Transformer active protection method and system based on multi-index quantification overload safety

Abstract

The invention provides a transformer active protection method and system based on multi-index quantification overload safety, which can be applied to a new energy grid-connected transformer. Specifically, according to the method, the overload safety and the operation risk of the transformer are quantified by evaluating the operation temperature, the fault rate, the insulation deterioration probability, the insulation failure probability and the like of the transformer in real time, and a new energy dispatching control center and a transformer circuit breaker are coordinated and matched with each other; and the evolution trend of the transformer from a heavy load state to an overload state and then to a tolerance limit state can be accurately grasped. On the premise that overload safety is guaranteed, active improvement of the overload capacity and the power transmission capacity of the transformer can be achieved, and therefore safe and stable operation of a new energy grid-connected system is guaranteed. Therefore, the method can effectively improve the safety protection accuracy of the transformer under the condition that the transformer is overloaded.

Description

Technical Field

[0001] The present invention relates to the technical field of power transformer status evaluation and safety protection control, and in particular to a transformer active protection method and system based on multi-indicator quantitative overload safety. Background Art

[0002] With the rapid increase in installed capacity and proportion of renewable energy power generation, building a new power system with renewable energy as one of the main power sources has become a development goal. The renewable energy grid-connected transformer is a special transformer that is mainly used in the field of renewable energy, such as photovoltaic and wind power grid-connected systems, to achieve the grid connection of renewable energy and efficient conversion of electric energy. The renewable energy grid-connected transformer plays a vital role in the renewable energy system, and can effectively convert and transmit signals to ensure the efficient operation of the system. However, since the development cycle of renewable energy is much shorter than the construction cycle of the power grid, the power transmission of renewable energy clusters is greatly restricted. The step-up transformer of the renewable energy station is overloaded, and the output of renewable energy has to be restricted, and a large number of wind and solar power are abandoned.

[0003] At present, for the overload safety problem of grid-connected transformers, the commonly used protection method is fast 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, this protection method cannot obtain accurate information on the overload safety tolerance capacity and its changing trend of the grid-connected transformer in real time, and cannot accurately grasp the degree and trend of the current state of the grid-connected transformer deviating from the safety critical value, and cannot judge the safe tolerance time of the transformer. At the same time, the high uncertainty and random power impact of the new energy grid-connected transformer is not considered in depth, and only a single deterministic indicator method is used to characterize overload safety, without considering the impact of the output of new energy units, load uncertainty, and ambient temperature changes on the overload operation of the transformer. This will affect the rationality of the transformer overload safety assessment results, lack of multi-dimensional uncertainty probability and other methods to quantify the overload safety and operation risks of the grid-connected transformer, resulting in the inability to accurately protect the transformer when the transformer is overloaded. Summary of the invention

[0004] The technical problem to be solved by the present invention is that when the transformer is overloaded, the overload safety of the transformer cannot be accurately evaluated, thereby resulting in the inability to accurately protect the transformer.

[0005] In order to solve the above technical problems, the present invention provides a transformer active protection method and system based on multi-index quantitative overload safety, which specifically adopts the following technical solutions:

[0006] In the first aspect, the present invention provides a transformer active protection method based on multi-index quantitative overload safety, comprising: first, obtaining the rated parameters of the target transformer, and determining the long-term allowable operating current value and the maximum allowable operating temperature of the target transformer, the rated parameters are used to characterize the specifications and performance of the target transformer. Then, monitoring the operating state of the target transformer, obtaining the current monitoring value and the meteorological environment parameter monitoring value of the target transformer. Next, according to the current monitoring value and the long-term allowable operating current value, through the transformer overload state judgment formula, determine whether the target transformer is in an overload state. In the case where the target transformer is in an overload state, determine the overload distance value according to the current monitoring value, and send an overload alarm signal and the overload distance value. According to the current monitoring value and the long-term allowable operating current value, through the transformer overload state judgment formula, determine whether the target transformer is in an overload state. Secondly, in the case where the target transformer is in an overload state, according to the rated parameters and the meteorological environment parameter monitoring values, through the current-temperature mapping relationship calculation formula, determine the overload transformer short-term allowable overload time of the target transformer. According to the rated parameters and meteorological environment parameters, the overload safety quantitative characterization indicators of the target transformer are determined, and the overload safety quantitative characterization indicators include: transformer operating temperature, failure rate, insulation degradation probability and insulation failure probability. Further, it is determined whether the transformer operating temperature, failure rate, insulation degradation probability and insulation failure probability exceed the corresponding preset overload safety boundary. In the case that at least one of the characterization indicators of the transformer operating temperature, failure rate, insulation degradation probability and insulation failure probability exceeds the corresponding preset overload safety boundary, the power load reduction amount is determined according to the output power load reduction calculation formula based on the current monitoring value, and the output load reduction signal is sent, and the output load reduction signal includes the power load reduction amount. According to the current monitoring value and the meteorological environment parameter monitoring value, it is determined whether the target transformer is in a state beyond the tolerance limit through the overload tolerance limit calculation formula. Finally, in the case that the target transformer is in a state beyond the tolerance limit, a trip signal is sent so that the target transformer performs a trip closure in response to the trip signal.

[0007] In combination with the first aspect, in an optional implementation, the transformer overload state criterion formula is:

[0008] I c >I alert ;

[0009] I alert =αI cmax ;

[0010] Among them, I c Indicates the current monitoring value, I alert represents the transformer heavy load current threshold, α represents the heavy load reliability factor, I cmax Indicates the long-term allowable operating current value.

[0011] In combination with the first aspect, in an optional implementation, the calculation formula of the overload distance value is:

[0012] I cd =I c -I alert ;

[0013] Among them, I cd Indicates the overload distance value, I c Indicates the current monitoring value, I alert Indicates the transformer heavy load current threshold.

[0014] In combination with the first aspect, in an optional implementation, the transformer overload state criterion formula is:

[0015] I c >I cmax ;

[0016] Among them, I c Indicates the current monitoring value, I cmax Indicates the long-term allowable operating current value.

