A method for measuring dielectric loss in casing

Abstract

This invention discloses a method for measuring the dielectric loss of a bushing. The bushing includes a conductive rod, a capacitor core, and an insulating shell arranged sequentially; the capacitor core includes capacitor screens arranged radially; the bushing dielectric loss measurement method includes: performing a low-insulation treatment on the outer surface of the insulating shell; constructing a dielectric loss measurement balance bridge; connecting a power line of the dielectric loss measurement balance bridge to the conductive rod, the power line being input with a preset voltage source; connecting test leads of the dielectric loss measurement balance bridge to the last capacitor screen; when the dielectric loss measurement balance bridge is balanced, determining the bushing dielectric loss value based on the parameters of the dielectric loss measurement balance bridge; wherein, the parameters of the dielectric loss measurement balance bridge include the resistance parameters and capacitance parameters of the dielectric loss measurement balance bridge. This solution eliminates the influence of humidity and the outer insulation of the bushing on the dielectric loss measurement, improving the accuracy of the bushing dielectric loss measurement.

Description

Technical Field

[0001] The embodiments of the present invention relate to transformer technology, and more particularly to a method for measuring bushing dielectric loss. Background Technology

[0002] Capacitive high-voltage bushings, as typical oil-paper insulated devices, are indispensable external connection components of power transformers. Data shows that bushing accidents in 110kV and above transformers account for a certain proportion of all accidents, and the proportion of bushing-related accidents increases with the voltage level.

[0003] Bushing testing is a crucial part of routine transformer testing. Moisture and aging of bushings can cause them to explode, leading to serious consequences. The capacitance and dielectric loss of bushings are key indicators of their operational quality. However, in field testing, dielectric loss is easily affected by the environment, leading to distorted values ​​and inaccurate judgments. Among the many influencing factors, ambient humidity is the most difficult to control. It directly affects the insulation of the bushing surface, thus influencing the dielectric loss test value. Moreover, its impact on the bushing dielectric loss test value is not unilateral; it can both increase and decrease the value, potentially leading to misjudgments or omissions during field testing. Summary of the Invention

[0004] This invention provides a bushing dielectric loss measurement method to eliminate the influence of humidity and bushing external insulation on dielectric loss measurement, thereby improving the accuracy of bushing dielectric loss testing.

[0005] This invention provides a method for measuring dielectric loss in a bushing, wherein the bushing includes a conductive rod, a capacitor core, and an insulating shell arranged sequentially; the capacitor core includes capacitor screens arranged radially; characterized in that the bushing dielectric loss measurement method includes:

[0006] The outer surface of the insulating housing is treated with low insulation.

[0007] Construct a balanced bridge for dielectric loss measurement;

[0008] The power supply line of the dielectric loss measurement balance bridge is connected to the conductive rod, and the power supply line is input with a preset voltage source; the test line of the dielectric loss measurement balance bridge is connected to the end capacitor screen.

[0009] When the dielectric loss measurement balancing bridge is balanced, the dielectric loss value of the bushing is determined according to the parameters of the dielectric loss measurement balancing bridge; wherein, the parameters of the dielectric loss measurement balancing bridge include the resistance parameters and capacitance parameters of the dielectric loss measurement balancing bridge.

[0010] Optionally, the insulating shell includes multiple ceramic skirts;

[0011] The low-insulation treatment on the outer surface of the insulating housing includes:

[0012] A resistor is connected in parallel between each of the two ceramic skirts.

[0013] Optionally, the low-insulation treatment on the outer surface of the insulating housing includes:

[0014] A low-insulation material is applied to the outer surface of the insulating shell.

[0015] Optionally, the insulating shell includes multiple ceramic skirts;

[0016] The low-insulation treatment on the outer surface of the insulating housing includes:

[0017] A reactance is connected in parallel between each of the two ceramic skirts.

[0018] Optionally, the insulating shell includes multiple ceramic skirts;

[0019] The low-insulation treatment on the outer surface of the insulating housing includes:

[0020] An impedance is connected in parallel between each of the two ceramic skirts.

