• 专利附录
  • 专利说明
  • 权利要求
  • 类似技术
  • 同族专利
  • 引用文献
  • 法律状态
  • 优先权
    • 专利摘要:
    the invention relates to a method of differential protection for generating a fault signal, in which the measured current values are respectively measured at at least two different measuring points (m1, m2) of a multiphase transformer (10) for each phase (a, b, c), the measured current values for each phase (a, b, c) are used to form differential current values and stabilization values, and the fault signal is generated if it is determined during a voltage test. trigger range that a pair of measured values of at least one of the phases (a, b, c), which is formed using one of the differential current values and the associated stabilization value in each case, is in a trigger range ( 23) predetermined. In order to be able to selectively and reliably distinguish an external fault from an internal fault, if the transformer (10) has a grounded neutral point (14), it is proposed that a zero phase sequence system current passing through the neutral point (14) is used to form the stabilization values. the invention also relates to a corresponding differential protection device (11) for carrying out such a differential protection method.
    公开号:BR112017009650B1
    申请号:R112017009650-1
    申请日:2014-11-14
    公开日:2022-01-18
    发明作者:Frank Mieske
    申请人:Siemens Aktiengesellschaft；
    IPC主号:
    专利说明:

    [001] The invention relates to a method of differential protection for generating a fault signal, in which current measurements are respectively taken at at least two different measurement points of a multiphase transformer for each phase, differential current values and values Stabilization measures are formed from the current measurements for each phase, and the fault signal is generated if it is determined, during a drive region test, that a pair of measurements, created with the aid of one of the differential current values and the respectively associated stabilization value of at least one of the phases is in a predetermined trigger region. The invention also relates to a corresponding electrical differential protection device for carrying out a differential protection method.
    [002] Differential protection devices to implement a differential protection method are employed, among other things, to monitor multi-phase transformers, eg three-phase, in power supply networks. Here, at at least two different measuring points of the monitored transformer, usually on both sides of the transformer, in the case of a two-sided transformer, the current passing through the measuring points is obtained for each phase and supplied to the protection device. in the form of current measurements. By addition, taking into account the arithmetic signal, the protection device forms differential current values that are used to evaluate the operational situation of the monitored transformer for each phase of the current measurements.
    [003] Since the transformer itself causes a change in amplitude and phase angle in the current flowing through it, current measurements from at least one side must be adjusted for its amplitude and phase angle. before forming the differential current values, so that current measurements are obtained for both sides of the transformer that can be compared to each other. For amplitude, this adjustment is usually made using the known transformer ratio. For the phase angle, an adjustment also takes place using the appropriate adjustment matrices. The respective adjustment matrix is derived, for example, from the vector group of the transformer, and can, for example, be taken from suitable tables. It is also possible, additionally, to carry out an automatic phase angle adjustment, for example by measuring the phase angle difference between the current measurements at the different measuring points of the transformer. Both amplitude and phase angle adjustments are sufficiently well known to experts, and therefore will not be explained in detail at this point.
    [004] Since, in the case of a transformer with a star point grounded on one side of the transformer, a zero sequence current can arise and affect the differential current measurement, an additional correction of a zero sequence current component of transformer current measurements is usually performed. A measured starpoint current or a zero sequence current calculated from the current measurements of the individual phases can be used for this purpose.
    [005] The formation of the differential current value is performed after proper adjustment of the amplitudes and phase angle of the current measurements and after a zero-sequence current correction.
    [006] In the no-fault case, the differential current values are in a range close to zero, since, in this case - simply put - the current that flows into the transformer also flows out of it again. If, on the other hand, differential current values arise that differ significantly from zero, these lead to the conclusion of a faulty operating state, for example an internal short circuit, so that the fault current must be interrupted by opening a switching equipment that isolates the transformer, such as power supply switches. For this purpose, the protection device generates a corresponding fault signal which is used to generate a trigger signal to cause the switches to open their switching contacts.
    [007] Since ideal conditions are not normally obtained in practice, such as a differential current that has a value of exactly zero in the no-fault case, a suitable comparison value must be found for the differential current. The so-called stabilization value, which is calculated, for example, by performing the sum of the sizes of the respective current values, is used for this purpose. Making the difference of the sizes of the respective current measurements, or the selection of the maximum value between the sizes of the values of the respective current measurements, are other possibilities to calculate stabilization values in transformer differential protection.
