CN115982535A - Method and system for determining temperature rise of off-line oil in forced oil circulation mode - Google Patents

Abstract

The invention provides a method and a system for determining off-line oil temperature rise in a forced oil circulation mode, wherein the method comprises the following steps: determining the oil bottom temperature rise, the oil top temperature rise and the oil average temperature rise of the transformer; calculating to obtain the oil speed and the oil flow distribution in the coil of the transformer by utilizing liquid heat transfer parameters corresponding to the oil bottom temperature rise, the oil top temperature rise and the oil average temperature rise; and determining the temperature rise of the coil in the forced oil circulation mode according to the calculated oil speed and oil flow distribution. According to the scheme, the oil speed and the oil flow distribution in the coil of the transformer are calculated by utilizing the liquid heat transfer parameters corresponding to the oil bottom temperature rise, the oil top temperature rise and the oil average temperature rise, and the accurate line oil temperature rise is determined through the oil speed and the oil flow distribution, so that the control difficulty of the coil temperature rise can be reduced or the overlarge temperature rise margin can be avoided.

Description

Method and system for determining temperature rise of off-line oil in forced oil circulation mode

technical field

The invention relates to the technical field of transformer equipment, in particular to a method and system for determining the temperature rise of off-line oil in a forced oil circulation mode.

Background technique

The forced oil circulation method is widely used in transformer cooling. The distribution of transformer oil between different coils does not match the heat loss of the coil itself, which will cause a large difference in the temperature rise of the line oil of different coils, and then Increasing the difficulty of controlling the temperature rise of the coil may cause the temperature rise margin to be too large. Therefore, there is an urgent need for a method that can accurately determine the temperature rise of the line oil.

Contents of the invention

In view of this, embodiments of the present invention provide a method and system for determining the temperature rise of line oil in a forced oil circulation mode, so as to accurately determine the temperature rise of line oil.

In order to achieve the above purpose, embodiments of the present invention provide the following technical solutions:

The first aspect of the embodiments of the present invention discloses a method for determining the temperature rise of off-line oil in the forced oil circulation mode, and the method includes:

Determine the oil bottom temperature rise, oil top temperature rise and oil average temperature rise of the transformer;

Using the liquid heat transfer parameters corresponding to the oil bottom temperature rise, the oil top temperature rise and the oil average temperature rise, calculate the oil velocity and oil flow distribution inside the coil of the transformer;

Through the calculated oil velocity and oil flow distribution, the line oil temperature rise of the coil in the forced oil circulation mode is determined.

Preferably, the oil bottom temperature rise, oil top temperature rise and oil average temperature rise of the transformer are determined, including:

Obtain the initial oil average temperature rise, initial oil top temperature rise and initial oil bottom temperature rise as the average temperature rise of the oil to be treated, the temperature rise of the oil top to be processed and the temperature rise of the oil bottom to be treated respectively;

Calculate the actual cooling capacity of the oil tank of the transformer by using the average temperature rise of the treated oil, the temperature rise of the top of the oil to be treated and the temperature rise of the bottom of the oil to be treated;

Determine the first oil average temperature rise, the first oil top temperature rise and the first oil bottom temperature rise through the actual cooling capacity;

If the difference between the first oil average temperature rise and the initial oil average temperature rise is less than a threshold, output the first oil average temperature rise, the first oil top temperature rise, and the first oil bottom temperature rise As the oil bottom temperature rise, oil top temperature rise and oil average temperature rise of the transformer;

If the difference between the average temperature rise of the first oil and the average temperature rise of the initial oil is greater than or equal to the threshold, the corresponding average temperature rise of the second oil is found by approximation according to the energy balance and the Newton iteration method, and through the first The average temperature rise of the second oil determines the temperature rise of the second oil top and the second oil bottom;

The average temperature rise of the oil to be treated, the temperature rise of the top of the oil to be treated and the temperature rise of the bottom of the oil to be treated are respectively updated to the average temperature rise of the second oil, the temperature rise of the second oil top and the For the second oil bottom temperature rise, return to the step of calculating the actual cooling capacity of the transformer oil tank by using the average temperature rise of the treated oil, the temperature rise of the top of the oil to be treated, and the temperature rise of the bottom of the oil to be treated.

Preferably, the liquid heat transfer parameters corresponding to the oil bottom temperature rise, the oil top temperature rise and the oil average temperature rise are used to calculate the oil velocity and oil flow distribution inside the coil of the transformer, including:

Using liquid heat transfer parameters corresponding to the oil bottom temperature rise, the oil top temperature rise, and the oil average temperature rise, analyzing a preset pressure drop equation to determine corresponding pressure drop data;

Through the pressure drop data, the oil velocity and oil flow distribution inside the coil of the transformer are calculated.

Preferably, the line oil temperature rise of the coil in the forced oil circulation mode is determined through the calculated oil velocity and oil flow distribution, including:

Analyzing the preset conductor temperature calculation model and oil temperature calculation model through the calculated oil velocity and oil flow distribution to obtain the conductor temperature;

Determining the difference between the conductor temperature and the average oil temperature of the transformer to obtain the line oil temperature rise of the coil in forced oil circulation mode.

Preferably, the second oil top temperature rise and the second oil bottom temperature rise are determined by the second oil average temperature rise, including:

calculating the oil temperature difference between the inlet oil temperature and the outlet oil temperature of the oil tank by using the average temperature rise of the second oil;

A second oil top temperature rise and a second oil bottom temperature rise are determined based on the oil temperature difference.

The second aspect of the embodiment of the present invention discloses a system for determining the temperature rise of off-line oil in the forced oil circulation mode. The system includes:

The first determination unit is used to determine the oil bottom temperature rise, oil top temperature rise and oil average temperature rise of the transformer;

A calculation unit, used to calculate the oil velocity and oil flow distribution inside the coil of the transformer by using the liquid heat transfer parameters corresponding to the oil bottom temperature rise, the oil top temperature rise and the oil average temperature rise;

The second determination unit is configured to determine the line oil temperature rise of the coil in the forced oil circulation mode through the calculated oil velocity and oil flow distribution.

