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Superconducting fault current limiter thesis writing

Superconducting fault current limiter thesis writing to eliminate the helium


FAULT-CURRENT LIMITERS (FCL) 1

Summary

Fault-current limiters using hot temperature superconductors offer a strategy to controlling fault-current levels on utility distribution and transmission systems. These fault-current limiters, unlike reactors or high-impedance transformers, will limit fault currents without adding impedance towards the circuit during normal operation. Growth and development of superconducting fault-current limiters has been went after by a number of utilities and electrical manufacturers all over the world, and commercial devices are expected to be shown through the turn from the century.

Fault-Current Problem

Electrical power system designers frequently face fault-current problems when expanding existing buses. Bigger transformers lead to greater fault-duty levels, forcing the substitute of existing buswork and switchgear not rated for that new fault duty. Alternatively, the present bus could be damaged and offered by several smaller sized transformers. Another alternative is use of merely one, large, high-impedance transformer, leading to degraded current regulation for the customers around the bus. The classic tradeoff between fault control, bus capacity, and system stiffness has endured for many years.

Other common system changes can lead to a fault control problem:

  • in certain areas, like the U . s . States, additional generation from cogenerators and independent power producers (IPPs) enhances the fault duty within a system
  • older but nonetheless operational equipment progressively becomes underrated through system growth some equipment, for example transformers in subterranean vaults or cables, can be quite costly to exchange
  • customers request parallel services that boost the longevity of their supply but enhance the fault duty

Superconductive FCL

Superconductors offer a method to break through system design constraints by presenting an impedance towards the electrical system that varies based on operating conditions.

Superconducting fault-current limiters normally operate with low impedance and therefore are “invisible” components within the electrical system. In case of a fault, the limiter inserts impedance in to the circuit and limits the fault current. With current limiters, the utility can offer a minimal-impedance, stiff system having a low fault-current level, as Fig. 4.5 shows.

Fig. 4.5. Fault control having a fault-current limiter.

In Fig. 4.5, a sizable, low-impedance transformer can be used to give a bus. Normally, the FCL has no effect on the circuit. In case of a fault, the limiter develops an impedance of .2 per unit (Z = 20%), and also the fault current ISC is reduced to 7,400 A. With no limiter, the fault current could be 37,000 A.

The introduction of hot temperature superconductors (HTS) enables the introduction of economical fault-current limiters. Superconducting fault-current limiters were first studied over two decades ago. The first designs used cold superconductors (LTS), materials that lose all resistance at temperatures a couple of levels above absolute zero. LTS materials are usually cooled with liquid helium, an ingredient both costly and hard to deal with. The invention in 1986 of hot temperature superconductors, which operate at greater temperatures and could be cooled by relatively affordable liquid nitrogen, restored curiosity about superconducting fault-current limiters.

Superconducting fault current limiter thesis writing single, large, high-impedance transformer

Fault-Current Limiter Applications

Fault-current limiters does apply in many distribution or transmission areas. Three primary applications areas are proven in Figs. 4.6, 4.7, and 4.8.

Fig. 4.6. Fault-current limiter within the primary position. The fault-current limiter FCL protects the whole bus.

Fig. 4.7. Fault-current limiter within the feeder position. The fault-current limiter FCL protects a person circuit around the bus. Underrated equipment could be selectively protected when needed in this way.

Fig. 4.8. Fault-current limiter within the bus-tie position. The 2 buses are tied, yet a faulted bus has got the full fault current of just one transformer.

Probably the most direct use of a fault-current limiter is incorporated in the primary position on the bus (Fig. 4.6). Advantages of an FCL within this application range from the following:

  • a bigger transformer may be used to meet elevated demand on the bus without breaker upgrades
  • a sizable, low impedance transformer may be used to maintain current regulation in the new electricity
  • I 2 t harm to the transformer is restricted
  • reduced fault-current flows within the high-current circuit that feeds the transformer, which minimizes the current dip around the upstream high-current bus throughout a fault around the medium-current bus

An FCL may also be used to safeguard individual loads around the bus (Fig. 4.7). The selective use of small , less costly limiters may be used to safeguard old or overstressed equipment that’s hard to replace, for example subterranean cables or transformers in vaults.