    [008] If a differential current value and an associated stabilization value are entered in a chain diagram, the respective measurement pair lies within or outside a specified trigger region, so that when evaluating the position of the pair of measurements, it is possible to reach a conclusion regarding the formation of the fault signal: the fault signal is generated if the measurement pair lies within the pre-defined trigger region.
    [009] Problems arise from this when, for example, one or more of the current transducers used, especially in the case of external faults at high currents, that is, faults located outside the monitored transformer, go into saturation, and the secondary current delivered by them not representing a correct picture of the primary side current curve. In such cases, a significant differential current may be incorrectly detected, and a fault signal generated as a result.
    [0010] A method of differential protection of the type mentioned above is known, for example, from WO 2008/025309 A1. In the known differential protection device, the current curves obtained at the different measurement points of a component of a power supply network, for example a transformer, are examined from the point of view of similarity, and the sensitivity of the triggering of the Differential protection is adjusted according to the detected similarity. What can be achieved in this way is that in the case of dissimilar current curves - for example resulting from transducer saturation - the sensitivity of the differential protection device is appropriately lowered, so as not to result in an undesired fault signal.
    [0011] A method of differential protection is also known from WO 2014/079511 A1, in which predicted future values of differential current values and stabilizing current values are determined by estimation based on some current measurements obtained, and the position of the respective pairs of measurements in a trigger region is checked for the decision to generate a fault signal.
    [0012] The invention is based on the objective of providing a method or a differential protection device to monitor a multiphase transformer to be able to distinguish an external fault from an internal fault selectively and reliably.
    [0013] In terms of method, this objective is achieved by a method of differential protection of the type mentioned above, in which the transformer has a grounded star point and a zero sequence current (symmetrical component system) passing through the point star is used to form the stabilization values.
    [0014] When performing a multiphase transformer method for transformers with a grounded star point, it was determined that by means of a zero sequence current correction performed in this case, the current measurements, and thus also the values of stabilization for that side of the transformer on which zero-sequence current correction is performed, become zero. As a result, the stabilizing current in this case only takes into account the load current flowing through the sides of the transformer that do not have a grounded star point, which can also have a value of zero when the transformer is unloaded, so that in this case - as a result of the lack of stabilization of the differential protection method - the risk of incorrect linkage arises - in particular in the case of external heavy current faults and/or in the presence of transducer saturation. By including the zero sequence current in the calculation of the stabilization values, the risk of triggering a fault for such cases can, however, be significantly reduced, since in this case, on account of the comparatively greater zero sequence current in the presence failure, suitably large stabilization values can always be formed.
    [0015] According to an advantageous form of the embodiment of the method according to the invention, a maximum value between the current measurements formed at the respective measuring points and the zero-sequence currents passing through the respective sides of the transformer is used as value respective stabilization.
    [0016] In this form of modality, the value of the zero sequence current is included, namely, advantageously directly at the level of the stabilization value.
    [0017] According to a further advantageous form of embodiment of the method according to the invention, it is provided that the zero sequence current is determined by measuring a current passing through the star point.
    [0018] This modality form is suitable when the starpoint current can be acquired by a dedicated current transducer. A possible way of measuring the starpoint current is known, for example, from DE4416048C1.
    [0019] As an alternative to this form of embodiment, it is also possible to provide, according to another advantageous form of the embodiment of the method according to the invention, that the zero sequence current is computationally determined from the current measurements obtained for the individual phases.
    [0020] This calculation can be based on current measurements IA, IB, IC on the transformer side comprising the star point as follows, and is known to experts as “zero sequence current elimination”: 31 IJ = IA + IB + I c •
    [0021] A separate current transducer to measure a current flowing through the star point is not needed in this case.
    [0022] The aforementioned objective is also achieved by means of an electrical differential protection device to form a fault signal, with terminals for direct or indirect connection to at least two different measurement points of a component of a power supply network. , and with an evaluation device that is designed to form differential current values and stabilization values using current measurements taken at the measurement points, and to generate a fault signal if a pair of measurements, formed using one of the current values differentials and the associated stabilization value, respectively, are located within a pre-defined trigger region.
