 METHOD AND APPARATUS FOR TRANSFORMER DIAGNOSIS
专利摘要:
Transformer and Transformer Diagnostic Method and Apparatus The present invention relates to a transformer diagnostic apparatus and method that can advantageously be used for online diagnosis of a transformer, and whereby transformer properties can be monitored and / or determined. the diagnostic method comprises collecting, for at least two different transformer loads, measurements of a current being indicative of the transformer load, as well as measurements of at least one additional transformer ac signal. the method further comprises deriving, from the collected measurements, at least two values of an amount that depends on a transformer property as well as a transformer load; and to determine, from the derived values, a set of coefficients of a relation of how the said quantity is expected to vary with transformer load. the method further comprises using the determined coefficient (s) when performing a transformer diagnosis. 公开号:BR112013014847B1 申请号:R112013014847-0 申请日:2011-11-17 公开日:2020-05-12 发明作者:Nilanga Abeywickrama；Tord Bengtsson 申请人:Abb Research Ltd； IPC主号:
专利说明:
Descriptive Report of the Invention Patent for METHOD AND APPARATUS FOR DIAGNOSIS OF TRANSFORMER AND TRANSFORMER. Technical Field [001] The present invention concerns the field of power transformers, and in particular the online diagnosis of transformers. Background [002] Transformers in general form an integral part of a power transmission system, providing the possibility to convert one voltage level into another. Transformers in power transmission systems often represent huge investments, and are typically not manufactured until ordered. In the event that a transformer in a power transmission system needs to be replaced, it is often a long process to perform a replacement. In order to avoid situations where a transformer needs to be replaced in a rescue action, it is desirable to detect a problem arising at an earlier stage, so that required maintenance or planned replacement can be performed. [003] Online monitoring systems for transformers have been designed to detect and indicate, while the transformer is in operation, deviations in transformer properties that may indicate a deterioration of the transformer status. Examples of properties that can be monitored are temperature, fuel dissolved gas and bushing capacitance. [004] Transformer impedance is an additional property that has been used in transformer diagnostics. Conventionally, transformer impedance has been Petition 870190090373, of 12/09/2019, p. 9/61 2/44 determined offline, that is, through measurements performed when the transformer is disconnected from the power transmission system. [005] In US2010 / 0188240 it is proposed to monitor the transformer impedance while the transformer is in operation. The possibility of online impedance monitoring would be of great benefit, since the impedance of a transformer carries useful information regarding the status of the transformer, and disconnecting a transformer from the power transmission system in order to determine the impedance is expensive. In US2010 / 0188240 it is proposed to obtain information about the transformer impedance when measuring current A and voltage E at the transformer terminals, and to generate (in a three-phase system) a 9x9 impedance matrix from such measurements using the relations EiH - EjL = Zijaij and AiH = ai1 + ai2 + ai3, where aij represents transformer terminal currents; the H and L indices indicate the high voltage side and the low voltage side, respectively; the indices i = 1, 2, 3 indicate phases of the high voltage terminals; and the indices j = 1, 2, 3 indicate phases of the low voltage terminals. As discussed in US2010 / 0188240, solving the system of equations obtained by the proposed analysis introduces considerable computational complexity, and a simplification of the model is therefore proposed. However, even if such simplification is not used, the precision of the results obtained by the proposed method will often not be sufficient for the purposes of transformer diagnosis. Summary [006] An objective of the present invention is to provide a more accurate method for online diagnostics of transformers. [007] This problem is addressed through a transformer diagnostic method that can be used for a transformer Petition 870190090373, of 12/09/2019, p. 10/61 3/44 having at least one load winding and one source winding. The method comprises collecting, for at least two different transformer loads, measurements of a current being indicative of the transformer load, and measurements of at least one additional transformer AC signal. The method additionally comprises deriving, from the collected measurements, at least two values of an amount that depends on at least one transformer property as well as the transformer load, and determining, from the derived values, a set of coefficients of a relation of as it is expected that said quantity will vary with transformer load. The method further comprises using at least one of said coefficients when performing a diagnosis of the transformer. [008] Through the inventive method a way is provided to determine values of transformer properties that are otherwise difficult to measure. In addition, the inventive diagnostic method can advantageously be used in online scenarios, thus facilitating monitoring and diagnosis without having to take the transformer offline. [009] The expression transformer AC signal is used here to refer to a signal from the set {I1, I2, V1 V2}, where I1, I2 are the currents through the transformer source and load windings, respectively, and V1, V2 are the voltages across the source and load sides of the transformer, respectively. [0010] Measurement collection can be performed when receiving measurement signals directly from measurement equipment, or when receiving measurement data from another source, such as a computer-readable memory or a different diagnostic device. [0011] The value of a coefficient can typically be described in terms of an expression involving at least one property Petition 870190090373, of 12/09/2019, p. 11/61 4/44 transformer. Some coefficients are really equal to the value of a transformer property, in which case the expression becomes simple. In one embodiment of the diagnostic method, performing a diagnosis comprises using at least one coefficient to obtain at least one transformer property, using the expression for how the coefficient depends on the transformer property (s). Consequently, in this modality, a value of a transformer property can be determined from online measurements, providing useful information regarding the status of the transformer. The determination of a transformer property can be repeated occasionally, by collecting additional measurements at different loads, and determining a new set of coefficients from which a new property value can be determined. [0012] In a diagnostic method, performing a diagnosis includes collecting an online monitoring measurement of at least one terminal AC signal on a first monitoring load; derive a value based on a measure of the amount of the monitoring measurement; and determining an expected value of the quantity in the first monitoring charge when using said ratio and said coefficient (s). The value based on the quantity measurement is then compared with the expected value of the quantity, in order to detect any transformer problem giving rise to a change in the quantity. Since the quantity depends on at least one transformer property, changes to a transformer property on which the quantity depends will be reflected in the quantity value. Consequently, through online quantity monitoring, online monitoring of the properties on which the quantity depends can be achieved effectively. If desired, the actual value of the transformer property (s) can be determined by indicating an Petition 870190090373, of 12/09/2019, p. 12/61 5/44 change. [0013] The collection of an online monitoring measurement and the comparison with the corresponding expected value can be repeated as often as necessary or desired, for example, in time ranges from seconds to years. Monitoring measurements can be performed on a regular basis, or on demand. [0014] The relationship with respect to how the quantity varies with transformer load can be a linear relationship, in which the slope and / or intersection at zero load are indicative of a transformer property. In one embodiment, the amount is the difference between the voltage across the terminals of a first winding on a first side of the transformer and the voltage across a second winding on a second side of the transformer as reflected to the first side. In an implementation of this modality in which the transformer has only one winding per side that carries significant power, the relationship corresponds to: AV = Z1I0 + I2, or n [0015] where Z1 is the impedance of the source winding; I0 is the magnetization current; n is the ratio of the number of turns of the source winding to the number of turns of the load winding; Zw is the total winding impedance; I2 is the load current; AV is the difference between the voltage across the terminals of the source winding and the voltage across the load winding as reflected to the source side; and AV 'is the difference between the voltage across the source winding as reflected to the load side and the voltage across the terminals of the load winding. In this modality, transformer properties of which the Petition 870190090373, of 12/09/2019, p. 13/61 6/44 coefficients of the relationship depend on the total winding impedance, the winding ratio, the magnetizing current and the source winding impedance. [0016] In another mode, the quantity is the source current. In an implementation of this modality in which the transformer has only one winding per side that carries significant power, the relationship corresponds to: I 1 - - 12 + 10, n [0017] where Ii is the source current; I2 is the load current; Io is the magnetization current; and n is the ratio of the number of turns of the source winding to the number of turns of the load winding. In this mode, information about the relationship between turns and the magnetizing current at high load can be obtained. [0018] Also in another mode, the amount is the loss of power in the transformer. In an implementation of this modality in which the transformer has only one winding per side that carries significant power, the relationship corresponds to: loss - VI + Z 0 2 + Z> 0 + Z 1 + Z wn I2I2 [0019] where Sperda is said loss of power; Z1 is the impedance of the source winding; Io is the magnetization current; n is the ratio of the number of turns of the source winding to the number of turns of the load winding; Zw is the total winding impedance; V1 is the voltage across the source winding and I2 is the load current. In this modality, the transformer properties on which the coefficients of the relationship depend are the total winding