[0021] Optionally, a resistor is connected in parallel between each of the two ceramic skirts, specifically:

[0022] The first end is the end of the conductive rod, and the last end is the grounding flange at the bottom of the insulating shell. Resistors are connected in parallel between each pair of ceramic skirts.

[0023] Optionally, the dielectric loss measurement balance bridge includes: a first variable resistor, a second resistor, a first variable capacitor, and a second capacitor;

[0024] The conductive rod of the sleeve is electrically connected to the power line of the dielectric loss measurement balance bridge, and is also electrically connected to the first terminal of the second capacitor.

[0025] The end capacitor screen of the sleeve is electrically connected to the first end of the first variable resistor; the second end of the first variable resistor is electrically connected to the first end of the second resistor and the first end of the first variable capacitor, and is grounded; the second resistor and the first variable resistor are connected in parallel; the second end of the second resistor and the second end of the first variable capacitor are both electrically connected to the second end of the second capacitor.

[0026] Optionally, the dielectric loss measurement balance bridge also includes a galvanometer;

[0027] The first end of the ammeter is electrically connected to the first end of the first variable resistor, and the second end of the ammeter is electrically connected to the second end of the first variable capacitor and the second resistor.

[0028] Optionally, when the dielectric loss measurement balancing bridge is balanced, the casing dielectric loss value is determined based on the dielectric loss measurement balancing bridge parameters, including:

[0029] When the ammeter reading is zero, the bushing dielectric loss value is determined based on the first variable resistor, the second resistor, the first variable capacitor, and the second capacitor.

[0030] In this embodiment of the invention, a low-insulation treatment is applied to the outer surface of the insulating shell; a dielectric loss measurement balance bridge is constructed; then, a power line for the dielectric loss measurement balance bridge is connected to the conductive rod, and the power line is input with a preset voltage source; test leads for the dielectric loss measurement balance bridge are connected to the end capacitor screen; when the dielectric loss measurement balance bridge is balanced, the dielectric loss value of the bushing is determined according to the parameters of the dielectric loss measurement balance bridge; wherein, the parameters of the dielectric loss measurement balance bridge include the resistance parameters and capacitance parameters of the dielectric loss measurement balance bridge. Because there is coupling between the outer surface of the insulating shell and the inner capacitor core, a coupling capacitance is generated. When the voltage at a certain position on the insulating shell differs from the voltage on the inner capacitor core at that position, a coupling current will be generated between the insulating shell and the capacitor core. This coupling current will affect the resistive component of the current on the final capacitor screen, thus affecting the dielectric loss measurement. This solution reduces the resistive component of the coupling current generated by the coupling capacitance between the insulating shell and the capacitor core by applying a low-insulation treatment to the outer surface of the insulating shell. This reduces the influence of the coupling current on the resistive component of the current on the final capacitor screen, thereby improving the accuracy of the dielectric loss measurement of the bushing by the balanced bridge and eliminating the influence of humidity and the outer insulation of the bushing on the dielectric loss measurement in the prior art. Attached Figure Description

[0031] Figure 1 This is a flowchart of a casing dielectric loss measurement method provided in an embodiment of the present invention;

[0032] Figure 2 This is a simplified structural diagram of a sleeve provided in an embodiment of the present invention;

[0033] Figure 3 This is an equivalent model diagram of the sleeve in an embodiment of the present invention;

[0034] Figure 4 yes Figure 3 Simulation results of the simulation model;

[0035] Figure 5 This is a schematic diagram of the dielectric loss measurement balanced bridge circuit provided in an embodiment of the present invention;

[0036] Figure 6 This is a schematic diagram of another casing dielectric loss measurement method provided in an embodiment of the present invention. Detailed Implementation

[0037] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and not intended to limit it. Furthermore, it should be noted that, for ease of description, the accompanying drawings show only the parts relevant to the present invention, and not all of the structures.