    [0023] It is provided according to the invention that the transformer has a grounded star point and that the evaluation device is designed to use a zero sequence current passing through the star point to form the stabilization values.
    [0024] An advantageous development of the differential protection device according to the invention provides that the evaluation device is designed to determine the respective stabilization value by means of determining a maximum value between the current measurements formed at the respective measuring points and the zero sequence currents passing through the respective sides of the transformer.
    [0025] In terms of obtaining the zero sequence current, it can also be provided that the differential protection device comprises a terminal for direct or indirect connection to a star point current measuring point, and that the evaluation device is designed to determine the zero sequence current by measuring a current passing through the star point, or that the evaluation device be designed to determine the zero sequence current computationally from the current measurements obtained for the individual phases.
    [0026] In terms of the differential protection device according to the invention, all the explanations regarding the differential protection method according to the invention made above and below also apply, and vice versa, in a similar way; in particular, the differential protection device according to the invention is designed to perform the differential protection method according to the invention in any arbitrary form of modality or a combination of arbitrary forms of modality. In terms of the advantages of the differential protection device according to the invention, references are also made to the advantages described for the differential protection method according to the invention.
    [0027] The invention is explained below in greater detail with reference to an example embodiment. The specific design of the modality example is not to be understood as restricting in any way the general design of the differential protection method according to the invention and the protection device according to the invention; on the contrary, individual design features of the modality example can be arbitrarily combined freely with each other and with the features described above.
    [0028] Here, Figure 1 shows a schematic view of a differential protection device that monitors a transformer; and Figures 2 to 4 show actuation diagrams with pairs of measurements of differential current values and settling values entered by way of example.
    [0029] For the sake of simplified illustration, a two-sided transformer is assumed in the context of the modality example. To apply the invention to transformers with more than two sides, the method described must be carried out for all other sides in a corresponding manner.
    [0030] Figure 1 shows a schematic view of a section of a three-phase electrical power supply system (A, B, C phase conductors) with a two-sided transformer 10 in a star-delta connection with a star point 14 grounded on the high voltage side 10a. Transformer 10 is monitored by means of a differential protection device 11 for the occurrence of internal faults (eg short circuits, phase-to-ground short circuits, winding faults). Current measurements IA, IB, IC are obtained for this purpose at a first measuring point M1 on the high voltage side 10a of transformer 10 by means of current measuring devices (e.g. inductive transducers or said unconventional transducers) , and are supplied to the corresponding terminals of a measurement taking device 12 of the differential protection device 11. Correspondingly, current measurements Ia, Ib, Ic are taken at a second measurement point M2 on a high voltage side 10a of transformer 10 by means of current measuring devices and are correspondingly provided to additional terminals of measurement taking device 12 of differential protection device 11. Current measurements IA, IB, IC, Ia, Ib, Ic can be transferred here in analogue or digital form to the measurement taking device 12. If current measurements IA, IB, IC, Ia, Ib, Ic are present as measurement analogous actions in the measurement device 12, they are filtered and subjected to an A/D conversion there. Otherwise, filtering and A/D conversion already takes place outside the measurement device 12, for example by means of a so-called remote terminal unit or a merge unit. The digitized measurements are transferred, in this case, to the differential protection device 11 via a process bus.
    [0031] The measurement taking device 12 is connected on its output side to an evaluation device 13 of the differential protection device 11, which may, for example, consist of an appropriately configured hardware computing component (ASIC, FPGA ), a central microprocessor assembly, a digital signal processor (DSP), or a combination of such devices. The evaluation device 13 is configured through software determined and/or hardware determined programming to use current measurements from both sides of transformer 10 to perform a differential protection method to be able to detect any internal faults and shut down. .
    [0032] Since changes in amplitude and phase angle of the current output on the low voltage side compared to the sizes present on the high voltage side occur in the current and voltage transformation by transformer 10, it is necessary, first of all, to perform the differential protection method, that the amplitude and phase angle of current measurements are adjusted. Such an adjustment with respect to the currents Ia, Ib, Ic on the low voltage side 10b of the transformer 10 is described below, although it would also be possible, alternatively or in addition, to adjust the current measurements of the high voltage side 10a.
