CN113673083A - Transformer direct-current magnetic biasing risk assessment method - Google Patents
Transformer direct-current magnetic biasing risk assessment method Download PDFInfo
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Abstract
The invention discloses a transformer direct-current magnetic bias risk assessment method, which comprises the following steps: detecting noise, vibration, temperature and neutral point direct current of the transformer; when the direct current of the neutral point of the transformer does not exceed a set threshold value, recording noise, vibration, temperature and dissolved gas in oil of the transformer as reference data; when the direct current of the neutral point of the transformer exceeds a set threshold value, recording noise, vibration, temperature and dissolved gas in oil of the transformer as evaluation data, and starting a risk evaluation program; the risk assessment program: judging whether the transformer has direct sunlight or not, if not, calculating risk evaluation factors by combining the evaluation data and the reference data with the correlation coefficient; if so, calculating risk assessment factors by combining the assessment data except the temperature and the reference data with the correlation coefficient; and performing risk evaluation on the direct current magnetic biasing of the transformer according to the calculated risk evaluation factor.
Description
Technical Field
The invention relates to the field of power safety monitoring, in particular to a transformer direct-current magnetic biasing risk assessment method.
Background
The main causes of the dc magnetic bias of the power system are the unipolar operation of the dc transmission line and the solar magnetic storm. With the development of the direct current transmission technology, tens of ultra-high voltage direct currents are built in China, a large-scale energy pattern of 'east transmission of western electricity' and 'south transmission of north electricity' is formed, and the development of national economy is favorably supported. However, with the increase of direct current engineering, the negative influence of direct current magnetic biasing of a power system is increasingly prominent, and according to literature reports, serious direct current magnetic biasing problems occur to direct currents and stream-Zhe direct currents in +/-800 kV days, so that the insulation abnormality and the emergency stop and pull events of the transformer are caused.
For the problem of the dc bias tolerance of the transformer, it is usually determined according to the rules of DL/T437-: the allowed direct current of each phase winding of the transformer is as follows: the rated current of the single-phase transformer is 0.3 percent, the rated current of the three-phase five-column transformer is 0.5 percent, and the rated current of the three-phase three-column transformer is 0.7 percent. However, since the standards have earlier written texts and do not have the capability of monitoring other states of the transformer, the dc upper limit value is simply specified according to different transformer types and capacities. Detailed evaluation and emergency strategy for transformers subjected to dc bias is not involved, but is precisely what is needed for on-site operation management.
At present, the main source of the direct current magnetic biasing of the power system is direct current engineering single-pole operation, and the single-pole operation is mostly emergency measures taken after a line or equipment fault and has unpredictability. When the single pole operates, the transformer affected by the direct current magnetic biasing in the area needs to be closely concerned, and risk assessment and emergency treatment of the direct current magnetic biasing are carried out according to the field operation condition. Most of the existing patents are focused on the development of a transformer direct-current magnetic bias simulation modeling algorithm and treatment monitoring equipment, and most of the existing patents do not relate to risk assessment and emergency strategies which are urgently needed by a field transformer.
When the transformer has a dc magnetic bias problem, the problems of aggravation of transformer vibration, increase of noise, abnormal heating and the like will be caused, and the transformer will be damaged in severe cases.
Disclosure of Invention
Aiming at the problem that the prior art lacks an effective evaluation method for the direct current magnetic bias of the transformer, the invention provides the risk evaluation method for the direct current magnetic bias of the transformer, which can comprehensively evaluate the direct current magnetic bias of the transformer and distinguish two conditions of direct sunlight or direct sunlight at the same time, so that the method is less interfered by the outside and has higher accuracy.
The technical scheme of the invention is as follows.
