Overload protection method and device for oil-immersed distribution transformer

Abstract

The application discloses an overload protection method for an oil-immersed distribution transformer, and the method comprises the following steps: collecting transformer low-voltage side loop current and transformer top layer insulation oil temperature in real time; presetting a first overload current threshold value, a second overload current threshold value, a first overload temperature threshold value, a second overload temperature threshold value, a first overload time threshold value and a second overload time threshold value which are matched with the transformer specification; judging whether the transformer is in a low-multiple overload operation state or a high-multiple overload operation state, and controlling a protection unit to perform a protection action. The application further discloses an overload protection device for the oil-immersed distribution transformer. The application solves the technical problems that pure current protection cannot adapt to the heat dissipation characteristics of the oil-immersed transformer and pure temperature protection has a response lag in the prior art.

Description

Technical Field

[0001] This invention relates to the field of power technology, and in particular to an overload protection method and device for an oil-immersed distribution transformer. Background Technology

[0002] Oil-immersed distribution transformers have their core windings installed inside a transformer tank filled with insulating oil for cooling and insulation of the core windings. When the transformer is overloaded or exceeds normal operating conditions, a protection device disconnects the low-voltage side circuit, providing overload protection and preventing winding overheating, insulation aging, oil deterioration, and thermal breakdown faults, thus ensuring equipment safety and power supply reliability.

[0003] However, existing overload protection schemes for oil-immersed distribution transformers mainly fall into two categories: one involves installing a low-voltage circuit breaker or fuse outside the transformer, detecting the current in the low-voltage side circuit, and disconnecting the low-voltage side circuit based on the duration of the overload current to achieve transformer protection; the other uses a distribution transformer monitoring device to detect the transformer's operating temperature through an externally installed temperature sensing unit, and controls the transformer protection to activate when the transformer temperature exceeds a preset protection temperature. However, this method relies solely on current for protection. Since oil-immersed transformers have good heat dissipation, simple current protection cannot effectively utilize the overload capacity of oil-immersed transformers, wasting the transformer's power supply capacity and potentially leading to inflated transformer capacity and material waste. If relying solely on temperature protection, when the overload current is large, the winding circuit heats up rapidly due to internal resistance, and the transformer insulating oil cannot dissipate heat quickly, causing excessively high local temperatures near the windings. The external distribution transformer monitoring device cannot detect the internal temperature in real time, resulting in delayed protection, winding burnout, and transformer damage. For example, the power transformer with a protection mechanism disclosed in Chinese patent document CN202222721073.2 lacks overload protection. Therefore, in order to solve the above-mentioned technical problem, there is an urgent need to propose an overload protection method and device for oil-immersed distribution transformers. Summary of the Invention

[0004] The main objective of this invention is to propose an overload protection method and device for oil-immersed distribution transformers, aiming to solve the technical problems in the prior art where pure current protection cannot adapt to the heat dissipation characteristics of oil-immersed transformers and pure temperature protection has a lag in response.

[0005] To achieve the above objectives, the present invention provides an overload protection method for an oil-immersed distribution transformer, wherein the overload protection method for the oil-immersed distribution transformer includes the following steps:

[0006] S1. Real-time acquisition of transformer low-voltage side circuit current and the temperature of the top insulating oil of the transformer ;

[0007] S2, Preset first overload current threshold that matches the transformer specifications. Second overload current threshold First overload temperature threshold Second overload temperature threshold First overload time threshold Second overload time threshold Among them, the first overload current threshold Less than the second overload current threshold First overload temperature threshold Less than the second overload temperature threshold First overload time threshold Greater than the second overload time threshold ;

[0008] S3, if the loop current >First overload current threshold And the loop current ≤ Second overload current threshold When the temperature is high, it is determined to be a low-overload operating state; if the temperature is low... ≥ First overload temperature threshold Output a warning signal and start an overload timer; if the overload timer is greater than or equal to the first overload time threshold... And the first overload temperature threshold ≤Temperature <Second overload temperature threshold or temperature ≥ Second overload temperature threshold When this happens, the control and protection unit trips, disconnecting the low-voltage side circuit of the transformer;

[0009] When the loop current >Second overload current threshold When the system is in a high-overload operating state, it outputs a warning signal and starts a high-overload timer. When the high-overload timer is greater than or equal to the second overload time threshold... When this occurs, the control and protection unit trips, disconnecting the low-voltage side circuit of the transformer.

