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Life Management And Extension of Power Transformers on the Island of Puerto Rico

Presented By:
Kenneth G. Peterson
Director of Substations-Large Projects
Luma Energy ServCo, LLC
Puerto Rico
TechCon 2024

Abstract

This paper will share current successes and existing struggles working within a damaged infrastructure as we face the challenge of dealing with global supply chain restraints along with the challenges on the Island of Puerto Rico as Luma Energy looks at various ways to extend the life of the utilities’ investments. The discussion will also include:

  • some of the leading challenges of inheriting an aging infrastructure
  • creating a new baseline
  • prioritizing a transformer replacement program
  • best practices and approach methods to these challenges.

Introduction

In September 2017, Puerto Rico’s electric system was completely devasted by the landfall of Hurricane María, resulting in the longest electrical blackout in modern U.S. history. Hurricane Maria damaged and destroyed several transmission and sub-transmission substations. Hurricane Maria made landfall near the town of Yabucoa on the Southern eastern coast of the island and proceeded on a northwestern path exiting the island through the municipality of Camuy. Upon landfall the hurricane maximum sustained winds were measured just under 155 mph, designated as a strong category 4 hurricane according the Saffir Simpson Scale, and this is 1 mph under the maximum scale of a category 5 (Pasch et al, 2018).

LUMA is a Puerto Rican company that, since June 1, 2021, operates and manages the electric power transmission and distribution system in Puerto Rico. LUMA is a company driven by a mission to transform the electrical transmission and distribution system to provide all Puerto Ricans with the reliable, resilient, cleaner, and affordable electrical grid they deserve. As a customer-centric company, LUMA’s entire workforce of more than 4,000 employees is focused on safely delivering an exceptional customer service experience to its 1.5 million customers and approximately 360 substations (lumapr.com, 2024).

Just over a year after managing and operating the Puerto Rico grid, Luma experienced hurricane Fiona. The hurricane made landfall on September 18th, 2022 at the extreme southwestern coast of Puerto Rico near Punta Tocon and proceeded northwest through the municipality of Mayaguez. Upon landfall the hurricane’s maximum sustained winds were measured at 85 mph, designated as a medium category 1 hurricane according to the Saffir Simpson Scale. The hurricane caused a power blackout to all of Puerto Rico for several days, once again demonstrating the need for more reliable power generation, transmission, and distribution systems on the island. At the peak of the disaster 99% to 100% of customers were reported to be without power (Pasch et al, 2023).

First Steps of our Asset Management Team

As LUMA began to manage the operations of Puerto Rico’s electric utility grid, FEMA facility assessments from post hurricane Maria were provided for all island utility substations. These assessments had some relevant data to use for visual and mechanical conditions of the 419 transmission and sub transmission transformers. After Hurricane Fiona was declared an emergency, similar FEMA assessments were conducted at all substations on the island. This allowed continued collaboration between the asset management team and system operators to continue to review transformer priorities.

After Hurricane Maria, the large blackout became an interest to the IEEE society with respect to reliability and resilience of the island’s electric infrastructure. Yes, this event was devastating, but why did this island wide blackout last for such a long period of time? Research also looked at the improving the grid requires a deeper understanding of technical, economic, financial, and political aspects. It can be argued that this disaster was combined with human and natural causes (Kwassinski et al, 2019). Although the disaster recovery focused on the entire grid system recovery, it also allowed the management team to begin focusing on the substation equipment including transformers. As damage assessments were being reviewed, engineering and asset management were able to collaborate and begin to look at short term goals for system reliability. This included, substation line arrester program, system protection and control upgrades, energy management system upgrades, animal guard program, circuit breaker replacement programs, and transformer replacement programs. Overall, these programs combined allow system protection improvements around the islands power transformers. Planning and implementation of these programs began early on for the asset and engineering teams to begin reducing through faults on the aging fleet of transformers.

As capital projects were being kicked off, asset management and system operations also started an oil analysis program to get a new baseline on the transformer and load tap changer (LTC) fleet. To kick off the program the team focused on lab analysis for DGA (Gas in Oil Analysis) Karl Fischer, Dissolved metals, inhibitor content, furan analysis and liquid power factor. Minimal data was available post commencement of LUMA, so this simple program allowed the field team to also have fresh visual mechanical look for transformer leaks. As data became available, needed oil processing and leaking caskets began to be addressed as needed. As simple as these first steps may seem for a normal utility, it was needed to start a maintenance approach rather than just a reactive approach. The lack of modernized specifications, conditioned-based monitoring, and natural weather events were priority concerns for the aging transformer fleet.

Replacement Plans

Asset management and engineering first needed to update and agree upon new technical specifications for the transformer replacement program. This process was implemented within the team’s subject matter experts to collaborate on IEEE standards and future improvement philosophy for the overall grid modernization. Other considerations and challenges that affected the team included rebuild vs. relocation of existing substations. Due to being a majority federally funded program, all assets in flood zones would not be sponsored unless relocated or elevated to be outside the flood zones per historical records and consensus from FEMA.

The replacement priories had begun an approach with current test and assessment data available, age of assets, critical loads for system reliability, and current transformers out of service. Teams were also looking at the health of mobile substations not currently deployed in the field that would be supporting installation process. As a result of the two prior hurricanes, multiple mobile substations were already deployed to support current out of service transformers. Therefore, some of the priorities had to be shifted to accommodate current out of service transformers to allow mobile substations to be added back to the program. In parallel, specifications were also implemented for new mobile substations to allow operational planning of system loads during the transformer replacement program. Other factors for the prioritization also included transformers to be included for substation rebuild/relocations planning. These challenges were all considered as the team began the procurement process for the programs.

