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    • 专利摘要:
    New procedure for the estimation of the dielectric severity in the isolation of transformers, which involves a first stage to obtain the envelope of the maximum voltage drop along the windings of the transformer taking into account all the standardized dielectric tests from the simulations of the detailed model of the transformer. Followed by a second stage to evaluate the transient voltage drop along the windings when the transformer is subjected to a transient event. Finally, a third stage to obtain the level of dielectric severity to which the isolation of the transformer is subjected due to the transitory event through the calculation of the relationship between the voltage drop along the windings produced by the transient event and the The envelope of the maximum voltage drop along the windings due to the standardized dielectric tests, whose method is characterized in that it is able to detect and locate the dielectrically weak points along the windings of the transformer. (Machine-translation by Google Translate, not legally binding)
    公开号:ES2674329A1
    申请号:ES201601100
    申请日:2016-12-28
    公开日:2018-06-28
    发明作者:Xosé Manuel LOPEZ FERNANDEZ；Casimiro ALVAREZ MARIÑO
    申请人:Universidade de Vigo；
    IPC主号:
    专利说明:

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    DESCRIPTION
    PROCEDURE FOR ESTIMATING DIELECTRIC SEVERITY IN THE ISOLATION OF TRANSFORMERS
    SECTOR OF THE TECHNIQUE
    The present invention is framed in the electrical sector and more specifically in relation to the monitoring, diagnosis, maintenance and intelligent management (Smart) systems of power transformers.
    BACKGROUND OF THE INVENTION
    Power transformers play a role! vital in the reliable operation of the transmission of electrical energy and must be designed to withstand the transient voltages both during standardized dielectric tests, and the transient voltages that originate in service.
    In practice, it is found that a high number of faults in the insulating structure of the power transformer are associated with the overvoltages generated by the transient phenomena originated in the power system to which the transformer is connected, events such as type pulses lightning, switch maneuvering operations, or energization, among others.
    A failure in a power transformer can have very high economic consequences, not only because e! Transformer is one of the most expensive device in the power grid, but also because it can lead to power cuts of incalculable cost in many cases. Therefore, the proper management of the transformer, and in particular of its insulating structure, is revealed as a crucial task.
    At present, different transformer insulation protection procedures are known, such as the one set forth in document ES2543013 (T3), which shows a protection procedure of a multi-phase electrical apparatus
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    powered by an electrical network, in particular a three-phase electrical transformer, or the one set out in document ES2188371 (A1), in which an insulation fault detection system is presented between windings of three-phase electric machine windings with at least one of them connected in triangle, for motors and transformers.
    Previous works, found in articles published in different scientific journals, study the dielectric severity to which the isolation of the transformer is subjected by evaluating the overvoltages in the frequency domain, such as R. Asano, et al, “Electrical Transient Interaction between Transformers and the Power System ”In: CIGRÉ A2-D1 Colloquium, Brugge, Belgium, 2007; Angelica da Costa & Oliveira Rocha, "Electrical Transient Interaction betwen Transformers and the Power System", In: CIGRE Session 2008 Paris, France; R. Ulisses et al., "Electrical Transient Interaction between Transformers and Power System - Brazilian Experience", In: International Conference on Power Systems Transients (IPST2009), Kyoto, Japan, 2009. X.M. Lopez-Fernandez et al .. "Simulation of Very High Frequency Transients in Power Transformers", in VI Workspot-International Workshop on Power Transformers Foz do Iguagu, Brazil, 2010.
    But this approach indicates the risk of severity globally, that is, it is not capable of assessing gravity and locating dielectrically weak points along the windings of the transformer, as proposed by this invention. The only information related to the present invention is found in the publication made by the inventors C. Alvarez-Mariño & X.M. Lopez-Fernandez on "Time Domain Severity Factor (TDSF): Induced Transient Voltage between Transformer and Vacuum Circuit Breakers", presented in 2012 and published in The International Journal for Computation and Mathematics in Electrical and Electronic Engineering (COMPEL).
