The power system reliability (sometimes grid reliability) is the probability of a normal operation of the

electrical grid An electrical grid is an interconnected network for electricity delivery from producers to consumers. Electrical grids vary in size and can cover whole countries or continents. It consists of:Kaplan, S. M. (2009). Smart Grid. Electrical Power ...

at a given time.

Reliability indices Reliability, reliable, or unreliable may refer to: Science, technology, and mathematics Computing * Data reliability (disambiguation), a property of some disk arrays in computer storage * High availability * Reliability (computer networking), a ...

characterize the ability of the electrical system to supply customers with electricity as needed by measuring the frequency, duration, and scale of supply interruptions. Traditionally two interdependent components of the power system reliability are considered: * power system adequacy, a presence in the system of sufficient amounts of

generation A generation refers to all of the people born and living at about the same time, regarded collectively. It can also be described as, "the average period, generally considered to be about 20–⁠30 years, during which children are born and gr ...

and

transmission Transmission may refer to: Medicine, science and technology * Power transmission ** Electric power transmission ** Propulsion transmission, technology allowing controlled application of power *** Automatic transmission *** Manual transmission *** ...

capacity; * power system security (also called operational reliability), an ability of the system to withstand real-time

contingencies The American Academy of Actuaries, also known as the Academy, is the body that represents and unites United States actuaries in all practice areas. Established in 1965, the Academy serves as the profession's voice on public policy and professional ...

(adverse events, e.g., an unexpected loss of generation capacity). Ability of the system to limit the scale and duration of an power interruptions is called ''resiliency''. The same term is also used to describe the reaction of the system to the truly catastrophic events.

Economics

Electric grid is an extremely important piece of

infrastructure Infrastructure is the set of facilities and systems that serve a country, city, or other area, and encompasses the services and facilities necessary for its economy, households and firms to function. Infrastructure is composed of public and priv ...

; a single daylong nationwide

power outage A power outage (also called a powercut, a power out, a power failure, a power blackout, a power loss, or a blackout) is the loss of the electrical power network supply to an end user. There are many causes of power failures in an electricit ...

can shave off 0.5% of the country's

GDP Gross domestic product (GDP) is a monetary measure of the market value of all the final goods and services produced and sold (not resold) in a specific time period by countries. Due to its complex and subjective nature this measure is often ...

. The cost of improvements is also high, so in practice a balance is sought to reach an "adequate level of reliability" at an acceptable cost.

Adequacy

Resource adequacy Resource adequacy (RA, also supply adequacy) in the field of electric power is the ability of the electric grid to satisfy the end-user power demand at any time (typically an issue at the peak demand). RA is a component of the electric system reliab ...

(RA, also supply adequacy) is the ability of the electric grid to satisfy the end-user power demand at any time (typically this is an issue at the

peak demand Peak demand on an electrical grid is simply the highest electrical power demand that has occurred over a specified time period (Gönen 2008). Peak demand is typically characterized as annual, daily or seasonal and has the unit of power. Peak dem ...

). For example, a sufficient unused

dispatchable generation Dispatchable generation refers to sources of electricity that can be programmed ''on demand'' at the request of power grid operators, according to market needs. Dispatchable generators may adjust their power output according to an order. Non-disp ...

capacity and

demand response Demand response is a change in the power consumption of an electric utility customer to better match the demand for power with the supply. Until the 21st century decrease in the cost of pumped storage and batteries electric energy could not be ...

resources shall be available to the electrical grid at any time so that equipment failures and fluctuations of power from

variable renewable energy Variable renewable energy (VRE) or intermittent renewable energy sources (IRES) are renewable energy sources that are not dispatchable due to their fluctuating nature, such as wind power and solar power, as opposed to controllable renewable ener ...

sources (e.g., due to wind dying down) can be accommodated. A typical

reliability index Reliability index is an attempt to quantitatively assess the reliability of a system using a single numerical value. The set of reliability indices varies depending on the field of engineering, multiple different indices may be used to characterize ...

for the adequacy is the

loss of load expectation Loss of load in an electrical grid is a term used to describe the situation when the available generation capacity is less than the system load. Multiple probabilistic reliability indices for the generation systems are using loss of load in their ...

(LOLE) of one event in 10 years ( one-day-in-ten-years criterion). Due to the possible need for the actual addition of physical capacity, adequacy planning is long term (for example,

PJM Interconnection PJM Interconnection LLC (PJM) is a regional transmission organization (RTO) in the United States. It is part of the Eastern Interconnection grid operating an electric transmission system serving all or parts of Delaware, Illinois, Indiana, Kentu ...

requires capacity purchases to be 4 years in advance of delivery).

Security

Security is the ability of the system to keep the real-time balance of the supply and demand, in particular immediately after a contingency by automatically ramping up generation and shedding the interruptible loads. Security relies on the

operating reserve In electricity networks, the operating reserve is the generating capacity available to the system operator within a short interval of time to meet demand in case a generator goes down or there is another disruption to the supply. Most power sys ...

. Historically, the

ancillary services Ancillary services are the services necessary to support the transmission of electric power from generators to consumers given the obligations of control areas and transmission utilities within those control areas to maintain reliable operations of ...

(e.g., the

inertial response Inertial response is a property of large synchronous generators, which contain large synchronous rotating masses, and which acts to overcome any immediate imbalance between power supply and demand for electric power systems, typically the electrica ...

) were provided by the spinning machinery of the

synchronous generator In an alternating current electric power system, synchronization is the process of matching the frequency of a generator or other source to a running network. An AC generator cannot deliver power to an electrical grid unless it is running at the sam ...

s, provisioning of these services got more complicated with proliferation of the inverter-based resources (e.g.,

solar photovoltaic A photovoltaic system, also PV system or solar power system, is an electric power system designed to supply usable solar power by means of photovoltaics. It consists of an arrangement of several components, including solar panels to absorb and co ...

s and grid batteries).

References

Sources

* * * *

External links

* {{electric-stub Electricity economics