- Email: [email protected]
High temperature superconducting cable field demonstration at Detroit Edison
Physica C 354 (2001) 49±54
www.elsevier.nl/locate/physc
High temperature superconducting cable ®eld demonstration at Detroit Edison Norman Steve a, Marco Nassi b, Massimo Bechis b,*, Pierluigi Ladie b, Nathan Kelley c, Cristopher Wake®eld c a
c
Pirelli Cables Limited, P.O. Box 6, Eastleigh, Hampshire S050 9YE, UK b Pirelli Cavi e Sistemi SpA, Viale Sarca 222, 20126 Milan, Italy Pirelli Cables and Systems, 710 Industrial Drive, Lexington, SC 29072-3755, USA
Abstract After nearly a decade of scienti®c and technological R&D eorts which led to the completion early in 1999 of a testing program on a complete 115 kV cable system prototype, Pirelli is ready to move high temperature superconducting (HTS) power cable systems out of the laboratory, into real-world applications. With ®nancial support from EPRI and US Department of Energy under its Superconductivity Partnership Initiative II with private industry, Pirelli Cables and Systems and Detroit Edison will install and operate the worldÕs ®rst HTS power cable to deliver electricity in a utility network. The participants in the project are Pirelli, Detroit Edison, American Superconductor Corp. (ASC), EPRI, Los Alamos National Lab (LANL) and Lotepro. Pirelli is leading the design and engineering activities for a demonstration program of a 24 kV, 100 MV A, three-phase warm dielectric cable system aiming at demonstrating a retro®t upgrade application at Detroit EdisonÕs Frisbie Station. Three Warm Dielectric cables will replace nine existing conventional cables while providing the same power capacity. Each HTS cable will carry 2400 A rms. The successful integration of the HTS cable system into the utility network will demonstrate the capability of a HTS system to operate a typical urban distribution system. This paper will describe the Detroit HTS project, highlighting the key engineering issues relating to the application of HTS cables in the context of this ®eld demonstration program. Ó 2001 Elsevier Science B.V. All rights reserved. Keywords: Cryogenic systems; HTS; Power cables
1. Historical background In the late eighties, the discovery that a new class of ceramic oxides exhibited superconducting properties at temperatures above the boiling point of liquid nitrogen (LN) renewed the interest for the
* Corresponding author. Tel.: +39-02-6442-3090; fax: +3902-6442-943. E-mail address: [email protected] (M. Bechis).
application of superconductivity to power systems. In 1988, the US Department of Energy (DOE) created the Superconductivity for Electric Systems Program in an eort to encourage the development of the new technology. In 1989, the Electric Power Research Institute initiated a project to investigate the potential of the new high temperature superconductors (HTS) for power transmission. Pirelli Cables has been active since this time with the development of HTS cable technology. In 1990, Pirelli started working with American Superconductor
0921-4534/01/$ - see front matter Ó 2001 Elsevier Science B.V. All rights reserved. PII: S 0 9 2 1 - 4 5 3 4 ( 0 1 ) 0 0 0 2 1 - 1
50
N. Steve et al. / Physica C 354 (2001) 49±54
Corporation (ASC) to develop the manufacturing technology to produce powder-in-tube based BSCCO superconducting tapes on an industrial scale with engineering properties usable in normal cable manufacturing facilities, and in 1992 performed with EPRI a design analysis to retro®t a conventional 115 kV±200 MV A pipe-type cables system with an HTS warm dielectric circuit providing 100% of ampacity increase [1]. Based on the conclusion of the development study, EPRI and Pirelli, with funding under phase one of the DOEÕs Superconducting Partnership Initiative, undertook a program in 1995 to develop this cable design into a prototype system including a joint, terminations and a cryogenic cooling system. In the framework of this program, a 50 m long HTS conductor was manufactured and tested: a critical current of 3300 A dc was measured in 1996 using 1 lV/cm criteria at 77 K, self-®eld [2,3]. The same conductor was then used in the manufacture of a complete cable prototype for operation at 115 kV. In 1997 and 1998, the complete cable system was installed and tested according to AEIC-CS2/97 and IEEE 48/96 speci®cations: the system passed all tests including hot impulse testing to 550 kV. 2. Field demonstration Building on the successful completion of the test program, Pirelli and its partners looked for a new opportunity to prove the technical feasibility and reliability of HTS transmission systems. Phase II of the DOEÕs Superconducting Partnership Initiative oered the opportunity to perform a demonstration of an HTS cable system in Detroit EdisonÕs distribution network. The project will result in the worldÕs ®rst HTS cable system installed underground and operating in a utility network, and will demonstrate the technical feasibility and operability of a likely early-market application of HTS. The project team includes: Pirelli Cables and Systems, who is project leader and responsible for the design, manufacture and installation of the cable system; Detroit Edison, to provide the demonstration site and the fundamental perspective and expertise of an electric utility; EPRI, who contributes by providing an overall industry perspective
