CN107560757B - Method and system for estimating upper oil temperature of air-cooled transformer - Google Patents

Method and system for estimating upper oil temperature of air-cooled transformer Download PDF

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CN107560757B
CN107560757B CN201710791703.4A CN201710791703A CN107560757B CN 107560757 B CN107560757 B CN 107560757B CN 201710791703 A CN201710791703 A CN 201710791703A CN 107560757 B CN107560757 B CN 107560757B
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thermal resistance
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oil temperature
oil
transformer
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CN107560757A (en
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李题印
屠永伟
邵双
易武
张鹏
闫立伟
孙微庭
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Hangzhou Power Equipment Manufacturing Co Ltd
Hangzhou Power Supply Co of State Grid Zhejiang Electric Power Co Ltd
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Hangzhou Power Equipment Manufacturing Co Ltd
Hangzhou Power Supply Co of State Grid Zhejiang Electric Power Co Ltd
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Abstract

The invention discloses an upper oil temperature estimation method and system for an air-cooled transformer, wherein the method comprises the following steps: acquiring the ambient temperature variation around the transformer of the upper oil temperature model, the load rate at the previous moment, the load rate variation, the transformer no-load loss and the transformer short-circuit loss; obtaining the equivalent thermal resistance of the air side, the equivalent thermal resistance of the insulating oil side and the equivalent thermal capacity in the transformer of the upper oil temperature model; and calculating the upper layer oil temperature change according to an upper layer oil temperature change formula. The method and the system provided by the invention take the environment temperature variation and the load rate into consideration, determine the relationship between the oil temperature variation and the environment temperature and the load coefficient variation, obtain the equation relationship between the variation and the environment temperature and the load coefficient variation according to the state equation of the top layer oil temperature, predict the variation of the top layer oil temperature after the system operation state is changed through the variation, and predict the corresponding variation of the top layer temperature after the system state is changed.

Description

Method and system for estimating upper oil temperature of air-cooled transformer
Technical Field
The invention relates to the technical field of hydraulic electricity, in particular to a method for estimating the upper oil temperature of an air-cooled transformer. In addition, the invention also relates to an upper oil temperature estimation system comprising the air-cooled transformer.
Background
During the peak-to-summer period, the load of the receiving-end power grid is often operated at a high position for a long time. The upper oil temperature of a main transformer of a heavy-duty transformer substation is influenced by various aspects such as load, high-temperature climate, old cooling equipment and the like, the temperature rise of the main transformer substation can reach more than 80 ℃, even higher, and the insulation safety of a main transformer winding is directly endangered. Therefore, the main transformer of the transformer substation is provided with an oil temperature measuring unit to monitor the oil temperature of the upper layer, but after the operation mode of the power grid is changed, the change situation after the oil temperature is estimated, and relevant measures such as increasing the rotating speed of a fan and the like are taken for the out-of-limit oil temperature.
The oil temperature measuring unit in the prior art cannot adjust adaptability along with the change of environment, so that the adaptability of the system is poor.
In summary, how to provide a method for estimating the upper oil temperature of an air-cooled transformer is an urgent problem to be solved by those skilled in the art.
Disclosure of Invention
In view of this, the present invention provides a method and a system for estimating an upper oil temperature of an air-cooled transformer, where the method can accurately estimate a variation trend of the upper oil temperature, and can reflect the variation trend of the upper oil temperature varying with an ambient temperature, so as to enhance an adaptive capacity of the air-cooled transformer.
In order to achieve the above purpose, the invention provides the following technical scheme:
an upper oil temperature estimation method for an air-cooled transformer comprises the following steps:
s1, obtaining environment temperature variation delta theta around the transformer of the upper oil temperature modelaLoad factor k at the previous time0Load factor change delta k, transformer no-load loss P0And short-circuit loss P of transformerk(ii) a Obtaining equivalent heat of the air side of the upper oil temperature modelResistance RathEquivalent thermal resistance R of insulating oil sideothAnd equivalent heat capacity C in the transformerth；
S2, calculating the upper layer oil temperature change delta theta according to the upper layer oil temperature change formulatoThe formula of the upper layer oil temperature change amount is as follows:
Figure BDA0001399388440000021
wherein x is oil index, d delta thetatoAnd/dt is the change rate of the upper oil temperature change.
Preferably, the equivalent thermal resistance R on the air side of the upper oil temperature model is obtained in S1athEquivalent thermal resistance R of insulating oil sideothAnd equivalent thermal capacitance within the transformer, including:
s11, obtaining a corresponding thermoelectric equivalent circuit by an upper oil temperature model of the transformer;
s12, obtaining equivalent thermal resistance R of the air side in the thermoelectric equivalent circuitathEquivalent thermal resistance R of insulating oil sideothAnd equivalent heat capacity C in the transformerth。
Preferably, in S11, the obtaining of the corresponding thermoelectric equivalent circuit from the upper oil temperature model of the transformer includes:
the heat pump in the upper oil temperature model is equivalent to a power supply in the thermoelectric equivalent circuit;
equating the heat transfer value in the upper oil temperature model to a resistance value in the thermoelectric equivalent circuit;
the oil temperature value in the upper layer oil temperature model is equivalent to the potential in the thermoelectric equivalent circuit;
and equating the heat absorption capacity of the object in the upper oil temperature model to be the capacitance in the thermoelectric equivalent circuit.
