A method for on-line monitoring of insulation state of low-voltage side bus of power transformer

Abstract

The application discloses an online monitoring method for the insulation state of a low-voltage side busbar of a power transformer, and belongs to the technical field of safe operation of power equipment. A fitting function f(i, t, v) of a busbar conductor temperature changing with a current i, a temperature t and a wind speed v is established, and a fitting function g(i, t, v) of a busbar insulation temperature changing with the current i, the temperature t and the wind speed v is established. A current signal, a temperature signal, a wind speed signal and an actual value T0 of the busbar insulation temperature of the low-voltage side busbar of the power transformer are obtained, and a simulated value T1' of the busbar conductor temperature and a simulated value T2' of the busbar insulation temperature are looked up in a database. A logical processing module is used to judge whether the actual value T0 of the busbar insulation temperature of the low-voltage side busbar of the power transformer is greater than the simulated value T1' of the busbar conductor temperature. If T0 is greater than T1', it is considered that the busbar insulation is failed or abnormal. The application can monitor the operation state of the busbar insulation of the low-voltage side busbar of the power transformer during the operation of the power transformer, and greatly improves the reliability and convenience of detection.

Description

Technical Field

[0001] A method for online monitoring of the insulation status of the low-voltage side busbar of a power transformer belongs to the technical field of safe operation of power equipment. Background Technology

[0002] Electrical energy is an energy source closely related to people's lives, industrial and agricultural production, and the socio-economic development. Power transformers, as crucial equipment in the power grid, play a vital role in changing voltage, connecting the grid, and distributing power. Electrically, their primary side connects to the high-voltage grid, while their low-voltage side is directly connected to users through the power grid. Power transformers typically operate outdoors and are susceptible to external environmental factors. Because their low-voltage side busbar insulation is constantly exposed to harsh conditions such as wind, rain, and sun exposure, its insulation capacity ages rapidly over a relatively short period, potentially leading to insulation failure at the transformer's outlet and resulting in equipment damage.

[0003] In actual operation, the transmission capacity of power transformers is often less than their rated capacity, resulting in insufficient utilization of the busbar's transmission capacity and hindering economic operation. When a line in the transmission system experiences a fault or an emergency power demand arises, the busbar, operating normally, can withstand this emergency load within the allowed capacity expansion time to ensure power supply reliability. However, as the transmission capacity of power transformers and the scale of the power grid increase, the system's short-circuit capacity and short-circuit current continuously increase. The current value on the low-voltage side of the power transformer is significantly higher than that on the high-voltage side (the multiple between the low and high voltage currents of a 35kV power transformer is close to 90 times). Since the power loss due to resistance in the circuit is proportional to the square of the current and the magnitude of the resistance, if the power transformer's outgoing line joints experience significant contact resistance due to poor contact, the consumed active power becomes considerable. Furthermore, all the active power consumed at the outgoing line joints is converted into heat energy, causing the outgoing line joints and their conductors to overheat, potentially burning out the connecting conductors and related equipment, leading to a fire and power outage.

[0004] When the low-voltage side busbar insulation of a power transformer fails, the enormous short-circuit electrodynamic and thermal effects will cause irreversible damage to the transformer winding insulation. This can lead to winding instability and deformation, resulting in equipment damage, or even damage to the transformer winding insulation, causing fires, large-scale power outages, and other accidents.

[0005] Real-time conductor temperature is a crucial indicator of busbar operating status. The busbar insulation used in this experiment is silicone rubber (SiR), which has a maximum permissible long-term operating temperature of 90°C. When the low-voltage side busbar of the power transformer operates under normal conditions, the conductor temperature remains within a safe range. However, if overloaded for a certain period, the conductor temperature will exceed the maximum permissible value after a certain temperature rise time. Prolonged overload operation will affect service life and may even lead to fire. Therefore, this method focuses on the operating temperature of the low-voltage side busbar of the power transformer to prevent long-term overload operation, which could cause localized excessively high temperatures exceeding the insulation's maximum tolerance, leading to insulation damage and further escalation of accidents. Therefore, to ensure power supply reliability and power quality, it is essential to monitor insulation temperature and overload conditions in real time.

