CN111638738A - Power transformer low-frequency heating critical frequency calculation and automatic control method - Google Patents

Power transformer low-frequency heating critical frequency calculation and automatic control method Download PDF

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CN111638738A
CN111638738A CN202010467449.4A CN202010467449A CN111638738A CN 111638738 A CN111638738 A CN 111638738A CN 202010467449 A CN202010467449 A CN 202010467449A CN 111638738 A CN111638738 A CN 111638738A
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transformer
frequency
low
voltage
frequency heating
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CN111638738B (en
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张晓东
刘博�
郑博谦
姜秉梁
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Baoding Electric Power Vocational And Technical College
State Grid Corp of China SGCC
Training Center of State Grid Jibei Electric Power Co Ltd
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Baoding Electric Power Vocational And Technical College
State Grid Corp of China SGCC
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    • G—PHYSICS
    • G05—CONTROLLING; REGULATING
    • G05D—SYSTEMS FOR CONTROLLING OR REGULATING NON-ELECTRIC VARIABLES
    • G05D23/00—Control of temperature
    • G05D23/19—Control of temperature characterised by the use of electric means
    • G05D23/30—Automatic controllers with an auxiliary heating device affecting the sensing element, e.g. for anticipating change of temperature

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Abstract

The invention discloses a method for calculating and automatically controlling the low-frequency heating critical frequency of a power transformer, which comprises the following steps: the low-voltage side of the tested transformer is short-circuited, and the high-voltage side of the tested transformer is introduced with low-frequency current; presetting transformer iron core saturation critical frequency fg(ii) a By adjusting the output voltage U of the low-frequency heating power supply1The current of the tested transformer winding is controlled, and further the temperature control of the transformer oil tank is realized. The invention adopts the preset transformer iron core saturation critical frequency fgThe method effectively prevents the transformer iron core from being saturated, prolongs the service life of the iron core and achieves the purpose of efficiently drying the transformer.

