Introduction
The importance of safe and reliable power in today’s world was never more apparent than on August 14. Beginning in late afternoon and lasting mere minutes, the largest blackout ever on the North American continent rolled across the northeastern and north central United States and into Canada. Upwards of 50 million people lost power, including all of New York City, with estimated economic losses hovering at $6 billion.
The blackout of 2003 is an extreme illustration of reliability issues electric utilities face everyday. The media is filled with examples of these more common, but still troublesome, events. Last summer, a distribution transformer serving the St. Louis Arch caught fire and forced the evacuation of 8,000 visitors. A substation fire in San Francisco caused a power outage for 120,000 customers the Saturday before Christmas. Both incidents translated energy company dollars into damage, restoration, and labor fees. In St. Louis, vacation days were ruined, and Bay Area retailers lost essential revenue during one of the busiest shopping days of the year.
The reliable distribution of power, what many of us take for granted, is performed through a complex choreograph of generation, transmission and distribution sectors of the industry. Though the blackout of 2003 shed serious media and regulatory light on the transmission component of this delivery system, many industry experts believe strengthening the distribution system will better ensure a higher level of reliable power. Transformers play a key role in making it happen.
In St. Louis and San Francisco, transformer malfunction was either directly responsible, or part of the larger problem, that caused these events.
Current Transformer Concerns
The economic boom created to feed the World War II war machine continued into the 1950’s and 1960’s. Power was needed to drive the strong national manufacturing base and fulfill the demands of suburban development. Power delivery systems were constructed, and substation and distribution transformers were a part of each and every one. The transformers, which adhered to fire safety and environmental codes and standards on the books at that time, were built to last with a life expectancy of up to 40 years. They were installed and often forgotten about.
The country’s reliance on power grew as it expanded. Populations increased and power tools and appliances replaced equipment that didn’t require electricity. Recent electric utility deregulation further taxed the grid. More has been asked of the installed equipment than it was designed to handle. Much of the older installed equipment, including transformers, is now coming to its useful end.
The number of aging transformers still active has concerned many in the industry. Factory Mutual (FM), a major insurance group, recently reported that the number of substation transformer failures is expected to rise by 500 percent within the next 10 years due to aging systems. The small amount of construction of new power systems and increasing loads on old systems is especially worrisome.
A survey reported by Hartford Steam Boiler, another insurance group, shows that most current failures occur in transformers with an average age of 18 years. As a result of failure incidents, utility companies have reported significant profit losses due to downtime and equipment replacement. One Northeastern power company recently estimated that 50 transformer incidents occur per year at a rate of approximately $10,000 per incident, costing the company $500,000 annually. The majority of these costs are directly related to the actual incident – taking the transformer offline, maintenance or equipment replacement, and getting the new or fixed transformer back online.
With aging transformers, the real risks to utilities and their customers are the potential ancillary costs in case of an eventful transformer failure. Many of these costs are related to the conventional petroleum-based mineral oil used in these older transformers. Mineral oil’s relatively low fire point and negative environmental profile place utilities at greater risk for property damage claims, extensive cleanup, casualties, environmental liability, and negative publicity should a transformer fail.
Shrinking capital expenditure budgets make it difficult for utilities to replace aging, and potentially dangerous, transformers with newer units. Fortunately, utilities have new options.
Changing the Standards
Short of costly equipment replacement, solutions to aging transformers must incorporate the following:
Years ago, industry and regulatory bodies tried to address some of these issues by creating a demand to produce a power delivery system focused on safety, equipment efficiency, and environmental protection. This movement included transformers. The focus was on transformer oils.
In 1978, a group of less-flammable transformer fluids were developed and approved by the National Electric Code® (NEC). The NEC created an industry standard that required a minimum open-cup fire of 300°C to be considered safer than conventional transformer oil. In 1984, the Underwriters Laboratories® (UL) collaborated with transformer manufacturers to combine fire resistant fluids with other methods of transformer protection. In the 90’s, Factory Mutual Engineering and Research produced the first Occupational Safety & Health Administration (OSHA)-recognized standard for liquid-filled transformers, suitable for indoor and outdoor installation, with greatly reduced fire safeguard requirements.