An FCL may be used within the bus-tie position (Fig. 4.8). This type of limiter will need merely a small load current rating but would provide the following advantages:

  • separate buses could be tied together with no large rise in the fault duty on either bus
  • throughout a fault, a sizable current drop over the limiter maintains current level around the unfaulted bus
  • the paralleled transformers lead to low system impedance and good current regulation tap-altering transformers could be prevented
  • excess capacity of every bus can be obtained to both buses, thus making better utilisation of the transformer rating

Superconductive Fault-Current Limiter Concepts

The easiest superconducting limiter concept, the series resistive limiter, exploits the nonlinear resistance of superconductors inside a direct way. A superconductor is placed within the circuit. For any full-load current of IFL. the superconductor could be designed to possess a critical current of 2IFL or 3IFL. Throughout a fault, the fault current pushes the superconductor right into a resistive condition and resistance R seems within the circuit.

The superconductor in the resistive condition may also be used like a trigger coil, pushing the majority of the fault current via a resistor or inductor. The benefit of this configuration, proven in Fig. 4.9, is it limits the power that must definitely be absorbed through the superconductor.

Fig. 4.9. Fault-current limiter with HTS trigger coil.

The fault-current limiter FCL normally is really a short over the copper inductive or resistive element Z. Throughout a fault, the resistance coded in the limiter shunts the present through Z, which absorbs the majority of the fault energy.

The trigger coil approach is suitable for transmission line applications, where many megawatt-seconds could be absorbed inside a series resistive limiter. The trigger coil configuration also enables an impedance associated with a phase position, from purely resistive to just about purely inductive, to become placed within the line.

Another concept utilizes a resistive limiter on the transformer secondary, using the primary in series within the circuit. This idea, highlighted in Fig. 4.10, yields a limiter appropriate for top-current circuits (IL 1000 A). One phase from the limiter is proven. A copper winding WCu is placed within the circuit and it is coupled for an HTS winding WHTS. During normal operation, a zero impedance is reflected towards the primary. Resistance coded in the HTS winding throughout a fault is reflected towards the primary and limits the fault.

The inductive limiter could be modeled like a transformer. The impedance of the limiter within the steady condition is almost zero, because the zero impedance from the secondary (HTS) winding is reflected towards the primary. In case of a fault, the big current within the circuit induces a sizable current within the secondary and also the winding loses superconductivity. The resistance within the secondary is reflected in to the circuit and limits the fault.

Fig. 4.10. Inductive fault-current limiter.

Japanese FCL Program

The driving factors for current limiters in Japan are somewhat not the same as individuals within the U . s . States, considering that IPPs and cogenerators aren’t as prevalent in Japan. Rather, the interest in power in Japanese urban centers keeps growing due to economic growth and elevated consumer utilization of electricity. Additionally, industrial utilization of computers along with other power-quality-sensitive equipment has forced the utilities to supply greater quality and much more reliable power. The quite effective method of improved power quality in Japan is to increase connections between various power systems and also to concentrate generation capacity in bigger, more effective units. Growing interconnection does, however, boost the maximum fault current available at any time within the system, which is quickly resulting in the requirement for breaker upgrades and system reconfigurations. Contributing to the complexness from the situation in Japan may be the limited room at substation sites, which could preclude breaker upgrades. The main need, as expressed by control over the Tokyo, japan Electrical Power Company (TEPCO), is perfect for a limiter for that nucleus from the Japanese transmission system, the 500 kV transmission grid.

