CN109033502B - Method for determining oil index of traction transformer - Google Patents

Method for determining oil index of traction transformer Download PDF

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CN109033502B
CN109033502B CN201810591848.4A CN201810591848A CN109033502B CN 109033502 B CN109033502 B CN 109033502B CN 201810591848 A CN201810591848 A CN 201810591848A CN 109033502 B CN109033502 B CN 109033502B
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oil
temperature
radiator
air
traction transformer
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CN109033502A (en
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周利军
唐浩龙
王健
王路伽
黄林
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Southwest Jiaotong University
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    • G06—COMPUTING; CALCULATING OR COUNTING
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Abstract

The invention discloses a method for determining the oil index of a traction transformer, which comprises the following steps: the method comprises the steps of obtaining related structure and physical parameters of the traction transformer, calculating the temperature rise of top oil by means of a global oil flow thermal model to wait for quantification, and performing regression calculation on an oil index by means of an oil index analytical model according to related data such as the temperature rise of the top oil, a load coefficient and the like. Compared with the reference value recommended by the IEEE standard, the oil index calculated by the method is more suitable for quickly estimating the temperature rise of the top oil of the traction transformer under multiple times of overload, and is beneficial to more accurately explaining the temperature rise change rule under a wide load interval.

Description

Method for determining oil index of traction transformer
Technical Field
The invention relates to the field of electric insulation online detection and fault diagnosis, in particular to a method for determining an oil index of a traction transformer.
Background
The traction transformer is used as a core device of a traction power supply system of a high-speed railway, and the efficient and safe operation of the traction transformer plays an important role in the operation development of high-speed railways. The service life of a traction transformer depends on the internal insulation properties, and thermal aging is a major factor in the degradation of its insulation properties, so the service life of a traction transformer is closely related to its internal temperature rise.
At present, a common means for determining the internal temperature rise of the transformer, including the top layer oil temperature rise and the hot point temperature rise, is carried out according to a two-section type temperature rise calculation formula in IEEE and IEC standards, but the two-section type temperature rise model is mainly suitable for a common oil-immersed power transformer which usually works in a rated state. For the traction transformer, due to the special working condition in the running of the train, the running load of the traction transformer has the characteristics of abrupt amplitude change, wide change interval, large fluctuation and the like, so that the calculation error of a two-section type temperature rise model is directly increased, and the monitoring precision of the oil temperature of the traction transformer is reduced.
Disclosure of Invention
The invention aims to provide a method for determining the oil index of a traction transformer, which considers the calculated value of the oil index of the transformer under multiple times of overload, so that the method is more suitable for calculating the temperature rise of the top oil of the traction transformer with a wide load interval.
The technical scheme for realizing the purpose of the invention is as follows:
a method for determining the oil index of a traction transformer comprises
The first step is as follows: make the top layer oil temperature of the traction transformer rise by delta TtopThe calculation model is as follows:
Figure GDA0002329526410000011
in the formula,. DELTA.Ttop,RThe temperature rise of the top layer oil under rated load is realized; r is the ratio of load loss to no-load loss under rated load; n is an oil index and is used for describing the variation trend of the temperature rise of the top layer oil along with the load; i ispuIs the load factor, TtopTop layer oil temperature, TambIs ambient temperature;
the second step is that: the oil index n is subjected to regression estimation by using a log-log linear regression model as follows:
Figure GDA0002329526410000012
in the formula
Figure GDA0002329526410000013
Identifying parameter n by using a least square method, namely:
Figure GDA0002329526410000021
in the formula (I), the compound is shown in the specification,
Figure GDA0002329526410000022
j is the number of samples, i is the label;
the top layer oil temperature TtopComprises the finding method of
Step 1: obtaining the structure and physical parameters of the traction transformer, including the height difference delta h of the cold core and the hot core and the height h of the windingwHeight h of radiatorrWinding vertical oil passage thermal hydraulic diameter DwThermal hydraulic diameter D of oil passage of radiatorrSpecific heat capacity of oil coilAir specific heat capacity cairOil density ρoilAir density ρairThermal expansion coefficient of oil βoilWinding on-way resistance coefficient fwOn-way resistance coefficient f of radiatorrTotal heat transfer coefficient U of radiator and flow area A of winding regionwThe flow area A of the radiatorrEffective heat dissipation area A of the radiatorRTemperature difference index lambda and ambient temperature Tamb。
Step 2: combining the formulas 1) to 3) below and the conditions in 4), and iteratively solving the volume flow G of the oil flow in the winding area by using a Newton-Raphson methodwVolume flow G of radiator oil flowrTop layer oil temperature TtopBottom layer oil temperature Tbom(ii) a The interior of the traction transformer is in single circulation, Gw＝Gr；
1) The heat buoyancy lift force and the fluid resistance in the winding vertical oil passage under the steady state condition reach balance, and the balance is as follows:
Figure GDA0002329526410000023
in the formula, gaIs the gravitational acceleration, S is the cooling circulation area,