Preferably, the first determination unit includes:

The acquisition module is used to obtain the initial oil average temperature rise, the initial oil top temperature rise and the initial oil bottom temperature rise as the average temperature rise of the oil to be processed, the temperature rise of the oil top to be processed and the temperature rise of the oil bottom to be processed respectively;

A calculation module, used to calculate the actual cooling capacity of the oil tank of the transformer by using the average temperature rise of the treated oil, the temperature rise of the top of the oil to be treated, and the temperature rise of the bottom of the oil to be treated;

A determining module, configured to determine the first oil average temperature rise, the first oil top temperature rise, and the first oil bottom temperature rise through the actual cooling capacity;

An output module, configured to output the first oil average temperature rise, the first oil top temperature rise, and the first oil top temperature rise if the difference between the first oil average temperature rise and the initial oil average temperature rise is less than a threshold. An oil bottom temperature rise as the oil bottom temperature rise, oil top temperature rise and oil average temperature rise of the transformer;

A processing module, configured to find the corresponding average temperature rise of the second oil by approximation according to energy balance and Newton iteration method if the difference between the average temperature rise of the first oil and the average temperature rise of the initial oil is greater than or equal to the threshold, And determine the second oil top temperature rise and the second oil bottom temperature rise through the second oil average temperature rise;

An update module, configured to update the average temperature rise of the oil to be treated, the temperature rise of the top of the oil to be treated, and the temperature rise of the bottom of the oil to be treated as the average temperature rise of the second oil, the temperature rise of the second oil top The temperature rise and the second oil bottom temperature rise are returned to execute the calculation module.

Preferably, the calculation unit is specifically configured to: use liquid heat transfer parameters corresponding to the oil bottom temperature rise, the oil top temperature rise, and the oil average temperature rise to analyze a preset pressure drop equation to determine The corresponding pressure drop data is obtained; through the pressure drop data, the oil velocity and oil flow distribution inside the coil of the transformer are calculated.

Preferably, the second determination unit is specifically configured to: analyze the preset conductor temperature calculation model and oil temperature calculation model to obtain the conductor temperature through the calculated oil velocity and oil flow distribution; determine the conductor temperature and The difference between the average oil temperatures of the transformers is used to obtain the line oil temperature rise of the coils in the forced oil circulation mode.

Preferably, the processing module is specifically configured to: use the second average oil temperature rise to calculate the oil temperature difference between the inlet oil temperature and the outlet oil temperature of the fuel tank; determine the second oil top temperature rise and the temperature difference based on the oil temperature difference The temperature rise of the second oil base.

Based on the method and system for determining the temperature rise of off-line oil in the forced oil circulation mode provided by the above-mentioned embodiments of the present invention, the method includes: determining the temperature rise of the oil bottom, the temperature rise of the oil top, and the average temperature rise of the oil; The liquid heat transfer parameters corresponding to the bottom temperature rise, oil top temperature rise and oil average temperature rise can be calculated to obtain the oil velocity and oil flow distribution inside the coil of the transformer; through the calculated oil velocity and oil flow distribution, the forced oil flow can be determined. The temperature rise of the line oil of the coil in the circulation mode. In this scheme, the liquid heat transfer parameters corresponding to the oil bottom temperature rise, oil top temperature rise and oil average temperature rise are used to calculate the oil speed and oil flow distribution inside the coil of the transformer, and then through the oil speed and oil flow distribution It is determined to obtain an accurate line oil temperature rise, thereby reducing the difficulty of controlling the coil temperature rise or avoiding excessive temperature rise margin.

Description of drawings

In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings that need to be used in the description of the embodiments or the prior art. Obviously, the accompanying drawings in the following description are only It is an embodiment of the present invention, and those skilled in the art can also obtain other drawings according to the provided drawings without creative work.

Fig. 1 is a flow chart of a method for determining the temperature rise of off-line oil in a forced oil circulation mode provided by an embodiment of the present invention;

Fig. 2 is a schematic diagram of the oil distribution of the winding and the oil guide box part provided by the embodiment of the present invention;

Fig. 3 is a schematic diagram of the pressure drop of two paths of a wire cake provided by the embodiment of the present invention;

Fig. 4 is a schematic diagram of the cooling temperature of the transformer provided by the embodiment of the present invention;

FIG. 5 is a schematic diagram of a grid provided by an embodiment of the present invention;

FIG. 6 is a schematic diagram of a grid part provided by an embodiment of the present invention;

Fig. 7 is a schematic diagram of grid elements of two line pies with intermediate horizontal oil passages provided by an embodiment of the present invention;

Fig. 8 is a flow chart for determining the oil bottom temperature rise, oil top temperature rise and oil average temperature rise of a transformer provided by an embodiment of the present invention;

Fig. 9 is a structural block diagram of a system for determining the temperature rise of off-line oil in forced oil circulation mode provided by an embodiment of the present invention.

Detailed ways

The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only some, not all, embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by persons of ordinary skill in the art without making creative efforts belong to the protection scope of the present invention.

In this application, the term "comprises", "comprises" or any other variation thereof is intended to cover a non-exclusive inclusion such that a process, method, article, or apparatus comprising a set of elements includes not only those elements, but also includes none. other elements specifically listed, or also include elements inherent in such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising a ..." does not exclude the presence of additional identical elements in the process, method, article or apparatus comprising said element.

It can be seen from the background technology that the distribution of transformer oil between different coils does not match the heat loss of the coil itself, which will cause a large difference in the temperature rise of the line oil of different coils, which will increase the difficulty of controlling the temperature rise of the coils. Or it will cause the temperature rise margin to be too large.

Therefore, the embodiment of the present invention provides a method and system for determining the temperature rise of off-line oil in the forced oil circulation mode, using the liquid heat transfer parameters corresponding to the temperature rise of the oil bottom, the temperature rise of the oil top, and the average temperature rise of the oil to calculate The oil speed and oil flow distribution inside the coil of the transformer, and then determine the accurate line oil temperature rise through the oil speed and oil flow distribution, which can reduce the difficulty of controlling the coil temperature rise or avoid excessive temperature rise margins.

It should be noted that in this scheme, various equations, linear interpolation and Newton iteration method (Newton-Raphson iteration method) are used to calculate the oil temperature rise (oil bottom temperature rise, oil top temperature rise and oil average temperature rise, etc. ), oil flow distribution and line oil temperature rise; the influence of the process coefficient is introduced in the calculation process, and the calculation results are corrected according to the actual situation, so as to obtain a more accurate line oil temperature rise; the following explains this scheme through various embodiments illustrate.

Referring to Fig. 1, it shows a flow chart of a method for determining the temperature rise of off-line oil in the forced oil circulation mode provided by an embodiment of the present invention. The determination method includes:

Step S101: Determine the oil bottom temperature rise, oil top temperature rise and oil average temperature rise of the transformer.

In the process of implementing step S101, the effective heat dissipation area and actual cooling capacity of the oil tank of the transformer are calculated, and the oil bottom temperature rise, oil top temperature rise and oil average temperature rise of the transformer are calculated by Newton iteration method. Specifically, using the Newton-Raphson method (Newton-Raphson method), combined with the total loss of the transformer, the heat dissipation capacity of the oil tank and the actual cooling capacity, the temperature rise of the oil bottom, the temperature rise of the oil top and the average temperature rise of the oil are calculated. The specific calculation method as follows:

The initial oil average temperature rise, initial oil top temperature rise and initial oil bottom temperature rise are obtained as the average temperature rise of the oil to be treated, the temperature rise of the top of the oil to be treated and the temperature rise of the bottom of the oil to be treated respectively. The actual cooling capacity of the oil tank of the transformer is calculated by using the average temperature rise of the treated oil, the temperature rise of the top of the oil to be treated and the temperature rise of the bottom of the oil to be treated. Through the actual cooling capacity, determine the average temperature rise of the first oil, the temperature rise of the first oil top and the temperature rise of the first oil bottom.

