Patent Application
20120262831
The present invention relates to a fault current limiter (FCL).
The invention has been developed primarily for a compact high voltage fault current limiter and will be described with reference to that application. However, the invention is not limited to that particular field of use and is also suitable for low voltage, medium voltage, extra-high voltage and ultra-high voltage fault current limiters.
Any discussion of the prior art throughout the specification should in no way be considered as an admission that such prior art is widely known or forms part of common general knowledge in the field.
There is an increasingly growing importance to ensure the stability of the electrical supply both on the small and large scale. One device of importance in ensuring such supply is a fault current limiter. Recently, magnetically saturated fault current limiters employing high permeability cores have been introduced to the market. Often these devices utilise a DC coil, superconducting or otherwise, for the magnetic saturation of a magnetic material. Upon the occurrence of a fault, the magnetically saturated material is often taken out of saturation to provide higher impedance to the fault current. Example fault current limiters relying upon magnetic saturation can be found in U.S. Pat. No. 7,193,825 to Darmann et al. and U.S. Pat. No. 7,551,410 to Darmann.
Open core fault current limiters are known, for example, from PCT Publication WO 2009/121143 to Darmann. While these fault current limiters offer efficacious functionality, it has been found that their application, in some instances, has been precluded from installations primarily due to packaging requirements. This is particularly relevant for existing electrical sub-stations in which there is a desire to retrofit a fault current limiter in a predetermined and confined space.
It is an object of the present invention to overcome or ameliorate at least one of the disadvantages of the prior art, or to provide a useful alternative.
According to a first aspect of the invention there is provided a fault current limiter including:
an input terminal for electrically connecting to a power source that provides a load current;
an output terminal for electrically connecting with a load circuit that draws the load current;
a magnetically saturable core having a longitudinally extending first portion and a second portion that extends longitudinally beyond the first portion;
an AC coil wound about the first portion for carrying the load current between the input terminal and the output terminal; and
a magnetically biasing system located closely adjacent to the second portion for magnetically biasing the core such that, in response to one or more characteristics of the load current, the AC coil moves from a low impedance state to a high impedance state.
In an embodiment, the AC coils require a predetermined physical clearance to an electrical earth and the magnetically biasing system is spaced apart from the core by less than the predetermined clearance.
In an embodiment, the magnetically biasing system includes at least one DC coil wound about and closely adjacent to the second portion.
In an embodiment, the DC coil has a notional inner surface with a first predetermined footprint and the AC coils have a notional outer surface with a second predetermined footprint that extends beyond the first footprint.
In an embodiment, the core is substantially non-uniform in cross-section.
In an embodiment, the core includes a third portion that extends longitudinally beyond the first portion.
In an embodiment, at least one DC coil is wound about and closely adjacent to the third portion.
In an embodiment, the core and the AC coil are housed within an enclosure and the at least one DC coil is outside the enclosure.
In an embodiment, the at least one DC coil is housed in a chamber.
In an embodiment, the enclosure and the DC coil include respective enclosure and DC coil footprints in a transverse plane and the DC coil footprint is no more than the enclosure footprint.
In an embodiment, the enclosure and the DC coil include respective enclosure and DC coil footprints in a transverse plane and the DC coil footprint is substantially the same as the enclosure footprint.
In an embodiment, the core, the AC coil and the at least one DC coil are housed within an enclosure.
In an embodiment, the core includes an array of longitudinally substantially coextensive posts and a plurality of AC coils respectively wound about one or more of the posts in the array, and wherein the posts in the array each have a first end and a second end and the posts are arranged such that the first ends collectively define the second portion and the second ends collectively define the third portion.
In an embodiment, the posts are substantially non-uniform in cross-section.
In an embodiment, the core is constructed from one or more of: a transformer steel lamination material; mild steel; other magnetic steel; ferrite material; an insulated high permeability compressed powder; and a ferromagnetic material.
In an embodiment, the enclosure includes a dielectric medium.
According to a second aspect of the invention there is provided a fault current limiter including:
at least three input terminals for electrically connecting to a three phase power source that provides a load current;
at least three output terminals for electrically connecting with a three phase load circuit that draws the load current;
a magnetically biasing system having a central cavity;
a longitudinally extending magnetically saturable core having a plurality of posts, wherein:
each post includes a first portion and a second portion and a third portion extending longitudinally oppositely away from the first portion; and
the second portion is received within the central cavity;
at least three AC coils each being wound about at least one of the first portions for carrying the load current between the input terminals and the output terminals, wherein the biasing system magnetically biases the core such that, in response to one or more characteristics of the load current, the AC coils move from a low impedance state to a high impedance state.