S＝Δh(Ttop-Tbom)+hr[Ttop-Tbom-ΔTlm-0.5(Ttop-Tamb)]，
wherein, Delta TlmIs the log mean temperature difference between the oil flow in the radiator and the outside air,
Figure GDA0002329526410000024
2) load loss Q generated by winding in steady statewEqual to the heat absorbed by the oil flow around it, i.e.
Qw＝ρoilcoilGw(Ttop-Tbom)；
3) The oil circulation reaches the final steady state, and the temperature of the oil in the radiator rises to the temperature of the air
Toil-Tair＝Ce-λh，
In the formula, Toil、TairThe oil flow temperature and the air temperature along the height direction h of the radiator are respectively; c is the difference between the bottom oil temperature and the ambient temperature;
winding loss QwThe heat generated will be transferred entirely to the outside air by the oil flow, i.e.
Qw＝UAR(Toil-Tair)＝UARCe-λh；
Wherein the content of the first and second substances,
Figure GDA0002329526410000031
Qw,Ris the rated load loss of the traction transformer;
4) the ambient temperature of the traction transformer during operation at standard atmospheric pressure is selected as the reference temperature.
The invention has the beneficial effects that the oil index analytical calculation method under the condition of multiple overload of the traction transformer based on the log-log linear regression function is provided, the calculated oil index is more suitable for calculating the temperature rise of the top oil of the traction transformer with a wide load interval, and compared with a reference value recommended by the IEEE standard, the method improves the calculation precision of the temperature rise of the top oil and has the following advantages:
1) when the top-layer oil temperature data of the traction transformer is obtained, calculation is performed mainly based on energy conservation and momentum conservation, and no limitation of a load coefficient exists;
2) the oil index can be calculated by selecting a multiple-time load interval, the special working condition of the traction transformer with wide load characteristics is considered, and compared with a common power transformer, the value of the oil index is more suitable for top oil temperature rise calculation of the traction transformer;
3) the method can be used for calculating the oil index of the traction transformer with different structures and has certain universality.
Drawings
FIG. 1 is a flow chart of the present invention.
Detailed Description
The present invention will be further described below.
The method comprises the following steps of firstly, obtaining related structure and physical property parameters of the known traction transformer:
height difference delta h of cold and hot cores and height h of windingwHeight h of radiatorrWinding vertical oil passage thermal hydraulic diameter DwThermal hydraulic diameter D of oil passage of radiatorrSpecific heat capacity of oil coilAir specific heat capacity cairOil density ρoilAir density ρairThermal expansion coefficient of oil βoilWinding on-way resistance coefficient fwOn-way resistance coefficient f of radiatorrTotal heat transfer coefficient U of radiator and flow area A of winding regionwThe flow area A of the radiatorrEffective heat dissipation area A of the radiatorRTemperature difference index lambda and ambient temperature Tamb。
Secondly, solving the undetermined unknowns, comprising the following steps: volume flow G of oil flow in the winding areawVolume flow G of radiator oil flowrTop layer oil temperature TtopBottom layer oil temperature TbomThe following are:
1) the heat buoyancy lift force and the fluid resistance in the winding vertical oil passage under the steady state condition reach balance, as shown in the formula:
Figure GDA0002329526410000032
in the formula, gaAs the gravitational acceleration, S is the cooling cycle area, defined as follows:
S＝Δh(Ttop-Tbom)+hr[Ttop-Tbom-ΔTlm-0.5(Ttop-Tamb)](2)
in the formula,. DELTA.TlmIs the log mean temperature difference between the oil flow in the radiator and the outside air, and is defined as:
Figure GDA0002329526410000033
when the inside of the transformer is single-cycle, the relation Gw＝GrIf true;
2) load loss Q generated by winding in steady statewEqual to the heat absorbed by its surrounding oil stream, i.e.:
Qw＝ρoilcoilGw(Ttop-Tbom) (4)
3) the oil circulation reaches the final steady state, the temperature of the oil in the radiator relative to the air rises:
Toil-Tair＝Ce-λh(5)
in the formula, Toil、TairThe oil flow temperature and the air temperature along the height direction h of the radiator are respectively; c is the difference between the bottom oil temperature and the ambient temperature;
winding loss QwThe heat generated will be transferred to the outside air entirely through the oil flow:
Qw＝UAR(Toil-Tair)＝UARCe-λh(6)
4) selecting the ambient temperature of the traction transformer in operation under the standard atmospheric pressure as a reference temperature;
in summary, combining the known parameters of the first step and the formulas and conditions in 1) to 4), the Newton-Raphson method (Newton-Raphson method) is used to iteratively solve the unknown quantity: gw、Gr、Ttop、Tbom(ii) a At the same time, the loss Q is caused by the winding loss and the rated loadw,RAnd load factor IpuThe following relationships exist:
Figure GDA0002329526410000041
therefore, according to the load factor IpuAnd calculating corresponding load loss, and solving the parameter to be solved under the load.
Step three, listing the temperature rise delta T of the top layer oiltopCalculating a model:
Figure GDA0002329526410000042
in the formula,. DELTA.Ttop,RThe temperature rise of the top layer oil under rated load is realized; r is the ratio of load loss to no-load loss under rated load; n is an oil index and is used for describing the variation trend of the temperature rise of the top layer oil along with the load;
the oil index n is subjected to regression estimation by using a log-log linear regression model, as shown in the following formula:
Figure GDA0002329526410000043
in the formula
Figure GDA0002329526410000044
Identifying parameter n by using a least square method, namely:
Figure GDA0002329526410000045
in the formula (I), the compound is shown in the specification,
Figure GDA0002329526410000051
j is the number of samples and i is the index.
And step four, substituting the top oil temperature rise data and the load coefficient calculated in the step two into the regression model determined in the step three to obtain an oil index n.