If the difference between the average temperature rise of the first oil and the average temperature rise of the initial oil is less than the threshold (such as 0.1), output the average temperature rise of the first oil, the temperature rise of the first oil top and the temperature rise of the first oil bottom as the oil bottom of the transformer Temperature rise, oil top temperature rise and oil average temperature rise.

If the difference between the average temperature rise of the first oil and the average temperature rise of the initial oil is greater than or equal to the threshold value, the corresponding average temperature rise of the second oil is found by approximation according to the energy balance and Newton iteration method, and the second oil average temperature rise is used to determine the second Oil top temperature rise and second oil bottom temperature rise. Specifically, the second oil average temperature rise is used to calculate the oil temperature difference between the inlet oil temperature and the outlet oil temperature of the fuel tank; based on the oil temperature difference, the second oil top temperature rise and the second oil bottom temperature rise are determined.

Update the average temperature rise of the oil to be processed, the temperature rise of the top of the oil to be processed, and the temperature rise of the bottom of the oil to be processed to the average temperature rise of the second oil, the temperature rise of the second oil top, and the temperature rise of the second oil bottom respectively, and return to the execution of the above "utilization The average temperature rise of the treated oil, the temperature rise of the top of the oil to be treated and the temperature rise of the bottom of the oil to be treated, and the actual cooling capacity of the oil tank of the transformer are calculated".

In some embodiments, the actual cooling capacity of the oil tank of the transformer is calculated by formula (1).

In formula (1), k1 and k2 are specified coefficients; the value range of k1 is 0.1-0.6 in the case of normal painting, and the value range of k1 is 0.01-0.3 in the case of metal surface; the value range of k2 0.9-1.3; At is the heat dissipation area of the fuel tank (the heat dissipation area is only the top area when there is a soundproof cover, and the heat dissipation area is the sum of the surrounding area and the top area under normal conditions); ΔT _av is the average oil temperature rise of the fuel tank (that is, the weighted average temperature).

It should be noted that the effective heat dissipation area of the oil tank is 60% of the actual heat dissipation area. Generally, the rated cooling capacity (including the cooler) refers to the cooling capacity when the temperature rise is 40K, so it needs to be converted to the actual temperature when calculating the actual cooling capacity. Lower cooling capacity. Specifically, the definition of the cooling capacity of the cooler is determined by the national standard, and the cooling capacity is converted by using the difference between the actual imported oil temperature and the ambient temperature, so as to obtain the actual cooling capacity.

It should be further explained that the average oil temperature rise of the fuel tank = (oil bottom temperature rise * coil partial area + oil top temperature rise * fuel tank top temperature)/total heat dissipation area of the fuel tank.

Step S102: Using liquid heat transfer parameters corresponding to oil bottom temperature rise, oil top temperature rise, and oil average temperature rise, calculate the oil velocity and oil flow distribution inside the coil of the transformer.

It should be noted that different oil bottom temperature rises, oil top temperature rises, and oil average temperature rises will lead to changes in liquid heat conduction parameters (such as thermal conductivity, specific heat capacity, density, viscosity), so the oil bottom temperature rise, oil top temperature The liquid heat transfer parameters corresponding to the temperature rise and the average oil temperature rise are calculated to obtain the oil velocity and oil flow distribution inside the coil of the transformer.

In the process of implementing step S102, the liquid heat transfer parameters corresponding to the temperature rise of the oil bottom, the temperature rise of the oil top and the average temperature rise of the oil are used to analyze the preset pressure drop equation to determine the corresponding pressure drop data; From the pressure drop data, the oil velocity and oil flow distribution inside the coil of the transformer are calculated.

Specifically, through the calculated oil bottom temperature rise, oil top temperature rise, and oil average temperature rise, the corresponding liquid heat transfer parameters (equivalent to oil performance parameters) are determined; combined with the actual oil circuit conditions and the preset pressure drop According to the equation, the pressure drop data of the oil pressure drop of the union pipe, the oil pressure drop of the angle ring system, the pressure drop of the oil guide hole, and the local pressure drop loss of the winding are calculated respectively. The sum of the oil pressure drop of the union pipe, the oil pressure drop of the angle ring system, the pressure drop of the oil guide hole, and the local pressure drop loss of the winding is equal to the pressure head of the fluid passing through the winding.

In some embodiments, a system of equations equal to the horizontal oil passage is determined according to the pressure drop balance around the line cake; due to the continuity of the oil (that is, the sum of the oil flow in the horizontal oil passage is equal to the total amount of oil flow), a nonlinear equation can be constructed By analyzing the nonlinear equations, the oil velocity and oil flow distribution inside the coil of the transformer can be obtained, as well as the oil flow.

In some embodiments, the pressure drop equation mentioned above includes the pressure drop balance equation of the overall flow path, the pressure drop balance equation of the body flow path, the pressure drop equation of the oil guide hole, the pressure drop equation of the corner ring system, etc.; Each pressure drop equation is explained separately.

Description of the pressure drop balance equation for the overall flow path:

The total oil quantity Q mainly depends on the pump capacity of the cooling system, and the winding pressure drop reduced by the pressure head generated by the buoyancy can be added to the cooling system pressure drop; the Bernoulli equation of the flow path through the cooler and the winding is as the formula ( 2), formula (2) is the pressure drop balance equation of the overall flow path.

ΔP _pump ＝ΔP _fcooler +ΔP _ft +ΔP _d1 +ΔP _f1 -g·h(ρ(T _b )-ρ(T ₁ )) (2)

In formula (2), ΔP _fcooler is the pressure drop of the cooling equipment outside the tank and the pipeline, ΔP _ft is the pressure drop of the pressure chamber in the pipeline and the oil tank, ΔP _d1 is the pressure drop in the oil guide (throttle) hole, and ΔP _f1 is Winding friction pressure drop, T _b is the oil temperature at the bottom, T ₁ is the average temperature of the coil, h is the height difference from the top to the bottom of the coil, ρ is the density of the oil, g h(ρ(T _b )-ρ(T ₁ ) ) is the buoyancy pressure head, g=9.8N/kg.

Explanation on the pressure drop balance equation of the body flow path:

It can be seen from the schematic diagram of the oil distribution of the winding and the oil guide box shown in Figure 2 that according to the Bernoulli equation, since the three different paths in Figure 2 start from the same point at the bottom and end at the same point on the top, the three different paths in Figure 2 The total pressure change is the same; based on the foregoing, the equations of a transformer with two physical windings (the number is only an example) can be obtained, and the equations include formula (3) to formula (5).

