A 10 kV distribution system transfer overvoltage test method

Abstract

A 10kV distribution system overvoltage test method accurately measures the overvoltage transmitted through the 400V neutral conductor to the enclosure of electrical equipment when a single-phase grounding fault occurs on the high-voltage side of a 10kV distribution transformer. This test method provides a theoretical verification method for researchers in this field. Furthermore, the test results can be used to guide the selection and modification of neutral point grounding methods within substations, the selection and modification of grounding methods for 10kV distribution transformers, and the configuration of repeated grounding electrodes on the low-voltage side of 10kV distribution transformers.

Description

Technical Field

[0001] The present invention relates to the technical field of overvoltage in power distribution networks, and in particular to a method for testing overvoltage transmission in a 10 kV power distribution system. Background Art

[0002] Currently, most 10kV distribution transformers use a shared grounding electrode for both the protective earth and the working ground. When a single-phase ground fault occurs on the high-voltage side of a distribution transformer, the fault current flowing through the distribution transformer grounding electrode raises the potential of the low-voltage neutral point. This overvoltage is then transmitted through the neutral line to the outer casing of user electrical equipment, potentially causing personal injury, equipment damage, fire, and other accidents, posing a serious threat to the power supply security of the distribution system. Furthermore, a local ground short circuit fault on the high-voltage side of the distribution transformer can also raise the surface potential, which is then transmitted through the earth to the distribution transformer grounding electrode, resulting in an overvoltage. The closer the fault point is to the distribution transformer grounding electrode, the higher the transmitted voltage.

[0003] The magnitude of the transferred overvoltage is dependent on a variety of factors, including the 10kV neutral point grounding method within the substation, the connection between the distribution transformer's operating and safety grounds, and the grounding method of the 400V distribution system. Substations typically use an ungrounded neutral point or arc suppression coil grounding system for the 10kV neutral point. When a single-phase ground fault occurs on a 10kV line, the fault current is low, resulting in a low transferred overvoltage. However, if a neutral point fault occurs in a low-resistance grounding system, the theoretical fault current can reach nearly 600A, generating a significant transferred overvoltage. Currently, some provinces and cities in China are gradually piloting low-resistance grounding, and the issue of transferred overvoltage has received increasing attention. However, current research is limited to theoretical studies and lacks practical field verification. Summary of the Invention

[0004] In order to overcome the deficiencies of the above technologies, the present invention provides a method for actually measuring the transferred overvoltage value generated on the low-voltage side when a shell-touching grounding fault occurs in a distribution transformer, thereby providing measured data for the transformation of the neutral point grounding method of the substation.

[0005] The technical solution adopted by the present invention to overcome the technical problems is:

[0006] A 10 kV distribution system transfer overvoltage test method, comprising:

[0007] a) Obtain the parameters of the substation neutral point grounding device and 10 kV line based on the substation 10 kV busbar neutral point grounding method;

[0008] b) Measure the equivalent grounding resistance of the distribution transformer;

[0009] c) Calculate the ground fault current and voltage on the high voltage side of the distribution transformer;

[0010] d) Simulate the shell-to-ground fault on the high-voltage side of the distribution transformer;

[0011] e) Measure the grounding electrode current and voltage of distribution transformer;

[0012] f) Compare the calculated values ​​with the measured values ​​to complete the 10 kV distribution system transmission overvoltage test.

[0013] Furthermore, the parameters of the 10 kV line obtained in step a) include:

[0014] a-1) Obtaining the system capacitance current I in a system with an ungrounded neutral point C ;

[0015] a-2) Obtain the maximum grounding current after compensation of the neutral point in the arc suppression coil grounding system;

[0016] a-3) Obtain the low-resistance value R0 and grounding impedance Z after the neutral point passes through the low-resistance grounding system T0 a-4) Obtain the line impedance Z between the 10 kV outgoing line start and the test distribution transformer l .

[0017] Furthermore, the steps for measuring the equivalent grounding resistance of the distribution transformer in step b) are as follows: b-1) determining the grounding method of the distribution transformer low-voltage system based on the grounding method of the distribution transformer safety ground and the work site; b-2) finding the grounding electrode of the distribution transformer and treating the above-ground part so that the metal part of the distribution transformer grounding electrode is exposed;

[0018] b-3) Use the ground resistance tester to clamp the ground electrode clamp to the exposed metal part of the distribution transformer ground electrode and measure the equivalent ground resistance R of the distribution transformer. Tequ .

