Method of detecting atmospheric corrosion for electrical equipment

Abstract

The invention relates to a method for detecting atmospheric corrosion to electrical equipment. It includes monitoring an electrical state of a plurality of metal structures operating as sensing elements embedded in the corrosion sensor. All of the metal structures have equal dimensions and are made of the same material having the same chemical structure, and are placed on the non-conductive substrate and in the electrical device. Each metal structure operates as a single sensing element and its electrical state is monitored. In addition, monitoring the electrical state of the metal structures includes assessing how many of the metal structures have been damaged due to corrosion. Corrosion progression is evaluated by comparing the number of damaged metal structures to a threshold.

Description

Technical Field

[0001] The present invention relates to a method for detecting atmospheric corrosion of electrical equipment. The method is used in various types of electrical equipment that are susceptible to atmospheric corrosion. In particular, the method is intended for use in electrical equipment that is used in the most aggressive corrosive atmospheres that can be found in the power distribution industry, chemical production plants, aircraft, automobile manufacturing, transportation infrastructure, offshore structures and the construction industry. Background Art

[0002] Atmospheric corrosion is the electrochemical degradation process of materials exposed to corrosive atmospheres. The sensitivity of materials to atmospheric corrosion depends on many factors, the most important of which are: the type and structure of the material, the presence of water, the composition of the atmosphere, humidity, and the ambient temperature. Particularly susceptible to atmospheric corrosion are metals and their alloys, such as copper, aluminum, iron, zinc, nickel, silver, steel, brass, and many other metals. The most aggressive corrosive atmospheres can be found in the power distribution industry, chemical production plants, aircraft, automobile manufacturing, transportation infrastructure, offshore structures, and the construction industry. These atmospheres are usually rich in many corrosive substances, such as, for example, chlorides, phosphates, nitrates, sulfates, carbonates, sulfur oxides, nitrogen oxides, carbon dioxide, hydrogen sulfide, which together with moisture and oxygen can cause severe metal corrosion.

[0003] Different electronic and electrical equipment are used in each of these environments and are particularly susceptible to damage from atmospheric corrosion because they are composed of various metals and alloys. The growing complexity and reliability requirements of electronic equipment and components have made atmospheric corrosion a significant issue.

[0004] In the prior art, corrosion sensors are known. For example, US8390306B2 discloses an atmospheric corrosion sensor. The corrosion sensor is based on a metal film resistor. The corrosion sensor includes a collection of multiple metal films with gradually increasing widths. The metal film is located on a non-conductive material. The corrosion sensor operates so that the resistance of each metal film is measured. Its resistance depends on its spatial dimension; therefore, atmospheric corrosion affects the spatial dimensions of the metal film and changes its resistance. When the width of the metal film is converted from metal to non-conductive oxide due to corrosion, the resistance changes due to the reduction of the conductive path. When the corrosive gas in the atmospheric environment in which the sensor operates erodes the metal of the metal film and transforms it into a non-conductive oxide, the width decreases, thereby increasing the resistance of the metal film. The operation of the corrosion sensor is optimized to work at a relatively low corrosion rate, and corrosion products are formed at a rate of about 30 nanometers per month or less. The corrosion sensor is designed to be used indoors. Therefore, when a certain degree of corrosion is detected via the sensor response, the internal atmosphere can be adjusted accordingly. In this solution, a reference sensor element can also be used, which is substantially not susceptible to corrosion caused by the atmosphere.

[0005] The corrosion detection device disclosed in US8723534B2 implements a similar principle. The device is based on a plurality of metal strips located on an insulating surface of a substrate. Each strip has a thickness different from another strip. Additionally, the metal strip includes an exposed strip portion that is permeable to a corrosion accelerating gas and a protected strip portion that is impermeable to the corrosion accelerating gas. The exposed strip portion and the protected strip portion are connected in series. During operation of the corrosion detection device, the exposed strip portion is corroded due to exposure to the corrosion accelerating gas from the outer surface and inward toward the substrate surface. When the thickness of the uncorroded portion decreases as the corresponding thickness of the corroded portion within each exposed strip portion increases, the resistance of the exposed strip portion changes, i.e., increases.