[0006] In existing technologies, conventional methods for detecting the contact condition of outgoing line connectors involve measuring the contact resistance of the connector with a DC resistance meter or measuring the operating temperature of the connector area with an infrared thermal imager after a power outage. Because this requires performing these measurements after power is cut off, it significantly impacts the reliability of the measurements and fails to provide real-time information about the operating condition of the outgoing line connectors. Furthermore, practical experience has shown that accidents caused by overheating or equipment burnout at power transformer outgoing line connectors are common during actual operation. Therefore, it is necessary to strengthen their operation and maintenance and real-time status monitoring. Summary of the Invention

[0007] The technical problem to be solved by the present invention is to overcome the shortcomings of the prior art and provide an online monitoring method for the insulation status of the low-voltage side busbar of a power transformer, which can identify the operating status of the low-voltage side busbar insulation during the operation of the power transformer and greatly improve the reliability of detection.

[0008] The technical solution adopted by this invention to solve its technical problem is: an online monitoring method for the insulation status of the low-voltage side busbar of a power transformer, characterized by the following steps:

[0009] S1 obtains the operating current range of the low-voltage side of the power transformer, busbar size, local temperature t and wind force v at different times;

[0010] S2 calculates the volumetric thermal power P of the low-voltage side busbar of the power transformer;

[0011] S3 obtained the low-voltage side busbar conductor temperature T1 and busbar insulation temperature T2 of the power transformer through finite element simulation software.

[0012] S4 establishes a fitting function f(i,t,v) for the busbar conductor temperature as a function of current i, temperature t, and wind speed, and a fitting function g(i,t,v) for the busbar insulation temperature as a function of current i, temperature t, and wind speed v.

[0013] During the actual monitoring process, S5 obtains the current signal, temperature signal, wind speed signal, and actual value T0 of the busbar insulation temperature on the low-voltage side of the power transformer. It then searches the database for the simulated values ​​T1' of the busbar conductor temperature and T2' of the busbar insulation temperature.

[0014] S6 determines whether the actual value T0 of the low-voltage side busbar insulation temperature of the power transformer is greater than the simulated value T1' of the busbar conductor temperature. If T0 is greater than T1', then the busbar insulation is considered to be in failure or abnormal. The excess temperature value of the busbar insulation is calculated as ΔT and sent to the monitoring station.

[0015] Preferably, an online monitoring system is used to monitor the power transformer.

[0016] Preferably, the online monitoring system includes a logic processing module, a signal acquisition module, and a communication module. The input terminal of the signal acquisition module is connected to the current acquisition unit and temperature acquisition unit on the low-voltage side of the power transformer, the output terminal of the signal acquisition module is connected to the input terminal of the logic processing module, and the output terminal of the logic processing module is connected to the input terminal of the communication module.

[0017] Preferably, the method further includes, under steady-state conditions, the heat of the low-voltage side busbar of the power transformer satisfies the following relationship:

[0018] Q R +Q t =Q1+Q f ;

[0019] Among them, Q R Q represents the heat loss per unit length of busbar resistance, expressed in W / m. t Q is the heat absorbed by the busbar per unit length from solar radiation, W / m; Q1 is the heat dissipation by air convection per unit length of the busbar, W / m; Q f This is the heat dissipation radiated per unit length of the busbar to the surrounding medium, expressed in W / m.

[0020] Preferably, the method further includes ensuring that the temperature rise of the low-voltage side busbar conductors of the power transformer satisfies the following relationship:

[0021] Q1+Q f =α w τ w F;

[0022] Where F is the total heat dissipation area of ​​the busbar conductors, m 2 ;α w It is the overall heat dissipation coefficient; τ w It is the stable value that the temperature rise of the busbar conductor tends to reach.

[0023] Preferably, the method further includes, when the low-voltage side busbar conductor of the current transformer carries current I for a long period of time, the stable temperature rise is:

[0024]

[0025] Where I is the current flowing through the busbar conductor, in A; and R is the resistance of the busbar conductor, in Ω.

