Patent Application
20120001645
This application claims priority from European Patent Application No. 10006744.6, filed on Jun. 30, 2010, the contents of which are relied upon and incorporated herein by reference in their entirety, and the benefit of priority under 35 U.S.C. 119 is hereby claimed.
The present invention concerns a combined electrical variable detection device, containing a number of single-phase current measuring modules arranged in a common frame, having a separate output cable/connection for each module.
Generally, in medium voltage switchgears, there is a need to use instrument current and voltage transformers in order to reduce current and voltage values of the plant or substation down to the values such as to be able to be detected by measurement and protection apparatus, and to make the secondary measurement and protection circuits galvanically independent of the primary power circuit, at the same time guaranteeing greater safety for operators.
A current and voltage detection/measurement in medium voltage networks is usually done by means of separate devices on each phase. For protection purposes, separate devices for residual current measurement and/or residual voltage measurement are needed as well.
A residual current transformer, also known as a zero sequence current transformer, is used for detection of earth leakage and earth fault protection. In such transformer, the three phases (cables or busbars) of a three phase system pass through the inner diameter of the current transformer. When the system is fault free, no current flows in the secondary winding of the residual current transformer. When there is an earth fault, the residual current or a zero sequence current of the system flows through the secondary winding of the residual current transformer and this operates the connected relay.
The three voltages of a balanced system sum to zero, but this is not the case if the system is subject to a single-phase earth fault. The residual voltage which exists in this case is significant in protective switchgear practice as a means of detecting earth fault conditions. The residual voltage of a system is measured by connecting the primary windings of a three single-phase voltage transformers in phase-to-ground connection and connecting the secondary windings in series or “open delta”. The output of the secondary windings connected in “open delta” is zero when balanced sinusoidal voltages are applied, but under conditions of imbalance a residual voltage of the system will be developed. The residual voltage is three times the zero sequence voltage.
Usually, all these devices described above are separate devices, which need to be fixed somewhere inside of the system in order to ensure proper position of primary conductors and mechanical stability of all components. Usually inductive instrument transformers are used for this purpose, nevertheless electronic instrument transformers, sometimes called also non-conventional instrument transformers or sensors, can also be used in order to fulfill the same needs.
In case of inductive current transformers, it is quite difficult to produce one unit having three single-phase transformers in one body. If it is done, solution could be quite bulky and heavy especially for protection purposes, where big dynamic range is required. Furthermore, one can place three single phase transformers/coils into one body in order to have a compact solution, but residual current measurement needs a separate device today.
Due to a presence of a ferromagnetic core in classical current transformers and resulting size and weight of the full solution, it is not so advantageous to combine together phase current measurements and even more the residual current measurement. Furthermore, the presence of the ferromagnetic core influences the magnetic field and a combination of several ferromagnetic cores, each designed for different rated primary currents, may affect the total magnetic field. It may cause higher non-liner behavior which then makes it more difficult to reach a required accuracy for each measurement.
Electronic current transformers or sensors are also used in the same way, but their use for residual current measurement is not so common in medium voltage applications and current transformers are rather used.
To be able to calculate an output power, one needs to measure both electric current and electric voltage. Both these measurements are necessary for some protection functions as well. A limiting factor for implementing of all necessary measuring elements in such case could be the space within medium voltage switchgears. New switchgear designs are being designed smaller and with challenging parameters, thus requiring smaller and compact measuring solutions, hardly achievable by conventional technologies of instrument transformers today.
Described herein are combined electrical variable detection devices not only for measuring a current in preferably three single phases, but also for measuring a voltage in at least one single phase at the same time, as well as including residual current and voltage measurement. The devices arrange relatively small measurement modules in a common frame, the measurement modules having a separate output cable/connection for each module, having an easy connection of the whole combined electrical variable detection device to output measuring and control units
In particular, the present invention includes embodiments of a combined electrical variable detection device comprising a number of single-phase current measuring modules arranged in a common frame, having a separate output cable/connection for each module, wherein at least one single-phase current measuring module is provided with a voltage detection device, the combined electrical variable detection device using one output cable/connection, the signal wires of which are coupled to said output cable/connections from said modules. In one preferred embodiment, all single-phase current measuring modules, e.g. Rogowski coils, are provided with a voltage detection device.