As a result of this real market pull there’s been a number of programs to build up fault-current limiters using a number of methods, with recent concentrate on superconducting limiters (Nakade 1994). Although FCLs aren’t a part of the NEDO budget, TEPCO has reported it spends about 100 million each year (

$a million) about this program, and a few resistive FCL jobs are apparently incorporated within the NEDO budget underneath the subject “Research of Superconducting Materials and Devices.”

Within the late 1980s, Seikei College manufactured a little-scale three-phase current-restricting reactor and shown effective operation. This three-phase system introduces a sizable unbalanced reactance within the system to limit currents within the situation of merely one-phase short and quenches introducing resistance within the circuit within the situation of the three-phase fault.

Mitsubishi Utility Company (MELCO) continues to be taking part in a MITI/NEDO FCL program since 1990. This can be a resistive limiter approach using HTS films on the strontium titanate substrate which has shown restricting of 400 A currents to 11.3 A. The Central Research Institute from the Electrical Power Industry (CRIEPI) is promoting the inductive limiter proven in Fig. 4.11 (Ichikawa and Okazaki 1995). This method, much like individuals of ABB and Siemens-Hydro Quebec, utilizes a cylinder of bulk BSCCO-2212 or BSCCO-2223 to split up an ordinary copper coil from an iron core. In normal operation, the area in the copper coil doesn’t penetrate the superconductor under fault conditions, however, the present caused within the superconductor will drive it normal, and also the magnetic field links the iron yoke. This greatly boosts the inductance from the copper coil, thus supplying current restricting. CRIEPI work has centered on ac magnetic shielding performance of bulk superconductors as well as their responses to fault currents. Additionally, introduction of the “control ring” within the system to soak up a few of the energy deposited throughout a fault has reduced the cooldown duration of the shield carrying out a faulted condition.

Fig. 4.11. Schematic diagram from the CRIEPI inductive FCL (Ichikawa and Okazaki 1995).

Probably the most extensive FCL enter in Japan continues to be the collaboration between TEPCO and Toshiba. The lengthy-term objective of the program is the introduction of a 500 kV limiter having a rated current of 8,000 A. Initial development has concentrated on a distribution-level limiter created for 6.6 kV.

As proven in Fig. 4.12, the FCL is created by connecting four superconducting coils inside a series-parallel configuration therefore the total inductance is minimized. Some coils can be used for every phase from the device, and restricting is accomplished by quenching the coils. The present form of the FCL proven in Fig. 4.13 utilizes a special low ac loss Nb-Ti conductor. Tests inside a circuit having a nominal short circuit current of 25.8 kA have effectively shown restricting to around 4,000 amps (Fig. 4.14).

Fig. 4.12. Configuration of coils within the TEPCO/Toshiba FCL (Nakade 1994, 34).

Fig. 4.13. Exterior look at the 6.6 kV 2,000 A-class current limiter. The coil is 420 mm across and 640 mm lengthy (Nakade 1994, 35).

Fig. 4.14. Current restricting characteristics of Toshiba FCL proven in Fig. 4.13 (Nakade 1994, 35).

Recent work has incorporated the development of HTS current results in lessen the refrigeration load from the system to levels that may be handled with a 4 K Gifford McMahon refrigerator. Over three generations from the device, heat leak continues to be reduced from 13.8 watts to three.4 watts, that is nearing the needed level.

TEPCO will build up a 3-phase limiter within the next 3 to 4 many test drive it within the grid in this particular century. You will find couple of distribution-level FCL applications observed in the TEPCO grid, however, and also the current plan’s introducing solid condition breakers for distribution before installing superconductive FCL.

The real application for that superconducting FCL reaches transmission voltages of 500 kV. The vista of TEPCO researchers is this fact current range will need the development of HTS coils (instead of LTS) to get rid of the helium gas in the system. Introduction of the transmission-level FCL around the grid is predicted about 2010.

