HV capacitors are key components in circuit breakers and capacitive voltage transformers, used in the transport and distribution of electrical energy in electric utility grids and other high-voltage installations worldwide.
There is a steadily increasing need for energy which is increasing the requirements for transmission and distribution, and a trend towards higher voltages. This means that the requirements for HV capacitor producers are getting tougher, particularly in terms of increasing reliability and cutting production times.
This article describes how Maxwell Technologies, which has around 65% of the worldwide market share for HV capacitors, is responding to these tougher requirements by implementing improvements at its manufacturing facility in Switzerland.
HV CAPACITOR APPLICATIONS
Around 80% of Maxwell’s HV capacitors are used in high-voltage circuit breakers for transmission and distribution applications. Dead tank breakers are mostly used in North America, live tank (AIS) breakers in Europe, and GIS breakers around the world. The other 20% are in HV applications that are related to transmission and distribution, for example in laboratory applications.
In live tank switchgear circuit breakers, grading capacitors are used to allow the high voltage to be distributed uniformly in the interrupting chambers. In dead tank breakers, coupling capacitors increase the breaking power of the switchgear.
GIS breakers, which also use grading capacitors, are very compact, mostly used in cities where there is no space to install the external breakers. They are also used for tough environments with extreme temperature.
Very high precision is required for laboratory, testing or calibration equipment, and high- quality high voltage capacitors are required for these applications.
The most important capability of a breaker is its ability to handle high voltage and current, for example 550kv and 40kA. Approximately 60% of the electric utility grid employs circuit breakers rated at an interrupting short-circuit current of 40kA, with most of the balance rated at 63kA. By adding a single coupling capacitor to the circuit breaker, upgrading it from 40kA to 63kA, the circuit receives substantially increased protection. HV capacitors are also used in some systems rated up to 80kA in specialized applications where there is very high power generation, such as in areas of high industrial density.
Maxwell’s revenue from HV capacitors is roughly split evenly between the three main markets: Americas (North and South), Europe and Asia. Infrastructure projects in China and other developing countries have been driving strong demand for some time, and there is also now increasing replacement and upgrading activity in the more mature European and North American markets.
TRENDS TO HIGHER VOLTAGE LEVELS
In the US, Europe and China, the most common transportation voltage level is 550kV. 800kV is also used in US, Canada, Korea and is tending to be applied in India and China. This is primarily due to the longer distances that power is transmitted over, requiring higher voltages to minimize transmission losses.
With losses related to the inverse square of voltage, the savings due to higher voltages can be substantial. The resistance of cables is fairly fixed, so increasing the voltage is the main way that transmission losses can be reduced. Also, by increasing the voltage and hence reducing current for a given power, a thinner and lighter cable can be used to carry the lower current.
For example, in China, there tends to be fewer, larger power plants with higher capacity, rather than smaller power plants every 100km or so. The Three Gorges power plant, for instance, supplies power over a huge area.
Worldwide energy demand is forecast to increase strongly – the US government’s Energy information Administration (EIA) has forecast the demand for electricity generation will nearly double between 2002 and 2025, from 14,275 billion kilowatt hours to 26,018 billion kilowatt hours (Source : EIA International Energy Outlook, July 2005, http://www.eia.doe.gov/oiaf/ieo/world.html). Other commentators have predicted this doubling will happen as quickly as 2016.
While the installed base of infrastructure will increase, particularly in developing markets, it will not double, supporting the need for higher voltages to increase capacity.
At the higher voltages, reliability and a proven track record become even more important factors in selecting HV capacitors, with operating lifetimes measured in decades not years.
IMPROVING THE PRODUCTION PROCESS
To respond to these changes in the HV capacitor market, and in particular to improve quality and reliability, there has been a need for improvements in the production process.