Preferably, the equivalent thermal resistance R on the air side in the thermoelectric equivalent circuit is obtained in S12athEquivalent thermal resistance R of insulating oil sideothThe method comprises the following steps:
s121, obtaining heat transfer of the transformerNatural commutation resistance R delivered to insulating oilonForced commutation resistance R transferred to insulating oilofThermal resistance R corresponding to different temperature insulating oil phase mixturebtAnd air natural convection thermal resistance R in air cooling and heat dissipationanForced convection thermal resistance R in air cooling heat dissipationafAnd thermal radiation resistance R of radiator and airdr；
S122, according to the following formula
Figure BDA0001399388440000031
Obtaining the equivalent thermal resistance R of the air sideathAnd equivalent thermal resistance R of insulating oil sideoth。
Preferably, the S121 includes:
s1211, obtaining the characteristic length l of the oil convection heat dissipation surfaceoEquivalent oil convection heat dissipation area AoThermal conductivity lambda related to oil temperatureo(θo) Reference oil temperature thetaoNo-load loss P of transformeroShort circuit loss P of transformerkUpper layer oil temperature thetatoAnd the bottom layer oil temperature thetabo；
And according to the formula
Figure BDA0001399388440000032
Obtaining the natural commutation thermal resistance RonForced commutation thermal resistance RofThermal resistance R corresponding to different temperature insulating oil phase mixturebt；
S1212, obtaining the characteristic length l of the air convection heat dissipation surfaceaAir convection heat dissipation area AaReference air temperature thetaaLogarithmic mean temperature difference theta of air and oiloaEquivalent radiation area Adr；
According to the formula
Figure BDA0001399388440000033
Obtaining the spaceNatural convective resistance of gas RanForced convection thermal resistance RafAnd radiation thermal resistance Rdr；
Wherein q iso、po、mo、noAnd CoIs an empirical coefficient; q. q.sa、pa、ma、naAnd CaIs an empirical coefficient;
Gro(θo)、Pro(θo)、Reo(θo) The Gravaffe number, the Prandtl number and the Reynolds number of the oil side are respectively;
Gra(θa)、Pra(θa) And Rea(θa) The Gravaffe number, the Prandtl number and the Reynolds number of the air side respectively;
σ is the Stefan-Boltzmann constant,. epsilon.is the radiation coefficient of the black body, and y and x are the oil mixing coefficient and the oil index.
An upper oil temperature estimation system of an air-cooled transformer comprises:
a model parameter obtaining device for obtaining the variation delta theta of the ambient temperature around the transformer of the upper oil temperature modelaLoad factor k at the previous time0No-load loss P of transformer0Short circuit loss P of transformerkLoad factor change amount Δ k;
an equivalent parameter obtaining device for obtaining equivalent thermal resistance R at the air side of the upper oil temperature modelathEquivalent thermal resistance R of insulating oil sideothAnd equivalent thermal capacitance within the transformer;
the oil temperature prediction calculation device is connected with the upper layer oil temperature model parameter acquisition device and the equivalent parameter acquisition device and is used for calculating the upper layer oil temperature change delta theta according to an upper layer oil temperature change formulatoThe formula of the upper layer oil temperature change amount is as follows:
Figure BDA0001399388440000041
wherein x is oil index, d delta thetatoAnd/dt is the change rate of the upper oil temperature change.