Fault-Current Limiters In Europe

Probably the most comprehensive FCL enter in Europe is the fact that being conducted with a collaboration between Electricit de France, GEC Alsthom, and Alcatel Alsthom Recherche. The program’s primary goal would be to provide FCLs for that 225 kV grid in France. The audience has selected a resistive limiter according to LTS material and it has shown effective operation at 40 kV (rms), by having an industrial demonstration around the French 63 kV grid expected in 1998. Look at in france they program is past the scope of the WTEC study, so no visit is made for this project. Verhaege et al. (1996) provide an introduction to we’ve got the technology and project status.

Two sites the WTEC panel visited in Europe addressed FCL: ABB in Baden-Daetwil, Europe, and Siemens in Erlangen, Germany. ABB is going after a fault-current limiter concept much like that described above for that CRIEPI program. It is called the “shielded iron core concept.” It utilizes a warm iron core enclosed with a superconducting shield inside a fiberglass Dewar. The copper primary coil is wound exterior for this Dewar. ABB has built and tested one hundred kW prototype using a collection of four Bi-2212 rings 8 cm lengthy, and 20 cm across. Operation what food was in 480 V with fault currents of 8 kA. A brand new ABB three-phase 1.2 MW FCL has become functioning inside a power station in Lntsch, Europe.

Siemens is following two routes for FCL inside a collaborative program with Hydro-Quebec Canada. In the Siemens corporate labs in Erlangen, the main focus continues to be on resistive limiters using YBCO thin film meander lines on YSZ or on YSZ and azure (Gromoll et al. 1996). The benefit of this method would be that the YBCO film includes a high normal condition resistance and isn’t shunted by normal metal, as will be the situation inside a composite powder-in-tube conductor. The video also offers really low heat capacity, which results in rapid switching towards the normal condition ( 1 ms) and the potential of rapid cooldown. Analysis by 1996 has figured that both peak let-through current and steady condition restricting current decrease as Jc is elevated. Additionally, the style of a limiter of functional size depends strongly on Jc — greater Jc enables a far more compact design. The main focus from the program has, therefore, been the fabrication of uniform high-Jc films of YBCO. Techniques investigated have incorporated pulsed laser deposition (PLD), thermal coevaporation, and magnetron sputtering on buffered p-YSZ, unbuffered p-YSZ, and azure. Biaxially textured YSZ buffer layers happen to be fabricated on area of the p-YSZ substrates by ion beam aided deposition. Current densities as much as 3×10 6 A/cm 2 happen to be achieved, as have good restricting performance and recovery occasions around the order of just one second. The following milestone for that project is construction of the 100 kVA limiter utilizing a cryocooler. Further information on the program receive within the Siemens site visit report (Appendix D).

Two additional German FCL projects started in The month of january 1997. The very first is a method study that’ll be adopted by construction of the demonstration FCL. This project is really a joint effort through the German utilities RWE, VEW, and Badenwerk, by EUS GmbH and FZK. The 2nd project involving the introduction of a little inductive limiter is underneath the auspices from the German Israel Foundation. The German participants are FZK, Hoechst AG, and also the utility Badenwerk the Israeli participants are Tel Aviv and Ben Gurion Universities. The job at Hydro-Quebec has led to the development and test of numerous devices since 1992 (Fig. 4.15). The most recent system operated at 450 V and 95 amps for any nominal power 43 kVA. Two various materials were evaluated for that superconducting shield: melt-cast Bi-2212 from Hoechst, and composite reaction textured (CRT) material from Cambridge. Although effective current restricting was shown, the limiter that used the Hoechst material unsuccessful throughout a 480 V short-circuit test as a result of fracture from the superconductor (Cave et al. 1996). Subsequent analysis by Hydro-Quebec established that thermal stress within the bulk superconductor gave rise towards the failure. The near-term future direction of the program will be worried about increasing the homogeneity, critical current density, and resistivity from the bulk superconductor.

Fig. 4.15. Power rating from the inductive limiter models built/tested at Hydro-Quebec 1992-95 (Cave et al. 1996).

