One Minute Summary - NERC PRC-028-1 

Disturbance Monitoring and Reporting Requirements for 

Inverter Based Resources 

Reference from Technical Rationale for Reliability Standard PRC-028-1 

Background:

The recent disturbance reports as below highlighted the need for disturbance monitoring for inverter-based resources (IBRs). 

• Blue Cut Fire 

• Canyon 2 Fire

• Odessa disturbances, 

Purpose:

Install disturbance monitoring equipment (DME) at wind and solar PV resources assisted with event analysis, performance monitoring, and IBR generating facility model validation.

1. 1. 1. High-resolution oscillography data.

      2. Plant SCADA data with one-second resolution.

      3. Sequence of events recording for all IBR units.

      4. High-resolution oscillography data from at least one IBR unit on each collector feeder.

Difference from PRC-002 Disturbance Monitoring and Reporting Requirements :

PRC-002 Purpose: 

Capture data to understand large-scale disturbances on the Bulk Electric System (BES).

PRC-002 Issues:

1. IBRs' response to certain faults can risk system reliability.

1. 1. Many IBRs involved in disturbances lacked adequate monitoring data.

Solution:

1. Instead of revising Reliability Standard PRC-002, a new standard PRC-028-1 for IBR monitoring requirements was introduced.

2. This decision was influenced by the Inverter-Based Resource Performance Task Force (IRPTF).

Responsibilities:

The following entities ensure adequate data availability for applicable Elements at IBR generating facilities:

1. Transmission Owners 

2. Generator Owners 

Mandated data: 

1. Sequence of events recording (SER) 

   • As the example, the SER data is required for circuit breakers 1, 5, 6, 7, and 8. 

   • Circuit breaker 1 is associated with the main power transformer. 

   • Circuit breakers 5, 6, 7, and 8 are associated with the collector bus.

2. Fault recording (FR)

   •  As the example, the FR data is required from high side terminals of the main power transformer.

3. Dynamic disturbance recording (DDR)

   • As the example, the DDR data is required from high side terminals of the main power transformer. 

Figure 1, reference from Technical Rationale for Reliability Standard PRC-028-1 

Requirement R1:

Aim: Capture SER (Sequence of Events Recording) data from circuit breakers and IBR (inverter-based resources) units within the IBR generating facility.

Specifics: At least one IBR unit connected to the last 10% of each collector feeder length must have data as specified in R1, Part 1.2.1 through 1.2.6.

1.2.1. All fault codes. 

1.2.2. All fault alarms. 

1.2.3. Change of operating mode. 

1.2.4. High and low voltage ride-through. 

1.2.5. High and low frequency ride-through. 

1.2.6. Control system command values, reference values, and feedback signals. 

Importance of Data to provides a detailed sequence of events timeline of the IBR generating facility's response during a power system disturbance.:

• • 1. The change of state of circuit breaker positions and IBR unit data.

    2. This data must be time-stamped according to Requirement R7 using a time-synchronized clock.

Analysis Process:

• • System disturbance analyses often start with evaluating SERs.

  • This helps in identifying the initiating event(s) and tracking the disturbance propagation.

  • Recording breaker operations is crucial to determine the interruption of flows during disturbances.

Why Record One IBR Unit in the Last 10% of the Collector Feeder Length:

• • Helps in analyzing the IBR unit's performance during BES (Bulk Electric System) disturbances that don't operate the interconnecting circuit breaker.

  • The last 10% of the collector feeder length is chosen because it might be the most challenging location for IBR units to maintain operation during a BES disturbance.

  • The "last 10%" would be the segment closest to the point where the collector feeder connects to the main transmission system or substation. 

Requirement R2:

Aim: Capture sufficient Fault Recording (FR) data for Elements at each IBR (Inverter-Based Resources) generating facility to analyze its response to system disturbances.

• • Recent disturbances showed a need for expanded monitoring at IBR sites.

  • Required electrical quantities can be directly measured or determined from sufficient FR data.

Plant Level FR Measurements:

• • Taken on high-side terminals of the main power transformer.