[0010] One preferred embodiment is that the first overload current threshold and the second overload current threshold Based on the pre-configured rated current of the low-voltage side of the transformer, and the first overload current threshold... Less than the second overload current threshold .

[0011] One preferred embodiment is that the first overload temperature threshold and the second overload temperature threshold Pre-configured based on the transformer insulation's temperature tolerance characteristics.

[0012] One preferred embodiment is the first overload time threshold. and the second overload time threshold Pre-configured based on the transformer's heat dissipation characteristics, and the first overload time threshold It is greater than the second overload time threshold.

[0013] One preferred embodiment is that the overload timing under the low-overload operating state is:

[0014]

[0015] in, For overload timing under low overload operating conditions, The first overload time threshold, The first performance coefficient of the transformer. This refers to the low-voltage side circuit current of the transformer. The first overload current threshold, The first overload temperature threshold, This is the second overload temperature threshold.

[0016] One preferred embodiment is that the high-overload timing under the high-overload operating state is as follows:

[0017]

[0018] in, For high-magnification overload timing under high-magnification overload operating conditions, This is the second performance coefficient of the transformer. The second overload current threshold, The second overload time threshold, This refers to the low-voltage side circuit current of the transformer.

[0019] An apparatus including the aforementioned overload protection method for an oil-immersed distribution transformer, comprising:

[0020] The system includes a temperature sensing unit, a current sensing unit, a control and management unit, an early warning unit, and a protection unit; the control and management unit is connected to the temperature sensing unit, the current sensing unit, the early warning unit, and the protection unit, respectively.

[0021] The temperature sensing unit is used to collect the temperature of the top insulating oil of the transformer.

[0022] The current sensing unit is used to collect the low-voltage side circuit current of the transformer.

[0023] The control and management unit is used to store transformer protection operating parameters, receive temperature and current data, perform protection calculations and judgments, and output corresponding action signals.

[0024] The early warning unit is used to receive early warning signals and output early warning instructions;

[0025] The protection unit is used to receive trip signals and disconnect the low-voltage side circuit of the transformer.

[0026] One preferred embodiment is that the transformer protection operating parameters include a first overload current threshold that matches the transformer specifications. Second overload current threshold First overload temperature threshold Second overload temperature threshold First overload time threshold Second overload time threshold .

[0027] One preferred embodiment is that the first overload current threshold Less than the second overload current threshold First overload temperature threshold Less than the second overload temperature threshold First overload time threshold Greater than the second overload time threshold .

[0028] In one preferred embodiment, the control and management unit is further configured to determine a low-multiple overload and a change in the temperature of the transformer top insulating oil. ≥ First overload temperature threshold When a high overload occurs, the overload timing function is triggered synchronously; and when a high overload is detected, the high overload timing function is triggered synchronously.

[0029] In the above technical solution of the present invention, the overload protection method for the oil-immersed distribution transformer includes the following steps: real-time acquisition of the low-voltage side circuit current of the transformer. and the temperature of the top insulating oil of the transformer Preset a first overload current threshold that matches the transformer specifications. Second overload current threshold First overload temperature threshold Second overload temperature threshold First overload time threshold Second overload time threshold Among them, the first overload current threshold Less than the second overload current threshold First overload temperature threshold Less than the second overload temperature threshold First overload time threshold Greater than the second overload time threshold If the loop current >First overload current threshold And the loop current ≤ Second overload current threshold When the temperature is high, it is determined to be a low-overload operating state; if the temperature is low... ≥ First overload temperature threshold Output a warning signal and start an overload timer; if the overload timer is greater than or equal to the first overload time threshold... And the first overload temperature threshold ≤Temperature <Second overload temperature threshold or temperature ≥ Second overload temperature threshold When the circuit current is high, the control and protection unit trips, disconnecting the low-voltage side circuit of the transformer; when the circuit current... >Second overload current threshold When the system is in a high-overload operating state, it outputs a warning signal and starts a high-overload timer. When the high-overload timer is greater than or equal to the second overload time threshold... When this occurs, the control and protection unit trips, disconnecting the low-voltage side circuit of the transformer. This invention solves the technical problems in the prior art where pure current protection cannot adapt to the heat dissipation characteristics of oil-immersed transformers and where pure temperature protection has a lag in response.

