A method for judging a core grounding state

Abstract

The present application relates to the field of power transformer manufacturing, and particularly relates to a core grounding state judgment method, which comprises the following steps: S1, obtaining the measured capacitance of each detection point between the transformer core grounding wire and the core; S2, comparing the measured capacitance with the comparative capacitance, and judging whether the grounding state of each level of lamination of the upper yoke of the core, each level of lamination of the lower yoke of the core and each level of lamination of the side column of the core is reliable. The present application can be used to judge in advance whether the grounding state of the product can meet the requirements, and the factory can take improvement treatment measures in advance in the semi-finished product stage.

Description

Technical Field

[0001] This invention relates to the field of power transformer manufacturing, specifically a method for determining the grounding status of the iron core. Background Technology

[0002] The windings and core of a transformer are the main components for transmitting and transforming electromagnetic energy. The core of a conventional power transformer is made of very thin silicon steel sheets stacked together. There is a certain surface resistance between the sheets to reduce eddy current losses. Due to the capacitance between the silicon steel sheets in the core, it can be regarded as a path with a certain capacitive reactance (the impedance of the resistance is tens of times that of the capacitive reactance, which can be ignored) in an alternating electric field. Therefore, each sheet of the core and each stage are connected into a whole through capacitive reactance. Only one point grounding is needed to clamp the potential of the entire stack of core sheets to ground potential.

[0003] During normal operation, an electric field exists between the energized windings and the oil tank, and the core and other metal components are situated within this electric field. Due to the uneven capacitance distribution and varying electric field strength among the silicon steel sheets in the core, unreliable grounding in certain areas of the core can lead to transformer dielectric losses and discharge phenomena. This can damage the solid insulation and oil insulation strength, causing the transformer to fail tests or negatively impacting its operational quality. If the problem is misdiagnosed, it will be difficult to resolve, resulting in significant direct and indirect losses.

[0004] In transformer manufacturing, it is generally required that the insulation resistance between the core grounding wire and the clamp, and between the core grounding wire and ground potential be no less than 500 megohms using a 2500-volt megohmmeter. This is used to verify that the insulation between the core and the clamp, and between the core and ground, meets the requirements. However, this measure cannot be used to determine the reliability of the grounding status between silicon steel sheets (excluding the portion where the core grounding wire is located) within the core at different stages in an alternating electric field.

[0005] In new product development, especially for low-frequency transformers and large-diameter core products where core grounding conditions can deteriorate, the ability of the internal core grounding to meet design requirements has never been a requirement in standards or by transformer manufacturers before. Even when anomalies occur during finished product testing, the direction of the problem cannot be accurately determined. If partial discharge, abnormal sounds, abnormal discharges, or chromatographic abnormalities are found during finished product testing, addressing the fault at this stage incurs significant losses in terms of manpower, resources, and reputation for the factory. Summary of the Invention

[0006] To address the issues of low efficiency and poor accuracy in detecting core grounding in existing technologies, this invention provides a method for judging the grounding status of the core. This method can determine whether the core grounding status is good at the semi-finished product stage and can be applied to various types of transformers, especially for low-frequency transformers and large-diameter core products where the core grounding status may deteriorate.

[0007] This invention is achieved through the following technical solution:

[0008] A method for determining the grounding status of an iron core includes the following steps:

[0009] S1, obtain the measured capacitance at each detection point between the transformer core grounding wire and the core;

[0010] S2. Compare the measured capacitance with the comparison capacitance to determine whether the grounding status of each stage of laminations on the upper yoke of the iron core, each stage of laminations on the lower yoke of the iron core, and each stage of laminations on the side column of the iron core is reliable.

[0011] Preferably, the capacitance between the transformer core grounding wire and the laminations of each stage of the yoke on the core is detected.

[0012] Preferably, the capacitance between the transformer core grounding wire and the laminations of each stage of the lower yoke is detected.

[0013] Preferably, the capacitance between the transformer core grounding wire and the laminations of each stage of the core is detected.

[0014] Preferably, the transformer is a transformer whose core is exposed to the air.