  • Provides data on the IBR facility's interconnection to the bulk power system.

  • For comprehensive fault analysis, phase-to-neutral voltage recording for each phase is essential.

  • Phase current and residual current are needed to differentiate between phase faults and ground faults.

  • These measurements help determine fault location, cause of relay operation, and the facility’s overall response.

IBR Units' Response to Disturbances:

• • Not all IBR units within a facility react identically to disturbances due to their wide geographic distribution.

  • Monitoring is required for some of the most geographically remote IBR units, especially those connected to the last 10% of each collector feeder length.

  • This ensures data is available to analyze individual IBR unit responses.

  • Recording from IBR unit terminals might be challenging for existing setups, so measurements can be taken from the high-side of the IBR unit transformer.

Dynamic Reactive Device:

• • Used within the IBR facility and often connected to a medium voltage collector bus.

  • Its output during disturbances is crucial to understand the plant's overall performance.

  • The measurements for this device are the same as those for the high-side of the main power transformer.

Recording of Electrical Quantities:

• • Essential for effective fault analysis.

  • FR data helps determine all fault types and complements Sequence of Events Recordings (SERs) in evaluating circuit breaker operations.

  • FR also displays the generator's output response to disturbances.

Current Recordings:

• • Typically, required electrical quantities are directly measured.

  • Some quantities, like residual or neutral currents, can be derived.

  • Neutral (residual) current is negligible under normal conditions but can be measured or calculated during a ground fault.

  • Neutral current (Ir) is calculated as: Ir = 3•I0 = IA + IB + IC, where I0 is the Zero-sequence current and IA, IB, IC are phase currents.

Voltage Recordings:

• • Voltages need to be recorded or accurately determined at applicable Elements as per Requirement R2.

Requirement R3:

Aim: Time-stamped pre- and post-trigger Fault Recording (FR) data assists in analyzing power system operations and determining if operations were as intended.

Odessa Disturbance Report Recommendations:

• • • Suggested high-resolution oscillography data at the point of interconnection and on individual IBR units.

    • A minimum recording rate of 128 samples per cycle is specified, considering the state-of-the-art for Disturbance Monitoring Equipment (DME) and storage limitations.

    • This rate is crucial for capturing transient events at individual IBR units.

Importance of Pre- and Post-Trigger Data:

• • • Along with Sequence of Events Recording (SER) data, it aids in analyzing Protection System operations post-fault to determine if the system operated as designed.

    • IBR units have fast-acting control systems with built-in protection functions.

    • Time-stamped FR data from IBR units is essential for analyzing their response to system disturbances.

    • BES faults usually last for a short duration (1 to 30 cycles). To capture the full response of a geographically spread IBR facility, a two-second total minimum record length synchronized to a common clock is necessary.

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Each Transmission Owner and Generator Owner shall have FR data as specified in Requirement R2 that meets the following:

3.1. High-side of the main power transformer FR data 

3.1.1. A single record or multiple records that include a pre-trigger record length of at least two cycles and a total record length of at least 2.0 

seconds for the same trigger point. 

3.1.2. A minimum recording rate of 128 samples per cycle. 

3.1.3. Trigger settings for at least the following: 

3.1.3.1. Neutral (residual) overcurrent. 

3.1.3.2. AC phase overvoltage and undervoltage. 

3.2. IBR unit level data 

3.2.1. A single record or multiple records that include a pre-trigger record length of at least two cycles and a total record length of at least 2 

seconds for the same trigger point.  

3.2.2. A minimum recording rate of 128 samples per cycle. 

3.2.3. Trigger settings for at least the following: 

3.2.3.1. AC Phase overvoltage and undervoltage. 

3.2.3.2. DC overvoltage, DC overcurrent, and DC reverse current. 

3.2.3.3. Overfrequency and underfrequency. 

3.3. Dynamic reactive device FR data 

3.3.1. A single record or multiple records that include a pre-trigger record length of at least two cycles and a total record length of at least 2.0 

seconds for the same trigger point. 

