A method for online transformer temperature monitoring data processing and thermal state assessment

Abstract

The present invention discloses a method for processing transformer temperature online monitoring data and evaluating thermal status. By monitoring the dynamic change relationship of temperature data online, a thermal status model with a time limit for temperature changes is constructed, and an online evaluation method for transformer thermal status is proposed. The data information of online monitoring is fully exploited to more accurately analyze the operating thermal status of the transformer, facilitate optimization of the control system, and improve equipment operating efficiency. Not only can the operating temperature of the transformer be dynamically and reasonably evaluated, but the control efficiency can be significantly improved compared to the traditional regulation after approaching the critical value. In addition, by expanding the time dimension, the misoperation caused by measurement errors can be reduced, the waste of manpower and material resources at the maintenance site can be reduced, and the efficiency of transformer fault diagnosis can be improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of medium frequency transformer safety, and in particular relates to a method for processing transformer temperature online monitoring data and evaluating thermal status. Background Art

[0002] For power transformers, the temperature status is closely linked to their safe and stable operation. During operation, transformers can overheat when exposed to short circuits, overloads, high ambient temperatures, or insufficient cooling and ventilation, accelerating insulation aging and reducing their service life. Excessively high winding temperatures can directly lead to transformer failure. Therefore, online, real-time monitoring of transformer operating temperature and assessment of the transformer's thermal status during operation are crucial.

[0003] Currently proposed insulation aging assessment models, such as those that relate lifespan to temperature and some temperature-feedback transformer cooling fan control schemes, are based on standard limits for transformer temperature. Exceeding a certain limit typically results in appropriate action. However, such assessment schemes only consider the temperature value, not the duration of the abnormal temperature event. These assessments are also susceptible to misjudgment due to corrupted data. Therefore, for oil-immersed transformers, it is necessary to develop a thermal assessment method that considers the dynamic temporal changes in temperature. Summary of the Invention

[0004] The purpose of the present invention is to provide a method for processing transformer temperature online monitoring data and evaluating thermal status, which can solve the problem that conventional transformer temperature data processing and evaluation methods fail to consider the information of temperature changes over time, make full use of the information of transformer online monitoring temperature data in the time dimension, and improve the accuracy of transformer thermal status evaluation.

[0005] In order to achieve the above object, the technical solution adopted by the present invention is: a method for processing transformer temperature online monitoring data and evaluating thermal status, comprising the following steps:

[0006] S1: Determine the categories of transformer temperature data collected online, including top oil temperature, winding hot spot temperature, temperature of metal parts in contact with fiber insulation material, hot spot temperature of other metal parts, etc. The measured temperature data categories are recorded as n here;

[0007] S2: Based on the type of transformer temperature data collected online, the transformer model, and the temperature limits specified under different loads, derive the temperature limits taking into account the temperature duration;

[0008] S3: The transformer temperature data collected online, a total of n, are traced back a fixed time period to form a thermal assessment temperature data unit, and the temperature value and its duration are counted;

[0009] S4: From the two aspects of temperature value and temperature duration, each type of collected temperature data is judged and assigned a status level;

[0010] S5: For the status evaluation results of n different temperature categories, the most serious level is taken as the overall thermal status evaluation result at the current moment;

[0011] S6: Move the time scale to the newly collected temperature value at the next moment, which includes the latest sampling data and the sampling data of a fixed length before the moment, which together constitute the input temperature data unit of the thermal assessment. Repeat steps S3 to S5 to obtain the overall thermal status assessment result of the transformer.

[0012] Furthermore, the measured temperature data category has at least one top oil temperature, so n ≥ 1;

[0013] Furthermore, the method for deriving the temperature limit considering the temperature duration is a three-element method of exponential relationship, including three elements: steady-state value, initial state value, and time constant. The formula is:

[0014] T r =T ∞ +(T0-T ∞ )*e^(-t / τ).

[0015] Among them, the initial state value is T0, and the steady state value is T ∞ , the time constant is τ.

[0016] Furthermore, the temperature data contained in the fixed time period is at least long enough to reflect the abnormal temperature state, and according to the thermal state determination condition, the time period must not be less than 30 minutes.

[0017] Furthermore, the time duration for determining the condition based on the thermal state should be more than 2 hours.

[0018] Furthermore, the statistical method of the temperature values ​​and their durations is that the input unit of the thermal assessment is temperature data of a fixed duration, all temperature values ​​within the time length are recorded, and for each temperature value, its duration is recorded, and the duration greater than or equal to the specified temperature value is also counted as the duration of the temperature value, thereby obtaining a series of temperature and corresponding duration data.