    Therefore, it would be desirable to overcome this limitation by obtaining the dielectric severity along the windings that can be applied to the different electrical devices, in order to detect and spatially and temporarily locate the dielectrically weak points along the windings associated with some type of transient event originated in the electrical system.
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    For this, the novelty of the present invention focuses on the process of estimating the dielectric severity in the insulation structure in power transformers expandable to other types of machines and electrical devices. The implementation of this invention would allow progress in the prevention and detection of failures in power transformers, contribute to the improvement of the reliability of the electrical system, increase the quality in the transmission and distribution of electrical energy, and manage through monitoring the life of the transformers, in line with the philosophy of intelligent management of the electricity grid of the future (Smart Grid).
    EXPLANATION OF THE INVENTION
    The invention relates to a new method for estimating the dielectric severity to which the structure of the electrical isolation of the power transformers can be subjected as a consequence of the transient eventualities injected into the terminals of the transformer from the electrical network of the electrical system to which It is connected, capable of being implemented in monitoring, diagnosis, maintenance and management schemes.
    The procedure consists in calculating the level of severity along the windings of the transformer through the relationship between the voltage drop in the windings during the transient event and the envelope of the maximum voltage drop in the windings of the tests standard dielectrics.
    The procedure is characterized by detecting and locating the dielectrically weak points along the windings of the transformer at each instant of time and comprises the following steps as shown in Figure 1:
    a) Calculation of the envelope of the temporal distribution of the maximum voltage drop along the windings of the transformer taking into account all standardized dielectric tests;
    b) Evaluation of the temporal distribution of the transient voltage drop along the windings of the transformer due to the transient event at the transformer terminals, this power system event may proceed;
    c) Obtaining the dielectric severity to which the structure is subjected
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    transformer insulation due to the transitional event of the previous stage;
    In a preferred embodiment, the calculation of the envelope of the temporal distribution of the maximum voltage drop along the windings of the transformer taking into account all standardized dielectric tests comprises:
    - Model the internal transient behavior of the transformer through a detailed model of the transformer.
    - Perform simulations of standardized dielectric tests using the transformer model of the previous point. Standardized dielectric tests consist of applying, in each of the transformer terminals, with the rest of the terminals connected to earth, the voltages normalized sequentially:
    - Calculate the temporal distribution of the internal transient voltage to ground of the transformer turns for each simulated normalized dielectric test in the previous point;
    - Calculate the voltage drop along the windings of the transformer from the temporary distribution of the internal transient voltage to ground of the turns of the transformer for each dielectric test calculated in the previous point;
    - Calculate the maximum voltage drop along the windings taking into account the voltage drop along the windings of each standardized dielectric test calculated from the previous point, thus determining the envelope of the maximum voltage drop of the dielectric tests normalized;
    In another preferred embodiment, the evaluation of the temporal distribution of the transient voltage drop along the windings of the transformer due to the transient event at the transformer terminals, this power system event being able to proceed comprises:
    - Obtain the transient earth voltages at the transformer terminals at each instant of time, recording any transient event that arrives at the transformer terminals produced in the power system to which the transformer is connected.
    - Simulate the internal transient behavior of the transformer using the detailed transformer model of the previous stage and considering the
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    Transient voltages at the transformer terminals of the previous point as the input voltages of the detailed model of! transformer.
    - Calculate the temporary temporary distribution to earth of the turns of the transformer during the transient event from the simulation of the previous point.
    - Calculate the transient voltage drop along the windings during the transient event from the calculation of the temporary temporary distribution to earth of the turns of the transformer of the previous point.
