Power and renewables

NERC Reliability Standard VAR-002-4 (R2): Understanding your “voltage schedule” to mitigate risk

Understanding your voltage schedule to mitigate risk

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Mickey Bellard

Mickey Bellard

Principal Consultant, Compliance Monitoring & Risk Management, Power Systems Advisory

On April 29, NERC’s Enforcement Actions 2021 post included a couple of VAR-002 Notice of Penalty violations in the amount of $420,000 for VAR-002-4 R2 and VAR-002-3 R2. These types of public postings provide detailed narratives on interesting facts and circumstances, root causes, and mitigation activities offering valuable insight on lessons learned and many other important takeaways.

I have been following the NERC VAR-002 standard for many years and was surprised by a few recent NERC penalties which were publicly posted on the NERC Enforcement and Mitigation site.

I’ve always had a strong interest in VAR-002, especially from a generation facility perspective. This likely goes back to my control operations days and the struggles I have seen in maintaining various voltage schedules while protecting the facility’s equipment.

The standard VAR-002-4 “ensures that generators provide reactive support and voltage control, within generating facility capabilities, in order to protect equipment and maintain reliable operation of the Interconnection.” A somewhat basic description of the purpose—but more prescriptive higher hurdles for generation facilities when dealing with VAR-002-4 (R2) and voltage schedules.

Here is the short summary of how it typically happens; "the Generator Operator (GOP) was in violation of VAR-002-4 R2, because it did not maintain the generator voltage or Reactive Power schedule (within each generating Facility’s capabilities) provided by the Transmission Operator (TOP), or otherwise meet the conditions of notification for deviations from the voltage.” This made me ask myself: how is this continuing to happen? For this example, I took a quick look at voltage schedules rather than reactive schedules.

After reviewing several cases, I identified a common theme: entities had less than adequate awareness of the expectations of the voltage schedule. In some cases, the voltage schedules may not have been adequately obtained or timely updated. The entities also lacked understanding of the parameters, thus creating problems for the generation facilities who are protecting their facility’s capabilities and monitoring all plant operating limits. In other cases, the voltage schedule was too aggressive for the area and the facility, but the GOP did not communicate this back to the TOP while incurring numerous deviations from the schedule.

What’s in the schedule? A typical voltage that a generator maintains is measured at the high side of the generator step-up transformer (GSU), unless otherwise specified. A voltage schedule is usually provided with a kV schedule value with parameters for kV high and kV low values that establish the voltage schedule tolerance band. Some voltage schedules have adjusted seasonal values (such as winter and spring) or adjusted peak or off-peak kV targets for certain conditions.

A few cases that resulted in non-compliances had expectations for the GOP to maintain a 500 kV bus’s prescribed voltage to +/- 5 kV; however, the entity exceeded this bandwidth on many occasions. In some cases, a 230kV schedule target had upper bandwidth targets of 237 kV and lower bandwidth targets of 229 kV, but the GOP could not maintain the targets or failed to notify the TOP. Another example of a case listed the TOP assigned voltage schedule to be 114kV to 120kV with a target of 117kV. The tolerance bands ranged from a more restrictive bandwidth of 1% to less restrictive tolerance bandwidth of 5% in some examples. In many cases, the GOP had limited awareness or details of the schedule, thus, was unclear of the expectations.

In several cases, notifications of not meeting the voltage schedule were not communicated to the TOP as there was a lack of proper knowledge of the schedule, bandwidths, and deviation limits—or simply not being aware of revised seasonal schedules or updated seasonal peak/off-peak targets.

There are a few key takeaways to note:

  1. It’s important to communicate with the TOP if a tolerance band is not achievable or is too restrictive.
  2. Ensure the generation facility has a TOP supplied voltage schedule that is up-to-date.

The recent VAR-002-4 penalties included several occurrences that did not meet the targets resulting in a violation risk factor (VRF) of medium and a violation severity level (VSL) of severe. This also resulted in a moderate and serious risk impacts to Bulk Electric System (BES). This classification could have impacted the penalty amount as well as other factors.

The bottom line is that not understanding your “voltage schedule” can create reliability issues—and in some cases, can result in significant penalties for repeated occurrences and excursions. To avoid these issues, be sure to review your voltage schedule periodically and set clear expectations on maintaining the parameters and targets.

Contact us:

Mickey Bellard

Mickey Bellard

Principal Consultant, Compliance Monitoring & Risk Management, Power Systems Advisory