The main steps to build a high voltage capacitor are as follows, listed in the order that the steps are followed:
• windings
• stack of windings
• assembly
• tightness test
• drying
• impregnation
• electrical test
The basic capacitor electrodes consist of aluminum foil and a dielectric. Maxwell’s capacitors have a dielectric that is paper, synthetic film, or a combination of both. A paper/polypropylene dielectric has been found to perform significantly better than previous paper dielectrics, with lower dielectric losses and a more stable capacitance/temperature relationship.
Capacitor units, made on a robotic production line from reels of aluminum foil and dielectric strips, are flattened and then welded to other units to build up a capacitor stack. Once the required stack is built, it is assembled into a casing.
This article focuses on the next three steps in the process: tightness test, drying and impregnation. It describes the changes made in the new process, the improvements achieved, and the benefits for customers.
MOTIVATION
In identifying the need for improvements, it was realized that by automating these process steps a linear flowing manufacturing process could be designed with time and cost optimized.
The objectives were set as follows: firstly, a 20% reduction in lead time, with a reduction of the process throughput time by a factor of 5. The fabrication lot was also to be reduced to the most economical quantity.
The number of processes was targeted for a reduction of 50%, and the production area reduced by 50%.
Perhaps most importantly for customers, targets were set to increase of the product quality and reliability. Finally, a requirement was set to reduce waste with oil to comply with the ISO 14000 certification
The project cost budget was set at $1 million US. Initially, the first price estimation was higher at $1.5 million US. After optimizing the processes, the project was able to be completed within the initial cost target.
The timescale for realizing the project was set at six months, and it was essential that the new installation should not create any delay in deliveries of the HV capacitors. These two targets were also met.
IMPLEMENTATION
Several cycles have been tested and several connection systems have been developed so that the drying time of the capacitor stack (after it has been placed inside the insulator housing) has been optimized without affecting the dryness of the active part before impregnation. Previously, many capacitors were dried together in a large drying chamber. The process has been changed so that fewer capacitors are dried in smaller drying chambers, while the number of chambers has been increased to maintain the same overall capacity.
The new system means that each drying and impregnation cycle now takes only two or three days, instead of 2 to 3 weeks as it did previously. Also, by using independent modular units, different technologies can be impregnated in the same time, which allows optimal fabrication lots and number of fabrication units to be defined, therefore maximizing the number of cycles per week and achieving better flexibility.
The assembly of the complete capacitors is done with “dry” parts. Full drying and impregnation is performed on the assembled unit. With this new process the throughput time has been dramatically reduced, because there is no contamination from humidity.
Previously, the tightness test that was made at the end of the process detected any problems very late after the assembling. With the new process, the tightness test is made directly after the assembly and the test time has been reduced from 72 hours to 5 minutes with a completely new test concept. As a result, if a disassembly is required for corrections, it can be made very quickly without creating any delay of deliveries.
Some of the ideas incorporated have been very simple, but still effective. For example, the porcelain insulators are now left in the packaging they are received in until the final electrical test stage. This means that the manual handling of the heavy insulators has been substantially reduced, which has cut the risk of damages. This has also helped reduce the fabrication area required, and also minimized packaging waste.
RESULTS
Manufacturing throughput time has been cut from 5 weeks to 1.5 weeks, while the lead time has been reduced from between 16 and 20 weeks, to only 12 weeks.
The fabrication lot has been reduced from 144 pieces to 6 pieces, and the number of core processes halved from 6 to 3. The new process also means that the production and storage area required have both been halved.
In terms of quality, the reject rate has been reduced by a factor of 10, from 0.5% to 0.05%.
There have also been improvements in quality. Comparing measurements between products manufactured with old and new processes, in the case of high stress loads the break down time of the capacitors could be increased from 500 hours to 700 hours.
Additional tightness tests with intentional leaks have also shown that the new system could detect the leakage on the first pass, where the previous system could not. This means that the first pass yield after the tightness test has been improved from 97% to over 99%.
Inventory is reduced, and with less handwork and clean working stations there has been a reduction in production costs, as well as an increase in staff motivation which has resulted in better productivity.