[0017] In combination with the first aspect, in an optional implementation, the meteorological environmental parameter monitoring value includes: the top oil temperature of the transformer in steady-state operation and the hot spot temperature of the transformer in steady-state operation. Then the above current-temperature mapping relationship calculation formula is:

[0018]

[0019] Among them, θ oilR Indicates the top oil temperature of the transformer in steady-state operation, θ hotR Indicates the hot spot temperature of the transformer in steady-state operation, θ hotRb Represents the steady-state hot spot temperature value of the target transformer after overload, θ hotRa represents the steady-state hot spot temperature value of the target transformer before overload, K represents the load value of the target transformer, τ oil represents the time constant of insulating oil, τ w represents the time constant of the winding, n represents the heat transfer nonlinear constant coefficient of the insulating oil, m represents the heat transfer nonlinear constant coefficient of the winding, and Q represents the ratio of the load loss to the no-load loss under the rated current operating condition of the target transformer.

[0020] In combination with the first aspect, in an optional implementation, the expression for the short-term allowable overload time of the overload transformer is:

[0021]

[0022] Among them, t equ Indicates the short-term allowable overload time of the overload transformer, τ equrepresents the equivalent time constant of the target transformer, C equ Represents the equivalent thermal capacity of the target transformer, R equ The equivalent thermal resistance of the heat transfer path from the inside to the outside of the target transformer, θ cmax Indicates the maximum allowable operating temperature of the target transformer.

[0023] In combination with the first aspect, in an optional implementation, the above failure rate is calculated as follows:

[0024]

[0025] Among them, P cf (t) represents the failure rate, β represents the shape parameter of the Weibull distribution, δ represents the empirical parameter, and θ cset It represents the steady-state reference temperature of the target transformer under rated conditions, T s1 represents the equivalent time that the target transformer has been in service before overloading, T equ It indicates the equivalent continuous operation time of the target transformer in a short time after overload, t indicates the monitoring time, t equ Indicates the short-term allowable overload time of the overload transformer, θ hot (t) represents the hot spot temperature of the transformer. The calculation formula for the probability of insulation degradation is:

[0026] H IDP =P(θ c >θ cset )=S IDP / M;

[0027] Among them, H IDP Indicates the probability of insulation degradation, S IDP Indicates the frequency of accelerated insulation aging or further deterioration of the insulation of the transformer during the overload equivalent time period, θ cset represents the steady-state reference temperature of the target transformer under rated conditions, θ c represents the transformer operating temperature, and M represents the total number of state sampling. The calculation formula for the insulation failure probability is:

[0028] H IFP =P(θ c >θ cmax )=S IFP / M;

[0029] Among them, H IFP represents the probability of insulation failure, S IFP Indicates the frequency of transformer failure and shutdown due to insulation problems within the overload equivalent time period.

[0030] In combination with the first aspect, in an optional implementation, the output power load reduction calculation formula is:

[0031]

[0032] Among them, P cut Indicates the power reduction, I c Indicates the current monitoring value, I cmax represents the long-term allowable operating current value, and K represents the load value of the target transformer.

[0033] In combination with the first aspect, in an optional implementation, the above overload tolerance limit calculation formula is:

[0034] ξ=(υ∩μ)∪ω;

[0035]

[0036] Wherein, ξ represents the first logic state variable, υ represents the second logic state variable, μ represents the third logic state variable, ω represents the fourth logic state variable, I c Indicates the current monitoring value, I cmax Indicates the long-term allowable operating current value, t c Indicates the overload time, I cmax Indicates the maximum allowable overload time, θ c Indicates the transformer operating temperature, θ cmax Indicates the maximum allowable operating temperature of the target transformer. When v and μ are both 1, or ω is 1, ξ is 1. When ξ is 1, it is determined that the target transformer is in a state of exceeding the tolerance limit.

[0037] The transformer active protection method based on multi-indicator quantified overload safety provided in the first aspect is adopted. For disturbances such as transformer overload with limited station output, the overload safety and operation risk of the target transformer (for example, new energy grid-connected transformer) are quantified in multiple dimensions such as real-time evaluation of the transformer operating temperature, failure rate, insulation degradation probability and insulation failure probability evaluation. The evolution trend of the target transformer from "heavy load state" to "overload state" and then to "tolerance limit state" can be accurately grasped through mutual coordination and cooperation with the new energy dispatching control center and the target transformer circuit breaker.

[0038] Moreover, the overall protection function setting architecture of this method is simple, fast and easy to implement. It can effectively achieve the active improvement of the overload capacity and transmission capacity of the target transformer while ensuring overload safety, thereby ensuring the safe and stable operation of the grid-connected system, and is an effective supplement to the traditional transformer overload or overload protection technology.

[0039] Therefore, this method can quantify the overload safety and operation risk of the grid-connected transformer through multi-dimensional uncertain probability, thereby improving the accuracy of transformer protection when the transformer is overloaded.