Preferably, the equivalent parameter acquiring device includes:
the equivalent circuit simulation device obtains a thermoelectric equivalent circuit according to the upper oil temperature model;
an acquirer for acquiring an equivalent thermal resistance R of an air side in the thermoelectric equivalent circuitathEquivalent thermal resistance R of insulating oil sideothAnd equivalent heat capacity C in the transformerth。
Preferably, the acquirer includes:
a thermal resistance acquirer for acquiring natural current conversion thermal resistance R of the transformer heat transferred to the insulating oilonForced commutation resistance R transferred to insulating oilofThermal resistance R corresponding to different temperature insulating oil phase mixturebtAnd air natural convection thermal resistance R in air cooling and heat dissipationanForced convection thermal resistance R in air cooling heat dissipationafAnd thermal radiation resistance R of radiator and airdr；
The thermal resistance calculating device is connected with the thermal resistance acquirer and is used for acquiring data in the thermal resistance acquirer according to a formula
Figure BDA0001399388440000051
Obtaining the equivalent thermal resistance R of the air sideathAnd equivalent thermal resistance R of insulating oil sideoth。
Preferably, the thermal resistance obtainer includes:
an oil side thermal resistance acquirer for acquiring the characteristic length l of the oil convection heat dissipation surfaceoEquivalent oil convection heat dissipation area AoThermal conductivity lambda related to oil temperatureo(θo) Reference oil temperature thetaoNo-load loss P of transformeroShort circuit loss P of transformerkUpper layer oil temperature thetatoAnd the bottom layer oil temperature thetabo(ii) a And according to the formula
Figure BDA0001399388440000052
Obtaining the natural commutation thermal resistance RonForced commutation thermal resistance RofThermal resistance R corresponding to different temperature insulating oil phase mixturebt；
An air side heat resistance acquirer for acquiring the characteristic length l of the air convection heat radiation surfaceaAir convection heat dissipation area AaReference air temperature thetaaLogarithmic mean temperature difference theta of air and oiloaEquivalent radiation area Adr(ii) a According to the formula
Figure BDA0001399388440000053
Obtaining the air natural convection thermal resistance RanForced convection thermal resistance RafAnd radiation thermal resistance Rdr；
Wherein q iso、po、mo、noAnd CoIs an empirical coefficient; q. q.sa、pa、ma、naAnd CaIs an empirical coefficient;
Gro(θo)、Pro(θo)、Reo(θo) The Gravaffe number, the Prandtl number and the Reynolds number of the oil side are respectively;
Gra(θa)、Pra(θa) And Rea(θa) The Gravaffe number, the Prandtl number and the Reynolds number of the air side respectively;
σ is the Stefan-Boltzmann constant,. epsilon.is the radiation coefficient of the black body, and y and x are the oil mixing coefficient and the oil index.
The method and the system provided by the invention consider the environment temperature variation and the load rate and determine the oil temperature variation delta thetatoFrom ambient temperature Delta thetaaThe equation relation between the variation and the environmental temperature and the variation of the load coefficient is obtained according to the state equation of the top layer oil temperature, and the variation of the top layer oil temperature after the system operation state is changed can be predicted by predicting the variation of the top layer oil temperature after the system state is changedThe amount of change.
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In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the provided drawings without creative efforts.
Fig. 1 is a schematic structural diagram of an oil circulation air-cooled transformer provided by the invention;
FIG. 2 is a thermoelectric equivalent circuit diagram of an upper oil temperature model of the oil circulation air-cooled transformer provided by the invention;
FIG. 3 is a simplified diagram of a thermoelectric equivalent circuit of an upper oil temperature model of the oil circulation air-cooled transformer provided by the invention;
FIG. 4 is a flowchart of a method for estimating an upper oil temperature of an air-cooled transformer according to the present invention;
fig. 5 is a schematic diagram of an upper oil temperature estimation system of an air-cooled transformer according to the present invention.
In fig. 5:
the system comprises a model parameter acquisition device 1, an equivalent parameter acquisition device 2 and an oil temperature prediction calculation device 3;
an equivalent circuit simulation device 21, an acquirer 22;
thermal resistance obtainer 221, thermal resistance calculation means 222, oil-side thermal resistance obtainer 2211, air-side thermal resistance obtainer 2212.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
The core of the invention is to provide a method and a system for estimating the upper oil temperature of an air-cooled transformer, which can accurately estimate the variation trend of the upper oil temperature, can reflect the variation trend of the upper oil temperature along with the variation of the environmental temperature, and enhance the adaptability of the air-cooled transformer.
Referring to fig. 1 to 4, fig. 1 is a schematic structural diagram of an oil circulation air-cooled transformer according to the present invention; FIG. 2 is a thermoelectric equivalent circuit diagram of an upper oil temperature model of the oil circulation air-cooled transformer provided by the invention; FIG. 3 is a simplified diagram of a thermoelectric equivalent circuit of an upper oil temperature model of the oil circulation air-cooled transformer provided by the invention; FIG. 4 is a flowchart of a method for estimating an upper oil temperature of an air-cooled transformer according to the present invention; fig. 5 is a schematic diagram of an upper oil temperature estimation system of an air-cooled transformer according to the present invention.
The invention provides a method for estimating the upper oil temperature of an air-cooled transformer.
Step S1: obtaining environmental temperature variation delta theta around transformer of upper oil temperature modelaLoad factor k at the previous time0Load factor change delta k, transformer no-load loss P0And short-circuit loss P of transformerk(ii) a Obtaining equivalent thermal resistance R of air side of upper oil temperature modelathEquivalent thermal resistance R of insulating oil sideothAnd equivalent heat capacity C in transformerth。
Step S2: calculating the upper oil temperature change delta theta according to the upper oil temperature change formulatoThe formula of the upper layer oil temperature change quantity is as follows:
Figure BDA0001399388440000071
wherein x is oil index, d delta thetatoAnd/dt is the change rate of the upper oil temperature change.
Note that, in step S1, the equivalent thermal resistance R on the air side of the upper oil temperature modelathEquivalent thermal resistance R of insulating oil sideothAnd equivalent heat capacity C in transformerthThe above values can be obtained according to the methods of the prior art for the correlation quantities obtained from the equivalence.
