1.1 BAL-002 Disturbance Control Standard

1. BAL-002 Disturbance Control Standard

• Balancing authority (BA) works to maintain the balance of generation, load, and interchange using Area Control Error (ACE).

• A BA must be prepared to handle disturbances, which are defined as unplanned, sudden generation or transmission failures that lead to under-generation.

• Events of this nature are referred to as Reportable Balancing Contingency Events.

• Prior to 2018, these events were known as Reportable Disturbances.

• In the context of this material, the terms Reportable Balancing Contingency Event, Reportable Event, and Reportable Disturbance are synonymous.

• Mnemonics: "BA keeps ACE balanced — but must also handle sudden Reportable Disturbances (a.k.a. contingency events) that cause big under-generation."

1.2. BAL-002 - Disturbance Control Standard

• The purpose of the BAL-002 Disturbance Control Standard is to ensure that the BA (or Reserve Sharing Group) balances resources and demand, then returns ACE to defined values after a Reportable Balancing Contingency Event occurs.

• Important to note that BAL-002 applies specifically to the loss of generation and does not pertain to loss of load, as Contingency Reserve is typically not activated for load loss.

• Mnemonics: "BAL-002: After a big generation loss (Reportable Event), quickly return ACE to normal — only for generation, not load loss."

1.3. Objectives and Purpose

• A BA is responsible for maintaining the balance of generation, load, and interchange via ACE and must also prepare for disturbances.

1.5. Terms Review

• ACE (Area Control Error): The instantaneous difference between a BA’s actual net interchange and scheduled net interchange, factoring in Frequency Bias effects.

• Balancing Contingency Event: A sudden loss of generation, loss of import, or abrupt return of demand (events separated by ≤1 minute) that initiate an unexpected change in ACE or a generation-demand imbalance.

• Contingency Reserves: Capacity that a BA can quickly deploy to respond to a Balancing Contingency Event.

• Contingency Event Recovery Period: Begins when resource output starts declining within the first minute of a Reportable Event and lasts for 15 minutes.

• Contingency Reserve Restoration Period: Lasts up to 90 minutes after the conclusion of the Recovery Period, during which reserves must be restored.

• Disturbance Control Standard (BAL-002): Establishes the timeframe for a BA to return ACE to acceptable limits following a disturbance.

• Most Severe Single Contingency (MSSC): The worst single contingency (measured in MW) identified by system models, causing the largest loss of resources required to serve firm demand and exports.

• Operating Reserve: Extra capacity beyond firm demand utilized for regulation, forecasting errors, outages, and protection; comprises spinning and non-spinning reserves.

• Reportable Balancing Contingency Event (Reportable Event): A Balancing Contingency Event with a MW loss ranging from 80% of MSSC to the full MSSC, triggering BAL-002 requirements.

• Reserve Sharing Group (RSG): A group comprising two or more BAs that collectively maintain, allocate, and share operating reserves to assist each other in recovering from contingencies.

• Mnemonics: "ACE is the balance meter; after a Reportable Event (big sudden loss), use Contingency Reserves in 15 min recovery + 90 min restoration per BAL-002."

1.6. Featured Video

• Contents and details found in the associated featured video are not included in this transcript.

1.7. Reserve Sharing Group

• Reserve Sharing Group (RSG): A consortium of two or more BAs that collaboratively manage, allocate, and supply operating reserves to support one another in recovering from contingencies.

• A BA can fulfill its Contingency Reserve commitments by joining an RSG instead of independently holding all reserves.

• When part of an RSG, members collectively assume the same responsibilities under BAL-002, including monitoring and compliance.

1.8. Operating Reserve Components

Operating Reserve – Purpose & Definition

• Load-Interchange-Generation Balance mandates that BAs and RSGs maintain extra reserve capacity beyond current demand.

• This additional capacity is utilized by the System Operator to accommodate normal demand increases or sudden generation loss (e.g., unit trip).

• Operating Reserve is defined as the capability above firm system demand that covers regulation, load forecasting errors, and equipment failures.

• Mnemonics: "Operating Reserve is the extra cushion that keeps the lights on when demand rises or a generator trips."