[0038] Figure 1 This is a flowchart of a casing dielectric loss measurement method provided in an embodiment of the present invention, as shown below. Figure 1 As shown, the method includes the following steps:

[0039] S110. Low insulation treatment on the outer surface of the insulating housing;

[0040] in, Figure 2 This is a simplified structural diagram of a sleeve provided in an embodiment of the present invention, as shown below. Figure 2 As shown, in this scheme, the bushing can be a capacitor-type transformer bushing or a wall bushing in a power system; each type of bushing includes a conductive rod 10, a capacitor core 20, and an insulating shell 30 arranged sequentially; the capacitor core 20 includes radially arranged capacitor screens; each radially arranged capacitor screen is a coaxial cylindrical capacitor insulation layer distributed radially, and the capacitor screen gradually shortens longitudinally from the inside to the outside, achieving a relatively uniform voltage distribution in the longitudinal direction; it should be noted that the bushing insulation is divided into inner insulation and outer insulation. The inner insulation is the capacitor core 20 completely immersed in high-quality insulating oil; the outer insulation is the insulating shell 30, which serves as electrical insulation and mechanical support. It can be understood that, referring to... Figure 2 After voltage is applied to the conductive rod 10, the internal insulation is divided by the series voltage division of each capacitor screen in the capacitor core 20, and the external insulation is divided by the voltage division of each ceramic skirt 31 in the insulating shell 30. Figure 3 This is an equivalent model diagram of the sleeve in an embodiment of the present invention, such as... Figure 3 As shown, the bushing structure can be equivalent to: the capacitor core 20 is equivalent to multiple capacitors connected in series, and the insulating shell 30 is equivalent to multiple resistors connected in series. The resistors are electrically connected in series, and the capacitors are electrically connected in series. Coupling capacitors 40 are generated between the insulating shell 30 and the capacitor core 20 at any position within the bushing. Generally, due to the coupling capacitors between the insulating shell 30 and the capacitor core 20, when the voltage at a certain position of the insulating shell 30 differs from the voltage of the capacitor core 20 at the same position, a coupling current is generated between the insulating shell 30 and the capacitor core 20. This coupling current affects the resistive component of the current on the final capacitor screen, thus affecting the dielectric loss measurement. It should also be explained that the balanced bridge can measure the dielectric loss of the bushing. The balanced bridge measurement of the bushing's dielectric loss reflects the relationship between the current phasor on the final capacitor screen and the phase angle of the voltage applied to the conductive rod, i.e., the magnitude of the resistive component of the current on the final capacitor screen. Generally, if the voltage applied to the conductive rod is constant, and the current on the final capacitor screen changes, the measured dielectric loss of the bushing will change.

[0041] To investigate the effect of coupling current on the end-screen current under different insulation levels of the insulating shell 30, i.e., its effect on the measured bushing dielectric loss, the study aims to... Figure 3 The equivalent model is used for simulation. The actual capacitance and dielectric loss of the bushing are set. The final screen current under different insulation performance of the insulating shell is solved based on the loop current method in the simulation algorithm, and then the measured dielectric loss of the bushing is obtained. When there is no significant difference between the measured dielectric loss of the bushing and the set actual dielectric loss of the bushing, the influence of the coupling current on the final screen current is low, and the dielectric loss measurement is accurate. Figure 4 yes Figure 3 Simulation results of the simulation model, such as Figure 4 As shown, the simulation results indicate that (1) when the surface insulation of the outer shell is sufficiently large (which can be understood as the equivalent resistance value of the outer shell in the simulation model being larger), the measured dielectric loss value is basically not deviated from the actual value; (2) when the surface insulation of the outer shell gradually decreases, for example, in actual field testing, when the environment is humid, the measured dielectric loss value of the bushing gradually increases; (3) when the surface insulation of the outer shell further decreases significantly, for example, when the location is near the sea or in an industrial area, and the pollution such as salt is relatively serious, the deviation of the measured dielectric loss value of the bushing gradually decreases and turns into a negative value, and the negative deviation gradually increases; (4) when the surface insulation of the outer shell is sufficiently small (which can be understood as the equivalent resistance value of the outer shell in the simulation model being smaller), the negative deviation will gradually decrease again until the measured value is almost without deviation from the actual value. The simulation results show that when the insulation of the outer surface of the insulating shell is sufficiently low, the influence of the coupling current on the resistive component of the final screen current is relatively small, and the dielectric loss measurement is accurate. Therefore, this solution uses low insulation treatment on the outer surface of the insulating shell to further reduce the influence of the coupling current on the resistive component of the final screen current, thereby improving the accuracy of dielectric loss measurement and eliminating the influence of humidity and the outer insulation of the bushing on dielectric loss measurement in existing technologies. It should be noted that the change in the insulation performance of the insulating shell is manifested in the simulation model as a change in the equivalent resistance value of the insulating shell.