impedance, the ratio between turns, the magnetizing current and the impedance of the source winding. Assuming that these properties are already known (for example, of the AV (AV ') and I2 relationships described above), information regarding power loss by Petition 870190090373, of 12/09/2019, p. 14/61 7/44 magnetization and winding power loss can be achieved. The loss of power in the transformer is a general indicator of many types of problems. When monitoring power loss, a quick indication can be obtained more often in the event of a problem. [0020] The problem is additionally addressed by means of a transformer diagnosis device and its modalities. The transformer diagnostic apparatus comprises: an input configured to receive signals indicative of AC signal measurements from a transformer, including measurements of the transformer load current; an output configured to deliver a transformer diagnostic result; and a coefficient generator (706) connected to the input. The coefficient generator is configured to collect, for at least two different transformer loads, measurements of a current being indicative of the transformer load, and measurements of at least one additional transformer AC signal. The coefficient generator is additionally configured to derive, from the collected measurements, at least two values of an amount that depends on a transformer property as well as a transformer load; and to determine, from the derived values, a set of coefficients of a relation of how the said quantity is expected to vary with transformer load. The transformer diagnostic apparatus additionally comprises a diagnostic mechanism arranged to use the set of coefficients in generating a diagnostic result. The diagnostic mechanism is connected to the coefficient generator and to the output of the transformer diagnostic device (possibly via additional components of the diagnostic device). [0021] The problem is also addressed by means of a transformer comprising a diagnostic device for Petition 870190090373, of 12/09/2019, p. 15/61 8/44 transformer. The transformer can be a single-phase transformer, or it can include additional phases. The transformer can have two or more windings per phase. In an implementation where the transformer comprises a tap-changer, the coefficient generator can be configured to generate a set of coefficients for each tap-changer tapping point. In such a mode, the status monitor can be configured to determine, if a deviation is detected, in which tap-changer position (s) the deviation occurs. With this it is achieved that a position where a fault has occurred can be located. [0022] The problem is further addressed by means of a computer program to provide a diagnosis of a transformer, where the computer program, when executed in a transformer diagnostic apparatus, causes the diagnostic apparatus to execute the inventive method . Brief Description of the Drawings [0023] Figure 1 is an illustration of an ideal transformer model. [0024] Figure 2a is an illustration of a transformer model considering effects of magnetization currents in the transformer core, dispersion inductances and real resistances of the primary and secondary windings. [0025] Figure 2b is an alternative illustration of the transformer model shown in figure 2a, in which the impedances on the load side have been reflected to the source side. [0026] Figure 2c is an alternative illustration of the transformer model shown in figures 2a and 2b, in which the impedances on the source side have been reflected on the load side. [0027] Figure 3 is a graph showing AV as a function of Petition 870190090373, of 12/09/2019, p. 16/61 9/44 I2 for a transformer, where Δν is the difference between the source terminal voltage and the load terminal voltage as seen from the source side and I2 is the load current, and where values other than Δν were obtained from voltage measurements source and terminal connections at different transformer loads. [0028] Figure 4 is a graph showing experimental results from I1 versus I2, where I1 is the source terminal current and I2 is the load current. [0029] Figure 5 is a flowchart schematically illustrating a modality of an inventive method. [0030] Figure 6a is a flowchart illustrating schematically an example of a use of a T (I2) relationship determined using the method shown in figure 5. [0031] Figure 6b is a flow chart schematically illustrating an additional example of a use of a T (I2) relationship determined using the method shown in figure 5. [0032] Figure 7a is an example of an embodiment of a diagnostic apparatus according to the invention. [0033] Figure 7b is an example of a modality of a coefficient generator. [0034] Figure 7c is an example of a status monitor modality. [0035] Figure 8 is an alternative illustration of a diagnostic apparatus, a coefficient generator, a transformer-owned value generator, or a status monitor. [0036] Figure 9 is a schematic illustration of a transformer having a tap-changer. Detailed Description [0037] In power transmission and distribution systems, transformers are typically used to transform a level of Petition 870190090373, of 12/09/2019, p. 17/61 10/44 voltage to one another and / or to provide galvanic isolation between different sections of an energy transmission system. A schematic illustration of a transformer 100 is shown in figure 1. Transformer 100 in figure 1 comprises a first winding 105, a second winding 110, a transformer core 113, a first pair of winding terminals 115a, 115b connected to the first winding 105 and a second pair of winding terminals 120a, 120b connected to the second winding 110. The voltage across the first winding 105 is indicated as V1, and the voltage across the second winding 110 is indicated as V2, while the current across the first winding winding 105 is indicated as I1 and the current through the second winding 110 is indicated as I2. The number of turns in the first winding is indicated as n1 and the number of turns in the second winding is indicated as n2, the ratio n1 / n2 being referred to below as the relationship between turns n. It should be noted that, although a frequently used convention is to have n greater than 1, n as defined in this document can be less than, equal to or greater than 1. In addition, in order to simplify the description, the tension across a winding 105/110 will often be referred to as a terminal voltage, and a current through a winding 105/110 will often be referred to as a terminal current, although in some winding configurations, for example, in a three-phase winding, voltages and currents terminals will not directly reflect the winding voltages / currents, but will provide a means of deriving the winding voltages / currents. [0038] In the description below, for ease of description, it will be assumed that the first winding 105 is the winding that is powered by a source, and the second winding 110 is the Petition 870190090373, of 12/09/2019, p. 18/61 11/44 winding that delivers power to a load. However, an opposite convention can be used instead. [0039] In an ideal transformer without losses, and consequently of 100% efficiency, the following relationships are maintained: Y_ = rr n i n 2 V 2 n i - = n n 2 n i · 1 = n 2 · 1 2 = n THE V 2 S source + - = n · Z load, where THE Z, load (la) (lb) (lc), [0040] where Zfonte is the impedance seen from the source side and Zcarga is the impedance seen from the load side. [0041] However, a real transformer experiences apparent power losses, including both active and reactive power losses. The main sources of apparent power loss include: • Core losses, referred to as core loss or unloaded loss: hysteresis losses and eddy current losses. • Winding losses: I2R losses, surface losses and proximity. • Erratic losses: Losses in the metallic parts of the transformer, for example, tank wall, due to erratic magnetic fields. [0042] In addition to the power loss, there is typically a voltage drop across the transformer, because of the magnetomotive force associated with magnetic dispersion flow and the resistance of the windings. [0043] Figure 2a shows an example of an equivalent circuit frequently used for a non-ideal transformer 100, referred to as a first order model of a transformer 100. In addition Petition 870190090373, of 12/09/2019, p. 19/61 12/44 of the transformer components shown in figure 1, that is, windings 105, 110, core 113 and winding terminals 115a, 115b and 120a, 120b, figure 2a also illustrates the effects of voltage drop across the transformer caused by magnetic dispersion flow and apparent power losses discussed above. In figure 2a, the effects causing such voltage drops and apparent power loss are illustrated by including, in the equivalent circuit, the following elements: • a resistance of the source winding, Ri; • a dispersion reactance of the source winding, Xi; • a load winding resistance, R2; • a load winding dispersion reactance, X2; • a resistance representing the core losses, Rm; and • a reactance representing the core magnetization, Xm; [0044] where R1 and X1 are connected in series with the source winding 105; R2 and X2 are connected in series with the load winding 110; and Rm and Xm, which are connected in parallel, form an equivalent branch element that is connected in parallel with the source winding 105. The equivalent current through the equivalent branch element is indicated as Io, while the voltage across the equivalent branch element is indicated as E1. The current Io will then be referred to as the magnetizing current I0. [0045] Often, the first order transformer model in figure 2a is described in terms of an equivalent model, in which impedances are seen only from a single side of the transformer. Such equivalent models simplify the analysis of the transformer model, since the voltage level in general is different on both sides. Figure 2b shows an equivalent first order transformer model in which the Petition 870190090373, of 12/09/2019, p. 20/61 13/44 load side impedances were reflected to the source side, while figure 2c shows an equivalent first order transformer model in which the source side impedances were reflected to the load side. The following notation is used in figures 2b and 2c: • R12: the resistance of the load winding reflected to the source side; • X12: the dispersion reactance of the reflected load winding towards the source side; • R21: the resistance of the reflected source winding to the R loading side, R21 =; n • X21: the dispersion reactance of the reflected source winding to the load side, X21 = -; n • Rm: the equivalent resistance representing the core losses, as seen from the source side; • Xm: the equivalent reactance representing the core magnetization, Xm; • 112 = • I21 = level 1. [0046] For purposes of ease of description only, the following description in general will be done in terms of the transformer model shown in figure 2b. However, an equivalent analysis can be made based on the equivalent transformer model shown in figure 