Components of Operating Reserve

• Operating Reserve is categorized into two principal types:

  • Regulating Reserve

  • Contingency Reserve

• Mnemonics: "Operating Reserve splits into Regulating (normal fine-tuning) and Contingency (emergency backup)."

Regulating Reserve

• It responds to Automatic Generation Control (AGC).

• It maintains ACE within acceptable limits during standard system operations.

• Must be provided as Spinning Reserve: Generation that is synchronized (online), unloaded, and immediately available for load pick-up.

• Mnemonics: "Regulating Reserve = Spinning Reserve on AGC – always spinning and ready for normal fluctuations."

Contingency Reserve

• This reserve allocates additional capacity specifically for unusual system conditions.

• It is utilized to address loss of generation contingencies (for instance, major generator outages).

• Managed by either the BA or Reserve Sharing Group.

• Unlike Regulating Reserve, it does not have to be spun up or utilized for AGC during standard operations.

• Mnemonics: "Contingency Reserve = Emergency backup for when things go wrong (big generation loss)."

• Overall Summary Mnemonic: "Operating Reserve = Regulating (spinning + AGC for normal ops) + Contingency (extra for sudden outages) – the system’s safety net above demand."

1.9. Contingency Reserve

• Contingency Reserve: The capacity accessible to a BA, which can be rapidly mobilized in response to a Reportable Balancing Contingency Event or Energy Emergency Alerts.

• It is a subset of Operating Reserve comprising:

  • Spinning Reserve (already online and synchronized)

  • Non-Spinning Reserve (capable of being activated quickly)

• Non-Spinning Reserve Includes:

  • Quick-start generation resources (e.g., gas turbines, hydro) capable of becoming operational and synchronized to reach load requirements in ≤10 minutes.

  • Controllable load resources, which may consist of contracted interruptible industrial load or demand response programs.

  • Coordinated modifications to Interchange Schedules (non-firm sales that are adjustable during a contingency).

• All non-spinning resources must be prepared to operate within the 15-minute Contingency Event Recovery Period.

• BAs are required to maintain sufficient Contingency Reserve, complying with the Disturbance Control Standard (BAL-002).

• Mnemonics: "Contingency Reserve = spinning + non-spinning (quick-start gen, interruptible load, or schedule cuts) — ready in 15 minutes for any big disturbance."

1.10. Most Severe Single Contingency

• Each BA or Reserve Sharing Group (RSG) must maintain its Contingency Reserve at a minimum of Most Severe Single Contingency (MSSC).

• MSSC: The most significant single contingency that would cause the largest MW loss of resources needed to meet firm demand and export commitments.

• Typically, MSSC equals the largest generating unit within the BA or RSG area.

• BAL-002 mandates that each BA or RSG:

  • Develop and uphold an Operating Process (as part of its Operating Plan) to identify its MSSC.

  • Retain Contingency Reserve equal to or exceeding MSSC consistently for reliability.

  • Ensure this Operating Process is reviewed and updated on an annual basis.

• Mnemonics: "Carry at least your MSSC (usually biggest unit) in Contingency Reserve — identify it yearly in your Operating Process."

1.11. Contingency Event Recovery Period

• All BAs within an Interconnection are interconnected via tie-lines.

• When a BA experiences a generator loss, it results in a drop in interconnection frequency and subsequent negative ACE for the deficient BA.

• Neighboring BAs automatically assist via Frequency Response (incorporating governor action and load dampening).

• This collective action mitigates frequency decline and stabilizes the grid.

• Assistance from other BAs increases tie-line flows, leading to inadvertent interchange.

• NERC specifies that the deficient BA (or RSG) must restore ACE to acceptable limits within the Contingency Event Recovery Period, defined as:

  • Starts when resource output begins to decrease in the initial minute of a Reportable Event and continues for 15 minutes.

• Employing Contingency Reserve promptly alleviates strain on neighboring BAs and limits disruptions across the overall Interconnection.

• Mnemonics: "Big generator loss → frequency drops, neighbors help via Frequency Response → fix your negative ACE within 15-minute Recovery Period to minimize tie-line stress."

1.12. ACE Recovery

• Following a Reportable Balancing Contingency Event, the Responsible Entity (BA or RSG) is obligated to restore its ACE to acceptable variables during the 15-minute Contingency Event Recovery Period.

