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    • 专利摘要:
    System configured for the mitigation of ferroresonances in voltage transformers, connected to the open protection triangle (11) formed by the protection windings of the set of voltage transformers connected to a power electrical network, comprising: a) a decision block (22), and b) a resistance emulator block (23), which in turn comprises a power converter (25) and an input voltage value processor (24). Method for the mitigation of ferroresonances in voltage transformers. (Machine-translation by Google Translate, not legally binding)
    公开号:ES2756923A1
    申请号:ES201800244
    申请日:2018-10-25
    公开日:2020-04-27
    发明作者:Canteli Mario Manana；Lopez Alberto Pigazo；Matorras Rafael Minguez；Lavin Marcos Alvarez；Alonso José Iván Rodriguez
    申请人:Viesgo Distribucion Electrica S L；Universidad de Cantabria；
    IPC主号:
    专利说明:

    [0001]
    [0002] Electronic system and method for the mitigation of ferroresonances in voltage transformers.
    [0003]
    [0004] Field of the Invention
    [0005]
    [0006] The present invention belongs to the field of electrical engineering, to the production and distribution of electrical energy, and more specifically to systems and methods of protection in measurement systems and networks, in the area of damping ferroresonances in voltage transformers used in electrical power systems.
    [0007]
    [0008] Background of the Invention
    [0009]
    [0010] The phenomenon of ferroresonance has its origin in the non-linear characteristics of the elements used in electrical power systems. Extraordinary operating / operating conditions can lead to unwanted oscillation modes which, in turn, can cause overvoltages and overcurrents.
    [0011]
    [0012] Electrical distribution systems with isolated neutral are especially susceptible to this phenomenon, due to the saturation of voltage transformers during the occurrence of events, such as earth faults, which excite oscillation frequencies of the system other than the nominal one, being able to result in this stable, but unwanted state of operation. Among other consequences, the appearance of fermoresonances in voltage transformers leads to an increase in temperature in transformers [1], damage due to heating of electrical equipment, breakage of insulators and even total or partial destruction of the transformer, as well as failure of system protections [2].
    [0013]
    [0014] The ferroresonances, based on their characteristics in the frequency domain [19], can be classified as subharmonic, fundamental, periodic and chaotic.
    [0015]
    [0016] There are several ways to prevent the occurrence of ferroresonances in isolated neutral electrical systems with voltage transformers. In an initial phase of system design it is possible to select parameters and configurations that minimize the possibility of occurrence of stable ferroresonances. For example, oversizing the transformers. Subsequently, the study of the system may give rise to the need to avoid certain types of operations that may result in transients that, in turn, produce ferroresonances. However, both approaches are preventive in nature and do not guarantee that ferroresonances are avoided. Only the use of appropriate damping systems can ensure adequate protection of the system [3].
    [0017]
    [0018] The usual configuration for the measurement of voltage in electrical systems with isolated neutral consists of the use of a set of three single-phase voltage transformers with two secondary windings, one for measurement and the other for protection. The protection windings are configured in an open triangle and a damping resistance is connected to it to mitigate the phenomenon. The choice of the most appropriate damping resistance value in each case requires prior knowledge of the electrical characteristics of the network at the connection point, of the set of voltage transformers, as well as their specific electrical characteristics [1] .
    [0019]
    [0020] In general, there are two approaches to buffer the occurrence of ferroresonances in electrical systems with voltage transformers: solutions on the primary side, such as those proposed in [4-8], and solutions on the secondary side [3, 9, 10].
    [0021] The use of saturable inductances in AC [4-5] and DC [6] allows limiting the fault current and avoiding the occurrence of ferroresonances in voltage transformers. In the case of transients that excite the appearance of ferroresonances, as a consequence of an overvoltage, the use of damping systems, such as the one shown in [7], can avoid the occurrence of ferroresonances. Also, oriented towards damping on the primary side, [8] shows the possibility of using certain equipment, such as FACTS, to help eliminate it. However, these teams work with the voltage level of the distribution network, much higher than the secondary level of the measurement transformer, thus being larger, more expensive and complex, and must comply with the associated insulation levels.
    [0022]
    [0023] The solutions available in the secondary of the voltage transformer can be classified into three main categories [9-10]: active, passive and electronics-based, also active. To these methods can be added the use of thermistors [3]. The use of any of the solutions in the first two categories results in losses during operating situations other than the nominal ones of the network, including that of ferro-resonance, while the third category uses electronic power devices to connect a damping resistor to the secondary protection in case of anticipation or detection of ferro-resonance.
    [0024]
    [0025] There are commercial teams in the first two categories [11-14]. In the third category there are patents, such as ES8201762, US3401272A or US6560128B1, and specialized literature [15-18]. The general scheme adopted in the third category consists in the series connection of power electronic devices, operating as static switches, with a resistive element that is the one that performs the damping of the ferroresonance in the protection winding. The equipment has a detection and control strategy that determines how to connect the damping resistance to the protection winding. However, mitigation is carried out by the damping resistance and the behavior of the system is dependent on its value. Within this category, the concept of a resistive emulator is presented in [20] that, by switching power electronic devices at a frequency several orders of magnitude greater than the nominal of the system, is capable of emulating the electrical behavior of a resistance.