[0040] In a second aspect, the present invention provides a transformer active protection system based on multi-index quantitative overload safety, the transformer active protection system is connected to a target transformer and a dispatching control center, and the dispatching control center is connected to a grid-connected system. Among them, the transformer active protection system is used to: obtain the rated parameters of the target transformer, and determine the long-term allowable operating current value and the maximum allowable operating temperature of the target transformer, and the rated parameters are used to characterize the specifications and performance of the target transformer. Monitor the operating state of the target transformer, and obtain the current monitoring value and the meteorological environment parameter monitoring value of the target transformer. According to the current monitoring value and the long-term allowable operating current value, through the transformer overload state judgment formula, determine whether the target transformer is in an overload state. In the case where the target transformer is in an overload state, determine the overload distance value according to the current monitoring value, and send an overload alarm signal and the overload distance value to the dispatching control center. According to the current monitoring value and the long-term allowable operating current value, through the transformer overload state judgment formula, determine whether the target transformer is in an overload state. In the case where the target transformer is in an overload state, determine the short-term allowable overload time of the overload transformer of the target transformer through the current-temperature mapping relationship calculation formula according to the rated parameters and the meteorological environment parameter monitoring values. According to the rated parameters and meteorological environment parameters, the overload safety quantitative characterization index of the target transformer is determined, and the overload safety quantitative characterization index includes: transformer operating temperature, failure rate, insulation degradation probability and insulation failure probability. Determine whether the transformer operating temperature, failure rate, insulation degradation probability and insulation failure probability exceed the corresponding preset overload safety boundary. In the case that at least one characterization index among the transformer operating temperature, failure rate, insulation degradation probability and insulation failure probability exceeds the corresponding preset overload safety boundary, determine the power load reduction amount according to the output power load reduction calculation formula according to the current monitoring value, and send an output load reduction signal to the dispatching control center so that the dispatching control center controls the grid-connected system to reduce the load according to the output load reduction signal, and the output load reduction signal includes the power load reduction amount. According to the current monitoring value and the meteorological environment parameter monitoring value, determine whether the target transformer is in a state beyond the tolerance limit through the overload tolerance limit calculation formula. In the case that the target transformer is in a state beyond the tolerance limit, send a trip signal to the target transformer and the dispatching control center so that the target transformer performs a trip closure in response to the trip signal.

[0041] It can be understood that the beneficial effects of the transformer active protection system based on multi-indicator quantitative overload safety provided by the second aspect can be referred to the beneficial effects in the first aspect and any possible design method thereof, and will not be repeated here. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 A flowchart of a transformer active protection method based on multi-index quantitative overload safety provided by an embodiment of the present invention;

[0043] Figure 2 A schematic diagram of the safety quantitative characterization results of an overload transformer using two indicators, transformer insulation aging rate and failure rate, for active protection of a new energy grid-connected transformer provided in an embodiment of the present invention;

[0044] Figure 3 A schematic diagram of the safety quantitative characterization result of an overload transformer using an operating temperature index for active protection of a new energy grid-connected transformer provided in an embodiment of the present invention;

[0045] Figure 4 A schematic diagram of the safety quantitative characterization result of an overload transformer using a real-time fault rate index for active protection of a new energy grid-connected transformer provided in an embodiment of the present invention;

[0046] Figure 5 A schematic diagram of an application scenario of a transformer active protection system based on multi-indicator quantitative overload safety provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0047] The following embodiments are described in detail, and examples thereof are shown in the accompanying drawings. When the following description refers to the drawings, unless otherwise indicated, the same numbers in different drawings represent the same or similar elements. The implementations described in the following embodiments do not represent all implementations consistent with the present application. They are only examples of systems and methods consistent with some aspects of the present application as detailed in the claims.

[0048] At present, for the overload safety problem of grid-connected transformers, the commonly used protection method is fast 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, this protection method cannot obtain accurate information on the overload safety tolerance capacity and its changing trend of the grid-connected transformer in real time, and cannot accurately grasp the degree and trend of the current state of the grid-connected transformer deviating from the safety critical value, and cannot judge the safe tolerance time of the transformer. At the same time, the high uncertainty and random power impact of the new energy grid-connected transformer is not considered in depth, and only a single deterministic indicator method is used to characterize overload safety, without considering the impact of the output of new energy units, load uncertainty, and ambient temperature changes on the overload operation of the transformer. This will affect the rationality of the transformer overload safety assessment results, lack of multi-dimensional uncertainty probability and other methods to quantify the overload safety and operation risks of the grid-connected transformer, resulting in the inability to accurately protect the transformer when the transformer is overloaded.

[0049] In order to solve the above problems, the embodiment of the present application provides a transformer active protection method and system based on multi-indicator quantified overload safety, which can be applied to the new energy grid-connected transformer in the new energy grid-connected system. Specifically, the method quantifies the overload safety and operation risk of the transformer in multiple dimensions by real-time evaluation of the transformer operating temperature, failure rate, insulation degradation probability and insulation failure probability evaluation of the transformer, and can accurately grasp the evolution trend of the transformer from "heavy load state" to "overload state" and then to "tolerance limit state" through mutual coordination and cooperation with the new energy dispatching control center and the transformer circuit breaker. Under the premise of ensuring overload safety, the overload capacity and power transmission capacity of the transformer are actively improved to ensure the safe and stable operation of the new energy grid-connected system. Therefore, it can effectively improve the accuracy of the safety protection of the transformer when the transformer is overloaded.

[0050] The solution provided by the embodiment of the present application is introduced below in conjunction with the accompanying drawings.

[0051] For details, see Figure 1 , which is a flow chart of a transformer active protection method based on multi-index quantitative overload safety provided by an embodiment of the present invention, such as Figure 1 As shown, the transformer active protection method based on multi-index quantitative overload safety provided by the present invention includes the following steps S101-S111:

[0052] S101. Obtain rated parameters of a target transformer, and determine a long-term allowable operating current value and a maximum allowable operating temperature of the target transformer.

[0053] Specifically, the target transformer may be a new energy grid-connected transformer to be protected. The rated parameters may be used to characterize the specifications and performance of the target transformer. For example, the rated parameters may be parameters such as the nameplate specifications of the target transformer.

[0054] In one implementation, the long-term allowable operating current value and the maximum allowable operating temperature of the target transformer can be determined based on the model of the target transformer and the operation and maintenance requirements of the site where the target transformer is located (for example, a new energy site).

[0055] S102: Monitor the operating status of the target transformer, and obtain the current monitoring value and meteorological environment parameter monitoring value of the target transformer.

[0056] Specifically, the operating status of the target transformer is monitored in real time. In one implementation, the current monitoring value of the target transformer can be collected and recorded in real time based on the monitoring unit. The meteorological environment parameter monitoring value of the target transformer can also be collected and recorded based on the micro-meteorological environment of the target transformer and the non-electrical quantity online monitoring unit.