The formula in step S2 is a formula of an oil temperature change amount derived from an equation of state of the top layer oil temperature, wherein the variables include an ambient temperature change amount Δ θaLoad factor k at the previous time0Load factor change delta k, transformer no-load loss P0And short-circuit loss P of transformerk。
After the environmental temperature variation and the load factor are considered by the formula, the oil temperature variation delta theta is determinedtoFrom ambient temperature Delta thetaaAnd a load factor change amount Δ k. According to the method, the equation relation between the variation of the top layer oil temperature and the variation of the environmental temperature and the load coefficient is obtained according to the state equation of the top layer oil temperature, and the variation of the top layer oil temperature after the system operation state is changed can be predicted by predicting the variation of the top layer oil temperature, so that the variation corresponding to the top layer temperature can be predicted after the system state is changed.
Referring to fig. 1, in the model of the present invention, the insulating oil is circulated in the transformer by the oil pump, the heat source of the transformer is mainly in the winding and core portions, which represent the heat source of the copper loss and the iron loss, respectively, and the oil of the transformer also has a small amount of dielectric loss. When the insulating oil flows to the vicinity of the winding, the heat of the winding and the iron core can be absorbed through convection heat transfer, and the heat can be transferred to the air through convection and radiation when the insulating oil circulates to the radiator. The oil temperature can also be lowered by ice if the temperature is too high.
On the basis of the above embodiment, the equivalent thermal resistance R on the air side of the upper layer oil temperature model is obtained in step S1athEquivalent thermal resistance R of insulating oil sideothAnd equivalent heat capacity in the transformer, comprising:
step S11: acquiring a corresponding thermoelectric equivalent circuit by an upper oil temperature model of the transformer;
step S12: obtaining equivalent thermal resistance R of air side in thermoelectric equivalent circuitathEquivalent thermal resistance R of insulating oil sideothAnd equivalent heat capacity C in transformerth。
On the basis of the foregoing embodiment, the step of obtaining the corresponding thermoelectric equivalent circuit from the upper oil temperature model of the transformer in step S11 includes:
the heat pump in the upper oil temperature model is equivalent to a power supply in a thermoelectric equivalent circuit;
the heat transfer value in the upper oil temperature model is equivalent to the resistance value in a thermoelectric equivalent circuit;
the oil temperature value in the upper oil temperature model is equivalent to the potential in a thermoelectric equivalent circuit;
and (4) equating the heat absorption capacity of the object in the upper oil temperature model to the capacitance in the thermoelectric equivalent circuit.
On the basis of the above-described embodiment, the equivalent thermal resistance R on the air side in the thermoelectric equivalent circuit is acquired in step S12athEquivalent thermal resistance R of insulating oil sideothThe method comprises the following steps:
step S121: obtaining natural commutation thermal resistance R of heat transfer of transformer to insulating oilonForced commutation resistance R transferred to insulating oilofThermal resistance R corresponding to different temperature insulating oil phase mixturebtAnd air natural convection thermal resistance R in air cooling and heat dissipationanForced convection thermal resistance R in air cooling heat dissipationafAnd thermal radiation resistance R of radiator and airdr；
Step S122: according to the formula
Figure BDA0001399388440000091
Obtaining the equivalent thermal resistance R of the air sideathAnd equivalent thermal resistance R of insulating oil sideoth。
On the basis of the above embodiment, step S121 specifically includes:
step S1211: obtaining the characteristic length l of the oil convection cooling surfaceoEquivalent oil convection heat dissipation area AoThermal conductivity lambda related to oil temperatureo(θo) Reference oil temperature thetaoNo-load loss P of transformeroShort circuit loss P of transformerkUpper layer oil temperature thetatoAnd the bottom layer oil temperature thetabo；
And according to the formula
Figure BDA0001399388440000092
Obtaining natural commutation thermal resistance RonForced commutation thermal resistance RofThermal resistance R corresponding to different temperature insulating oil phase mixturebt；
Step S1212: obtaining the characteristic length l of the air convection cooling surfaceaAir convection heat dissipation area AaReference air temperature thetaaLogarithmic mean temperature difference theta of air and oiloaEquivalent radiation area Adr；
According to the formula
Figure BDA0001399388440000093
Obtaining the natural convection thermal resistance R of airanForced convection thermal resistance RafAnd radiation thermal resistance Rdr；
Wherein q iso、po、mo、noAnd CoIs an empirical coefficient; q. q.sa、pa、ma、naAnd CaIs an empirical coefficient;
Gro(θo)、Pro(θo)、Reo(θo) The Gravaffe number, the Prandtl number and the Reynolds number of the oil side are respectively;
Gra(θa)、Pra(θa) And Rea(θa) The Gravaffe number, the Prandtl number and the Reynolds number of the air side respectively;
σ is the Stefan-Boltzmann constant,. epsilon.is the radiation coefficient of the black body, and y and x are the oil mixing coefficient and the oil index.
