Interchange scheduling is one of the areas where system operators lose points on the NERC RC exam because the terminology is precise and the standards (INT-004 and INT-006) require you to know exactly who does what, and when. If you can't clearly separate Arranged Interchange, Confirmed Interchange, and Implemented Interchange — and the role the Reliability Coordinator plays in evaluating each — the exam questions will trap you.
Why This Matters in the Control Room
Every megawatt that crosses a Balancing Authority boundary rides on an E-Tag. If a tag is bad, reliability data is bad, ACE is wrong, and market settlements go sideways. RCs are the last line of reliability review before an interchange transaction gets implemented — and NERC INT-006 is very specific about the evaluation window and who must be consulted.
Test Tips: How INT-004 & INT-006 Show Up on the Exam
- Know the four Interchange states cold. Arranged → Confirmed → Implemented → Ramp start. INT-004 governs submission of the Arranged Interchange; INT-006 governs the reliability evaluation of it. Questions love to swap these definitions.
- Attribute the roles correctly. The Interchange Authority (IA), Purchasing-Selling Entity (PSE), Balancing Authority (BA), Transmission Service Provider (TSP), and Reliability Coordinator (RC) each have distinct duties on a tag. If a question describes an entity approving or denying a tag on reliability grounds, that's the RC or BA — not the PSE.
- Memorize the evaluation timing. INT-006 requires the reliability evaluation of an Arranged Interchange to be completed within the timeframe defined in the standard prior to the interchange start time. Watch for distractors that shift responsibility to the PSE or drop the RC out of the loop.
- Understand "reliability adjustment" vs. "denial." An RC that identifies a reliability concern can direct a reduction, curtailment, or denial — but the mechanism goes through the Interchange Authority via a Reliability Adjustment (INT-009 governs modification of a Confirmed Interchange for reliability). Exam questions blur these; you need to keep the pathway straight.
- Ramp is not instantaneous. Standard ramp is 10 minutes centered on the top of the hour (5 minutes before to 5 minutes after) unless otherwise agreed. Any question that shows a step-change interchange is testing whether you catch the ramp violation.
- E-Tag = the record. If it's not on the tag, it didn't happen. Undocumented interchange is a reliability and compliance issue — not a workaround.
5 Practice Questions
- A PSE submits an Arranged Interchange tag 25 minutes before the scheduled start. Under INT-006, who is responsible for performing the reliability evaluation of that Arranged Interchange before it becomes Confirmed?
- A. The Purchasing-Selling Entity
- B. The Transmission Owner along the path
- C. The Reliability Coordinator and Balancing Authority in whose area the transaction sources, sinks, or transits
- D. The Interchange Authority alone
- An RC identifies that a Confirmed Interchange transaction, if implemented, will cause a flow that exceeds an SOL on an internal path. What is the correct action pathway?
- A. Direct the BA to ignore the tag
- B. Contact the PSE directly and have them cancel the deal
- C. Initiate a Reliability Adjustment through the Interchange Authority to modify or curtail the transaction
- D. Wait until after implementation and then issue a TLR
- Which of the following best describes "Implemented Interchange"?
- A. The interchange schedule that the source and sink BAs use in their ACE equations during the ramp and operating hour
- B. The E-Tag as first submitted by the PSE
- C. The maximum path capability confirmed by the TSP
- D. The forecasted next-hour interchange
- Standard interchange ramp between Balancing Authorities, unless otherwise agreed upon, is:
- A. Instantaneous at the top of the hour
- B. 10 minutes, centered on the top of the hour
- C. 30 minutes, beginning at the top of the hour
- D. 60 minutes, beginning 30 minutes before the hour
- During an evaluation of an Arranged Interchange, the RC in an intermediate (transit) area determines the transaction is acceptable, but the sink-area RC identifies a reliability concern. What must happen for the Arranged Interchange to become Confirmed?
- A. It becomes Confirmed automatically because most RCs approved
- B. The sink RC's concern must be resolved — the transaction cannot become Confirmed while any responsible RC or BA has an unresolved reliability denial
- C. The IA overrides the sink RC
- D. The PSE re-submits the tag as an emergency schedule
Answer Key & Explanations
- C. INT-006 assigns the reliability evaluation of an Arranged Interchange to the RCs and BAs in the source, sink, and intervening areas. The PSE submits and the IA administers, but reliability review belongs to the RC and BA.
- C. The proper mechanism is a Reliability Adjustment coordinated through the Interchange Authority (governed by INT-009 for modification of a Confirmed Interchange). The RC does not unilaterally tell the BA to ignore a tag, and TLR is a separate congestion-management tool under IRO-006, not the primary curtailment path for a specific tagged transaction.
- A. Implemented Interchange is the interchange value the source and sink BAs actually use in their ACE calculations during the ramp and operating hour. The E-Tag begins as Arranged, becomes Confirmed after successful reliability evaluation, and is Implemented when the BAs use it operationally.
- B. Industry-standard ramp between BAs is 10 minutes, centered on the top of the hour (5 minutes before to 5 minutes after), unless the affected BAs mutually agree to a different ramp.
- B. Any responsible RC or BA can deny an Arranged Interchange on reliability grounds. All reliability concerns must be resolved before the transaction can be Confirmed — reliability review is a consensus function, not a majority vote, and the IA does not override an RC on reliability.
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