and experience introducing new technologies to the utility industry; ASC, to provide the HTS tapes for use in the construction of the cable; Los Alamos National Laboratory (LANL), for experimental evaluation of AC losses in conductor assemblies, and Lotepro Corporation, which will manufacture and deliver the cryogenic refrigeration system. As shown in Fig. 1, the site for the demonstration is located at the Frisbie substation in Detroit, Michigan; the HTS cables will connect the low voltage side of a 120±24 kV transformer, with a circuit rating of 100 MV A, to the 24 kV bus in the building which is a distance approximately 120 m away from the transformer. Originally, 9 oilimpregnated-paper insulated cables were required to carry the load. The HTS circuit will accomplish the task using only three cables, leaving the remaining ducts available for other uses. At full power each HTS cable will carry 2400 A. The installation site oers an ideal environment for the ®rst demonstration of an HTS cable system: · it requires 2400 A, enough to prove HTS cablesÕ high ampacity performance; · its length, 120 m, allows Pirelli to demonstrate its HTS cable manufacturing capability; · installation through existing underground 4 in. ®ber±bitumen ducts is typical of the conditions which will be encountered in other retro®t applications; · the Frisbie substation has three 120±24 kV transformers, of which only two are needed to serve customer load, leaving the spare unit available for the demonstration. This equipment redundancy reduces the power reliability risks of the HTS demonstration project to Detroit EdisonÕs customers. 3. Cable design The installation environment at Frisbie substation provides a good example of the challenges that will be encountered when retro®tting a circuit in an urban area. First, installation inside the existing nominal 4 in. diameter ducts limits the outer diameter of each cable, this demands compact cable construction. At the same time the installation
N. Steve et al. / Physica C 354 (2001) 49±54
51
Fig. 1. Circuit route at Frisbie substation. During installation, the HTS cables will be pulled through existing underground 4 in. diameter ®ber±bitumen ducts and have to pass several 90° bends.
route, with several 90° bends, calls for light, robust and ¯exible cables to facilitate the installation procedure. The most appropriate HTS design solution to match these stringent requirements is the warm dielectric cable [4]. This design has several advantages, such as the potential to carry, at approximately the same level of losses, more than twice the power of a conventional cable. Also it uses well-proven dielectric materials and has accessories derived from conventional designs, which require similar installation procedures as a conventional system. As shown in Fig. 2, the warm dielectric design features a conductor consisting of superconducting tapes wound around a ¯exible hollow former. LN ¯ows inside the former to maintain the conductor at cryogenic temperature. A ¯exible cryostat is applied over the conductor assembly to provide thermal insulation. This is a vacuum insulated region between two coaxial stainless steel corrugated tubes; radiative multi-layer thermal insulation is applied between the tubes to
minimize radiative heat inleak from the outside. The outer cryostat wall will be very near to the ambient temperature. The electric insulation is applied over the cryostat, as noted above the outer cryostat wall is near ambient temperature and so the dielectricÕs operating environment will be the same as in conventional cables, which allows the use of conventional materials. The Detroit demonstration system will employ an extruded ethylene propylene rubber (EPR) insulation. The cable is then covered with an outer copper shield and an extruded sheath as mechanical protection. 4. Accessories The demonstration project will include six cable terminations. In addition to performing the same dielectric function as its conventional counterpart, each termination must also handle the transition from superconducting to normal conducting
52
N. Steve et al. / Physica C 354 (2001) 49±54
Fig. 2. Schematic representation of a warm dielectric superconducting cable. The electric insulation is applied over the cryostat, so its operating environment is the same as in conventional cables.