3.3.2. A minimum recording rate of 128 samples per cycle. 

3.3.3. Trigger settings for at least the following: 

3.3.3.1. Neutral (residual) overcurrent. 

3.3.3.2. AC phase overvoltage and undervoltage. 

Requirement R4:

Aim:  Each Generator Owner and Transmission Owner shall have continuous dynamic Disturbance recording (DDR) data and storage to determine the following electrical quantities for each main power transformer(s) it owns.

Importance of DDR Data:

• • Large scale system disturbances evolve over extended periods, making Dynamic Disturbance Recording (DDR) data crucial for event analysis.

  • DDR data helps identify causes and the IBR (Inverter-Based Resources) generating facility's response to these disturbances.

  • Continuous recording and storage are vital to ensure data availability for the entire event.

  • State-of-the-art DDR equipment supports continuous recording.

Nature of DDR Data:

• • Captures the dynamic response of the IBR facility to system disturbances.

  • Used for analyzing both short-term and long-term complex power system events.

  • Typically stored as RMS values or phasor values, unlike the directly sampled data in Fault Recording (FR) data.

Usage of DDR:

• • Measures transient response to disturbances during balanced post-fault conditions.

  • Sufficient to provide a single phase-to-neutral voltage or positive sequence voltage and current for each main power transformer.

  • Only one frequency recording is needed for all main power transformers within an IBR facility since they operate at the same frequency.

  • Recording all three phases of voltage/current isn't mandatory. However, they can be used to compute and record the positive sequence value(s).

  • Electrical quantities for Real Power and Reactive Power can be directly measured or determined.

Data Requirements for PRC-028-1:

• • Based on a system configuration where all normally closed circuit breakers on a BES (Bulk Electric System) bus are closed.

Significance in Disturbance Analysis:

• • Understanding the dynamic response of generating resources is crucial.

  • Necessary to have DDR on the high-side of the main power transformer(s) to capture the IBR facility's response adequately.

Requirement R4, Part 4.1:

• • Requires either one phase-to-neutral or positive sequence voltage.

  • Phase-to-phase voltage recording is also acceptable.

  • Given the BES's balanced operating condition, phase-to-neutral quantities can be derived from phase-to-phase quantities if needed.

Requirement R5:

Aim:  DDR data should have the electrical quantities identified below:

• Input sampling rate of at least 960 samples per second.

• Output recording rate of electrical quantities of at least 60 times per second.

Input Sampling Rate:

• • At least 960 samples per second is required.

  • This corresponds to 16 samples per cycle on the input side of the DDR (Dynamic Disturbance Recording) equipment.

  • Ensures accurate calculation of recorded measurements, such as complex voltages and frequency.

  • This rate is consistent with the one specified in the Reliability Standard PRC-002.

Output Recording Rate:

• • Electrical quantities should be recorded at least 60 times per second.

  • This rate refers to the recording speed of the device.

  • Recording at least 60 times per second is adequate to monitor the IBR (Inverter-Based Resources) generating facility's response during power system disturbances.

  • Given that the control system associated with IBRs is fast-acting, a higher frequency recording is essential to accurately reconstruct events.

  • An output recording rate of 60 times per second strikes a balance between capturing high-frequency events and not significantly increasing data storage requirements.

Requirement R6:

Aim:  Time synchronize all SER, FR, and DDR data to meet the following: 

• Synchronization to Coordinated Universal Time (UTC) with or without a localtime offset. 

• Synchronized device clock accuracy within ± 100 microseconds of UTC. 

Importance of Time Synchronization:

• • • Essential for aligning large volumes of geographically dispersed records from various recording sources.

    • Coordinated Universal Time (UTC) is the recognized standard, using atomic clocks for precision.

    • All data should be in UTC format, with or without the local time offset.

Accuracy of Time Synchronization:

• • • Only applies to the clock used for synchronizing the monitoring equipment.

    • Equipment measuring electrical quantities should be time synchronized to ± 100 microsecond accuracy.