A transformer direct-current magnetic biasing risk assessment method comprises the following steps:
detecting noise, vibration, temperature and neutral point direct current of the transformer;
when the direct current of the neutral point of the transformer does not exceed a set threshold value, recording noise, vibration, temperature and dissolved gas in oil of the transformer as reference data;
when the direct current of the neutral point of the transformer exceeds a set threshold value, recording noise, vibration, temperature and dissolved gas in oil of the transformer as evaluation data, and starting a risk evaluation program;
the risk assessment program: judging whether the transformer has direct sunlight or not, if not, calculating risk evaluation factors by combining the evaluation data and the reference data with the correlation coefficient; if so, calculating risk assessment factors by combining the assessment data except the temperature and the reference data with the correlation coefficient;
and performing risk evaluation on the direct current magnetic biasing of the transformer according to the calculated risk evaluation factor.
The invention can comprehensively evaluate the influence of the transformer direct current magnetic bias, the evaluation parameters of the invention comprise direct current, vibration, noise, temperature and oil chromatogram data directly related to the transformer direct current magnetic bias, and the evaluation parameters are divided into two conditions according to the direct sunlight or not, and the influence needs to be eliminated because the temperature on the surface of the transformer is greatly influenced by the sunlight.
Preferably, the calculation formula of the risk assessment factor is as follows:
wherein I is the direct current measured at the neutral point of the transformer, I0Is a reference current;
n is the maximum noise measured during DC magnetic biasing of the transformer, N0The noise measurement is a sound level meter with the unit of dB, and is the reference noise which is the maximum background noise when no direct current magnetic bias exists;
g is the measured maximum value on the surface of the transformer oil tankLarge vibration acceleration, G0The vibration acceleration measured on the surface of the transformer without direct current magnetic biasing is taken as a reference acceleration, and the unit of the vibration acceleration is gravity acceleration g;
Tpthe maximum temperature difference of the side surface of the transformer is adopted, and the temperature adopts an absolute temperature scale, and the unit of the absolute temperature scale is Kelvin;
k0the coefficient of dissolved gas in oil is determined by the contents of hydrogen, total hydrocarbon and acetylene in the transformer oil, and if the contents of hydrogen, total hydrocarbon and acetylene in the oil are all lower than the specification requirements, k is0If any of the values exceeds 1, k is0＝2；
k1、k2、k3The current coefficient, the noise coefficient and the vibration coefficient are respectively used for representing the weight of each component for evaluating the direct current magnetic bias; k is a radical of4K is the temperature coefficient when sunlight shines directly into the transformer4When no sunlight is directly irradiated or at night, the temperature participates in the evaluation of the DC magnetic bias, and k is the time when the temperature does not participate in the evaluation4＝0.5。
Preferably, the neutral point direct current is measured by using a current transformer based on a hall effect, and the current transformer comprises an open type current clamp and a feed-through current transformer, wherein the open type current clamp is a portable current clamp, and the feed-through current transformer is a fixed type online monitoring device.
Preferably, the noise is measured by using a sound pressure meter, the specified contour line is 0.3m away from the reference emission surface when the air cooling equipment stops operating or the self-cooling transformer is stopped, the measurement height is 1m away from the reference emission surface when the air cooling equipment is put into operation, each transformer measures 8 points, and the front and rear measurement positions are the same.
Preferably, the vibration measurement is completed through an acceleration sensor and is fixed on the transformer shell through a magnetic base; the vibration test points are selected at the middle part of the long shaft of the transformer, at least 5 points are selected for each transformer, 1 point at the protruding part of the adjacent reinforcing rib of the transformer shell and 4 points at the sunken part are selected, and the test points are the same each time.
Preferably, the temperature is measured by using a thermal infrared imager, and the measurement mode is that the maximum temperature difference value is obtained by respectively scanning and detecting 4 side surfaces of the transformer oil tank.
Preferably, the data of the dissolved gas in the oil is acquired by an oil chromatography online monitoring device carried by the transformer or laboratory offline detection data is adopted.
Preferably, the set threshold value of the neutral point direct current is 3 amperes.