    [0026] From the point of view of the electrical system operators, the prevention of ferroresonance events due to the presence of voltage transformers is not trivial. On the one hand, the characteristics of the network change dynamically, depending on the configuration and state of operation of the network, which makes it difficult to choose the optimal value of the damping resistance. On the other hand, the characteristics of the voltage transformers connected to the same electrical network, and more specifically their magnetization curves, are diverse, hindering the deployment of a specific damping solution, especially when facilities outside the network operator have also of voltage transformer kits. Additionally, although the use of resistors can be, in general, a valid solution for damping fermoresonances in voltage transformers, the permanent connection of this to the open triangle of protection of the set of voltage transformers can thermally deteriorate them during events other than ferroresonance, as is the case of ground faults. The passive and active solutions in [3, 9, 10] suffer one, or both, of the two indicated drawbacks.
    [0027]
    [0028] With reference to the electronics-based damping equipment, in ES8201762, US3401272A, US6560128B1 and [15-18], the electronic power devices are used as switches that allow to connect and disconnect the damping resistance, which must be designed for the conditions specific in which the phenomenon of ferroresonance occurs, which limits the possibility of deploying solutions that cover a wide casuistry. On the other hand, the electronic power devices used in these Patents and works are only suitable for operation at low switching frequencies, typically in the tens of hundreds of Hz range, limiting the damping possibilities of certain types of ferroresonance, for example of fundamental type [3, 19], where some of the energy of the phenomenon must be dissipated at a higher frequency.
    [0029]
    [0030] Within the category of electronic-based damping equipment, the solution proposed in [20] consists of a booster power converter that emulates a resistance, Re, connected to the network by means of a gc parameter established by the emulator controller. However, due to the restriction of the booster converter, whereby the output voltage must be greater than the input voltage, situations can occur in which Re during the ferroresonance event, preventing its adequate damping. Consequently, the solution in [20] requires a design that is appropriate to the specific conditions of the ferroresonance, which are not entirely predictable, which also limits the deployment possibilities of the solution.
    [0031]
    [0032] References
    [0033]
    [0034] [1] S. Misák and J. Fulnecek, "The influence of ferro reson anee on a temperature of voltage transformers in undeground mines," 2017 18th International Scientific Conference on Electric Power Engineering (EPE), Kouty nad Desnou, 2017, pp. 1-4. doi:
    [0035] 10.1109 / EPE.2017.7967361.
    [0036]
    [0037] [2] S. Rezaei, "Adaptive overcurrent protection against ferroresonance," in IET Generation, Transmission & Distribution, vol. 12, no. 7, pp. 1573-1588, 4102018. doi:
    [0038] 10.1049 / iet-gtd.2017.0651.
    [0039]
    [0040] [3] E. Price, "A tutorial on ferroresonance," 201467th Annual Conference for Protective Relay Engineers, College Station, TX, 2014, pp. 676-704. doi:
    [0041] 10.1109 / CPRE.2014.6799036.
    [0042]
    [0043] [4] H.R. Abbasi Fordoei, H. Heydari, S.A. Afsari, "Elimination of chaotic ferroresonance in power transformer by ISFCL”, International Journal of Electrical Power & Energy Systems, Volume 68, 2015, Pages 132-141, ISSN 0142-0615.
    [0044]
    [0045] [5] Hamid Reza Abbasi Fordoei, Ahmad Gholami, Seyyed Hamid Fathi, Ataollah Abbasi, “'A new approach to eliminating of chaotic ferroresonant oscillations in power transformer”, International Journal of Electrical Power & Energy Systems, Volume 67, 2015, Pages 152 -160, ISSN 0142-0615.
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    [0047] [6] H. Radmanesh, A. Heidary, S. H. Fathi and G. Babamalek Gharehpetian, "Dual function fen'oresonance and fault current limiter based on DC reactor," in IET Generation, Transmission & Distribution, vol. 10, no. 9, pp. 2058-2065, 692016. doi:
    [0048] 10.1049 / iet-gtd.2015.1032.
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    [0050] [7] T. Abdelazim, T. J. Dionise and R. Yanniello, "Protecting voltage transformers from switching induced transients and ferroresonance," 2016 IEEE-IAS / PCA Cement Industry Technical Conference, Dallas, TX, 2016, pp. 1-17. doi:
    [0051] 10.1109 / CITCON.2016.7742671.
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    [0053] [8] S. Rezaei, "Impact of transmission Une and plant outage on ferroresonance in AC transmission system and new suppression method," 13th IET International Conference on AC and DC Power Transmission (ACDC 2017), Manchester, 2017, pp. 1-6. doi:
    [0054] 10.1049 / cp.2017.0069.
    [0055] [9] C. Venkatesh, K. Shanti Swarup, “Performance assessment of distance protection fed by capacitor voltage transformer with electronic ferro-resonance suppression circuit”, Electric Power Systems Research, Volume 112, 2014, Pages 12-19, ISSN 0378- 7796.
    [0056]
    [0057] [10] SA Khan, AHA Bakar, NA Rahim and C. Tan, "Analysis of ferroresonance suppression and transient response performances for various ferroresonance suppression circuits in capacitive voltage transformers," 3rd IET International Conference on Clean Energy and Technology (CEAT) 2014, Kuching, 2014, pp. 1-6. doi: 10.1049 / cp.2014.1474.
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    [0059] [11] VT Guard Pro / VT Guard Pro - D Solution for Ferroresonance Elimination, ABB, Videnska 117, 61900 Bmo, Czech Republic, 2016.
    [0060]
    [0061] [12] Damping Unit Against Ferro Resonance Oscillation, RITZ, Hamburg, Germany, 2013.