[0030] In this invention, multiple sets of thresholds matching the transformer specifications are pre-stored, and adaptive parameters can be configured for oil-immersed transformers of different capacities and processes, avoiding protection malfunctions caused by general parameters and improving the compatibility of the solution with different scenarios.

[0031] In this invention, the current range is divided into low-multiple overload operation state and high-multiple overload operation state, and different protection mechanisms are matched for each. Under low-multiple overload, short-term overcapacity operation is allowed, while under high-multiple overload, priority is given to ensuring equipment safety, thus balancing power supply reliability and equipment life.

[0032] In this invention, an independent early warning unit is integrated, which prioritizes the output of an early warning signal when an overload is detected. This can inform maintenance personnel of the overload risk in advance, facilitate the early transfer of loads, reduce the number of unplanned power outages, and improve power supply reliability. Attached Figure Description

[0033] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0034] Figure 1 This is a schematic diagram of an overload protection method for an oil-immersed distribution transformer according to an embodiment of the present invention;

[0035] Figure 2 This is a schematic diagram of an overload protection device for an oil-immersed distribution transformer according to an embodiment of the present invention.

[0036] The realization of the objective, functional characteristics and advantages of the present invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0037] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0038] It should be noted that all directional indicators (such as up, down, etc.) in the embodiments of the present invention are only used to explain the relative positional relationship and movement of each component in a certain specific posture (as shown in the figure). If the specific posture changes, the directional indicator will also change accordingly.

[0039] Furthermore, in this invention, descriptions involving "first," "second," etc., are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined with "first" or "second" may explicitly or implicitly include at least one of that feature.

[0040] Furthermore, the technical solutions of the various embodiments of the present invention can be combined with each other, but only if they are based on the ability of those skilled in the art to implement them. When the combination of technical solutions is contradictory or cannot be implemented, it should be considered that such combination of technical solutions does not exist and is not within the scope of protection claimed by the present invention.

[0041] See Figure 1 According to one aspect of the present invention, the present invention provides an overload protection method for an oil-immersed distribution transformer, wherein the overload protection method for the oil-immersed distribution transformer includes the following steps:

[0042] S1. Real-time acquisition of transformer low-voltage side circuit current and the temperature of the top insulating oil of the transformer ;

[0043] S2, Preset first overload current threshold that matches the transformer specifications. Second overload current threshold First overload temperature threshold Second overload temperature threshold First overload time threshold Second overload time threshold Among them, the first overload current threshold Less than the second overload current threshold First overload temperature threshold Less than the second overload temperature threshold First overload time threshold Greater than the second overload time threshold ;

[0044] S3, if the loop current >First overload current threshold And the loop current ≤ Second overload current threshold When the temperature is high, it is determined to be a low-overload operating state; if the temperature is low... ≥ First overload temperature threshold Output a warning signal and start an overload timer; if the overload timer is greater than or equal to the first overload time threshold... And the first overload temperature threshold ≤Temperature <Second overload temperature threshold or temperature ≥ Second overload temperature threshold When this happens, the control and protection unit trips, disconnecting the low-voltage side circuit of the transformer;

[0045] When the loop current >Second overload current threshold When the system is in a high-overload operating state, it outputs a warning signal and starts a high-overload timer. When the high-overload timer is greater than or equal to the second overload time threshold... When this occurs, the control and protection unit trips, disconnecting the low-voltage side circuit of the transformer.

[0046] Specifically, in this embodiment, the first overload current threshold and the second overload current threshold Based on the pre-configured rated current of the low-voltage side of the transformer, and the first overload current threshold... Less than the second overload current threshold .

