By Michael Tate, NERC Reliability Specialist
VAR-002, a standard with roots back to the 2003 blackout, is a trending audit item for Generator Operators. Some generators are constrained by a narrow voltage schedule issued by their Transmission Operator and do not realize it. NERC and the Reliability Entities have made it a priority to seek out GOPs/GOs with limited knowledge of their designated voltage schedule and identify if any prolonged swings in voltage have not been reported.
While protection systems settings were found to the be the initial cause of the 2003 Blackout, improper AVR settings were a catalyst. The Blackout was the primary reason NERC Standards were made enforceable. At the time, many of the generators in the region set their Automatic Voltage Regulators in Power factor or VAR mode. This contributed to the cascading failures causing 531 generating units to shut down leaving approximately 50 Million customers with no power. VAR-002 was modified in the spirit of this issue, where generators must maintain their automatic voltage regulator (AVR) in service and in either voltage controlling mode or the mode instructed by the TOP while also maintaining awareness of the voltage both before and after the transformer. It is this standard that holds the GOP accountable for Voltage levels. Specifically, Requirements R1 and R2 call on the GOP to always stay in automatic voltage control mode and maintain its voltage schedule issued by its TOP.
In the past 2 years, many NERC Audits have included VAR-002 Requirements R1 and R2 in their scope. Typically, the Regional Entities will select operating dates for your facility and collect data to ascertain any long swings in voltage or changes in reactive power outside the schedule. Should any event occur for more than 30 minutes, a GOP must provide documentation of its notification to the TOP. These two pieces of evidence are crucial if there is a voltage excursion.
With Internal Controls in mind, the diligence of the Regional Entities has stepped up a notch for VAR-002, Version 4.1 As a result, they have noted that not only should Generator Operators know the voltage before the GSU but GOPs must have a conversion for the Line voltage on the other side of the GSU. In other words, within the control room, a Generation Facility should be aware of their voltage schedule; both the Generator voltage and Transmission Line voltage via a paper posting and/or a DCS Display with alarm. To NERC, this ensures that Operators, Plant Engineers and Plant Managers are aware of their voltage schedule, its tolerances and the current voltage level regardless of where it is monitored.
While your Voltage Schedule is issued by the TOP, your Transmission Owner can issue a modified voltage schedule. Under VAR-001, Requirement R1, Transmission Operators determine and provide the voltage schedule overall, leaving Transmission Owners with the unofficial task of notifying the GOPs with the information. However, in very few cases, TOs will further constrain GOPs and their voltage schedule by shrinking the gap of the voltage tolerance up and/or down. For example, on a 115 kV line, a TOP may set the schedule for 117 kV with a tolerance of +/- 3 kV, leaving room for viable voltage swings. In the same scenario, a TO may issue a voltage schedule to a GOP with the same voltage but decrease the tolerance to +/- 2 kV further constraining the Generator.
As a generation facility, you should review the voltage schedules to determine if they have one of these voltage constraints. Consider these tips to accurately maintain your Voltage schedule
- Check your voltage schedule.
- Compare it to the area constraints to determine if there is a mismatch.
- Talk to transmission owners (TOs) about opening ranges that are too small or difficult to manage.
- Ensure the voltage you are monitoring is at the same level as the schedule.
- If monitored voltage is not at the same level as the schedule, post a conversion table for the control room operators.
- Keep in mind TOs need to see this from a Generator Operators point of view, so the conversation may require some research on the typical voltage swings your system may incur.
- The goal is to come to agreement on what would work best for your Generator Operator while respecting the demands of the voltage schedule.
Luckily, most TOPs have posted their voltage schedule with operation guidelines and manuals, so a quick Google search should get you started. And remember, while there are many standards to watch out for, the ones that helped conceive NERC, like VAR-002, will always be scrutinized.