[0019] Furthermore, the state level division is based on the processing strategy that can be carried out, and is divided into level 1, level 2, and level 3 according to the severity of the thermal state. Level 1 temperature overheating requires measures such as reducing the load and removing the transformer. Level 2 temperature overheating requires a warning signal to be issued. Level 3 is a normal state that can operate for a long time.

[0020] Furthermore, the T ∞The steady-state value uses the normal periodic load temperature limit as the temperature limit; the T0 initial state value uses the short-term emergency load temperature limit as the temperature limit, and the short-term emergency load must not exceed 30 minutes; the time constant τ is calculated using the long-term emergency load temperature limit as the temperature limit for a duration of 30 minutes.

[0021] Furthermore, the distinction between level 1 and level 2 in the thermal state severity is based on the derived temperature limit T 12 =T r The distinction between level 2 and level 3 is set according to the national standard for transformer oil deterioration. 23 =T ∞ / T0*T r .

[0022] Beneficial Effects of the Invention: The proposed method for processing online transformer temperature monitoring data and assessing thermal status fully utilizes the time dimension of online transformer temperature monitoring data to implement online transformer thermal status assessment that combines temperature values ​​with duration. By incorporating time information, transformer thermal status assessment is no longer limited to a single standard value. The assessment results are more consistent with the actual transformer operation, and the set dynamic temperature threshold is more reasonable, improving the early warning effectiveness of temperature values ​​during the operation of oil-immersed power transformers. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is a flow chart of oil-immersed transformer temperature online monitoring data processing and thermal status assessment according to the present invention;

[0024] Figure 2 1. It is a schematic diagram of the state division boundary of the top oil temperature of the large oil-immersed transformer according to the present invention;

[0025] Figure 3 Schematic diagram of the state limit of the hot spot temperature of the winding of the large oil-immersed transformer according to the present invention;

[0026] Figure 4 is a schematic diagram of the iteration of temperature data used as input in the evaluation method. DETAILED DESCRIPTION

[0027] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0028] Example 1:

[0029] This embodiment discloses a method for processing online temperature monitoring data and evaluating thermal status of an oil-immersed power transformer. The process is as follows: Figure 1 As shown, the following steps are included:

[0030] Step 1: Determine the transformer temperature data category that can be collected online. The transformer temperature data category is the winding hot spot temperature of a large power transformer.

[0031] Step 2: Based on the national standard "Guidelines for Loading Oil-Immersed Power Transformers", the hot spot temperature of the winding of a large power transformer shall not exceed 120°C under normal cyclic load, 140°C under long-term emergency load, and 160°C under short-term emergency load.

[0032] The temperature limit is set with an exponential relationship, including three elements: steady-state value, initial state value, and time constant. The normal periodic load temperature limit is used as the steady-state value T of the temperature limit. ∞ , the short-term emergency load temperature limit is used as the initial state value T0 of the temperature limit. Since the short-term emergency load cannot exceed 30 minutes, the temperature of more than 30 minutes is unlikely to exceed the long-term emergency load temperature limit. The time constant value τ can be set based on this. The temperature limit formula is: T r =T ∞ +(T0-T ∞ )*e^(t / τ).

[0033] For the winding hot spot temperature: T ∞ =120℃, T0=160℃, in minutes τ=30 / ln2. Therefore, the winding hot spot temperature limit is T r =120+(160-120)*e^(-ln2 / 30*t), unit Celsius, see Figure 2 The boundary between the light gray area and the white area.

[0034] The transformer thermal state is divided into level 1, level 2, and level 3. Level 1 means that the transformer thermal state is more serious and measures such as reducing the load and disconnecting the transformer need to be taken. Level 2 means that there is overheating and a warning signal may need to be issued. Level 3 thermal state is normal and no measures need to be taken.

[0035] The assessment limit T of the thermal state of the power transformer is determined r Then, set it as the dividing line T between level 1 thermal state and level 2 thermal state 12 , with T ∞ / T0 ratio multiplied by the temperature limit T r As the dividing line between level 2 and level 3 thermal states. For the winding hot spot temperature T 23 =120 / 160*T r , unit Celsius, see Figure 2 The boundary between the dark gray area and the light gray area in the figure.

[0036] Step 3: Go back a fixed time period before the current moment to form a thermal assessment temperature data unit. Here, a time period of 2 hours is used. All temperature values ​​within this time period are recorded, and for each temperature value, its duration is recorded. The duration greater than or equal to a certain temperature value is also counted as the duration of the temperature value. By counting each temperature value and its duration, a series of temperature and corresponding duration data can be obtained.

