CN118010127B - Live-line testing method for actual oil level of transformer oil storage cabinet - Google Patents

Abstract

The present invention relates to the technical field of oil level measurement, and specifically to a live testing method for the actual oil level of a transformer oil storage tank, wherein a liquid pressure sensor is installed at the oil inlet of the transformer oil tank to obtain the transformer oil pressure at the oil inlet of the transformer oil tank; the vertical height of the actual oil level in the transformer oil storage tank from the oil inlet of the transformer oil tank is calculated; a test point is selected and a main unit of the test device is installed; the vertical height between the test point and the oil level at the oil inlet is calculated; the distance and angle between the test point and a certain point on the surface of the oil storage tank are measured; the vertical height between the test point and the laser irradiation point on the surface of the oil storage tank is calculated; and the oil level is indicated on the outer surface of the oil storage tank. The present invention is easy to operate, reduces the number and duration of power outages of the equipment, shortens the test time, reduces the test workload, and significantly improves the safety of the test process.

Description

A method for testing the actual oil level of a transformer oil storage cabinet under voltage

Technical Field

The invention relates to the technical field of oil level measurement, and in particular to a live testing method for the actual oil level of a transformer oil storage cabinet.

Background Art

Transformer oil level generally refers to the oil level of the transformer oil conservator, which is an important non-electrical parameter for the operation of oil-immersed transformers. The transformer oil conservator is a container connected to the oil tank to adapt to the change in oil volume in the transformer oil tank. The oil level of the transformer oil conservator should not be lower than the minimum oil level to ensure that the internal components of the transformer are adequately cooled and insulated; the oil level of the oil conservator should not be higher than the maximum oil level to avoid transformer oil overflow when the transformer is running at high temperature or full load. The oil conservator indicates the oil level through the oil level gauge.

Transformer oil conservators are divided into open and sealed types. Large oil-immersed transformers all use sealed oil conservators. The oil level gauges of sealed oil conservators mostly use mechanical pull-rod structures or float structures. Due to damage and jamming of transmission components, damage and loosening of floats, oil level gauge damage accidents often occur. Some transformers are equipped with oil level online monitoring systems based on principles such as pressure sensors, which can achieve quantitative, real-time and remote measurement of the oil level in the transformer oil conservator. However, they have the disadvantages of complex structure, high cost, transformer power outage installation, inconvenient calibration, etc., and long-term operation stability and reliability need to be tested, and false alarms and data interruptions may occur. Therefore, it is necessary to verify the oil level of the oil conservator regularly. Common methods include checking the oil temperature-oil level curve, measuring the oil level by the communicating vessel method, and measuring the oil level by the infrared temperature measurement method.

Among the above methods, checking the oil temperature-oil level curve is the most convenient. However, if the transformer is not filled with the specified amount of oil during installation, or if the transformer is replenished or drained during operation, there will be a deviation between the actual oil temperature-oil level curve and the standard oil temperature-oil level curve, which will affect the verification result. The communicating vessel method can intuitively indicate the corresponding position of the oil level of the oil pillow, but it is necessary to prepare long connecting pipes, insulating rods and other tools for on-site testing, and at least two people are required to cooperate. For large transformers, since the oil pillow is high from the ground, it is also necessary to climb up, which poses certain safety risks. In addition, the oil storage cabinet of some transformers is located directly above the oil tank, and the distance between the oil storage cabinet and the live bushing and lead wire is close, resulting in insufficient safety distance for live oil level measurement, so the transformer needs to be shut down for testing. It can be seen that the communicating vessel method is time-consuming and labor-intensive to measure the oil level, with low efficiency, and may require the transformer to be shut down for testing. The principle of infrared imaging to detect transformer oil level is to use the temperature difference between the contact oil and the contact capsule on the surface of the oil conservator to measure the surface temperature of the oil conservator using the temperature sensing effect of infrared rays. The image taken by the infrared imager is analyzed by color to determine the actual oil level of the transformer. Since the transformer oil in the oil pillow basically does not participate in the heat exchange inside the transformer oil tank, the temperature difference between its oil temperature and the ambient temperature is small. Especially when the transformer load is low, the oil level line position of the oil conservator taken by the infrared imager is blurred and difficult to identify.

In summary, there is an urgent need for a fast and accurate on-site testing method for the oil level of a transformer oil conservator.