    [0033] For amplitude related adjustment, current measurements Ia, Ib, Ic are adjusted using the transform ratio n. This gives the ratio of the number of windings in the high-voltage winding to those in the low-voltage winding, and determines the related change in current amplitude during the transformation process. A phase angle adjustment between the high voltage side and the low voltage side is also performed. The change in phase angle primarily results from the constructively predetermined group of vectors and the position of any touch switch. These adjustments are sufficiently well known, and therefore not explained in greater detail at this point. After adjusting the amplitude and phase angle, adjusted current measurements I'a, I'b, I'c are present on the output side.
    [0034] On the high voltage side 10a of transformer 10, a zero-sequence current component I0 may occur as a result of the starpoint 14 grounding. This is compensated by an appropriate correction prior to executing the differential protection method. . The following equation represents the zero sequence current correction for the current measurements IA, IB, IC taken on the 10a high voltage side:

    [0035] IA, IB, IC here represent the current measurements, corrected for the zero sequence current, of the high voltage side 10a; I0 represents the zero sequence current.
    [0036] The zero sequence current I0 can be determined here, for example, computationally, from the current measurements IA, IB, IC:3I0=IA +IB +IC.
    [0037] The zero sequence current can alternatively be determined by measuring the starpoint current ISt if an appropriate measuring device is present in the current path between starpoint 14 and ground, and transmitted to the differential protection device 11 (not shown in Figure 1).
    [0038] Amplitude-adjusted and phase angle-adjusted current measurements I'a, I'b, I'c of the low voltage side 10b can now be employed in conjunction with sequence current corrected current measurements zero IA, IB, IC obtained on the high voltage side 10a, for the differential protection comparison. With the formation of a respective IDif differential current value, the difference between the sizes of the current measurements that belong, in each case, to a phase, is formed here:

    [0039] To dynamically adjust the differential protection method to the size of the current flowing at a given instant, and to compensate for any transducer errors in the current measuring devices used, an IStab stabilization value is additionally formed for each phase in the current measurements corrected for zero sequence current, or from current measurements adjusted for amplitude and phase angle IA, IB, IC and I'a, I'b, I'c, respectively. The incorrectly determined differential current value IDif that results from transducer errors specifically increases in proportion to the current passing through the transformer, and, in the case of external short-circuit currents, can increase so strongly with transducer saturation that, without stabilization would lead to tripping, although the fault is not located within the protection region, i.e. within transformer 10.
    [0040] Based on the calculated differential current value IDif and the associated stabilization value IStab, the position of a pair of measurements comprising the calculated differential current value IDif and the stabilization value IStab is verified for each phase in a diagram of drive. If the measurement pair of at least one of the phases of transformer 10 is located within a trigger region, a fault signal indicating the fault is generated, and can be used by the differential protection device 11 to form a trigger signal. TRIP to a supply switch (not shown in Figure 1), to prevent further damage to transformer 10. The TRIP trigger signal causes the supply switch to open the appropriate switching contacts to disconnect transformer 10 from the rest of the mains supply. Energy supply.
    [0041] In conventional approaches, the IStab stabilization value of transformers is determined either as the sum of the sizes of current measurements corrected with zero sequence current or adjusted accordingly.
    either as the size of the difference of current measurements corrected with zero sequence current or adjusted accordingly
    or as the maximum value current measurements corrected with zero sequence current or adjusted accordingly

    [0042] The equations above are formulated as an example, in each case, for phase A of transformer 10; the equations to calculate the stabilization values IStab,B and IStab,C for the other two phases B, C must be set accordingly.
    [0043] With this type of conventional stabilization value formation, however, weaknesses have arisen in terms of handling the zero sequence current at a grounded star point in the presence of external heavy current faults and transducer saturation that can occur. Such an external fault, i.e. located outside the transformer, between phase A and ground at fault location F in the cable section between generator 15 and transformer 10 is illustrated in Figure 1. This external fault must be recognized as such by the differential protection device 11, and must not lead to undesired actuation.