[0037] Step 4: Based on the statistically obtained temperature values ​​and their durations, Figure 2 The thermal state division boundary in the figure is as follows: the dark gray area is level 3, the light gray area is level 2, and the white area is level 1. The collected winding hot spot temperature data is judged as the thermal state level at this moment.

[0038] Step 5: The thermal state result obtained based on the hot spot temperature evaluation is used as the transformer thermal state evaluation result at the current moment.

[0039] Step 6: Move the time scale to the next temperature value collected, such as Figure 4 As shown, the evaluation input temperature data unit includes the latest sampling data and the sampling data of a fixed length before the moment, and steps 3 to 5 are repeated to obtain the thermal state evaluation result of the transformer at the next moment.

[0040] Through the above steps, thermal status assessment of large oil-immersed power transformers based on online monitoring data of winding hot spot temperature can be achieved.

[0041] Example 2:

[0042] This embodiment discloses a method for processing online temperature monitoring data and evaluating thermal status of an oil-immersed power transformer, comprising the following steps:

[0043] Step 1: Determine the type of transformer temperature data that can be collected online. The transformer temperature data type is the top oil temperature of a large power transformer.

[0044] Step 2: Based on the national standard "Guidelines for Loading Oil-Immersed Power Transformers", the top oil temperature of large transformers shall not exceed 105°C under normal cyclic load, 115°C under long-term emergency load, and 115°C under short-term emergency load.

[0045] According to the temperature limit formula T r =T ∞ +(T0-T ∞ )*e^(t / τ), for the top oil temperature: T ∞=105℃, T0=115℃. Since the limit of the top oil temperature under long-term and short-term emergency loads is 115℃, the time constant is set according to the time constant of the hot spot temperature of the large transformer winding, with the unit of minutes being τ=30 / ln2.

[0046] Therefore, the top oil temperature limit is T r =105+(115-105)*e^(-ln2 / 30*t), unit Celsius, see Figure 3 The boundary between the light gray area and the white area in the figure.

[0047] The assessment limit T of the thermal state of the power transformer is determined r Then, set it as the dividing line T between level 1 thermal state and level 2 thermal state 12 , with T ∞ / T0 ratio multiplied by the temperature limit T r As the dividing line between level 2 and level 3 thermal states. For the top oil temperature T 23 =105 / 115*T r , unit Celsius, see Figure 3 The boundary between the dark gray area and the light gray area in the figure.

[0048] Step 3: trace back a fixed time period from the current moment to form a thermal assessment temperature data unit. Here, the time period is 2 hours. Count each temperature value and its duration to obtain a series of temperature and corresponding duration data.

[0049] Step 4: Based on the statistically obtained temperature values ​​and their durations, Figure 3 The thermal state division boundary in the figure is as follows: the dark gray area is level 3, the light gray area is level 2, and the white area is level 1. The collected top oil temperature data is judged as the thermal state level at this moment.

[0050] Step 5: The thermal state result obtained based on the top oil temperature assessment is used as the transformer thermal state assessment result at the current moment.

[0051] Step 6: Move the time scale to the newly collected temperature value at the next moment, and repeat steps 3 to 5 to obtain the thermal status assessment result of the transformer at the next moment.

[0052] Through the above steps, thermal status assessment of large oil-immersed power transformers based on online monitoring data of top oil temperature can be achieved.

[0053] Example 3:

[0054] This embodiment discloses a method for processing online temperature monitoring data and evaluating thermal status of an oil-immersed power transformer, comprising the following steps:

[0055] Step 1: Determine the types of transformer temperature data that can be collected online. The transformer temperature data types include the winding hot spot temperature and top oil temperature of a medium-sized power transformer.

[0056] Step 2, based on the national standard "Guidelines for Loading Oil-Immersed Power Transformers", stipulates that the hot spot temperature of the winding of a medium-sized power transformer under normal cyclic load shall not exceed 120°C, and the top oil temperature shall not exceed 105°C; under long-term emergency load, the hot spot temperature of the winding shall not exceed 140°C, and the top oil temperature shall not exceed 115°C; under short-term emergency load, the hot spot temperature of the winding shall not exceed 160°C, and the top oil temperature shall not exceed 115°C.