The essential features of the invention include: the direct-current magnetic bias influence of the transformer can be comprehensively evaluated; the evaluation parameters comprise direct current, vibration, noise, temperature and oil chromatogram data directly related to the direct current magnetic bias of the transformer; according to the formula for evaluating the direct current magnetic bias of the transformer, different parameters are given different weights according to the importance degree, and the accurate evaluation of the direct current magnetic bias of the transformer is realized.
Drawings
FIG. 1 is a flow chart of an embodiment of the present invention;
FIG. 2 is a schematic view of a single pole earth return mode of operation;
fig. 3 is a schematic diagram of a dc-to-ground current into an ac system.
Detailed Description
The technical solution of the present application will be described with reference to the following examples. In addition, numerous specific details are set forth below in order to provide a better understanding of the present invention. It will be understood by those skilled in the art that the present invention may be practiced without some of these specific details. In some instances, methods, means, elements and circuits that are well known to those skilled in the art have not been described in detail so as not to obscure the present invention.
The direct current transmission systems in China are both double-end systems, one end of each direct current transmission system is a rectifying station, and the other end of each direct current transmission system is an inverter station. According to the needs of engineering, there are many operation modes: a monopole earth return operation mode, a monopole metal return operation mode, a bipolar symmetric operation mode, a bipolar asymmetric operation mode, a homopolar parallel earth return operation mode and the like. In the operation modes, the unipolar metal loop operation mode has no direct current flowing into the ground, the bipolar symmetrical operation mode has only small unbalanced current flowing into the ground, and the two operation modes can not cause obvious difference of direct current potentials on the earth surface and can not cause direct current magnetic biasing of the transformer.
In the initial stage of construction of a bipolar direct-current transmission system, one pole is put into operation immediately after construction, and at the moment, a single-pole earth return line operation mode is generally adopted; in addition, after the bipolar system is built, if one pole fails or exits due to maintenance, the sound pole can also operate in a single-pole earth return mode. As shown in fig. 2, the sound pole dc high voltage line forms a loop with the ground, and the dc ground current is equal to the system operating current on the line.
The path of the dc power transmission system ground current into the ac power transmission system can be illustrated with reference to fig. 3.
The dc bias has a large negative effect on the power system, which mainly includes:
(1) influence on transformers
When direct current enters the transformer, the half-cycle magnetic saturation of the transformer core is caused, the magnetic leakage is increased, and the metal structural part and the oil tank are overheated; the direct current magnetic biasing can also cause the magnetostriction of the iron core to be more serious, so that the vibration of the transformer is aggravated and the noise is increased; meanwhile, due to harmonic distortion, the loss of the transformer is increased, and the efficiency is reduced.
(2) Influence on shunt capacitors
The direct current magnetic biasing of the transformer generates a large amount of harmonic waves, so that the total voltage harmonic distortion rate is increased, and under the influence of the harmonic waves, harmonic overcurrent can be caused at the low voltage side of the transformer substation to cause accidents such as bulging, explosion and the like of the capacitor.
(3) Influence on relay protection
Direct current flowing through an alternating current power grid easily causes direct current magnetic biasing of the current transformer, so that the transmission characteristic of the current transformer is changed, and the alternating current protection is rejected or mistakenly operated. Meanwhile, the transformer generates direct current magnetic biasing to increase the content of second harmonic in the differential current of the transformer, so that the differential protection of the transformer has the risk of secondary harmonic error locking.
In fig. 3, the converter station a and the converter station b form a double-end direct-current transmission system, and when the single-pole ground loop mode is operated, the direct-current operating current I isdcI.e. the earth current, IdcAnd reflows through the earth electrode and the earth. In IdcUnder the action of the magnetic field, the ground surface potential varies, as shown in the lower part of the figure. When I isdcThe potential is increased when the grounding electrode enters the ground from the converter station B, and the potential is reduced when the grounding electrode flows out from the converter station A. Because the neutral point direct grounding transformer and the alternating current transmission line form a direct current low-resistance path between the two transformer substations, the potential difference enables larger direct current to enter a transformer winding through the neutral point of the transformer, thereby causing the problems of noise increase, vibration aggravation, local overheating and the like of the transformer, and generating serious direct current magnetic biasing effect.