P ₁ -P ₂ =ρ(T _m1 )·g·h+ΔP _f1 +ΔP _d1 (3)

P ₁ -P ₂ =ρ(T _m2 )·g·h+ΔP _f2 +ΔP _d2 (4)

P ₁ -P ₂ =ρ(T _m3 )·g·h+ΔP _fs (5)

In formula (3) to formula (5), ΔP _f1 and ΔP _f2 are the friction pressure drop of the winding, ΔP _d1 and ΔP _d2 are the pressure drop in the oil guide hole (to provide the required oil flow), ΔP _fs is Bypass hole (pressure relief hole) pressure drop.

It should be noted that ΔP _f1 and ΔP _f2 are only related to oil flow; coil average oil temperatures T _m1 and T _m2 can be calculated from coil loss and oil flow; the density function is known, that is, ρ(T) is also related to oil flow ; If the total oil quantity is known, it means that the unknown quantities in formula (3) to formula (5) are ΔP _d1 , ΔP _d2 , ΔP _fs , P ₁ -P ₂ . Wherein, ΔP _fs can be determined by formula (6).

In the formula (6), Q _fs is the flow rate of the bypass holes, T _m3 is the average temperature of the oil, and A _by is the area of all the bypass holes on one side.

According to the size and quantity of the bypass hole, the required pressure drop under the specified oil flow rate can be obtained, and the pressure drop in the hole is a function of the oil flow, and Q ₁ , Q ₂ and Q can be calculated by combining the following formula (7). _fs .

Q _tot ＝(Q ₁ +Q ₂ +Q _fs )*Nlimb (7)

In formula (7), Q ₁ is the oil flow of coil 1, Q ₂ is the oil flow of coil 2, Q _tot is the total oil flow, and Nlimb is the stem volume.

It should be noted that ΔP _f1 and ΔP _f2 are functions of Q ₁ and Q ₂ respectively, and T _m1 and T _m2 may also be functions of Q ₁ and Q ₂ , so it can be calculated by integrating the above formula (3) to formula (7) Q ₁ , Q ₂ , and Q _fs .

Explanation on the pressure drop equation of the oil guide hole:

The pressure drop of the oil guide hole can be calculated by the flow velocity, specifically, it can be calculated by the formula (8),

In formula (8), u _s is the flow rate of oil passing through the oil guide hole (in m/s), ζ is the hole pressure drop coefficient, and ρ is the density of oil (in kg/m ³ ).

It should be noted that u _s can be calculated by using the coil oil flow Q _wi , specifically, u _s can be calculated by formula (9).

In formula (9), N _ho is the hole number of winding i, d _ho is the hole diameter, and Q _wi is the oil flow rate of coil i.

By combining formula (8) and formula (9), formula (10) can be obtained.

It should be noted that when the Reynolds number ≥ 10 ⁴ , the pore pressure drop coefficient ζ is about 2.6-3.8; when the Reynolds number is < 10 ⁴ -10 ⁵ , the pore pressure drop coefficient ζ is about 1.8-2.4; The reduction coefficient ζ can be determined by formula (11) and formula (12).

和

为不同雷诺数下的经验系数。In formula (11) and formula (12), Re _is Reynolds number, V is kinematic viscosity (unit is m ² /s),

and

is the empirical coefficient at different Reynolds numbers.

Explanation of the pressure drop equation for the corner ring system:

The pressure drop equation of the corner ring system is shown in formula (13).

ΔP _collar = (F1*Q+F2*NY)×ρ×Q(13)

In the formula (13), F1 is the pressure drop coefficient (related to the local resistance coefficient, and related to the angle ring form), F2 is the pressure drop coefficient (related to the channel pressure drop, and related to the side ratio coefficient of the oil channel, each The length of the pipeline, the equivalent diameter of the channel, the distance between the angle rings and the circumference of the oil passage are related), Q is the oil flow rate, NY is the kinematic viscosity, and ρ is the density of the oil.

Explanation of the pressure drop balance equation of the oil baffle (or oil baffle):

It should be noted that each winding has multiple oil baffles, through which the windings are partitioned; a partition is formed between every two oil baffles, and the sum of the pressure drop of all partitions is the pressure drop of the entire winding. After calculating the pressure drop balance for each zone, the oil velocity and oil flow in the winding can be calculated.

Specifically, the oil velocity and oil flow in the winding can be solved by the following equations a to c.

Equation a: Based on the pressure drop balance around the line cake, the number of equations that can be formed is equal to the number of horizontal oil passages minus 1. Equation b: Form an equation based on oil continuity (ie, the sum of the oil flow in the horizontal pipeline is equal to the total amount of oil flow). Equation c: Based on the pressure head of the winding is equal to the pressure drop forms an equation.

Since the pressure drop balance includes the velocity in the horizontal oil passage (which is an unknown quantity), the number of unknowns is equal to the number of horizontal oil passages; other unknowns are the total oil flow; the velocity of the vertical pipeline can be determined by the velocity of the horizontal oil passage and the total oil flow flow is determined. This means that the number of unknowns is equal to the number of horizontal oil passages+1 (the number of oil passages+1), and since there are equations of the number of oil passages+1, the above equations a to c are solvable. However, the above equations a to c contain unknowns of nonlinear functions, so they need to be solved by a numerical method for solving nonlinear equation systems by computer.

When calculating the pressure drop balance in the two oil baffles, it can be seen from the schematic diagram of the pressure drop of two paths of a line pie shown in Figure 3, define two lines around each line pie 1-3-4 and 1-2-4 The static pressure changes on different paths can be used to obtain the equations required to solve the oil velocity, and then a series of equations (the number of oil passages - 1). In the case of a given oil flow, continuity defines that the sum of the oil flows in the horizontal oil passage is equal to the total oil flow, and the following formula (14) can be obtained based on the Bernoullis equation.

In formula (14), P1 is the pressure at position 1 in Fig. 3, P2 is the pressure at position 2 in Fig. 3, ΔP _f is the friction loss, V ₁ is the oil velocity at position 1, and V ₂ is the oil at position 2 speed, h ₁ is the height of position 1, and h ₂ is the height of position 2.

The formula (15) should be satisfied for the upper and lower paths of each line cake of the coil.