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    [0063] [13] BE - Choke module for suppressing ferro-resonance, ELEQ, Tukseweg 130, 8331 LH Steenwijk, The Netherlands.
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    [0065] [14] Ferro-damp ferroresonance protection, RION ELEKTR1K ELEKTRONIK BILI§IM SAN. SEE IT. LTD. §YOU. Tuzla, İstanbul, Türkiye.
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    [0067] [15] Mohammad Navaei, Ali Akbar Abdoos, Majid Shahabi, “A new control unit for electronic ferroresonance suppression Circuit in capacitor voltage transformers”, International Journal of Electrical Power & Energy Systems, Volume 99, 2018, Pages 281-289, ISSN 0142 -0615.
    [0068]
    [0069] [16] Ming Yang, Wenxia Sima, Lijun Chen, Pan Duan, Potao Sun, Tao Yuan, "Suppressing ferroresonance in potential transformers using a model-free active-resistance controller", International Journal of Electrical Power & Energy Systems, Volume 95, 2018, Pages 384-393, ISSN 0142-0615.
    [0070]
    [0071] [17] Y. N. Ryzhkova and S. A. Tsyruk, "Ferroresonance suppression in distribution networks," 2016 2nd International Conference on Industrial Engineering, Applications and Manufacturing (ICIEAM), Chelyabinsk, 2016, pp. 1-4. doi: 10.1109 / ICIEAM.2016.7911458.
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    [0073] [18] W. Sima, M. Yang, Q. Yang, T. Yuan and M. Zou, "Simulation and experiment on a flexible control method for ferroresonance," in IET Generation, Transmission & Distribution, vol. 8, no.
    [0074] 10, pp. 1744-1753, October 2014. doi: 10.1049 / iet-gtd.2014.0046.
    [0075]
    [0076] [19] Ph. Ferrad, "Cahier Technique Schneider n ° 190, Ferroresonance", Schneider Electric, 1998.
    [0077]
    [0078] [20] E. Bayona, F. López, R. Martínez, R. Mínguez, J.I. Rodríguez, C. Capellán, P. Lamo, F.J. Azcondo, M. Mañana, A. Pigazo, M. Alvarez, "'Active devices for the mitigation of ferroresonances in voltage transformers in isolated neutral distribution electrical networks", CIGRE Workshop line monitoring, Santander, 2017.
    [0079]
    [0080] Summary of the Invention
    [0081]
    [0082] The present invention tries to solve the aforementioned drawbacks by means of a configured system and method for the mitigation of ferroresonances in voltage transformers.
    [0083]
    [0084] The system is connected to the open protection triangle formed by the protection windings of the set of voltage transformers connected to a power grid, and comprises: a) a decision block, and b) a resistance emulator block, which it also includes a power converter and a processor for the input voltage value; such that the input terminals of the resistance emulator block and the decision block are connected to the terminals of the open protection triangle, said terminals providing the input voltage to the system va .
    [0085]
    [0086] - the input of the decision block is connected to the input of the processor of the input voltage value; and the output of the decision block is connected to the resistance emulator block, activating it with the resistance value to be emulated for the mitigation of the ferro resonance or deactivating it, such that the decision block comprises a circuitry configured to 1) compare the voltage of input to the system goes with a programmable reference value; 2) configure the selected time to start mitigating the tamo ferroresonance phenomenon ; and 3) communicate with the processor of the input voltage value to indicate the value of the equivalent resistance Re
    [0087]
    [0088] - the input voltage value processor is connected to the open protection triangle in order to acquire the value of the input voltage to the system va , to the decision block, which provides it with the value of the equivalent resistance Re , and to the power converter, such that the input voltage value processor is configured so that from the equivalent resistance value Re, obtaining the time ton in which the switching state of the at least one active switch that forms part changes. of the power converter, and generate, from this value ton, a control signal c with two possible levels (digital) that applies to the power converter, with an edge at the beginning of each switching period and with an opposite edge in ton ;
    [0089]
    [0090] - The power converter is a commutator, AC / DC, unidirectional and of the elevator-reducer type , and it is connected to the open triangle of protection in order to process the energy of the ferroresonance, and to the processor of the voltage value of input, which provides the control signal, c , such that the operating state of said power converter is configured to adjust its switching state with the indication of the control signal c, and such that when the power converter is active, it imposes the form of a to be proportional to va , because the power converter emulates the equivalent resistance obtained by the decision block, and behaves in this way by means of the control signal c provided by the processor the value of the input voltage;
    [0091]
    [0092] - The load block (direct current area, DC) of the power converter receives power from the open protection triangle to which the system is connected (alternating current area, AC).
    [0093]
    [0094] In a possible embodiment, the implementation of the decision block consists of an anti-aliasing filter and a controller, with analog and digital input-output interfaces.
    [0095]
    [0096] In a possible embodiment, the input voltage value processor is an FPGA-type programmable digital device. Alternatively, the input voltage value processor is a dedicated integrated circuit, as is the case with the L6561 for embodiments that place the converter in the limit operating mode between continuous and discontinuous driving mode.
    [0097]
    [0098] In a possible embodiment, the power converter charging block is an energy storage / heatsink / converter.
    [0099]
    [0100] In a possible embodiment, the power converter presents a first AC / DC stage consisting of a diode rectifier, and a second Flyback step-up-type DC-DC power conversion stage , comprising an inductor and a materialized switch by two power devices that operate as switches, and it adopts resistance emulator mode.