Example (b):
in order to deal with the dc magnetic biasing effect, the present embodiment provides a transformer dc magnetic biasing risk assessment method, as shown in fig. 1, including the following steps:
and detecting the noise, vibration, temperature and neutral point direct current of the transformer.
When the direct current of the neutral point of the transformer does not exceed a set threshold value, recording noise, vibration, temperature and dissolved gas in oil of the transformer as reference data;
when the direct current of the neutral point of the transformer exceeds a set threshold value, recording noise, vibration, temperature and dissolved gas in oil of the transformer as evaluation data, and starting a risk evaluation program. The set threshold for neutral dc current is 3 amps.
Risk assessment program: judging whether the transformer has direct sunlight or not, if not, calculating risk evaluation factors by combining the evaluation data and the reference data with the correlation coefficient; and if the risk assessment factor exists, calculating the risk assessment factor by combining the assessment data except the temperature and the benchmark data with the correlation coefficient.
And performing risk evaluation on the direct current magnetic biasing of the transformer according to the calculated risk evaluation factor.
The embodiment can comprehensively evaluate the influence of the direct current magnetic bias of the transformer, the evaluation parameters of the evaluation parameters comprise direct current, vibration, noise, temperature and oil chromatogram data directly related to the direct current magnetic bias of the transformer, and the evaluation parameters are divided into two conditions according to the direct irradiation of sunlight or not, so that the influence needs to be eliminated because the temperature on the surface of the transformer is greatly influenced by the sunlight.
Wherein, the calculation formula of the risk assessment factor is as follows:
wherein I is the direct current measured at the neutral point of the transformer, I0The reference current is generally 12 amperes;
n is the maximum noise measured during DC magnetic biasing of the transformer, N0The noise measurement is a sound level meter with the unit of dB, and is the reference noise which is the maximum background noise when no direct current magnetic bias exists;
g is the maximum vibration acceleration measured on the surface of the transformer oil tank, G0The vibration acceleration measured on the surface of the transformer without direct current magnetic biasing is taken as a reference acceleration, and the unit of the vibration acceleration is gravity acceleration g;
Tpthe maximum temperature difference of the side surface of the transformer is adopted, and the temperature adopts an absolute temperature scale, and the unit of the absolute temperature scale is Kelvin;
k0the coefficient of dissolved gas in the oil is determined by the contents of hydrogen, total hydrocarbon and acetylene in the transformer oil, and if the content of hydrogen in the oil is lower than 150uL/L, the content of total hydrocarbon is lower than 150uL/L and the content of acetylene is lower than 5uL/L according to the regulations, k is0If any of the values exceeds 1, k is0＝2；
k1、k2、k3The current coefficient, the noise coefficient and the vibration coefficient respectively represent the weight of each component on the DC magnetic bias evaluation, and are generally set to be 0.7, 0.2 and 0.1; k is a radical of4K is the temperature coefficient when sunlight shines directly into the transformer4When no sunlight is directly irradiated or at night, the temperature participates in the evaluation of the DC magnetic bias, and k is the time when the temperature does not participate in the evaluation4＝0.5。
The measuring tools used in the embodiment are all common tools, wherein the current transformer based on the hall effect is adopted for measuring the neutral point direct current, and comprises an open type current clamp and a through current transformer, the open type current clamp is a portable current clamp, and the through current transformer is a fixed type online monitoring device.
The noise measurement adopts a sound pressure meter, for the air cooling equipment stopping operation or the self-cooling transformer, the specified contour line should be 0.3m away from the reference emission surface, the transformer in the air cooling equipment operation should be 2m away from the reference emission surface, the measurement height is 1m away from the ground, each transformer measures 8 points, and the front and back measurement positions are the same.