ΔP _ai + ΔP _bi + ΔP _exi + ΔPdin + ΔPein + ΔPcin = ΔP _{ai + 1} + ΔP _{bi + 1} + ΔP _{exi + 1} + ΔPdout + ΔPeout + ΔPcout (15)

In formula (15), ΔP _ai is the static pressure drop at the inlet of the 1-2-4 path in Fig. 3, and ΔP _bi is the frictional pressure drop in the horizontal oil passage of the 1-2-4 path in Fig. 3 (with Z _frh (U _i ) correlation), ΔP _exi is the static pressure drop at the outlet of the 1-2-4 path in Fig. 3, ΔPdin is the frictional pressure drop of the vertical oil passage in the 1-2-4 path in Fig. The buoyancy pressure head of the vertical oil channel in the 4 path, ΔPcin is the increase of the oil flow rate of the vertical oil channel when the oil in the oil channel of node i+1 enters the vertical pipeline, and ΔP _ai+1 is the static pressure at the inlet of the path 1-3-4 in Figure 3 ΔP _bi+1 is the friction pressure drop of the 1-3-4 path in the horizontal oil channel in Figure 3, ΔP _exi+1 is the static pressure drop (0) at the outlet of the 1-3-4 path in Figure 3, and ΔPdout is The frictional pressure drop of the vertical oil passage outside the path 1-3-4 in Figure 3, ΔPeout is the buoyancy pressure head of the vertical oil passage outside the path 1-3-4 in Figure 3, and ΔPcout is the oil flowing to the i+1 oil passage The pressure change caused by the reduction of the oil flow velocity in the vertical oil passage when part of the outflow, _Ui is the average velocity, and _Zfrh is the friction pressure drop function (the performance of the fluid is given as a function including temperature).

It can be understood that the solution to the velocity distribution must make the sum of the oil flows between the horizontal oil passages equal to the oil flow 1 input at the bottom of the separator, which makes the additional oil flow continuity equation as in Equation (16).

In formula (16), A _I is the cross-sectional area of the I-th oil passage (the area of the oil passage perpendicular to the oil flow direction), U _I is the oil flow rate of the I-th oil passage, and NK is the two gears in the winding The number of oil passages between oil rings.

Combining the above formulas (15) and (16), the pressure drop between the two oil retaining rings can be calculated by formula (17).

The pressure recovery due to the velocity reduction in the vertical pipe is given by Equation (18).

In the formula (18), K1 is an empirical coefficient (such as 1.1625), U _OUT is the speed of the horizontal oil passage (the speed of the outer vertical oil passage), and the subscripts 1 and 0 of U _OUT are equivalent to the selection of i in Figure 3 value.

The static pressure drop due to the acceleration of the oil flow into the horizontal pipe is given by Equation (19).

In formula (19), K2 is an empirical coefficient (such as 1.55), and U ₁ is the speed of the coil oil passage.

The specific content of laminar pressure drop in the horizontal oil passage is as formula (20) and formula (21).

ΔP _b1 =Z _frh (U ₁ )(20)

ΔP _exi =0(21)

In formula (21), Z _frh is the friction pressure drop function.

In the vertical pipeline between the guide rings, the pressure drop of the friction pipeline and the number of oil passages between the two guide rings are summed by formula (22).

In a vertical duct intersecting with a horizontal duct, the static pressure drop resulting from the increase in velocity is given by Equation (23).

In the formula (23), U _ink is the speed of the inner vertical oil circuit (between the paper cylinder and the coil in the body).

In some embodiments, the total voltage drop of the winding is calculated by formula (24).

ΔP _totW = (NP-1)*ΔP _g +ΔP _collar (24)

In formula (24), NP is the number of oil deflector rings, ΔP _g is the pressure drop of two oil deflector rings, and ΔP _collar is the pressure drop of the bottom insulating angle ring system.

In some embodiments, when the fluid is heated by the wall, the velocity distribution of the horizontal oil gallery will be disturbed by the natural convection generated by the wall heating during the calculation of the friction loss in the oil gallery; this heat-generated flow is perpendicular to The general direction of flow, like turbulent flow, increases the pressure drop. Another effect caused by heating is the temperature-dependent change in viscosity across the flow cross-section (which also affects pressure drop); considering the two aforementioned effects, equation (25) is obtained.

f _h =f _v *[1+C] (25)

In formula (25), f _h is the coefficient of the temperature change between the complementary wall and the fluid, f _v is the coefficient related to the Prandtl number of the surface temperature of the coil and the Prandtl number of the average oil temperature, and C is the coefficient perpendicular to the general flow The coefficient of the additional pressure drop of the natural convection engine in the direction (related to the Grashof number).

In some embodiments, if the oil circulation of the external cooler is generated by a pump during the calculation of the head pressure, and if the oil goes directly to the oil tank (not to the windings), this is called forced oil. Assume that excess oil is pumped in so that part of the oil flows between the winding and the oil tank, thereby making the temperature change of the transformer as shown in the schematic diagram of the cooling temperature of the transformer provided in Fig. 4 .

Oil at the same temperature as the bottom of the tank (TB in Figure 4) is available in the upper part of the winding; at the top of the tank, hot oil from the winding is mixed with cold oil passing outside the winding, marked by lines in Figure 4 Area (1-2-3-1) provides the available indenter for winding 1, the specific content of the indenter is as formula (26).

ΔP ₁ =∮ρ*g*d _h (26)

In formula (26), d _h is the height of the winding.

Combining the above contents, it can be seen that the pressure head of each winding can be expressed as a function of an unknown quantity Q, and the specific content is shown in formula (27) and formula (28).

In formula (27) and formula (28), _P1 is the coil loss, Q1 is the coil flow rate, Cp is the specific heat capacity of oil, and γ is the coefficient of oil density change with temperature.

The above content is related to the pressure drop balance equation. The pressure drop data will affect the oil velocity and oil flow distribution; therefore, the pressure drop data can be calculated through the pressure drop balance equation, and then the oil velocity and oil flow distribution can be calculated using the pressure drop data.

Step S103: Determine the line oil temperature rise of the coil in the forced oil circulation mode through the calculated oil velocity and oil flow distribution.

In the process of implementing step S103, the conductor temperature is obtained by analyzing the preset conductor temperature calculation model and oil temperature calculation model through the calculated oil velocity and oil flow distribution. Determine the difference between the conductor temperature and the average oil temperature of the transformer to obtain the line oil temperature rise of the coil in forced oil circulation mode.

That is to say, the difference between the conductor temperature and the average oil temperature of the transformer is calculated, and the difference is the line oil temperature rise; or in other words, the line oil temperature rise = conductor temperature - oil average temperature.

In some embodiments, the relevant content of the conductor temperature calculation model and the oil temperature calculation model are respectively explained through the following content.

Explanation on the conductor temperature calculation model:

It should be noted that when the amount of oil passing through the coil is known, and the temperature difference between the top and the bottom is also known, the speed difference of the horizontal oil passage between the two oil retaining rings is relatively large, which means The oil in the low velocity line (and the adjacent wire cake) will reach a higher temperature than the oil in the high velocity line (and the adjacent oil pan).

Based on the above content, when calculating the temperature distribution between the two oil deflecting rings, the area between the two oil deflecting rings is divided into grids, and the grids obtained by division can be seen in the grid schematic diagram provided in Figure 5, the conductor and oil passages are included in this mesh.

In the grid schematic diagram provided in Figure 5, the number of radial divisions is determined by the number of conductors, and the number of axial divisions is determined by the number of horizontal pipes between the two oil rings; specifically, the grid points can be calculated by formula (29) total.