    [0101]
    [0102] In a possible embodiment, depending on the mitigation and power needs, two or more systems of the invention are coupled in parallel, that is, connected to the terminals of the open protection triangle, such that, with each system, the nominal power The whole set increases successively and the equivalent resistance applied to the open protection triangle varies in a greater interval.
    [0103]
    [0104] In another aspect of the invention, a method is provided for mitigating ferroresonance in voltage transformers using the system defined above. The method comprises the stages of:
    [0105]
    [0106] - the decision block determines components of the input voltage to the system v & in different frequency bands, and based on the reference values determines whether or not there is ferroresonance and its severity;
    [0107]
    [0108] - in case of occurrence of the ferroresonance, the decision block based on the input voltage to the system v & and the time selected to mitigate the phenomenon of ferroresonance tamo, obtains the value of the equivalent resistance Re, according to the equation:
    [0109]
    [0110]
    [0111]
    [0112] where:
    [0113]
    [0114] the resistors Ri and R 2 depend on v & and limit the maximum (Ri) and minimum (R2) value of the equivalent resistance;
    [0115] the tac time corresponds to the instant of time at which the resistance emulator starts its operation;
    [0116]
    [0117] - then, the input voltage value processor determines, from the equivalent resistance value Re, the time ton in which the switching state of the at least one active switch that is part of the power converter changes;
    [0118]
    [0119] - from this value ton the input voltage value processor generates a control signal c with two possible levels (digital) that it applies to the power converter, with one edge at the beginning of each switching period and one edge opposite in ton such that the switching state of the power converter switches, conduction and non-conduction, is established by the control signal c;
    [0120]
    [0121] - then, the power converter is activated with the indication (control signal c) of the input voltage value processor, which indicates at each moment whether the converter transistor conducts current ( ton) or blocks voltage ( toff) and the sequence of times ton and ton results in the waveform and current amplitude imposed by the power converter, necessary to achieve synchronization between the input current to the system i¿ and the input voltage to the system v &
    [0122]
    [0123] - the operation of the power converter results in an energy transfer from the open protection triangle to which the system is connected (AC area, AC) to the load block (DC area, DC);
    [0124] such that every once in a while, the decision block obtains a new equivalent resistance value, the input voltage value processor updates the ton value and therefore the control signal c, and the power converter emulates the updated equivalent resistance , guaranteeing the synchronization of voltage and intensity.
    [0125]
    [0126] In a possible embodiment, the decision block, in a first phase, obtains the effective value of the input voltage v & in at least two frequency bands i) around the fundamental defined by the maximum and minimum frequencies of the network, according to establish the applicable standards, ii) other frequencies or those frequency ranges that are considered of interest; in a second phase, it compares the effective values of each of the frequency bands with the limits established for i) the detection of the conditions of occurrence of the ferroresonance and ii) the confirmation of the occurrence of the ferroresonance; and in a third phase, it determines if these levels are maintained for the time necessary to require or maintain the activation signal of the resistance emulator block.
    [0127]
    [0128] Brief description of the figures
    [0129]
    [0130] In order to help a better understanding of the characteristics of the invention, in accordance with a preferred example of practical embodiment thereof, and to complement this description, a set of drawings is included as an integral part thereof, the character of which is illustrative and not limiting. In these drawings:
    [0131]
    [0132] Figure 1 shows a detail of the connection of the system of the invention to the open triangle of protection of the set of voltage measurement transformers.
    [0133]
    [0134] Figure 2 shows a block diagram of the system of the invention.
    [0135]
    [0136] Figure 3 shows a schematic of the control signal c , according to a possible embodiment of the invention.
    [0137]
    [0138] Figure 4 shows a graph of the mitigating effect of the system of the invention, according to a possible embodiment of the invention.
    [0139]
    [0140] Detailed description of the invention
    [0141]
    [0142] In this text, the term "comprises" and its variants should not be understood in an exclusive sense, that is, these terms are not intended to exclude other technical characteristics, additives, components or steps.
    [0143]
    [0144] In addition, the terms "approximately", "substantially", "around", "some", etc. should be understood as indicating values close to those that accompany these terms, since due to calculation or measurement errors, it is impossible to achieve these values with complete accuracy.
    [0145]
    [0146] The characteristics of the system of the invention, as well as the advantages derived from them, will be better understood with the following description, made with reference to the drawings listed above.
    [0147]
    [0148] The following preferred embodiments are provided by way of illustration, and are not intended to be limiting of the present invention. Furthermore, the present invention covers all possible combinations of particular and preferred embodiments indicated herein. For those skilled in the art, other objects, advantages, and features of the invention will emerge in part from the description and in part from the practice of the invention.
    [0149] Next, the electronic system and method of the invention for the mitigation of fermoresonances in voltage transformers through the use of electronic power converters operating as resistive emulators, according to the same scheme of Figures 1 and 2, are described. The system of the invention 10 is connected to the open protection triangle 11 formed by the protection windings of the set of voltage transformers connected to a power electrical network.
    [0150]
    [0151] The system comprises two parts with different tasks: a) a decision block 22; and b) a resistance emulator block 23, which in turn comprises a power converter 25 and an input voltage value processor 24. The resistance emulator block 23 and decision block 22 assembly make up the system of the invention.