BENEFITS TO CUSTOMERS
Most importantly, what does this mean for customers?
Firstly, delivery time has been reduced from 16 weeks to 12 weeks. The process is now also more flexible, enabling the impregnation in parallel of different technologies without increasing the lead time.
The production capacity has been increased through the flexibility of modular units. Additional process units can be installed very quickly and easily to increase the production capacity if required.
Then, the reliability of HV capacitors has been improved with the new process. One factor is that the active part is now impregnated without any contact with the humidity in air. With the reduction in manual handling, the risk of damage is reduced – in fact; there have been zero porcelain breaks during handling in the first year of operation of the new process. By investing in smaller, module units for the drying/impregnation cycle, there is now also no risk of big quantities of defect capacitors due to a single problem in this cycle. www.maxwell.com n
About the Authors
Alain R. Riedo - Senior Vice President, General Manager of Maxwell Technologies SA, Rossens, Switzerland
Alain Riedo joined Maxwell Technologies SA, formerly Montena Components, as Director of Sales in 1988, and was appointed General Manager in 1994. He has overall responsibility for Maxwell's global high voltage capacitor and equipment businesses and oversees the company's ultracapacitor business in Europe.
Matthias Stammbach - Dir. Sales & Marketing HV-capacitor, Maxwell Technologies SA, Rossens, Switzerland
Matthias Stammbach joined Maxwell Technologies SA as Sales & Marketing Manager in 2004. He has worldwide responsibility in sales & marketing activities for CONDIS high voltage capacitors by Maxwell Technologies SA.
Etienne Savary - Dir. Core design HV-capacitor, Maxwell Technologies SA, Rossens, Switzerland
Etienne Savary joined Maxwell Technologies SA, formerly Montena Components SA resp. CONDIS SA, as design engineer in 1986, was appointed Quality Manager in 1990 and Business Unit Manager in 1996. He has now responsibility for research and development for CONDIS high voltage capacitor by Maxwell Technologies SA.
There is a steadily increasing need for energy which is increasing the requirements for transmission and distribution, and a trend towards higher voltages. This means that the requirements for HV capacitor producers are getting tougher, particularly in terms of increasing reliability and cutting production times.
This article describes how Maxwell Technologies, which has around 65% of the worldwide market share for HV capacitors, is responding to these tougher requirements by implementing improvements at its manufacturing facility in Switzerland.
HV CAPACITOR APPLICATIONS
Around 80% of Maxwell’s HV capacitors are used in high-voltage circuit breakers for transmission and distribution applications. Dead tank breakers are mostly used in North America, live tank (AIS) breakers in Europe, and GIS breakers around the world. The other 20% are in HV applications that are related to transmission and distribution, for example in laboratory applications.
In live tank switchgear circuit breakers, grading capacitors are used to allow the high voltage to be distributed uniformly in the interrupting chambers. In dead tank breakers, coupling capacitors increase the breaking power of the switchgear.
GIS breakers, which also use grading capacitors, are very compact, mostly used in cities where there is no space to install the external breakers. They are also used for tough environments with extreme temperature.
Very high precision is required for laboratory, testing or calibration equipment, and high- quality high voltage capacitors are required for these applications.
The most important capability of a breaker is its ability to handle high voltage and current, for example 550kv and 40kA. Approximately 60% of the electric utility grid employs circuit breakers rated at an interrupting short-circuit current of 40kA, with most of the balance rated at 63kA. By adding a single coupling capacitor to the circuit breaker, upgrading it from 40kA to 63kA, the circuit receives substantially increased protection. HV capacitors are also used in some systems rated up to 80kA in specialized applications where there is very high power generation, such as in areas of high industrial density.
Maxwell’s revenue from HV capacitors is roughly split evenly between the three main markets: Americas (North and South), Europe and Asia. Infrastructure projects in China and other developing countries have been driving strong demand for some time, and there is also now increasing replacement and upgrading activity in the more mature European and North American markets.
