Main transformer system active protection method for multi-index quantification overload safety at extreme high temperature

Abstract

The invention relates to the technical field of power system state evaluation and safety protection control, in particular to a main transformer system active protection method for multi-index quantification overload safety at extreme high temperature. According to the scheme, for disturbance such as station output limited transformation overload, overload safety and operation risks of the main transformer system are quantified from multiple dimensions such as real-time evaluation of the operation temperature, the fault rate, the insulation aging probability and failure probability evaluation of the main transformer system, and the overload safety and the operation risks of the main transformer system are obtained through mutual coordination and cooperation with a regulation and control center and a main transformer system circuit breaker; the evolution trend of the main transformer system in the state of'heavy load-overload-tolerance limit 'is accurately grasped, the overload capacity of the main transformer system is fully excavated on the premise of ensuring safety, and the conveying capacity and safe and stable operation of the main transformer system are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of power system status evaluation and safety protection control, and in particular to a main transformer system active protection method for quantitative overload safety with multiple indicators under extremely high temperatures. Background Art

[0002] With the rapid development of new power systems, the installed capacity and proportion of domestic power generation are also increasing rapidly. In new power systems, the main transformer system (main transformer system) plays a vital role, which can effectively convert and transmit signals to ensure the efficient operation of the power system. At present, for the overload safety problem of the main transformer system, the protection strategy usually adopted is the rapid locking backup protection, and the stabilization device implements emergency control measures such as cutting the machine and cutting the load to eliminate the overload. However, the existing protection method cannot obtain accurate information on the overload safety tolerance capacity and its changing trend of the main transformer system in real time, and cannot accurately grasp the degree and trend of the current state of the main transformer system deviating from the safety critical value, and cannot judge the safety tolerance time of the main transformer system.

[0003] In addition, the existing protection methods do not consider the high uncertainty and random power impact of the main transformer system in depth. They only characterize overload safety through a single deterministic method of indicators, and do not consider the impact of unit processing, load uncertainty, and ambient temperature changes on the overload operation of the main transformer system. This will inevitably affect the rationality of the main transformer system overload safety assessment results, and lack multi-dimensional uncertainty probability and other methods to quantify the overload safety and operation risks of the main transformer system. Therefore, there are still defects in the methods and protection strategies for multi-indicator quantitative characterization of the overload safety of the main transformer system. How to fully tap the overload capacity of the main transformer system under the premise of ensuring safety and improve the transmission capacity and safe and stable operation of the main transformer system has become a technical problem that technicians in this field need to solve urgently. Summary of the invention

[0004] The technical problem solved by the present invention is to provide an active protection method for the main transformer system with multi-indicator quantification of overload safety under extremely high temperatures to solve the technical problems that the existing power system protection methods are unable to obtain accurate information on the overload safety tolerance capacity and its changing trend of the main transformer system in real time, and are unable to accurately grasp the degree and trend of the current state of the main transformer system deviating from the safety critical value, and lack multi-dimensional uncertain probability and other methods to quantify the overload safety and operation risks of the main transformer system.

[0005] The basic solution provided by the present invention is a method for actively protecting a main transformer system with multi-index quantitative overload safety under extreme high temperature, comprising the following steps:

[0006] S1: Collect the allowable operating current value and the maximum allowable operating temperature of the main transformer system;

[0007] S2: Real-time collection of the main transformer system current value and meteorological environment parameter set, and judging whether an overload situation occurs according to the real-time collected current value; if the overload state criterion is not met, then continue to execute S2; if the overload state criterion is met, it indicates that the main transformer system enters an overload situation, and execute S3;

[0008] S3: Calculate the overload distance value based on the real-time collected current value, and send a heavy load alarm signal and the overload distance value to the control center; determine whether the main transformer system is overloaded based on the real-time current value; if the overload state criterion is not met, continue to execute S2; if the overload state criterion is met, it indicates that the main transformer system is in an overload state, and execute S4;

[0009] S4: According to the electrothermal coupling characteristics of the main transformer system, a current-temperature mapping relationship calculation formula is established to calculate the short-term allowable overload time of the overloaded main transformer system;

[0010] S5: According to the quantitative characterization index calculation formula of the main transformer system overload safety, four indicators including the main transformer system operating temperature, failure rate, insulation degradation probability and insulation failure probability are calculated;