    [0152]
    [0153] The input terminals of the resistance emulator block 23 (power converter 25 and input voltage value processor 24) and the decision block 22 are connected to the open protection triangle terminals, said terminals providing the input voltage to the system it goes. Furthermore, the resistance emulator block 23 imposes the input current to the system i¿ that circulates through the open protection triangle.
    [0154]
    [0155] Throughout the present description, it will be called the input voltage to the system, and tj to the input current to the system; however, it is important to note that the input voltage to the system is the same as the voltage between the terminals of the open protection triangle; and the current input to the system is the same as the current flowing through the secondary in a triangle configuration, once it is connected to the invention.
    [0156]
    [0157] a) The input of decision block 22 is connected to the input of the processor for the value of input voltage 24; and the output of decision block 22 is connected to resistance emulator block 23, activating it with the resistance value to be emulated for the mitigation of the ferroresonance or deactivating it.
    [0158]
    [0159] Decision block 22 determines from the input voltage to the system will if, by comparing one or more reference values, the operating conditions of the voltage transformers of the triangle protection may result in a situation of ferroresonance and , if applicable, confirms this unwanted mode of operation. The decision block 22 determines the instants of activation and stop of the resistance emulator block 23. Depending on the selected operating mode, the activation occurs either when the operating conditions can give rise to the occurrence of a ferroresonance, or once its occurrence has been confirmed, to proceed with its mitigation. The time elapsed between the confirmation of the occurrence of the ferroresonance and the activation of the mitigator is configurable.
    [0160]
    [0161] To do this, decision block 22 determines components of the input voltage to the system is in different frequency bands, and depending on the reference values determines whether or not ferroresonance and its severity.
    [0162]
    [0163] In case of occurrence of the ferroresonance, the decision block 22 activates the resistance emulator block 23 presenting an equivalent resistance Re adjustable according to the severity of the ferroresonance, thus controlling the way of extracting the energy associated with the phenomenon.
    [0164]
    [0165] That is, the decision block 22, from the input voltage to the system va and the time selected to mitigate the phenomenon of iron resonance tamo, obtains the value of the equivalent resistance Re, according to the equation:
    [0166]
    [0167]
    [0168]
    [0169] Where:
    [0170]
    [0171] The resistors Ri and R 2 depend on vu and limit the maximum ( Ri) and minimum ( R 2 ) value of the equivalent resistance. This information (operating thresholds) is provided by decision block 22 based on the configuration made by the user. An equivalent resistance less than R 2 implies a transformer overload, while an equivalent resistance greater than Ri can make it difficult to mitigate the ferroresonance in the required time.
    [0172]
    [0173] The tact time corresponds to the instant of time at which the resistance emulator block 23 begins its operation.
    [0174]
    [0175] In an embodiment of the invention, the decision block 22, in a first phase, obtains the effective value of the input voltage vu in at least two frequency bands i) around the fundamental, ii) other frequencies or those intervals of frequencies considered of interest. A person skilled in the art will understand that the frequency band around the fundamental is defined by the maximum and minimum frequencies of the network, as established by the applicable standards. In a second phase, it compares the effective values of each of the frequency bands with the limits established for i) the detection of the conditions of occurrence of the ferroresonance and ii) the confirmation of the occurrence of the ferroresonance. In a third phase, it determines if these levels are maintained for the time necessary to require or maintain the activation signal of the resistance emulator block 23.
    [0176]
    [0177] The circuitry of the decision block 22 must be that which allows 1) comparing the input voltage to the vu system with a programmable reference value; 2) configure the selected time to start mitigating the tamo ferroresonance phenomenon ; and 3) communicate with the processor of the input voltage value 24 to indicate the value of the equivalent resistance Re. In a specific embodiment, an anti-aliasing filter and a controller have been used, with analog and digital input-output interfaces. , for the implementation of decision block 22, although a person skilled in the art will understand that other configurations are possible.
    [0178]
    [0179] b) The resistance emulator block 23 is configured to transform the energy of the ferroresonance with an effect equivalent to that produced by the connection of a variable resistance whose value is controlled by the voltage in the open protection triangle. As indicated above, the resistance emulator block 23 comprises the input voltage value processor 24 and the power converter 25.
    [0180]
    [0181] - The input voltage value processor 24 is connected to the terminals of the open protection triangle in order to acquire the value of the input voltage to the system v &. In addition, it is connected to decision block 22, which provides it with the value of the equivalent resistance Re, and to power converter 25.
    [0182]
    [0183] The input voltage value processor 24 determines, from the input voltage to the system vu and the equivalent resistance value Re, the input current to the system U, using the equation:
    [0184]
    [0185] U = Vu / Re [2] In addition, the input voltage value processor 24 obtains the time ton in which the switching state of the at least one active switch that is part of the power converter 25 changes.
    [0186]
    [0187] This value, tan, depends on the type of power converter 25 used and its mode of operation: continuous mode of operation in which the current through the inductor or inductors is never zero, discontinuous mode of operation in which part of the period Switching current through the inductor or one of the inductors is zero or limit between the continuous and discontinuous conduction mode in which the current through the inductor or one of the inductors becomes zero at the end of the switching period.
