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The Frequency Response in the interconnections within North America has been a topic of discussion within numerous groups concerned with the reliability of the Bulk Electric System for many years. With the changing mix of generation across the interconnections this concern has received more focused attention over the past several years. Reliability standards have been developed to ensure that balancing areas or reserve sharing groups are sufficiently supporting the interconnection-wide frequency. Both FERC and NERC have initiated efforts to assess the current situation and to determine if changes are necessary to the rules and regulations regarding the provision and compensation of primary frequency response.
The generation mix in the MISO system as well as across North America is changing. Generation in the MISO system is expected to undergo a significant change driven by the retirement of baseload generation, mostly coal, and increased integration of natural gas, wind, solar, distributed generation and demand side resources. The power system has historically relied on large coal generation to ensure reliable frequency response and control. The operating characteristics of the replacement power sources (especially asynchronously connected, low inertia renewable generation) are different from those of the traditional, thermal generation. The load composition on the system is also expected to change with the proliferation of demand side resources including distributed generation – further impacting the system operating characteristics. It is reasonable to expect that these changes will not only continue the declining frequency trend, but potentially could accelerate the decline as well.
With this background, it is evident that it would be useful to develop and improve tools and processes for ongoing measurement and trending of MISO’s frequency performance. Also, it would be useful to assess if our dynamics models are able to replicate the actual system performance with reasonable accuracy. Measurements available from actual system performance can be used to improve model parameters, as needed. These are base business reliability items, which MISO will pursue.
Additionally, the following questions arise:
As the fuel mix changes, at what point would MISO’s frequency response be inadequate?
a) How can we determine that?
b) What are some of the plausible future scenarios around:
c) Is there a need to better understand how to model dynamic behavior of distributed resources?
Is there a potential need to revising any of our tariff requirements (eg: generation interconnection agreements) or market mechanisms (eg: frequency control requirements and compensation) to ensure continued reliable frequency response?
In summary, the fuel mix and hence the operating characteristics of the MISO system have begun to change and are expected to continue to change significantly going forward such that the frequency response performance would be degraded and could potentially be unreliable. In order to prepare for the inevitable change, MISO needs to improve current processes for measuring and trending system performance, validate dynamic model using the current system performance as a baseline, develop reasonable future scenarios to understand the impact of the evolving generation mix on MISO’s frequency response and possibly investigate the need for revised tariff requirements and market mechanisms to ensure continued system reliability and efficiency.
FERC has recently (February 2018) issued Order 842 that requires newly interconnecting generating facilities, both synchronous and non-synchronous, to install, maintain, and operate equipment capable of providing primary frequency response as a condition of interconnection. While this requirement has the potential to alleviate some of the issues around declining frequency response, there is still a significant amount of generation projects in the queue already that may not fall within the purview of this Order and interconnect without necessarily having the capability of providing primary frequency response. As such, MISO will continue with the evaluation as originally scoped, with a possibility of additional sensitivities that include the frequency responsive requirements on future generation.
formerly RSC-004