[0011] S6: judging whether the main transformer system exceeds the overload safety boundary according to the calculated index values; if it does not exceed the overload safety boundary, continue to execute S2; if it exceeds the overload safety boundary, it indicates that the main transformer system enters an overload emergency situation, and execute S7;

[0012] S7: The main transformer system enters an overload emergency situation, calculates the power load reduction amount, and sends an output load reduction signal to the control center;

[0013] S8: comprehensively judge whether the main transformer system exceeds the tolerance limit according to the operating temperature value and overload time of the main transformer system; if the tolerance limit state criterion is not met, continue to execute S2; if the tolerance limit state criterion is met, it indicates that the main transformer system exceeds the tolerance limit, and execute S9;

[0014] S9: Send trip signals to the main transformer system circuit breaker and the control center respectively, and take active protection action to cut off the overloaded main transformer system to avoid damage to the main transformer system due to overload exceeding the tolerance limit, and end the work.

[0015] Furthermore, the meteorological environment parameter set S in S2 C Including: Main transformer system ambient temperature θ e 、Top oil temperature of main transformer system in steady state operation θ oilR and the main transformer system steady-state operation hot spot temperature θ hotR .

[0016] Furthermore, the overload state criterion in S2 is:

[0017] I c >I alert,I alert =αI cmax

[0018] In the formula, I c is the real-time current value; I alert is the heavy load current threshold of the main transformer system; α is the heavy load reliability coefficient; I cmax It is the allowable operating current value.

[0019] Further, in S3, the overload distance value I cd =I c -I alert ; Overload status criterion: I c >I cmax .

[0020] Further, in S4, the current-temperature mapping relationship is:

[0021]

[0022] In the formula, θ oil and θ hot They are the top oil temperature of the main transformer system in steady state operation and the hot spot temperature in steady state operation; θ Ra and θ hotRb are the steady-state hotspot temperatures before and after the main transformer system is overloaded; K is the load value of the main transformer system, that is, the ratio of the real-time current value to the rated current value; τ oil and τ w are the time constants of the main transformer system insulating oil and winding respectively; n and m are the nonlinear constant coefficients of heat transfer of the main transformer system insulating oil and winding respectively; Q is the ratio of load loss to no-load loss under the rated current operation condition of the main transformer system;

[0023] Short-term allowable overload time t of main transformer system equ The calculation includes:

[0024]

[0025] In the formula, τ equ is the equivalent time constant of the main transformer system; θ cmax is the maximum allowable operating temperature; C equ The equivalent thermal melt value of the main transformer system; R equ The equivalent thermal resistance of the heat transfer path from the inside to the outside of the main transformer system.

[0026] Furthermore, the S5 quantitative characterization index calculation formula is:

[0027] The operating temperature of the main transformer system includes the top oil temperature θ oil (t) and hot spot temperature θ hot (t), calculated by the current-temperature mapping relationship;

[0028] Main transformer system failure rate P cf (t) The calculation formula includes:

[0029]

[0030] Where β is the shape parameter of the Weibull distribution; δ is the empirical parameter; t is the time; θ cset The steady-state reference temperature of the main transformer system under rated operating conditions; T s1 and T equ They are the equivalent time that the main transformer system has been in service before the overload and the equivalent short-term continuous operation time after the overload;

[0031] Main transformer system degradation probability H IDP and the insulation failure probability of the main transformer system H IFP The calculation formulas are:

[0032] H IDP =P(θ c >θ cset )=S IDP / M

[0033] H IFP =P(θ c >θ cmax )=S IFP / M

[0034] In the formula, S IDP The frequency of accelerated insulation aging or further deterioration of insulation in the main transformer system during the overload equivalent time period; S IFP It is the frequency of failure and shutdown of the main transformer system due to insulation problems during the overload equivalent time period; M is the total number of state sampling.

[0035] Furthermore, the overload safety margin x in S6 cmax for:

[0036] x cmax ={θ cmax ,P cfmax ,H IDPmax ,H IFPmax}

[0037] In the formula, θ cmax , P cfmax , H IDPmax , H IFPmax are the operating temperature of the main transformer system θ c , failure rate P cf , insulation degradation probability H IDP and insulation failure probability H IFP The upper limit values ​​of the four indicators constitute the overload safety boundary of the main transformer system.