    [0188]
    [0189] For example, for a power converter 25 reducer-riser with Flyback type insulation , with a single switch, operating in discontinuous conduction mode and with commutation period, T, and L, the magnetization inductance seen from the primary of the magnetic component that provides insulation, ton is calculated using the following equation:
    [0190]
    [0191]
    [0192]
    [0193] For example, in the case of imposing on this converter the operation at the limit between continuous and discontinuous driving mode and considering a ratio of turns between the secondary and primary winding of the magnetic component that provides insulation N 2 / N 1 = n and a output voltage vo. ton would be obtained by the following equation:
    [0194] 25
    [0195] 2 L ( v. ^ [4] to 1 n
    [0196] R e V v o
    [0197]
    [0198] From this value t, and as shown in Figure 3, the processor of the value of the input voltage 24 generates a control signal c with two possible levels (digital) that applies to the power converter 25, a sidewall at the beginning of each switching period and with an opposite flank in ton . That is, the switching state of the power converter switches 25, conduction and non-conduction, is established by the control signal c, often typically several orders of magnitude greater than the nominal of the network.
    [0199]
    [0200] The input voltage value processor 24 of the resistance emulator block 23, which controls the operation of the power converter 25 can be digital or analog.
    [0201]
    [0202] In the first case, an FPGA-type programmable digital device is preferably used. In the second case, a dedicated integrated circuit, as in the case of the L6561, for embodiments that place the converter in the limit operating mode between continuous and discontinuous driving mode.
    [0203]
    [0204] - The power converter 25 is connected to the terminals of the open protection triangle in order to process the energy of the ferroresonance. In addition, it is connected to the processor of the input voltage value 24, which provides it with the control signal, c. The power converter 25 comprised in the resistance formulator block 23 is a commutated, AC / DC, one-way power converter 25 of the buck-buck type .
    [0205] 1) switched to allow, through at least one switch, the selection of the driving and non-driving (blocking) states and, thus, adjust Re ;
    [0206] 2) AC / DC because the input to the power converter 25 comes from the electrical network and is therefore always alternating;
    [0207]
    [0208] 3) unidirectional because the objective of the system of the invention is to extract the energy of the ferroresonance from the electrical network, but not to inject it again during the time in which the ferronresonance is mitigated;
    [0209]
    [0210] 4) of the elevator-reducer type so that it is possible to adjust Re continuously throughout the entire ferroresonance mitigation process, without restrictive conditions between the input and output voltage values.
    [0211]
    [0212] The power converter 25 is activated by the indication (control signal c ) of the processor of the value of the input voltage 24. The signal c indicates at each moment whether the transistor of the power converter 25 conducts current ( ton) or blocks voltage ( totr) and the sequence of times ton and torr results in the waveform and current amplitude i¿ necessary to fulfill the value of Re . Therefore, when the power converter 25 is activated, it imposes the form of i¿ to be proportional to v &. The constant of proportionality between v & e i¿, Re, is also indicated by the processor of the input voltage value 24. The operation of the power converter 25 results in a transfer of energy from the protection triangle to which the system is connected (alternating current zone, AC) to the load block (direct current zone, DC). The load block of the power converter 25 can be an energy storage system, an energy dissipator 5 or another energy storage / dissipator / converter system, depending on the utility that the energy extracted from the network wants to give during ferroresonance.
    [0213]
    [0214] A person skilled in the art will understand that the synchronization between the input current to the system i¿ and the input voltage to the system v & is necessary to achieve the resistance emulation effect. Otherwise, if the current and intensity were not in phase, the behavior of the system and method of the invention would no longer be equivalent to that of a resistance. The system and method of the invention allows this synchronization thanks to the control signal c. That is, the power converter 25 emulates the equivalent resistance obtained by the decision block 22, and behaves in this way by means of the control signal c provided by the processor of the value of the input voltage 24.
    [0215]
    [0216] The method of the invention for the mitigation of iron resonances in voltage transformers is a dynamic method, hence its great interest, since the equivalent resistance is variable and adjusts to the conditions of the network. That is, every so often (for example, on the rising edge of each switching period), decision block 22 obtains an equivalent resistance value. Next, the input voltage value processor 24 updates the ton value, and hence the control signal c . This update of c , allows the power converter to emulate the updated equivalent resistance 25, guaranteeing the synchronization of voltage and current. That is, the average value of the input current to the system i¿ each switching period takes the form (amplitude and phase) of the current reference obtained through v & tending to obtain a unity power factor during the mitigation of the ferroresonance. As a consequence, a behavior equivalent to a variable resistance controlled by the value of the input voltage to the system, v & is obtained.
    [0217]
    [0218] The synchronization and control of the power converter 25 as a resistance emulator is achieved with a control signal c applied to the power converter 25, which meets certain characteristics depending on the converter used:
    [0219] - indirect, step-down type converters ( Buck-Boost, Flyback, Cuk, SEPIC ...) operating at constant switching frequency (constant ton + ton ) or constant driving time (constant ton )
    [0220]
    [0221] In a possible embodiment, the power converter 25 has a first AC / DC stage consisting of a diode rectifier, and a second Flyback step -up- type power conversion DC / DC stage , comprising an inductor and a switch materialized by two power devices that operate as switches, and adopts the resistance emulator mode, that is, in such a way that the initial and final value of the input current to the system i¿ is ideally zero in each switching period and the maximum value is proportional to the input voltage.
    [0222]
    [0223] In this exemplary embodiment, the second DC / DC stage is configured so that, without the need for linear current control, the result is that the average value of input current to the system in each switching period, which is also the current that circulates through the inductor, is proportional to the input voltage v & and therefore operation as resistance emulator is guaranteed. A person skilled in the art will understand that the operation as resistance emulation can also be obtained with another type of non-linear or linear control, without necessarily working on the border between continuous and discontinuous driving mode.