The derivation of the equivalent circuit and the formula of the change in the upper oil temperature will be described below, with reference to FIG. 2, in which the heat source of the transformer winding is generated by a current source qtEquivalence, including winding, core and stray losses; cthEquivalent heat capacity R formed by insulating oil, winding, oil tank and the like in transformeron、RofFor transferring heat from transformer to insulating oilThe current generation and forced current generation thermal resistance; rbtThe oil cooling device is characterized in that thermal resistances corresponding to mixing of insulating oil phases with different temperatures in a conventional forced oil circulation mode are achieved, cold oil at a pump port is fed into oil passages of a coil, a coil cake and an iron core under certain pressure in a forced oil circulation guide cooling mode, the internal oil temperature is distributed more uniformly, and at the moment, R is approximately considered to be Rbt＝0；RdrRadiation thermal resistance, R, for heat transfer from a radiator to ambient airanAnd RafThe thermal resistance of natural convection and forced convection of air in air cooling heat dissipation. The calculation formula of the thermal resistance is as follows:
Figure BDA0001399388440000101
Figure BDA0001399388440000102
the equivalent reduction of the thermal resistance of the equivalent thermal model can be simplified into the following formula:
Figure BDA0001399388440000103
qtthe expression represents the no-load loss and the short-circuit loss and is as follows: q. q.st＝(P0+k2Pk)x
The equation of state of the upper oil temperature can be given according to fig. 1 to 3:
Figure BDA0001399388440000111
the above formula being a temperature theta instead of a potential, e.g. winding temperature thetawFrom ambient temperature thetaaForm a thermal resistance Roth、RathThe voltage difference between them. CthTo be a heat capacity, a capacitance characteristic is exhibited in a thermoelectric equivalent model in relation to the specific heat of an object. q. q.stIs a current source and represents the power of a heat source.
In order to obtain the relationship between the upper layer oil temperature change amount and the load rate change amount and the environment temperature change amount, the above formula is linearized to obtain the formula:
Figure BDA0001399388440000112
wherein P is0，PkCan be derived from the nameplate parameter,. DELTA.thetaa、Δk、Δθto、dΔθto/dt、k0Respectively representing the change of the ambient temperature, the change of the load factor, the change of the top layer oil temperature change rate and the load factor at the previous moment. Delta thetaa(t)＝θa(t)-θa(t-1) is the ambient temperature variation; delta thetato(t)＝θup(t)-θupAnd (t-1) is the oil temperature increment.
In practice, the load always changes first, which then leads to a change in the oil temperature and the ambient temperature, which lags behind the load change. the time t-1 is the current time, the time t is the future time, and the time interval between the time t-1 and the time t is delta t. At time t-1, the load factor is k0Then the load is increased by delta k, the load rate k being S/SN，SNThe rated capacity of the transformer, S the apparent power of the transformer,
Figure BDA0001399388440000113
wherein, U is the transformer line voltage, and I is the transformer line current, can obtain through measuring. The oil temperature Δ θ to (t) to be increased is calculated by equation (9). Since the ambient temperature change is relatively small, the ambient temperature increment Δ θ a (t) of equation (9) may use the last period increment Δ θ a (t-1), and the ambient temperature may be obtained by a temperature sensor placed in the air. The oil temperature increment change rate is as follows:
dΔθto(t)/dt＝[Δθto(t)-Δθto(t)]/Δt＝[θto(t)-2θto(t-1)+θto(t-2)]/Δt。
θto(t-1)、θtoand (t-2) are respectively a current value and a historical value, and can be measured by a fuel tank top layer temperature sensor.
By temperature and load rateThe parameters x and C are estimated from historical data by using a nonlinear least square methodth、Roth、RathAnd finally, predicting the change amount of the top layer oil temperature according to the currently measured load rate change amount.
In addition to the method for estimating the upper oil temperature of the air-cooled transformer provided by each embodiment, the invention also provides a system for estimating the upper oil temperature of the air-cooled transformer, which is used for realizing the method and comprises the following steps: the device comprises a model parameter acquisition device 1, an equivalent parameter acquisition device 2 and an oil temperature prediction calculation device 3.
The model parameter obtaining device 1 is used for obtaining the ambient temperature variation delta theta around the transformer of the upper oil temperature modelaLoad factor k at the previous time0No-load loss P of transformer0Short circuit loss P of transformerkAnd a load factor change amount Δ k.
It should be noted that the parameters and variables acquired by the model parameter acquiring device 1 are characteristic values related to the transformer itself, and the ambient temperature variation Δ θ can be measured by a sensoraAnd acquiring other parameters by other measuring or acquiring modes.
The equivalent parameter acquisition device 2 is used for acquiring equivalent thermal resistance R at the air side of the upper oil temperature modelathEquivalent thermal resistance R of insulating oil sideothAnd equivalent thermal capacitance within the transformer.