In one embodiment, the combined electrical variable detection device is provided with a residual-current detection device surrounding more than one of said single-phase current measuring modules in said common frame.
In another embodiment, the combined electrical variable detection device combines three phase-current measuring modules, each of which is provided with the corresponding phase-voltage detection device, all phase-current measuring modules and phase-voltage detection devices being placed together with a residual-current detection device in said common frame and all the devices and modules being positioned close to each other.
In another embodiment, at least one of the phase-current measuring modules is/are fixed in said common frame, said common frame being designed for embedding of more phase-current measuring modules than the number that is/are actually fixed. Yet another is that voltage detection devices contain resistive or capacitive dividers for voltage detection.
In many cases it is advantageous to provide the device with other sensing elements as a temperature measuring device or even with a residual-voltage detection device.
In the accompanying drawings, structural embodiments are illustrated that, together with the detailed description provided below, describe exemplary embodiments of a combined electrical variable device. One of ordinary skill in the art will appreciate that a component may be designed as multiple components or that multiple components may be designed as a single component.
Further, in the accompanying drawings and description that follow, like parts are indicated throughout the drawings and written description with the same reference numerals, respectively. The figures are not drawn to scale and the proportions of certain parts have been exaggerated for convenience of illustration.
All Rogowski coils are embedded in the single-phase current and voltage measuring modules 1 and the residual-current detection device 3 are placed in the same body/case, i.e. in the same common frame 2. This common frame 2 with the single-phase current and voltage measuring modules 1 and the residual-current detection device 3 has openings 4 for entry of the primary conductors of each phase. Openings 4 could be made oval in order to accommodate flat-type of busbars or they can have also circular shape fitting better to rounded primary conductors. Common frame 2 is also equipped with means for mechanical fixations in order to ensure proper positioning of the device and to avoid mechanical damage.
In preferred embodiments, the single-phase current and voltage measuring modules 1 use Rogowski coils as single-phase current sensors. These three single-phase current and voltage measuring modules 1 are placed and fixed in one common frame 2. The same common frame 2 can be also able to accommodate residual current detection device 3. This residual current detection device 3 can be placed into the common frame 2 from the same side as proposed in
Though in the embodiments shown in the
In case a capacitive voltage divider is used, it needs a primary electrode to be connected to the high potential, i.e. to the measured voltage. In case the primary conductor is directly casted within the sensor body, this primary electrode can be avoided. Another part of capacitive voltage divider is capacitive electrode. This capacitive electrode can be fixed to the single-phase current sensor, but it needs an insulation in between in case that conductive or semiconductive layer is used for the single-phase current sensor. Such unit can have again only one output connector 6, but more of them can be used when needed. There could be also a cable or secondary terminals instead of the output connector 6. Unit needs to be equipped with some fixation means and with a place for primary conductor.
The combined electrical variable detection device can contain one or two single-phase current and voltage measuring modules 1 and two or one single-phase current measuring modules that are arranged in a common frame 2. Such device would contain three modules as in already described embodiments, but only one or two modules contain a voltage detection device.
The reason for placing all modules 1, 3 with devices for measuring single-phase current and voltage and residual-current into one body is the aim to reduce total volume occupied, production costs, necessary fixation and assembly work during installation and to provide a single current device measuring all currents needed for measurement and protection purposes. Another important new proposed feature is an assembly of these single-phase measurement units. The assembly can consist of three single-phase units/modules that could be produced and tested separately to reduce potential production losses and then placed/fixed in common frame 2. The same modules 1 could then be used for different frames respecting different applications or different phase distances needed.