1 The overall description of fault limiters that preceeds the nation-by-country program discussion is tailored, with permission, from an in-house tutorial of yankee Superconductor Corporation (Brockenborough 1996)

FAULT-CURRENT LIMITERS (FCL) 1

Summary

Fault-current limiters using hot temperature superconductors offer a strategy to controlling fault-current levels on utility distribution and transmission systems. These fault-current limiters, unlike reactors or high-impedance transformers, will limit fault currents without adding impedance towards the circuit during normal operation. Growth and development of superconducting fault-current limiters has been went after by a number of utilities and electrical manufacturers all over the world, and commercial devices are expected to be shown through the turn from the century.

Fault-Current Problem

Electrical power system designers frequently face fault-current problems when expanding existing buses. Bigger transformers lead to greater fault-duty levels, forcing the substitute of existing buswork and switchgear not rated for that new fault duty. Alternatively, the present bus could be damaged and offered by several smaller sized transformers. Another alternative is use of merely one, large, high-impedance transformer, leading to degraded current regulation for the customers around the bus. The classic tradeoff between fault control, bus capacity, and system stiffness has endured for many years.

Other common system changes can lead to a fault control problem:

  • in certain areas, like the U . s . States, additional generation from cogenerators and independent power producers (IPPs) enhances the fault duty within a system
  • older but nonetheless operational equipment progressively becomes underrated through system growth some equipment, for example transformers in subterranean vaults or cables, can be quite costly to exchange
  • customers request parallel services that boost the longevity of their supply but enhance the fault duty

Superconductive FCL

Superconductors offer a method to break through system design constraints by presenting an impedance towards the electrical system that varies based on operating conditions. Superconducting fault-current limiters normally operate with low impedance and therefore are “invisible” components within the electrical system. In case of a fault, the limiter inserts impedance in to the circuit and limits the fault current. With current limiters, the utility can offer a minimal-impedance, stiff system having a low fault-current level, as Fig. 4.5 shows.

Fig. 4.5. Fault control having a fault-current limiter.

In Fig. 4.5, a sizable, low-impedance transformer can be used to give a bus. Normally, the FCL has no effect on the circuit. In case of a fault, the limiter develops an impedance of .2 per unit (Z = 20%), and also the fault current ISC is reduced to 7,400 A. With no limiter, the fault current could be 37,000 A.

The introduction of hot temperature superconductors (HTS) enables the introduction of economical fault-current limiters. Superconducting fault-current limiters were first studied over two decades ago. The first designs used cold superconductors (LTS), materials that lose all resistance at temperatures a couple of levels above absolute zero. LTS materials are usually cooled with liquid helium, an ingredient both costly and hard to deal with. The invention in 1986 of hot temperature superconductors, which operate at greater temperatures and could be cooled by relatively affordable liquid nitrogen, restored curiosity about superconducting fault-current limiters.

Fault-Current Limiter Applications

Fault-current limiters does apply in many distribution or transmission areas. Three primary applications areas are proven in Figs. 4.6, 4.7, and 4.8.

Fig. 4.6. Fault-current limiter within the primary position. The fault-current limiter FCL protects the whole bus.

Fig. 4.7. Fault-current limiter within the feeder position. The fault-current limiter FCL protects a person circuit around the bus. Underrated equipment could be selectively protected when needed in this way.

Fig. 4.8. Fault-current limiter within the bus-tie position. The 2 buses are tied, yet a faulted bus has got the full fault current of just one transformer.

Probably the most direct use of a fault-current limiter is incorporated in the primary position on the bus (Fig. 4.6). Advantages of an FCL within this application range from the following:

  • a bigger transformer may be used to meet elevated demand on the bus without breaker upgrades
  • a sizable, low impedance transformer may be used to maintain current regulation in the new electricity
  • I 2 t harm to the transformer is restricted
  • reduced fault-current flows within the high-current circuit that feeds the transformer, which minimizes the current dip around the upstream high-current bus throughout a fault around the medium-current bus

An FCL may also be used to safeguard individual loads around the bus (Fig. 4.7). The selective use of small , less costly limiters may be used to safeguard old or overstressed equipment that’s hard to replace, for example subterranean cables or transformers in vaults.