2c. [0047] Conventionally, the magnitude of the equivalent circuit components listed above can be determined by means of offline measurements. The total impedance Zw of the transformer windings, often referred to as the Petition 870190090373, of 12/09/2019, p. 21/61 14/44 short-circuit impedance Zw, can be estimated off-line as the ratio between an applied voltage and the current drawn by the transformer on the source side while the load side is short-circuited, where the total winding impedance corresponds to the sum the series impedance Z1 of the source side winding and the series impedance Z12 of the load side winding as seen from the source side, ie Zw = Z1 + Z12 = (R1 + jX1) + (R12 + jX12). [0048] Z12 is often referred to as the impedance reflected on the source side, and can be expressed as Z12 = n 2 Z2. The resistance of a winding (according to Ri and R12) can be measured using conventional methods, for example, by applying a voltage and measuring the resulting current in a steady state. In addition, values of the components Rm and Xm of the magnetization tap can be estimated when performing measurements without load, during which only the magnetizing current Io flows to the transformer. [0049] In addition, once the short-circuit impedance Zw has been determined by means of off-line measurements, another fundamental characteristic of the transformer can be determined, namely the n-turn relationship. The relationship between turns can be determined off-line by means of unloaded voltage measurements, using the following relationship, where the influence of the magnetizing current is often overlooked: Vi = nV + Z1I0 «nV (2) [0050] However, as mentioned earlier, more frequent monitoring of the transformer is desired than can be achieved viable via offline measurements. [0051] The method presented in US2010 / 0188240, in which online measurements of terminal voltages and currents are used to calculate transformer impedance values, can provide a Petition 870190090373, of 12/09/2019, p. 22/61 15/44 gross estimate of transformer impedance in an online scenario. However, US2010 / 0188240 does not take into account any magnetizing current, but assumes that the total voltage drop across windings 105 and 110 is caused by the load current on the transformer impedance (which in US2010 / 0188240 is defined as an impedance matrix). The influence of the magnetizing current on the impedance and winding calculations is often not negligible and, moreover, this influence is not constant, so that the accuracy of any values of the transformer impedance derived by using the method suggested in US2010 / 0188240 will typically be lower. [0052] An improved analysis of the results of measurements of voltages and currents of terminals during operation of a transformer 100 is suggested below. According to the invention, a diagnosis of a transformer 100 can be obtained by collecting, for at least two different transformer loads, measurements of a current being indicative of the transformer load, as well as measurements of at least one additional terminal AC signal. . From such measurements, the coefficients of a relationship between a quantity T and the transformer load can be established, where the quantity T depends on a transformer property to be determined as well as the transformer load, while being obtainable at the same time. collected measurements. [0053] When using the ratio coefficients describing how the quantity T is expected to vary under load, a value of a transformer property, on which the value of T depends, can be derived. A T amount can typically be described as a sum of a load dependent term and a term that is load independent, although T quantities having other load dependencies can be considered. Petition 870190090373, of 12/09/2019, p. 23/61 16/44 [0054] When using a quantity T that is obtainable from measurements of at least one AC signal, where quantity T depends on the transformer property to be determined as well as the transformer load, the transformer property can be extracted from the variation of quantity T with transformer load. Thus, when performing measurements on at least two different transformer loads, an adequate analysis of the quantity variation with load will give information regarding the value of the property to be determined. As will be seen below, examples of transformer properties that can be determined by means of an analysis as described above are the short-circuit impedance Zw, the relationship between turns n and the magnetizing current I0. [0055] The suggested analysis can be used to determine, from online measurements of terminal AC signals, an absolute value of a transformer property. In addition, the analysis can be used in online monitoring of the status of the transformer. When using the analysis for online monitoring purposes, the coefficients of the relationship between the amount of transformer I2 load and load are typically determined first under circumstances reflecting a normal transformer state. The value of the amount T is then monitored, so that any significant deviation in the value of the amount T as measured from the amount T as obtained by using the given ratio of T and normal state load will be detected. [0056] By taking into account the magnetization current in the transformer when determining the relationship between the quantity T and the transformer load I2, the monitoring accuracy and the accuracy of determining the absolute value of the transformer property will be improved. [0057] The T (Is) ratio used in the analysis, for example, can be Petition 870190090373, of 12/09/2019, p. 24/61 17/44 based on the equivalent circuit of the first order model shown in figure 2a. In this context, a transformer property is related to the parameters of the first order transformer model, often in a way in which a transformer property of interest is represented by a transformer model parameter. As will be seen below, useful quantities T, whose load dependence can provide information about interesting transformer properties, include the terminal current I1 on the source side of the transformer (which in the convention used in this document is the primary side ), the difference between the load-side terminal voltage V1 and the load-side voltage V12 as seen from the source side, this difference referred to below as the AV voltage drop, and the loss of power lost in the transformer . [0058] In figure 2b it can be seen that the terminal voltages, Vi and V2, and the terminal currents, I1 and I2, which are all measurable quantities, show a relationship in a non-ideal transformer different from that presented for a transformer ideal in expressions (1a) and (1b). However, the non-measurable quantities V12 and I12, corresponding to the charge voltage and charge current as seen from the source side, are related to V2 and I2 in the same way that Vi and I1 are related to V2 and I2 in the expressions (1a ) and (1b): n i V 2 V 12 n 1 = -> - = - = n Π 2 V 2 Π. (3a) n i Z 12 = n 2 · 1 2 = n A2 (3b) [0059] Thus, if the relationship between turns n is known, the load voltage V12 as seen from the source side can be obtained from the terminal load voltage V2, and the voltage drop AV can thus be obtained from measurements: Petition 870190090373, of 12/09/2019, p. 25/61 18/44 AV = Vi - V12 = Vi - nV 2 (4a), [0060] where the expression (4a) is an expression based on measurement to obtain a value of Δ / (being an example of a quantity T) of signal measurements Transformer AC. As will be seen below, a value of the relationship between turns n can be obtained from an analysis of an additional quantity T, or can be assumed to adopt the nominal value. [0061] The voltage drop Δ / represents the voltage drop caused by the magnetizing current Io and the current h 2 (load current reflected on the source side) flowing through the transformer impedance (according to figure 2). Assuming the first order transformer model, Δ / alternatively can be expressed as: àv = i, - = (Λ, + ι ϋ + ((jf t + τ (fi t2 + jx t2 )) = Λ Λ + 4- Z L2 ) 'i l2 = + Z w / 12 = (4b). [0062] Thus, assuming that the magnetizing current Io is constant, the voltage drop versus load can be described by a linear expression, with the slope of the dependence corresponding to the total winding impedance Z w . At high loads, the variations in the magnetizing current Io are insignificant, and the linear relationship of the expression (4b) will describe exactly the relationship between the voltage and the transformer load. In this respect, high loads, for example, could be loads for which h is greater or approximately equal to 101o. The intersection of this linear dependence with the Δ / axis at zero load corresponds to the product of the magnetizing current Io by the first winding impedance Zi. As will be seen below, the high load magnetizing current Io can be obtained from studies of the source side current h versus load current l 2 , and thus the winding impedance of source Zi can be determined from the intersection of the expression linear (4b). The winding impedance Petition 870190090373, of 12/09/2019, p. 26/61 19/44 load Z12 can then be determined from the total winding impedance Zw determined by the gradient of the linear expression (4b). [0063] A useful relationship between the source side current I1 and the transformer load, expressed as the load side current I2, can be identified by studying figure 2: I i = - I 2 + I o ( 5 a) n [0064] Here, the quantity T is the source current, which can be obtained simply from I1 measurements: I1 = I1 (5b), [0065] where expression (5b) is a measurement-based expression to obtain a value of I1 from measurements of a transformer terminal AC signal. [0066] Thus, the source side current I1 shows a linear dependence on the load side current I2, where the slope of the dependence corresponds to the inverse of the relationship between turns of transformer n. Thus, from measurements of the source side current I1 at different loads, a value of the ratio between turns n can be obtained. [0067] Furthermore, as can be seen from the expression (5a), the intersection with the axis I1 at zero load corresponds to the magnetizing current I0. Consequently, by measuring the source side current at different loads, and extrapolating the linear dependence expressed in (5a) for zero load, a value of the magnetizing current I0 can be obtained. [0068] Thus, once an expected relationship between a quantity T (such as AV or I1) and the transformer load I2 has been determined, any deviation in a transformer property (such as Zw, I0 or n) from which the amount T depends can be detected by means of additional measurements of the AC signals of Petition 870190090373, of 12/09/2019, p. 27/61 20/44 suitable terminal. [0069] As seen in expressions (4b) and (4a), both the amounts AV and h show a linear load dependence. When the T (h) ratio is a linear expression, the coefficients of the linear expression can be determined, from the measured values obtained in step 503, by means of