Frequency Response Compliance Monitoring Using Synchrophasor Data

With increase in penetration of PMUs in the power system, generating units or the power plant are being monitored through PMUs which provide high-resolution data directly from their high voltage or low voltage generating transformer terminal. This enables monitoring of dynamic behavior of individual generating units. Another way is to monitor the entire power plant’s dynamic behavior. This can be done with placement of PMUs on its evacuation lines. Both options help in monitoring of entire plant's dynamic behavior with high sampled data. One of the best applications of such PMU data would be the checking of frequency response compliance.

Frequency response is also known as primary frequency response (PFR) or governor response. Primary frequency response (PFR) monitoring enables verifying performance of individual generating units/generating facilities following Frequency measurable events (FMEs) in accordance with requirements of standards or grid code or interconnection guidelines as applicable.?PFR is automatic, not driven by any centralized system, and begins within seconds after occurrence of event rather than minutes.??It responds to changes in load-generation imbalance which is observed as changes in frequency changes.??Because the loss of a large generator is much more likely than a sudden loss of an equivalent amount of load, frequency response is typically discussed in the context of a loss of a large generator [1].

With conventional SCADA data many times monitoring of primary frequency response becomes a challenging task. SCADA data which is not time-synchronized and has lower samples per second resolution does not reflect the true primary response. Thus, compliance monitoring becomes a challenging task. With synchrophasor data, this compliance monitoring is now very accurate and entire plant dynamic behaviour during frequency response events can be observed [2].

One example for frequency response compliance monitoring is provided below. In India, generating plants have to provide governor response up to 105% of their running capacity (generation level) during a frequency event. In below PMUs are installed at various power stations’ outgoing lines. PMU monitors the net of ex-bus power evacuation through the transmission lines from various power plants. Thus, summation of power flow through all evacuation lines of generating station provides the overall plant power output after its auxiliary power consumption.?

Below figures shows the response of power plants A, B and E respectively during a frequency event caused by generation loss in the Indian grid as monitored using synchrophasor data. It can be observed that :

• Generating plant B has provided a good response. Its generation has increased through governor fast valving action post event, and it provided a sustained good response.

• Generating plant A has provided a good initial response however, its response got withdrawn quickly and oscillation is observed in overall plant output. Further, after around 1 minute its generation further increased. This provided the input that governor control is not properly tuned.

• In case of generating power plant E, its generation increased promptly with frequency drop however the response could not be sustained and withdrawn immediately in next 30 seconds.

Such dynamic monitoring has helped the compliance monitoring agency to provide feedback to power plants A and E to tune governors to improve their primary frequency response [3]. This is one of the use cases of Synchrophasor usage for primary frequency response measurement. Similarly, AGC response can also be monitored with availability of PMU on the each of generating unit. Presently it can be monitored for overall plant with evacuation lines having PMUs measurement.

References

[1]????NERC, “Frequency Response Standard Background Document”, November 2012

[2] ?? Vivek Pandey, Srinivas Chitturi, “Primary frequency response in an RE-rich grid-Operational experience of the Western Regional Grid”, National conference on Renewable Energy Technologies and its Integration with Grid 2018, Vadodara, India

[3] Chandan Kumar, Alok Pratap Singh, Saibal Ghosh, Akash Modi, Saurav Kumar Sahay, "Compliance monitoring using synchrophasor technology in Indian power system?", 2022 CIGRE Canada Conference & Expo,?Calgary, Alberta, Oct.31 – Nov. 3, 2022 https://www.researchgate.net/publication/365776722_Compliance_monitoring_using_synchrophasor_technology_in_Indian_power_system