[0038] Further, the power load reduction amount calculation in S7 includes:

[0039]

[0040] Where P cut The power load reduction value is calculated based on the overload condition of the main transformer system, and the output load reduction signal is sent to the control center.

[0041] Furthermore, the calculation formula for the overload tolerance limit of the main transformer system in S8 is:

[0042]

[0043] ζ=(v∩μ)∪ω

[0044] In the formula, v, μ, ω, and ζ are all logical state variables. When v and μ variables are both 1, or ω variable is 1, ζ variable is assigned a value of 1, which means that the overload tolerance limit criterion of the main transformer system is met.

[0045] Furthermore, S8 also includes: when the overload tolerance limit indicates that the overload state of the main transformer system continues, and the aforementioned power load reduction method also fails to meet the requirements, when the operating temperature of the main transformer system reaches the maximum allowable operating temperature, or the tolerance time reaches the allowed time, the overloaded main transformer system is actively protected and cut off to prevent the main transformer system from burning due to excessive temperature.

[0046] The principles and advantages of the present invention are as follows: the active protection method of the main transformer system with multi-indicator quantitative overload safety under extreme high temperature of the present scheme, for disturbances such as transformer overload with limited station output, quantifies the overload safety and operation risk of the main transformer system from multiple dimensions such as real-time evaluation of the operating temperature, failure rate, insulation aging probability and failure probability evaluation of the main transformer system, and accurately grasps the evolution trend of the main transformer system in the state of "heavy load → overload → tolerance limit" through mutual coordination and cooperation with the control center and the main transformer system circuit breaker, fully taps the overload capacity of the main transformer system under the premise of ensuring safety, and improves the transmission capacity and safe and stable operation of the main transformer system. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 This is a flowchart of the steps of an embodiment of the method for active protection of a main transformer system with multi-indicator quantitative overload safety under extreme high temperature of the present invention.

[0048] Figure 2 This is a diagram showing the results of the safety quantitative characterization of an overloaded main transformer system using operating temperature indicators for active protection in an embodiment of the active protection method for a main transformer system with multiple indicators for quantifying overload safety under extremely high temperatures of the present invention.

[0049] Figure 3This is a flow chart of the results of the active protection of the main transformer system with multiple indicators for quantifying overload safety under extreme high temperature according to the embodiment of the present invention, which uses real-time failure rate indicators to quantify the safety of the overloaded main transformer system. DETAILED DESCRIPTION

[0050] The following is further described in detail through specific implementation methods:

[0051] The specific implementation process is as follows:

[0052] Embodiment 1

[0053] Embodiment 1 is basically as shown in the attached Figure 1 As shown, a method for actively protecting a main transformer system with multiple indicators for quantitative overload safety under extreme high temperature includes the following steps:

[0054] S1: Collect the allowable operating current value and the maximum allowable operating temperature of the main transformer system;

[0055] S2: Real-time collection of the main transformer system current value and meteorological environment parameter set, and judging whether an overload situation occurs according to the real-time collected current value; if the overload state criterion is not met, then continue to execute S2; if the overload state criterion is met, it indicates that the main transformer system enters an overload situation, and execute S3;

[0056] S3: Calculate the overload distance value based on the real-time collected current value, and send a heavy load alarm signal and the overload distance value to the control center; determine whether the main transformer system is overloaded based on the real-time current value; if the overload state criterion is not met, continue to execute S2; if the overload state criterion is met, it indicates that the main transformer system is in an overload state, and execute S4;

[0057] S4: According to the electrothermal coupling characteristics of the main transformer system, a current-temperature mapping relationship calculation formula is established to calculate the short-term allowable overload time of the overloaded main transformer system;

[0058] S5: According to the quantitative characterization index calculation formula of the main transformer system overload safety, four indicators including the main transformer system operating temperature, failure rate, insulation degradation probability and insulation failure probability are calculated;

[0059] S6: judging whether the main transformer system exceeds the overload safety boundary according to the calculated index values; if it does not exceed the overload safety boundary, continue to execute S2; if it exceeds the overload safety boundary, it indicates that the main transformer system enters an overload emergency situation, and execute S7;

[0060] S7: The main transformer system enters an overload emergency situation, calculates the power load reduction amount, and sends an output load reduction signal to the control center;

[0061] S8: comprehensively judge whether the main transformer system exceeds the tolerance limit according to the operating temperature value and overload time of the main transformer system; if the tolerance limit state criterion is not met, continue to execute S2; if the tolerance limit state criterion is met, it indicates that the main transformer system exceeds the tolerance limit, and execute S9;

[0062] S9: Send trip signals to the main transformer system circuit breaker and the control center respectively, and take active protection action to cut off the overloaded main transformer system to avoid damage to the main transformer system due to overload exceeding the tolerance limit, and end the work.