an appropriate linear regression method, such as, for example, a least squares fit . [0070] The loss of power Sperda inside the transformer 100, on the other hand, is a quantity T that shows a quadratic dependence on the load. The loss of power Sperda can be obtained as the difference between the apparent power input Sent and the apparent power output Ssaí of transformer 100: s loss (6a) [0071] The expression (6a) represents a measurement-based expression for the power loss. When measuring the AC signals h, h, Vi and V2 a measured value of Sperda can be determined, s m p edl d d a °. [0072] Furthermore, assuming that the first order transformer model applies, the power loss (Sioss) can be expressed in terms of the load current I2 as follows: = (^^ 2, /,) 4 + /, /, 4 + /, ^ = ^ 4-2) ^ + 4 ^ + 4 ^ + 4) ^ + 41 +2 ,, ^ = J2 / ^ 33 J n = ^ 4 + ζϊ- + d - + / π = 44 + z, + / „, = n) π η π π = <ι + ^; + ί | 4Γ [0073] where Z1 is the impedance of the source winding 105 and Z12 is the impedance of the load winding 110 reflected to the source side. [0074] From a set of measurements of the AC h, I2, V1 and V2 signals performed at different loads, the coefficients a, b and b of the expression (6b) can be determined, for example, by means of an adjustment of least squares . Using the S per da (l2) ratio Petition 870190090373, of 12/09/2019, p. 28/61 21/44 determined, the power loss can be monitored in online monitoring measurements in order to detect a deviation from the expected value obtained by expression (6b), using the derived coefficients. A deviation from the power loss measured from the expected relationship provided by expression (6b) could, for example, be used as an activation for further analysis of the measured values, for example, an analysis using expression (4b) and / or (5a). In addition, the expression coefficients (6b) could be used to obtain information about the value of the transformer properties Io, n, Zw and Zi. In combination with information obtained from studies of other T quantities such as AV or I2, or from other sources of information (for example, assuming that the nominal ratio between turns applies), a value of these transformer properties can be obtained from the coefficients determined at , be c. In addition, the term in expression (6b), referred to as a, provides an unloaded loss value at rated voltage when V1 equals the rated voltage. [0075] Assuming that the first-order transformer model applies, the loss of power Sperda can be divided into Inna cnntrihi licãn Ha marinAtiTacÃn a niitraQ παγΗα ^ AiráticaQ amagn in a contribution of magiieuzation and other erratic losses s ^. ^ A , here is a license Haq nArrlac Ha AnrnlamAntn venroiwnenfo. a contribution of winding losses, I * S - VI * _ VI * - VI * _ n V - - VI * _ VI * - ° loss y 1 1 1 y 2 1 2 y 1 1 1 ny 2 y U1 y 12 n V. I _ (V _ V) I - V (I - I) + AV. I «VI + ΛΚ. j (6c) * 1 1 1 V1) 1 12 * 1 V1 1 12) ' 1 12 1 1 0' J- 12 I TT- t *. at TZ ± 2 çrmagn. winding V j 0 + ΔΓ --- ô rda + ô rda . 1 0 n Loss erda [0076] When separating the loss of power Sperda in a contribution of magnetization S m / g d n a and a contribution of loss of winding çdei nr ^^ i <^ i m ^ i nt ) cnmn in AYhrAccãfi nndAmoQ nhtAr infnrmacãn such as in expression (6c), we can obtain additional information regarding the origin of any loss of power Petition 870190090373, of 12/09/2019, p. 29/61 Unexpected 22/44. The power loss contributions can be determined from the values of the magnetizing current Io and the ratio between turns not determined according to the above. [0077] Information relating to increases in one or both of the power loss contributions in an unexpected way can be used to identify whether a problem has occurred in core 113 and / or in windings 105/110. Furthermore, if there is an unexpected increase in power loss, without an increase in one or the other of the magnetization contribution and the winding loss contribution, we can conclude that the increase is caused by an additional power loss source. [0078] Analysis of a T quantity can give information regarding more than one transformer property, depending on which transformer properties influence the quantity as a load function. For example, analysis of linear dependence Ii (I2) can provide information regarding the relationship between turns n (inclination) and the magnetizing current Io (intercession). In addition, an analysis can be performed on more than one T quantity, obtained from the same data set, in order to obtain information about more than one transformer property. For example, measurements of I and V at different loads can be used to obtain information regarding any combination of the Sperda (l2), I1I2 and AV (b) quantities. Different amounts T could then be used to derive values for different transformer properties. Alternatively, or in addition, different amounts T can be used to derive values for the same transformer property (s) in order to check the consistency of the results. In addition, more than one T quantity can be used when an analysis of a T quantity as a load function provides a combination (product / quotient) value of more than Petition 870190090373, of 12/09/2019, p. 30/61 23/44 a transformer property - additional T quantity (s) could then be used to separate the properties that were determined as a combination. For example, if n, Zi, Io and Zw are all unknown, an analysis of AV as a function of charge (according to expression 4b) can provide information about the combinations Z1I0 and Zw / n. An analysis of Sperda as a load function can provide a value for additional combinations of transformer properties n, Z1, Io and Zw; and a separation of the combinations could be made accordingly by using combination values obtained from both AV and Sperda. [0079] As mentioned earlier, signal measurements Terminal AC can be used to monitor a transformer property over time in order to detect changes in the transformer property. Changes detected in the impedance of transformer Zw typically indicate that there is a problem of contact and / or deformation / geometric displacement of the windings. Contact problems can include, for example, broken winding elements, terminal contact problems, increased resistance at contact points, for example, on a tap-changer, etc. Geometric deformation / displacement of the windings will typically alter the winding reactance X. Deviations in the imaginary part of the impedance of transformer Zw are typically associated with issues relating to the transformer geometry, while deviations in the real part are typically associated with contact problems. [0080] Changes detected in the relationship between turns n typically indicate turns from turn to turn, such as short circuits between turns. [0081] Changes detected in the magnetizing current Io Petition 870190090373, of 12/09/2019, p. 31/61 24/44 typically indicate a deteriorated transformer core 113, such as, for example, unwanted grounding of the core 113, mechanical lamination and joint deformation forming the core 113, shorting of core laminating packages, or eddy currents significant in other parts of the transformer, for example, around the surface of the core 113, etc. [0082] Thus, when monitoring one or more transformer properties, meaningful information regarding the status of transformer 100 can be obtained. Experimental results performed on measurements collected from a transformer 100 are shown in figures 3 and 4. The AC signals shown in figures 3 and 4 are complex magnitudes and, to simplify the graphs, the absolute values of the AC signals are shown in the graphs. [0083] In figure 3, experimental results of AV are plotted as a function of I2. The transformer used for this analysis is a 160 MVA, 220/11 kV three-phase transformer and n = 8.1163'10 -2 turns ratio. The plotted values refer to one of the phases. In order to investigate the sensitivity of the determination of the transformer properties in the assumed value of the relationship between n turns, the analysis was performed for three different values of n: The results forming the average line were obtained using the nominal nnominal turns relationship, the results forming the bottom line were obtained using n = 0.99-nnominal while n = 1.01-nnominal was used to obtain the results of the top line. As can be seen in the graph in figure 3, a small error in the assumed value of n will not significantly influence the value of the total impedance deduced Z12. For example, in the experimental arrangement illustrated by the graph in figure 3, a change of 1% in n will change the total winding impedance Zw deducted from the linear fit only by about Petition 870190090373, of 12/09/2019, p. 32/61 25/44 0.05%. Thus, we can conclude that the winding impedance Zw can be determined with high precision, even when the assumed value of the relationship between turns n is slightly wrong. In addition, as discussed earlier, the n-turn relationship can be determined exactly using the expression (5a), and such a determined value can be used in a transformer AV analysis. The influence of an incorrect value of n will typically be more considerable in the unloaded voltage drop and, consequently, in order to obtain an accurate analysis result of the components of the unloaded voltage drop term, a ratio between turns determined when using the expression (5a) can be useful. [0084] In figure 4, experimental results from Ii are plotted as a function of I2 for the same transformer (and same phase) as the results shown in figure 3. A line corresponding to the linear expression (5a) is also included in the graphic. A value of the magnetizing current I0 can be obtained from the graph in figure 4, such as the intersection of the linear socket with the axis I1 at zero load. This value will correspond to the magnetization current I0 at high load (typically, the magnetization current at low load deviates slightly from this value, since the magnetization of the core 113 shows a non-linear behavior, and there is also a small increase in the supply voltage under very light load). Consequently, in order to reduce the influence of the variation of I0 with load, we could advantageously include only measurements where I1 is greater or approximately equal to 10I0 when performing an analysis of the relation Ii (I2), as well as for the AV analysis discussed in relation to expression (4b) and figure 3. [0085] Since Ii and I2 are complex numbers, a linear fit can result in a value of n having a small imaginary part. Petition 870190090373, of 12/09/2019, p. 33/61 26/44 Since the relationship between turns must be a real number, the magnitude of the imaginary part obtained by the line fitting reflects the accuracy of the fitting. A small imaginary part in general can be neglected, while a more significant imaginary part indicates that the precision of the fit is insufficient. A verification of the magnitude of the imaginary part of n could therefore serve as a consistency test for the analysis of n, as well as Io and