[0006] Moreover, JP2016138751A discloses a method for determining corrosion of electrical equipment mainly based on a resistance-type corrosion sensor. It includes the following steps:

[0007] extracting a first resistance value from the resistance-type corrosion sensor,

[0008] Extract the integration time as the operating time of the corrosion sensor,

[0009] Extract reference data for specified environmental standards,

[0010] estimating the remaining life of the electrical device based on the extracted first resistance value, the integration time and the reference data,

[0011] An estimated remaining life ratio, which is a ratio of the remaining life estimated based on the resistance value,

[0012] The calculated remaining life ratio is compared with a preset threshold value,

[0013] When the threshold is exceeded, a warning is output based on the above comparison.

[0014] The steps of the method are implemented in an arithmetic processing unit.

[0015] Obviously, in the prior art, devices and methods for detecting atmospheric corrosion based on resistance are known. They are called continuous methods. In such continuous methods, a single metal layer of a predefined thickness is usually used and its resistance is measured so that the corrosion progress can be monitored continuously and in time. Sometimes, another metal layer that is protected from corrosion is also used to compensate for temperature changes and other environmental factors that are not directly related to corrosion. The continuous method provides more information, but requires expensive analog circuits to measure very low resistance changes. Despite the use of high-precision measurement circuits, the sensitivity of this method is usually limited by the sensing structure in the form of a planar metal layer, which is not permeable to corrosive gases and only its surface is involved in the corrosion process.

[0016] On the other hand, the so-called discrete method is also known. Similar to the continuous method, it is based on a sensor comprising a plurality of metal layers that differ in spatial dimensions, for example in thickness. Its electrical continuity is checked, so that the corrosion process can only be monitored in discrete steps. The discrete method requires lower costs. However, the answer is limited to the combination of binary states of each of the sensors used.

[0017] question

[0018] Known methods and devices for sensing atmospheric corrosion are based on sensing elements with metal layers of different sizes. Ideally, the sensing element with the thinnest metal layer should be destroyed first, while the thickest should be destroyed last. Similarly, the resistance in the sensing element with the thinnest metal layer should increase fastest, while the resistance in the thickest metal layer should increase slowest.

[0019] However, the corrosion process may affect the sensing element in a random manner. Therefore, in practical applications, there is no guaranteed ideal established method for destroying the sensing element or an ideal method for increasing the resistance. Especially if the sensing elements are subject to different conditions, such as unequal humidity due to condensation of water vapor. The conditions leading to corrosion may differ significantly in different locations even if they are locations in the same electrical device, i.e., one of the sensing elements may be closer to the heat source and another farther away due to unequal temperature distribution within the device. Summary of the invention

[0020] Essence of the Invention

[0021] The present invention relates to a method for detecting atmospheric corrosion of electrical equipment, comprising monitoring the electrical state of a plurality of metal structures operating as sensing elements, the sensing elements being placed on a non-conductive substrate and being located in the electrical equipment. The essence of the invention is:

[0022] Each metal structure operates as a single sensing element and its electrical state is monitored.

[0023] Monitoring the electrical condition of metal structures involves assessing how much of the metal structure has been damaged by corrosion.

[0024] where all metal structures are of equal size and are made of the same material with the same chemical structure,

[0025] By comparing the number of damaged metal structures with a threshold value, the corrosion progress of metal parts included in the electrical equipment is evaluated.

[0026] This is good when the metal film is used as a metal structure.

[0027] It is desirable to utilize a statistical method to assess corrosion progression based on the number of damaged sensing elements compared to the total number of sensing elements located in a specific area of ​​the device.

[0028] This is advantageous if the continuity of the metal film is monitored.

[0029] This is also good when groups of sensing elements are located in different locations within a single electrical device.

[0030] It is also advantageous if the statistical distribution of damaged metal films over time is used to set the threshold value.

[0031] Advantages of the present invention

[0032] Early detection of atmospheric metal corrosion that may lead to failure of electrical equipment is a major advantage of the present invention. The present invention allows prediction of the service life of electronic and electrical equipment in a specific environment, and planning of repair and maintenance actions to prevent critical failures and equipment downtime. All predictions are based on measured atmospheric metal corrosion rates.