Summary of the invention

Based on the above purpose, the present invention provides a method for testing the actual oil level of a transformer oil conservator under power.

A live testing method for the actual oil level of a transformer oil storage cabinet comprises the following steps:

S1: Install a liquid pressure sensor at the oil inlet of the transformer tank to obtain the transformer oil pressure p at the oil inlet of the transformer tank;

S2: Using the measured transformer oil pressure p at the transformer oil tank oil inlet, transformer oil density and temperature, calculate the vertical height h of the actual oil level in the transformer oil storage cabinet from the transformer oil tank oil inlet according to the liquid pressure formula;

S3: Select a test point and install the test device host, measure the distance and angle between the test point and the oil extraction port, emit a first laser from the test device host to the oil extraction port, obtain the distance d ₁ between the test point and the transformer tank oil extraction port based on the phase distance measurement principle, and use the attitude measurement sensor to measure the pitch angle θ ₁ between the line between the two points and the horizontal plane;

S4: Calculate the vertical height of the oil level between the test point and the oil intake port: Calculate the vertical height h ₁ of the oil level between the test point and the oil intake port according to d ₁ and θ ₁ ;

S5: Measure the distance and angle between the test point and a point on the surface of the oil conservator: Shoot a second laser from the test point to any point on the surface of the oil conservator, obtain the distance d ₂ between the test point and the point irradiated by the laser on the surface of the oil conservator based on the phase distance measurement principle, and use the attitude measurement sensor to measure the pitch angle θ ₂ between the line between the two points and the horizontal plane;

S6: Calculate the vertical height between the test point and the laser irradiation point on the surface of the oil conservator: Calculate the vertical height h ₂ between the test point and the laser irradiation point on the surface of the oil conservator according to d ₂ and θ ₂ ;

S7: Indicating the oil level on the outer surface of the oil conservator: adjusting the angle _θ2 so that _h2 = _hh1 , then the position of the point irradiated by the laser on the surface of the oil conservator is the actual oil level in the oil conservator.

Furthermore, h ₁ in S4 is calculated as: h ₁ =d ₁ ×sinθ ₁ .

Furthermore, h ₂ in S6 is calculated as: h ₂ =d ₂ ×sinθ ₂ .

Further, h in S2 is calculated as: Where p is the transformer oil pressure, ρ is the density of the transformer oil, and g is the acceleration due to gravity.

Furthermore, the phase-based ranging principle for calculating _d1 includes:

emitting a first laser from a test point to a surface of the oil conservator, and receiving the first laser reflected from the surface of the oil conservator;

The phase difference between the emitted first laser and the received first laser is measured. The phase difference is caused by the propagation distance of the laser wave. The distance is the round-trip distance, that is, twice the distance from the test point to the oil extraction port.

The actual length of the round-trip path of the laser is calculated by using the phase difference and the wavelength of the laser. The formula is: Where, _d1 is the one-way distance from the test point to the oil extraction port. is the phase difference, and λ is the wavelength of the laser.

Furthermore, the phase-based ranging principle for calculating _d2 includes:

emitting a second laser from the test point to the oil extraction port, and receiving the second laser reflected from the oil extraction port;

The phase difference between the emitted second laser and the received second laser is measured. The phase difference is caused by the propagation distance of the laser wave, which is the round-trip distance, that is, twice the distance from the test point to the oil extraction port.

The actual length of the round-trip path of the laser is calculated by using the phase difference and the wavelength of the laser. The formula is: Where, _d2 is the one-way distance between the test point and the laser irradiation point on the surface of the oil storage tank, is the phase difference, and λ is the wavelength of the laser.

Furthermore, the test point is selected at a location where there are no obstructions between the test point and the transformer oil inlet and the transformer oil storage cabinet.

Furthermore, the test device host includes a laser ranging module and a posture measurement sensor, the laser ranging module is used to emit a first laser and a second laser, and the posture measurement sensor is used to measure the angle between a line between two points and a horizontal plane.

Beneficial effects of the present invention:

The present invention provides an energized testing method for the actual oil level of a transformer oil storage cabinet, which can quickly and accurately obtain the transformer oil pillow without shutting down the transformer, is easy to operate, reduces the number and duration of equipment power outages, shortens the testing time, reduces the testing workload, and significantly improves the safety of the testing process.