An oil temperature prediction calculation device 3 connected with the upper layer oil temperature model parameter acquisition device and the equivalent parameter acquisition device and used for calculating the upper layer oil temperature change delta theta according to the upper layer oil temperature change formulatoThe formula of the upper layer oil temperature change quantity is as follows:
Figure BDA0001399388440000121
wherein x is oil index, d delta thetatoAnd/dt is the change rate of the upper oil temperature change.
It should be noted that, the above structures are all used to implement the method for estimating the upper oil temperature of the air-cooled transformer, and the description of the above method can be referred to for related processes.
After the environmental temperature variation and the load factor are considered by the formula, the oil temperature variation delta theta is determinedtoFrom ambient temperature Delta thetaaAnd a load factor change amount Δ k. According to the method, the equation relation between the variation of the top layer oil temperature and the variation of the environmental temperature and the load coefficient is obtained according to the state equation of the top layer oil temperature, and the variation of the top layer oil temperature after the system operation state is changed can be predicted by predicting the variation of the top layer oil temperature, so that the variation corresponding to the top layer temperature can be predicted after the system state is changed.
On the basis of the above-described embodiment, the equivalent parameter acquiring apparatus 2 includes an equivalent circuit simulating apparatus 21 and an acquirer 22.
Wherein, the equivalent circuit simulation device 21 obtains the thermoelectric equivalent circuit according to the upper oil temperature model by the equivalent circuit simulation device 21.
The obtaining device 22 is used for obtaining equivalent thermal resistance R of an air side in a thermoelectric equivalent circuitathEquivalent thermal resistance R of insulating oil sideothAnd equivalent heat capacity C in transformerth。
In the embodiment, the upper oil temperature model forms a thermoelectric equivalent circuit through equivalent action, and the equivalent mode can refer to the equivalent process in the prior art.
On the basis of the above-described embodiment, the obtainer 22 includes the thermal resistance obtainer 221 and the thermal resistance calculation device 222.
Wherein, the thermal resistance obtainer 221 is used for obtaining the natural commutation thermal resistance R of the heat transfer of the transformer to the insulating oilonForced commutation resistance R transferred to insulating oilofThermal resistance R corresponding to different temperature insulating oil phase mixturebtAnd air natural convection thermal resistance R in air cooling and heat dissipationanForced convection thermal resistance R in air cooling heat dissipationafAnd thermal radiation resistance R of radiator and airdr。
The thermal resistance calculating device 222 is connected to the thermal resistance acquirer 221 for acquiring data in the thermal resistance acquirer according to a formula
Figure BDA0001399388440000131
Obtaining the equivalent thermal resistance R of the air sideathAnd equivalent thermal resistance R of insulating oil sideoth。
On the basis of the above-described embodiment, the thermal resistance obtainer 221 includes an oil-side thermal resistance obtainer 2211 and an air-side thermal resistance obtainer 2212.
The oil side thermal resistance obtainer 2211 is used for obtaining the characteristic length l of the oil convection heat dissipation surfaceoEquivalent oil convection heat dissipation area AoThermal conductivity lambda related to oil temperatureo(θo) Reference oil temperature thetaoNo-load loss P of transformeroShort circuit loss P of transformerkUpper layer oil temperature thetatoAnd the bottom layer oil temperature thetabo(ii) a And according to the formula
Figure BDA0001399388440000132
Obtaining natural commutation thermal resistance RonForced commutation thermal resistance RofThermal resistance R corresponding to different temperature insulating oil phase mixturebt。
The air side thermal resistance obtainer 2212 is used for obtaining the characteristic length l of the air convection heat dissipation surfaceaAir convection heat dissipation area AaReference air temperature thetaaLogarithmic mean temperature difference theta of air and oiloaEquivalent radiation area Adr(ii) a And according to the formula
Figure BDA0001399388440000141
Obtaining the natural convection thermal resistance R of airanForced convection thermal resistance RafAnd radiation thermal resistance Rdr；
Wherein q iso、po、mo、noAnd CoIs an empirical coefficient; q. q.sa、pa、ma、naAnd CaIs an empirical coefficient;
Gro(θo)、Pro(θo)、Reo(θo) The Gravaffe number, the Prandtl number and the Reynolds number of the oil side are respectively;
Gra(θa)、Pra(θa) And Rea(θa) The Gravaffe number, the Prandtl number and the Reynolds number of the air side respectively;
σ is the Stefan-Boltzmann constant,. epsilon.is the radiation coefficient of the black body, and y and x are the oil mixing coefficient and the oil index.
The corresponding meanings of the various variables, references and constants referred to in this application are as follows.