[0019] Furthermore, the steps for calculating the ground fault current and voltage of the high-voltage side of the distribution transformer in step c) are as follows: c-1) For a neutral point ungrounded system, the formula U T0 =I C R Tequ The transfer overvoltage U when the medium and high voltage side touches the shell and is grounded is calculated. T0 ;

[0020] c-2) For a neutral point grounded arc suppression coil system, the formula U T0 =10R Tequ The transfer overvoltage U when the high voltage side touches the shell and is grounded is calculated. T0 ;

[0021] c-3) For a neutral point grounded system with a small resistance, the formula The transfer overvoltage U when the high voltage side touches the shell and is grounded is calculated. T0 , where U N is the system phase voltage.

[0022] Furthermore, the step of simulating a grounding fault on the high-voltage side of the distribution transformer in step d) is as follows: d-1) making an artificial grounding electrode at a straight-line distance greater than 10 meters from the grounding electrode of the distribution transformer as a zero potential reference point;

[0023] d-2) Connect a pole-mounted circuit breaker between the A-phase incoming line on the high-voltage side of the distribution transformer and the distribution transformer casing, and place the circuit breaker controller on an insulating pad 10 meters away from the distribution transformer grounding electrode;

[0024] d-3) A 10kV core-through zero-sequence current transformer is placed on the conductor between the distribution transformer housing and the circuit breaker, and the primary side of a 10kV single-phase voltage transformer is connected between the neutral point and the zero potential reference point on the low-voltage side of the distribution transformer;

[0025] d-4) Disconnect all outgoing air switches on the low-voltage side of the distribution transformer and disconnect all neutral lines connected to users on the low-voltage side of the distribution transformer; d-5) Use a ground resistance tester to measure the grounding electrode resistance value R of the distribution transformer again. T .

[0026] Furthermore, the step of measuring the grounding electrode current and voltage of the distribution transformer in step e) is as follows: e-1) connecting the secondary sides of the zero-sequence current transformer and the zero-sequence voltage transformer to a portable fault recorder, setting the fault recorder to self-start recording, and setting the voltage sudden change starting value to 10V;

[0027] e-2) Connect the secondary sides of the zero-sequence current transformer and zero-sequence voltage transformer to the zero potential reference point with wires; e-3) Modify the settings of the test line protection devices in the substation: change the primary value of the overcurrent stage I setting to 600A and the time to 0s; change the primary value of the overcurrent stage II setting to 300A and the time to 3s; and disable all other protection functions;

[0028] e-4) The switch is remotely closed through the pole-mounted circuit breaker controller, triggering a shell-to-ground fault. After the fault lasts for 2 seconds, the circuit breaker is remotely opened.

[0029] Furthermore, the step of comparing the calculated value with the measured value in step f) is as follows:

[0030] f-1) Read the fault current I from the fault recorder f , fault voltage U f ;

[0031] f-2) Determine the equations for an ungrounded neutral point system and a grounded arc suppression coil system Is it true? f-3) Determine whether the equation is true in a system where the neutral point is grounded by a small resistance. Is it true?

[0032] Preferably, the maximum ground current after compensation in step a-2) is 10A.

[0033] Preferably, in step b-2), the area of ​​the exposed metal portion of the grounding electrode of the distribution transformer is greater than or equal to the area of ​​the clamp of the grounding electrode clamp of the ground resistance tester.

[0034] Preferably, in a 10 kV system, in step c-3) U N The value is 6000V.

[0035] The beneficial effect of this invention is that it can accurately measure the overvoltage transmitted to the enclosure of electrical equipment via the 400V neutral conductor when a single-phase grounding fault occurs on the high-voltage side of a 10kV distribution transformer. This test method provides a theoretical verification method for researchers in this field. Furthermore, the test results can be used to guide the selection and modification of neutral point grounding methods within substations, the selection and modification of grounding methods for 10kV distribution transformers, and the configuration of redundant grounding electrodes on the low-voltage side of 10kV distribution transformers. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 This is the test wiring diagram of the present invention. DETAILED DESCRIPTION

[0037] The following is combined with Figure 1 The present invention will be further described.

[0038] A 10 kV distribution system transfer overvoltage test method, comprising:

[0039] a) Based on the neutral point grounding method of the substation's 10 kV busbar, obtain the parameters of the substation's neutral point grounding device and the 10 kV line.

[0040] b) Measure the equivalent grounding resistance of the distribution transformer.

[0041] c) Calculate the current and voltage of the shell-to-ground fault on the high-voltage side of the distribution transformer.

[0042] d) Simulate the shell grounding fault on the high-voltage side of the distribution transformer.

[0043] e) Measure the grounding electrode current and voltage of the distribution transformer.

[0044] f) Compare the calculated values ​​with the measured values ​​to complete the 10 kV distribution system transmission overvoltage test.