• Target ACE is contingent upon the pre-event ACE value:

  • If the pre-event ACE was positive, recover to zero (0).

  • If the pre-event ACE was negative, recover only to the pre-event negative value (do not exceed it).

• If a subsequent contingency occurs during the 15-minute recovery duration, the required ACE recovery amount is reduced by the MW loss attributable to the new event.

• Mnemonics: "After a Reportable Event, bring ACE back to zero (if it was positive) or back to its pre-event negative value — within 15 minutes."

1.13. Reportable Balancing Contingency Event

• The purpose of BAL-002 is to guarantee that a BA or Reserve Sharing Group re-balances its resources and demand following a Reportable Balancing Contingency Event.

• Definition of a Reportable Balancing Contingency Event:

  • Any unexpected loss occurring within a one-minute interval leading to an ACE decline with MW loss:

  • ≥ 80% of the MSSC, and

  • ≤ 100% of the MSSC.

• Each Interconnection has a minimum MW threshold that counts as reportable, even if it is below 80% of the MSSC, with varying minimums across regions:

  • Eastern Interconnection: 900 MW

  • ERCOT: 800 MW

  • Western & Quebec Interconnections: 500 MW

• Examples illustrate this:

  • For the Western Interconnection with MSSC = 800 MW:

  • 80% of MSSC = 640 MW

  • Minimum reportable threshold is 500 MW, so any loss ≥ 500 MW is recorded.

  • For the Eastern Interconnection with MSSC = 800 MW:

  • 80% of MSSC = 640 MW, required to report any losses ≥ 640 MW.

• Mnemonics: "Reportable Event = big sudden loss between 80% of MSSC and full MSSC (or the Interconnection minimum: 900 East / 800 ERCOT / 500 West & Quebec)."

1.18. Multiple Contingencies

• Multiple Balancing Contingency Events occurring within one minute are regarded as a single event.

• If the aggregate MW loss falls between 80% and 100% of the MSSC (or meets the Interconnection minimum), it qualifies as a Reportable Balancing Contingency Event.

• The 15-minute Contingency Event Recovery Period then applies, and compliance with BAL-002 is mandated.

• Example for Eastern Interconnection:

  • If MSSC = 1000 MW and reporting threshold = 800 MW:

  • A 500 MW unit and a 400 MW unit trip within 60 seconds → Total loss = 900 MW.

  • Since 900 MW > 800 MW, it is treated as one Reportable Event.

  • The BA is required to restore ACE to acceptable levels within 15 minutes.

• Mnemonics: "Multiple trips within 1 minute = one event; if total loss ≥ 80% of MSSC, you get only 15 minutes to fix ACE."

1.19. Exemptions from Compliance

• Typically, after a Reportable Balancing Contingency Event, the Responsible Entity (BA or RSG) must revert ACE to acceptable ranges within 15 minutes.

• However, exemptions to this requirement may be invoked under certain conditions:

  • Exemption 1 – Energy Emergency Situation:

  • The BA or RSG (or at least one member) is:

    • Under an Energy Emergency Alert (EEA) as declared by a Reliability Coordinator.

    • Utilizing Contingency Reserve to mitigate an operating emergency according to its Emergency Operating Plan.

    • Having depleted Contingency Reserve below its MSSC; and

    • Must notify the Reliability Coordinator with an ACE recovery plan and target recovery time.

  • Exemption 2 – Single Event Larger Than MSSC:

  • The Responsible Entity faces multiple contingencies considered as a single event, yet the total loss exceeds the MSSC.

  • Exemption 3 – Multiple Events Over Extended Time:

  • The Responsible Entity suffers several Balancing Contingency Events during the cumulative Recovery Period (15 min) + Restoration Period (90 min), and total loss exceeds MSSC.

• Mnemonics: "15-minute ACE recovery is waived if: EEA emergency + notification, one huge event > MSSC, or multiple events over 105 minutes totaling > MSSC."

1.20. Exemption Examples

• Normal protocol mandates that the Responsible Entity must revert ACE within 15 minutes after any Reportable Balancing Contingency Event; however, exceptions can occur:

  • Example 1 – Energy Emergency Alert (EEA):

  • BA has MSSC = 600 MW (80% threshold = 480 MW) on a particularly hot day with elevated load and numerous forced outages.