Since the late 1970’s, thousands of less-flammable liquid-filled transformers have been in service, and 10 less-flammable dielectric coolants have been approved as an alternative to mineral oil. Approved coolants include high molecular weight hydrocarbons (HMWH), dimethylsiloxanes (silicone), synthetic polyol esters (POE), and polyalphaolefins (PAO).
Despite their success and improvement in many ways over traditional transformer mineral oil, none of these fluids provide the total solution utilities require in the 21st century to deal with aging transformers.
The Ester-Based Solution
The most beneficial transformer fluids must provide a better balance of performance internally and better degradability externally than most of the newer transformer coolants can provide. New fluids to the market look beyond the fire safety improvements of the coolants manufactured in the 70’s and 80’s to better fulfill today’s utility needs – regulatory adherence, life extension, and improved performance. The search for this solution led manufacturers to investigate ester-based fluids.
Synthetic ester dielectric fluids have excellent dielectric properties and are considerably more biodegradable than mineral oil-based fluids. Yet, the high cost of synthetic ester dielectric fluids restricts its mainstream usage. Synthetic esters are used mainly for traction and mobile transformers and specialty applications.
Natural esters such as seed (vegetable) oil-based fluids were historically known to be unsuitable in transformers. This changed after the development of environmentally safe performance improvement additives and stabilizers. These products, combined with modern transformer design practices, limit fluid exposure to moisture and oxygen. In addition, beneficial properties of the natural esters were identified that were not provided by other dielectric fluids.
Fire Safety and Environmental Compliance
In 1997 a transformer containing the world’s first seed oil-based dielectric coolant was introduced. The transformer fluid had the highest fire and flash points in the industry and was quickly and completely biodegradable. The use of a food grade natural ester base – in this case soy oil – enabled the manufacturer to produce a transformer coolant that met or exceeded current industry environmental and fire safety standards and codes.
Since the time of this introduction, seed oilbased dielectric coolants have continued to meet the needs of the marketplace, including fire safety and environmental compliance.
At least one natural ester fluid has the highest published flash and fire points, at 333°C and 360°C, respectively. FM and UL list some natural ester fluids as a less-flammable dielectric liquid for use in complying with NEC and insurance requirements. Both FM and UL list natural esters for indoor and outdoor installations, typically without fire extinguishing provisions or firewall requirements.
More importantly for utilities with an installed base of mineral-oil transformers, the fire point and flash point properties of natural esters are transferable in retrofill applications. One natural ester manufacturer states that up to 7.5 percent mixture of mineral oil has little impact on the fire point of their product.
When it comes to the environmental protection, food grade seed oil-based dielectric coolants have significant advantages. One seed oilbased transformer fluid is the first transformer material to receive the U.S. Environmental Protection Agency (EPA) ETV (Environmental Technologies Verification) status confirming its published environmental claims.
Life Extension and Improved Performance
Transformer performance typically relates directly to the condition of its paper insulation. As the insulation paper begins to age and weaken, so does the transformer. Water generation and retention is one of the primary causes of accelerating paper insulation degradation an lowering the dielectric performance of the insulation system.
Traditional mineral oil transformer fluids allow the insulation paper to gather water in its fiber. Seed oil-based coolants actually help draw existing moisture out of the paper and prevent water generation from the paper. Accelerated insulation life testing has shown that with seed oil-based coolants paper life can be extended 5 to 8 times, in comparison to aging in mineral oil. Dielectric performance retention also remains high.
Because of this, transformers filled with seed oil-based fluid can 1) be run within their standard operating parameters longer, doubling or better the life of the transformer, or 2) be operated beyond the faceplate ratings without loss of insulation life. (It is important that other transformer components be assessed to determine if they can support the higher operating temperatures.) In either case, using seed oil-based transformer coolant offers utilities a competitive dollar per KVA capacity, while reducing fire and environmental risks.
For utilities operating transformers within standard parameters, the benefit is obvious; they can delay the eventual replacement of the transformer, significantly improving the cash flow of the utility. As even medium power substation transformers can cost upwards of $500,000 to $1 million, this is a major benefit to organizations managing ever-shrinking capital expenditure budgets.
However, some utilities find themselves in the second scenario. Using seed oil-based coolant allows them to provide up to 15 percent more power to their consumers with equipment already in operation. This also provides savings, as they may not have to upgrade transformers to accommodate a larger demand.