Description

Power transformer low-frequency heating critical frequency calculation and automatic control method
Technical Field
The invention relates to the technical field of transformer equipment, in particular to a method for calculating and automatically controlling low-frequency heating critical frequency of a power transformer.
Background
The transformer is one of the core components of the operation of the power system, and the good insulation performance of the transformer is an important guarantee for the safe operation of the power system. Moisture in the insulation material has a very large influence on the insulation of power transformers, in particular high voltage power transformers. Because the distribution of direct current voltage is determined by the resistivity of the material, the change of the water content directly causes the resistivity of the insulating material to change, thereby causing the local distortion of an electric field, possibly causing a discharge breakdown accident in severe cases and seriously influencing the operation safety of the transformer.
In the field installation process of the large transformer, the most critical link is to prevent the large transformer from being affected with damp. The existing on-site drying treatment method is an oil filter hot oil circulation method, has long treatment time and low efficiency, and particularly cannot be heated to the temperature required by the process when the environmental temperature is low, so that the ideal drying effect is difficult to achieve.
The transformer low-frequency short-circuit heating drying method is an insulation drying method developed on the basis of the traditional power frequency short-circuit method, the transformer insulation heating treatment is carried out by adopting the low-frequency short-circuit heating method, the required power capacity can be obviously reduced, the voltage applied at a voltage application end is reduced, a special reactive power compensation device is not needed, and the main problem of short-circuit heating under the power frequency condition is solved.
When the dryer body is heated by the transformer by adopting a low-frequency short-circuit method, the lower the frequency of a power supply applied to a transformer winding, the higher the power factor of the power supply, the smaller the equipment volume and the more economical the test. However, the transformer core is easily saturated at low frequency, and when the transformer core is saturated, the transformer core will be overheated, which causes insulation damage between silicon steel sheets and even serious faults such as iron core melting.
Disclosure of Invention
The invention provides a method for calculating and automatically controlling the low-frequency heating critical frequency of a power transformer, which aims to solve the problem of serious faults such as insulation damage between silicon steel sheets and even iron core melting caused by overheating of a transformer iron core when the transformer is heated and dried by a low-frequency short circuit method, so as to prevent the transformer iron core from being saturated, prolong the service life of the iron core and achieve the aim of efficiently drying the transformer.
In order to solve the technical problems, the technical scheme adopted by the invention is as follows.
A method for calculating the low-frequency heating critical frequency of a power transformer comprises the following specific steps:
s1, according to the main magnetic flux of the transformer
Figure BDA0002513123940000021
Calculating a formula, and determining a constraint condition which is satisfied by the voltage and the frequency applied to the high-voltage side of the transformer;
s2, obtaining the terminal voltage applied to the high-voltage side winding of the transformer by the equivalent short circuit of the transformer;
s3, the terminal voltage applied to the high-voltage side winding of the transformer in the step S2 is brought into the constraint condition that the voltage and the frequency of the high-voltage side of the transformer in the step S1 should meet, and the saturation critical frequency f of the transformer core is obtainedgAnd (5) expressing.
Further optimizing the technical scheme, the main magnetic flux of the transformer
Figure BDA0002513123940000022
The calculation formula is as follows:
Figure BDA0002513123940000023
in the formula: e1-high side no-load induced potential; u shape1N-high side rated voltage; f. ofN-a nominal frequency; n is a radical of1-high side winding number of turns;
the constraint conditions that the voltage and the frequency applied to the high-voltage side of the transformer should meet are as follows:
Figure BDA0002513123940000024
obtaining by simultaneous method:
Figure BDA0002513123940000025
when heating at low frequency, the transformerThe change of the voltage and the frequency of the high-voltage side satisfies the above formula
Figure BDA0002513123940000026
And in the process, the transformer iron core can be ensured to be in a non-saturated state.
In step S2, the terminal voltage applied to the high-voltage side winding of the transformer is:
Figure BDA0002513123940000031
in the formula:
z-short circuit impedance converted to high voltage side;
Rk-converting the short-circuit resistance of each phase to the high-voltage side;
x-converts to the short-circuit reactance of each phase on the high-voltage side;
Xkconversion to high-side short-circuit reactance per phase, X, at nominal operationk＝2πfN。
In step S3, the voltage across the high-voltage winding of the transformer in step S2 is brought into the constraint condition that the voltage and frequency of the high-voltage winding of the transformer in step S1 should satisfy, and when the primary-side input current I of the transformer is equal to or higher than the predetermined value, the primary-side input current I is adjusted to be smaller than the predetermined value1When the value is a certain value, the following are provided:
Figure BDA0002513123940000032
further solving the above formula when the current is I1The frequency constraint condition for ensuring that the transformer iron core is in the unsaturated region is as follows:
Figure BDA0002513123940000033
from the above
Figure BDA0002513123940000034
It can be known that the saturation critical frequency f of the transformer coregThe expression is as follows:
Figure BDA0002513123940000035
from the above
Figure BDA0002513123940000036
It can be known that the saturation critical frequency of the transformer core can be determined by the rated parameter (U) of the transformer1N，fN，Rk，Xk) And a given current I1And (6) directly calculating.
A power transformer low-frequency heating automatic control method comprises the following steps:
s10, short-circuiting the low-voltage side of the tested transformer, and introducing low-frequency heating current to the high-voltage side of the tested transformer;
s20, presetting the saturation critical frequency f of the transformer core according to claim 4g；
S30, adjusting output voltage U of low-frequency heating power supply1The oil temperature T of the top layer of the tested transformer oil tank is controlled.
In the further optimized technical scheme, between the step S20 and the step S30, the top oil temperature T of the tested transformer oil tank is fed back to the main control board, and compared with the preset temperature in the main control board, whether the temperature difference exists is judged;
if the temperature difference exists, the main control board sends a control signal to the low-frequency heating power supply; after the low-frequency heating power supply receives the control signal, the low-frequency heating power supply outputs a voltage U1And (6) carrying out adjustment.
According to the technical scheme, the oil temperature T at the top layer of the oil tank of the tested transformer is fed back to the main control board through the temperature transmitter.
Due to the adoption of the technical scheme, the technical progress of the invention is as follows.
The invention is based on the main magnetic flux of the transformer
Figure BDA0002513123940000041
Calculating a formula, and determining a constraint condition which is satisfied by the voltage and the frequency applied to the high-voltage side of the transformer; by transformers or the likeThe short-circuit is used for obtaining the terminal voltage applied to the high-voltage side winding of the transformer; the terminal voltage applied to the high-voltage side winding of the transformer in the step S2 is brought into the constraint condition that the voltage and the frequency of the high-voltage side of the transformer in the step S1 should meet, and the saturation critical frequency f of the transformer core is obtainedgAnd then the low-voltage side of the transformer is short-circuited, the high-voltage side of the transformer is introduced with low-frequency heating current, the heat generated by the load loss of the transformer is utilized to heat the insulation of the transformer, and the saturation critical frequency f of the iron core of the transformer is presetgBy adjusting the output voltage U of the low-frequency heating power supply1The current of the transformer winding is controlled, so that the temperature control of the transformer oil tank is realized, the saturation of the transformer iron core is avoided in the adjusting process, the service life of the iron core is prolonged, and the purpose of efficiently drying the transformer is achieved.
Drawings
FIG. 1 is a schematic diagram of a low-frequency heating automatic control method of a power transformer according to the present invention;
fig. 2 is a circuit block diagram of an automatic control device for low-frequency heating of a power transformer according to the present invention.
Detailed Description
The invention will be described in further detail below with reference to the figures and specific examples.
A method for calculating the low-frequency heating critical frequency of a power transformer comprises the following specific steps:
s1, according to the main magnetic flux of the transformer
Figure BDA0002513123940000051
And calculating a formula, and determining a constraint condition which is satisfied by the voltage and the frequency applied to the high-voltage side of the transformer.
Main magnetic flux of transformer
Figure BDA0002513123940000052
The calculation formula is as follows:
Figure BDA0002513123940000053
in the formula: e1High pressure sideNo-load induced potential; u shape1N-high side rated voltage; f. ofN-a nominal frequency; n is a radical of1-high side winding number of turns;
the constraint conditions that the voltage and the frequency applied to the high-voltage side of the transformer should meet are as follows:
Figure BDA0002513123940000054
obtaining by simultaneous method:
Figure BDA0002513123940000055
when the low-frequency heating is carried out, the voltage and the frequency of the high-voltage side of the transformer change to satisfy the formula
Figure BDA0002513123940000056
And in the process, the transformer iron core can be ensured to be in a non-saturated state.
And S2, obtaining the terminal voltage applied to the high-voltage side winding of the transformer by the equivalent short-circuit of the transformer.
In step S2, the terminal voltage applied to the high-voltage side winding of the transformer is:
Figure BDA0002513123940000057
in the formula:
z-short circuit impedance converted to high voltage side;
Rk-converting the short-circuit resistance of each phase to the high-voltage side;
x-converts to the short-circuit reactance of each phase on the high-voltage side;