Zw. Low load measurements, in which Io deviates significantly from the high load value, will influence the value derived from n in order to increase the imaginary part. Consequently, the linear fit could advantageously be done using the high load values. [0086] The magnetizing current Io typically varies with the source voltage Vi. Consequently, the measurements used to obtain a relationship between a quantity T and the load of transformer I2 should preferably be performed at similar source voltages Vi. In addition, if the analysis is used in an online monitoring situation, the source voltage V1 at which transformer monitoring takes place should preferably be similar to the voltage level at which the relationship was established. Measurements in which the source voltage V1 deviates significantly from the nominal voltage could consequently be advantageously excluded from the analysis. [0087] In figure 5, a flowchart is shown that schematically illustrates a modality of an inventive method in which an analysis as previously discussed is used when diagnosing the status of a transformer 100. In step 500, measurements of the load current, as well as well as at least one additional AC signal, run at different loads. In step 503, measured values of T are derived at different charges, using an expression Petition 870190090373, of 12/09/2019, p. 34/61 27/44 based on an appropriate measure (according to expressions (4a), (5b) and (6a)). In step 505, a set of at least one coefficient of a T (h) ratio is determined by fitting the measured T values into the applicable T (I2) ratio (according to expressions (4b), (5a) and (6b)) . Steps 500, 503 and 505 can be referred to as a diagnostic awareness phase. [0088] In step 510 of figure 5, the coefficients determined in step 505 are used to analyze the status of transformer 100. [0089] In figure 6a, a modality of step 510 of the method of figure 5 is shown as a step 600. In step 600, the coefficients obtained in step 505 are used to obtain the value of one or more transformer properties. In some cases, a coefficient itself represents the value of a transformer parameter, in which case step 600 is very simple. Table 1 provides an overview of examples of different amounts T that can be used to determine or monitor transformer properties using different modalities of the invention. Examples of transformer properties that can be obtained by analyzing the different T (h) relationships are also given. The AC signals that are used to obtain a T value are also shown, including the AC signal used to determine the load. The load is typically obtained from I2 measurements. Table 1. Examples of T quantities that can be used to determine or monitor transformer properties using different modalities of the invention. Quantity T T (G) ratio Transformer properties in SignalsB.C AV Z AV = I 0 + —I 2 n ZwZiIo in high load nI2Vi & V2 Petition 870190090373, of 12/09/2019, p. 35/61 28/44 Quantity T T (U) ratio Properties oftransformer SignalsB.C Ii 1 ~ ~ L + I 0 n I0 in high load n I2 & I1 Sperda * * Ç —VI * + 7 1 0 1 2, Z 1 2 1 2 Ç loss ~ V 1 1 0 + 7 1 + -2 nn ZwZ1I0 in high load n I1 & I2Vi & V2 [0090] A flowchart is shown in figure 6b that schematically illustrates an additional example of how the coefficients, determined in step 505, can be used in analyzing the status of a transformer 100. The flowchart in figure 6b illustrates an example of a process online monitoring according to the invention. In step 605, a maximum acceptable deviation DESVmáx is determined, representing the maximum acceptable deviation of a measured value of T from a value of T derived by using an expected T (I2) ratio. This is typically done by analyzing the measurement results obtained in step 500. In an implementation, DESVmax is determined as a certain number b of standard deviations σ, DESVmax = bσ. Other ways of determining the DEVmax can be considered, such as, for example, as the maximum deviation of a certified set of measurements, or as a fixed value. In an implementation where DESVmax is based on standard deviation, a specific load value of σ can be determined for each load on which measurements have been performed. Additional values of σ could then be extrapolated for loads where measurements are not available, if necessary. Alternatively, a general estimate of σ can be obtained from the distribution of T fitting - T measured T slot where measured T is a measured value of T in a particular load, while Tencaixe is the expected T value of the ratio obtained in step 505 in the load Petition 870190090373, of 12/09/2019, p. 36/61 29/44 privately. In an implementation, a combination of a general estimate of σ and specific load values of σ is used, so that the general estimate of σ is used when there is no specific value of σ load obtained from measurements on the particular load, benefiting thus of the narrower specific load distribution when measurements are available on the particular load, using a general estimate of the DEVmax in other loads. [0091] In step 610 of figure 6b, a measurement of load monitoring, as well as of the additional AC signal (s) required in order to obtain a value of T, is performed (according to Table 1). A T value, referred to as T monitoring, is then determined from the monitoring measurement. In step 615, the deviation of monitoring T from the expected value Tencaixe in the present load is determined. This deviation is t - T in an implementation defined as. In addition, T slot in step 615, it is determined whether the deviation of T monitoring from Tencaixe exceeds the maximum acceptable deviation, DEVmax [0092] If the present deviation of T monitoring from T slot is less than the DESVmax, a additional monitoring measurement is performed when reintroducing step 610. As shown in figure 6b, the reintroduction of step 610 can be preceded by a new DEVmax determination (according to path b in figure 6b), or step 610 can be entered using the previous value of the DESVmax (according to path a). If several monitoring measurements are performed at a similar load, a new definition of the maximum acceptable deviation can be obtained by including the monitoring measurement (s) obtained in step 610 in the T distribution in which the value of the STREAM is based. A new DESVmax determination, for example, could also be useful if a new load range, for which monitoring has not been performed previously, had been introduced. Petition 870190090373, of 12/09/2019, p. 37/61 30/44 [0093] If it is found in step 615 that the present deviation from T monitoring from Tencaixe exceeds the DESVmax, so step 620 is introduced. In step 620, appropriate action is taken. In an implementation, the action performed in step 620 is to determine the present value of a transformer property obtainable in quantity T (according to Table 1). An additional analysis of the status of transformer 100 can also be activated by introducing step 620, in order to determine the cause of such deviation. Such additional analysis, or diagnosis of the transformer, for example, could include checking the temperature, gas level, an analysis based on an additional T (i 2 ) quantity, etc. In an implementation, entering step 620 will activate more frequent monitoring measurements to allow careful observation of the development of the transformer's status. In one implementation, entering step 620 will trigger an alarm, the alarm indicating to an operator of transformer 100 that further investigation into the status of transformer 100 is desired. Such an alarm could, for example, be a light indication, an audible indication, the transmission of an e-mail message or an SMS to a predetermined e-mail address or cell phone number, or any suitable alarm, or a combination thereof . A possible additional action to be taken in step 620 is to perform a planned disconnection of transformer 100 in order to perform offline investigations based on a different analysis technique. [0094] The value of the DEVmax will typically depend on what actions will be performed in step 620 if a deviation from the expected value of T is detected. If the action to be performed is to plan a disconnection of transformer 100, the desired value of the STVmax will typically be greater than the value if the action in step 620 is Petition 870190090373, of 12/09/2019, p. 38/61 31/44 perform an additional analysis of the measured data, or increase the rate of monitoring measurements. Adequate values of DESVmáx, for example, could be within the range of 6σ-8σ for the activation of a planned disconnection of transformer 100; within the range of 4σ-6σ to emit an alarm; and within the 2σ-4σ range to increase the rate of monitoring measurements and perform additional analysis. A set of two or more DEVmax values can be defined for the same monitoring procedure, if desired, so that a first action is activated by deviation exceeding a first DESVmax, a second action is activated by deviation from a according to DESVmáx, etc. [0095] The method of figure 6b can include a step 600 in which a value of the transformer property is determined from the ratio T (i 2 ) provided by the coefficients determined in step 505. Consequently, the determination and monitoring flowchart shown in the figures 6a and 6b can be combined. For example, step 615 could, instead of checking the quantity T, involve a verification as to whether the value of a transformer property, derived from the quantity T, deviates from the value of the property obtained by the coefficients determined in step 505. Such determination of the present value of a transformer property would involve collecting measurements at different loads, and performing a new fitting of the measured values for the applicable T (I2) ratio. [0096] Currents and voltages Vi, V2, I1 and I2 as used above represent the fundamental frequency components at 50/60 Hz of currents and voltages, respectively. These currents and voltages are complex quantities and, for example, can be expressed as phasors. The phasor of a current / voltage, for example, can be determined by applying a Fast Fourier Transform to a continuous measurement of the voltage / current in a pair of Petition 870190090373, of 12/09/2019, p. 39/61 32/44 relevant terminals 115, 120, or when applying a Transform Fourier discrete to a set of samples of the relevant voltage / current, where the sampling rate, for example, could be 1000 Hz. In order to improve the accuracy of the phasor value, an average of several phasors could be determined, by example, as a moving average. In a monitoring situation, in general there is no pressure because of time, and ample time can be consumed in collecting the measurement results, if desired. Other ways of obtaining phasor values from measurements can be used. [0097] The fundamental frequency of a power transmission system can occasionally deviate from the nominal frequency of 50/60 Hz. For example, in Europe, a deviation of ± 0.2% is generally tolerated. Frequency variations can influence the measured