[0026] Preferably, the volumetric thermal power P of the low-voltage side busbar of the power transformer is:

[0027] P = I 2 R / V;

[0028] Where I is the operating current of the low-voltage side busbar of the power transformer, R is the resistance of the low-voltage side busbar core of the power transformer, and V is the volume of the low-voltage side busbar core of the power transformer.

[0029] Preferably, the method further includes the following formula: the relationship between the insulation conductivity of the low-voltage side busbar of the power transformer and temperature and electric field strength is:

[0030]

[0031] Where A is a constant related to the insulation of the low-voltage side busbar of the power transformer, with units of V / (Ω·m). 2 ); q is the activation energy, in eV; q is the electron charge, in C; k b 1 is Boltzmann constant, in J / K; T is busbar insulation temperature, in K; B is electric field coefficient, in m / V; E is electric field strength, in kV / mm.

[0032] Compared with the prior art, the beneficial effects of this invention are:

[0033] This online monitoring method for the insulation status of the low-voltage side busbar of a power transformer is based on an actual power transformer model. By analyzing the steady-state temperature and transient temperature rise of the busbar and verifying it with finite element method, it overcomes the shortcomings of traditional thermal circuit models that cannot calculate the transient temperature rise of clustered cables. Ultimately, it realizes the dynamic capacity expansion calculation of the busbar under constant load and variable load, so that the busbar can fully transmit power under good insulation operating conditions.

[0034] This online monitoring method for the insulation contact status of the low-voltage side busbar of a power transformer allows for monitoring of the operating status of the low-voltage side busbar insulation during transformer operation, greatly improving the reliability and convenience of the monitoring.

[0035] In this online monitoring method for the insulation status of the low-voltage side busbar of a power transformer, real-time measurement and estimation analysis are performed under the actual operating conditions of the power transformer, including actual load current, actual ambient temperature, etc., which can more accurately reflect its operating status, and the measurement results are more reliable. Moreover, it can predict future temperature changes of the busbar. If the temperature exceeds the limit specified in the regulations or the rate of change increases significantly, it can issue a real-time alarm signal to the power transformer operation manager, effectively preventing accidents from occurring. Attached Figure Description

[0036] Figure 1 This is an electrical schematic diagram of an online monitoring system for the contact status of power transformer outgoing line joints.

[0037] Figure 2 This is a block diagram illustrating the principle of an online monitoring system for the contact status of power transformer outgoing line joints.

[0038] The components are: 1. Incoming line; 2. High-voltage side disconnecting switch; 3. High-voltage side circuit breaker; 4. Power transformer; 5. Low-voltage side current transformer; 6. Low-voltage side temperature sensor; 7. Low-voltage side busbar; 8. Low-voltage side circuit breaker; 9. Low-voltage side disconnecting switch; 10. Low-voltage busbar. Detailed Implementation

[0039] Figures 1-2 This is the preferred embodiment of the present invention, which is described below in conjunction with the accompanying drawings. Figures 1-2 The present invention will be further described below.

[0040] like Figures 1-2 As shown: This online monitoring system for the contact status of the outgoing line joints of a power transformer includes a signal acquisition module, a logic processing module, and a communication module. The outputs of the temperature sensor, current transformer, wind speed sensor, and ground temperature sensor are simultaneously connected to the input of the signal acquisition module. The output of the signal acquisition module is connected to the input of the logic processing module, the output of the logic processing module is connected to the input of the communication module, and the output of the communication module is connected to the client. The logic processing module can be implemented using a conventional controller, such as a PLC, and the signal acquisition module can be implemented using a conventional signal acquisition circuit. The current transformer serves as the current acquisition unit, and the temperature sensor serves as the temperature acquisition unit.