Current Life Extension

As discussed previously, the LUMA procurement process can be challenging as many of the programs are federal funded. Adding to long lead times and logistic challenges other programs were added in the short and long term. Load balancing studies as well as phase balancing studies were implemented in the system to reduce or prevent overloading of transformers and nuisance tripping. Several LTC’s within the system were also found to be non-operational, therefore, a study was implemented to review repair or replacement of LTC’s. A dedicated crew was deployed to perform transformer infrared inspections to support a hotspot repair program. During this program, other offline inspections and tests were conducted when outages were requested for hotspot repairs. Overall, the system is fragile, and the challenge is getting back to a maintenance approach rather than a reactive one. A long-term maintenance approach is being reviewed to accommodate both the existing aging fleet, and the new transformer replacement programs.

During the 4th quarter of 2023 we recently added a pilot program to monitor hydrogen gases. Two locations were chosen for this program based on previous oil analysis. With the existing aging fleet and no past online monitoring program, this allows system operations to have a snapshot of online monitoring as we work on other future programs for DGA online monitoring. This pilot program also allows the team real time data for the asset and operations teams to support justifications for additional online monitoring of our fleet island wide.

An additional program added to our damage assessments was offline testing. As discussed, the system does not currently have online monitoring and not all assets have current test records. This program was implemented to continue to support our substation damage assessment and will support current records of our transformer fleet. Offline test to be implemented for the transformer fleet will be Overall Power Factor and bushing Power Factor, Excitation Current tip up test, Sweep Frequency Response Analysis (SFRA Test), Turn Test Ratio (TTR), Insulation Resistance Testing, DC Winding Resistance, Mechanical Trip Test, Arrester Test, Fan Operation, Pump Test, and other applicable test specific to manufacturer protection schemes. The implementation of these assessments allows the asset management to have a new baseline of the health of the transformer and expedite the much-needed updated maintenance records.

Why is this Urgent?

In July of 2023 Luma had a large 544 MVA 230/115 kV transformer fault. During our analysis, it was discovered that the tertiary winding had collapsed during the fault event, unfortunately ending the life of the 1972 vintage transformer. This 230/115 kV transformer failure places the entire eastside of the island in a critical situation as a similar sized 230/115 kV transformer on the southside had failed during hurricane Maria. Since July of 2023, the transmission operations center has had to build many systems contingency to allow crews scheduling other necessary repairs on the 230/115 kV system. It is very difficult now as the system cannot isolate certain lines on the Eastside of the island due to the July failed unit being out of service. The failed unit has already been removed off-site and we are awaiting on a purchase of a used transformer that the LUMA team has been in the process of procuring since July 2023. We have experienced significant delays due to Procurement and Contracts. The client has also recently provided a response that this unit may have an additional 6 month delay due to permitting. The team is in the process of analyzing if we should use a 230/115 kV transformer from one of the sister stations on the west or east island temporarily until the new transformer arrives sometime in the year 2025. The operations crews are pre-installing a duct package and new control cables for the replacement transformer to alleviate any additional delays.

Being a federal project adds to the other challenges discussed such as logistics planning, permitting, and long lead times. The transformer was on the long-term replacement plan; however, it had not been purchased prior to the failure. Even the used transformer purchased only provides the system with about 50% capacity of the original transformer. Fortunately for LUMA past system studies indicate about 800MW of load has decreased since 2008 on the island that will allow system operations to be in a more stable state with a smaller capacity MVA.

Conclusion

Many past and present challenges have been discussed in this paper, but we still need to continue the journey to improve system reliability and resiliency. Many of the programs initiated will indeed support reliability and some other long-term goals focus on substation resiliency. Resiliency is important as the past hurricanes were discussed, and the result was 100% island outage. One of the major concerns is flood zones. To improve upon this threat the team will be implementing flood mitigation strategies by relocating or elevating structures above the base flood elevation by two feet, installing proper drainage, and retention structures. To support wind mitigation, the long-term plan is to reinforce buildings and adopt gas insulated substations. For better system reliability new designs will include adopting ring bus configuration at most sites, and redundant DC systems with backup generators. With these goals and the wealth of knowledge within LUMA team, we are very optimistic to continue our life management and system reliability programs to support Puerto Ricans with the reliable, resilient, cleaner, and affordable electrical grid they deserve.

References

A. Kwasinski, N. Andrade, M.J. Castro-Sitiriche, and E. O’neill-Carrilo. “Hurricane Maria Effects on Puerto Rico Electric Power Infrastructure”, IEEE Power and Energy Technology Systems Journal Volume 6, NO. 1, March 2019, 85-94.

Luma newsroom, Critical Electric Infrastructure Progress Announced For Puerto Rico, about Luma https://lumapr.com.

R. J. Pasch, A. B. Penny, and R. Berg, ‘‘Hurricane Maria,’’ Nat. Ocean. Atmos. Admin. (NOAA), Silver Spring, MD, USA, Tech. Rep. AL152017, Apr. 2018.

R. J. Pasch, B.J. Reinhart, and L. Alaka, ‘‘Hurricane Fiona,’’ Nat. Ocean. Atmos. Admin. (NOAA), Silver Spring, MD, USA, Tech. Rep. AL072022, Mar. 2023.

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