elements, control the thermal transition from cryogenic temperature to ambient temperature through the connecting element (current lead), and provide a hydraulic connection for LN circulation. The terminations designed for the demonstration features a conventional outdoor insulator combined with a novel cryogenic portion. The conventional part consists of a pre-molded 24 kV stress cone to manage the electric stress inside the insulator where the cable screen is interrupted. The selection of the insulator and design of the stress cone are performed following standard design criteria relevant to extruded cables. The cryogenic portion consists of a thermally isolated currentlead through which the connection of the LN circuit is realized. Event though the three phases can be installed in complete sections, one will be spliced with a pre-molded joint located in MH13465 to train Detroit Edison personnel on its installation method. The techniques applied are partially based on the ones developed during the 115 kV program. Special features are also included to solder the superconductor tapes to a normal current connector and to seal the cryostat.
5. Refrigeration system The use of HTS materials requires operation of the cable system at very low temperatures, around 196°C (77 K). This is accomplished by pumping sub-cooled LN through the system at suciently elevated pressure to suppress boiling. While ¯owing along the HTS system, the refrigerant absorbs the energy dissipated into the circuit and carries it to a cryogenic refrigeration unit, which removes the absorbed heat and returns the coolant to the initial temperature. The energy loss mechanisms include thermal losses through the cryostat, hydraulic losses of the coolant ¯ow, AC losses in the superconducting material and joule losses at the normal conductor/HTS transition points. Because the refrigeration unit is of fundamental importance for the operation of an HTS transmission system, its reliability and availability must be very high. In addition, utility industry has no experience with the technologies related to refrigeration at cryogenic temperatures, and the reliance of the electrical network on the operation of an external mechanical system, coupled with utilitiesÕ responsibility for
N. Steve et al. / Physica C 354 (2001) 49±54
reliable service to their customers, creates a challenge [5]. Recognizing the criticality of the refrigeration plant to the operation of the cable system, maximum eort has been applied to engineer a reliable cryogenic unit that is representative of a system which could be used in commercial applications [6]. The complete system will be designed and manufactured by Lotepro Corporation, based on speci®cations developed by Pirelli. A simpli®ed process ¯ow diagram of the cold box is provided in Fig. 3. The primary helium refrigerator cools the LN ¯owing through the HTS cables using the wellknown Brayton cycle with two turbines in series and two counter current heat exchangers. The reliability of this type of refrigeration has been proved by many successful installations all over the world. A backup system is implemented to deliver the refrigeration capacity in case of unavailability of the primary helium cycle, to prevent interruptions of the HTS cables operation. LN supplied by a bulk storage tank is boiled at subatmospheric pressure into a LN±LN heat exchanger to ensure almost the same ¯ow supply temperature as that guaranteed by the helium refrigerator. The LN circulation system consists of
53
two redundant cryogenic pumps that provide the necessary pressure head to maintain LN circulation through the HTS cables. The pressurization system is included to limit pressure change due to coolant volume ¯uctuations during cable load transients. 6. Conclusions Currently HTS cables systems have been successfully demonstrated in few laboratory scale prototypes, but the commercial introduction of this new technology requires moving those successes to more complete systems. For this reason the US DOE and EPRI are providing ®nancial support to a demonstration program that will result in the worldÕs ®rst installation of an HTS transmission system in a utility network. The program includes the underground installation of three warm dielectric cables into DetroitÕs distribution network which will replace nine conventional cables, with the same circuit rating. The HTS circuit will connect the low voltage side of a 120±24 kV transformer to a 24 kV bus approximately 120 m away. At full load each cable will
Fig. 3. Simpli®ed process ¯ow diagram of the refrigeration system cold box. The primary refrigerator is based on a well-known helium Brayton cycle; 100% backup is provided with sub-atmospheric boiling LN.