According to a third aspect of the invention there is provided a fault current limiter including:
an input terminal for electrically connecting to a power source that provides a load current;
an output terminal for electrically connecting with a load circuit that draws the load current;
an AC coil wound about a longitudinally extending first portion of a magnetically saturable core for carrying the load current between the input terminal and the output terminal, wherein the core and the AC coil are housed within an enclosure; and
a magnetically biasing system located adjacent the core for magnetically biasing the core such that, in response to one or more characteristics of the load current, the AC coil moves from a low impedance state to a high impedance state, and wherein the enclosure and the biasing system include respective enclosure and biasing system footprints in a transverse plane and the biasing system footprint is no more than the enclosure footprint.
In an embodiment, the magnetically biasing system includes at least one DC coil wound about the core.
In an embodiment, the core includes a second portion which extends longitudinally beyond the first portion and the DC coil is wound about the second portion.
In an embodiment, the core includes a third portion that extends longitudinally beyond the first portion.
In an embodiment, at least one DC coil is wound about the third portion.
In an embodiment, the enclosure and DC coil footprints are substantially coextensive.
In an embodiment, the DC coil footprint lies within the enclosure footprint.
According to a fourth aspect of the invention there is provided an enclosure for a fault current limiter, the enclosure including:
a first port for receiving an input terminal for electrically connecting to a power source that provides a load current;
a second port an output terminal for electrically connecting with a load circuit that draws the load current;
a first zone for receiving a first portion of a magnetically saturable core, the first zone having a predetermined first transverse footprint;
a second zone that extends longitudinally beyond the first zone for receiving a second portion of the core, the second zone having a predetermined second transverse footprint that is no more than the first footprint;
an AC coil wound about the first portion for carrying the load current between the input terminal and the output terminal; and
a magnetically biasing system located adjacent the second portion for magnetically biasing the core such that, in response to one or more characteristics of the load current, the AC coil moves from a low impedance state to a high impedance state.
In an embodiment, the magnetically biasing system includes at least one DC coil wound about the second portion.
Embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings in which:
The following description and Figures make use of reference numerals to assist the addressee understand the structure and function of the illustrated embodiments. Like reference numerals are used in different embodiments to designate features having the same or similar function and/or structure.
The drawings need to be viewed as a whole and together with the associated text in this specification. In particular, some of the drawings selectively omit features to provide greater clarity about the specific features being described. While this is done to assist the reader, it should not be taken that those features are not disclosed or are not required for the operation of the relevant embodiment.
Where use is made of the term “an embodiment” in relation to a feature, that is not to be taken as indicating there is only one embodiment in which that feature is able to be used, or that that feature is not able to be used in combination with other features not illustrated as being in the same embodiment. It will be appreciated by the skilled addressee that while some features are mutually exclusive within a single embodiment, others are able to be combined.
Referring to
The voltage VS in this embodiment is 33 kV. However, in other embodiments alternative voltages are used. Examples of commonly used voltages include 132 kV, 66 kV, 33 kV and many other voltages that will be known to those skilled in the art.
As best shown in
Three copper-based insulated AC coils 20, 21 and 22 are each wound about respective first portions 16 for carrying load current ILOAD between terminals 10 to respective terminals 11. DC coils 12 magnetically biases core 14 such that, in response to one or more characteristics of load current ILOAD, AC coils 20, 21 and 22 move from a low impedance state to a high impedance state.
Each AC coil 20, 21 and 22 has two coil segments that are wound in opposite senses about respective first portions 16. For example, coil 20 has two coil segments 20a and 20b. Coil segment 20a is electrically connected to terminal 10 via high voltage, high current insulated conductor 23. Similarly, coil segment 20b is electrically connected to terminal 11 via high voltage, high current insulated conductor 24. The respective coil segments of coils 21 and 22 are similarly connected to terminals 10 and 11 via respective high voltage, high current insulated conductors 23 and 24.
It will be appreciated that in other embodiments, the magnetically biasing system includes other than DC coils for magnetically biasing the core. In some of these other embodiments, the magnetically biasing system is located adjacent or located closely adjacent to the core to provide the magnetic bias.
In some embodiments, the magnetically biasing system includes a greater or lesser number of DC coils. Moreover, in some embodiments, the DC coils are constructed from other than HTS. For example, in specific embodiments, use is made of DC coils constructed from copper-based material such as a copper alloy or electrical grade copper.