[0033] Despite the fact that all the metal structures acting as a single corrosion sensor are produced with the same material and dimensions, are located within the same equipment and at least work under similar conditions, each of the sensing elements will break at a different time due to the different effects of the corrosion process on them. The physical properties of the sensing elements will change in independent processes. Despite this fact, the destruction time can be predicted based on a statistical distribution model. In particular, the destruction time can be predicted based on a statistical distribution model, in particular based on a quasi-Gaussian statistical distribution model, such as a modification of the negative elements of the Gaussian distribution when they are reset to 0. Therefore, the main group of sensing elements will have similar destruction times due to corrosion, and some sensing elements will be destroyed earlier, and some later than the main group. The statistical distribution of damaged sensing elements over time allows setting a threshold level - when a warning or alarm should be issued to notify maintenance personnel that the corrosion within the protected equipment observed by the corrosion sensor based on multiple sensing elements (metal structures, in particular metal films) has reached a certain level and some action needs to be taken, and many sensing elements are damaged by corrosion.

[0034] The information about the state of each of the sensing elements or a structure comprising a plurality of sensing elements may be further used for statistical processing and based on the statistical data information about the corrosion progression within the device may be evaluated.

[0035] If the sensing elements are not of equal size and material, this observation may not be possible, as it is unclear whether the cause of the different corrosion times is due to differences in the metal structure. Therefore, sensing elements of different thicknesses are not used, thereby also reducing the manufacturing cost of the corrosion sensor.

[0036] Additionally, using multiple corrosion sensors including sensing elements of the same type located in different locations in a single electrical device can give information about the location of damaged sensing elements, which can be combined with an analysis about the entire fleet of devices. Thus, parts of the device that are more susceptible to atmospheric corrosion processes can be indicated based on statistical information. This information can be used for further fleet analysis and to improve the next revision of electrical devices containing corrosion sensors with sensing elements.

[0037] As an example, if the sensing element of a corrosion sensor placed in a given section of equipment is always the first to be damaged due to the corrosion process, this can be used to point out that this section of the equipment is not sufficiently protected compared to other parts of the equipment where other sensing elements are located. Thus, the area that is more susceptible to corrosion is detected. This is an important circumstance that can be used during the further development of the monitored equipment. As already mentioned, this observation may not be possible if the metal structures are not equal.

[0038] All calculations are based on statistical methods. Despite the fact that statistical calculations can be complex, in the case of atmospheric metal corrosion detection, very simple methods can be used. Therefore, when a method is performed, it does not require large computing power. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Embodiments of the subject matter of the invention are presented in the accompanying drawings, in which:

[0040] Figure 1 A circuit based on multiple corrosion sensors is presented, where the state of each of them is observed individually by a microcontroller;

[0041] Figure 2 A circuit based on multiple corrosion sensors connected within a single monitoring structure is presented;

[0042] Figure 3 A plot of the resistance in hours of a single corrosion sensor of the same size and material over time is presented;

[0043] Figure 4 It is the group of sensing elements placed in different areas of the protected equipment in the schematic. DETAILED DESCRIPTION

[0044] In an example, a circuit based on a corrosion sensor having a plurality of sensing elements has been used in an air insulated switchgear. The corrosion sensor can be used in various electrical devices, in particular industrial drives and drive systems.

[0045] The corrosion sensor comprises a plurality of sensing elements and monitors the electrical state of each sensing element. The corrosion sensing element is in the form of a metal film, made of a corrodible metal or metal alloy, in particular copper, aluminum, iron, zinc, nickel, silver, steel and brass. However, other structures of the corrosion sensing element are possible, such as a metal plate. The corrosion sensor may comprise a film of any kind of suitable material susceptible to atmospheric corrosion. Particularly susceptible to atmospheric corrosion are metals and their alloys, such as copper, aluminum, iron, zinc, nickel, silver, steel, brass.

[0046] In this embodiment, the sensing elements are in the form of metal films made of copper and placed on a non-conductive substrate. All metal films have equal spatial dimensions and are made of copper with the same chemical structure. The electrical state of each metal film is monitored. In a first embodiment, the sensing elements S1, S2, ... SN ( Figure 1 ) is observed. Since the resistance of the sensing elements S1, S2, ...SN can be very low, they are placed in series with resistors R1, R2, ...RN in order to limit the current through them. While the metal film is not damaged, it is connected to the power supply through the resistor, so a high state can be recognized on the microcontroller input, while after the metal film is damaged by corrosion, the internal pull-down causes the detection of a low state on the microcontroller input.