[0015] Preferably, the formula for calculating the comparison capacitor is: C = (0.1 × 50 / f), where C is the comparison capacitor and f is the product frequency.

[0016] Preferably, in S2, when the measured capacitance at a certain detection point is greater than the comparison capacitance, it is determined that the grounding at that detection point is good.

[0017] Preferably, for transformer products with a frequency of 50 Hz, if the measured capacitance between the core lead wire and the silicon steel sheet of the core is greater than the comparison capacitance by 0.1 microfarads during the semi-finished product stage, then the core can be considered to be well grounded.

[0018] Preferably, for transformer products with frequencies greater than or less than 50 Hz, if the capacitive reactance in air between the core lead wire and the core silicon steel sheet is not higher than 30 kΩ when measured at the semi-finished product stage, then the core is well grounded.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] This invention provides a method for determining the grounding status of a core. It can identify the grounding status of the core and determine internal problems within the core (in a normal grounding scenario with only one grounding point). This allows for early assessment of whether the product's grounding status meets requirements, enabling factories to take corrective measures at the semi-finished product stage, reducing losses from rework and improving the quality of the final product. Furthermore, it can identify and distinguish whether abnormal grounding areas are located on the upper yoke, lower yoke, or adjacent columns of the core. Attached Figure Description

[0021] Figure 1 This is a partial schematic diagram of the iron core capacitance measurement.

[0022] Figure 2 This is a partial schematic diagram of the measurement of the iron core grounding wire and the iron core yoke.

[0023] In the diagram, 1 is the grounding wire; 2 is the capacitance meter; 3 is the upper yoke of the core; 4 is the lower yoke of the core; and 5 is the side post of the core. Detailed Implementation

[0024] The present invention will be further described in detail below with reference to specific embodiments. These descriptions are for explanation purposes only and are not intended to limit the scope of the invention.

[0025] This invention discloses a method for determining the grounding status of an iron core, referring to... Figure 1 , 2 This includes the following steps:

[0026] S1, obtain the measured capacitance at each detection point between the transformer core grounding wire 1 and the core. The transformer is one whose core is exposed to air, i.e., a transformer with a completed core assembly or a core with completed lead wire manufacturing. At this time, the core includes the upper yoke 3, the lower yoke 4, the main column, the side column 5, and the grounding wire 1. The detection points include the laminations of each stage of the upper yoke 3, the laminations of each stage of the lower yoke 4, and the laminations of each stage of the side column 5. In this embodiment, a capacitance meter 2 is used to obtain the measured capacitance.

[0027] First set of capacitance data: The measurement location of the capacitance meter is as follows Figure 2 As shown, the capacitance between the transformer core grounding wire 1 and the laminations of each stage of the yoke 3 on the core;

[0028] The second set of capacitance data: capacitance between the transformer core grounding wire 1 and the lower yoke 4 of the core at each stage of laminations;

[0029] The third set of capacitance data: capacitance between the various laminations of the transformer core grounding wire 1 and the core side column 5.

[0030] S2. Compare the measured capacitance with the comparison capacitance to determine whether the grounding status of each stage of laminations of the upper yoke 3, the lower yoke 4, and the side column 5 of the core is reliable. That is, when the measured capacitance at a certain detection point is greater than the comparison capacitance, it is determined that the grounding at that detection point is good.

[0031] The formula for calculating the comparison capacitance is: C = (0.1 × 50 / f), where C is the comparison capacitance in microfarads and f is the product frequency.

[0032] The capacitance value needs to be calculated based on different operating and testing conditions. For 50 Hz frequency transformer products, if the measured capacitance between the core lead wire and the core silicon steel sheet is greater than the comparison capacitance by 0.1 microfarads (this value is obtained in combination with the product structure and process), then the core can be considered to be well grounded. At this time, the capacitive reactance converted to air (the expression for capacitive reactance is Xc=1 / (2πf C)) is not higher than 30 kΩ.