[0042] Low insulation treatment can be understood as artificially reducing the insulation performance of the insulating shell, that is, reducing the equivalent resistance value of the insulating shell in the simulation model. It should be noted that the equivalent resistance value of the insulating shell is generally in the GΩ range. According to the simulation results, the insulation performance of the insulating shell needs to be reduced to the MΩ level or even lower to achieve better accuracy in measuring bushing dielectric loss.

[0043] Optional, refer to Figure 2The insulating housing 30 includes a plurality of ceramic skirts 31; the outer surface of the insulating housing is treated with low insulation, including: a resistor connected in parallel between each pair of ceramic skirts 31, or a reactance connected in parallel between each pair of ceramic skirts 31; or an impedance connected in parallel between each pair of ceramic skirts. To further explain the simulation results, after the insulating shell 30 is connected in parallel with each parallel resistor, reactance, or impedance, when it acts with the coupling capacitance of the capacitor core 20, the coupling current is almost capacitive relative to the phase of the preset voltage source of the power line. Its effect on the resistive component of the final capacitor screen current is negligible. Thus, even if the coupling current is generated due to the difference between the voltage at a certain position on the insulating shell 30 and the voltage on the internal capacitor core at that position, it will not affect the accuracy of the subsequent dielectric loss measurement balance bridge measurement of the bushing dielectric loss. It should be noted that the parallel resistors between each pair of ceramic skirts are specifically connected as follows: with the end B1 of the conductive rod 10 as the starting end and the grounding flange B2 at the bottom of the insulating shell 30 as the ending end, resistors are connected in parallel between each pair of ceramic skirts 31 sequentially from the beginning to the end. Specifically, on the one hand, considering the effect of adding parallel resistors on improving the accuracy of bushing dielectric loss measurement, the resistance value should be as small as possible; on the other hand, considering the matching of resistor power, the power consumption of each parallel resistor should be less than or equal to the power provided by the preset voltage source, and the resistance value of each parallel resistor should not be too small; moreover, the rated power and size matching of the resistor itself should also be considered, and each parallel resistor should be arranged as evenly as possible on the insulating shell.

[0044] Optionally, a low-insulation treatment may be applied to the outer surface of the insulating housing 30, including applying a low-insulation material to the outer surface of the insulating housing 30.

[0045] Low-insulating materials include salt water, chemical materials, sprays, foams, semiconductor materials, etc., which have relatively low insulation resistance values. No specific type of low-insulating material is specified here.

[0046] S120. Construct a balanced bridge for dielectric loss measurement;