[0063] The overall protection function setting architecture of this method is simple, fast and easy to implement. It can effectively realize the active improvement of the overload capacity and transmission capacity of the main transformer system under the premise of ensuring overload safety. By targeting disturbances such as transformer overload with limited station output, the overload safety and operation risk of the main transformer system are quantified from multiple dimensions such as real-time evaluation of the main transformer system operating temperature, failure rate, insulation aging probability and failure probability evaluation. Through mutual coordination and cooperation with the control center and the main transformer system circuit breaker, the evolution trend of the main transformer system in the state of "heavy load → overload → tolerance limit" is accurately grasped. Under the premise of ensuring safety, the overload capacity of the main transformer system is fully exploited to improve the transmission capacity and safe and stable operation of the main transformer system.

[0064] Specifically, in S1, the rated parameters of the main transformer system under extreme high temperature weather are obtained according to the nameplate specifications of the main transformer system, and the long-term allowable operating current value I of the main transformer system is determined. cmax and the maximum allowable operating temperature θ cmax The values ​​of relevant parameters depend on the main transformer system model and station operation and maintenance requirements.

[0065] In S2, the operating status of the main transformer system is monitored in real time, and the real-time current value I of the main transformer system is collected and recorded based on the monitoring unit. c And the meteorological environment parameter collection S C , meteorological environment parameter set S C Including: Main transformer system ambient temperature θ e 、Top oil temperature of main transformer system in steady state operationθ oilR and the main transformer system steady-state operation hot spot temperature θ hotR . Then the main transformer system overload state criterion formula is established:

[0066] I c >I alert ,I alert =αI cmax

[0067] In the formula, I alert is the heavy load current threshold of the main transformer system; α is the heavy load reliability coefficient, usually 0.85-0.9; I cmax The allowable operating current value is based on the real-time monitored main transformer system current value I cDetermine whether an overload condition occurs; if the overload condition criterion is not met, continue to execute S2; if the overload condition criterion is met, it indicates that the main transformer system enters an overload condition, and execute S3.

[0068] In S3, the overload distance value I is calculated based on the current value collected in real time. cd =I c -I alert , send heavy load alarm signal and overload distance value to the control center; judge whether the main transformer system is overloaded according to the real-time current value. Among them, the overload status criterion is: I c >I cmax .

[0069] If the overload state criterion is not met, then S2 is continued to be executed. If the overload state criterion is met, it indicates that the main transformer system has entered an overload state, and S4 is executed.

[0070] In S4, according to the electrothermal coupling characteristics of the main transformer system, the current-temperature mapping relationship calculation formula is established:

[0071]

[0072] In the formula, θ oil and θ hot They are the top oil temperature of the main transformer system in steady state operation and the hot spot temperature in steady state operation; θ Ra and θ hotRb are the steady-state hotspot temperatures before and after the main transformer system is overloaded; K is the load value of the main transformer system, that is, the ratio of the real-time current value to the rated current value; τ oil and τ w are the time constants of the insulating oil and winding of the main transformer system respectively; n and m are the nonlinear constant coefficients of heat transfer of the insulating oil and winding of the main transformer system respectively, both of which depend on the specifications of the main transformer system; Q is the ratio of load loss to no-load loss under the rated current operating condition of the main transformer system.

[0073] When setting the maximum allowable operating temperature of the main transformer system θ cmax After that, the short-term allowable overload time t of the overload main transformer system can be calculated. equ :

[0074]

[0075] In the formula, τ equ is the equivalent time constant of the main transformer system; θ cmax is the maximum allowable operating temperature; C equ The equivalent thermal melt value of the main transformer system; R equ The equivalent thermal resistance of the heat transfer path from the inside to the outside of the main transformer system.