Xkconversion to high-side short-circuit reactance per phase, X, at nominal operationk＝2πfN。
S3, the terminal voltage applied to the high-voltage side winding of the transformer in the step S2 is brought into the constraint condition that the voltage and the frequency of the high-voltage side of the transformer in the step S1 should meet, and the saturation critical frequency f of the transformer core is obtainedgAnd (5) expressing.
In step S3, the voltage applied to the high-voltage side winding of the transformer in step S2 is brought into the constraint condition that the voltage and frequency of the high-voltage side of the transformer in step S1 should satisfy, and when the primary-side input current I of the transformer is equal to or less than the predetermined value1When the value is a certain value, the following are provided:
Figure BDA0002513123940000061
further solving the above formula when the current is I1The frequency constraint condition for ensuring that the transformer iron core is in the unsaturated region is as follows:
Figure BDA0002513123940000062
from the above
Figure BDA0002513123940000063
It can be known that the saturation critical frequency f of the transformer coregThe expression is as follows:
Figure BDA0002513123940000064
from the above
Figure BDA0002513123940000065
It can be known that the saturation critical frequency of the transformer core can be determined by the rated parameter (U) of the transformer1N，fN，Rk，Xk) And a given current I1And (6) directly calculating.
A low-frequency automatic heating device of a power transformer comprises a low-frequency heating power supply and a control system, and is shown in a combined figure 2.
The low-frequency heating power supply adopts an AC-DC-AC converter to output low-frequency current of 0.01-1 Hz. The low-frequency heating power supply comprises a diode AC/DC module and an IGBT DC/AC module, and the power supply is a 380V power supply.
The control system comprises a main control board, an operation keyboard, an LED display module, a driving protection circuit, a current transformer, a temperature transmitter, a temperature regulator and a current regulator.
The operation keyboard is connected with the main control board through I/O, and the output end of the operation keyboard is connected with the input end of the main control board. The input end of the LED display module is connected with the output end of the main control board and used for displaying data information. The output end of the temperature transmitter is connected with the input end of the main control board.
The invention also includes a current loop and a temperature control loop. The inner ring is a current ring, and the main function is to realize the output current I of the low-frequency heating power supply1Control, for low-frequency heating, of the power supply output current I1At a constant value, typically for improved heating efficiency, the output current may be set to a nominal value I1N. The outer ring is a temperature control ring, and the main function is to realize the control of the temperature T of the transformer oil tank.
The temperature transmitter can acquire the oil temperature T at the top layer of the transformer oil tank and convert the temperature signal from an analog signal into an electric signal of 0-20 mA. The temperature range of the temperature feedback signal is 0-85 ℃. Both the temperature regulator and the current regulator are PI controlled. The output signal of the temperature regulator is used as a given signal of the current inner loop and is compared with the feedback current signal. The current range of the current feedback is 0-I1NAnd the voltage range is 0-5 V. the current regulator regulates the low-frequency heating power supply according to the current difference △ I, and the purpose of controlling the oil temperature of the transformer automatically is achieved by changing the output voltage of the low-frequency heating power supply.
An automatic control method for low-frequency heating of a power transformer is disclosed, and shown in fig. 1, the method is performed based on an automatic low-frequency heating device of the power transformer, and comprises the following steps:
and S10, the low-voltage side of the tested transformer is short-circuited, and the high-voltage side of the tested transformer is introduced with low-frequency heating current. The heat generated by the load loss of the transformer is used for heating the insulation of the transformer so as to achieve the purpose of insulation drying.
S20, presetting the saturation critical frequency f of the transformer coregIn the invention, the output current frequency f of the low-frequency heating power supply is preset by operating a keyboardgIn (1). Output current frequency f of low-frequency heating power supplygAt which the transformer can be guaranteed to be below rated powerWhen the working condition of the current is adjusted, the iron core of the transformer is ensured to be in an unsaturated state.
S30, adjusting output voltage U of low-frequency heating power supply1The oil temperature T of the top layer of the tested transformer oil tank is controlled.
Between the step S20 and the step S30, the top oil temperature T of the tested transformer tank is fed back to the main control board through the temperature transmitter, and compared with the preset temperature in the main control board, it is determined whether there is a temperature difference.
If the temperature difference exists, the main control board sends a control signal to the low-frequency heating power supply; after the low-frequency heating power supply receives the control signal, the low-frequency heating power supply outputs a voltage U1And adjusting to achieve the purpose of controlling the output current and further realize the control of the insulation temperature of the tested transformer.