The vibration measurement is completed through an acceleration sensor and is fixed on the transformer shell through a magnetic base; the vibration test points are selected at the middle part of the long shaft of the transformer, at least 5 points are selected for each transformer, 1 point at the protruding part of the adjacent reinforcing rib of the transformer shell and 4 points at the sunken part are selected, and the test points are the same each time.
The temperature is measured by adopting a thermal infrared imager in a mode of scanning and detecting 4 side surfaces of the transformer oil tank respectively to obtain the maximum temperature difference value.
And the data of the gas dissolved in the oil is acquired by an oil chromatography online monitoring device carried by the transformer or the data is detected by adopting a laboratory offline mode.
The substantive features of this embodiment include: the direct-current magnetic bias influence of the transformer can be comprehensively evaluated; the evaluation parameters comprise direct current, vibration, noise, temperature and oil chromatogram data directly related to the direct current magnetic bias of the transformer; according to the formula for evaluating the direct current magnetic bias of the transformer, different parameters are given different weights according to the importance degree, and the accurate evaluation of the direct current magnetic bias of the transformer is realized.
Through the description of the above embodiments, those skilled in the art will understand that, for convenience and simplicity of description, only the division of the above functional modules is used as an example, and in practical applications, the above function distribution may be completed by different functional modules according to needs, that is, the internal structure of a specific device is divided into different functional modules to complete all or part of the above described functions.
In the embodiments provided in this application, it should be understood that the disclosed structures and methods may be implemented in other ways. For example, the above-described embodiments with respect to structures are merely illustrative, and for example, a module or a unit may be divided into only one logic function, and may have another division manner in actual implementation, for example, a plurality of units or components may be combined or may be integrated into another structure, or some features may be omitted or not executed. In addition, the shown or discussed mutual coupling or direct coupling or communication connection may be an indirect coupling or communication connection through some interfaces, structures or units, and may be in an electrical, mechanical or other form.
Units described as separate parts may or may not be physically separate, and parts displayed as units may be one physical unit or a plurality of physical units, may be located in one place, or may be distributed to a plurality of different places. Some or all of the units can be selected according to actual needs to achieve the purpose of the solution of the embodiment.
In addition, functional units in the embodiments of the present application may be integrated into one processing unit, or each unit may exist alone physically, or two or more units are integrated into one unit. The integrated unit can be realized in a form of hardware, and can also be realized in a form of a software functional unit.
The integrated unit, if implemented in the form of a software functional unit and sold or used as a stand-alone product, may be stored in a readable storage medium. Based on such understanding, the technical solutions of the embodiments of the present application may be essentially or partially contributed to by the prior art, or all or part of the technical solutions may be embodied in the form of a software product, where the software product is stored in a storage medium and includes several instructions to enable a device (which may be a single chip, a chip, or the like) or a processor (processor) to execute all or part of the steps of the methods of the embodiments of the present application. And the aforementioned storage medium includes: various media capable of storing program codes, such as a usb disk, a removable hard disk, a Read Only Memory (ROM), a Random Access Memory (RAM), a magnetic disk, or an optical disk.
The above description is only for the specific embodiments of the present application, but the scope of the present application is not limited thereto, and any person skilled in the art can easily conceive of the changes or substitutions within the technical scope of the present application, and shall be covered by the scope of the present application. Therefore, the protection scope of the present application shall be subject to the protection scope of the claims.