[0047] in, Figure 5 This is a schematic diagram of the dielectric loss measurement balanced bridge circuit provided in an embodiment of the present invention; as shown. Figure 2 and 5As shown, the dielectric loss measurement balance bridge includes: a first variable resistor Rt, a second resistor R2, a first variable capacitor Ct, and a second capacitor C2; the conductive rod 10 of the sleeve 01 under test is electrically connected to the power line 11 of the dielectric loss measurement balance bridge, and is also electrically connected to the first end of the second capacitor C2; the end capacitor screen 21 of the sleeve 01 under test is electrically connected to the first end of the first variable resistor Rt; the second end of the first variable resistor Rt is electrically connected to the first end of the second resistor R2 and the first end of the first variable capacitor Ct, and is grounded; the second resistor R2 and the first variable resistor Rt are connected in parallel; the second end of the second resistor R2 and the second end of the first variable capacitor Ct are both electrically connected to the second end of the second capacitor C2. Figure 5 As shown, the dielectric loss measurement balance bridge also includes a galvanometer I; the first end of the galvanometer I is electrically connected to the first end of the first variable resistor Rt, and the second end of the galvanometer I is electrically connected to the second end of the first variable capacitor Ct and the second resistor R2.

[0048] S130. Connect the power supply line of the dielectric loss measurement balance bridge to the conductive rod, and input a preset voltage source to the power supply line; connect the test line of the dielectric loss measurement balance bridge to the end capacitor screen.

[0049] The voltage applied by the preset voltage source is the same as the voltage applied to the capacitor core. The voltage applied to the capacitor core may or may not be equal to the voltage of the insulating shell; there is no limitation on the magnitude of the voltage between the capacitor core and the insulating shell. The power supply line of the dielectric loss measurement balance bridge is connected to the conductive rod, and its test leads are connected to the final capacitor screen for subsequent measurement of the dielectric loss value of the bushing.

[0050] S140. When the dielectric loss measurement balance bridge is balanced, the dielectric loss value of the bushing is determined according to the dielectric loss measurement balance bridge parameters; wherein, the dielectric loss measurement balance bridge parameters include the dielectric loss measurement balance bridge resistance parameters and the dielectric loss measurement balance bridge capacitance parameters.

[0051] The working principle of the dielectric loss measurement balance bridge for bushing under test is as follows: Adjusting the first variable resistor Rt and the first variable capacitor Ct to balance the bridge, the ammeter reading is 0. At this point, according to the bridge balance principle, the capacitance parameter C and resistance parameter R of the bushing under test are determined, thereby determining the dielectric loss value of the bushing under test. Specifically, adjusting the first variable resistor Rt and the first variable capacitor Ct, the bridge is balanced, and the ammeter reading is 0. Based on the first variable resistor Rt, the second resistor R2, the first variable capacitor Ct, and the second variable capacitor C2, the dielectric loss value of the bushing is determined to be tanδ=ωR2C. t , where w is the frequency of the preset voltage source.

[0052] This invention also provides a method for measuring casing dielectric loss. Figure 6 This is a schematic diagram of another casing dielectric loss measurement method provided in an embodiment of the present invention, as shown below. Figure 6As shown, the casing dielectric loss measurement method includes the following steps:

[0053] S210. Construct a balanced bridge for dielectric loss measurement;

[0054] S220. Connect the power supply line of the dielectric loss measurement balance bridge to the conductive rod, and input the preset voltage source to the power supply line; connect the test line of the dielectric loss measurement balance bridge to the end capacitor screen.

[0055] S230. Apply a preset voltage value between each pair of ceramic skirts; wherein, the preset voltage value between each pair of ceramic skirts is consistent with the voltage on the capacitor screen inside the bushing at that position.

[0056] S240. When the dielectric loss measurement balance bridge is balanced, the dielectric loss value of the bushing is determined according to the parameters of the dielectric loss measurement balance bridge; wherein, the parameters of the dielectric loss measurement balance bridge include the resistance parameters and capacitance parameters of the dielectric loss measurement balance bridge.

[0057] In this embodiment, due to the coupling effect between the outer insulating shell and the inner capacitor core, a coupling capacitance is generated. When the voltage at a certain position on the insulating shell differs from the voltage on the inner capacitor core at that position, a coupling current will be generated between the insulating shell and the capacitor core. This coupling current will affect the resistive component of the current on the final capacitor screen, thus affecting the dielectric loss measurement. In this embodiment, a preset voltage value is applied between each pair of ceramic skirts. The preset voltage value at each position between the two ceramic skirts is consistent with the voltage on the inner capacitor screen of the bushing at that position. That is, when the voltage at each point on the capacitor core is consistent with the voltage of the outer insulating shell at the same position, the coupling capacitance between the insulating shell and the capacitor core will not generate a coupling current, thus not affecting the current on the final capacitor screen, and therefore not affecting the dielectric loss measurement, improving the accuracy of the dielectric loss measurement.