[0057] Among them, the meteorological environment parameter monitoring values ​​may include: transformer ambient temperature, transformer steady-state operation top oil temperature and transformer steady-state operation hot spot temperature. The current monitoring value and the meteorological environment parameter monitoring value can be used to quantitatively evaluate the overload safety of the target transformer.

[0058] S103. Determine whether the target transformer is in an overload state according to the current monitoring value and the long-term allowable operating current value and the transformer overload state criterion formula.

[0059] In the embodiment of the present invention, a transformer overload state criterion formula can be established, and whether the target transformer is in an overload state can be determined by the transformer overload state criterion formula according to the current monitoring value and the long-term allowable operating current value.

[0060] In some embodiments, the transformer overload state criterion is:

[0061]

[0062] In formula (1), I c Indicates the current monitoring value, I alert represents the transformer heavy load current threshold, α represents the heavy load reliability factor, I cmax Indicates the long-term allowable operating current value. cmax It can be preset according to prior knowledge, specification parameters of the target transformer and actual protection application requirements. The value range of α can be, for example, 0.85-0.9.

[0063] Taking the transformer overload state criterion shown in formula (1) as an example, when I c >I alert If the target transformer is in a heavy load state, it can be determined that the target transformer is in a heavy load state. Otherwise, it can be determined that the target transformer is not in a heavy load state, and S102 is continued.

[0064] S104. When the target transformer is in an overload state, determine an overload distance value according to the current monitoring value, and send an overload alarm signal and the overload distance value.

[0065] Furthermore, when the target transformer is in an overload state, the overload distance value can be determined according to the current monitoring value. Then, an overload alarm signal and an overload distance value can be sent to a dispatching control center (e.g., a new energy grid-connected dispatching control center). This can warn the dispatching control center that the target transformer is in an overload state, and the dispatching control center can also adjust the load in the system according to the overload distance value to reduce the load of the target transformer.

[0066] In some embodiments, the calculation formula of the overload distance value is:

[0067] I cd=I c -I alert (2)

[0068] In formula (2), I cd Indicates the overload distance value, I c Indicates the current monitoring value, I alert Indicates the transformer heavy load current threshold.

[0069] S105. Determine whether the target transformer is in an overload state according to the current monitoring value and the long-term allowable operating current value by using a transformer overload state criterion formula.

[0070] In the embodiment of the present invention, a transformer overload state criterion formula may also be established, and whether the target transformer is in an overload state may be determined by the transformer overload state criterion formula according to the current monitoring value and the long-term allowable operating current value.

[0071] In some embodiments, the transformer overload state criterion is:

[0072] I c >I cmax (3)

[0073] In formula (3), I c Indicates the current monitoring value, I cmax Indicates the long-term allowable operating current value.

[0074] Taking the transformer overload state criterion formula shown in formula (3) as an example, when I c >I cmax If the target transformer is in an overload state, it can be determined that the target transformer is in an overload state. Otherwise, it can be determined that the target transformer is not in an overload state, and S102 is continued.

[0075] S106. When the target transformer is in an overload state, determine the overload transformer short-term allowable overload time of the target transformer according to the rated parameters and the meteorological environment parameter monitoring values ​​through the current-temperature mapping relationship calculation formula.

[0076] Furthermore, when the target transformer is in an overload state, a current-temperature mapping relationship calculation formula can be established in combination with the electrothermal coupling characteristics of the target transformer to calculate the short-term allowable overload time of the overload transformer.

[0077] In some embodiments, the current-temperature mapping relationship is calculated as:

[0078]

[0079] In formula (4), θ oilR Indicates the top oil temperature of the transformer in steady-state operation, θ hotR Indicates the hot spot temperature of the transformer in steady-state operation, θhotRb Represents the steady-state hot spot temperature value of the target transformer after overload, θ hotRa represents the steady-state hot spot temperature value of the target transformer before overload, K represents the load value of the target transformer, τ oil represents the time constant of insulating oil, τ w represents the time constant of the winding, n represents the heat transfer nonlinear constant coefficient of the insulating oil, m represents the heat transfer nonlinear constant coefficient of the winding, and Q represents the ratio of the load loss to the no-load loss under the rated current operating condition of the target transformer.

[0080] Among them, n and m can depend on the transformer specifications, K, τ oil , τ w , n, m and Q can be determined based on the rated parameters obtained in S101.

[0081] In some embodiments, the expression for the short-term allowable overload time of the overload transformer is:

[0082]

[0083] In formula (5), t equ Indicates the short-term allowable overload time of the overload transformer, τ equ represents the equivalent time constant of the target transformer, C equ Indicates the equivalent thermal capacity of the target transformer, C equ It can be obtained based on the internal insulation oil, winding and oil tank heat transfer path of the target transformer, R equ The equivalent thermal resistance of the heat transfer path from the inside to the outside of the target transformer, θ cmax Indicates the maximum allowable operating temperature of the target transformer.

[0084] Among them, θ cmax It can be preset based on prior knowledge, specification parameters of the target transformer and the requirements of the actual protection application. equ The values ​​of the internal insulating oil, winding and oil tank heat transfer path of the target transformer can be determined based on the rated parameters obtained in S101.

[0085] S107. Determine the quantitative characterization index of overload safety of the target transformer based on the rated parameters and meteorological environment parameters.

[0086] In the embodiment of the present invention, a quantitative characterization index of overload safety of a target transformer may be established. Specifically, the quantitative characterization index of overload safety includes: transformer operating temperature, failure rate, insulation degradation probability and insulation failure probability.

[0087] In some embodiments, the transformer operating temperature can be determined by the expression shown in equation (4) above.

[0088] The failure rate is calculated as:

[0089]

[0090] In formula (6), P cf (t) represents the failure rate, β represents the shape parameter of the Weibull distribution, δ represents the empirical parameter, and θ cset It represents the steady-state reference temperature of the target transformer under rated conditions, T s1 represents the equivalent time that the target transformer has been in service before overloading, T equ It indicates the equivalent continuous operation time of the target transformer in a short time after overload, t indicates the monitoring time, t equ Indicates the short-term allowable overload time of the overload transformer, θ hot (t) represents the hot spot temperature of the transformer.