The present invention, by combining a liquid pressure sensor, a laser ranging technology and a posture measurement sensor, can not only quickly and accurately measure the actual oil level in the transformer oil storage cabinet when the transformer is in operation, that is, when energized, but also avoids transformer service interruption caused by power outages, thereby greatly improving the efficiency and safety of maintenance work.

The present invention reduces the error and safety risk caused by traditional methods through precise calculation and measurement, and improves the reliability and accuracy of the test. The application of this test method is of great significance for ensuring the normal operation of oil-immersed transformers and extending their service life, and also provides a more efficient and safe technical means for transformer maintenance.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to more clearly illustrate the technical solutions in the present invention or the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings in the following description are only for the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

FIG1 is a schematic diagram of the measurement principle of an embodiment of the present invention;

FIG. 2 is a schematic flow chart of a measurement method according to an embodiment of the present invention.

DETAILED DESCRIPTION

In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with specific embodiments.

It should be noted that, unless otherwise defined, the technical terms or scientific terms used in the present invention should be understood by people with ordinary skills in the field to which the present invention belongs. The words "first", "second" and similar words used in the present invention do not indicate any order, quantity or importance, but are only used to distinguish different components. "Include" or "comprise" and similar words mean that the elements or objects appearing before the word include the elements or objects listed after the word and their equivalents, without excluding other elements or objects. "Connect" or "connected" and similar words are not limited to physical or mechanical connections, but may include electrical connections, whether direct or indirect. "Up", "down", "left", "right" and the like are only used to indicate relative positional relationships. When the absolute position of the described object changes, the relative positional relationship may also change accordingly.

As shown in Figure 1-2, a live testing method for the actual oil level of a transformer oil conservator is shown.

(1) Measuring the oil pressure at the oil inlet of the transformer: Install a liquid pressure sensor 1 at the oil inlet of the transformer tank to obtain the transformer oil pressure p at the oil inlet. The pressure sensor 1 and the oil inlet can be connected by threads or other means. When testing, open the oil drain valve at the oil inlet so that the pressure sensor 1 can contact the transformer oil to test the pressure. The requirements of the pressure sensor 1 in the present invention are that it can withstand the pressure of the transformer oil at the oil inlet and the accuracy meets the measurement requirements. Other aspects, such as the principle of the pressure sensor, are not specified. For the convenience of subsequent calculations, the pressure sensor 1 should have the function of displaying the pressure value on the spot, or transmitting the measured pressure value by wire or wireless means.

(2) Calculation of the oil level in the oil conservator: Since the liquid pressure depends only on the density of the liquid and the height of the liquid surface, and has nothing to do with the shape of the container, and since the transformer oil conservator and the transformer oil tank are connected via a gas relay and associated pipelines, that is, the transformer oil in the transformer oil conservator and the transformer oil tank are connected, the vertical distance between the oil surface in the oil conservator and the oil tapping port can be calculated based on the oil pressure at the oil tapping port, as shown in h in Figure 1. Since the density of the liquid is related to the temperature, when calculating the pressure p, the transformer oil density is converted according to the oil temperature indicated by the transformer oil temperature gauge. Since the oil temperature in the transformer oil tank is inconsistent with the oil temperature in the oil storage cabinet, and the temperature at each point in the transformer is also inconsistent, the transformer oil density is not a constant. However, considering that the sum of the total amount of oil in the oil storage cabinet and its connecting pipeline with the transformer oil tank accounts for a small proportion of the oil volume in the transformer oil tank (generally, the capacity of the transformer oil storage cabinet is configured as 10% of the transformer oil tank capacity), and the transformer oil temperature difference at each point in the transformer oil tank is small, the transformer oil density corresponding to the temperature indicated by the transformer oil temperature gauge is used. The error between the oil level height of the oil storage cabinet calculated by combining the measured liquid pressure at the oil inlet and the actual oil level height is within an acceptable range, and h is calculated as: Here, p is the measured oil pressure at the oil tapping port, ρ is the density of the transformer oil, and g is the acceleration of gravity. Through this formula, the vertical height h of the actual oil level in the oil conservator relative to the oil tapping port can be calculated.