[0057] According to the temperature limit formula T r =T ∞ +(T0-T ∞ )*e^(t / τ), for the winding hot spot temperature: T ∞ =120℃, T0=160℃, in minutes τ=30 / ln2, so the winding hot spot temperature limit is T r =120+(160-120)*e^(-ln2 / 30*t), unit: Celsius; for top oil temperature: T ∞ =105℃, T0=115℃. Since the limit of the top oil temperature under long-term and short-term emergency loads is 115℃, the time constant is set according to the time constant of the hot spot temperature of the large transformer winding, in units of minutes τ=30 / ln2, so the top oil temperature limit is T r =105+(115-105)*e^(-ln2 / 30*t), unit: degrees Celsius.

[0058] The assessment limit T of the thermal state of the power transformer is determined r Then, set it as the dividing line T between level 1 thermal state and level 2 thermal state 12 , with T ∞ / T0 ratio multiplied by the temperature limit T r As the dividing line between level 2 and level 3 thermal states. For the winding hot spot temperature T 23 =120 / 160*T r , unit is degrees Celsius; for the top oil temperature T 23 =105 / 115*T r , unit is degrees Celsius.

[0059] Step 3: trace back a fixed time period from the current moment to form a thermal assessment temperature data unit. Here, the time period is 2 hours. Count each temperature value and its duration to obtain a series of temperature and corresponding duration data.

[0060] Step 4: According to the statistically obtained temperature values ​​and their durations, the collected temperature data are judged based on the thermal state division boundaries to serve as the thermal state level at this moment.

[0061] Step 5: Based on the thermal status results obtained by the hot spot temperature assessment and the thermal status results obtained by the top oil temperature assessment, the most serious level is taken as the overall thermal status assessment result at the current moment;

[0062] Step 6: Move the time scale to the newly collected temperature value at the next moment, and repeat steps 3 to 5 to obtain the thermal status assessment result of the transformer at the next moment.

[0063] Through the above steps, the thermal state assessment of the medium-sized oil-immersed power transformer based on the online monitoring data of the winding hot spot temperature and the top oil temperature can be realized.

[0064] In order to make a more comprehensive and accurate judgment on the thermal state of the power transformer, it is necessary to obtain the relationship between the temperature and duration that reflects the heat resistance of the transformer. According to the transformer temperature limit under different loads specified in the national standard "Load Guidelines for Oil-Immersed Power Transformers", combined with the allowable duration of different loads, the limit of the allowable duration of the transformer temperature can be derived.

[0065] For transformer models, including oil-immersed distribution transformers, oil-immersed medium transformers, oil-immersed large transformers, for different load categories, including normal periodic loads, long-term emergency loads, short-term emergency loads.

[0066] The temperature limit is set with an exponential relationship, including three elements: steady-state value, initial state value, and time constant. The normal periodic load temperature limit is used as the steady-state value T of the temperature limit. ∞ , the short-term emergency load temperature limit is used as the initial state value T0 of the temperature limit. Since the short-term emergency load shall not exceed 30 minutes, it is considered that the high temperature lasting more than 30 minutes is based on the long-term emergency load temperature limit as the temperature limit, and the time constant value τ is set based on this. The formula is: T r =T ∞ +(T0-T ∞ )*e^(-t / τ).

[0067] A temperature sensor is installed on the top layer of the oil-immersed transformer, which can collect the top oil temperature online. Therefore, the thermal state of the transformer can at least be evaluated by the top oil temperature. If the transformer is equipped with a fiber optic temperature sensor, the winding hot spot temperature can be collected, etc. It is necessary to integrate various temperature collection data for thermal state evaluation.

[0068] According to the severity of the transformer thermal state, it is divided into level 1, level 2, and level 3. Level 1 means that the transformer thermal state is more serious and measures such as reducing the load and disconnecting the transformer need to be taken. Level 2 means that there is overheating and a warning signal may need to be issued. Level 3 thermal state is normal and no measures need to be taken.

[0069] After determining the assessment limit of the thermal state of the power transformer T r Then, set it as the boundary between level 1 thermal state and level 2 thermal state, with T ∞ / T0 ratio multiplied by the temperature limit T r As the dividing line between level 2 and level 3 thermal states, T ∞ The ratio of / T0 ensures that the shortest duration of the temperature limit does not exceed the specified normal allowable limit, is far away from the specified attention value, can meet the transformer oil deterioration temperature specified in the national standard, has stable working performance, and is acceptable for long-term operation.

[0070] When evaluating the thermal status of a transformer, the temperature data used as the evaluation input must be at least long enough to reflect the abnormal temperature state. Based on the thermal status judgment conditions, the duration must not be less than 30 minutes and is usually more than 2 hours.

