By Nicholas Waters, Key Account Manager
Bachmann electronic Corp
Meeting operational compliance within the ERCOT region for wind sites is important from a safety perspective and, failure to do so, can result in hefty fines for project owners. This was motivation for one 170-MW Texas wind facility — which lacked the necessary hardware to collect high-resolution frequency data required for demonstrating compliance — to seek a third-party solution. New hardware and software developments make it possible to provide the necessary data outlined in standard BAL-001-TRE-1, and automatically acquire and archive complete history for the site, enabling site operators to reconstruct grid events down to the second with mHz frequency resolution.
In April 2015, NERC released a standard entitled, Primary Frequency Response in the ERCOT Region (BAL-001-TRE-1). Its purpose is to “maintain interconnection steady-state frequency within defined limits.” By establishing tight limits for frequency tolerances and corrective actions, grid stability is ensured throughout the region. Balancing Authorities, operators, and owners are also provided with performance metrics for their role in the integrity of the grid.
Wind farms operating in the ERCOT region work with defined frequency limits for which they are allowed to supply power to the grid. These limits are defined by the Max Deadband, a term that describes safe operating bounds around the ideal frequency of 60.000 Hz, at which the grid should be operating. Within BAL-001-TRE-1, the Max Deadband is stated as ±0.017 Hz for wind turbines, meaning that if the frequency on the grid is measured outside the operating limits defined by the Max Deadband, the Balancing Authority needs to issue curtailment commands to the plant operators.
Each exceeded measurement of the Max Deadband is called a Frequency Measureable Event (FME) and the time at which the event occurs is denoted by t(0). The amount of curtailment required for a given site is dependent on the size of the site and the frequency deviation from the Max Deadband.
Here’s the formula for calculating how much curtailment is needed when the frequency deviation has exceeded the Max Deadband:
Total curtailment needed = [(Total MW capacity for site)/2.983 Hz] x Hz over max deadband
Ctotal needed = [Tsite cap / 2.983 Hz] x Dmax
where Ctotal needed = Total curtailment needed, MW; Tsite cap = Total site capacity, MW; and Dmax = Max deadband, Hz.
Each time an FME occurs, the standard states that the Balancing Authority is required to notify the Compliance Enforcement Authority (in this case, ERCOT) within 14 calendar days and provide detailed frequency data pre and post-event.
A wind operator is responsible for making the appropriate corrective action to bring his or her site back into the defined operating range. In addition, the wind operator is required to collect and provide specific frequency data for the wind farm — demonstrating corrective actions, response, and frequency correction in a timely manner. Although a more detailed description of the formulas can be found within the standard, the calculations rely on one-second frequency data with mHZ frequency resolution. A window of this one-second frequency data must be provided, which captures 16 seconds prior to the FME and 60 seconds, following the FME.
It is important to note that the responsibility of providing this data falls on the wind-farm owner and operator.
The standard provides Balancing Authorities, wind owners and operators with a 30-month implementation plan divided into four compliance milestones. Failure to achieve full compliance within 30 months can result in fines.
At the time of this request, the wind-farm owner in this case had already faced fines. Due to the hardware limitations of the site, the existing governor was incapable of acquiring the data necessary for performing the frequency response calculations outlined within the standard.
Using Bachmann’s Grid Measurement and Protection module, the GMP232/x, an M1 solution was developed that recorded a one-second sliding window average of the grid frequency and archived each second’s frequency average with respective date and timestamps. Due to the frequency resolution achievable through the GMP232 module, the one-second frequency data was collected with 0.1 mHz resolution, but rounded to the nearest mHz for this application. Frequency, power, and power factor were also acquired and archived with corresponding date and timestamps for post processing.
The power values were recorded with kW resolution. Curtailment required based on actual frequency was also calculated and stored. Daily files containing 86,400 data entries per day (one-second frequency average/sec generated for each second of the day) were automatically saved in CSV format, organized into monthly folders, and compressed into a single annual folder at the end of each year.
The M1 controller interfacing with the GMP module was programmed to upload data to a server and clear old data stored locally on the device. In the event that communication to the unit is disrupted, the controller is capable of storing nearly three years of data on its 4-GB CF Card. Once communication is reestablished, the M1 system then uploads the backlogged data to the server.
An initial proposal suggested solely providing the frequency data around each FME needed for computing the values specified in the standard. The downside of such a narrowly focused solution was twofold. One, it failed to provide any context surrounding each FME. Without additional information leading up to or following the event, it was impossible to recalculate the frequency response measurements or recreate previous events.
Second, this suggestion was far from future proof in the event that new modifications to the standard become implemented in coming years. High resolution, one-second frequency data for each day, month, and year let the customer recalculate previous calculations and perform additional calculations that may be required by future modifications to the standard. This allowed the customer to see if their previous operational strategy would continue to be in compliance going forward or if additional modifications would be needed.
Since deployment, the GMP232 module has successfully provided the data needed to calculate necessary frequency performance values and bring the site into compliance with BAL-001-TRE-1. It has also let the owner retroactively analyze their site’s frequency, power, and power factor data for previous years, with minimal data storage demand on their server.
Although this project was developed to satisfy requirements for a wind site operating within the ERCOT region, it is compatible with any operating wind farm that contains voltage and current transformers at the wind farm feed-in point (connection point to the grid) in any electric reliability council. Most wind farms typically include hardware for measuring the wind farm’s power and frequency at the grid connection point. However, the frequency resolution achievable through the GMP232 module, coupled with automated historization of FMEs and power data, allow customers to reconstruct grid events, making this solution unique.
Bachmann’s M1 setup, which uses the GMP232 module, provides increased resolution and accuracy, and the ability to build a complete history for the site’s performance down to the second of operation. This GMP/M1 setup only requires access to the voltage and current transformer located at the connection point to the grid to make its measurements.
An intro to ERCOT
According to its website, the Electricity Reliability Council of Texas (ERCOT) manages the flow of electric power along the Texas Interconnection and oversees the majority of the state’s electric load. With over 40,000 circuit miles of high-voltage transmission under its governance, ERCOT’s primary focus is to ensure the following:
- System reliability, including planning and operations
- Open access to transmission
- Retail switching process for customer choice
- Wholesale market settlement for electricity production and delivery.
Having over 90% of the state’s electric load under its governance, the ERCOT region covers nearly the entire state of Texas with a relatively small number of counties along the state’s perimeter falling into the Western Electricity Coordinating Council, Southwest Power Pool, and the Southeastern Electric Reliability Council.