[0091] Among them, δ, θ cset , T s1 , T equ It can be obtained based on prior knowledge, or preset based on the specification parameters of the target transformer and the requirements of the actual protection application.

[0092] The calculation formula for the probability of insulation degradation is:

[0093] H IDP =P(θ c >θ cset )=S IDP / M (7)

[0094] In formula (7), H IDP Indicates the probability of insulation degradation, S IDP It indicates the frequency of accelerated insulation aging or further deterioration of the insulation of the transformer during the overload equivalent time period, S IDP It can be obtained based on prior knowledge. cset represents the steady-state reference temperature of the target transformer under rated conditions, θ c Represents the transformer operating temperature, and M represents the total number of state sampling times.

[0095] The calculation formula for the insulation failure probability is:

[0096] H IFP =P(θ c >θ cmax )=S IFP / M (8)

[0097] In formula (8), H IFP represents the probability of insulation failure, S IFP It indicates the frequency of transformer failure and shutdown due to insulation problems during the overload equivalent time period.IFP It can be obtained based on prior knowledge.

[0098] S108. Determine whether the transformer operating temperature, failure rate, insulation degradation probability, and insulation failure probability exceed corresponding preset overload safety boundaries.

[0099] Furthermore, the preset overload safety boundaries (i.e., upper limit boundary values) corresponding to the transformer operating temperature, failure rate, insulation degradation probability, and insulation failure probability can be preset according to prior knowledge, specification parameters of the target transformer, and the requirements of the actual protection application.

[0100] Exemplarily, the expressions of the preset overload safety margins corresponding to the transformer operating temperature, failure rate, insulation degradation probability, and insulation failure probability are respectively as follows:

[0101] x cmax ={θ cmax , P cfmax , H IDPmax , H IFPmax} (9)

[0102] In formula (9), x cmax represents the preset overload safety boundary set of the quantitative characterization index of overload safety, θ cmax Indicates the preset overload safety margin corresponding to the transformer operating temperature, P cfmax represents the preset overload safety margin corresponding to the failure rate, H IDPmax represents the preset overload safety margin corresponding to the probability of insulation degradation, H IFPmax Indicates the preset overload safety margin corresponding to the insulation failure probability.

[0103] S109. When at least one of the characterization indicators of the transformer operating temperature, failure rate, insulation degradation probability and insulation failure probability exceeds the corresponding preset overload safety boundary, the power load reduction amount is determined according to the output power load reduction calculation formula based on the current monitoring value, and an output load reduction signal is sent, and the output load reduction signal includes the power load reduction amount.

[0104] Next, if at least one of the transformer operating temperature, failure rate, insulation degradation probability and insulation failure probability exceeds the corresponding preset overload safety boundary, it is determined that the target transformer enters an overload emergency situation. Otherwise, continue to execute S102.

[0105] Furthermore, an output power load reduction calculation formula may be established to calculate the power load reduction amount, and an output load reduction signal including the power load reduction amount may be sent.

[0106] In some embodiments, the output power load reduction calculation formula is:

[0107]

[0108] In formula (10), P cut Indicates the power reduction, I c Indicates the current monitoring value, I cmax represents the long-term allowable operating current value, and K represents the load value of the target transformer.

[0109] S110. Determine whether the target transformer is in a state exceeding the tolerance limit according to the current monitoring value and the meteorological environment parameter monitoring value by using the overload tolerance limit calculation formula.

[0110] In an embodiment of the invention, further, an overload tolerance limit calculation formula can be established to comprehensively judge whether the target transformer exceeds the tolerance limit, that is, whether it is in a state of exceeding the tolerance limit, based on the current monitoring value and the meteorological environment parameter monitoring value, combined with the transformer operating temperature value and the overload time.

[0111] In some embodiments, the overload tolerance limit calculation formula is:

[0112] ξ=(v∩λ)∪ω (11)

[0113]

[0114]

[0115] In formula (11) to formula (14), ξ represents the first logic state variable, υ represents the second logic state variable, μ represents the third logic state variable, ω represents the fourth logic state variable, I c Indicates the current monitoring value, I cmax Indicates the long-term allowable operating current value, t c Indicates the overload time, I cmax Indicates the maximum allowable overload time, θ c Indicates the transformer operating temperature, θ cmax Indicates the maximum allowable operating temperature of the target transformer.

[0116] As shown in equations (11) to (14), when both υ and μ are 1, or ω is 1, ξ is 1. When ξ is 1, it can be determined that the target transformer is in a state beyond the tolerance limit.

[0117] S111 . When a target transformer is in a state of exceeding a tolerance limit, a trip signal is sent, so that the target transformer performs a trip shutdown in response to the trip signal.

[0118] Finally, when it is determined that the target transformer is in a state beyond the tolerance limit, a trip signal can be sent to the target transformer so that the target transformer (circuit breaker) performs a trip closure in response to the trip signal. In this way, the overloaded target transformer can be removed by active protection action, the target transformer can be protected, and damage to the target transformer due to overload beyond the tolerance limit can be avoided, and the work is ended.

[0119] By adopting the transformer active protection method based on multi-indicator quantified overload safety provided by the embodiment of the present invention, for disturbances such as transformer overload with limited station output, the overload safety and operation risk of the target transformer (for example, new energy grid-connected transformer) are quantified from multiple dimensions such as real-time evaluation of the transformer operating temperature, failure rate, insulation degradation probability and insulation failure probability evaluation. The evolution trend of the target transformer from "heavy load state" to "overload state" and then to "tolerance limit state" can be accurately grasped through mutual coordination and cooperation with the new energy control center and the target transformer circuit breaker.