  • Reliability Coordinator designates an Energy Emergency Alert.

  • BA’s Contingency Reserves drop below MSSC, following the trip of a 500 MW generator, constituting a Reportable Event (500 MW > 480 MW).

  • The BA is exempt from the 15-minute ACE recovery requirement under EEA, but must notify the Reliability Coordinator and provide an ACE recovery plan with a target recovery time.

  • Example 2 – Single Event Larger Than MSSC:

  • The same BA (MSSC = 600 MW) loses a 400 MW unit, followed by a 250 MW unit 30 seconds later.

  • This is treated as a single event—aggregate loss = 650 MW, exceeding MSSC.

  • Excludes the BA from the 15-minute compliance requirement.

• Key Point: In both exemption examples, the BA is still tasked with deploying any available Contingency Reserve.

• Mnemonics: "Exempt if under EEA with low reserves (and notify RC) or if total loss > MSSC — still deploy reserves, but no 15-min clock."

1.21. Contingency Reserve Restoration Period

• After a Reportable Balancing Contingency Event, the Responsible Entity must return ACE to mandated levels within the 15-minute Recovery Period by activating Contingency Reserve.

• The obligation persists even after ACE restoration, as the Responsible Entity must fully reinstate its Contingency Reserve during the Restoration Period, which is typically 90 minutes, commencing immediately after the 15-minute Recovery Period ends (totaling 105 minutes after the event initiation).

Restoration Strategies

• To replenish reserves, BA/RSG can:

  • Activate slower-generating resources (not bound by the quick-start 10-minute rule).

  • Purchase power from external entities.

• The restored reserves must be prepared to allow the BA to address potential subsequent Reportable Events.

• Mnemonics: "15 min to fix ACE + 90 min to restore reserves = be ready for the next contingency."

1.22. Reporting Requirements — CR Form 1

• Following any Reportable Balancing Contingency Event, the Responsible Entity must achieve 100% ACE recovery within the designated 15-minute Contingency Event Recovery Period.

• It must complete NERC CR Form 1 for each Reportable Event, which calculates the percentage of ACE recovery for that particular incident.

• If ACE is restored to the designated value within 15 minutes, this equates to a 100% recovery rate.

• Conversely, if ACE fails to be returned within the 15-minute window, recovery is less than 100%.

• A failure to meet the 100% recovery target often leads to a self-reported violation.

• Mnemonics: "100% ACE recovery required every Reportable Event — document it on NERC CR Form 1 or self-report the violation."

1.23. Reporting Example

• Reporting Event and CR Form 1 Example:

  • With BA's MSSC = 980 MW, Reportable threshold = 784 MW (80% of MSSC), a generator trips at 7:10, losing 800 MW, constituting a Reportable Event (800 > 784 MW).

  • The BA activates Contingency Reserve to restore ACE within the 15-minute timeframe.

  • At 7:20, a second generator trips with a loss of 150 MW. Although these events are distinct (more than 60 seconds apart), the subsequent occurrence takes place during the recovery period of the first event.

  • The second event lowers the required ACE recovery of the first event by 150 MW.

  • The target becomes that the BA must return ACE to -150 MW by the end of the 15-minute recovery period (pre-event ACE was 0, reduced by the second loss).

  • Mnemonics: "Second trip during recovery lowers the target — recover to pre-event ACE minus the new loss (here: 0 – 150 = –150 MW)."

1.24. Reporting Example - Using CR Form

• In the previous example where MSSC = 980 MW and reportable threshold = 784 MW:

  • An 800 MW unit trips at 7:10, marking it as a Reportable Event.

  • At 7:20, a 150 MW unit trips during the 15-min recovery period.

  • Required target: Return ACE to -150 MW by the end of the 15-minute period (pre-event ACE was 0, adjusted by the second loss).

  • Using NERC CR Form 1 for compliance assessment of percent adherence:

  • If the most positive ACE reached following the second event is -150 MW (the minimum necessary), it denotes 100% compliance.

  • If the most positive ACE reaches only -190 MW (falling short of requirements), it shows 95% compliance.

  • Mnemonics: "CR Form 1 checks your best ACE in the 15 minutes — hit the exact target (-150 MW) for 100%, fall short and compliance drops (e.g., -190 MW = 95%)."