An FCL may be used within the bus-tie position (Fig. 4.8). This type of limiter will need merely a small load current rating but would provide the following advantages:

  • separate buses could be tied together with no large rise in the fault duty on either bus
  • throughout a fault, a sizable current drop over the limiter maintains current level around the unfaulted bus
  • the paralleled transformers lead to low system impedance and good current regulation tap-altering transformers could be prevented
  • excess capacity of every bus can be obtained to both buses, thus making better utilisation of the transformer rating

Superconductive Fault-Current Limiter Concepts

The easiest superconducting limiter concept, the series resistive limiter, exploits the nonlinear resistance of superconductors inside a direct way. A superconductor is placed within the circuit. For any full-load current of IFL. the superconductor could be designed to possess a critical current of 2IFL or 3IFL. Throughout a fault, the fault current pushes the superconductor right into a resistive condition and resistance R seems within the circuit.

The superconductor in the resistive condition may also be used like a trigger coil, pushing the majority of the fault current via a resistor or inductor. The benefit of this configuration, proven in Fig. 4.9, is it limits the power that must definitely be absorbed through the superconductor.

Fig. 4.9. Fault-current limiter with HTS trigger coil.

The fault-current limiter FCL normally is really a short over the copper inductive or resistive element Z. Throughout a fault, the resistance coded in the limiter shunts the present through Z, which absorbs the majority of the fault energy.

The trigger coil approach is suitable for transmission line applications, where many megawatt-seconds could be absorbed inside a series resistive limiter. The trigger coil configuration also enables an impedance associated with a phase position, from purely resistive to just about purely inductive, to become placed within the line.

Another concept utilizes a resistive limiter on the transformer secondary, using the primary in series within the circuit. This idea, highlighted in Fig. 4.10, yields a limiter appropriate for top-current circuits (IL 1000 A). One phase from the limiter is proven. A copper winding WCu is placed within the circuit and it is coupled for an HTS winding WHTS. During normal operation, a zero impedance is reflected towards the primary. Resistance coded in the HTS winding throughout a fault is reflected towards the primary and limits the fault.

The inductive limiter could be modeled like a transformer. The impedance of the limiter within the steady condition is almost zero, because the zero impedance from the secondary (HTS) winding is reflected towards the primary. In case of a fault, the big current within the circuit induces a sizable current within the secondary and also the winding loses superconductivity. The resistance within the secondary is reflected in to the circuit and limits the fault.

Fig. 4.10. Inductive fault-current limiter.

Japanese FCL Program

The driving factors for current limiters in Japan are somewhat not the same as individuals within the U . s . States, considering that IPPs and cogenerators aren’t as prevalent in Japan. Rather, the interest in power in Japanese urban centers keeps growing due to economic growth and elevated consumer utilization of electricity. Additionally, industrial utilization of computers along with other power-quality-sensitive equipment has forced the utilities to supply greater quality and much more reliable power. The quite effective method of improved power quality in Japan is to increase connections between various power systems and also to concentrate generation capacity in bigger, more effective units. Growing interconnection does, however, boost the maximum fault current available at any time within the system, which is quickly resulting in the requirement for breaker upgrades and system reconfigurations. Contributing to the complexness from the situation in Japan may be the limited room at substation sites, which could preclude breaker upgrades. The main need, as expressed by control over the Tokyo, japan Electrical Power Company (TEPCO), is perfect for a limiter for that nucleus from the Japanese transmission system, the 500 kV transmission grid.

As a result of this real market pull there’s been a number of programs to build up fault-current limiters using a number of methods, with recent concentrate on superconducting limiters (Nakade 1994). Although FCLs aren’t a part of the NEDO budget, TEPCO has reported it spends about 100 million each year (

$a million) about this program, and a few resistive FCL jobs are apparently incorporated within the NEDO budget underneath the subject “Research of Superconducting Materials and Devices.”