[0041] The current transformer is the low-voltage side current transformer 5 installed between the power transformer 4 and the low-voltage side busbar 7; the temperature sensor is the low-voltage side temperature sensor 6 installed between the power transformer 4 and the low-voltage side busbar 7; the wind speed sensor is the low-voltage side wind speed sensor installed between the power transformer 4 and the low-voltage side busbar 7; and the surface air temperature sensor is the surface air temperature sensor installed between the power transformer 5 and the low-voltage side busbar 7.

[0042] Incoming line 1 connects to the high-voltage side of power transformer 4, and the low-voltage side of power transformer 4 connects to low-voltage busbar 10. A high-voltage side disconnecting switch 2 and a high-voltage side circuit breaker 3 are connected in series between incoming line 1 and the high-voltage side of power transformer 4. A low-voltage side temperature sensor 6, a low-voltage side current transformer 5, a low-voltage side busbar 7, a low-voltage side circuit breaker 8, and a low-voltage side disconnecting switch 9 are connected in series between the low-voltage side of power transformer 4 and low-voltage busbar 10. A low-voltage side wind speed sensor and a surface temperature sensor are also installed on the low-voltage side of power transformer 4.

[0043] The signal acquisition module receives data from temperature sensors, current transformers, wind speed sensors, and surface air temperature sensors, and sends the data to the logic processing module. After receiving the corresponding data, the logic processing module performs calculations, analyzes the calculation results, and then sends the analyzed information to the communication module, which then sends it to the client.

[0044] A method for online monitoring of the insulation status of the low-voltage side busbar of a power transformer includes the following steps:

[0045] S1 obtains the operating current range of the low-voltage side of the power transformer, the busbar size, and the local temperature t and wind force v at different times.

[0046] The current signal of the low-voltage side busbar 7 of the power transformer is obtained and simultaneously sent to the logic processing module.

[0047] S2 calculates the volumetric thermal power P of the low-voltage side busbar of the power transformer.

[0048] The volumetric heat power P of the low-voltage side busbar of the power transformer is:

[0049] P = I 2 R / V;

[0050] Where I is the operating current of the low-voltage side busbar of the power transformer, R is the resistance of the low-voltage side busbar core of the power transformer, and V is the volume of the low-voltage side busbar core of the power transformer.

[0051] S3 obtained the low-voltage side busbar conductor temperature T1 and busbar insulation temperature T2 of the power transformer through finite element simulation software.

[0052] The relationship between the insulation conductivity of the low-voltage side busbar of a power transformer and temperature and electric field strength is as follows:

[0053]

[0054] Where A is a constant related to the insulation of the low-voltage side busbar of the power transformer, with units of V / (Ω·m). 2 ); q is the activation energy, in eV; q is the electron charge, in C; k b 1 is Boltzmann constant, in J / K; T is busbar insulation temperature, in K; B is electric field coefficient, in m / V; E is electric field strength, in kV / mm.

[0055] The control equations involved in modeling with the finite element simulation software COMSOL are as follows: the applied voltage and current are based on the electric field control equation, the temperature distribution is based on the heat transfer control equation, and the Joule heat generated by the conductor is based on the electrothermal coupling control equation. The control equations should include the electric field module, the heat transfer module, and the electrothermal coupling module.

[0056] The governing equations for the electric field module are:

[0057]

[0058] J = σE + J e ;

[0059]

[0060]

[0061] in, J is the vector differential operator; J is the current density vector, with units of A / m. 3 ; via Q j,V It is a current source, with units of A / m. 3 σ is electrical conductivity, in S / m; E is electric field strength, in V / m; V is electric potential, in V; J e Externally injected current density, in A / m 3 D is the displacement vector; t is time.

[0062] The control equations for the heat transfer module are:

[0063]

[0064]

[0065]

[0066] Where ρ is density, with units of kg / m³. 3 C p ρ is the constant-pressure heat capacity, in J / (kg·K); u is the temperature vector of heat transfer in the solid, in m / s; T is the temperature, in K; q is the conduction heat flux, in W / m³. 2 Q represents the heating power of the heat source, measured in W / m³. 3 q0 is the initial value of the heat flux transferred, in W / m³. 2 Q tedIt is a thermoelastic damping heat source, with units of W / m. 3 ; k is the thermal conductivity, with units of W / (m·K); d z It is the thickness of the region in the out-of-plane direction, and the unit is m.