N _M ＝(N _C +2)*(2*N _K +1)(29)

In formula (29), N _c is the number of conductors on a line cake, and N _k is the number of horizontal oil passages.

It can be understood that in FIG. 5 , (Ti,j) represents the average temperature of the rectangle, which can be considered as the temperature and heat source in the rectangle are all concentrated in the center of the rectangle. Inside the conductor, heat is dissipated uniformly at the rate Pw. Thermal resistance in conductors is negligible. It is shown by finite element calculations that all isotherms are concentrated on the insulator, which means that the temperature difference over the insulator is negligible and the area of copper is also negligible.

As shown in the schematic diagram of the grid part shown in FIG. 6 , the grid part can be represented by a thermal resistance grid. The specific contents of the thermal resistances R ₂₅ and R ₄₅ in Fig. 6 are as formula (30). The thermal resistances R ₁₅ and R ₃₅ are composed of the heat conduction in the insulating material and the heat transfer between the insulation and the oil, and the specific content is shown in formula (31).

In formula (30) and formula (31), I is the insulation thickness (both sides, in m), λ _i is the thermal conductivity of the insulating material (w/m/k), and A _V is the contact between copper wires Area, A _H is the surface area of the oil passage of the turn wire, and α is the heat transfer coefficient between the oil and the insulation (w/m^2*k).

No additional heat is stored at a point when the steady state is reached, so Equation (32) and Equation (33) can be determined.

∑P _ij +P _w *dV＝0(33)

In formula (32) and formula (33), P _ij is the heat flow from grid point i to j, dV is the conductor volume, T _i is the temperature at point i, T _j is the temperature at point j, and R _ij is the temperature from point i to point j. The thermal resistance at point j, P _w is the loss per unit volume.

This concludes the description of the conductor temperature calculation model.

Explanation about the oil temperature calculation model:

When the oil flow is in the horizontal oil passage, the oil flow is heated from both sides, as shown in Figure 7. The schematic diagram of the mesh elements of the two line cakes with the middle horizontal oil passage, the heat of conductor 1 and conductor 3 passes through the conduction in the insulation and the oil The convection in the flow passes into the oil; the oil flows from point "5" to point "4" and then heats from T5 to T4. According to the energy balance, formula (34) can be obtained, and formula (34) is the oil temperature calculation model.

When R ₁₅ =R ₃₅ , formula (35) can be determined.

In formula (34) and formula (35), T ₁ to T ₅ are the temperatures of points "1" to "5", C _P0 is the specific heat capacity, U is the oil velocity in the oil passage, and Ai is the area through which the oil passage passes.

The effective cooling area of the conductor to the pipe is as formula (36).

A _H ＝(π*D-Nw*W)*(b+(Cc-1)*i) (36)

In formula (36), Nw is the number of pads, W is the width of pads, b is the width of a single wire, Cc is a correction coefficient (value range is 0-1), and i is the thickness of double-sided insulation.

The overall heat transfer coefficient α _tot is defined as formula (37).

In formula (37), α is the heat transfer coefficient between the insulation and the oil, and _λi is the thermal conductivity of the insulation.

It should be noted that the correction term Cc is introduced to compensate for the fact that the heat flow in the insulation is not completely one-dimensional. The heat from the conductor not only flows to the oil passage through the conductor width, but also part of the insulation width is helpful for heat transfer; Cc is related to the total heat transfer The correction coefficient related to the thermal coefficient α _tot , the value of Cc can be 0.8.

The above is the relevant description about the oil temperature calculation model.

When the heat transfer coefficient and area are known, a system of equations contains an equation in which the sum of the heat generated by each grid point, the heat input, and the heat output is zero, and the line oil of the coil can be obtained by solving this system of equations temperature rise.

Specifically, since the oil velocity and oil flow distribution affect the conductor temperature calculation model and the oil temperature calculation model, the conductor temperature can be obtained by solving the conductor temperature calculation model and the oil temperature calculation model, so that the coil line under the forced oil circulation mode can be calculated Oil temperature rises. Specific analysis of formula (32), formula (33) and formula (34) can get the conductor temperature.

From the above steps S101 to S103, it can be seen that this solution calculates the oil flow resistance value of each coil under different oil flow rates through the resistance of the transformer oil flowing in the body; the oil flow resistance values in different coils should be equal The principle of determining the oil flow distribution in the different coils. Then, through iterative calculation of the oil flow distribution and the actual oil flow, the oil flow distribution between the coils and the actual oil flow can meet the resistance balance and resistance and power balance in the body at the same time, and finally determine the actual oil flow and the oil flow of each coil, etc. data. After completing the calculation of the flow characteristics of the transformer oil during the operation of the transformer, the line oil temperature rise of the coil can be calculated.

In the embodiment of the present invention, the liquid heat transfer parameters corresponding to the oil bottom temperature rise, oil top temperature rise, and oil average temperature rise are used to calculate the oil velocity and oil flow distribution inside the coil of the transformer, and then through the oil velocity and The oil flow distribution determines the accurate line oil temperature rise, which can reduce the difficulty of controlling the coil temperature rise or avoid excessive temperature rise margin.

In order to better explain the determination of the oil bottom temperature rise, oil top temperature rise and oil average temperature rise of the transformer involved in step S101 of FIG. 1 in the above-mentioned embodiment of the present invention, the oil bottom temperature rise, oil The flow chart of top temperature rise and oil average temperature rise is illustrated as an example, and Fig. 8 includes the following steps:

Step S801: Obtain the initial oil average temperature rise, the initial oil top temperature rise, and the initial oil bottom temperature rise as the average temperature rise of the oil to be treated, the temperature rise of the oil top to be processed, and the temperature rise of the oil bottom to be treated respectively.

Step S802: Calculate the actual cooling capacity of the oil tank of the transformer by using the average temperature rise of the treated oil, the temperature rise of the top of the oil to be treated, and the temperature rise of the bottom of the oil to be treated.

In the process of implementing step S802, the corresponding actual cooling capacity is calculated by using the average temperature rise of the treated oil, the temperature rise of the top of the oil to be treated and the temperature rise of the bottom of the oil to be treated, combined with the consumption and the cooling capacity of the oil tank.

Step S803: Calculate the average temperature rise of the first oil under the actual cooling capacity, and calculate the oil temperature difference between the inlet oil temperature and the outlet oil temperature.

Step S804: Calculate the first oil top temperature rise and the first oil bottom temperature rise.

Step S805: Whether the difference between the average temperature rise of the first oil and the average temperature rise of the initial oil is less than 0.1. If yes, execute step S806; if not, execute step S807.

Step S806: Jump out of the loop and output the first average oil temperature rise, the first oil top temperature rise, and the first oil bottom temperature rise as the oil bottom temperature rise, oil top temperature rise, and oil average temperature rise of the transformer.