phasor value, so that the accuracy of determining transformer properties is reduced if measurements are performed at different frequencies. In order to improve the accuracy of the determined transformer properties, the frequency of energy transmission can be monitored, and measurements that are performed at a particular frequency (for example, 50/60 Hz), or over a certain frequency range (for example, example, 50/60 Hz ± 0.1%), can be selected for the determination of transformer quantities. [0098] Figures 7a-7c schematically illustrate a modality of a transformer diagnostic apparatus 700. In figure 7a, the transformer diagnostic apparatus 700 is shown as comprising an input 702, an output 704, a coefficient generator 706, a transformer property value generator 708 and a status monitor 710. Input 702 is arranged to receive an I2 signal indicative of the load current, as well as by Petition 870190090373, of 12/09/2019, p. 40/61 33/44 minus an additional AC signal Ii, Vi and / or V2. Input 702 is connected to measuring equipment (not shown), such as current and voltage transformers, arranged to measure AC signals at the source and the load winding terminals 115/120 of a transformer 100. Input 702 is connected to an input of the coefficient generator 706. The coefficient generator 706 is arranged to generate, from input signals received at input 702, the coefficients C of a relation T (b) (according to expressions (4b), (5a) and (6b)). An output of the coefficient generator 706, in the mode of the diagnostic apparatus 700 shown in figure 7a, is connected to a transformer property value generator 708 as well as to a status monitor 710. The transformer property value generator 708 is configured to generate, from the coefficients C received from the coefficient generator 706, a value of at least one property of transformer P (where P, for example, can be the relationship between turns n, the short-circuit impedance Zw, the impedance source winding, the load winding impedance and / or the high load magnetizing current I0). As shown in figure 7a, the transformer property value generator 708 of figure 7a is further configured to produce a signal indicative of the P value. The transformer property value generator 708 has a memory for storing the shape of a or more T (I2) relations (according to the expressions (4b), (5a) and (6b)), from which a value of a transformer property can be determined once the coefficients are known, as previously described. [0099] The input of the status monitor 710 is additionally connected to input 702 and arranged to receive signals indicative of measured load and additional AC signal (s). In one embodiment, discussed in relation to figure 7c, the status monitor 710 is additionally arranged to receive a set {T, I2} of Petition 870190090373, of 12/09/2019, p. 41/61 34/44 T measurements with the corresponding I2 loads of the coefficient generator 706, as indicated by the dashed line. Status monitor 710 is configured to monitor the status of transformer 100, and to generate an action signal A if any significant deviation from expected behavior is detected. The outputs of the transformer property value generator 708 and the status monitor 710 are connected to output 704 of the transformer diagnostic apparatus 700. Output 704 is arranged to deliver a diagnostic result signal, of which A and P form examples. [00100] Transformer value generator 708 and status monitor 710 form two different examples of transformer diagnostic mechanisms that use a set of coefficients generated by the coefficient generator 706 when generating a diagnostic result. Other modalities of the diagnostic apparatus 700, where only one of the transformer property value generator 708 and the status monitor 710 is present, are also envisaged. [00101] In figure 7b, a modality of a coefficient generator 706 is shown in more detail. The coefficient generator 706 of figure 7b comprises an input 712, an output 714, a T generator 716 arranged to determine a measured value (T measured) of a property T; a temporary storage of T 718 and a plug-in generator of T (h) 720. The T 716 generator is arranged to receive the load signal I2 as well as a suitable selection of the additional AC signal (s) I1, Vi and / or V2, depending on what quantity T the generator of T 716 is arranged to generate. From these received signals, the T 716 generator is configured to generate a measured value of a T property, using an appropriate expression (according to the expressions (4a), (5b) and (6a)), and to produce the value together with a load value I2 in which the value of T was obtained. The output of the T 716 generator is connected to the Petition 870190090373, of 12/09/2019, p. 42/61 35/44 temporary storage of T 718, which is arranged to store a set of different T values received from the T 716 generator together with an indication of the load I2 at which the T value was obtained. The temporary storage output of T 718 is connected to the input of the generator of T (h) 720, and arranged to deliver a signal indicative of a set {T, I2} of T values, for example, upon request of the plug-in generator of T (I2), upon manual request, or when a number of T values have been received. The T (I2) generator 720 is configured to fit the received set of values {T, I2} into the appropriate T (I2) ratio (according to step 505 in figure 5), for example, by means of a least squares adjustment also known in the art. The T (b) generator 720 is additionally configured to send, to output 714, a signal C indicative of the coefficients resulting from the fitting operation performed. In a modality of the coefficient generator 706, output 714 is additionally connected to an output of the temporary storage of T 718, so that a signal of {T, 12} can be generated at output 714. [00102] In figure 7c, a modality of a status monitor 710 is shown in more detail. The status monitor 710 comprises an input 722, an output 724, a coefficient memory 725, a Tencaixe generator 726, a Monitoring 728, a DEVmax generator 730 and comparator 732. The status monitor 710 additionally comprises at least one action mechanism, of which an additional analysis activator 734, an alarm generator 736 and a planned output activator 738 are shown as examples. The input 722 of the status monitor 710 of figure 7c is arranged to receive a signal c indicative of a set of coefficients of a T (h) ratio, an I2 signal indicative of a current transformer load, at least one AC signal of Petition 870190090373, of 12/09/2019, p. 43/61 36/44 additional current Ii, Vi and / or V2, and a set of values {T, I2}, which were typically collected during a knowledge process. The coefficient memory 725 is connected to input 722 and arranged to receive a C signal, and to store the coefficients for future use. The memory of coefficients 725, in one implementation, can be arranged to store more than one set of coefficients c, representing different fits of the relation T (I2) executed in different data sets {T, I2}. An output of the coefficient memory is connected to the Tencaixe generator 726. In one implementation, the coefficient memory 725 is arranged to deliver a signal indicative of the coefficients c upon request from the Tencaixe generator. The Tencaixe generator 726 is additionally connected to input 722 and arranged to receive an I2 signal indicative of the current transformer load. The Tencaixe generator 726 is configured to derive, from a received I2 signal and an appropriate T (h) ratio, using coefficients C received from the coefficient memory 725, an embedded value of T, Tencaixe, in the present load. Examples of T (h) relationships are given in expressions (4b), (5a) and (6b). The Tencaixe generator 726 is additionally arranged to deliver a Tencaixe signal, indicative of a derived value, at an output. [00103] The T28 monitoring generator, on the other hand, is configured to derive a T value from an expression based on the corresponding appropriate measurement, examples of which are given in expressions (4a), (5b) and (6a). The monitoring generator 728 is connected to input 722 and arranged to receive an appropriate selection of AC signals I1, I2, V1 and V2, the selection depending on which quantity T is to be determined. The Tmonitoring generator 728 is additionally arranged to deliver a Tmonitoring signal, indicative of a derived value, to an output. The 728 T monitoring generator typically works on the Petition 870190090373, of 12/09/2019, p. 44/61 37/44 same way as the T 716 generator, and in fact could be implemented by the same hardware / software. [00104] Comparator 732 is connected to the outputs of the Tencaixe generator 726 and the Tmonitoramento generator 728. The comparator 732 is configured to determine if the deviation of a Tmonitoring value from the corresponding Tencaixe value exceeds a maximum acceptable deviation. 732 is arranged to deliver, upon determining that the deviation from a T monitoring value received from a corresponding Tencaixe value exceeds the DESVmax, a TR trigger signal. [00105] The DEVmax, for example, could be a fixed value, or it could, as in the modality of figure 7c, be determined from the set of data {T, I2} used when determining the coefficients c. The DESVmax generator 730 of figure 7c is arranged to receive a set of data {T, I2}, and configured to derive a value from the DESVmax of the set, for example, using a method described in relation to step 605 of figure 6b. The DESVmáx generator 730 of figure 7c includes a memory to store a value derived from DESVmáx, and is arranged to deliver a value of DESVmáx in an output connected to comparator 732. In implementations in which DESVmáx assumes a fixed value, the generator of DESVmax 730 can be reduced to a memory. [00106] A status monitor 710 additionally includes at least one action mechanism, connected to the output of comparator 732 and configured to generate an action signal Ai if a deviation has been detected by comparator 732. The status monitor 710 of figure 7c includes the following mechanisms of action: an additional analysis trigger 734, an alarm trigger 736 and a planned stop activator 738. Different mechanisms of action for a status monitor 710 can be called up in different situations; for example, the additional analysis activator 734 can be called Petition 870190090373, of 12/09/2019, p. 45/61 38/44 when a first deviation is detected, an alarm generator 736 can then be called if further analysis indicates that an operator's attention is required, a planned output activator 738 can be called if the deviation is of a certain magnitude, etc. [00107] Transformer diagnostic apparatus 700 has been described previously in terms of a single T quantity used in analyzing the status of the transformer. However, a transformer diagnostic apparatus 700 can be configured to use two or more different T amounts in the diagnosis. Two or more T quantities, for example, could be monitored in parallel, or a deviation in a first T quantity could trigger the