Claims (1)

1. A method of determining the oil index of a traction transformer comprising
The first step is as follows: make the top layer oil temperature of the traction transformer rise by delta TtopThe calculation model is as follows:
Figure FDA0002329526400000011
in the formula,. DELTA.Ttop,RThe temperature rise of the top layer oil under rated load is realized; r is the ratio of load loss to no-load loss under rated load; n is an oil index and is used for describing the variation trend of the temperature rise of the top layer oil along with the load; i ispuIs the load factor, TtopTop layer oil temperature, TambIs ambient temperature;
the second step is that: the oil index n is subjected to regression estimation by using a log-log linear regression model as follows:
Figure FDA0002329526400000012
in the formula
Figure FDA0002329526400000013
Identifying parameter n by using a least square method, namely:
Figure FDA0002329526400000014
in the formula (I), the compound is shown in the specification,
Figure FDA0002329526400000015
j is the number of samples, i is the label;
the top layer oil temperature TtopComprises the finding method of
Step 1: obtaining the structure and physical parameters of the traction transformer, including the height difference delta h of the cold core and the hot core and the height h of the windingwHeight h of radiatorrWinding vertical oil passage thermal hydraulic diameter DwThermal hydraulic diameter D of oil passage of radiatorrSpecific heat capacity of oil coilAir specific heat capacity cairOil density ρoilAir density ρairThermal expansion coefficient of oil βoilWinding on-way resistance coefficient fwOn-way resistance coefficient f of radiatorrTotal heat transfer coefficient U of radiator and flow area A of winding regionwThe flow area A of the radiatorrEffective heat dissipation area A of the radiatorRTemperature difference index lambda and ambient temperature Tamb；
Step 2: combining the formulas 1) to 3) below and the conditions in 4), and iteratively solving the volume flow G of the oil flow in the winding area by using a Newton-Raphson methodwVolume flow G of radiator oil flowrTop layer oil temperature TtopBottom layer oil temperature Tbom(ii) a The interior of the traction transformer is in single circulation, Gw＝Gr；
1) The heat buoyancy lift force and the fluid resistance in the winding vertical oil passage under the steady state condition reach balance, and the balance is as follows:
Figure FDA0002329526400000016
in the formula, gaIs the gravitational acceleration, S is the cooling circulation area,
S＝Δh(Ttop-Tbom)+hr[Ttop-Tbom-ΔTlm-0.5(Ttop-Tamb)]，
wherein, Delta TlmIs the log mean temperature difference between the oil flow in the radiator and the outside air,
Figure FDA0002329526400000021
2) load loss Q generated by winding in steady statewEqual to the heat absorbed by the oil flow around it, i.e.
Qw＝ρoilcoilGw(Ttop-Tbom)；
3) The oil circulation reaches the final steady state, and the temperature of the oil in the radiator rises to the temperature of the air
Toil-Tair＝Ce-λh，
In the formula, Toil、TairThe oil flow temperature and the air temperature along the height direction h of the radiator are respectively; c is the difference between the bottom oil temperature and the ambient temperature;
winding load loss QwThe heat generated will be transferred entirely to the outside air by the oil flow, i.e.
Qw＝UAR(Toil-Tair)＝UARCe-λh；
Wherein the content of the first and second substances,
Figure FDA0002329526400000022
Qw,Ris the rated load loss of the traction transformer;
4) the ambient temperature of the traction transformer during operation at standard atmospheric pressure is selected as the reference temperature.
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