    • The accuracy of the data itself isn't mandated due to inherent delays in measuring electrical quantities, algorithm calculations, and other factors.

Monitoring Devices Internal Clocks:

• • • Should maintain ± 100 microsecond accuracy for time synchronization.

    • IEEE Std 2800 requires DME recording plant-level data to be synchronized to ± 1 microsecond accuracy.

    • The set accuracy requirement of ± 100 microsecond balances the need for accuracy with the practical limitations of equipment.

IBRs and Time Synchronization:

• • • IBRs, unaffected by inertial time constants, can rapidly change power production.

    • Accurate time synchronization is crucial to understand and analyze control decisions during disturbances across multiple plants with potentially hundreds of IBR units.

    • Examples of IBR's fast response include:

      1. 90% response to a three-phase fault in <40 ms.

      2. Central power plant controllers can issue updated commands in about 40 ms upon detecting system condition changes.

      3. Standard closed-loop voltage control response can be <200 ms.

      4. Instantaneous Inverter protective trip decisions, such as AC or DC overvoltage or reverse DC current, can be made in less than 10 ms.

Requirement R7:

Aim: Data Retrievability

• • Data must be retrievable for a minimum of 30 calendar days, including the day it was recorded.

  • This period allows for communication between entities regarding events and data retrieval needs.

  • The requester must be aware of the 30-day limit to ensure timely data requests.

  • Retaining data beyond 30 days can be expensive and unnecessary.

  • Modern equipment makes 30-day retrievability feasible.

  • If an event occurs on Day 1 and a data request is made on Day 6, the data must be provided within 30 days or after a granted extension. However, if requested on Day 31, the entity isn't out of compliance if it doesn't have the data.

Data Provision Requirement:

• • Entities must provide SER, FR, and DDR data upon requests from the Reliability Coordinator, Regional Entity, or NERC.

  • Data should be provided within 30 calendar days or a granted extension.

  • Entities can request an extension to the 30-day submission requirement.

Standardized Formatting and Naming:

• • Helps in timely disturbance analysis.

  • Formatting and naming conventions for SER, FR, and DDR are consistent with the Reliability Standard PRC-002.

SER Data - Requirement R7, Part 7.3:

• • Data should be in a simple ASCII Comma Separated Value (CSV) format as per Attachment 1.

  • Standardized format helps in integrating data from multiple entities to develop a detailed sequence of events timeline.

FR and DDR Data - Requirement R7, Part 7.4:

• • Data should be in the IEEE C37.111 Standard for Common Format for Transient Data Exchange (COMTRADE) format.

  • IEEE C37.111 is an established industry standard.

  • The 2013 revision of IEEE C37.111 includes an annex for synchrophasor data application.

Naming Convention - Requirement R7, Part 7.5:

• • Data files should be named according to the IEEE C37.232 Standard for Common Format for Naming Time Sequence Data Files (COMNAME).

  • A common naming practice is essential for efficient event analysis and investigation.

Requirement R8:

Aim: within 90 calendar days of the discovery of a failure of the recording capability for the SER, FR, or DDR data

• •  Restore the recording capability, or 

  • Submit a Corrective Action Plan (CAP) to the Regional Entity and implement it. 

Restoration Requirement:

• • • Entities are required to restore the recording capability for SER, FR, or DDR data within 90 calendar days upon discovering a failure.

Rationale for 90-Day Period:

• • • The 90-day timeframe strikes a balance between:

      • Providing a reasonable time for entities to restore capability.

      • Ensuring recording capability isn't unavailable for an extended period.

Exceptions and Corrective Action:

• • • If restoration within 90 days isn't feasible due to constraints like budget cycles, service crews, vendor availability, necessary outages, etc.:

      • The entity must submit a Corrective Action Plan to the Regional Entity.

      • The entity is then obligated to implement this plan.

Definition of Failure:

• • • A recording capability being out of service for maintenance and/or testing for more than 90 calendar days is considered a failure.

    • However, an outage of the monitored Element doesn't count as a failure of the disturbance monitoring capability.