54
N. Steve et al. / Physica C 354 (2001) 49±54
deliver 2400 A, for a circuit rating of 100 MV A. The project is led by Pirelli Cables and Systems, who is responsible for the design, manufacture and installation of the system. Once connected to the distribution grid, the HTS system will experience the same daily operating conditions of a conventional cable, which will prove its reliability and robustness. Ultimately, the program will demonstrate to the electric utilities that HTS cables can be viable alternative to solve power system design problems, which in turn will improve the service provided to their customers. Acknowledgements The authors would like to acknowledge the accomplishment of this work under the support of phase two of the DOE Oce of Energy TechnologyÕs Superconducting Partnership Initiative.
References [1] D.W. Von Dollen, P. Metra, M. Rahman, Design concept of a room temperature dielectric HTS cable, Proc. Am. Power Conf., Chicago, April 1993, p. 1206. [2] M. Nassi, L. Gherardi, M. Rahman, D. Von Dollen, Design, Development, and Testing of the First FactoryMade High Temperature Superconducting Cable for 115 kV±400 MVA, CIGRE, Session 1998. [3] N. Kelley, M. Nassi, M. Rahman, et al., Applications of HTS Cables to Power Transmission: State-of-the-Art and Opportunities, Proc. IEEE Trans. Dist. Conf., New Orleans, April 1999. [4] M. Nassi, S. Norman, N. Kelley, et al., High Temperature Superconducting Cable System at Detroit Edison, Proc. T&D World Conf. Exposition, Cincinnati, Ohio, April 2000. [5] N. Kelley, M. Bechis, Cryogenic Refrigeration Systems for a Warm Dielectric High Temperature Superconducting Power Cable System, The 12th Intersociety Cryogenic Symposium at 2000 AIChE Spring Meeting, Atlanta, March 2000. [6] M. Bechis, J.J. Clausen, D. Von Dollen, et al., Cryogenic Refrigeration for HTS Power Cables, Proc. ICEC 18, Mumbai, February 2000.
www.elsevier.nl/locate/physc
High temperature superconducting cable ®eld demonstration at Detroit Edison Norman Steve a, Marco Nassi b, Massimo Bechis b,*, Pierluigi Ladie b, Nathan Kelley c, Cristopher Wake®eld c a
c
Pirelli Cables Limited, P.O. Box 6, Eastleigh, Hampshire S050 9YE, UK b Pirelli Cavi e Sistemi SpA, Viale Sarca 222, 20126 Milan, Italy Pirelli Cables and Systems, 710 Industrial Drive, Lexington, SC 29072-3755, USA
Abstract After nearly a decade of scienti®c and technological R&D eorts which led to the completion early in 1999 of a testing program on a complete 115 kV cable system prototype, Pirelli is ready to move high temperature superconducting (HTS) power cable systems out of the laboratory, into real-world applications. With ®nancial support from EPRI and US Department of Energy under its Superconductivity Partnership Initiative II with private industry, Pirelli Cables and Systems and Detroit Edison will install and operate the worldÕs ®rst HTS power cable to deliver electricity in a utility network. The participants in the project are Pirelli, Detroit Edison, American Superconductor Corp. (ASC), EPRI, Los Alamos National Lab (LANL) and Lotepro. Pirelli is leading the design and engineering activities for a demonstration program of a 24 kV, 100 MV A, three-phase warm dielectric cable system aiming at demonstrating a retro®t upgrade application at Detroit EdisonÕs Frisbie Station. Three Warm Dielectric cables will replace nine existing conventional cables while providing the same power capacity. Each HTS cable will carry 2400 A rms. The successful integration of the HTS cable system into the utility network will demonstrate the capability of a HTS system to operate a typical urban distribution system. This paper will describe the Detroit HTS project, highlighting the key engineering issues relating to the application of HTS cables in the context of this ®eld demonstration program. Ó 2001 Elsevier Science B.V. All rights reserved. Keywords: Cryogenic systems; HTS; Power cables
1. Historical background In the late eighties, the discovery that a new class of ceramic oxides exhibited superconducting properties at temperatures above the boiling point of liquid nitrogen (LN) renewed the interest for the
* Corresponding author. Tel.: +39-02-6442-3090; fax: +3902-6442-943. E-mail address: [email protected] (M. Bechis).