[0076] S5 establishes a quantitative characterization index calculation formula for the overload safety of the main transformer system, including four indicators: the operating temperature of the main transformer system, the failure rate, the probability of insulation degradation, and the probability of insulation failure, among which:

[0077] The operating temperature of the main transformer system includes the top oil temperature θ oil (t) and hot spot temperature θ hot (t), calculated by the current-temperature mapping relationship;

[0078] Main transformer system failure rate P cf (t) The calculation formula includes:

[0079]

[0080] Where β is the shape parameter of the Weibull distribution; δ is the empirical parameter; t is the time; θ cset The steady-state reference temperature of the main transformer system under rated operating conditions; T s1 and T equ They are the equivalent time that the main transformer system has been in service before the overload and the equivalent short-term continuous operation time after the overload;

[0081] Main transformer system degradation probability H IDP and the insulation failure probability of the main transformer system H IFP The calculation formulas are:

[0082] H IDP =P(θ c >θ cset )=S IDP / M

[0083] H IFP =P(θ c >θ cmax )=S IFP / M

[0084] In the formula, S IFP The frequency of accelerated insulation aging or further deterioration of insulation in the main transformer system during the overload equivalent time period; S IFP It is the frequency of failure and shutdown of the main transformer system due to insulation problems during the overload equivalent time period; M is the total number of state sampling.

[0085] In S6, it is determined whether the main transformer system exceeds the overload safety boundary according to the calculated index values; if it does not exceed the overload safety boundary, S2 is continued to be executed; if it exceeds the overload safety boundary, it indicates that the main transformer system enters an overload emergency situation, and S7 is executed.

[0086] In S7, the main transformer system enters an overload emergency situation, calculates the power load reduction, and sends an output load reduction signal to the control center. The power load reduction calculation includes:

[0087]

[0088] Where P cut The power load reduction value is calculated based on the overload condition of the main transformer system, and the output load reduction signal is sent to the control center.

[0089] S8 comprehensively judges whether the main transformer system exceeds the tolerance limit based on the operating temperature value and overload time of the main transformer system; the calculation formula for the overload tolerance limit of the main transformer system is:

[0090]

[0091] ζ=(v∩μ)∪ω

[0092] In the formula, v, μ, ω, and ζ are all logical state variables. When v and μ variables are both 1, or ω variable is 1, ζ variable is assigned a value of 1, which means that the overload tolerance limit criterion of the main transformer system is met.

[0093] If the tolerance limit state criterion is not met, S2 is continued to be executed. If the tolerance limit state criterion is met, it indicates that the main transformer system exceeds the tolerance limit, and S9 is executed. In addition, in S8, when the overload tolerance limit indicates that the main transformer system overload state continues, and the aforementioned power load reduction method also fails to meet the requirements, when the operating temperature of the main transformer system reaches the maximum allowable operating temperature, or the tolerance time reaches the allowed time, the overloaded main transformer system is actively protected and cut off to prevent the main transformer system from burning due to excessive temperature.

[0094] Finally, in S9, a trip signal is sent to the main transformer system circuit breaker and the control center respectively, and the active protection action cuts off the overloaded main transformer system to protect the main transformer system and avoid damage to the main transformer system due to overload exceeding the tolerance limit, thus completing the work.

[0095] In the specific implementation of this embodiment, in the grid-connected main transformer system of a new energy wind farm, 30 identical double-fed wind turbines are connected in parallel to the power collection test system, arranged in a 10×3 manner, with a single-machine power capacity of 1.5MW, and a collector line voltage value of 35kV, which is then connected to the main power grid through a 220kV step-up transformer. The wind farm test system grid-connected step-up main transformer system protection parameters are shown in Table 1-1. Assuming that the wind power system transmission channel has an overload fluctuation under extreme high temperature weather, the grid-connected transformer active protection method of the present invention is verified.

[0096] Table 1-1 Requirements for protection parameters of the grid-connected booster main transformer system of the wind farm test system

[0097] State variables Quantity / result Transformer model SFS11-90000 / 220 Maximum allowable operating temperature 160℃ Reference temperature under rated conditions 120℃ Real-time failure rate upper limit 1.0×10-5

[0098] By comparing the active protection method for the new energy grid-connected main transformer system of the present invention during overload in a high temperature environment with the method without taking protection control measures, the corresponding simulation results are obtained. Figure 2 and Figure 3 shown. Figure 2 The results of the safety quantitative characterization of the overloaded main transformer system using the operating temperature index in the embodiment of the present invention; Figure 3 This is the result of the safety quantitative characterization of the overloaded main transformer system using the real-time failure rate index in the embodiment of the present invention.