Claims (8)
1. A transformer direct current magnetic biasing risk assessment method is characterized by comprising the following steps:
detecting noise, vibration, temperature and neutral point direct current of the transformer;
when the direct current of the neutral point of the transformer does not exceed a set threshold value, recording noise, vibration, temperature and dissolved gas in oil of the transformer as reference data;
when the direct current of the neutral point of the transformer exceeds a set threshold value, recording noise, vibration, temperature and dissolved gas in oil of the transformer as evaluation data, and starting a risk evaluation program;
the risk assessment program: judging whether the transformer has direct sunlight or not, if not, calculating risk evaluation factors by combining the evaluation data and the reference data with the correlation coefficient; if so, calculating risk assessment factors by combining the assessment data except the temperature and the reference data with the correlation coefficient;
and performing risk evaluation on the direct current magnetic biasing of the transformer according to the calculated risk evaluation factor.
2. The method for evaluating the risk of the direct current magnetic bias of the transformer according to claim 1, wherein the risk evaluation factor is calculated by the following formula:
wherein I is the direct current measured at the neutral point of the transformer, I0Is a reference current;
n is the maximum noise measured during DC magnetic biasing of the transformer, N0As reference noise, as maximum background noise in the absence of DC bias, noiseThe measurement is performed by a sound level meter, and the unit of the sound level meter is dB;
g is the maximum vibration acceleration measured on the surface of the transformer oil tank, G0The vibration acceleration measured on the surface of the transformer without direct current magnetic biasing is taken as a reference acceleration, and the unit of the vibration acceleration is gravity acceleration g;
Tpthe maximum temperature difference of the side surface of the transformer is adopted, and the temperature adopts an absolute temperature scale, and the unit of the absolute temperature scale is Kelvin;
k0the coefficient of dissolved gas in oil is determined by the contents of hydrogen, total hydrocarbon and acetylene in the transformer oil, and if the contents of hydrogen, total hydrocarbon and acetylene in the oil are all lower than the specification requirements, k is0If any of the values exceeds 1, k is0＝2；
k1、k2、k3The current coefficient, the noise coefficient and the vibration coefficient are respectively used for representing the weight of each component for evaluating the direct current magnetic bias; k is a radical of4K is the temperature coefficient when sunlight shines directly into the transformer4When no sunlight is directly irradiated or at night, the temperature participates in the evaluation of the DC magnetic bias, and k is the time when the temperature does not participate in the evaluation4＝0.5。
3. The method for assessing risk of dc magnetic bias of transformer according to claim 1 or 2, wherein the measurement of the dc current at the neutral point is performed by using a hall effect based current transformer, which comprises an open current clamp and a feedthrough current transformer, the former is a portable current clamp, and the latter is a fixed online monitoring device.
4. The method for evaluating the risk of direct current magnetic biasing of the transformer according to claim 1 or 2, wherein the noise is measured by using a sound pressure meter, the specified contour line is 0.3m away from the reference emission surface when the air cooling device stops operating or the air cooling device is self-cooled, the measurement height is 1m away from the reference emission surface when the air cooling device is put into operation, each transformer measures 8 points, and the front measurement position and the rear measurement position are the same.
5. The risk assessment method for direct current magnetic biasing of a transformer according to claim 1 or 2, wherein the measurement of the vibration is performed by an acceleration sensor and is fixed on the transformer housing by a magnetic base; the vibration test points are selected at the middle part of the long shaft of the transformer, at least 5 points are selected for each transformer, 1 point at the protruding part of the adjacent reinforcing rib of the transformer shell and 4 points at the sunken part are selected, and the test points are the same each time.
6. The transformer direct-current magnetic bias risk assessment method according to claim 1 or 2, wherein the temperature is measured by using a thermal infrared imager, and the measurement mode is that the maximum temperature difference value is obtained by respectively scanning and detecting 4 side surfaces of a transformer oil tank.
7. The method for assessing the risk of direct current magnetic biasing of the transformer according to claim 1 or 2, wherein the data of the dissolved gas in the oil is acquired by an oil chromatography online monitoring device of the transformer or data is detected offline by a laboratory.
8. The method for assessing risk of dc magnetic bias of transformer according to claim 1, wherein the set threshold of the dc current at neutral point is 3 a.
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