application of superconductivity to power systems. In 1988, the US Department of Energy (DOE) created the Superconductivity for Electric Systems Program in an eort to encourage the development of the new technology. In 1989, the Electric Power Research Institute initiated a project to investigate the potential of the new high temperature superconductors (HTS) for power transmission. Pirelli Cables has been active since this time with the development of HTS cable technology. In 1990, Pirelli started working with American Superconductor
0921-4534/01/$ - see front matter Ó 2001 Elsevier Science B.V. All rights reserved. PII: S 0 9 2 1 - 4 5 3 4 ( 0 1 ) 0 0 0 2 1 - 1
50
N. Steve et al. / Physica C 354 (2001) 49±54
Corporation (ASC) to develop the manufacturing technology to produce powder-in-tube based BSCCO superconducting tapes on an industrial scale with engineering properties usable in normal cable manufacturing facilities, and in 1992 performed with EPRI a design analysis to retro®t a conventional 115 kV±200 MV A pipe-type cables system with an HTS warm dielectric circuit providing 100% of ampacity increase [1]. Based on the conclusion of the development study, EPRI and Pirelli, with funding under phase one of the DOEÕs Superconducting Partnership Initiative, undertook a program in 1995 to develop this cable design into a prototype system including a joint, terminations and a cryogenic cooling system. In the framework of this program, a 50 m long HTS conductor was manufactured and tested: a critical current of 3300 A dc was measured in 1996 using 1 lV/cm criteria at 77 K, self-®eld [2,3]. The same conductor was then used in the manufacture of a complete cable prototype for operation at 115 kV. In 1997 and 1998, the complete cable system was installed and tested according to AEIC-CS2/97 and IEEE 48/96 speci®cations: the system passed all tests including hot impulse testing to 550 kV. 2. Field demonstration Building on the successful completion of the test program, Pirelli and its partners looked for a new opportunity to prove the technical feasibility and reliability of HTS transmission systems. Phase II of the DOEÕs Superconducting Partnership Initiative oered the opportunity to perform a demonstration of an HTS cable system in Detroit EdisonÕs distribution network. The project will result in the worldÕs ®rst HTS cable system installed underground and operating in a utility network, and will demonstrate the technical feasibility and operability of a likely early-market application of HTS. The project team includes: Pirelli Cables and Systems, who is project leader and responsible for the design, manufacture and installation of the cable system; Detroit Edison, to provide the demonstration site and the fundamental perspective and expertise of an electric utility; EPRI, who contributes by providing an overall industry perspective
and experience introducing new technologies to the utility industry; ASC, to provide the HTS tapes for use in the construction of the cable; Los Alamos National Laboratory (LANL), for experimental evaluation of AC losses in conductor assemblies, and Lotepro Corporation, which will manufacture and deliver the cryogenic refrigeration system. As shown in Fig. 1, the site for the demonstration is located at the Frisbie substation in Detroit, Michigan; the HTS cables will connect the low voltage side of a 120±24 kV transformer, with a circuit rating of 100 MV A, to the 24 kV bus in the building which is a distance approximately 120 m away from the transformer. Originally, 9 oilimpregnated-paper insulated cables were required to carry the load. The HTS circuit will accomplish the task using only three cables, leaving the remaining ducts available for other uses. At full power each HTS cable will carry 2400 A. The installation site oers an ideal environment for the ®rst demonstration of an HTS cable system: · it requires 2400 A, enough to prove HTS cablesÕ high ampacity performance; · its length, 120 m, allows Pirelli to demonstrate its HTS cable manufacturing capability; · installation through existing underground 4 in. ®ber±bitumen ducts is typical of the conditions which will be encountered in other retro®t applications; · the Frisbie substation has three 120±24 kV transformers, of which only two are needed to serve customer load, leaving the spare unit available for the demonstration. This equipment redundancy reduces the power reliability risks of the HTS demonstration project to Detroit EdisonÕs customers. 3. Cable design The installation environment at Frisbie substation provides a good example of the challenges that will be encountered when retro®tting a circuit in an urban area. First, installation inside the existing nominal 4 in. diameter ducts limits the outer diameter of each cable, this demands compact cable construction. At the same time the installation
N. Steve et al. / Physica C 354 (2001) 49±54
51
Fig. 1. Circuit route at Frisbie substation. During installation, the HTS cables will be pulled through existing underground 4 in. diameter ®ber±bitumen ducts and have to pass several 90° bends.