    In another preferred embodiment, obtaining the dielectric severity to which the insulating structure of the transformer is subjected due to the transient event of the previous stage comprises:
    - Calculate the value of the level of dielectric severity in the insulating structure of the transformer through the relationship between the voltage drop along the windings during the transient event of the second stage and the envelope of the maximum voltage drop at along the windings of the first stage standardized dielectric tests;
    - Check the value of the dielectric severity level in the transformer insulating structure calculated in the previous point where if the value of the severity level at each internal point of the windings is less than the unit, the transformer insulating structure is working within the safety margins, and therefore it is sized to withstand the surges caused by the transitory event. Otherwise, if the value of the severity level at an internal point of the windings is greater than the unit, the isolation of the transformer is potentially weak at that internal point and it will be exposed to failures;
    BRIEF DESCRIPTION OF THE DRAWINGS
    To complement the description that is being made and in order to help a better understanding of the characteristics of the invention, a set of drawings is attached as an integral part of said description, where illustrative and non-limiting nature has been represented. next:
    Figure 1.- Shows the flow chart of the invention.
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    Figure 2.- Shows the diagram of a phase of a transformer. LV: Low voltage coil; X0 and X1: Low voltage coil terminals; HV1: High voltage lower coil; HV2: High voltage upper coil; H0 and H1; High voltage coil terminals; V60: Node 21 corresponding to terminal H0; V70: Node 1 corresponding to terminal H1.
    Figure 3.- Shows the envelope of the maximum voltage drop along the windings of a transformer, taking into account all the standard dielectric tests of the transformer. Envelope: envelope of the maximum voltage drop in the windings of the standard dielectric tests .; SW: normalized maneuver pulse, from English “switching impulse waveform”; LW: normalized lightning impulse, from English “lightning impulse waveform”; CW6us: Wave cut, from English Chopped “waveform”, 6 microseconds; CW65us: Wave cut , of the English Chopped “waveform”, of 5 microseconds; CW4us: Wave cut, of the English Chopped “waveform”, of 4 microseconds; CW3us: Wave cut, of the Chopped English
    "Waveform", of 3 microseconds; CW2us: Chopped English Wave Cut
    "Waveform", of 2 microseconds.
    Figure 4.- Shows the temporal distribution of the transient voltage to ground that excites the transformer from a terminal due to the transient event that reaches the
    transformer and shows the transient ground voltage at the two internal points,
    indicated in Figure 2, of a transformer, as a transient response due to the transient event.
    Figure 5.- Shows the maximum voltage drop along the windings due to the transient event that reaches the transformer and the envelope of the dielectric tests.
    Figure 6 - Shows the level of severity to which the insulating structure of the transformer is subjected along the windings due to the transient event that reaches the transformer.
    PREFERRED EMBODIMENT OF THE INVENTION
    The flow chart of the procedure to which the invention relates is shown in Figure 1. From the transformer geometry, as is the case in Figure 2, the detailed model of the transformer is constructed to model the internal transient behavior of the windings of the transformer when simulating the standard dielectric tests and the transient event in terminals of the
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    transformer. On the one hand, the temporary distribution of the internal transient voltage to ground along the windings of the transformer is obtained for each standardized dielectric test through simulations with the detailed model of the transformer. Once the voltage distribution is available, the distribution of the voltage drop along the windings for each dielectric test is calculated and then the envelope of the maximum voltage drop along the windings is determined taking into account count all simulated standard dielectric tests as the example shown in Figure 3.
    On the other hand, the values of the transient earth voltages at the transformer terminals are obtained due to any transient event that excites the transformer, which can come from the network of the power system to which it is connected. Considering these transient voltages at the transformer terminals, the transient event is simulated and the internal transient voltages to earth along the windings during the transient event are calculated. For example, the temporal distribution of the transient earth voltage that is measured at terminal H1 (point V70 in Figure 2) of the transformer and the temporal response at an internal point of a winding (point V60 in Figure 2) thereof , as shown in Figure 4. Next, the distribution of the voltage drop along the windings during the transient event is evaluated as shown in Figure 5.