Other potential functional benefits of the seed oil dielectric coolants include: reduced minimum clearance insurance requirement to equipment and buildings, elimination of water vapor formation under sudden overload conditions, elimination of detectable sludge, lower gassing tendency, and potentially an improved internal voltage stress distribution.
Field Test
Alliant Energy initiated a study in 2001 to determine the feasibility of changing to a seed oilbased dielectric coolant in a traditional substation transformer. Alliant reviewed test data on the extension of the life of the transformer, fire safety characteristics, and the environmental profile with hopes to bring financial benefits to the company. The study included replacing mineral oil in a 50-MVA transformer at a substation in Cedar Rapids, Iowa with a seed oil dielectric fluid. The step-up transformer was manufactured by Pennsylvania Transformer in 1957, having a primary voltage of 69 kV and 350 kV BIL rating. The unit was retrofilled on October 28, 2001 and is currently functioning as anticipated.
The study completed by Alliant Energy was the first of its kind in the United States to test seed oil fluid in a medium power transformer. Based on positive results generated through the prototype retrofill (see table), Alliant Energy has recently initiated a systematic program of mineral oil replacement in power transformers.
Conclusion
Transformers play a critical role in the delivery of safe and reliable power essential to the nation’s economic growth, security, and our overall quality of life. Transformers installed during the heyday of electrical infrastructure growth, the 50’s and 60’s, are coming to the end of their lifecycle at a time when shrinking capital expenditure budgets and the uncertain ROI brought on by deregulation has made it difficult for utilities to invest money purchasing new transformers.
Electric utilities can now purchase distribution and power transformers and retrofill existing mineral oil filled transformers with tested seed oil-based coolants. These natural esters provide reduced fire and environmental impact risks and improved insulation life. The new coolants will help ensure a higher-level of overall performance from the power delivery system.
About the Author
McShane is Product Line Manager for Dielectric Fluids at Cooper Power Systems. Professional activities include IEEE TC Task Force Chair for Ester Based Dielectric Coolants. He is the principal inventor of four US patents relating to dielectric fluids. Several of his safety related proposals have been adopted by US and International Codes and Standards.
He can be reached at pmcshane@cooperpower.com
The importance of safe and reliable power in today’s world was never more apparent than on August 14. Beginning in late afternoon and lasting mere minutes, the largest blackout ever on the North American continent rolled across the northeastern and north central United States and into Canada. Upwards of 50 million people lost power, including all of New York City, with estimated economic losses hovering at $6 billion.
The blackout of 2003 is an extreme illustration of reliability issues electric utilities face everyday. The media is filled with examples of these more common, but still troublesome, events. Last summer, a distribution transformer serving the St. Louis Arch caught fire and forced the evacuation of 8,000 visitors. A substation fire in San Francisco caused a power outage for 120,000 customers the Saturday before Christmas. Both incidents translated energy company dollars into damage, restoration, and labor fees. In St. Louis, vacation days were ruined, and Bay Area retailers lost essential revenue during one of the busiest shopping days of the year.
The reliable distribution of power, what many of us take for granted, is performed through a complex choreograph of generation, transmission and distribution sectors of the industry. Though the blackout of 2003 shed serious media and regulatory light on the transmission component of this delivery system, many industry experts believe strengthening the distribution system will better ensure a higher level of reliable power. Transformers play a key role in making it happen.
In St. Louis and San Francisco, transformer malfunction was either directly responsible, or part of the larger problem, that caused these events.
Current Transformer Concerns
The economic boom created to feed the World War II war machine continued into the 1950’s and 1960’s. Power was needed to drive the strong national manufacturing base and fulfill the demands of suburban development. Power delivery systems were constructed, and substation and distribution transformers were a part of each and every one. The transformers, which adhered to fire safety and environmental codes and standards on the books at that time, were built to last with a life expectancy of up to 40 years. They were installed and often forgotten about.
The country’s reliance on power grew as it expanded. Populations increased and power tools and appliances replaced equipment that didn’t require electricity. Recent electric utility deregulation further taxed the grid. More has been asked of the installed equipment than it was designed to handle. Much of the older installed equipment, including transformers, is now coming to its useful end.
The number of aging transformers still active has concerned many in the industry. Factory Mutual (FM), a major insurance group, recently reported that the number of substation transformer failures is expected to rise by 500 percent within the next 10 years due to aging systems. The small amount of construction of new power systems and increasing loads on old systems is especially worrisome.