[0047] Specifically, in this embodiment, the first overload temperature threshold and the second overload temperature threshold Pre-configured based on the transformer insulation's temperature tolerance characteristics.

[0048] Specifically, in this embodiment, the first overload time threshold and the second overload time threshold Pre-configured based on the transformer's heat dissipation characteristics, and the first overload time threshold It is greater than the second overload time threshold.

[0049] Specifically, in this embodiment, the overload timing under the low-multiplier overload operating state is as follows:

[0050]

[0051] in, For overload timing under low overload operating conditions, The first overload time threshold, The first performance coefficient of the transformer. This refers to the low-voltage side circuit current of the transformer. The first overload current threshold, The first overload temperature threshold, This is the second overload temperature threshold.

[0052] Specifically, in this embodiment, the high-multiplier overload timing under the high-multiplier overload operating state is as follows:

[0053]

[0054] in, For high-magnification overload timing under high-magnification overload operating conditions, This is the second performance coefficient of the transformer. The second overload current threshold, The second overload time threshold, This refers to the low-voltage side circuit current of the transformer.

[0055] See Figure 2 According to another aspect of the present invention, the present invention provides an overload protection device for an oil-immersed distribution transformer, wherein the overload protection device for the oil-immersed distribution transformer includes: a temperature sensing unit, a current sensing unit, a control management unit, an early warning unit, and a protection unit; the control management unit is connected to the temperature sensing unit, the current sensing unit, the early warning unit, and the protection unit respectively.

[0056] The temperature sensing unit is used to collect the temperature of the top insulating oil of the transformer.

[0057] The current sensing unit is used to collect the low-voltage side circuit current of the transformer.

[0058] The control and management unit is used to store transformer protection operating parameters, receive temperature and current data and perform protection calculations, make judgments based on the protection operating parameters, and output corresponding action signals.

[0059] The early warning unit is used to receive early warning signals and output early warning instructions;

[0060] The protection unit is used to receive trip signals and disconnect the low-voltage side circuit of the transformer.

[0061] Specifically, in this embodiment, the transformer protection operation parameters include a first overload current threshold that matches the transformer specifications. Second overload current threshold First overload temperature threshold Second overload temperature threshold First overload time threshold Second overload time threshold .

[0062] Specifically, in this embodiment, the first overload current threshold Less than the second overload current threshold First overload temperature threshold Less than the second overload temperature threshold First overload time threshold Greater than the second overload time threshold .

[0063] Specifically, in this embodiment, the control management unit is further configured to determine a low-multiplier overload and the temperature of the transformer top insulating oil. ≥ First overload temperature threshold When a high overload occurs, the overload timing function is triggered synchronously; and when a high overload is detected, the high overload timing function is triggered synchronously.

[0064] Specifically, in this embodiment, the transformer generates load losses during operation. These losses are mainly caused by the heat generated by the internal resistance of the high- and low-voltage circuits when current flows through them. The transformer dissipates heat through the insulating oil, causing the insulating oil temperature to rise. Under normal operating conditions, the heat generation power and heat dissipation power of the transformer are equal, and the insulating oil temperature remains stable. When the transformer is overloaded, due to the increased load losses, the heat generation power exceeds the heat dissipation power. Therefore, the temperature of the transformer windings and insulating oil continues to rise, causing a decrease in the insulating oil's effectiveness, performance degradation, and ultimately, insulation breakdown, leading to transformer failure. The transformer's structure, specifications, and manufacturing process all affect this, thus requiring different protection operating parameters to address the overload operation risk of the transformer. This invention pre-loads the corresponding transformer protection operating parameters according to the transformer's specifications and collects the low-voltage side circuit current of the transformer in real time. and the temperature of the top insulating oil of the transformer To perform protection judgment and calculation;

[0065] When the transformer is in normal operation, the current detected by the current sensing unit is the normal current, and the temperature detected is also the normal operating temperature.