TRENDS TO HIGHER VOLTAGE LEVELS
In the US, Europe and China, the most common transportation voltage level is 550kV. 800kV is also used in US, Canada, Korea and is tending to be applied in India and China. This is primarily due to the longer distances that power is transmitted over, requiring higher voltages to minimize transmission losses.
With losses related to the inverse square of voltage, the savings due to higher voltages can be substantial. The resistance of cables is fairly fixed, so increasing the voltage is the main way that transmission losses can be reduced. Also, by increasing the voltage and hence reducing current for a given power, a thinner and lighter cable can be used to carry the lower current.
For example, in China, there tends to be fewer, larger power plants with higher capacity, rather than smaller power plants every 100km or so. The Three Gorges power plant, for instance, supplies power over a huge area.
Worldwide energy demand is forecast to increase strongly – the US government’s Energy information Administration (EIA) has forecast the demand for electricity generation will nearly double between 2002 and 2025, from 14,275 billion kilowatt hours to 26,018 billion kilowatt hours (Source : EIA International Energy Outlook, July 2005, http://www.eia.doe.gov/oiaf/ieo/world.html). Other commentators have predicted this doubling will happen as quickly as 2016.
While the installed base of infrastructure will increase, particularly in developing markets, it will not double, supporting the need for higher voltages to increase capacity.
At the higher voltages, reliability and a proven track record become even more important factors in selecting HV capacitors, with operating lifetimes measured in decades not years.
IMPROVING THE PRODUCTION PROCESS
To respond to these changes in the HV capacitor market, and in particular to improve quality and reliability, there has been a need for improvements in the production process.
The main steps to build a high voltage capacitor are as follows, listed in the order that the steps are followed:
• windings
• stack of windings
• assembly
• tightness test
• drying
• impregnation
• electrical test
The basic capacitor electrodes consist of aluminum foil and a dielectric. Maxwell’s capacitors have a dielectric that is paper, synthetic film, or a combination of both. A paper/polypropylene dielectric has been found to perform significantly better than previous paper dielectrics, with lower dielectric losses and a more stable capacitance/temperature relationship.
Capacitor units, made on a robotic production line from reels of aluminum foil and dielectric strips, are flattened and then welded to other units to build up a capacitor stack. Once the required stack is built, it is assembled into a casing.
This article focuses on the next three steps in the process: tightness test, drying and impregnation. It describes the changes made in the new process, the improvements achieved, and the benefits for customers.
MOTIVATION
In identifying the need for improvements, it was realized that by automating these process steps a linear flowing manufacturing process could be designed with time and cost optimized.
The objectives were set as follows: firstly, a 20% reduction in lead time, with a reduction of the process throughput time by a factor of 5. The fabrication lot was also to be reduced to the most economical quantity.
The number of processes was targeted for a reduction of 50%, and the production area reduced by 50%.
Perhaps most importantly for customers, targets were set to increase of the product quality and reliability. Finally, a requirement was set to reduce waste with oil to comply with the ISO 14000 certification
The project cost budget was set at $1 million US. Initially, the first price estimation was higher at $1.5 million US. After optimizing the processes, the project was able to be completed within the initial cost target.
The timescale for realizing the project was set at six months, and it was essential that the new installation should not create any delay in deliveries of the HV capacitors. These two targets were also met.
IMPLEMENTATION
Several cycles have been tested and several connection systems have been developed so that the drying time of the capacitor stack (after it has been placed inside the insulator housing) has been optimized without affecting the dryness of the active part before impregnation. Previously, many capacitors were dried together in a large drying chamber. The process has been changed so that fewer capacitors are dried in smaller drying chambers, while the number of chambers has been increased to maintain the same overall capacity.