analysis of an additional quantity, etc. [00108] The components of the transformer diagnostic apparatus 700 described in relation to figures 7a-7c can be implemented by using an appropriate combination of hardware and software. In figure 8, an alternative way of schematically illustrating a modality of a diagnostic apparatus 700 is shown. Figure 8 shows a diagnostic device 700 comprising a processor 800 connected to memory 805, as well as input 702 and output 704. Memory 805 comprises computer-readable media that stores computer program (s) 810 , which (s) when performed by the processing device 800 causes the diagnostic apparatus 700 to perform the method illustrated in figure 5 (or a modality thereof). In other words, the diagnostic apparatus 700 and its mechanisms 706, 708 and 710 in this mode are implemented with the help of corresponding program modules from the computer program 810. [00109] Processor 800, in an implementation, can be one or more physical processors. The processor can be a single Petition 870190090373, of 12/09/2019, p. 46/61 39/44 CPU (Central Processing Unit), or can comprise two or more processing units. For example, the processor may include general purpose microprocessors, instruction set processors and / or related chip sets and / or special use microprocessors such as ASICs (Application Specific Integrated Circuits). The processor may also comprise board memory for purposes of caching. Memory 805 comprises a computer-readable medium in which computer program modules, as well as pertinent data, are stored. The 805 memory can be any type of non-volatile computer-readable memory, such as a hard drive, a flash memory, a CD, a DVD, an EEPROM, etc. or a combination of different computer-readable memories. The computer program modules described above, in alternative modalities, can be distributed in different computer program products in the form of memories inside a 700 diagnostic device. [00110] Many transformer installations are equipped with a protection system arranged to measure the voltages and currents of terminals in order to allow quick disconnection of the transformer, should any problem occur that is detectable by the protection system. In general, such a protection system is arranged to react only to instantaneous values, and monitoring of currents and voltages in the transformer is not performed. Despite this, the same current and voltage measurement sensors, as used for the protection system, could, if desired, also be used for the purposes of monitoring the technology described in this document. Thus, measurements to be used in determining transformer properties and / or in monitoring transformer properties in general could be obtained without the need for Petition 870190090373, of 12/09/2019, p. 47/61 40/44 major investments in hardware. Suitable current measurement equipment, for example, could be current transformers. Suitable voltage measurement equipment, for example, could be voltage transformers. In the monitoring application, deviations in quantities can be monitored, instead of the actual values of the quantities, and consequently the accuracy requirements of the measuring equipment are less than in a monitoring method where the real value of a transformer property is required . If the same measuring equipment is used both to establish the T (h) ratio (s) and for monitoring measurements, any displacement at the equipment's output can be disregarded for monitoring purposes. [00111] In a transformer 100 having a tap-changer through which the n-turn ratio can be varied, further analysis of the measurement results in some scenarios could provide information regarding the location of a fault giving rise to a deviation from from the expected value of a transformer property. A 105/110 winding being equipped with a tap-changer 900 is shown schematically in figure 9, where tap-changer 900 is shown to have six different taps 905, each equipped with a tap selector switch 910 and by means of which six different states of tap-changer 900 can be achieved, each state providing a particular number of winding turns. A switch switch 915 is also provided, the switch switch being arranged to be in one of two different positions, where in a first position a winding terminal 115 / 120a is connected to a first set of tap selector switches 910, and in a second position the winding terminal 115 / 120a is connected to a second set of tap selector switches. When closing a Petition 870190090373, of 12/09/2019, p. 48/61 41/44 private tap selector switch 910 and ensure that the switch tap 915 is in a position in which the private tap selector switch 910 is connected to the winding terminal 115 / 120a, a particular state of tap tap changer 900 will be achieved. [00112] For a quantity T that depends on the relationship between turns n, the coefficients for the relationship between the quantity T and the load current I2 will depend on the state of the tap selector 900. Consequently, coefficients for a relationship between one or more quantities T and I2 can be determined for more than one state (and possibly for each one) of tap-changer 900, thus giving different expected values of the transformer property (s) for different states of tap-changer 900. Monitoring of (s) transformer property (s) while tap-changer 900 is in different states can thus give information about the location of a fault giving rise to deviations in a transformer property, depending on the fault location in relation to the location of the faults different leads 905. For example, if the resistance of one of the switch selector switches 910 is increased, for example, because of carbonization or other c ontaminations, the AV voltage drop value obtained from the ratio (4a) only deviates from the expected value when the tap-changer is in the corresponding position. Similarly, if a turn-to-turn failure occurred in a part of a winding 105, 110 that can be disconnected via tap switch 900, the turn ratio value obtained from the turn (5a) will only deviate from the value expected when tap-changer 900 is in a state where the part where the fault has occurred is connected between winding terminals 115 / 120a and 115 / 120b. Petition 870190090373, of 12/09/2019, p. 49/61 42/44 [00113] In the above, several modalities of the present invention were developed by using the equivalent circuit for a non-ideal transformer 100 shown in figure 2b, where the impedances, voltages and currents on the load side were reflected on the source side . The equivalent model for a non-ideal transformer 100 shown in figure 2c, in which the impedance, current and voltages from the source side are reflected to the load side, alternatively could be used in these modalities of the transformer diagnostic technique discussed above. When using the equivalent model of figure 2c, expressions (5a) and (5b), as well as expressions (6a) - (6c), will remain unchanged. However, instead of using expressions (4a) and (4b), the following expressions could be used advantageously: (W). θ ΔΓ + (4b ·). [00114] Furthermore, the previous discussion was made in terms of a transformer 100 having two windings. In some applications, a transformer 100 having three or more windings can be used. Any winding (s) present in addition to the source and load windings discussed above will be referred to below as additional winding (s). Additional winding (s) can be source winding (s) and / or load winding (s). Often, the energy in any additional winding (s) is negligible or approximately constant, and does not have to be considered for the purposes of determining / monitoring transformer properties - the error caused by such currents is typically negligible. and / or constant. However, even if the energy dissipation in one or more additional windings was significant, the inventive determination / monitoring described above could still be done. Depending on the configuration Petition 870190090373, of 12/09/2019, p. 50/61 43/44 of the additional winding (s), expressions (4a) - (6c) can be adapted in this way. As an example, for a transformer with two load windings and one source winding, the expression (5a) can be successfully adapted to: i (5a *), [00115] where index 3 denotes the additional winding. From the expression (5a *), the magnetizing current Io and the relations between n2 / ni and ns / m turns can be found with a two-dimensional fit, for example, using stochastic variations in h and I3 and at least three measurements. [00116] In the same configuration, the expression (4b) can be adapted to be separated into a relation for each load winding i, such as 4V ,, = V, V, = 2,1, + Ζ, Ι Β = Z, L, + Z, l M + (Z, + Z,) I U = Ζ, (Γ. + Ι | 3 ) + ^, Λ 2 V | = V 1 - V 5 = Z 1 + Z i 3 = 1 2 L 3 (1 + 10 ,,) + Z WL3 l, 3 Mb ·) Πτ. [00117] When the relations between turns, n, / ni, are known, this set of relations determines the winding impedances using a two-dimensional fit for the two load currents. Furthermore, in this configuration, the expression (6a) is simply the difference between energy flowing in and out of transformer 100: s pe r da = v ^ -v ^ -vpl (θθ *) [00118] A similar adaptation of the expressions (4b) - (6c) can be made for a transformer 100 of any winding configuration. In general, when the total number of transformer windings is N, the transformer properties can be obtained by using an N-1 dimensional socket of at least Petition 870190090373, of 12/09/2019, p. 51/61 44/44 N measurements. [00119] The previous description of the inventive method and apparatus for transformer diagnosis was given only in terms of a single phase. However, the method can be applied for the diagnosis of transformers of any number of phases, and in particular for three-phase transformers. The method can be applied for each of the transformer phases separately, once the individual currents through the windings and voltages have been determined. Phase configuration often implies that the terminal current / voltages do not directly give the individual currents and voltages. An Δ-Υ configuration, for example, results in a 30 degree phase shift between the source and load side terminal currents and voltages, as well as a difference in magnitude by a factor of 3 between the terminal current and the winding current on the Δ side and between terminal to terminal voltage and winding voltage on the Y side. Individual currents and voltages can typically be determined from measurements of terminal currents and voltages, as described, for example, US6507184 B1. [00120] In the description below, for ease of description, the term monitor a quantity will be used to refer to monitoring a quantity or monitoring a property derived from a quantity value. [00121] Those skilled in the art will realize that the technology presented in this document is not limited to the modalities revealed in the attached drawings and in the previous detailed description, which are presented for illustration purposes only, but which can be implemented in several different ways.