    [0044] In the case of the illustrated, single-pole external fault, in contact with the ground and fed through the grounded transformer, the short-circuit current -IKA passes through the transformer's star point 14 as zero sequence current I0 ( the short-circuit current that flows is suggested in Figure 1 by arrows; the size of the respective short-circuit current that flows is suggested by the number of arrows, where more arrows refer to a larger short-circuit current). The short circuit current is represented on the high voltage side 10a of the transformer 10 equally on all three phases A, B, C. The zero sequence current I0, on the other hand, is not represented on the low voltage side 10b of the transformer. transformer 10, as this is deployed as a delta winding. For this reason, in transformer differential protection, before the formation of the differential current value IDif and the stabilization value IStab, the zero sequence current correction explained above is performed with respect to those sides of transformer 10 that have a ground (in In this example, it is only the high voltage side 10a).
    [0045] In terms of the single pole fault in Figure 1, the fault current on the high voltage side 10a is equal in size in terms of amplitude and phase angle on all three phases. The following therefore applies to the high voltage side 10b when transformer 10 is unloaded:

    [0046] Current measurements treated with zero current from the high voltage side 10a therefore generate according to equation (1):

    [0047] As can be seen from the above equation, if only the short-circuit current IKA is considered, i.e. without taking into account the load current, the current measurements treated with zero sequence current on the high voltage side 10a becomes zero. The above-mentioned conventional calculation methods for the settling values therefore lead to settling values which only take into account the load current on the low voltage side 10b of transformer 10. When the transformer is unloaded, such load current can also be zero, so that a stabilization value of zero (or close to zero) is determined.
    [0048] If a cable current transducer does not transmit current accurately (for example, when the transducer is saturated, but also as a result of improper measurements), the incorrect component in the previous method is represented with equal proportions in the value differential current and the stabilization value. This ratio of approximately 1 appears on the drive diagram as a characteristic fault line in the case of single-sided power supply internal fault, and unwanted start-up occurs. This case is illustrated by way of example in the actuation diagram of Figure 2, which, for the sake of simplicity (as is also true of the subsequent actuation diagrams in Figures 3 and 4), is drawn only for one phase, for example, the phase A. In the drive diagram, pairs of measurements consisting of determined differential current values and associated stabilization values are checked to examine their position. The characteristic fault line 20 can be seen as a diagonal in the drive diagram. The characteristic drive line 21 separates the drive region 23 from the normal region 24. The measurement pair 25 of the differential current value IDif1 and the conventionally calculated IStab1 is located in the drive region 24 and therefore takes - despite the fault is external - to a drive.
    [0049] To solve this problem, it is proposed that the calculation of the stabilization value be modified, so that the stabilization value is determined also taking into account a zero sequence current that is present. The stabilization value is preferably formed by means of a selection of the maximum value between the respective current measurements, adjusted and/or corrected for zero sequence current if relevant, for each phase, as well as from the zero sequence current measured or calculated (considered below for phase A as an example:

    [0050] Here, I0,S1 and I0,S2 represent the zero sequence currents measured or calculated on the respective sides of the transformer (S1: side 1, the high voltage side 10a in the current case; S2: side 2, the high voltage side low voltage 10b in the current case). If a zero sequence current is not present - as is the case here for the low voltage side 10b - this term is correspondingly omitted from the determination of the stabilization value; in the present case, it follows that only the zero sequence current I0,S1 on the high voltage side is included in the calculation of the stabilization value. The stabilization value is determined separately for each phase. The number of sides of the transformer in use on which zero-sequence currents occur, and which therefore require zero-sequence current correction, also determines the number of zero-sequence currents to be considered for forming the stabilization value.
    [0051] As a result of the modified determination of the stabilization value, an incorrectly formed zero sequence current is now directly included in the stabilization of the differential protection method, and is properly considered in the trigger region verification. The illustrated solution therefore solves the problem of incorrect triggering in the case of an external fault illustrated in Figure 1. This is illustrated by way of example in Figure 3. If the value of the differential current value IDif1 remains the same compared to the actuation diagram in Figure 2, the significantly higher zero-sequence current is now included in the calculation of the stabilization value IStab. As a result, instead of the stabilization value IStab1 used in the case of Figure 2, the larger value IStab2 is now used; the measurement pair 31 comprising IDif1 and IStab2 is now located in the normal region 24. Correspondingly, the triggering is not initiated by the differential protection device 11 for external fault.