The movement of AC coils 20, 21 and 22 from a low impedance to a high impedance state increases the impedance in the current path through which ILOAD must flow. This limits ILOAD as VS and VT are relatively tightly controlled. It will be appreciated that FCL 6 is designed such that, in use, ILOAD is limited to no more than IMAX. This ensures that the current carried by transformer 2 is limited which, in turn, provides overload protection for that transformer.
In the embodiment of
In this particular embodiment, the pairs of posts are located adjacent to one another, as best shown in
In other embodiments, it will be appreciated that the posts in each pair of posts are arranged other than adjacent to each other. For example, in the embodiment of
Other embodiments include posts that have other than a substantially constant and uniform transverse cross-section.
The posts 15 are constructed with stacked transformer steel laminations. In other embodiments, use is made of one or more of mild steel or other forms of magnetic steel ferrite materials or ferromagnetic material or granular material such as a core made from consolidated ferromagnetic powder, or a glassy amorphous core.
Referring again to
In other embodiments, the DC coils are also housed within the oil tank 27 and immersed within a common dielectric medium 28. This arrangement is particularly applicable to embodiments where the DC coils are formed of copper, copper alloy or other suitable conductor.
In other embodiments use is made of a single cryogenic chamber for both coils, or a single cryogenic chamber for a single DC coil.
Core 31 includes a pair of parallel elongate longitudinally coextensive like posts 15. Posts 15 each have a first end 33 and a second end 34 that is spaced apart from the respective first ends. Posts 15 are arranged such that the ends 33 are adjacent with each other and collectively define portion 17, and ends 34 are adjacent with each other to collectively define portion 18.
AC coil 32 has two coil segments 32a and 32b that are oppositely wound about respective portions 16. Posts 15 and AC coils 32 are housed within tank 27 and immersed within dielectric medium 28.
Tank 27 includes a generally cylindrical longitudinally extending first zone 36 for receiving portion 16 and having a longitudinal axis 37. As best shown in
It will be appreciated that in other embodiments, the zones are other than generally cylindrical and the footprints are other than circular in cross section. In other embodiments, footprints 41 and 42 are substantially equal and overlying with footprint 38.
Referring again to
Similarly to the
Again, it will be appreciated that in other embodiments, the magnetically biasing system includes other than DC coils for magnetically biasing the core. In some embodiments, DC coils 50a and 50b have a notional inner surface with a predetermined footprint and AC coil 32 has a notional outer surface with a predetermined footprint that extends beyond the footprint of the notional inner surface of DC coils 50a and 50b.
In some embodiments of the invention, the magnetically biasing system is located adjacent the core such that the biasing system is in abutment with the core. For example, in embodiments where the biasing system is in the form of at least one DC coil housed within the tank and immersed within a common dielectric, the DC coil is located closely adjacent the core such that it abuts the core. In some embodiments where the DC coil is housed in a cryogenic chamber located outside the tank, the DC coil is located closely adjacent to the core such that the DC coil abuts the cryogenic chamber, the chamber abuts the tank and the tank abuts the core. It will be appreciated that in some embodiments where the DC coil is housed in a cryogenic chamber, the DC coil, cryogenic chamber, tank and core are not all in abutment. That is, one or more of the DC coil, cryogenic chamber, tank and core are in abutment, but not all. It will be appreciated that these abovementioned embodiments also apply where the magnetically biasing system includes more than one DC coil and where the biasing system is other than a DC coil. As a specific example with reference to
Referring to
It will be appreciated that in other embodiments, the distance between DC coil 50a and sub-wall 47b need not necessarily be less than the distance between DC coil 50a and sub-wall 47a. Similarly, the distance between DC coil 50b and sub-wall 47c need not necessarily be less than the distance between DC coil 50b and sub-wall 47a.
Referring to
In this specification there are descriptions of specific embodiments that use relative terms such as “upper”, “lower”, “top”, “base” and the like. This originates from the primary installed orientation of the FCL being an upright or vertical configuration as shown in the Figures. It will be appreciated by those skilled in the art that for some installations, where the vertical packaging constraints are the key limitation, that the FCLs of the embodiments are able to be orientated in a horizontal configuration. Accordingly, in such embodiments, the relative terms mentioned above need to be read in the context of the orientation of the FCL. It will also be appreciated that, in other embodiments, the FCL is inclined with respect to both the vertical and horizontal configurations mentioned above.
In some embodiments, the AC coils require a predetermined physical clearance to an electrical earth and the DC coils are spaced apart from the core by less than the predetermined clearance.