    Finally, the voltage drop along the windings during the transient event is compared with the envelope of the maximum voltage drop of the standard dielectric tests as shown in Figure 5, calculating the level of dielectric severity at which it is The insulating structure of the transformer is subjected as shown in Figure 6. The level of dielectric severity is calculated as the ratio between the voltage drop along the windings during the transient event and the envelope of the maximum voltage drop of the standard dielectric tests. If the value of the dielectric severity level at an internal point of the transformer is less than the unit, the insulation structure at that internal point withstands surges due to the transient event with safety margin. Otherwise, the isolation of the transformer may be at potential risk of failure. For example, the internal points between points 7 and 12 of Figure 6 have a lower level of dielectric severity than the unit so the structure
    Insulator in this area supports surges due to the transient event. However, the internal points between points 2 and 6 and between points 13 and 21 of Figure 6 have a higher level of dielectric severity than the unit, so that the insulation in these areas is at potential risk of failure.
    权利要求:
    Claims (9)
    [1]
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    1. Procedure for estimating dielectric severity in transformer isolation characterized by detecting and locating dielectrically weak points along the windings of the transformer comprising the following stages:
    a) Calculate the envelope of the temporal distribution of the maximum voltage drop along the windings of! transformer taking into account standardized dielectric tests;
    b) Evaluate the temporal distribution of the transient voltage drop along the windings of the transformer due to the transient event injected into the transformer terminals;
    c) Obtain the dielectric severity to which the insulating structure of the transformer is subjected due to the transient event of the previous stage.
    [2]
    2. Method according to claim 1, characterized in that step a) the calculation of the envelope is characterized by comprising the following calculations:
    - Calculation of the temporal distribution of the internal transient voltage to ground of the transformer turns for each standardized dielectric test;
    - Calculation of the temporal distribution of the voltage drop along the windings of the transformer for each dielectric test;
    - Calculation of the maximum voltage drop along the windings taking into account all standardized dielectric tests.
    [3]
    3. Method according to claim 2, characterized in that the calculation of the temporal distribution of the internal transient voltage to ground of the turns of the transformer for each dielectric test is obtained from the transient simulation of each dielectric test using a model of the internal transient behavior of the transformer
    [4]
    4. Method according to claims 2 and 3, characterized in that the calculation of the temporal distribution of the voltage drop along the windings of the transformer for each dielectric test of the transformer is obtained from the temporal distribution of the internal transient voltage a land of the turns of the transformer.
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    [5]
    5. Method according to claim 2, characterized in that the calculation of the maximum voltage drop along the windings of the transformer for the dielectric tests is obtained by selecting the maximum value of the voltage drop calculated at each internal point of the windings of all the standardized dielectric tests that were simulated.
    [6]
    Method according to claim 1, characterized in that step b) the evaluation of the temporal distribution of the transient voltage drop along the windings of the transformer due to the transient event, consisting of:
    - Measure the transient earth voltages at the transformer terminals at each instant of time when the transformer is reached by the transient event;
    - Simulate the internal transient behavior of the transformer using the detailed transformer model and considering the transient voltages at the transformer terminals due to the transient event as the input voltages of the detailed transformer model.
    - Calculate the temporary temporal distribution to earth of the turns of the transformer during the transient event from the transient simulation.
    - Calculate the transient voltage drop along the windings during the transient event from the calculation of the temporary temporary distribution to earth of the turns of the transformer.
    [7]
    Method according to claim 1, characterized in that step c) obtaining the dielectric severity to which the transformer insulating structure is subjected due to the transient event comprises:
    - Calculate the value of the level of dielectric severity of the internal insulation of the transformer according to the relationship between the voltage drop along the windings during the transient event of the second stage and the envelope of the maximum voltage drop along the windings of the first stage standardized dielectric tests;
    - Check the value of the severity level in the transformer insulation structure at each internal point of the windings.
    [8]
    8. Method according to claim 7, characterized in that when the value of the
    severity level at each internal point of the windings is lower than the unit indicates that the transformer insulating structure is working within the safety margins and allows to withstand the surges caused by the transient event, otherwise, if the value is higher to the unit, the 5 isolation of the transformer will be exposed to risk of failure, situation
    in which dielectrically weak points have been detected and located in the windings of the transformer.
    [9]
    9. Use of the method according to claims 1 to 8, in monitoring systems, diagnosis, maintenance and intelligent management (Smart) of transformers of
    power as well as other machines and electrical devices of the electrical system.
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