    [0224] In the case of using a diode rectifier, if the output current of the diode rectifier, which is the input current to the switched power converter 25, maintains the same shape as the output voltage of the diode rectifier, then the input current The diode rectifier maintains the same shape as the input voltage v &, achieving operation as a resistance emulator.
    [0225]
    [0226] Depending on the mitigation and power needs, it is possible to couple in parallel, that is, connected to the terminals of the open protection triangle, two or more systems of the invention. With each system, the nominal power of the entire assembly will increase successively, and the equivalent resistance applied to the open protection triangle varies over a larger interval. A person skilled in the art will understand that, if the power converter 25 includes galvanic isolation, the outputs of various systems of the invention connected to the same v &, can also be connected, obtaining a unified output. In the case of using different systems of the invention or not having insulation, the outputs of each system will be independent. Decision block 22 is unique to each system.
    [0227]
    [0228] The operation of the system of the invention is as follows: decision block 22 monitors the input voltage of the system v &. When the measurement has frequency components and eigenvalues of a ferroresonance, it activates the resistance emulator block 23. During the mitigation of the ferroresonance, the amplitude of the input voltage signal of the system v & allows the decision block 22 to establish the level of energy of the ferroresonance and, from this, establishes the most appropriate value of equivalent resistance, Re , to apply.
    [0229]
    [0230] In the resistance emulator block 23, the input voltage value processor 24 uses the system input voltage measurement v & and the equivalent resistance value to be emulated to establish the control signal from the power converter 25. By operating this with an efficiency close to unity, the energy processed by the electronic power converter during mitigation is transferred to a load block, where the energy is stored and dissipated, depending on the operation of the electronic power converter.
    [0231] The mitigating effect of the system of the invention is observed in figure 4, where the input voltage of the system v & is shown for a subharmonic type ferroresonance. During the fault, the equivalent resonant circuit increases its energy. Once the protections are activated the ferroresonance appears in the voltage transformer, at the instant ton. The mitigator detection block holds Re M until it confirms the ferroresonance and activates the resistive emulator at the tact instant by reducing Re to values typically in the ten ohms. The resistance emulator, activated in tact, by means of the voltage processing block, forms the waveform of the input current to the system i¿ during the mitigation and, its amplitude, is modulated by Re. As a result of the Re applied to the open triangle of protection, the ferroresonance is damped in the tamo instant .
    [0232]
    [0233] As an alternative to the described detection strategy, it is possible to use other existing detection strategies, such as the one based on the measurement of vibrations and noise contained in patent ES 2 617 105 B2. However, it should be considered that not all detection strategies allow establishing which set of voltage transformers is at risk of suffering ferroresonance and, in this case, the mitigator could only be activated in the event of occurrence of ferroresonance. Such is the case of the patent ES 2617 105 B2. Furthermore, detection strategies in the literature do not establish the Re value .
    [0234]
    [0235] The operating principle of the system of the invention is based on that of the resistive emulators presented in [20]. Unlike the solution in [20], the resistive emulator topologies selected for the invention allow obtaining an equivalent resistance dependent, per se, on the energy of the ferroresonance, allowing to decouple this effect in the design of the power stage and the controller.
    [0236]
    [0237] The system of the invention behaves equivalently to a variable resistance, whose value depends on the energy of the ferroresonance and is independent of the type of ferroresonance considered. The equivalent resistance value is dynamically adjusted by the controller used. In addition, the system is capable of detecting the operating conditions prior to the occurrence of a ferroresonance in voltage transformers and can act preventively, before it occurs, or once it occurs, minimizing the effect on the voltage transformer and mitigating the phenomenon.
    [0238]
    [0239] The power of the system can be adapted depending on the application or infrastructure where it is going to be used, according to the state of the art of semiconductor devices and magnetic materials, considering for the design the maximum voltage that the system must withstand. If the maximum energy expected to be extracted in the ferro-resonance situation exceeds the specifications of the mitigating module, the number of necessary systems can be arranged in parallel, which are connected to the open protection triangle formed by the protection windings of the voltage transformers.
    权利要求:
    Claims (9)
    [1]
    1. System configured for the mitigation of ferroresonances in voltage transformers, connected to the open protection triangle (11) formed by the protection windings of the set of voltage transformers connected to a power electrical network, comprising: a) a block for decision (22), and b) a resistance emulator block (23), which in turn comprises a power converter (25) and a processor for the input voltage value (24); such that the input terminals of the resistance emulator block (23) and the decision block (22) are connected to the terminals of the open protection triangle (11), said terminals providing the input voltage to the system v & where:
    - the input of the decision block (22) is connected to the input of the processor of the input voltage value (24); and the output of the decision block (22) is connected to the resistance emulator block (23), activating it with the resistance value to be emulated for the mitigation of the ferroresonance or deactivating it, such that the decision block (22) comprises a circuitry configured to 1) compare the input voltage to the system v & with a programmable reference value; 2) configure the selected time to start mitigating the tamo ferroresonance phenomenon and 3) communicate with the processor of the input voltage value (24) to indicate the value of the equivalent resistance Re
    - the input voltage value processor (24) is connected to the terminals of the open protection triangle (11) in order to acquire the value of the input voltage to the system v &, and to the decision block (22) , which gives the value of the equivalent resistance Re, and to the power converter (25), such that the processor of the input voltage value (24) is configured to obtain the time from the equivalent resistance value Re ton in which the switching state of the at least one active switch that is part of the power converter (25) changes, and generate, from this value ton, a control signal c with two possible levels (digital) that applies to the power converter (25), with one edge at the beginning of each switching period and with an opposite edge in ton;
    - the power converter (25) is a commutated, AC / DC, unidirectional and elevator-reducer type converter , and is connected to the terminals of the open protection triangle (11) in order to process the energy of the ferroresonance, and to the input voltage value processor (24), which provides it with the control signal, c, such that the operating state of said power converter (25) is configured to adjust its switching state with the indication of the control signal c, and such that when the power converter (25) is activated, it imposes the form of i¿ so that it is proportional to v &, because the power converter (25) emulates the equivalent resistance obtained by the decision block (22), and behaves in this way by means of the control signal c provided by the processor for the value of the input voltage (24);
    - The load block (direct current area, DC) of the power converter (25) receives the energy from the open protection triangle (11) to which the system is connected (alternating current area, AC).