(3) Measure the distance and angle between the test point and the oil extraction port: select a location with no obstructions between the transformer oil extraction port and the transformer oil storage cabinet as the test point, and measure the distance and angle between the test point and the oil extraction port. In one embodiment, the specific steps are to fix the test device host 2 at the test point. The test device host 2 mainly includes a laser ranging module and a posture measurement sensor. The laser ranging module is used to shoot a laser beam from the test point to the oil extraction port, and based on the phase test principle, obtain the distance between the test point and the oil extraction port, as shown in _d1 in Figure 1. _d1 is calculated as:

The phase difference between the emitted first laser and the received first laser is measured. The phase difference is caused by the propagation distance of the laser wave. The distance is the round-trip distance, that is, twice the distance from the test point to the oil extraction port.

The actual length of the round-trip path of the laser is calculated by using the phase difference and the wavelength of the laser. The formula is: Where, _d1 is the one-way distance from the test point to the oil extraction port, is the phase difference, λ is the wavelength of the laser, and the calculation of _d2 is the same as _d1 .

The attitude measurement sensor is used to measure the laser emitted by the laser ranging module 3, that is, the pitch angle between the line between the test point and the oil extraction port and the horizontal plane, as shown by _θ1 in Figure 1. In order to ensure that the angle _θ1 measured by the attitude measurement sensor is the pitch angle between the laser beam pointing from the test point to the oil extraction port and the horizontal plane, the attitude measurement sensor should be fixed together with the laser ranging module, and the angle should be calibrated before testing.

(4) Calculate the vertical height between the test point and the oil level at the oil intake port: The vertical height between the test point and the oil level in the oil storage tank can be calculated based on d ₁ and θ ₁ , as shown by h ₁ in FIG1 . As can be seen from FIG1 , h ₁ = d ₁ × sinθ ₁ .

(5) Measuring the distance and angle between the test point and a point on the surface of the oil conservator: In one embodiment, the specific steps are to use the laser ranging module in the test device host 2 to shoot a laser beam from the test point to the surface of the oil conservator, and based on phase ranging or other test principles, obtain the distance between the test point and the point on the surface of the oil conservator illuminated by the laser, as shown by _d2 in Figure 1, and use the attitude measurement sensor to measure the pitch angle of the line between the two points and the horizontal plane, as shown by _θ2 in Figure 1.

(6) Calculate the vertical height between the test point and the oil level in the oil conservator: The vertical height between the test point and the oil level in the oil conservator can be calculated based on d ₂ and θ ₂ , as shown by h ₂ in FIG. 1 . As can be seen from FIG. 1 , h ₂ = d ₂ × sinθ ₂ .

(7) Indicating the oil level on the outer surface of the oil conservator: Adjust _θ2 so that _h2 = _hh1 = _h2 ', then the position of the point on the surface of the oil conservator where the laser is irradiated is the actual oil level in the oil conservator. In this step, adjusting _θ2 is achieved by changing the position of the point on the surface of the oil conservator where the laser beam emitted by the laser ranging module in the main unit 2 of the test device is irradiated. In one embodiment, the adjustment of _θ2 is performed manually by the tester, and the main unit 2 of the test device has the function of continuously measuring and displaying _h2 , so the tester can compare the value of _h2 with the value of _h2 ' until the tester believes that the two are substantially equal.

In another embodiment, the adjustment of θ ₂ is automatically performed by the test device host 2, which is fixed on a fixed bracket and has a calculation control module and a drive device capable of adjusting the host angle θ _2. The calculation control module of the test device host 2 compares the value of h ₂ with the value of h ₂ ' after completing the first h ₂ calculation. If it is found that h ₂ >h ₂ ', θ ₂ is reduced stepwise by the drive device, and then the control module calculates the value of h ₂ again and compares it with the value of h ₂ ', and continuously adjusts until the measurement error h ₂ -h ₂ ' is less than the program setting value. On the contrary, the calculation control module compares the value of h ₂ with the value of h ₂ ' after completing the first h ₂ calculation. If it is found that h ₂ <h ₂ ', θ ₂ is increased stepwise by the drive device, and then the control module calculates the value of h ₂ again and compares it with the value of h ₂ ', and continuously adjusts until the measurement error h ₂ '-h ₂ is less than the program setting value.

Those skilled in the art should understand that the discussion of any of the above embodiments is merely illustrative and is not intended to imply that the scope of the present invention is limited to these examples. Under the concept of the present invention, the technical features in the above embodiments or different embodiments may be combined, the steps may be implemented in any order, and there are many other variations of the different aspects of the present invention as described above, which are not provided in detail for the sake of simplicity.

