Matrix-type superconducting fault current limiter

Details Matrix-type superconducting fault current limiter Matrix-type superconducting fault current limiter

2002-01-17

2003-12-16

Donovan, Lincoln (Department: 2832)

Electricity: magnetically operated switches, magnets, and electr

Magnets and electromagnets

Superconductive type

C324S318000, C361S019000

Reexamination Certificate

active

06664875

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to a current limiting device for use in electric power transmission and distribution systems.
BACKGROUND OF THE INVENTION
In electric power transmission and distribution systems, a fault current condition may result from events such as lightning striking a power line, or downed trees or utility poles shorting the power lines to ground. Such events create a surge of current through the electric power grid system (EPGS) that can cause serious damage to the EPGS equipment. Switchgears are deployed within electric distribution and transmission substations to protect substation equipment from such damages. However, due to the continuing growth of power demands and increased inter- and/or intra-connections between power distribution networks, transmission networks, and power generation sources, fault current level could be increasing to a level that exceeds the original fault current interrupting capabilities of the switchgears. Application of current limiters would reduce the available fault current to a safer level where the switchgears can perform their protective function for the EPGS, without resorting to other expensive measures such as replacing all the switchgears or building new substations.
Superconductors, especially high-temperature superconducting (HTS) materials, are well suited for use in a current limiting device because of their intrinsic properties that can be manipulated to achieve the effect of a “variable impedance” under certain operating conditions. A superconductor, when operated within a certain temperature and external magnetic field range (i.e., the “critical temperature” (T
C
) and “critical magnetic field” (H
C
) range), exhibits no electrical resistance if the current flowing through it is below a certain threshold (i.e., the “critical current level” (J
C
)), and is therefore said to be in a “superconducting state.”
However, if the current exceeds this critical current level the superconductor will undergo a transition from its superconducting state to a “normal resistive state.” This transition of a superconductor from a superconducting state to a normal resistive state is termed “quenching”. Quenching can occur if any one or any combination of the three factors, namely the operating temperature, external magnetic field or current level, exceeds their corresponding critical level.
The surface plot shown in
FIG. 1
illustrates the inter-dependency among these three factors (T
C
, H
C
, and J
C
) for a typical superconducting material. As shown in
FIG. 1
, the surface plot includes three axes T, H, and J, where T
C
is the critical temperature below which the superconducting material must be cooled to remain in the superconducting state, where H
C
is the critical magnetic field above which the superconducting material cannot be exposed in order to remain in a superconducting state, and where J
C
is the critical current density in the superconducting material that cannot be exceeded for the superconductor to remain in a superconducting state.
The “critical J-H-T surface” represents the outer boundary outside of which the material is not in a superconducting state. Consequently, the volume enclosed by the critical J-H-T surface represents the superconducting region for the superconducting material.
A superconductor, once quenched, can be brought back to its superconducting state by changing the operating environment to within the boundary of its critical current, critical temperature and critical magnetic field range, provided that no thermal or structural damage was done during the quenching of the superconductor. An HTS material can operate near the liquid nitrogen temperature (77K) as compared with a low-temperature superconducting (LTS) material that operates near liquid helium temperature (4K). Manipulating properties of a HTS material is much easier because of its higher and broader operating temperature range.
The quenching of a superconductor to the normal resistive state and subsequent recovery to the superconducting state corresponds to a “variable impedance” effect. A superconducting device with such characteristics is ideal for a current limiting application. Such a device can be designed so that under normal operating conditions, the operating current level is always below the critical current level of the superconductors, therefore no power loss (I
2
R loss) will result during the process. When the fault occurs the fault current level exceeds the critical current level of the superconducting device thus creating a quenching condition. By the same token, mechanisms altering the device operating temperature and/or magnetic field level can be put in place either as a catalyst or an assistant to achieving fast quenching and recovery of such a superconducting device.
McDougall, et al., U.S. Pat. No. 6,043,731, entitled “Current Limiting Device,” describes a superconductor device that uses an active control mechanism to adjust the critical current level of a superconductor. Under the normal operating condition, a magnetic field is applied to the superconductor, causing its critical current level to be less than the maximum. An active control scheme is in place to adjust the critical current density of the superconductor under the fault condition so that its critical current level is below the fault current level, triggering the quenching of the superconductor, thus introducing the current limiting impedance into the circuit it is connected to. After the fault current is limited, this control mechanism is used to increase the critical current level of the superconductor causing the superconductor to return to its superconducting state. A drawback of the current limiting device of McDougall, et al. it that it requires an active control scheme incorporating an external power supply source to achieve the effect of “adjustable impedance,” which increases the complexity and cost of the design and raises reliability issues.
Saravolac, U.S. Pat. No. 6,137,388, dated Oct. 24, 2000 and entitled “Resistive Superconducting Current Limiter,” describes a superconductor that is placed inside a nonmetallic cryostat filled with a cooling medium to maintain the superconductor in a superconductive state. A foil winding is connected in series with the superconductor by current leads and the cryostat is placed inside the winding. Under normal operating conditions, the current in the foil winding generates a persistent magnetic field that is parallel to the superconductor, with the current below the critical current level and the persistent magnetic field below the critical magnetic field of the superconductor. In the event of a fault, the current in the foil winding increases to a level that generates a magnetic field that exceeds the critical magnetic field of the superconductor and triggers the superconductor to a resistive state. This invention does achieve passive triggering of the superconductor quenching. A drawback of Saravolac's current limiting device of it that the foil winding that provides trigger magnetic field during a fault also puts the superconductor in a persistent magnetic field under normal operating mode. This persistent magnetic field is sufficient enough to degrade the superconductor's performance. Furthermore, it would be very difficult to locate superconducting materials in the uniformed magnetic field region within such a device to reduce mechanical stress exerted by the Lorentz force (i.e., Force (F) acting on a moving particle with charge q and velocity v in a magnetic field B, where F=q v×B). In addition, there will always be a voltage drop across this device because of the inductive nature of the foil windings and substantial I
2
R loss associated with such a design.
It is therefore an object of this invention to provide a current limiter that, under normal operating condition, will pass current through path(s) composed of only superconducting components that are not under any influence of an external magnetic field.
It is another object of this invention to provide

Affiliated with

Also associated with

Rating

Matrix-type superconducting fault current limiter does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Matrix-type superconducting fault current limiter, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Matrix-type superconducting fault current limiter will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-3128210