Claims (7)

1. A method for calculating the low-frequency heating critical frequency of a power transformer is characterized by comprising the following specific steps of:
s1, determining the constraint condition that the voltage and the frequency applied to the high-voltage side of the transformer should meet according to the calculation formula of the main magnetic flux phi m of the transformer;
s2, obtaining the terminal voltage applied to the high-voltage side winding of the transformer by the equivalent short circuit of the transformer;
s3, the terminal voltage applied to the high-voltage side winding of the transformer in the step S2 is brought into the constraint condition that the voltage and the frequency of the high-voltage side of the transformer in the step S1 should meet, and the saturation critical frequency f of the transformer core is obtainedgAnd (5) expressing.
2. The method for calculating the critical frequency of low-frequency heating of a power transformer as claimed in claim 1, wherein the primary magnetic flux Φ m of the transformer is calculated by the following formula:
Figure FDA0002513123930000011
in the formula: e1-high side no-load induced potential; u shape1N-high side rated voltage; f. ofNRated frequencyRate; n is a radical of1-high side winding number of turns;
the constraint conditions that the voltage and the frequency applied to the high-voltage side of the transformer should meet are as follows:
Figure FDA0002513123930000012
obtaining by simultaneous method:
Figure FDA0002513123930000013
when the low-frequency heating is carried out, the voltage and the frequency of the high-voltage side of the transformer change to satisfy the formula
Figure FDA0002513123930000014
And in the process, the transformer iron core can be ensured to be in a non-saturated state.
3. The method for calculating the critical frequency of low-frequency heating of a power transformer as claimed in claim 2, wherein in step S2, the terminal voltage applied to the high-side winding of the transformer is:
Figure FDA0002513123930000021
in the formula:
z-short circuit impedance converted to high voltage side;
Rk-converting the short-circuit resistance of each phase to the high-voltage side;
x-converts to the short-circuit reactance of each phase on the high-voltage side;
Xkconversion to high-side short-circuit reactance per phase, X, at nominal operationk＝2πfN。
4. The method for calculating the critical frequency of low-frequency heating of a power transformer as claimed in claim 3, wherein in step S3, the voltage applied to the winding terminal on the high-voltage side of the transformer in step S2 is brought into step S1When the voltage and frequency of the high-voltage side of the transformer are within the constraint condition that the primary side input current I of the transformer is within1When the value is a certain value, the following are provided:
Figure FDA0002513123930000022
further solving the above formula when the current is I1The frequency constraint condition for ensuring that the transformer iron core is in the unsaturated region is as follows:
Figure FDA0002513123930000023
from the above
Figure FDA0002513123930000024
It can be known that the saturation critical frequency f of the transformer coregThe expression is as follows:
Figure FDA0002513123930000025
from the above
Figure FDA0002513123930000026
It can be known that the saturation critical frequency of the transformer core can be determined by the rated parameter (U) of the transformer1N，fN，Rk，Xk) And a given current I1And (6) directly calculating.
5. A power transformer low-frequency heating automatic control method is characterized by comprising the following steps:
s10, short-circuiting the low-voltage side of the tested transformer, and introducing low-frequency heating current to the high-voltage side of the tested transformer;
s20, presetting the saturation critical frequency f of the transformer core according to claim 4g；
S30, adjusting output voltage U of low-frequency heating power supply1The oil temperature T of the top layer of the tested transformer oil tank is controlled.
6. The automatic control method for low-frequency heating of power transformer as claimed in claim 5, wherein between the steps S20 and S30, the temperature T of the top oil of the tested transformer tank is fed back to the main control board, and compared with the preset temperature in the main control board, it is determined whether there is a temperature difference;
if the temperature difference exists, the main control board sends a control signal to the low-frequency heating power supply; after the low-frequency heating power supply receives the control signal, the low-frequency heating power supply outputs a voltage U1And (6) carrying out adjustment.
7. The automatic control method for low-frequency heating of the power transformer as claimed in claim 6, wherein the top oil temperature T of the tested transformer tank is fed back to the main control panel by the temperature transmitter.
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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN112888092A (en) * 2021-01-19 2021-06-01 深圳市默贝克驱动技术有限公司 Low-frequency heating device of large-capacity power transformer

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Publication number Priority date Publication date Assignee Title
JPH04288803A (en) * 1991-03-18 1992-10-13 Alps Electric Co Ltd Low frequency transformer
CN104333930A (en) * 2014-10-27 2015-02-04 国家电网公司 Selecting method for transformer low frequency heating frequency based on square wave modulation
CN106024308A (en) * 2016-05-19 2016-10-12 天津送变电工程公司 Construction method for heating ultra-high voltage transformer oil with low-frequency current short circuit method
CN106841875A (en) * 2017-03-01 2017-06-13 国家电网公司 Three-Phase Distribution Transformers temperature rise test system and method based on alternating low frequency heating
CN106908745A (en) * 2017-01-10 2017-06-30 云南电力试验研究院(集团)有限公司 A kind of experiment and the computational methods of ferromagnetic element excitation property and open circuit loss based on low-frequency square-wave

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPH04288803A (en) * 1991-03-18 1992-10-13 Alps Electric Co Ltd Low frequency transformer
CN104333930A (en) * 2014-10-27 2015-02-04 国家电网公司 Selecting method for transformer low frequency heating frequency based on square wave modulation
CN106024308A (en) * 2016-05-19 2016-10-12 天津送变电工程公司 Construction method for heating ultra-high voltage transformer oil with low-frequency current short circuit method
CN106908745A (en) * 2017-01-10 2017-06-30 云南电力试验研究院(集团)有限公司 A kind of experiment and the computational methods of ferromagnetic element excitation property and open circuit loss based on low-frequency square-wave
CN106841875A (en) * 2017-03-01 2017-06-13 国家电网公司 Three-Phase Distribution Transformers temperature rise test system and method based on alternating low frequency heating

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN112888092A (en) * 2021-01-19 2021-06-01 深圳市默贝克驱动技术有限公司 Low-frequency heating device of large-capacity power transformer
CN112888092B (en) * 2021-01-19 2023-08-08 深圳市默贝克驱动技术有限公司 Low-frequency heating device of high-capacity power transformer

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