[0033] If the measured capacitance is lower than the comparison capacitance, it is necessary to make a comprehensive judgment based on the subsequent test frequency and the corresponding field strength. At this time, the factory can consider taking improvement measures in advance, such as changing the grounding method of the transformer core to increase its capacitance, checking the binding status, and adding shielding to the transformer core.

[0034] For transformer products with frequencies greater than or less than 50 Hz, if the capacitive reactance in air between the core lead wire and the silicon steel sheet of the core is not higher than 30 kΩ during the semi-finished product stage, that is, the comparison capacitance is greater than (0.1 × 50 / f) microfarads, then the core can be considered to be well grounded.

[0035] The product is designed to operate at a frequency of 50Hz. The capacitance between the core grounding wire 1 and the laminations of each stage of the core yoke 3 is measured. If the capacitance data detected in the above process is all greater than 0.1 microfarads, it can be determined that the core yoke 3 is well grounded. If some or all of the capacitance data detected in the core yoke 3 are less than 0.1 microfarads, it can be determined that there is a grounding problem in the part of the core yoke 3 with the smaller capacitance data.

[0036] This invention provides a method for determining the grounding status of a core. By measuring the capacitance between the core grounding wire and the upper yoke, lower yoke, and side post of the core, it is possible to determine whether there is a grounding problem in the core during the semi-finished product stage. If the capacitance data detected in the above process are all within a reasonable range, the core grounding can be determined to be good. If some or all of the capacitance data are abnormally low, it can be determined that there may be a grounding problem at the location where the capacitance data is abnormally low. At this time, the factory can consider taking improvement measures in advance, such as changing the product grounding method or adding shielding.

[0037] A core grounding status judgment device employs a core grounding status judgment method, comprising a data acquisition module and a data comparison module. The data acquisition module is used to acquire the measured capacitance at each detection point between the transformer core grounding wire and the core. The data comparison module is used to compare the measured capacitance with the detected capacitance to determine whether the grounding status of each stage of laminations of the upper yoke, lower yoke, and side column of the core is reliable.

[0038] A terminal device includes a memory, a processor, and a computer program stored in the memory and running on the processor. When the processor executes the computer program, it implements the steps of a method for determining the grounding status of the iron core.

[0039] A computer-readable storage medium storing a computer program, wherein when the computer program is executed by a processor, the steps of a method for determining the grounding status of an iron core are implemented.

[0040] The above description is merely a preferred embodiment of the present invention and is not intended to limit the technical solution of the present invention in any way. Those skilled in the art should understand that, without departing from the spirit and principles of the present invention, the technical solution can be modified and replaced in several simple ways, and these modifications and replacements are all within the scope of protection covered by the claims.

Claims

1. A method for determining the grounding status of an iron core, characterized in that, Includes the following steps: S1, obtain the measured capacitance at each detection point between the transformer core grounding wire and the core; The transformer in question is one in which the core is exposed to the air. Detect the capacitance between the transformer core grounding wire and the laminations of each stage of the yoke on the core; Detect the capacitance between the transformer core grounding wire and the laminations of each stage of the lower yoke; Detect the capacitance between the transformer core grounding wire and the laminations of each stage of the core; S2, compare the measured capacitance with the comparison capacitance to determine whether the grounding status of each stage of laminations on the upper yoke of the iron core, each stage of laminations on the lower yoke of the iron core, and each stage of laminations on the side column of the iron core is reliable. Among them, when the measured capacitance at a certain detection point is greater than the comparison capacitance, it is determined that the grounding at that detection point is good; For transformer products with a frequency of 50 Hz, if the measured capacitance between the core lead wire and the core silicon steel sheet is greater than the comparison capacitance by 0.1 microfarads during the semi-finished product stage, then the core can be considered to be well grounded. For transformer products with frequencies greater than or less than 50 Hz, if the capacitive reactance in air between the core lead wires and the silicon steel sheets of the core is not higher than 30 kΩ when measured at the semi-finished product stage, then the core is well grounded.

2. The method for determining the grounding status of a core according to claim 1, characterized in that, The formula for calculating the comparison capacitance is: C = (0.1 × 50 / f ),in, C For comparison capacitors, f For product frequency.

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