Within the late 1980s, Seikei College manufactured a little-scale three-phase current-restricting reactor and shown effective operation. This three-phase system introduces a sizable unbalanced reactance within the system to limit currents within the situation of merely one-phase short and quenches introducing resistance within the circuit within the situation of the three-phase fault.

Mitsubishi Utility Company (MELCO) continues to be taking part in a MITI/NEDO FCL program since 1990. This can be a resistive limiter approach using HTS films on the strontium titanate substrate which has shown restricting of 400 A currents to 11.3 A. The Central Research Institute from the Electrical Power Industry (CRIEPI) is promoting the inductive limiter proven in Fig. 4.11 (Ichikawa and Okazaki 1995). This method, much like individuals of ABB and Siemens-Hydro Quebec, utilizes a cylinder of bulk BSCCO-2212 or BSCCO-2223 to split up an ordinary copper coil from an iron core. In normal operation, the area in the copper coil doesn’t penetrate the superconductor under fault conditions, however, the present caused within the superconductor will drive it normal, and also the magnetic field links the iron yoke. This greatly boosts the inductance from the copper coil, thus supplying current restricting. CRIEPI work has centered on ac magnetic shielding performance of bulk superconductors as well as their responses to fault currents. Additionally, introduction of the “control ring” within the system to soak up a few of the energy deposited throughout a fault has reduced the cooldown duration of the shield carrying out a faulted condition.

Fig. 4.11. Schematic diagram from the CRIEPI inductive FCL (Ichikawa and Okazaki 1995).

Probably the most extensive FCL enter in Japan continues to be the collaboration between TEPCO and Toshiba. The lengthy-term objective of the program is the introduction of a 500 kV limiter having a rated current of 8,000 A. Initial development has concentrated on a distribution-level limiter created for 6.6 kV.

As proven in Fig. 4.12, the FCL is created by connecting four superconducting coils inside a series-parallel configuration therefore the total inductance is minimized. Some coils can be used for every phase from the device, and restricting is accomplished by quenching the coils. The present form of the FCL proven in Fig. 4.13 utilizes a special low ac loss Nb-Ti conductor. Tests inside a circuit having a nominal short circuit current of 25.8 kA have effectively shown restricting to around 4,000 amps (Fig. 4.14).

Fig. 4.12. Configuration of coils within the TEPCO/Toshiba FCL (Nakade 1994, 34).

Fig. 4.13. Exterior look at the 6.6 kV 2,000 A-class current limiter. The coil is 420 mm across and 640 mm lengthy (Nakade 1994, 35).

Fig. 4.14. Current restricting characteristics of Toshiba FCL proven in Fig. 4.13 (Nakade 1994, 35).

Recent work has incorporated the development of HTS current results in lessen the refrigeration load from the system to levels that may be handled with a 4 K Gifford McMahon refrigerator. Over three generations from the device, heat leak continues to be reduced from 13.8 watts to three.4 watts, that is nearing the needed level.

TEPCO will build up a 3-phase limiter within the next 3 to 4 many test drive it within the grid in this particular century. You will find couple of distribution-level FCL applications observed in the TEPCO grid, however, and also the current plan’s introducing solid condition breakers for distribution before installing superconductive FCL.

The real application for that superconducting FCL reaches transmission voltages of 500 kV. The vista of TEPCO researchers is this fact current range will need the development of HTS coils (instead of LTS) to get rid of the helium gas in the system. Introduction of the transmission-level FCL around the grid is predicted about 2010.

Fault-Current Limiters In Europe

Probably the most comprehensive FCL enter in Europe is the fact that being conducted with a collaboration between Electricit de France, GEC Alsthom, and Alcatel Alsthom Recherche. The program’s primary goal would be to provide FCLs for that 225 kV grid in France. The audience has selected a resistive limiter according to LTS material and it has shown effective operation at 40 kV (rms), by having an industrial demonstration around the French 63 kV grid expected in 1998. Look at in france they program is past the scope of the WTEC study, so no visit is made for this project. Verhaege et al. (1996) provide an introduction to we’ve got the technology and project status.