RonNatural commutation resistance for transferring heat of the transformer to insulating oil;
Rofto force commutation thermal resistance;
Rbtthermal resistance corresponding to the mixing of insulating oil phases at different temperatures in a conventional forced oil circulation mode;
l0the characteristic length of the oil convection heat dissipation surface;
A0equivalent oil convection heat dissipation area;
λ0(θ0) Is the thermal conductivity associated with the oil temperature;
θ0as a reference oil temperature (the average oil temperature may be considered near the windings);
P0no-load loss of the transformer;
Pkshort circuit loss for the transformer;
θtoand thetaboThe upper and bottom oil temperatures.
k is a load factor;
y and x are oil mixing coefficient and oil index;
q0、p0、m0、n0and C0Is an empirical coefficient;
Gro(θ0) Is the Greever number of dawn, Pro(θ0) Is the prandtl number and Reo(θ0) Is the Reynolds number.
RanNatural thermal convection resistance of air in air cooling heat dissipation;
Rafthermal resistance for forced convection in air-cooled heat dissipation;
Rdris the thermal radiation resistance of the radiator and the air;
θ a is an average value of the air temperature near the radiator selected in the calculation as a reference temperature;
Adris the equivalent radiation area;
θoais the log mean temperature difference of air and oil.
CthEquivalent heat capacity formed by insulating oil, windings, an oil tank and the like in the transformer;
sigma is the Stefan-Boltzmann constant and epsilon is the radiation coefficient of the black body.
Except for the main steps and structures of the method and system for estimating the upper oil temperature of the air-cooled transformer provided by the above embodiments, the structures of other parts are referred to the prior art, and are not described herein again.
The embodiments in the present description are described in a progressive manner, each embodiment focuses on differences from other embodiments, and the same and similar parts among the embodiments are referred to each other.
The method and the system for estimating the upper oil temperature of the air-cooled transformer are described in detail above. The principles and embodiments of the present invention are explained herein using specific examples, which are presented only to assist in understanding the method and its core concepts. It should be noted that, for those skilled in the art, it is possible to make various improvements and modifications to the present invention without departing from the principle of the present invention, and those improvements and modifications also fall within the scope of the claims of the present invention.

Claims (2)

1. An upper oil temperature estimation method for an air-cooled transformer is characterized by comprising the following steps:
s1, obtaining environment temperature variation delta theta around the transformer of the upper oil temperature modelaLoad factor k at the previous time0Load factor change delta k, transformer no-load loss P0And short-circuit loss P of transformerk(ii) a Obtaining equivalent thermal resistance R of the air side of the upper oil temperature modelathEquivalent thermal resistance R of insulating oil sideothAnd equivalent heat capacity C in the transformerth；
S2, calculating the upper layer oil temperature change delta theta according to the upper layer oil temperature change formulatoThe formula of the upper layer oil temperature change amount is as follows:
Figure FDA0002295628190000011
wherein x is oil index, d delta thetatoThe/dt is the change rate of the upper layer oil temperature change;
obtaining the equivalent thermal resistance R of the air side of the upper oil temperature model in the S1athEquivalent thermal resistance R of insulating oil sideothAnd equivalent thermal capacitance within the transformer, including:
s11, obtaining a corresponding thermoelectric equivalent circuit by an upper oil temperature model of the transformer;
s12, obtaining equivalent thermal resistance R of the air side in the thermoelectric equivalent circuitathEquivalent thermal resistance R of insulating oil sideothAnd equivalent heat capacity C in the transformerth；
In S11, the thermoelectric equivalent circuit corresponding to the upper oil temperature model of the transformer is obtained by the upper oil temperature model of the transformer, and the thermoelectric equivalent circuit includes:
the heat pump in the upper oil temperature model is equivalent to a power supply in the thermoelectric equivalent circuit;
equating the heat transfer value in the upper oil temperature model to a resistance value in the thermoelectric equivalent circuit;
the oil temperature value in the upper layer oil temperature model is equivalent to the potential in the thermoelectric equivalent circuit;
equating the heat absorption capacity of the object in the upper oil temperature model to be the capacitance in the thermoelectric equivalent circuit;
obtaining the equivalent thermal resistance R of the air side in the thermoelectric equivalent circuit in the S12athEquivalent thermal resistance R of insulating oil sideothThe method comprises the following steps:
s121, obtaining natural commutation thermal resistance R of the transformer heat transferred to insulating oilonIs transmitted toForced commutation thermal resistance R of insulating oilofThermal resistance R corresponding to different temperature insulating oil phase mixturebtAnd air natural convection thermal resistance R in air cooling and heat dissipationanForced convection thermal resistance R in air cooling heat dissipationafAnd thermal radiation resistance R of radiator and airdr；
S122, according to the formula
Figure FDA0002295628190000021
Obtaining the equivalent thermal resistance R of the air sideathAnd equivalent thermal resistance R of insulating oil sideoth；
The S121 includes:
s1211, obtaining the characteristic length l of the oil convection heat dissipation surfaceoEquivalent oil convection heat dissipation area AoThermal conductivity lambda related to oil temperatureo(θo) Reference oil temperature thetaoNo-load loss P of transformeroShort circuit loss P of transformerkUpper layer oil temperature thetatoAnd the bottom layer oil temperature thetabo；
And according to the formula
Figure FDA0002295628190000022
Obtaining the natural commutation thermal resistance RonForced commutation thermal resistance RofThermal resistance R corresponding to different temperature insulating oil phase mixturebt；
S1212, obtaining the characteristic length l of the air convection heat dissipation surfaceaAir convection heat dissipation area AaReference air temperature thetaaLogarithmic mean temperature difference theta of air and oiloaEquivalent radiation area Adr；
According to the formula
Figure FDA0002295628190000023
Obtaining the air natural convection thermal resistance RanForced convection thermal resistance RafAnd radiation thermal resistance Rdr；
Wherein q iso、po、mo、noAnd CoIs an empirical coefficient; q. q.sa、pa、ma、naAnd CaIs an empirical coefficient;
Gro(θo)、Pro(θo)、Reo(θo) The Gravaffe number, the Prandtl number and the Reynolds number of the oil side are respectively;
Gra(θa)、Pra(θa) And Rea(θa) The Gravaffe number, the Prandtl number and the Reynolds number of the air side respectively;
σ is the Stefan-Boltzmann constant,. epsilon.is the radiation coefficient of the black body, and y and x are the oil mixing coefficient and the oil index.
