Understanding the role of Reliability and Resilience in Electric Grid Operations and Planning – GWC Mag

When I committed to write a foundational piece on Reliability and Resilience in the Electric Grid, I thought this would be “cake walk”. My thought was to go to the NERC Glossary, find the “official definition” of each term and cut/paste; DONE. As Mark Twain once stated “It’s not the things you don’t know that get you into trouble, it’s the things you know for certain that just isn’t so.” Touche to Mr. Clements! There are no standalone “official NERC definitions” for “Reliability” or “Resilience”.

Ok, this is going to take some work! I will need to construct an understanding of “Reliability” and “Resilience” from the “puzzle piece parts” in the NERC glossary, and my own experiences working at an ISO/RTO, to convey an understanding of and the relationship between reliability and resilience. Let’s start with the terms used to describe the concept of “Reliability”, based on the NERC Glossary as the authoritative source.

Reliability Standard

A requirement, approved by the United States Federal Energy Regulatory Commission under Section 215 of the Federal Power Act, or approved or recognized by an applicable governmental authority in other jurisdictions, to provide for Reliable Operation of the Bulk-Power System. The term includes requirements for the operation of existing Bulk-Power System facilities, including cybersecurity protection, and the design of planned additions or modifications to such facilities to the extent necessary to provide for Reliable Operation of the Bulk-Power System, but the term does not include any requirement to enlarge such facilities or to construct new transmission capacity or generation capacity.

Reliable Operation

Operating the elements of the [Bulk-Power System] within equipment and electric system thermal, voltage, and stability limits so that instability, uncontrolled separation, or cascading failures of such system will not occur as a result of a sudden disturbance, including a cybersecurity incident, or unanticipated failure of system elements.

Resource Planner

The entity that develops a long-term (generally one year and beyond) plan for the resource adequacy of specific loads (customer demand and energy requirements) within a Planning Authority area.

Reliability Coordinator

The entity that is the highest level of authority who is responsible for the Reliable Operation of the Bulk Electric System, has the Wide Area view of the Bulk Electric System, and has the operating tools, processes and procedures, including the authority to prevent or mitigate emergency operating situations in both next-day analysis and real-time operations. The Reliability Coordinator has the purview that is broad enough to enable the calculation of Interconnection Reliability Operating Limits, which may be based on the operating parameters of transmission systems beyond any Transmission Operator’s vision.

System Operator

An individual at a Control Center of a Balancing Authority, Transmission Operator, or Reliability Coordinator, who operates or directs the operation of the Bulk Electric System (BES) in Real-time.

From a consumer perspective “Reliability” translates into one simple concept “The lights come on when you flick the switch”. If the lights don’t come on, then you lack electric reliability.

Now that we know what “Reliability” means we can move on to understanding “Resilience”, again we need to use the puzzle pieces provided by NERC in order to construct the picture.

Disturbance

1. An unplanned event that produces an abnormal system condition. 2. Any perturbation to the electric system. 3. The unexpected change in ACE that is caused by the sudden failure of generation or interruption of load.

Remedial Action Scheme

A scheme designed to detect predetermined System conditions and automatically take corrective actions that may include, but are not limited to, adjusting or tripping generation (MW and Mvar), tripping load, or reconfiguring a System(s).

RAS accomplish objectives such as:

• Meet requirements identified in the NERC Reliability Standards;

• Maintain Bulk Electric System (BES) stability;

• Maintain acceptable BES voltages;

• Maintain acceptable BES power flows;

• Limit the impact of Cascading or extreme events.

The following do not individually constitute a RAS:

a. Protection Systems installed for the purpose of detecting Faults on BES Elements and isolating the faulted Elements

b. Schemes for automatic underfrequency load shedding (UFLS) and automatic undervoltage load shedding (UVLS) comprised of only distributed relays

c. Out-of-step tripping and power swing blocking

d. Automatic reclosing schemes

e. Schemes applied on an Element for non-Fault conditions, such as, but not limited to, generator loss-of-field, transformer top-oil temperature, overvoltage, or overload to protect the Element against damage by removing it from service

f. Controllers that switch or regulate one or more of the following: series or shunt reactive devices, flexible alternating current transmission system (FACTS) devices, phase-shifting transformers, variable-frequency transformers, or tap-changing transformers; and, that are located at and monitor quantities solely at the same station as the Element being switched or regulated

g. FACTS controllers that remotely switch static shunt reactive devices located at other stations to regulate the output of a single FACTS device

h. Schemes or controllers that remotely switch shunt reactors and shunt capacitors for voltage regulation that would otherwise be manually switched

i. Schemes that automatically de-energize a line for a non-Fault operation when one end of the line is open

j. Schemes that provide anti-islanding protection (e.g., protect load from effects of being isolated with generation that may not be capable of maintaining acceptable frequency and voltage)

k. Automatic sequences that proceed when manually initiated solely by a System Operator

l. Modulation of HVdc or FACTS via supplementary controls, such as angle damping or frequency damping applied to damp local or inter-area oscillations

m. Sub-synchronous resonance (SSR) protection schemes that directly detect sub-synchronous quantities (e.g., currents or torsional oscillations) 

n. Generator controls such as, but not limited to, automatic generation control (AGC), generation excitation [e.g. automatic voltage regulation (AVR) and power system stabilizers (PSS)], fast valving, and speed governing

Reserve Sharing Group

A group whose members consist of two or more Balancing Authorities that collectively maintain, allocate, and supply operating reserves required for each Balancing Authority’s use in recovering from contingencies within the group. Scheduling energy from an Adjacent Balancing Authority to aid recovery need not constitute reserve sharing provided the transaction is ramped in over a period the supplying party could reasonably be expected to load generation in (e.g., ten minutes). If the transaction is ramped in quicker (e.g., between zero and ten minutes) then, for the purposes of disturbance control performance, the areas become a Reserve Sharing Group.

From these piece parts we can see that “Reliability” depends on all of the activities that go into providing “Resilience”. Resilience depends on careful planning and diligent operations by the people responsible for ensuring reliability that considers the long term need for electricity demand and the possible disturbance scenarios that can impact the reliable flow of electricity and take the precautions and actions needed to address long term resource adequacy for reliability and “ride through” resilience relating to real-time operational disturbances to ensure that consumers “lights go on, when they flick the switch (Reliability) and will reliably remain on for as long as the consumer desires” (Resilience).

That’s reliability and resilience in action, from the consumer perspective.

People that would like a deeper technical understanding of resilience and reliability and metrics used to measure reliability, like LOLE, are referred to this report from the IEEE “Resilience Framework, Methods, and Metrics for the Electricity Sector”, PES-TR83.

Many thanks to Ryan D. Quint, PhD, PE, Founder and CEO, Elevate Energy for his review of this article and providing a pointer to the IEEE report cited above, PES-TR83.