[0066] When the transformer is operating under low overload conditions, the current sensing unit detects a low overload current. Due to the overload, the transformer oil temperature begins to rise slowly. When the temperature sensing unit detects that the transformer oil temperature has reached the first overload temperature threshold... When the control management unit determines that it is in a warning state, it controls the warning unit to output a warning signal and starts the overload timer;

[0067] When a low-multiplier overload current persists, the transformer oil temperature continues to rise. The current and temperature sensing units collect current and oil temperature data in real time. The control and management unit performs fault diagnosis based on preset transformer protection operating parameters. When the low-multiplier overload current persists, the insulating oil temperature reaches the first overload temperature threshold. Second overload temperature threshold Between, and the overload time is greater than or equal to the first overload time threshold. At this time, the control management unit controls the protection unit to realize the device protection trip, disconnect the low-voltage side circuit of the transformer, thereby protecting the transformer;

[0068] In another scenario, if the overload current persists, the oil temperature rises rapidly, and the insulating oil temperature exceeds or equals the second overload temperature threshold. Even if the overload time is less than the first overload time threshold At this time, the control management unit also controls the protection unit to trip the device protection circuit, disconnecting the low-voltage side circuit of the transformer, thereby protecting the transformer; that is, when the circuit current... >First overload current threshold And the loop current ≤ Second overload current threshold When the current is low, it is determined to be a low overload current, and the protection action is performed according to the low overload current.

[0069] When loop current is detected >Second overload current threshold When the transformer is in a high-overload operating state, the current sensing unit detects that the low-voltage side circuit current exceeds the high-overload current setting value. The control management unit then determines that a warning state is in effect, controls the warning unit to output a warning signal, and starts the protection action timing. Because the windings heat up rapidly during a high-overload, the insulating oil cannot quickly cool the transformer. Therefore, if the high-overload current persists for the preset protection action time, the control management unit controls the protection unit to trip the protection device, disconnecting the transformer's low-voltage side circuit and thus protecting the transformer.

[0070] Specifically, in this embodiment, taking a 25KVA 7.62kV / 120(240)kV single-phase oil-immersed distribution transformer as an example, its low-voltage circuit rated current is 104A. If the transformer's first performance coefficient... =0.0572, the second performance coefficient of the transformer =1, the transformer protection operating parameters are: first overload current threshold. =208A, Second Overload Current Threshold =832A, First overload temperature threshold =85℃, second overload temperature threshold =105℃, first overload time threshold =10min and second overload time threshold =5s; When the low-voltage circuit current is 208A, it is in a low-overload operation state. Under the low-overload operation state, long-term operation is achieved through temperature protection, effectively utilizing the transformer's capacity and overload capacity, reducing material usage, and saving energy and protecting the environment; When the overload temperature reaches 85℃, the warning output is activated, and the protection action is executed after 10 minutes; If the low-voltage circuit current is 1040A, it is in a high-overload operation state, and the protection action is executed after 3.2s. Under the high-overload operation state, rapid protection action is achieved, solving the problems of transformer winding burnout and insulation breakdown.

[0071] Specifically, in this embodiment, a 7.62kV / 120(240)kV single-phase oil-immersed distribution transformer with a specification of 25KVA is used for testing, and the setting parameters are as follows:

[0072] =208A, =1040A, =85℃, =105℃, =55min, =10s, =0.0572, =1; see Table 2 for measured protection data;

[0073] Table 2. Protective Measured Data

[0074]

[0075] The above are merely preferred embodiments of the present invention and do not limit the patent scope of the present invention. All equivalent structural transformations made using the contents of the present invention's specification and drawings under the inventive concept of the present invention, or direct / indirect applications in other related technical fields, are included within the patent protection scope of the present invention.