route, with several 90° bends, calls for light, robust and ¯exible cables to facilitate the installation procedure. The most appropriate HTS design solution to match these stringent requirements is the warm dielectric cable [4]. This design has several advantages, such as the potential to carry, at approximately the same level of losses, more than twice the power of a conventional cable. Also it uses well-proven dielectric materials and has accessories derived from conventional designs, which require similar installation procedures as a conventional system. As shown in Fig. 2, the warm dielectric design features a conductor consisting of superconducting tapes wound around a ¯exible hollow former. LN ¯ows inside the former to maintain the conductor at cryogenic temperature. A ¯exible cryostat is applied over the conductor assembly to provide thermal insulation. This is a vacuum insulated region between two coaxial stainless steel corrugated tubes; radiative multi-layer thermal insulation is applied between the tubes to
minimize radiative heat inleak from the outside. The outer cryostat wall will be very near to the ambient temperature. The electric insulation is applied over the cryostat, as noted above the outer cryostat wall is near ambient temperature and so the dielectricÕs operating environment will be the same as in conventional cables, which allows the use of conventional materials. The Detroit demonstration system will employ an extruded ethylene propylene rubber (EPR) insulation. The cable is then covered with an outer copper shield and an extruded sheath as mechanical protection. 4. Accessories The demonstration project will include six cable terminations. In addition to performing the same dielectric function as its conventional counterpart, each termination must also handle the transition from superconducting to normal conducting
52
N. Steve et al. / Physica C 354 (2001) 49±54
Fig. 2. Schematic representation of a warm dielectric superconducting cable. The electric insulation is applied over the cryostat, so its operating environment is the same as in conventional cables.
elements, control the thermal transition from cryogenic temperature to ambient temperature through the connecting element (current lead), and provide a hydraulic connection for LN circulation. The terminations designed for the demonstration features a conventional outdoor insulator combined with a novel cryogenic portion. The conventional part consists of a pre-molded 24 kV stress cone to manage the electric stress inside the insulator where the cable screen is interrupted. The selection of the insulator and design of the stress cone are performed following standard design criteria relevant to extruded cables. The cryogenic portion consists of a thermally isolated currentlead through which the connection of the LN circuit is realized. Event though the three phases can be installed in complete sections, one will be spliced with a pre-molded joint located in MH13465 to train Detroit Edison personnel on its installation method. The techniques applied are partially based on the ones developed during the 115 kV program. Special features are also included to solder the superconductor tapes to a normal current connector and to seal the cryostat.