FCL 70 includes three AC coils wound about portion 16, where each coil has two coil segments. While in
The six posts 15 and all the six coil segments are housed entirely within the oil tank 27 which contains a dielectric medium such as transformer oil, vegetable oil, or synthetic ester 28.
FCL 70 includes a magnetically biasing system having two longitudinally spaced apart HTS DC coils 78 wound about and closely adjacent to respective portions 17 and 18 for magnetically biasing core 71 such that, in response to one or more characteristics of the load current ILOAD, the coil segments move from a low impedance state to a high impedance state. Each DC coil 78 is housed in cryogenic chamber 29 located outside tank 27.
It will be appreciated that in other embodiments, ends 103 and 104 are flared other than having the outer edges 105 and 106 and the inner edges 107 and 108 of ends 103 and 104 respectively extend uniformly transversely outwardly and inwardly beyond portion 16. For example, in some embodiments, ends 103 and 104 are flared such that the outer edges 105 and 106 and the inner edges 107 and 108 respectively extend transversely outwardly and inwardly beyond portion 16, but not uniformly. Furthermore, in other embodiments, it will be appreciated that the posts are configured in other ways such that the core is substantially non-uniform in cross-section.
In other embodiments, it will be appreciated that the magnetically biasing system includes other than a DC coil for magnetically biasing the core.
Three single phase FCLs are shown in
The DC coil separation in each FCL is:
The steel core height, HCORE, in each FCL is:
The dimensions of additional laminated steel core flared portions of
Referring to
The switch 213 in the test circuit is closed after allowing the circuit to come to steady state. The prospective fault current is measured with the steel cores taken out of the structure and only the AC coils remaining in the circuit.
Fault current experiments were carried out on the FCLs of
Referring to
Table 2 summarises the steady state fault current results obtained on the FCLs illustrated in
In a similar way, fault current experiments were carried out on the FCLs of
Table 3 summarises the steady state fault current results obtained on the FCLs illustrated in
The experimental results of
In some embodiments, by using the FCLs of
The term “footprint” as used herein, unless otherwise specified, should be understood as the underlying surface area required to accommodate a structure or device. The footprint available to accommodate an FCL is often a critical design parameter as it is common to retrofit an FCL in an existing electrical sub-station or other facility where the available surface area is limited due to the need to maintain safe physical separation of disparate pieces of equipment that are operating at high voltages. The footprint is often expressed in terms of available area on a surface. The specification can be in terms of an absolute maximum area or footprint on the surface, or an area or footprint having one or more of a maximum length and a maximum breadth on the surface. It will be appreciated that the term “footprint” can also be interpreted as meaning the area taken up by some object, or the space or area of a 2-dimensional surface enclosed within a boundary. That is, the shape of the footprint need not be regular and is, in some embodiments, defined by a complex or irregular shape.
The embodiments of the invention described above provide for a smaller footprint through the inclusion of one or a combination of features such as:
As used herein, unless otherwise specified the use of the ordinal adjectives “first”, “second”, “third”, etc., to describe a common object, merely indicate that different instances of like objects are being referred to, and are not intended to imply that the objects so described must be in a given sequence, either temporally, spatially, in ranking, or in any other manner.
Furthermore, while some embodiments described herein include some but not other features included in other embodiments, combinations of features of different embodiments are meant to be within the scope of the invention, and form different embodiments, as would be understood by those skilled in the art. For example, in the following claims, any of the claimed embodiments can be used in any combination.
In the description provided herein, numerous specific details are set forth. However, it is understood that embodiments of the invention may be practiced without these specific details. In other instances, well-known methods, structures and techniques have not been shown in detail in order not to obscure an understanding of this description.
It is to be noticed that the term coupled, when used in the claims, should not be interpreted as being limited to direct connections only. The terms “coupled” and “connected”, along with their derivatives, may be used. It should be understood that these terms are not intended as synonyms for each other. Thus, the scope of the expression a device A coupled to a device B should not be limited to devices or systems wherein an output of device A is directly connected to an input of device B. It means that there exists a path between an output of A and an input of B which may be a path including other devices or means. “Coupled” may mean that two or more elements are either in direct physical or electrical contact or that two or more elements are not in direct contact with each other but yet still co-operate or interact with each other.
Those skilled in the art will recognise that these are examples applied to specific designs that were manufactured and that detailed results for other designs with different construction details will differ. The main conclusions and pattern of results are to be considered.
Although the invention has been described with reference to specific examples it will be appreciated by those skilled in the art that it may be embodied in many other forms.