Claims

1. An overload protection method for an oil-immersed distribution transformer, characterized in that, Includes the following steps: S1. Real-time acquisition of transformer low-voltage side circuit current and the temperature of the top insulating oil of the transformer ; S2, Preset first overload current threshold that matches the transformer specifications. Second overload current threshold First overload temperature threshold Second overload temperature threshold First overload time threshold Second overload time threshold Among them, the first overload current threshold Less than the second overload current threshold First overload temperature threshold Less than the second overload temperature threshold First overload time threshold Greater than the second overload time threshold ; S3, if the loop current >First overload current threshold And the loop current ≤ Second overload current threshold When the temperature is low, it is determined to be in a low-overload operating state; if the temperature is high... ≥ First overload temperature threshold Output a warning signal and start an overload timer; if the overload timer is greater than or equal to the first overload time threshold... And the first overload temperature threshold ≤Temperature <Second overload temperature threshold or temperature ≥ Second overload temperature threshold When this happens, the control and protection unit trips, disconnecting the low-voltage side circuit of the transformer; When the loop current >Second overload current threshold When the system is in a high-overload operating state, it outputs a warning signal and starts a high-overload timer. When the high-overload timer is greater than or equal to the second overload time threshold... When this occurs, the control and protection unit trips, disconnecting the low-voltage side circuit of the transformer.

2. The overload protection method for an oil-immersed distribution transformer according to claim 1, characterized in that, First overload current threshold and the second overload current threshold Based on the pre-configured rated current of the low-voltage side of the transformer, and the first overload current threshold... Less than the second overload current threshold .

3. The overload protection method for an oil-immersed distribution transformer according to any one of claims 1-2, characterized in that, First overload temperature threshold and the second overload temperature threshold Pre-configured based on the transformer insulation's temperature tolerance characteristics.

4. An overload protection method for an oil-immersed distribution transformer according to any one of claims 1-2, characterized in that, First overload time threshold and the second overload time threshold Pre-configured based on the transformer's heat dissipation characteristics, and the first overload time threshold It is greater than the second overload time threshold.

5. An overload protection method for an oil-immersed distribution transformer according to any one of claims 1-2, characterized in that, The overload timing under the low-multiplier overload operating state is as follows: in, For overload timing under low overload operating conditions, The first overload time threshold, The first performance coefficient of the transformer. This refers to the low-voltage side circuit current of the transformer. The first overload current threshold, The first overload temperature threshold, This is the second overload temperature threshold.

6. An overload protection method for an oil-immersed distribution transformer according to any one of claims 1-2, characterized in that, The high-magnification overload timing under the high-magnification overload operating state is as follows: in, For high-magnification overload timing under high-magnification overload operating conditions, This is the second performance coefficient of the transformer. The second overload current threshold, The second overload time threshold, This refers to the low-voltage side circuit current of the transformer.

7. An apparatus comprising an overload protection method for an oil-immersed distribution transformer as described in any one of claims 1-6, characterized in that, include: Temperature sensing unit, current sensing unit, control and management unit, early warning unit, and protection unit; The control and management unit is connected to the temperature sensing unit, the current sensing unit, the early warning unit, and the protection unit, respectively. The temperature sensing unit is used to collect the temperature of the top insulating oil of the transformer. The current sensing unit is used to collect the low-voltage side circuit current of the transformer. The control and management unit is used to store transformer protection operating parameters, receive temperature and current data, perform protection calculations and judgments, and output corresponding action signals. The early warning unit is used to receive early warning signals and output early warning instructions; The protection unit is used to receive trip signals and disconnect the low-voltage side circuit of the transformer.

8. An overload protection device for an oil-immersed distribution transformer according to claim 7, characterized in that, The transformer protection operating parameters include a first overload current threshold that matches the transformer specifications. Second overload current threshold First overload temperature threshold Second overload temperature threshold First overload time threshold Second overload time threshold .

9. An overload protection device for an oil-immersed distribution transformer according to claim 7, characterized in that, First overload current threshold Less than the second overload current threshold First overload temperature threshold Less than the second overload temperature threshold First overload time threshold Greater than the second overload time threshold .

10. An overload protection device for an oil-immersed distribution transformer according to claim 7, characterized in that, The control and management unit is also used to determine low-level overload and the temperature of the transformer top insulating oil. ≥ First overload temperature threshold When a high overload occurs, the overload timing function is triggered synchronously; and when a high overload is detected, the high overload timing function is triggered synchronously.

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