[0120] Moreover, the overall protection function setting architecture of this method is simple, fast and easy to implement. It can effectively achieve the active improvement of the overload capacity and transmission capacity of the target transformer while ensuring overload safety, thereby ensuring the safe and stable operation of the grid-connected system, and is an effective supplement to the traditional transformer overload or overload protection technology.

[0121] Therefore, this method can quantify the overload safety and operation risk of the grid-connected transformer through multi-dimensional uncertain probability, thereby improving the accuracy of transformer protection when the transformer is overloaded.

[0122] In some embodiments, in order to verify the feasibility and effectiveness of the transformer active protection method based on multi-index quantitative overload safety provided by the embodiments of the present invention, an analysis test was conducted.

[0123] For example, taking the target transformer as a new energy grid-connected transformer, it is assumed that a parallel collection test system of 30 identical double-fed wind turbines is included, arranged in a 10×3 manner, with a single-machine power capacity of 1.5MW, a collector line voltage of 35kV, and then connected to the main power grid through a 220kV new energy grid-connected transformer. The parameters of the active protection of the new energy grid-connected transformer are shown in Table 1. Assuming that an overload fluctuation occurs in the wind power system transmission channel, the transformer active protection method based on multi-indicator quantitative overload safety implemented by the present invention is verified.

[0124] Table 1 Requirements for active protection parameters of new energy grid-connected transformers

[0125]

[0126] By comparing the transformer active protection method based on multi-index quantitative overload safety provided by the embodiment of the present invention during overload period with the method without taking protection control measures, corresponding simulation results are obtained. Figure 2 A schematic diagram of the safety quantitative characterization results of an overload transformer using two indicators, transformer insulation aging rate and failure rate, for active protection of a new energy grid-connected transformer provided in an embodiment of the present invention. Figure 3 A schematic diagram of the safety quantitative characterization results of an overload transformer using an operating temperature index for active protection of a new energy grid-connected transformer provided in an embodiment of the present invention. Figure 4 A schematic diagram of the safety quantitative characterization results of an overload transformer using a real-time fault rate indicator for active protection of a new energy grid-connected transformer provided in an embodiment of the present invention.

[0127] like Figure 2 As shown, the insulation degradation rate and insulation failure probability of the new energy grid-connected transformer using the transformer active protection method based on multi-indicator quantified overload safety provided by the embodiment of the present invention are lower than those of the new energy grid-connected transformer that is overloaded and has no protection control measures.

[0128] like Figure 3 As shown, curve 301 represents the operating temperature change of the new energy grid-connected transformer using the transformer active protection method based on multi-indicator quantified overload safety provided by the embodiment of the present invention, and curve 302 represents the operating temperature change of the new energy grid-connected transformer without taking protection control measures. It can be seen that the operating temperature of the new energy grid-connected transformer using the transformer active protection method based on multi-indicator quantified overload safety provided by the embodiment of the present invention is lower than that of the new energy grid-connected transformer that is overloaded and has not taken protection control measures.

[0129] like Figure 4 As shown, curve 401 represents the change in the failure rate of the new energy grid-connected transformer using the active transformer protection method based on multi-indicator quantified overload safety provided by the embodiment of the present invention, and curve 302 represents the change in the failure rate of the new energy grid-connected transformer without taking protective control measures. It can be seen that the failure rate of the new energy grid-connected transformer using the active transformer protection method based on multi-indicator quantified overload safety provided by the embodiment of the present invention is lower than that of the new energy grid-connected transformer that is overloaded and has not taken protective control measures.

[0130] It can be seen that the implementation of the multi-indicator quantitative overload safety active protection of new energy grid-connected transformers proposed in the embodiment of the present invention can evaluate the overload safety and operation risk of new energy grid-connected transformers in multiple dimensions such as operating temperature, failure rate, insulation aging probability and failure probability evaluation in real time, and can effectively reduce control, and through mutual coordination and cooperation with the new energy control center and the transformer circuit breaker, accurately grasp the evolution trend of the new energy grid-connected transformer from "heavy load state" to "overload state" and then to "tolerance limit state". Under the premise of ensuring overload safety, the overload capacity and transmission capacity of the new energy grid-connected transformer can be actively improved, thereby ensuring the safe and stable operation of the new energy grid-connected system.

[0131] The embodiment of the present invention also provides a transformer active protection system based on multi-indicator quantitative overload safety. Figure 5 A schematic diagram of an application scenario of a transformer active protection system based on multi-index quantitative overload safety provided by an embodiment of the present invention is shown in FIG. Figure 5 As shown, the transformer active protection system 510 based on multi-indicator quantitative overload safety is connected to the target transformer 520 and the dispatching control center 530, the dispatching control center 530 is connected to the grid-connected system 540, and the target transformer 520 is also connected to the main power grid 550.

[0132] Among them, the target transformer 520 can be a new energy grid-connected transformer, the dispatching control center 530 can be a new energy grid-connected electroplating control center, and the grid-connected system 540 can be a new energy grid-connected system (such as a wind farm).

[0133] Specifically, the transformer active protection system 510 based on multi-index quantitative overload safety is used for:

[0134] First, the rated parameters of the target transformer 520 are obtained, and the long-term allowable operating current value and the maximum allowable operating temperature of the target transformer 520 are determined. The rated parameters are used to characterize the specifications and performance of the target transformer 520.

[0135] Then, the operating status of the target transformer 520 is monitored to obtain the current monitoring value and meteorological environment parameter monitoring value of the target transformer 520; the meteorological environment parameter monitoring value includes: transformer ambient temperature, transformer steady-state operation top oil temperature and transformer steady-state operation hot spot temperature.

[0136] Secondly, according to the current monitoring value and the long-term allowable operating current value, the transformer overload state criterion formula is used to determine whether the target transformer 520 is in an overload state.

[0137] When the target transformer 520 is in an overload state, the overload distance value is determined according to the current monitoring value, and an overload alarm signal and the overload distance value are sent to the dispatching control center 530 .

[0138] Next, according to the current monitoring value and the long-term allowable operating current value, a transformer overload state criterion formula is used to determine whether the target transformer 520 is in an overload state.