A survey reported by Hartford Steam Boiler, another insurance group, shows that most current failures occur in transformers with an average age of 18 years. As a result of failure incidents, utility companies have reported significant profit losses due to downtime and equipment replacement. One Northeastern power company recently estimated that 50 transformer incidents occur per year at a rate of approximately $10,000 per incident, costing the company $500,000 annually. The majority of these costs are directly related to the actual incident – taking the transformer offline, maintenance or equipment replacement, and getting the new or fixed transformer back online.
With aging transformers, the real risks to utilities and their customers are the potential ancillary costs in case of an eventful transformer failure. Many of these costs are related to the conventional petroleum-based mineral oil used in these older transformers. Mineral oil’s relatively low fire point and negative environmental profile place utilities at greater risk for property damage claims, extensive cleanup, casualties, environmental liability, and negative publicity should a transformer fail.
Shrinking capital expenditure budgets make it difficult for utilities to replace aging, and potentially dangerous, transformers with newer units. Fortunately, utilities have new options.
Changing the Standards
Short of costly equipment replacement, solutions to aging transformers must incorporate the following:
- Adhere to stricter current environmental and fire safety codes and standards
- Maintain or improve transformer performance to better deal with the slow but steady rise in load
- Extend the useful life of the transformer to forestall any capital purchases
Years ago, industry and regulatory bodies tried to address some of these issues by creating a demand to produce a power delivery system focused on safety, equipment efficiency, and environmental protection. This movement included transformers. The focus was on transformer oils.
In 1978, a group of less-flammable transformer fluids were developed and approved by the National Electric Code® (NEC). The NEC created an industry standard that required a minimum open-cup fire of 300°C to be considered safer than conventional transformer oil. In 1984, the Underwriters Laboratories® (UL) collaborated with transformer manufacturers to combine fire resistant fluids with other methods of transformer protection. In the 90’s, Factory Mutual Engineering and Research produced the first Occupational Safety & Health Administration (OSHA)-recognized standard for liquid-filled transformers, suitable for indoor and outdoor installation, with greatly reduced fire safeguard requirements.
Since the late 1970’s, thousands of less-flammable liquid-filled transformers have been in service, and 10 less-flammable dielectric coolants have been approved as an alternative to mineral oil. Approved coolants include high molecular weight hydrocarbons (HMWH), dimethylsiloxanes (silicone), synthetic polyol esters (POE), and polyalphaolefins (PAO).
Despite their success and improvement in many ways over traditional transformer mineral oil, none of these fluids provide the total solution utilities require in the 21st century to deal with aging transformers.
The Ester-Based Solution
The most beneficial transformer fluids must provide a better balance of performance internally and better degradability externally than most of the newer transformer coolants can provide. New fluids to the market look beyond the fire safety improvements of the coolants manufactured in the 70’s and 80’s to better fulfill today’s utility needs – regulatory adherence, life extension, and improved performance. The search for this solution led manufacturers to investigate ester-based fluids.
Synthetic ester dielectric fluids have excellent dielectric properties and are considerably more biodegradable than mineral oil-based fluids. Yet, the high cost of synthetic ester dielectric fluids restricts its mainstream usage. Synthetic esters are used mainly for traction and mobile transformers and specialty applications.
Natural esters such as seed (vegetable) oil-based fluids were historically known to be unsuitable in transformers. This changed after the development of environmentally safe performance improvement additives and stabilizers. These products, combined with modern transformer design practices, limit fluid exposure to moisture and oxygen. In addition, beneficial properties of the natural esters were identified that were not provided by other dielectric fluids.
Fire Safety and Environmental Compliance
In 1997 a transformer containing the world’s first seed oil-based dielectric coolant was introduced. The transformer fluid had the highest fire and flash points in the industry and was quickly and completely biodegradable. The use of a food grade natural ester base – in this case soy oil – enabled the manufacturer to produce a transformer coolant that met or exceeded current industry environmental and fire safety standards and codes.
Since the time of this introduction, seed oilbased dielectric coolants have continued to meet the needs of the marketplace, including fire safety and environmental compliance.
At least one natural ester fluid has the highest published flash and fire points, at 333°C and 360°C, respectively. FM and UL list some natural ester fluids as a less-flammable dielectric liquid for use in complying with NEC and insurance requirements. Both FM and UL list natural esters for indoor and outdoor installations, typically without fire extinguishing provisions or firewall requirements.