5. Refrigeration system The use of HTS materials requires operation of the cable system at very low temperatures, around 196°C (77 K). This is accomplished by pumping sub-cooled LN through the system at suciently elevated pressure to suppress boiling. While ¯owing along the HTS system, the refrigerant absorbs the energy dissipated into the circuit and carries it to a cryogenic refrigeration unit, which removes the absorbed heat and returns the coolant to the initial temperature. The energy loss mechanisms include thermal losses through the cryostat, hydraulic losses of the coolant ¯ow, AC losses in the superconducting material and joule losses at the normal conductor/HTS transition points. Because the refrigeration unit is of fundamental importance for the operation of an HTS transmission system, its reliability and availability must be very high. In addition, utility industry has no experience with the technologies related to refrigeration at cryogenic temperatures, and the reliance of the electrical network on the operation of an external mechanical system, coupled with utilitiesÕ responsibility for
N. Steve et al. / Physica C 354 (2001) 49±54
reliable service to their customers, creates a challenge [5]. Recognizing the criticality of the refrigeration plant to the operation of the cable system, maximum eort has been applied to engineer a reliable cryogenic unit that is representative of a system which could be used in commercial applications [6]. The complete system will be designed and manufactured by Lotepro Corporation, based on speci®cations developed by Pirelli. A simpli®ed process ¯ow diagram of the cold box is provided in Fig. 3. The primary helium refrigerator cools the LN ¯owing through the HTS cables using the wellknown Brayton cycle with two turbines in series and two counter current heat exchangers. The reliability of this type of refrigeration has been proved by many successful installations all over the world. A backup system is implemented to deliver the refrigeration capacity in case of unavailability of the primary helium cycle, to prevent interruptions of the HTS cables operation. LN supplied by a bulk storage tank is boiled at subatmospheric pressure into a LN±LN heat exchanger to ensure almost the same ¯ow supply temperature as that guaranteed by the helium refrigerator. The LN circulation system consists of
53
two redundant cryogenic pumps that provide the necessary pressure head to maintain LN circulation through the HTS cables. The pressurization system is included to limit pressure change due to coolant volume ¯uctuations during cable load transients. 6. Conclusions Currently HTS cables systems have been successfully demonstrated in few laboratory scale prototypes, but the commercial introduction of this new technology requires moving those successes to more complete systems. For this reason the US DOE and EPRI are providing ®nancial support to a demonstration program that will result in the worldÕs ®rst installation of an HTS transmission system in a utility network. The program includes the underground installation of three warm dielectric cables into DetroitÕs distribution network which will replace nine conventional cables, with the same circuit rating. The HTS circuit will connect the low voltage side of a 120±24 kV transformer to a 24 kV bus approximately 120 m away. At full load each cable will
Fig. 3. Simpli®ed process ¯ow diagram of the refrigeration system cold box. The primary refrigerator is based on a well-known helium Brayton cycle; 100% backup is provided with sub-atmospheric boiling LN.
54
N. Steve et al. / Physica C 354 (2001) 49±54
deliver 2400 A, for a circuit rating of 100 MV A. The project is led by Pirelli Cables and Systems, who is responsible for the design, manufacture and installation of the system. Once connected to the distribution grid, the HTS system will experience the same daily operating conditions of a conventional cable, which will prove its reliability and robustness. Ultimately, the program will demonstrate to the electric utilities that HTS cables can be viable alternative to solve power system design problems, which in turn will improve the service provided to their customers. Acknowledgements The authors would like to acknowledge the accomplishment of this work under the support of phase two of the DOE Oce of Energy TechnologyÕs Superconducting Partnership Initiative.
References [1] D.W. Von Dollen, P. Metra, M. Rahman, Design concept of a room temperature dielectric HTS cable, Proc. Am. Power Conf., Chicago, April 1993, p. 1206. [2] M. Nassi, L. Gherardi, M. Rahman, D. Von Dollen, Design, Development, and Testing of the First FactoryMade High Temperature Superconducting Cable for 115 kV±400 MVA, CIGRE, Session 1998. [3] N. Kelley, M. Nassi, M. Rahman, et al., Applications of HTS Cables to Power Transmission: State-of-the-Art and Opportunities, Proc. IEEE Trans. Dist. Conf., New Orleans, April 1999. [4] M. Nassi, S. Norman, N. Kelley, et al., High Temperature Superconducting Cable System at Detroit Edison, Proc. T&D World Conf. Exposition, Cincinnati, Ohio, April 2000. [5] N. Kelley, M. Bechis, Cryogenic Refrigeration Systems for a Warm Dielectric High Temperature Superconducting Power Cable System, The 12th Intersociety Cryogenic Symposium at 2000 AIChE Spring Meeting, Atlanta, March 2000. [6] M. Bechis, J.J. Clausen, D. Von Dollen, et al., Cryogenic Refrigeration for HTS Power Cables, Proc. ICEC 18, Mumbai, February 2000.