[0139] When the target transformer 520 is in an overload state, the overload transformer short-term allowable overload time of the target transformer 520 is determined according to the rated parameters and the meteorological environment parameter monitoring values ​​through the current-temperature mapping relationship calculation formula.

[0140] Then, the overload safety quantitative characterization index of the target transformer 520 is determined according to the rated parameters and the meteorological environment parameters. The overload safety quantitative characterization index includes: transformer operating temperature, failure rate, insulation degradation probability and insulation failure probability.

[0141] Determine whether the transformer operating temperature, failure rate, insulation degradation probability and insulation failure probability exceed the corresponding preset overload safety boundaries.

[0142] When at least one of the characterizing indicators of the transformer operating temperature, failure rate, insulation degradation probability and insulation failure probability exceeds the corresponding preset overload safety boundary, the power load reduction amount is determined according to the output power load reduction calculation formula based on the current monitoring value, and an output load reduction signal is sent to the dispatching control center 530, so that the dispatching control center 530 controls the grid-connected system 540 to reduce the load according to the output load reduction signal, and the output load reduction signal includes the power load reduction amount.

[0143] Secondly, according to the current monitoring value and the meteorological environment parameter monitoring value, it is determined whether the target transformer 520 is in a state exceeding the tolerance limit through the overload tolerance limit calculation formula.

[0144] Finally, when the target transformer 520 is in a state beyond the tolerance limit, a trip signal is sent to the target transformer 520 and the dispatch control center 530, so that the target transformer 520 performs a trip shutdown in response to the trip signal.

[0145] The transformer active protection system based on multi-index quantified overload safety provided by the embodiment of the present invention is used to quantify the overload safety and operation risk of the target transformer (for example, the new energy grid-connected transformer) from multiple dimensions such as real-time evaluation of the transformer operating temperature, failure rate, insulation degradation probability and insulation failure probability evaluation for disturbances such as station output-limited transformer overload. The target transformer can be accurately grasped from the evolution trend of the target transformer from "heavy load state" to "overload state" and then to "tolerance limit state" through mutual coordination with the new energy control center and the target transformer circuit breaker. In this way, the method can quantify the overload safety and operation risk of the grid-connected transformer by means of multi-dimensional uncertain probabilities, thereby improving the accuracy of protecting the transformer when the transformer is overloaded.

[0146] Through the description of the above implementation methods, technical personnel in the relevant field can clearly understand that for the convenience and simplicity of description, only the division of the above-mentioned functional modules is used as an example. In actual applications, the above-mentioned functions can be assigned to different functional modules as needed, that is, the internal structure of the device can be divided into different functional modules to complete all or part of the functions described above.

[0147] In the description of the present invention, “plurality” means at least two, for example, two, three, etc., unless otherwise clearly and specifically defined.

[0148] In the present invention, unless otherwise clearly specified and limited, the terms "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements, unless otherwise clearly defined. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0149] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, without contradiction.

[0150] Similar parts between the embodiments provided in this application can be referenced to each other. The specific implementation methods provided above are only a few examples under the general concept of this application and do not constitute a limitation on the protection scope of this application. For those skilled in the art, any other implementation methods expanded based on the scheme of this application without creative work belong to the protection scope of this application.

Claims

1. A transformer active protection method based on multi-index quantitative overload safety, characterized in that: include: Acquire the rated parameters of the target transformer, and determine the long-term allowable operating current value and the maximum allowable operating temperature of the target transformer, wherein the rated parameters are used to characterize the specifications and performance of the target transformer; Monitor the operating status of the target transformer and obtain the current monitoring value and meteorological environment parameter monitoring value of the target transformer; According to the current monitoring value and the long-term allowable operating current value, determining whether the target transformer is in an overload state by using a transformer overload state criterion formula; When the target transformer is in an overload state, determining an overload distance value according to the current monitoring value, and sending an overload alarm signal and the overload distance value; According to the current monitoring value and the long-term allowable operating current value, determining whether the target transformer is in an overload state by using a transformer overload state criterion formula; When the target transformer is in an overload state, determining the overload transformer short-term allowable overload time of the target transformer according to the rated parameters and the meteorological environment parameter monitoring values ​​through a current-temperature mapping relationship calculation formula; Determining the overload safety quantitative characterization index of the target transformer according to the rated parameters and the meteorological environment parameters, wherein the overload safety quantitative characterization index includes: transformer operating temperature, failure rate, insulation degradation probability and insulation failure probability; Respectively determining whether the transformer operating temperature, the failure rate, the insulation degradation probability, and the insulation failure probability exceed corresponding preset overload safety boundaries; When at least one of the characterizing indicators of the transformer operating temperature, the failure rate, the insulation degradation probability and the insulation failure probability exceeds the corresponding preset overload safety boundary, the power load reduction amount is determined according to the current monitoring value by using the output power load reduction calculation formula, and an output load reduction signal is sent, wherein the output load reduction signal includes the power load reduction amount; According to the current monitoring value and the meteorological environment parameter monitoring value, determining whether the target transformer is in a state exceeding the tolerance limit through an overload tolerance limit calculation formula; In the case that the target transformer is in a state of exceeding the tolerance limit, a trip signal is sent so that the target transformer performs a trip shutdown in response to the trip signal.

2. The method according to claim 1, characterized in that The transformer overload state criterion formula is: I c >I alert ; I alert =αI cmax ; Among them, I c Indicates the current monitoring value, I alert represents the transformer heavy load current threshold, α represents the heavy load reliability factor, I cmax Indicates the long-term allowable operating current value.

3. The method according to claim 1, characterized in that The calculation formula of the overload distance value is: I cd =I c -I alert ; Among them, I cd Indicates the overload distance value, I c Indicates the current monitoring value, I alert Indicates the transformer heavy load current threshold.