[0067] The control equations for the electrothermal coupling module are:

[0068]

[0069] Q e =J·E;

[0070]

[0071] Among them, Q e Electromagnetic heat source, unit is W / m 3 J is the current density vector, with units of A / m. 3 .

[0072] S4 establishes a fitting function f(i,t,v) for the busbar conductor temperature as a function of current i, temperature t, and wind speed, and a fitting function g(i,t,v) for the busbar insulation temperature as a function of current i, temperature t, and wind speed v.

[0073] The signal acquisition module acquires the insulation temperature signal of the low-voltage side busbar 7 of the power transformer, and sends the insulation temperature signal of the low-voltage side busbar 7 of the power transformer to the logic processing module.

[0074] The signal acquisition module obtains the wind speed of the low-voltage side busbar 7 of the power transformer, and sends the wind speed signal of the low-voltage side busbar 7 of the power transformer to the logic processing module.

[0075] The signal acquisition module obtains the surface temperature of the low-voltage side busbar 7 of the power transformer, and sends the surface temperature signal of the low-voltage side busbar 7 of the power transformer to the logic processing module.

[0076] The fitting function f(i,t,v) is obtained by simulating the local air temperature and wind speed of the power transformer, the current under normal and fault conditions of the busbar, and the conductor temperature of the low-voltage side of the power transformer. The function f(i,t,v) is then fitted using the 1stopt curve fitting platform, employing a set of formulas with three independent variables and one dependent variable: y=(i^p1)*((1+p2*v) / (p3+p4*v))+p5+p6 / t;

[0077] Where i represents the independent variable, busbar conductor current, in A; t represents the independent variable, local air temperature of the power transformer, in K; v represents the local wind speed of the power transformer; and y represents the dependent variable, simulated busbar conductor temperature T1, in K.

[0078] The independent and dependent variable data are input into the 1stopt curve fitting platform to calculate the coefficients p1-p6 of the fitting function, thus obtaining the fitting function f(i,t,v) for the busbar conductor temperature T1'.

[0079] The fitting function g(i,t,v) is obtained by simulating the local air temperature and wind speed of the power transformer, the current under normal and fault conditions of the busbar, and the insulation temperature of the low-voltage side busbar of the power transformer. The function g(i,t,v) is then fitted using the 1stopt curve fitting platform, employing a set of formulas with three independent variables and one dependent variable: y=(i^p1)*((1+p2*v) / (p3+p4*v))+p5+p6 / t;

[0080] Where i represents the independent variable, busbar conductor current, in A; t represents the independent variable, local air temperature of the power transformer, in K; v represents the local wind speed of the power transformer; and y represents the dependent variable, simulated busbar conductor temperature T1, in K.

[0081] The independent and dependent variable data are input into the 1stopt curve fitting platform to calculate the coefficients p1-p6 of the fitting function, thus obtaining the fitting function g(i,t,v) for the busbar insulation temperature T1'.

[0082] During the actual monitoring process, S5 obtains the current signal, temperature signal, wind speed signal and actual value T0 of the busbar insulation temperature on the low-voltage side of the power transformer. The logic processing module searches the database for the simulated values ​​T1' of the busbar conductor temperature and T2' of the busbar insulation temperature.

[0083] The logic processing module uses the current signal, wind speed signal, and ground temperature signal of the low-voltage side busbar 7 of the power transformer obtained by the signal acquisition module to find the fitting function, and uses the fitting functions f(i,t,v) and g(i,t,v) to calculate the conductor temperature T1' and insulation temperature T2' of the low-voltage side busbar of the power transformer.

[0084] The S6 logic processing module determines whether the actual value T0 of the low-voltage side busbar insulation temperature of the power transformer is greater than the simulated value T1' of the busbar conductor temperature. If T0 is greater than T1', then the busbar insulation is considered to be faulty or abnormal. The module calculates the excess temperature value ΔT of the busbar insulation and sends it to the monitoring station.