[0071] According to the thermal status assessment results of different online temperatures such as top oil temperature and hot spot temperature, the most serious level in the assessment results is taken as the overall thermal status assessment result of the transformer.

[0072] The beneficial effects of this embodiment are: it can accurately evaluate the thermal state of the operating transformer, make full use of the time dimension information of the transformer temperature online monitoring data, set the dynamic temperature threshold more reasonably, significantly improve the early warning effect of the temperature value during the operation of the oil-immersed power transformer, realize dynamic early warning and scientific decision-making, reduce the investment of a large amount of manpower and material resources at the maintenance site, and improve the operation and maintenance level of power equipment.

[0073] The above is only a preferred embodiment of the present invention and is not intended to limit the scope of implementation of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and substitutions can be made without departing from the technical principles of this patent. These improvements and substitutions should also be regarded as the scope of protection of this patent.

Claims

1. A method for processing transformer temperature online monitoring data and evaluating thermal status, characterized in that: The following steps are involved: S1: Determine the categories of transformer temperature data collected online, including top oil temperature, winding hot spot temperature, temperature of metal parts in contact with fiber insulation materials, and hot spot temperature of other metal parts. The measured temperature data categories are recorded as n here; S2: Based on the types of transformer temperature data collected online, the transformer model, and the temperature limits specified under different loads, derive the temperature limits that take into account the temperature duration. Transformer models include: oil-immersed distribution transformers, oil-immersed medium transformers, and oil-immersed large transformers. Load types include: normal periodic loads, long-term emergency loads, and short-term emergency loads. S3: The transformer temperature data collected online, a total of n, are traced back a fixed time period to form a thermal assessment temperature data unit, and the temperature value and its duration are counted; S4: Determine the collected temperature data based on the temperature value and temperature duration, and assign the current status level of the measured transformer; S5: For the status evaluation results of n different temperature categories, the most serious level is taken as the overall thermal status evaluation result at the current moment; S6: Move the time scale to the newly collected temperature value at the next moment, including the latest sampling data and the sampling data of a fixed length before the moment, which together constitute the input temperature data unit of the thermal assessment. Repeat steps S3 to S5 to obtain the overall thermal status assessment result of the transformer; The method for deriving the temperature limit considering the temperature duration is a three-element method of exponential relationship, including steady-state value, initial state value and time constant. The normal periodic load temperature limit is used as the steady-state value T of the temperature limit. ∞ The short-term emergency load temperature limit is used as the initial state value T0 of the temperature limit. The short-term emergency load is less than or equal to 30 minutes. For high temperatures greater than 30 minutes, the long-term emergency load temperature limit is used as the temperature limit, and the time constant value τ is set based on this. The formula is: T r =T ∞ +(T0-T ∞ )*e^(-t / τ); The temperature limit is T r , the initial state value is T0, the steady state value is T ∞ , the time constant is τ, and the current time is t.

2. The method for online transformer temperature monitoring data processing and thermal state assessment according to claim 1, characterized in that: The measured temperature data category has at least one top oil temperature, so n≥1.

3. The method for online transformer temperature monitoring data processing and thermal state assessment according to claim 1, characterized in that: The fixed time duration includes a time length of temperature data that is at least sufficient to reflect an abnormal temperature state, and according to the thermal state determination condition, the time length must not be less than 30 minutes.

4. The method for processing transformer temperature online monitoring data and evaluating thermal status according to claim 3, characterized in that: The time period for determining the condition based on the thermal state is more than 2 hours.

5. The method for online transformer temperature monitoring data processing and thermal state assessment according to claim 1, characterized in that: The statistical method for the temperature values ​​and their durations is as follows: the input unit of the thermal assessment is temperature data of a fixed duration, all temperature values ​​within the time length are recorded, and for each temperature value, its duration is recorded. The duration greater than or equal to the specified temperature value is also counted as the duration of the temperature value, thereby obtaining a series of temperature and corresponding duration data.

6. The method for processing transformer temperature online monitoring data and evaluating thermal status according to claim 1, characterized in that: The state levels are divided according to the processing strategy and the severity of the thermal state into level 1, level 2 and level 3. Level 1 overheating requires load reduction and transformer disconnection, level 2 overheating requires a warning signal, and level 3 is a normal state that can operate for a long time.

7. The method for online transformer temperature monitoring data processing and thermal state assessment according to claim 6, characterized in that: The distinction between levels 1 and 2 in the thermal state severity is based on the derived temperature limit T 12 =T r The distinction between level 2 and level 3 is based on the standard of transformer oil deterioration set as T 23 =T ∞ / T0*T r .

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