Step S807: Find the corresponding average temperature rise of the second oil by approximation according to energy balance and Newton iteration method.

Step S808: Calculate the oil temperature difference between the inlet oil temperature and the outlet oil temperature of the fuel tank.

Step S809: Determine the second oil top temperature rise and the second oil bottom temperature rise based on the oil temperature difference, and update the average temperature rise of the oil to be processed, the temperature rise of the top of the oil to be processed, and the temperature rise of the bottom of the oil to be processed to the second oil average temperature rise, respectively. The temperature rise, the second oil top temperature rise and the second oil bottom temperature rise return to step S802.

The above are the relevant instructions on determining the line oil temperature rise in the forced oil circulation mode. After the line oil temperature rise is determined, if the obtained line oil temperature rise makes the winding temperature rise exceed the agreement set value or the national standard value, The temperature rise of the line oil can be re-determined by modifying the parameters of the oil guide box, the parameters of the oil passages of the inner and outer body, the parameters of the oil baffle plate, the parameters of the angle ring system and the relevant parameters of the coil, until the determined temperature rise of the line oil meets the standard.

Corresponding to the method for determining the off-line oil temperature rise in the forced oil circulation mode provided by the above-mentioned embodiment of the present invention, see Fig. 9, the embodiment of the present invention also provides a system for determining the off-line oil temperature rise in the forced oil circulation mode A block diagram of the structure, the determination system includes: a first determination unit 901, a calculation unit 902 and a second determination unit 903;

The first determination unit 901 is used to determine the oil bottom temperature rise, oil top temperature rise and oil average temperature rise of the transformer.

The calculation unit 902 is used to calculate the oil velocity and oil flow distribution inside the coil of the transformer by using the liquid heat transfer parameters corresponding to the oil bottom temperature rise, the oil top temperature rise and the oil average temperature rise.

In a specific implementation, the calculation unit 902 is specifically used to: use the liquid heat transfer parameters corresponding to the oil bottom temperature rise, oil top temperature rise, and oil average temperature rise to analyze the preset pressure drop equation to determine the corresponding pressure drop Data; through the pressure drop data, calculate the oil speed and oil flow distribution inside the coil of the transformer.

The second determination unit 903 is configured to determine the line oil temperature rise of the coil in the forced oil circulation mode through the calculated oil velocity and oil flow distribution.

In a specific implementation, the second determining unit 903 is specifically configured to: analyze the preset conductor temperature calculation model and oil temperature calculation model to obtain the conductor temperature through the calculated oil velocity and oil flow distribution; determine the conductor temperature and the transformer The difference between the average temperature of the oil to obtain the line oil temperature rise of the coil under the forced oil circulation mode.

In the embodiment of the present invention, the liquid heat transfer parameters corresponding to the oil bottom temperature rise, oil top temperature rise, and oil average temperature rise are used to calculate the oil velocity and oil flow distribution inside the coil of the transformer, and then through the oil velocity and The oil flow distribution determines the accurate line oil temperature rise, which can reduce the difficulty of controlling the coil temperature rise or avoid excessive temperature rise margin.

Preferably, in combination with the content shown in FIG. 9, the first determination unit 901 includes: an acquisition module, a calculation module, a determination module, an output module, a processing module, and an update module; the execution principles of each module are as follows:

The obtaining module is used to obtain the initial oil average temperature rise, the initial oil top temperature rise and the initial oil bottom temperature rise as the average temperature rise of the oil to be processed, the temperature rise of the oil top to be processed and the temperature rise of the oil bottom to be processed respectively.

The calculation module is used to calculate the actual cooling capacity of the oil tank of the transformer by using the average temperature rise of the treated oil, the temperature rise of the top of the oil to be treated and the temperature rise of the bottom of the oil to be treated.

The determination module is used to determine the average temperature rise of the first oil, the temperature rise of the first oil top and the temperature rise of the first oil bottom through the actual cooling capacity.

An output module, configured to output the average temperature rise of the first oil, the temperature rise of the first oil top, and the temperature rise of the first oil bottom as the oil temperature rise of the transformer if the difference between the average temperature rise of the first oil and the average temperature rise of the initial oil is less than a threshold value. Bottom temperature rise, oil top temperature rise and average oil temperature rise.

The processing module is used to find the corresponding average temperature rise of the second oil by approximation according to the energy balance and the Newton iteration method if the difference between the average temperature rise of the first oil and the average temperature rise of the initial oil is greater than or equal to the threshold value, and through the second The average oil temperature rise determines the second oil top temperature rise and the second oil bottom temperature rise.

In a specific implementation, the processing module is specifically used to: use the second average oil temperature rise to calculate the oil temperature difference between the inlet oil temperature and the outlet oil temperature of the fuel tank; determine the second oil top temperature rise and the second oil bottom temperature rise based on the oil temperature difference .

an update module, configured to update the average temperature rise of the oil to be processed, the temperature rise of the top of the oil to be processed, and the temperature rise of the bottom of the oil to be processed into the average temperature rise of the second oil, the temperature rise of the second oil top, and the second temperature rise of the bottom of the oil, respectively, Returns the execution calculation module.

In summary, the embodiments of the present invention provide a method and system for determining the temperature rise of off-line oil in the forced oil circulation mode, using the liquid heat transfer parameters corresponding to the temperature rise of the oil bottom, the temperature rise of the oil top and the average temperature rise of the oil , calculate the oil speed and oil flow distribution inside the coil of the transformer, and then determine the accurate line oil temperature rise through the oil speed and oil flow distribution, so as to reduce the difficulty of controlling the coil temperature rise or avoid excessive temperature rise margins .

Each embodiment in this specification is described in a progressive manner, the same and similar parts of each embodiment can be referred to each other, and each embodiment focuses on the differences from other embodiments. In particular, for the system or the system embodiment, since it is basically similar to the method embodiment, the description is relatively simple, and for related parts, please refer to the part of the description of the method embodiment. The systems and system embodiments described above are only illustrative, and the units described as separate components may or may not be physically separated, and the components shown as units may or may not be physical units, that is It can be located in one place, or it can be distributed to multiple network elements. Part or all of the modules can be selected according to actual needs to achieve the purpose of the solution of this embodiment. It can be understood and implemented by those skilled in the art without creative effort.

Professionals can further realize that the units and algorithm steps of the examples described in conjunction with the embodiments disclosed herein can be implemented by electronic hardware, computer software or a combination of the two. In order to clearly illustrate the possible For interchangeability, in the above description, the composition and steps of each example have been generally described according to their functions. Whether these functions are executed by hardware or software depends on the specific application and design constraints of the technical solution. Skilled artisans may use different methods to implement the described functions for each specific application, but such implementation should not be regarded as exceeding the scope of the present invention.