The new system means that each drying and impregnation cycle now takes only two or three days, instead of 2 to 3 weeks as it did previously. Also, by using independent modular units, different technologies can be impregnated in the same time, which allows optimal fabrication lots and number of fabrication units to be defined, therefore maximizing the number of cycles per week and achieving better flexibility.
The assembly of the complete capacitors is done with “dry” parts. Full drying and impregnation is performed on the assembled unit. With this new process the throughput time has been dramatically reduced, because there is no contamination from humidity.
Previously, the tightness test that was made at the end of the process detected any problems very late after the assembling. With the new process, the tightness test is made directly after the assembly and the test time has been reduced from 72 hours to 5 minutes with a completely new test concept. As a result, if a disassembly is required for corrections, it can be made very quickly without creating any delay of deliveries.
Some of the ideas incorporated have been very simple, but still effective. For example, the porcelain insulators are now left in the packaging they are received in until the final electrical test stage. This means that the manual handling of the heavy insulators has been substantially reduced, which has cut the risk of damages. This has also helped reduce the fabrication area required, and also minimized packaging waste.
RESULTS
Manufacturing throughput time has been cut from 5 weeks to 1.5 weeks, while the lead time has been reduced from between 16 and 20 weeks, to only 12 weeks.
The fabrication lot has been reduced from 144 pieces to 6 pieces, and the number of core processes halved from 6 to 3. The new process also means that the production and storage area required have both been halved.
In terms of quality, the reject rate has been reduced by a factor of 10, from 0.5% to 0.05%.
There have also been improvements in quality. Comparing measurements between products manufactured with old and new processes, in the case of high stress loads the break down time of the capacitors could be increased from 500 hours to 700 hours.
Additional tightness tests with intentional leaks have also shown that the new system could detect the leakage on the first pass, where the previous system could not. This means that the first pass yield after the tightness test has been improved from 97% to over 99%.
Inventory is reduced, and with less handwork and clean working stations there has been a reduction in production costs, as well as an increase in staff motivation which has resulted in better productivity.
BENEFITS TO CUSTOMERS
Most importantly, what does this mean for customers?
Firstly, delivery time has been reduced from 16 weeks to 12 weeks. The process is now also more flexible, enabling the impregnation in parallel of different technologies without increasing the lead time.
The production capacity has been increased through the flexibility of modular units. Additional process units can be installed very quickly and easily to increase the production capacity if required.
Then, the reliability of HV capacitors has been improved with the new process. One factor is that the active part is now impregnated without any contact with the humidity in air. With the reduction in manual handling, the risk of damage is reduced – in fact; there have been zero porcelain breaks during handling in the first year of operation of the new process. By investing in smaller, module units for the drying/impregnation cycle, there is now also no risk of big quantities of defect capacitors due to a single problem in this cycle. www.maxwell.com n
About the Authors
Alain R. Riedo - Senior Vice President, General Manager of Maxwell Technologies SA, Rossens, Switzerland
Alain Riedo joined Maxwell Technologies SA, formerly Montena Components, as Director of Sales in 1988, and was appointed General Manager in 1994. He has overall responsibility for Maxwell's global high voltage capacitor and equipment businesses and oversees the company's ultracapacitor business in Europe.
Matthias Stammbach - Dir. Sales & Marketing HV-capacitor, Maxwell Technologies SA, Rossens, Switzerland
Matthias Stammbach joined Maxwell Technologies SA as Sales & Marketing Manager in 2004. He has worldwide responsibility in sales & marketing activities for CONDIS high voltage capacitors by Maxwell Technologies SA.
Etienne Savary - Dir. Core design HV-capacitor, Maxwell Technologies SA, Rossens, Switzerland
Etienne Savary joined Maxwell Technologies SA, formerly Montena Components SA resp. CONDIS SA, as design engineer in 1986, was appointed Quality Manager in 1990 and Business Unit Manager in 1996. He has now responsibility for research and development for CONDIS high voltage capacitor by Maxwell Technologies SA.