[0058] Note that the above description is merely a preferred embodiment of the present invention and the technical principles employed. Those skilled in the art will understand that the present invention is not limited to the specific embodiments described herein, and various obvious changes, readjustments, and substitutions can be made without departing from the scope of protection of the present invention. Therefore, although the present invention has been described in detail through the above embodiments, the present invention is not limited to the above embodiments, and may include many other equivalent embodiments without departing from the concept of the present invention, the scope of which is determined by the scope of the appended claims.

Claims

1. A method for measuring dielectric loss in a bushing, wherein the bushing comprises a conductive rod, a capacitor core, and an insulating shell arranged sequentially; the insulating shell comprises multiple ceramic skirts; the capacitor core comprises capacitor screens arranged radially; characterized in that, The casing dielectric loss measurement method includes: The outer surface of the insulating housing is subjected to a low-insulation treatment; wherein the low-insulation treatment on the outer surface of the insulating housing includes: connecting a resistor in parallel between each pair of ceramic skirts; or connecting a reactance in parallel between each pair of ceramic skirts; or connecting an impedance in parallel between each pair of ceramic skirts. Construct a balanced bridge for dielectric loss measurement; The power supply line of the dielectric loss measurement balance bridge is connected to the conductive rod, and the power supply line is input with a preset voltage source; the test line of the dielectric loss measurement balance bridge is connected to the end capacitor screen. When the dielectric loss measurement balancing bridge is balanced, the dielectric loss value of the bushing is determined according to the parameters of the dielectric loss measurement balancing bridge; wherein, the parameters of the dielectric loss measurement balancing bridge include the resistance parameters and capacitance parameters of the dielectric loss measurement balancing bridge.

2. The casing dielectric loss measurement method according to claim 1, characterized in that, The low-insulation treatment on the outer surface of the insulating housing includes: A low-insulation material is applied to the outer surface of the insulating shell.

3. The casing dielectric loss measurement method according to claim 1, characterized in that, A resistor is connected in parallel between each of the two ceramic skirts, specifically: The first end is the end of the conductive rod, and the last end is the grounding flange at the bottom of the insulating shell. Resistors are connected in parallel between each pair of ceramic skirts.

4. The casing dielectric loss measurement method according to claim 1, characterized in that, The dielectric loss measurement balance bridge includes: a first variable resistor, a second resistor, a first variable capacitor, and a second capacitor; The conductive rod of the sleeve is electrically connected to the power line of the dielectric loss measurement balance bridge, and is also electrically connected to the first terminal of the second capacitor. The end capacitor screen of the sleeve is electrically connected to the first end of the first variable resistor; the second end of the first variable resistor is electrically connected to the first end of the second resistor and the first end of the first variable capacitor, and is grounded; the second resistor and the first variable resistor are connected in parallel; the second end of the second resistor and the second end of the first variable capacitor are both electrically connected to the second end of the second capacitor.

5. The casing dielectric loss measurement method according to claim 4, characterized in that, The dielectric loss measurement balance bridge also includes a galvanometer; The first end of the ammeter is electrically connected to the first end of the first variable resistor, and the second end of the ammeter is electrically connected to the second end of the first variable capacitor and the second resistor.

6. The casing dielectric loss measurement method according to claim 5, characterized in that, When the dielectric loss measurement balancing bridge is balanced, the dielectric loss value of the bushing is determined based on the parameters of the dielectric loss measurement balancing bridge, including: When the ammeter reading is zero, the bushing dielectric loss value is determined based on the first variable resistor, the second resistor, the first variable capacitor, and the second capacitor.

Images