The use of electronic instrument transformers enables such combination in case that no ferromagnetic material is used. Absence of ferromagnetic material should not limit the use of current sensors, e.g. Rogowski coils, when phase current and residual current measurements are combined together.
In one embodiment, this invention thus proposes to use three modules 1, e.g. based on Rogowski coil principle, to be used in one common frame. Each module containing one Rogowski coil can be produced and tested separately thus decreasing the risk that some failure may be noticed after assembly into the common frame 2. Advantage of this solution is a possibility to use the same modules also for other phase distances without influencing module or coil design, only different common frame 2 would be in such case needed.
One can include also residual current measurement into this common frame. Furthermore, other measurements could be integrated as well (e.g. temperature, vibration, dust, humidity) in case that space allows it. There could be several output cables and/or terminals or connectors from each sensing element used as an interface of such combined device to other connected devices, nevertheless such combined solution/device enables the use of a single cable/connector containing all signal wires thus simplifying installation in a given application.
Residual voltage could be measured by means of voltage dividers, connected to all three phases of a three-phase system. If one connects outputs of these voltage dividers to open-delta connection, residual voltage could be measured there and it would show a possible asymmetry in the network caused e.g. by a ground fault. Residual voltage could be also measured by using only high impedances (either resistive and/or capacitive) connected separately to all three phases on one side, the other side of impedances from all three phases being interconnected. In this case, residual voltage could be measured between this interconnection point and ground. Best fit of given method/device for residual voltage measurement depends on system network design and its grounding.
Combined electrical variable detection device, in the sense of this invention proposal, could integrate the following functions: (1) three single-phase current measurements and at least one single-phase voltage measurement consisting of three single-phase current and voltage measuring modules integrated into one common frame; (2) phase-currents and voltage measurements+residual current measurement; (3) phase-currents measurements+phase-voltage measurements+residual current measurement+temperature measurement; (4) phase-currents measurements+phase-voltage measurements+residual voltage measurement+temperature measurement+any other sensor available with present solutions; (5) phase-currents measurements+phase-voltage measurements+residual current and voltage measurement+temperature measurement+any other sensor available with present solutions
Preferably, the present devices are used with electronic instrument transformers which do not contain any ferromagnetic materials; nevertheless their use could be allowed in case of satisfactory shielding of magnetic field around these parts, when having appropriate shape of such parts or in case that internal construction is done in such a way, that the internal influences are minimized.
In case of electronic voltage transformers the residual voltage information could be obtained either from calculation of the phase-voltage measurements or it can be made by using voltage dividers of any of the mentioned types.
To the extent that the term “includes” or “including” is used in the specification or the claims, it is intended to be inclusive in a manner similar to the term “comprising” as that term is interpreted when employed as a transitional word in a claim. Furthermore, to the extent that the term “or” is employed (e.g., A or B) it is intended to mean “A or B or both.” When the applicants intend to indicate “only A or B but not both” then the term “only A or B but not both” will be employed. Thus, use of the term “or” herein is the inclusive, and not the exclusive use. See, Bryan A. Garner, A Dictionary of Modern Legal Usage 624 (2d. Ed. 1995). Also, to the extent that the terms “in” or “into” are used in the specification or the claims, it is intended to additionally mean “on” or “onto.” Furthermore, to the extent the term “connect” is used in the specification or claims, it is intended to mean not only “directly connected to,” but also “indirectly connected to” such as connected through another component or components.
While the present application illustrates various embodiments, and while these embodiments have been described in some detail, it is not the intention of the applicant to restrict or in any way limit the scope of the appended claims to such detail. Additional advantages and modifications will readily appear to those skilled in the art. Therefore, the invention, in its broader aspects, is not limited to the specific details, the representative embodiments, and illustrative examples shown and described. Accordingly, departures may be made from such details without departing from the spirit or scope of the applicant's general inventive concept.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10006744.6 | Jun 2010 | EP | regional |