[0085] The logic processing module determines whether the calculated actual value T0 of the low-voltage side busbar insulation temperature of the power transformer exceeds the simulated value T1' of the busbar conductor temperature. If it exceeds T1', it executes step S5; if it does not exceed T1', it returns to step S1.

[0086] The logic processing module sends an alarm signal, calculates the exceeded temperature value ΔT, and uploads the detection results.

[0087] The formula for calculating ΔT is: ΔT=T0-T2'.

[0088] The specific working process and working principle are as follows:

[0089] Preliminary work: Data on the dimensions of the low-voltage side busbar of the power transformer, current i, and local temperature and wind speed changes were collected. The conductor temperature T1' and insulation temperature T2' of the low-voltage side busbar of the power transformer were calculated through simulation. The function f(i,t,v) was fitted by the influence of independent variables current i, temperature and wind speed on the conductor temperature T1', and the function g(i,t,v) was fitted by the influence of independent variables current i, temperature and wind speed on the insulation temperature T2'.

[0090] Monitoring work: The signal acquisition unit collects data based on the preset signals of the low-voltage side of the power transformer. The collected data includes the current signal, air temperature signal and wind speed signal of the low-voltage side busbar 7 of the power transformer, which are collected by the low-voltage side current transformer 5, and the above signals are sent to the logic processing module.

[0091] The logic processing module performs calculations based on the data sent by the signal acquisition unit, and calculates the conductor temperature T1' and insulation temperature T2' of the low-voltage side busbar 7 of the power transformer through a fitting function.

[0092] The logic processing module determines whether the calculated actual value T0 of the low-voltage side busbar insulation temperature of the power transformer exceeds the simulated value T1' of the busbar conductor temperature. If it exceeds T1', a warning signal is issued and the detection result is sent to the client.

[0093] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any other way. Any person skilled in the art may make changes or modifications to the above-disclosed technical content to create equivalent embodiments. However, any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the protection scope of the present invention.

Claims

1. A method for online monitoring of the insulation status of the low-voltage side busbar of a power transformer, characterized in that: Includes the following steps: S1 obtains the operating current range of the low-voltage side of the power transformer, busbar size, local temperature t and wind force v at different times; S2 calculates the volumetric thermal power P of the low-voltage side busbar of the power transformer; S3 obtained the low-voltage side busbar conductor temperature T1 and busbar insulation temperature T2 of the power transformer through finite element simulation software. S4 establishes a fitting function f(i,t,v) for the busbar conductor temperature as a function of current i, temperature t, and wind speed, and a fitting function g(i,t,v) for the busbar insulation temperature as a function of current i, temperature t, and wind speed v. The fitting function f(i,t,v) is obtained by simulating the local air temperature and wind speed of the power transformer, the current under normal and fault conditions of the busbar, and the conductor temperature of the low-voltage side of the power transformer. Finally, the function f(i,t,v) is obtained by fitting the data through the 1stopt curve fitting platform. It uses a set of formulas with three independent variables and one dependent variable, namely: y=(i^p1)*((1+p2*v) / (p3+p4*v))+p5+p6 / t; Where i represents the independent variable, busbar conductor current, in A; t represents the independent variable, local air temperature of the power transformer, in K; v represents the local wind speed of the power transformer; and y represents the dependent variable, simulated busbar conductor temperature T1, in K. The independent and dependent variable data are input into the 1stopt curve fitting platform to calculate the coefficients p1-p6 of the fitting function, and thus the fitting function f(i,t,v) of the busbar conductor temperature T1' is obtained. The fitting function g(i,t,v) is obtained by simulating the local air temperature and wind speed of the power transformer, the current under normal and fault conditions of the busbar, and the insulation temperature of the low-voltage side busbar of the power transformer. Finally, the function g(i,t,v) is obtained by fitting the data through the 1stopt curve fitting platform. It uses a set of formulas with three independent variables and one dependent variable, namely: y=(i^p1)*((1+p2*v) / (p3+p4*v))+p5+p6 / t; Where i represents the independent variable, busbar conductor current, in A; t represents the independent variable, local air temperature of the power transformer, in K; v represents the local wind speed of the power transformer; and y represents the dependent variable, simulated busbar conductor temperature T1, in K. The independent and dependent variable data are input into the 1stopt curve fitting platform to calculate the coefficients p1-p6 of the fitting function, and thus the fitting function g(i,t,v) of the busbar insulation temperature T1' is obtained. During the actual monitoring process, S5 obtains the current signal, temperature signal, wind speed signal, and actual value T0 of the busbar insulation temperature on the low-voltage side of the power transformer. It then searches the database for the simulated values ​​T1' of the busbar conductor temperature and T2' of the busbar insulation temperature. S6 determines whether the actual value T0 of the low-voltage side busbar insulation temperature of the power transformer is greater than the simulated value T1' of the busbar conductor temperature. If T0 is greater than T1', then the busbar insulation is considered to be in failure or abnormal. The excess temperature value of the busbar insulation is calculated as ΔT and sent to the monitoring station. The relationship between the insulation conductivity of the low-voltage side busbar of a power transformer and temperature and electric field strength is as follows: ； Where A is a constant related to the insulation of the low-voltage side busbar of the power transformer, with units of V / (Ω·m). 2 ); q is the activation energy, in eV; q is the electron charge, in C; k b 1 is Boltzmann constant, in J / K; T is busbar insulation temperature, in K; B is electric field coefficient, in m / V; E is electric field strength, in kV / mm.