More importantly for utilities with an installed base of mineral-oil transformers, the fire point and flash point properties of natural esters are transferable in retrofill applications. One natural ester manufacturer states that up to 7.5 percent mixture of mineral oil has little impact on the fire point of their product.
When it comes to the environmental protection, food grade seed oil-based dielectric coolants have significant advantages. One seed oilbased transformer fluid is the first transformer material to receive the U.S. Environmental Protection Agency (EPA) ETV (Environmental Technologies Verification) status confirming its published environmental claims.
Life Extension and Improved Performance
Transformer performance typically relates directly to the condition of its paper insulation. As the insulation paper begins to age and weaken, so does the transformer. Water generation and retention is one of the primary causes of accelerating paper insulation degradation an lowering the dielectric performance of the insulation system.
Traditional mineral oil transformer fluids allow the insulation paper to gather water in its fiber. Seed oil-based coolants actually help draw existing moisture out of the paper and prevent water generation from the paper. Accelerated insulation life testing has shown that with seed oil-based coolants paper life can be extended 5 to 8 times, in comparison to aging in mineral oil. Dielectric performance retention also remains high.
Because of this, transformers filled with seed oil-based fluid can 1) be run within their standard operating parameters longer, doubling or better the life of the transformer, or 2) be operated beyond the faceplate ratings without loss of insulation life. (It is important that other transformer components be assessed to determine if they can support the higher operating temperatures.) In either case, using seed oil-based transformer coolant offers utilities a competitive dollar per KVA capacity, while reducing fire and environmental risks.
For utilities operating transformers within standard parameters, the benefit is obvious; they can delay the eventual replacement of the transformer, significantly improving the cash flow of the utility. As even medium power substation transformers can cost upwards of $500,000 to $1 million, this is a major benefit to organizations managing ever-shrinking capital expenditure budgets.
However, some utilities find themselves in the second scenario. Using seed oil-based coolant allows them to provide up to 15 percent more power to their consumers with equipment already in operation. This also provides savings, as they may not have to upgrade transformers to accommodate a larger demand.
Other potential functional benefits of the seed oil dielectric coolants include: reduced minimum clearance insurance requirement to equipment and buildings, elimination of water vapor formation under sudden overload conditions, elimination of detectable sludge, lower gassing tendency, and potentially an improved internal voltage stress distribution.
Field Test
Alliant Energy initiated a study in 2001 to determine the feasibility of changing to a seed oilbased dielectric coolant in a traditional substation transformer. Alliant reviewed test data on the extension of the life of the transformer, fire safety characteristics, and the environmental profile with hopes to bring financial benefits to the company. The study included replacing mineral oil in a 50-MVA transformer at a substation in Cedar Rapids, Iowa with a seed oil dielectric fluid. The step-up transformer was manufactured by Pennsylvania Transformer in 1957, having a primary voltage of 69 kV and 350 kV BIL rating. The unit was retrofilled on October 28, 2001 and is currently functioning as anticipated.
The study completed by Alliant Energy was the first of its kind in the United States to test seed oil fluid in a medium power transformer. Based on positive results generated through the prototype retrofill (see table), Alliant Energy has recently initiated a systematic program of mineral oil replacement in power transformers.
Conclusion
Transformers play a critical role in the delivery of safe and reliable power essential to the nation’s economic growth, security, and our overall quality of life. Transformers installed during the heyday of electrical infrastructure growth, the 50’s and 60’s, are coming to the end of their lifecycle at a time when shrinking capital expenditure budgets and the uncertain ROI brought on by deregulation has made it difficult for utilities to invest money purchasing new transformers.
Electric utilities can now purchase distribution and power transformers and retrofill existing mineral oil filled transformers with tested seed oil-based coolants. These natural esters provide reduced fire and environmental impact risks and improved insulation life. The new coolants will help ensure a higher-level of overall performance from the power delivery system.
About the Author
McShane is Product Line Manager for Dielectric Fluids at Cooper Power Systems. Professional activities include IEEE TC Task Force Chair for Ester Based Dielectric Coolants. He is the principal inventor of four US patents relating to dielectric fluids. Several of his safety related proposals have been adopted by US and International Codes and Standards.
He can be reached at pmcshane@cooperpower.com