The above description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the scope of the invention. Therefore, the present invention will not be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims (10)

1. A method for determining a drop oil temperature rise in a forced oil circulation mode, the method comprising:

determining the oil bottom temperature rise, the oil top temperature rise and the oil average temperature rise of the transformer;

calculating the oil speed and the oil flow distribution inside the coil of the transformer by utilizing the liquid heat transfer parameters corresponding to the oil bottom temperature rise, the oil top temperature rise and the oil average temperature rise;

and determining the temperature rise of the coil oil under the forced oil circulation mode according to the calculated oil speed and oil flow distribution.

2. The method of claim 1, wherein determining the oil bottom temperature rise, the oil top temperature rise, and the oil average temperature rise of the transformer comprises:

acquiring initial oil average temperature rise, initial oil top temperature rise and initial oil bottom temperature rise to be respectively used as the average temperature rise of the oil to be treated, the temperature rise of the oil top to be treated and the temperature rise of the oil bottom to be treated;

calculating the actual cooling capacity of the oil tank of the transformer by utilizing the average temperature rise of the treated oil, the top temperature rise of the oil to be treated and the bottom temperature rise of the oil to be treated;

determining a first average oil temperature rise, a first top oil temperature rise and a first bottom oil temperature rise according to the actual cooling capacity;

if the difference value between the first average oil temperature rise and the initial average oil temperature rise is smaller than a threshold value, outputting the first average oil temperature rise, the first top oil temperature rise and the first bottom oil temperature rise to serve as the bottom oil temperature rise, the top oil temperature rise and the average oil temperature rise of the transformer;

if the difference value of the first average oil temperature rise and the initial average oil temperature rise is larger than or equal to the threshold value, a corresponding second average oil temperature rise is approximately searched according to energy balance and a Newton iteration method, and a second top oil temperature rise and a second bottom oil temperature rise are determined according to the second average oil temperature rise;

and updating the average temperature rise of the oil to be treated, the top temperature rise of the oil to be treated and the bottom temperature rise of the oil to be treated into the second average temperature rise of the oil, the second top temperature rise of the oil and the second bottom temperature rise of the oil respectively, and returning to execute the step of calculating the actual cooling capacity of the oil tank of the transformer by using the average temperature rise of the oil to be treated, the top temperature rise of the oil to be treated and the bottom temperature rise of the oil to be treated.

3. The method of claim 1, wherein calculating an oil velocity and an oil flow distribution inside a coil of a transformer using liquid heat transfer parameters corresponding to the oil bottom temperature rise, the oil top temperature rise, and the oil average temperature rise comprises:

analyzing a preset pressure drop equation by utilizing liquid heat transfer parameters corresponding to the oil bottom temperature rise, the oil top temperature rise and the average oil temperature rise to determine and obtain corresponding pressure drop data;

and calculating the oil speed and the oil flow distribution inside the coil of the transformer according to the pressure drop data.

4. The method of claim 1 or 3, wherein determining the line oil temperature rise of the coil in forced oil circulation by the calculated oil velocity and oil flow distribution comprises:

analyzing a preset conductor temperature calculation model and an oil temperature calculation model through the calculated oil speed and oil flow distribution to obtain the conductor temperature;

determining the difference between the conductor temperature and the average transformer oil temperature to obtain the line oil temperature rise of the coil in a forced oil circulation mode.

5. The method of claim 2, wherein determining a second oil top temperature rise and a second oil bottom temperature rise from the second oil average temperature rise comprises:

calculating an oil temperature difference between the inlet oil temperature and the outlet oil temperature of the oil tank by using the second oil average temperature rise;

a second oil top temperature rise and a second oil bottom temperature rise are determined based on the oil temperature difference.

6. A system for determining a drop in oil temperature in forced oil circulation mode, the system comprising:

the first determining unit is used for determining the oil bottom temperature rise, the oil top temperature rise and the oil average temperature rise of the transformer;

the calculation unit is used for calculating and obtaining the oil speed and the oil flow distribution inside the coil of the transformer by utilizing the liquid heat transfer parameters corresponding to the oil bottom temperature rise, the oil top temperature rise and the oil average temperature rise;

and the second determining unit is used for determining and obtaining the line oil temperature rise of the coil in the forced oil circulation mode through the calculated oil speed and oil flow distribution.

7. The system according to claim 6, wherein the first determination unit comprises:

the system comprises an acquisition module, a temperature control module and a temperature control module, wherein the acquisition module is used for acquiring the average temperature rise of initial oil, the top temperature rise of initial oil and the bottom temperature rise of initial oil to be respectively used as the average temperature rise of oil to be treated, the top temperature rise of oil to be treated and the bottom temperature rise of oil to be treated;

the calculation module is used for calculating the actual cooling capacity of the oil tank of the transformer by utilizing the average temperature rise of the treated oil, the top temperature rise of the oil to be treated and the bottom temperature rise of the oil to be treated;

the determining module is used for determining the first average oil temperature rise, the first top oil temperature rise and the first bottom oil temperature rise according to the actual cooling capacity;

an output module, configured to output the first average oil temperature rise, the first average oil top temperature rise, and the first average oil bottom temperature rise as an oil bottom temperature rise, an oil top temperature rise, and an average oil temperature rise of the transformer if a difference between the first average oil temperature rise and the initial average oil temperature rise is smaller than a threshold;

the processing module is used for approximately searching for corresponding second oil average temperature rise according to energy balance and a Newton iteration method if the difference value of the first oil average temperature rise and the initial oil average temperature rise is larger than or equal to the threshold value, and determining second oil top temperature rise and second oil bottom temperature rise according to the second oil average temperature rise;

and the updating module is used for respectively updating the average temperature rise of the oil to be treated, the top temperature rise of the oil to be treated and the bottom temperature rise of the oil to be treated into the second average temperature rise of the oil, the second top temperature rise of the oil and the second bottom temperature rise of the oil, and returning to execute the calculating module.

8. The system according to claim 6, characterized in that said computing unit is specifically configured to: analyzing a preset pressure drop equation by utilizing liquid heat transfer parameters corresponding to the oil bottom temperature rise, the oil top temperature rise and the average oil temperature rise to determine and obtain corresponding pressure drop data; and calculating the oil speed and the oil flow distribution inside the coil of the transformer according to the pressure drop data.

9. The system according to claim 6 or 8, wherein the second determination unit is specifically configured to: analyzing a preset conductor temperature calculation model and an oil temperature calculation model through the calculated oil speed and oil flow distribution to obtain the conductor temperature; determining the difference between the conductor temperature and the average transformer oil temperature to obtain the line oil temperature rise of the coil in a forced oil circulation mode.

10. The system of claim 7, wherein the processing module is specifically configured to: calculating an oil temperature difference between the inlet oil temperature and the outlet oil temperature of the oil tank by using the second oil average temperature rise; a second oil top temperature rise and a second oil bottom temperature rise are determined based on the oil temperature difference.

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