The present invention is intended to cover all such substitutions, modifications and variations that fall within the broad scope of the claims. Therefore, any omissions, modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims (6)

1. A method for testing the actual oil level of a transformer oil storage cabinet under power, characterized in that it comprises the following steps: S1: Install a liquid pressure sensor at the oil inlet of the transformer tank to obtain the transformer oil pressure p at the oil inlet of the transformer tank; S2: Using the measured transformer oil pressure p at the transformer oil tank oil inlet, transformer oil density and temperature, calculate the vertical height h of the actual oil level in the transformer oil storage cabinet from the transformer oil tank oil inlet according to the liquid pressure formula; S3: Select a test point and install the test device host, measure the distance and angle between the test point and the oil extraction port, emit a first laser from the test device host to the oil extraction port, obtain the distance d ₁ between the test point and the transformer tank oil extraction port based on the phase distance measurement principle, and use the attitude measurement sensor to measure the pitch angle θ ₁ between the line between the two points and the horizontal plane; S4: Calculate the vertical height of the oil level between the test point and the oil intake port: Calculate the vertical height h ₁ of the oil level between the test point and the oil intake port according to d ₁ and θ ₁ ; S5: Measure the distance and angle between the test point and a point on the surface of the oil conservator: Shoot a second laser from the test point to any point on the surface of the oil conservator, obtain the distance d ₂ between the test point and the point irradiated by the laser on the surface of the oil conservator based on the phase distance measurement principle, and use the attitude measurement sensor to measure the pitch angle θ ₂ between the line between the two points and the horizontal plane; The phase-based ranging principle for calculating _d1 includes: emitting a first laser from a test point to a surface of the oil conservator, and receiving the first laser reflected from the surface of the oil conservator; The phase difference between the emitted first laser and the received first laser is measured. The phase difference is caused by the propagation distance of the laser wave. The distance is the round-trip distance, that is, twice the distance from the test point to the oil extraction port. The actual length of the round-trip path of the laser is calculated by using the phase difference and the wavelength of the laser. The formula is: Where, _d1 is the one-way distance from the test point to the oil extraction port. is the phase difference, λ is the wavelength of the laser; The phase-based ranging principle for calculating _d2 includes: emitting a second laser from the test point to the oil extraction port, and receiving the second laser reflected from the oil extraction port; The phase difference between the emitted second laser and the received second laser is measured. The phase difference is caused by the propagation distance of the laser wave, which is the round-trip distance, that is, twice the distance from the test point to the oil extraction port. The actual length of the round-trip path of the laser is calculated by using the phase difference and the wavelength of the laser. The formula is: Where, _d2 is the one-way distance between the test point and the laser irradiation point on the surface of the oil storage tank, is the phase difference, λ is the wavelength of the laser; S6: Calculate the vertical height between the test point and the laser irradiation point on the surface of the oil conservator: Calculate the vertical height h ₂ between the test point and the laser irradiation point on the surface of the oil conservator according to d ₂ and θ ₂ ; S7: Indicating the oil level on the outer surface of the oil conservator: adjusting the angle _θ2 so that _h2 = _hh1 , then the position of the point irradiated by the laser on the surface of the oil conservator is the actual oil level in the oil conservator. 2 . The method for testing the actual oil level of a transformer oil conservator under power on condition that claim 1 , wherein h ₁ in S4 is calculated as: h ₁ =d ₁ ×sin θ ₁ . 3 . 3 . The method for testing the actual oil level of a transformer oil conservator under power on condition that claim 1 , wherein h ₂ in S6 is calculated as: h ₂ =d ₂ ×sinθ ₂ . 4. A live testing method for the actual oil level of a transformer oil conservator according to claim 1, characterized in that h in S2 is calculated as: Where p is the transformer oil pressure, ρ is the density of the transformer oil, and g is the acceleration due to gravity. 5. A live testing method for the actual oil level of a transformer oil conservator according to claim 1, characterized in that the test point is selected as a location where there is no obstruction between the test point and the transformer oil inlet and the transformer oil conservator. 6. The method for testing the actual oil level of a transformer oil storage cabinet under power on according to claim 1 is characterized in that the main unit of the testing device comprises a laser ranging module and a posture measurement sensor, the laser ranging module is used to emit a first laser and a second laser, and the posture measurement sensor is used to measure the angle between a line between two points and a horizontal plane.