[0099] have Figure 2 , Figure 3 It can be seen that the multi-index quantitative overload safety active protection of the main transformer system proposed in the present invention can evaluate the operating temperature, failure rate, insulation aging probability and failure probability evaluation of the main transformer system in real time and quantify its overload safety and operation risks in multiple dimensions, and can effectively reduce control, and through mutual coordination with the control center and the transformer circuit breaker, accurately grasp the evolution trend of the main transformer system in the "heavy load → overload → tolerance limit" state, and under the premise of ensuring overload safety, realize the active improvement of the overload capacity and transmission capacity of the main transformer system under extreme high temperature weather, and ensure the safe and stable operation of the power system.

[0100] The above are only embodiments of the present invention. Common knowledge such as the known specific structures and characteristics in the scheme is not described in detail here. Ordinary technicians in the relevant field know all the common technical knowledge in the technical field to which the invention belongs before the application date or priority date, can obtain all the existing technologies in the field, and have the ability to apply conventional experimental means before that date. Ordinary technicians in the relevant field can improve and implement this scheme in combination with their own abilities under the enlightenment given by this application. Some typical known structures or known methods should not become obstacles for ordinary technicians in the relevant field to implement this application. It should be pointed out that for those skilled in the art, without departing from the structure of the present invention, several deformations and improvements can be made, which should also be regarded as the scope of protection of the present invention, and these will not affect the effect of the implementation of the present invention and the practicality of the patent. The scope of protection required by this application shall be based on the content of its claims, and the specific implementation methods and other records in the specification can be used to interpret the content of the claims.

Claims

1. A multi-index quantitative overload safety active protection method for main transformer system under extreme high temperature, characterized in that: Includes steps: S1: Collect the allowable operating current value and the maximum allowable operating temperature of the main transformer system; S2: Real-time collection of the main transformer system current value and meteorological environment parameter set, and judging whether an overload situation occurs according to the real-time collected current value; if the overload state criterion is not met, then continue to execute S2; if the overload state criterion is met, it indicates that the main transformer system enters an overload situation, and execute S3; S3: Calculate the overload distance value based on the real-time collected current value, and send a heavy load alarm signal and the overload distance value to the control center; determine whether the main transformer system is overloaded based on the real-time current value; if the overload state criterion is not met, continue to execute S2; if the overload state criterion is met, it indicates that the main transformer system is in an overload state, and execute S4; S4: According to the electrothermal coupling characteristics of the main transformer system, a current-temperature mapping relationship calculation formula is established to calculate the short-term allowable overload time of the overloaded main transformer system; S5: According to the quantitative characterization index calculation formula of the main transformer system overload safety, four indicators including the main transformer system operating temperature, failure rate, insulation degradation probability and insulation failure probability are calculated; S6: judging whether the main transformer system exceeds the overload safety boundary according to the calculated index values; if it does not exceed the overload safety boundary, continue to execute S2; if it exceeds the overload safety boundary, it indicates that the main transformer system enters an overload emergency situation, and execute S7; S7: The main transformer system enters an overload emergency situation, calculates the power load reduction amount, and sends an output load reduction signal to the control center; S8: comprehensively judge whether the main transformer system exceeds the tolerance limit according to the operating temperature value and overload time of the main transformer system; if the tolerance limit state criterion is not met, continue to execute S2; if the tolerance limit state criterion is met, it indicates that the main transformer system exceeds the tolerance limit, and execute S9; S9: Send trip signals to the main transformer system circuit breaker and the control center respectively, and take active protection action to cut off the overloaded main transformer system to avoid damage to the main transformer system due to overload exceeding the tolerance limit, and end the work.

2. The active protection method for main transformer system with multi-index quantitative overload safety under extreme high temperature according to claim 1 is characterized in that: The meteorological environment parameter set S in S2 C Including: Main transformer system ambient temperature θ e 、Top oil temperature of main transformer system in steady state operationθ oilR and the main transformer system steady-state operation hot spot temperature θ hotR .

3. The active protection method for main transformer system with multi-index quantitative overload safety under extreme high temperature according to claim 2 is characterized in that: The heavy load state criterion in S2 is: I c >I alert ,I alert =αI cmax In the formula, I c is the real-time current value; I alert is the heavy load current threshold of the main transformer system; α is the heavy load reliability coefficient; I cmax It is the allowable operating current value.