    [2]
    2. The system of the previous claim, where the implementation of the decision block (22) consists of an anti-aliasing filter and a controller, with analog and digital input-output interfaces.
    [3]
    3. The system of any of the preceding claims, wherein the input voltage value processor (24) is a FPGA-type programmable digital device.
    [4]
    4. The system of either of claims 1 and 2, wherein the input voltage value processor (24) is a dedicated integrated circuit, as is the case with the L6561 for Embodiments that place the power converter (25) in the limit operating mode between the continuous and discontinuous driving mode.
    [5]
    5. The system of any of the preceding claims, wherein the power converter charging block (25) is an energy storage / heatsink / converter system.
    [6]
    6. The system of any of the preceding claims, wherein the power converter (25) has a first AC / DC stage consisting of a diode rectifier, and a second step-down-type DC / DC power converter. Flyback, which includes an inductor and a switch materialized by two power devices that operate as switches, and adopts the limit mode between continuous and discontinuous conduction.
    [7]
    7. The system of any of the preceding claims, where depending on the mitigation and power needs, two or more systems of the invention are coupled in parallel, that is, connected to the terminals of the open protection triangle (11), such that with each system, the nominal power of the entire assembly increases successively and the equivalent resistance applied to the open protection triangle (11) varies over a larger interval.
    [8]
    8. Method for the mitigation of ferroresonances in voltage transformers using the system according to any of the preceding claims, characterized in that it comprises the steps of:
    - the decision block (22) determines components of the input voltage to the system v & in different frequency bands, and based on the reference values determines whether or not there is ferroresonance and its severity;
    - in the event of the occurrence of the ferroresonance, the decision block (22) from the input voltage to the system v & and the time selected to mitigate the phenomenon of ferroresonance tamo, obtains the value of the equivalent resistance Re according to the equation :
    r R
    1 ^ __ iV ' e ) [1] R = R a _ t mo _ la _ c > t t' 4 /
    v R 1 J
    35
    where:
    the resistors Ri and R 2 depend on v & and limit the maximum ( Ri) and minimum (R2) value of the equivalent resistance;
    the tact time corresponds to the instant of time in which the resistance formulator block (23) begins its operation;
    - then, the input voltage value processor (24) determines, from the equivalent resistance value Re, the time ton in which the switching state of the at least one active switch that is part of the power converter changes. power (25);
    - from this value ton the input voltage value processor (24) generates a control signal c with two possible levels (digital) that it applies to the power converter (25), with an edge at the beginning of each period switching and with an opposite flank in ton , such that the switching state of the power converter switches (25), conduction and non-conduction, is established by the control signal c ;
    - then, the power converter (25) is activated with the indication (control signal c) of the processor of the value of the input voltage (24), which indicates at each moment whether the transistor of the power converter (25) conducts current ( ton) or blocks voltage ( toff) and the sequence of times ton and toff results in the waveform and current amplitude imposed by the power converter (25), necessary to achieve the synchronization between the input current to the system i¿ and the input voltage to the system v &;
    - the operation of the power converter (25) results in an energy transfer from the open protection triangle (11) to which the system (AC area, AC) is connected to the load block (DC area, DC );
    such that every so often, the decision block (22) obtains a new equivalent resistance value, the processor of the input voltage value (24) updates the value ton , and therefore the control signal c, and the converter (25) emulates the updated equivalent resistance, guaranteeing the synchronization of voltage and current.
    [9]
    9. The method of the previous claim where the decision block (22), in a first phase, obtains the effective value of the input voltage vj in at least two frequency bands i) around the fundamental defined by the maximum frequencies and minimum of the network, as established by the applicable standards, ii) the rest of the frequencies or those frequency intervals that are considered of interest; in a second phase, it compares the effective values of each of the frequency bands with the limits established for i) the detection of the conditions of occurrence of the ferroresonance and ii) the confirmation of the occurrence of the ferroresonance; and in a third phase, it determines if these levels are maintained for the time necessary to require or maintain the activation signal of the resistance emulator block (23).
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    同族专利:
    公开号 | 公开日
    ES2756923B8|2021-04-09|
    ES2756923B2|2021-02-16|
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    ES201800244A|ES2756923B8|2018-10-25|2018-10-25|Electronic system and method for the mitigation of ferroresonances in voltage transformers|ES201800244A| ES2756923B8|2018-10-25|2018-10-25|Electronic system and method for the mitigation of ferroresonances in voltage transformers|
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