energy consumed; this is illustrated in Figure 1, where the beam is perfectly balanced on the balance point.
When customer load increases, the amount of power produced at power plants is ramped up to match energy with load. When customer load decreases, the amount of power produced at power plants is ramped down to match energy with load.
Figure 2 shows power grid operations during fault conditions. When faults occur, the transfer path between energy production facilities and consumers becomes distorted. Additionally, the amount of energy transmitted from production facilities and the amount of energy required by consumers are both reduced. The amount of distortion is a function of initial conditions. The distortions and changes occur in much less than one second.
When faults are cleared, a new transfer path is established. Energy production and energy consumption are increased until a new balance point is established. At this point, there can be one of two potential outcomes: the grid returns to normal, balanced operating conditions; or the grid balance gets further distorted because energy consumption exceeds energy production, as shown in Figure 3.
If a new balance point is not established in a few seconds, a wide area blackout occurs. The amount of distortion is a function of initial conditions and newly established, post-fault conditions.
Important Power System Parameters
A wide area blackout is the result of a combination of three important power system parameters: triggering events, risk factors, and voltage recovery. Let’s take a closer look at each of these three.
Triggering events are tipping points that may lead to a wide area blackout. During normal system operations, energy produced by power plants, windfarms, solar farms, etc., matches energy consumed by homeowners, businesses, and industry. Occasionally, a fault will trigger a mismatch in energy production and consumption. The fault type and duration determine if the fault will trigger a wide area blackout.
A three phase fault on a high voltage facility (345 KV, 500 KV, 765 KV) is the most likely triggering event. Fault duration, the power system response to the fault, is calculated in milliseconds. On the power grid, a 100 millisecond fault is long event, and a 200 millisecond fault is a very long event. The longer the fault duration, the more likely a wide area blackout will result.
Risk factors are variables that influence recovery. Some risk factors include:
System load: wide area blackouts are more likely to occur during peak load conditions when many power generators are operating near their maximum ratings (above 80% of their nameplate rating).
System voltage: wide area blackouts are more likely to occur if system voltage is less than nominal voltage before a fault occurs.
Type of electric power generating facility: traditional generators have voltage controls and speed controls that can quickly increase generator voltage and power output.
Predominant load type: loads, such as fan motors, pump motors, air conditioner motors, and space heaters, respond differently when voltage dips occur.
Spinning reserve, watts: Electric utilities schedule reserve power equal to the nameplate rating of the largest generator that is operating.
Spinning reserve, excitation: Electric utilities need to provide excitation energy to each transformer, transmission line, distribution line, and motor.
Fault induced delayed voltage recovery (FIDVR) is the final consideration. When voltage recovery extends beyond 10 seconds, a wide area blackout is likely.
Table 1 lists important considerations for each parameter:
On any given day, the probability that a triggering event will result in a wide area blackout can be estimated using the values listed in Table 2.
If the sum of the assessed values for risk factors is less than 100, it is unlikely that a triggering event will result in a wide area blackout. If the sum of the assessed values for risk factors is greater than 150, a triggering event will result in a wide area blackout.
Table 3 uses hypothetical risk factors on a future date to illustrate the values outlined in Table 2. On this hypothetical, though realistic, day in August, the power system is operating on the third day of a heat spell where temperatures have been above 90 degrees Fahrenheit. With these risk factors in place, it is very likely that a wide area blackout will occur if a triggering event occurs.
Infrequent But Concerning
Wide area blackouts are infrequent, happening about once every ten years. If they are so infrequent, why are they a concern?
Disruption to essential services, business operations, and industrial production have impacts that persist for days after power is restored. Rivers and streams can be polluted when digesters at sewage treatment plants overflow. Food that thawed in restaurant freezers must be discarded and replaced. Nuclear power plants must be inspected, and limiting conditions of operation must be resolved before power production can resume.
The Northeast blackout of 2003 is estimated to have cost $6 billion. Costs include losses in sales and manufacturing, as well as food and medication that spoiled without refrigeration. The cost to individuals is often not accounted for. When negligence is discovered, individual electric utilities are assessed multi-million dollar civil penalties.
As renewable energy becomes a key source of electric power, wide area blackouts may become more frequent. Although it is difficult to predict when and where a wide area blackout will occur, the conditions that lead to wide area blackouts are well understood.
After wide area blackouts occur in the U.S., the North American Electric Reliability Corporation (NERC) addresses deficiencies. For example, NERC Reliability Standard FAC-08, Facility Ratings, addresses deficiencies that led to the 1965 blackout. VAR-001, Voltage and Reactive Control addresses deficiencies that led to the 2003 blackout. TOP-001, Transmission Operation, addresses deficiencies that led to the 2011 blackout.
NERC’s Reliability Guideline: Improvements to Interconnection Requirements for BPS-Connected Inverter-Based Resource, should likely reduce the risk presented by renewable energy sources. The UK wide area blackout may have been prevented if recommendations listed in NERC’s interconnection guideline were implemented. This guideline, however, only addresses one of the risk factors.
As this series on wide area blackouts continues, we will explore each of these concepts in greater detail. To learn more about Prescient’s wide area blackout risk assessment service, or to discuss the concept of wide area blackouts in greater detail, contact us.