4. The method according to claim 1, characterized in that: The transformer overload state criterion formula is: I c >I cmax ; Among them, I c Indicates the current monitoring value, I cmax Indicates the long-term allowable operating current value.

5. The method according to claim 1, characterized in that The meteorological environment parameter monitoring values ​​include: the top oil temperature of the transformer in steady state operation and the hot spot temperature of the transformer in steady state operation; the current-temperature mapping relationship calculation formula is: Among them, θ oilR represents the top oil temperature of the transformer in steady state operation, θ hotR represents the hot spot temperature of the transformer in steady state operation, θ hotRb represents the steady-state hot spot temperature value of the target transformer after overload, θ hotRa represents the steady-state hot spot temperature value of the target transformer before overload, K represents the load value of the target transformer, τ oil represents the time constant of insulating oil, τ w represents the time constant of the winding, n represents the heat transfer nonlinear constant coefficient of the insulating oil, m represents the heat transfer nonlinear constant coefficient of the winding, and Q represents the ratio of the load loss to the no-load loss under the rated current operating condition of the target transformer.

6. The method according to claim 5, characterized in that The expression of the short-time allowable overload time of the overload transformer is: Among them, t equ Indicates the short-term allowable overload time of the overload transformer, τ equ represents the equivalent time constant of the target transformer, C equ Represents the equivalent thermal capacity of the target transformer, R equ represents the equivalent thermal resistance of the heat transfer path from the inside to the outside of the target transformer, θ cmax Indicates the maximum allowable operating temperature of the target transformer.

7. The method according to claim 1, characterized in that The calculation formula of the failure rate is: Among them, P cf (t) represents the failure rate, β represents the shape parameter of Weibull distribution, δ represents the empirical parameter, θ cset It represents the steady-state reference temperature of the target transformer under rated conditions, T s1 represents the equivalent time that the target transformer has been in service before being overloaded, T equ It indicates the equivalent continuous operation time of the target transformer in a short time after overload, t indicates the monitoring time, t equ Indicates the short-term allowable overload time of the overload transformer, θ hot (t) represents the hot spot temperature of the transformer; The calculation formula for the insulation degradation probability is: H IDP =P(θ c >θ cset )=S IDP / M; Among them, H IDP represents the insulation degradation probability, S IDP Indicates the frequency of accelerated insulation aging or further deterioration of the insulation of the transformer during the overload equivalent time period, θ cset represents the steady-state reference temperature of the target transformer under rated conditions, θ c represents the operating temperature of the transformer, and M represents the total number of state sampling; The calculation formula for the insulation failure probability is: H IFP =P(θ c >θ cmax )=S IFP / M; Among them, H IFP represents the insulation failure probability, S IFP It indicates the frequency of failure and shutdown of the transformer due to insulation problems within the overload equivalent time period.

8. The method according to claim 1, characterized in that: The output power load reduction calculation formula is: Among them, P cut Indicates the power reduction, I c Indicates the current monitoring value, I cmax represents the long-term allowable operating current value, and K represents the load value of the target transformer.

9. The method according to claim 1, characterized in that: The overload tolerance limit calculation formula is: ξ=(v∩μ)∪ω; Wherein, ξ represents the first logic state variable, υ represents the second logic state variable, μ represents the third logic state variable, ω represents the fourth logic state variable, I c Indicates the current monitoring value, I cmax Indicates the long-term allowable operating current value, t c Indicates the overload time, I cmax Indicates the maximum allowable overload time, θ c represents the transformer operating temperature, θ cmax Indicates the maximum allowable operating temperature of the target transformer; When both υ and μ are 1, or ω is 1, ξ is 1; When the ξ is 1, it is determined that the target transformer is in a state of exceeding the tolerance limit.

10. A transformer active protection system based on multi-index quantitative overload safety, characterized in that: The transformer active protection system is connected to the target transformer and the dispatching control center, and the dispatching control center is connected to the grid-connected system; the transformer active protection system is used to: Acquire the rated parameters of the target transformer, and determine the long-term allowable operating current value and the maximum allowable operating temperature of the target transformer, wherein the rated parameters are used to characterize the specifications and performance of the target transformer; Monitor the operating status of the target transformer and obtain the current monitoring value and meteorological environment parameter monitoring value of the target transformer; According to the current monitoring value and the long-term allowable operating current value, determining whether the target transformer is in an overload state by using a transformer overload state criterion formula; When the target transformer is in an overload state, determining an overload distance value according to the current monitoring value, and sending an overload alarm signal and the overload distance value to the dispatching control center; According to the current monitoring value and the long-term allowable operating current value, determining whether the target transformer is in an overload state by using a transformer overload state criterion formula; When the target transformer is in an overload state, determining the overload transformer short-term allowable overload time of the target transformer according to the rated parameters and the meteorological environment parameter monitoring values ​​through a current-temperature mapping relationship calculation formula; Determining the overload safety quantitative characterization index of the target transformer according to the rated parameters and the meteorological environment parameters, wherein the overload safety quantitative characterization index includes: transformer operating temperature, failure rate, insulation degradation probability and insulation failure probability; Respectively determining whether the transformer operating temperature, the failure rate, the insulation degradation probability, and the insulation failure probability exceed corresponding preset overload safety boundaries; In the case where at least one of the characterizing indicators of the transformer operating temperature, the failure rate, the insulation degradation probability and the insulation failure probability exceeds the corresponding preset overload safety boundary, the power load reduction amount is determined according to the current monitoring value by using the output power load reduction calculation formula, and an output load reduction signal is sent to the dispatching control center, so that the dispatching control center controls the load reduction of the grid-connected system according to the output load reduction signal, and the output load reduction signal includes the power load reduction amount; According to the current monitoring value and the meteorological environment parameter monitoring value, determining whether the target transformer is in a state exceeding the tolerance limit through an overload tolerance limit calculation formula; In the case that the target transformer is in a state of exceeding the tolerance limit, a trip signal is sent to the target transformer and the dispatching control center, so that the target transformer performs a trip shutdown in response to the trip signal.

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