Two sites the WTEC panel visited in Europe addressed FCL: ABB in Baden-Daetwil, Europe, and Siemens in Erlangen, Germany. ABB is going after a fault-current limiter concept much like that described above for that CRIEPI program. It is called the “shielded iron core concept.” It utilizes a warm iron core enclosed with a superconducting shield inside a fiberglass Dewar. The copper primary coil is wound exterior for this Dewar. ABB has built and tested one hundred kW prototype using a collection of four Bi-2212 rings 8 cm lengthy, and 20 cm across. Operation what food was in 480 V with fault currents of 8 kA. A brand new ABB three-phase 1.2 MW FCL has become functioning inside a power station in Lntsch, Europe.

Siemens is following two routes for FCL inside a collaborative program with Hydro-Quebec Canada. In the Siemens corporate labs in Erlangen, the main focus continues to be on resistive limiters using YBCO thin film meander lines on YSZ or on YSZ and azure (Gromoll et al. 1996). The benefit of this method would be that the YBCO film includes a high normal condition resistance and isn’t shunted by normal metal, as will be the situation inside a composite powder-in-tube conductor. The video also offers really low heat capacity, which results in rapid switching towards the normal condition ( 1 ms) and the potential of rapid cooldown. Analysis by 1996 has figured that both peak let-through current and steady condition restricting current decrease as Jc is elevated. Additionally, the style of a limiter of functional size depends strongly on Jc — greater Jc enables a far more compact design. The main focus from the program has, therefore, been the fabrication of uniform high-Jc films of YBCO. Techniques investigated have incorporated pulsed laser deposition (PLD), thermal coevaporation, and magnetron sputtering on buffered p-YSZ, unbuffered p-YSZ, and azure. Biaxially textured YSZ buffer layers happen to be fabricated on area of the p-YSZ substrates by ion beam aided deposition. Current densities as much as 3×10 6 A/cm 2 happen to be achieved, as have good restricting performance and recovery occasions around the order of just one second. The following milestone for that project is construction of the 100 kVA limiter utilizing a cryocooler. Further information on the program receive within the Siemens site visit report (Appendix D).

Two additional German FCL projects started in The month of january 1997. The very first is a method study that’ll be adopted by construction of the demonstration FCL. This project is really a joint effort through the German utilities RWE, VEW, and Badenwerk, by EUS GmbH and FZK. The 2nd project involving the introduction of a little inductive limiter is underneath the auspices from the German Israel Foundation. The German participants are FZK, Hoechst AG, and also the utility Badenwerk the Israeli participants are Tel Aviv and Ben Gurion Universities. The job at Hydro-Quebec has led to the development and test of numerous devices since 1992 (Fig. 4.15). The most recent system operated at 450 V and 95 amps for any nominal power 43 kVA. Two various materials were evaluated for that superconducting shield: melt-cast Bi-2212 from Hoechst, and composite reaction textured (CRT) material from Cambridge. Although effective current restricting was shown, the limiter that used the Hoechst material unsuccessful throughout a 480 V short-circuit test as a result of fracture from the superconductor (Cave et al. 1996). Subsequent analysis by Hydro-Quebec established that thermal stress within the bulk superconductor gave rise towards the failure. The near-term future direction of the program will be worried about increasing the homogeneity, critical current density, and resistivity from the bulk superconductor.

Fig. 4.15. Power rating from the inductive limiter models built/tested at Hydro-Quebec 1992-95 (Cave et al. 1996).

1 The overall description of fault limiters that preceeds the nation-by-country program discussion is tailored, with permission, from an in-house tutorial of yankee Superconductor Corporation (Brockenborough 1996)


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