New Requirements for SSR Studies to Address Emerging SSFR Risks

ERCOT recently introduced NPRR1283 to address the emerging risk of Sub-Synchronous Ferro-Resonance (SSFR), a complex electrical phenomenon within power systems that can occur due to interactions between the system’s main power transformer (MPT) and nearby series capacitors when energizing transformers. If not properly managed, SSFR has the potential to produce significant overvoltages and lead to equipment damage. ERCOT has identified SSFR as an increasingly relevant risk that can occur even when a generator is not yet synchronized to the grid.  The risk is particularly acute for projects located close to series capacitors and using transformers with low saturation characteristics. 

ERCOT recorded two significant SSFR events in 2023, one of which occurred during initial commissioning, emphasizing the critical need for early risk assessments. Mitigating SSFR risks following transformer procurement poses significant challenges because typical solutions often necessitate extensive system configuration changes. These adjustments carry technical trade-offs along with considerable financial and operational implications.  

Incorporating comprehensive SSFR analysis and mitigation strategies during the transformer specification and procurement phase instead, can address these financial and operational implications before they become an issue. With early SSFR studies, experts can identify MPTs with higher saturation knee points during procurement, enhancing the project’s capacity to tolerate voltage fluctuations and markedly reducing vulnerability to SSFR. 

𝗞𝗲𝘆 𝗖𝗵𝗮𝗻𝗴𝗲𝘀 𝗶𝗻 𝗡𝗣𝗥𝗥𝟭𝟮𝟴𝟯: 

• SSR studies, including SSFR scenarios, must be completed prior to Initial Energization rather than before Initial Synchronization. 
• Required SSFR assessments must consider transformer energization scenarios, especially those involving open low-voltage sides and radial connections to nearby series capacitors. 

EPE is your trusted partner in navigating SSFR challenges. Our specialized team brings deep technical expertise in SSFR studies, system modeling, and mitigation strategies.  

EPE’s Protection & Controls (P&C) team supports the implementation of SSFR-specific relay protection schemes, while our system studies group can evaluate the need for transformers with higher saturation knee points early in the design process. Together, these capabilities enable us to help you proactively identify and mitigate SSFR risks—before they escalate into costly operational issues. 

Don’t wait until transformer procurement to assess your project. Address costly potential problems early on by contacting our experts using the form below.