2. The utility model provides an air-cooled transformer upper oil temperature predicts system which characterized in that includes:
a model parameter acquisition device (1) for acquiring the ambient temperature variation Delta theta around the transformer of the upper oil temperature modelaLoad factor k at the previous time0No-load loss P of transformer0Short circuit loss P of transformerkLoad factor change amount Δ k;
an equivalent parameter acquisition device (2) for acquiring equivalent thermal resistance R of the air side of the upper oil temperature modelathEquivalent thermal resistance R of insulating oil sideothAnd equivalent heat capacity C in the transformerth；
An oil temperature prediction calculation device (3) connected with the upper layer oil temperature model parameter acquisition device and the equivalent parameter acquisition device and used for calculating the upper layer oil temperature change delta theta according to an upper layer oil temperature change formulatoThe formula of the upper layer oil temperature change amount is as follows:
Figure FDA0002295628190000031
wherein x is oil index, d delta thetatoDt is upper oil temperature changeA rate of change of a variable;
the equivalent parameter acquisition device (2) comprises:
the equivalent circuit simulation device (21) is used for obtaining a thermoelectric equivalent circuit according to the upper oil temperature model;
an acquirer (22) for acquiring an equivalent thermal resistance R of an air side in the thermoelectric equivalent circuitathEquivalent thermal resistance R of insulating oil sideothAnd equivalent heat capacity C in the transformerth；
The acquirer (22) includes:
a thermal resistance obtainer (221) for obtaining a natural commutation thermal resistance R of the transformer heat transfer to the insulating oilonForced commutation resistance R transferred to insulating oilofThermal resistance R corresponding to different temperature insulating oil phase mixturebtAnd air natural convection thermal resistance R in air cooling and heat dissipationanForced convection thermal resistance R in air cooling heat dissipationafAnd thermal radiation resistance R of radiator and airdr；
A thermal resistance calculating device (222) connected with the thermal resistance acquirer and used for acquiring data in the thermal resistance acquirer according to a formula
Figure FDA0002295628190000041
Obtaining the equivalent thermal resistance R of the air sideathAnd equivalent thermal resistance R of insulating oil sideoth；
The thermal resistance obtainer (221) includes:
an oil side thermal resistance obtainer (2211) for obtaining the characteristic length l of the oil convection heat dissipation surfaceoEquivalent oil convection heat dissipation area AoThermal conductivity lambda related to oil temperatureo(θo) Reference oil temperature thetaoNo-load loss P of transformeroShort circuit loss P of transformerkUpper layer oil temperature thetatoAnd the bottom layer oil temperature thetabo(ii) a And according to the formula
Figure FDA0002295628190000042
Obtaining the natural commutation thermal resistance RonForced commutation thermal resistance RofThermal resistance R corresponding to different temperature insulating oil phase mixturebt；
An air side thermal resistance acquirer (2212) for acquiring the characteristic length l of the air convection heat dissipation surfaceaAir convection heat dissipation area AaReference air temperature thetaaLogarithmic mean temperature difference theta of air and oiloaEquivalent radiation area Adr(ii) a According to the formula
Figure FDA0002295628190000043
Obtaining the air natural convection thermal resistance RanForced convection thermal resistance RafAnd radiation thermal resistance Rdr；
Wherein q iso、po、mo、noAnd CoIs an empirical coefficient; q. q.sa、pa、ma、naAnd CaIs an empirical coefficient;
Gro(θo)、Pro(θo)、Reo(θo) The Gravaffe number, the Prandtl number and the Reynolds number of the oil side are respectively;
Gra(θa)、Pra(θa) And Rea(θa) The Gravaffe number, the Prandtl number and the Reynolds number of the air side respectively;
σ is the Stefan-Boltzmann constant,. epsilon.is the radiation coefficient of the black body, and y and x are the oil mixing coefficient and the oil index.
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