权利要求:
Claims (12) [1] 1. Transformer diagnostic method for a transformer (100) having at least one load winding (105) and a source winding (110), the method comprising collecting (500), in a transformer diagnostic apparatus comprising a processor (800), for at least two different transformer loads, measurements of a current being indicative of the transformer load, and measurements of at least one additional transformer AC signal; derive (503), in the transformer diagnostic apparatus from the collected measurements, at least two values of an amount that depends on at least one transformer property as well as the transformer load; determine (505), in the transformer diagnostic apparatus from the derived values, a set of coefficients of a relationship of how the said quantity is expected to vary with the transformer load; characterized by the fact that, said relationship is based on a transformer model in which effects of magnetization currents in the transformer core, dispersion inductances and real resistances of the primary and secondary windings are considered, and the method comprises derivating, in the apparatus transformer diagnosis using at least one of said coefficients, a value of at least one of at least one transformer property: the total winding impedance, Zw; the impedance of a source winding, Zi; the impedance of a load winding, Z2; the relationship between turns, n; and the magnetization current, I0, and the value of a transformer property is related to at least one parameter of said model of Petition 870190090373, of 12/09/2019, p. 53/61 [2] 2/5 transformer. 2. Diagnostic method according to claim 1, characterized by the fact that it additionally comprises, in the transformer diagnostic apparatus, collecting an online monitoring measurement of at least one terminal AC signal in a first monitoring load; derive, in the transformer diagnostic apparatus, a value based on a measurement of the quantity of the monitoring measurement; determine, in the transformer diagnostic apparatus, an expected value of the quantity in the first monitoring load, using said ratio and said coefficient (s); compare, in the transformer diagnostic apparatus, the value based on a measure of the quantity with the expected value in order to detect any transformer problem giving rise to a change in the quantity. [3] 3. Method according to claim 2, characterized by the fact that it additionally comprises, in the transformer diagnostic apparatus, collecting additional online monitoring measurement (s) from at least one AC terminal signal in at least one additional charge; determine, in the transformer diagnostic apparatus, from online monitoring measurements, an additional set of at least one coefficient for said relationship; derive, in the transformer diagnostic apparatus from the additional coefficient (s), an additional value of said transformer property; and comparing, in the transformer diagnostic apparatus, the first value and the additional value of the transformer property in order to detect any changes in said property. Petition 870190090373, of 12/09/2019, p. 54/61 3/5 [4] Method according to any one of claims 1 to 3, characterized by the fact that said relationship of how the quantity varies with transformer load is a linear relationship, in which the inclination and / or the intersection at zero load are indicative of a transformer property. [5] 5. Method according to claim 4, characterized by the fact that said amount is the difference (AV, AV ') between the voltage across the terminals of a first winding on a first side of the transformer and the voltage across a second winding on a second side of the transformer as reflected to the first side. [6] 6. Method according to claim 4, characterized by the fact that the quantity is the source current. [7] Method according to any one of claims 1 to 3, characterized by the fact that said amount is the loss of power within the transformer. [8] 8. Method according to any one of the preceding claims, characterized by the fact that the step of determining a set of coefficients of a relationship comprises performing a N-1 dimensional fit of at least N values derived from the quantity, where N represents the number of windings of the transformer to be diagnosed. [9] 9. Transformer diagnostic apparatus, comprising: an input configured to receive signals indicative of AC signal measurements from a transformer, including measurements indicative of the transformer load current; an output configured to deliver a transformer diagnostic result; a processor (800) connected to the input and arranged Petition 870190090373, of 12/09/2019, p. 55/61 4/5 to collect, for at least two different transformer loads, measurements of a current being indicative of the transformer load, and measurements of at least one additional transformer AC signal; derive, from the collected measurements, at least two values of an amount that depends on at least one transformer property as well as the transformer load, determine, from the derived values, a set of coefficients of a relationship of how it is expected that the said quantity varies with transformer load, characterized by the fact that said relationship is based on a transformer model, in which the effects of magnetization currents in the transformer core, dispersion inductances and actual resistances of the primary and secondary windings are considered , and the processor is further configured to determine, using at least one coefficient from the coefficient set, a value of at least one of the following transformer properties: the short-circuit impedance, Zw; the impedance of a source winding, Zi; the impedance of a load winding, Z2; the relationship between turns, n; and the magnetization current, Io, the value of the transformer property being related to at least one parameter of said transformer model. [10] 10. Diagnostic apparatus according to claim 8, characterized by the fact that the processor is additionally arranged to collect an online monitoring measurement of at least one terminal AC signal in a first monitoring load; Petition 870190090373, of 12/09/2019, p. 56/61 5/5 derive a value based on a measure of the quantity of the monitoring measurement; determine an expected value of the quantity in the first monitoring load using said ratio and a set of determined coefficients; compare a value based on a measure of the quantity with a corresponding expected value in order to detect any transformer problem giving rise to a change in the quantity. [11] 11. Transformer, characterized by the fact that it comprises a transformer diagnostic apparatus as defined in claim 9 or 10. [12] Transformer according to claim 11, characterized by the fact that it additionally comprises a bypass switch, in which the processor is arranged to generate a set of coefficients for each of the bypass switch points; and the status monitor is configured to determine, if a deviation is detected, in which tap-changer position (s) the deviation occurs.
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同族专利:
公开号 | 公开日 US9322866B2|2016-04-26| PL2466322T3|2014-04-30| CN103328990B|2017-03-22| BR112013014847A2|2016-10-18| WO2012079906A1|2012-06-21| CN103328990A|2013-09-25| ES2439279T3|2014-01-22| KR20130113504A|2013-10-15| EP2466322B1|2013-09-11| EP2466322A1|2012-06-20| US20130282312A1|2013-10-24| KR101532495B1|2015-06-29|
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法律状态:
2018-12-18| B06F| Objections, documents and/or translations needed after an examination request according art. 34 industrial property law| 2019-08-13| B06U| Preliminary requirement: requests with searches performed by other patent offices: suspension of the patent application procedure| 2020-03-17| B09A| Decision: intention to grant| 2020-05-12| B16A| Patent or certificate of addition of invention granted|Free format text: PRAZO DE VALIDADE: 20 (VINTE) ANOS CONTADOS A PARTIR DE 17/11/2011, OBSERVADAS AS CONDICOES LEGAIS. | 2020-06-09| B25A| Requested transfer of rights approved|Owner name: ABB SCHWEIZ AG (CH) | 2020-06-23| B25G| Requested change of headquarter approved|Owner name: ABB SCHWEIZ AG (CH) |
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申请号 | 申请日 | 专利标题 EP10195712.4A|EP2466322B1|2010-12-17|2010-12-17|Method and apparatus for transformer diagnosis| EP10195712.4|2010-12-17| PCT/EP2011/070356|WO2012079906A1|2010-12-17|2011-11-17|Method and apparatus for transformer diagnosis| 相关专利
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