4. The active protection method for main transformer system with multi-index quantitative overload safety under extreme high temperature according to claim 3 is characterized in that: In S3, the overload distance value I cd =I c -I alert ; Overload status criterion: I c >I cmax .

5. The active protection method for main transformer system with multi-index quantitative overload safety under extreme high temperature according to claim 4 is characterized in that: In S4, the current-temperature mapping relationship is: In the formula, θ oil and θ hot They are the top oil temperature of the main transformer system in steady state operation and the hot spot temperature in steady state operation; θ Ra and θ hotRb are the steady-state hot spot temperatures before and after the main transformer system is overloaded; K is the load value of the main transformer system, that is, the ratio of the real-time current value to the rated current value; τ oil and τ w are the time constants of the main transformer system insulating oil and winding respectively; n and m are the nonlinear constant coefficients of heat transfer of the main transformer system insulating oil and winding respectively; Q is the ratio of load loss to no-load loss under the rated current operation condition of the main transformer system; Short-term allowable overload time t of main transformer system equ The calculation includes: In the formula, τ equ is the equivalent time constant of the main transformer system; θ cmax is the maximum allowable operating temperature; C equ is the equivalent thermal melt value of the main transformer system; R equ The equivalent thermal resistance of the heat transfer path from the inside to the outside of the main transformer system.

6. The active protection method for main transformer system with multi-index quantitative overload safety under extreme high temperature according to claim 5 is characterized in that: The S5 quantitative characterization index calculation formula is: The operating temperature of the main transformer system includes the top oil temperature θ oil (t) and hot spot temperature θ hot (t), calculated by the current-temperature mapping relationship; Main transformer system failure rate P cf (t) The calculation formula includes: Where β is the shape parameter of the Weibull distribution; δ is the empirical parameter, t is the time; θ cset The steady-state reference temperature of the main transformer system under rated operating conditions; T s1 and T equ They are the equivalent time that the main transformer system has been in service before the overload and the equivalent short-term continuous operation time after the overload; Main transformer system degradation probability H IDP and the insulation failure probability of the main transformer system H IFP The calculation formulas are: H IDP =P(θ c >θ cset )=S IDP / M H IFP =P(θ c >θ cmax )=S IFP / M In the formula, S IDP The frequency of accelerated insulation aging or further deterioration of insulation in the main transformer system during the overload equivalent time period; S IFP It is the frequency of failure and shutdown of the main transformer system due to insulation problems during the overload equivalent time period; M is the total number of state sampling.

7. The active protection method for main transformer system with multi-index quantitative overload safety under extreme high temperature according to claim 6 is characterized in that: The S6 overload safety margin x cmax for: x cmax ={θ cmax ,P cfmax ,H IDPmax ,H IFPmax } In the formula, θ cmax , P cfmax , H IDPmax , H IFPmax are the operating temperature of the main transformer system θ c , failure rate P cf , insulation degradation probability H IDP and insulation failure probability H IFP The upper limit values ​​of the four indicators constitute the overload safety boundary of the main transformer system.

8. The active protection method for main transformer system with multi-index quantitative overload safety under extreme high temperature according to claim 7 is characterized in that: The power reduction amount calculation in S7 includes: Where P cut The power load reduction value is calculated based on the overload condition of the main transformer system, and the output load reduction signal is sent to the control center.

9. The active protection method for main transformer system with multi-index quantitative overload safety under extreme high temperature according to claim 8 is characterized in that: Furthermore, the calculation formula for the overload tolerance limit of the main transformer system in S8 is: In the formula, v, μ, ω, and ζ are all logical state variables. When v and μ variables are both 1, or ω variable is 1, ζ variable is assigned a value of 1, which means that the overload tolerance limit criterion of the main transformer system is met.

10. The active protection method for main transformer system with multi-index quantitative overload safety under extreme high temperature according to claim 9 is characterized in that: The S8 also includes: when the overload tolerance limit indicates that the main transformer system is in a continuous overload state, and the aforementioned power load reduction method also fails to meet the requirements, when the operating temperature of the main transformer system reaches the maximum allowable operating temperature, or the tolerance time reaches the allowed time, active protection is performed to cut off the overloaded main transformer system to prevent the main transformer system from burning due to excessive temperature.

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