[0047] In the second embodiment, a common monitoring structure is used to monitor the sensing elements S1, S2, SN ( Figure 2 ) is observed. Although the sensing element is not damaged by corrosion, the associated resistor is used as part of the parallel connection, and after the corrosion sensor Sx is broken, the associated resistor Rx is no longer used as part of the monitoring structure, so the resistance of the parallel connection changes, and the voltage observed by the voltage divider (the upper half is the parallel connection of all connected resistors) also changes.

[0048] The above-described monitoring of the electrical state of a plurality of metal films operating as sensing elements provides information about the state of each of the metal films which is used for statistical processing. Based on the statistical data, information about the progression of corrosion within the device is evaluated.

[0049] Despite the fact that all sensing elements are produced with the same material and dimensions and operate under the same conditions, the corrosion process does not affect them in the same way within the same device. Conditions within the same device may change, for example due to differences in temperature or humidity. Sensing elements may operate at different temperatures because there may be thermal differences even on a single printed circuit board, which may be caused by different distances from the heat source. As a result, each of the metal films will break down at a different time ( Figure 3). The damage time is distributed according to a statistical distribution model, so some metal films will be destroyed earlier and some later than the main group, which has a similar damage time due to corrosion. Therefore, monitoring the electrical state of the metal film includes evaluating how much of the metal film has been damaged due to corrosion.

[0050] The statistical distribution of damaged sensing elements over time allows setting a threshold level - when a warning or alarm should be issued to notify maintenance personnel when some action needs to be taken, the circuit has observed that corrosion within the protected equipment has reached a certain level based on multiple sensing elements, and many sensing elements are damaged by corrosion.

[0051] The progression of corrosion can be assessed based on the number of sensing elements affected by the corrosion process as a percentage of the total number of sensing elements within the electrical device. Depending on the type of equipment, specific thresholds may be set for different maintenance and operational actions. In the following table, w, x, y, and z represent the percentage of damaged sensing elements, and the relationship between them is given by the inequality:

[0052] w <x<y<z

[0053]

[0054] In yet another embodiment, a corrosion sensor having multiple sensing elements has been implemented in an industrial drive system as a protected device. The sensing elements have been installed in different areas of the protected device ( Figure 4 )middle:

[0055] Area A: sensing elements S1A, S2A...SNA;

[0056] Area B: sensing elements S1B, S2B...SNB;

[0057] Region C: sensing elements S1C, S2C...SNC.

[0058] If sensing elements located in one of the regions (e.g., sensing elements S1C, S2C ... SNC located in region C) are damaged by corrosion in a much shorter time than other regions, this is an indication that the region is more susceptible to corrosion processes than other regions within the same device.

Claims

1. A method of detecting atmospheric corrosion against an electrical device, the method comprising monitoring the electrical state of a plurality of metallic structures operating as sensing elements, the metallic structures being placed on a non-conductive substrate and being located in the electrical device, Features: Each metal structure works as a single sensing element and the electrical state of each metal structure is monitored. Monitoring the electrical condition of the metal structure includes assessing how much of the metal structure has been damaged due to corrosion, where all metal structures are of equal size and are made of the same material with the same chemical structure, By comparing the number of damaged metal structures with a threshold value, corrosion progress of the metal structures included in the electrical device is evaluated.

2. The method according to claim 1, characterized in that: A metal film is used as the metal structure.

3. The method according to claim 1 or 2, characterized in that: The corrosion progression is assessed using statistical methods based on a comparison of the number of damaged sensing elements with the total number of sensing elements located in a specific area of ​​the device.

4. The method according to any one of claims 2 to 3, characterized in that The continuity of the metal film is monitored.

5. The method according to any one of claims 1 to 4, characterized in that Groups of sensing elements are located in different locations within a single electrical device.

6. The method according to any one of claims 1 to 5, characterized in that The statistical distribution of damaged metal structures over time is used to set the threshold.

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