2. The method for online monitoring of the insulation status of the low-voltage side busbar of a power transformer according to claim 1, characterized in that: An online monitoring system is used to inspect power transformers.

3. The method for online monitoring of the insulation status of the low-voltage side busbar of a power transformer according to claim 2, characterized in that: The online monitoring system includes a logic processing module, a signal acquisition module, and a communication module. The input terminal of the signal acquisition module is connected to the current acquisition unit and temperature acquisition unit on the low-voltage side of the power transformer. The output terminal of the signal acquisition module is connected to the input terminal of the logic processing module, and the output terminal of the logic processing module is connected to the input terminal of the communication module.

4. The method for online monitoring of the insulation status of the low-voltage side busbar of a power transformer according to claim 1, characterized in that: The method further includes the following relationship: under steady-state conditions, the heat of the low-voltage side busbar of the power transformer satisfies the following relationship: ； Among them, Q R Q represents the heat loss per unit length of busbar resistance, expressed in W / m. t Q is the heat absorbed by the busbar per unit length from solar radiation, W / m; Q1 is the heat dissipation by air convection per unit length of the busbar, W / m; Q f This is the heat dissipation radiated per unit length of the busbar to the surrounding medium, expressed in W / m.

5. The method for online monitoring of the insulation status of the low-voltage side busbar of a power transformer according to claim 4, characterized in that: The method further includes ensuring that the temperature rise of the low-voltage side busbar conductors of the power transformer satisfies the following relationship: ； Where F is the total heat dissipation area of ​​the busbar conductors, m 2 ; It is the overall heat dissipation coefficient; It is the stable value that the temperature rise of the busbar conductor tends to reach.

6. The method for online monitoring of the insulation status of the low-voltage side busbar of a power transformer according to claim 5, characterized in that: The method also includes a stable temperature rise when the low-voltage side busbar conductor of the current transformer carries a current I for a long period of time: ； Where I is the current flowing through the busbar conductor, in A; and R is the resistance of the busbar conductor. .

7. The method for online monitoring of the insulation status of the low-voltage side busbar of a power transformer according to claim 1, characterized in that: The volumetric thermal power P of the low-voltage side busbar of the power transformer is: P=I 2 R / V; Where I is the operating current of the low-voltage side busbar of the power transformer, R is the resistance of the low-voltage side busbar core of the power transformer, and V is the volume of the low-voltage side busbar core of the power transformer.

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