    [0052] The Figure shows, as an example, the case of an internal failure (not illustrated in Figure 1). As a result of the differential current value IDif2, which is now larger, the measurement pair 41 comprising IDif2 and IStab21 now lies in the trigger region 23. The differential protection device 11 correspondingly initiates a triggering of a power switch to turn off the internal failure.
    [0053] The solution described advantageously allows the previously known and proven basic principles of the standard differential current protection to be maintained, with the same settings for the characteristic drive curve 21, so that, in relation to this, no modified configuration should be done. The formation of the IDif differential current value is also not modified. Changes only occur in the way the IStab stabilization value is formed. This is also important, in order to avoid a stabilization above the necessary in the case of internal failures, with an operation below the possible associated. At the same time, improved stabilization is achieved in the event of external faults.
    权利要求:
    Claims (6)
    [0001]
    1. Differential protection method for generating a fault signal, in which - current measurements are respectively taken at at least two different measuring points (M1, M2) of a multiphase transformer (10) for each phase (A, B, Ç); - differential current values and stabilization values are formed from the current measurements for each phase (A, B, C); and - the fault signal is generated if it is determined, during a trigger region test, that a pair of measurements, created with the aid of one of the differential current values and the respectively associated stabilization value, of at least one of the phases (A, B, C) are in a predetermined drive region (23); characterized by the fact that: - the transformer (10) has a grounded star point (14); and - a zero sequence current passing through the star point (14) is used to form the stabilization values; and - a maximum value between the current measurements formed at the respective measurement points (M1, M2) and the zero sequence currents passing through the respective sides (10a, 10b) of the transformer (10) is used.
    [0002]
    2. Differential protection method according to claim 1, characterized in that: - the zero sequence current is determined by measuring a current passing through the star point (14).
    [0003]
    3. Differential protection method according to claim 1, characterized by the fact that: - the zero sequence current is computationally determined from the current measurements obtained for the individual phases (A, B, C).
    [0004]
    4. Electrical differential protection device (11) to form a fault signal - with terminals for direct or indirect connection to at least two different measuring points (M1, M2) of a multiphase transformer (10), and - with a device (13) which is designed to form differential current values and stabilization values using current measurements taken at the measurement points (M1, M2), and to generate a fault signal if a pair of measurements, formed using one of the differential current values and the associated stabilization value, respectively, are located in a pre-defined activation region (23), characterized by the fact that: - the transformer (10) has a grounded star point (14); and - the evaluation device (13) is designed to use a zero sequence current passing through the star point (14) to form the stabilization values; and - the evaluation device (13) is designed to determine the respective stabilization value by means of determining a maximum value between the current measurements formed at the respective measurement points (M1, M2) and the zero sequence currents passing by the respective sides (10a, 10b) of the transformer (10) is used.
    [0005]
    5. Differential protection device (11) according to claim 4, characterized in that: - the differential protection device (11) comprises a terminal for direct or indirect connection to a star point current measuring point ; and - the evaluation device is designed to determine the zero sequence current by measuring a current passing through the star point (14).
    [0006]
    6. Differential protection device (11) according to claim 4, characterized in that: - the evaluation device (13) is designed to compute the zero sequence current computationally from the current measurements obtained for the phases (A, B, C) individual.
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    法律状态:
    2020-03-31| B06U| Preliminary requirement: requests with searches performed by other patent offices: procedure suspended [chapter 6.21 patent gazette]|
    2021-08-24| B06A| Patent application procedure suspended [chapter 6.1 patent gazette]|
    2021-11-03| B09A| Decision: intention to grant [chapter 9.1 patent gazette]|
    2022-01-18| B16A| Patent or certificate of addition of invention granted [chapter 16.1 patent gazette]|Free format text: PRAZO DE VALIDADE: 20 (VINTE) ANOS CONTADOS A PARTIR DE 14/11/2014, OBSERVADAS AS CONDICOES LEGAIS. |
    优先权:
    申请号 | 申请日 | 专利标题
    PCT/EP2014/074610|WO2016074742A1|2014-11-14|2014-11-14|Differential protection method and differential protection device for performing a differential protection method|
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