[0045] This invention provides a distribution system overvoltage test method that accurately measures the overvoltage transmitted through the 400V neutral conductor to the enclosure of electrical equipment when a single-phase grounding fault occurs on the high-voltage side of a 10kV distribution transformer. This test method provides a theoretical verification method for researchers in this field. Furthermore, the test results can be used to guide the selection and modification of neutral point grounding methods within substations, the selection and modification of grounding methods for 10kV distribution transformers, and the configuration of redundant grounding electrodes on the low-voltage side of 10kV distribution transformers.

[0046] Example 1:

[0047] The parameters of the 10 kV line obtained in step a) include:

[0048] a-1) Obtaining the system capacitance current I in a system with an ungrounded neutral point C .

[0049] a-2) Obtain the maximum grounding current after compensation of the neutral point through the arc suppression coil grounding system.

[0050] a-3) Obtain the low-resistance value R0 and grounding impedance Z after the neutral point passes through the low-resistance grounding system T0 .

[0051] a-4) Obtain the line impedance Z between the 10 kV outgoing line start and the test distribution transformer l .

[0052] Example 2:

[0053] The steps for measuring the equivalent grounding resistance of the distribution transformer in step b) are as follows:

[0054] b-1) Determine the grounding method for the distribution transformer's low-voltage system based on the grounding method for the distribution transformer's safety ground and work area. b-2) Locate the distribution transformer's grounding electrode and treat the above-ground portion to expose the metal portion of the distribution transformer's grounding electrode.

[0055] b-3) Use the ground resistance tester to clamp the ground electrode clamp to the exposed metal part of the distribution transformer ground electrode and measure the equivalent ground resistance R of the distribution transformer. Tequ .

[0056] Example 3:

[0057] The steps for calculating the ground fault current and voltage on the high voltage side of the distribution transformer in step c) are as follows: c-1) For a neutral point ungrounded system, the formula U T0 =I C R Tequ The transfer overvoltage U when the medium and high voltage side touches the shell and is grounded is calculated. T0 .

[0058] c-2) For a neutral point grounded arc suppression coil system, the formula U T0 =10R Tequ The transfer overvoltage U when the high voltage side touches the shell and is grounded is calculated. T0 .

[0059] c-3) For a neutral point grounded system with a small resistance, the formula The transfer overvoltage U when the high voltage side touches the shell and is grounded is calculated. T0 , where U N is the system phase voltage.

[0060] Example 4:

[0061] The steps of simulating the high-voltage side shell-to-ground fault of the distribution transformer in step d) are as follows:

[0062] d-1) Make an artificial grounding electrode as the zero potential reference point at a straight-line distance of more than 10 meters from the grounding electrode of the distribution transformer.

[0063] d-2) Connect a pole-mounted circuit breaker between the A-phase incoming line on the high-voltage side of the distribution transformer and the distribution transformer casing, and place the circuit breaker controller on an insulating pad 10 meters away from the distribution transformer grounding electrode.

[0064] d-3) The 10kV core-through zero-sequence current transformer is placed on the conductor between the transformer housing and the circuit breaker. The primary side of the 10kV single-phase voltage transformer is connected between the neutral point and the zero potential reference point on the low-voltage side of the transformer. Figure 1 d-4) Disconnect all outgoing air switches on the low-voltage side of the distribution transformer and disconnect all neutral lines connected to users on the low-voltage side of the distribution transformer. d-5) Use the ground resistance tester to measure the grounding electrode resistance value R of the distribution transformer again. T .

[0065] Example 5:

[0066] The steps of measuring the grounding electrode current and voltage of the distribution transformer in step e) are as follows:

[0067] e-1) Connect the secondary sides of the zero-sequence current transformer and zero-sequence voltage transformer to a portable fault recorder. Set the fault recorder to self-start recording, and set the voltage sudden change startup value to 10V.

[0068] e-2) Connect the secondary sides of the zero-sequence current transformer and zero-sequence voltage transformer to the zero potential reference point with wires to ensure safety.

[0069] e-3) Modify the settings of the test line protection devices within the substation: change the primary value of the overcurrent stage I setting to 600A and the duration to 0s; change the primary value of the overcurrent stage II setting to 300A and the duration to 3s; and disable all other protection functions. The principle for modifying the settings is to ensure that the entire line can clear the fault without delay in the event of a phase-to-phase short circuit, and that the protection operation time in the event of a single-phase ground fault is greater than the duration of the manual ground test.

[0070] e-4) The switch is remotely closed through the pole-mounted circuit breaker controller, triggering a shell-to-ground fault. After the fault lasts for 2 seconds, the circuit breaker is remotely opened.

[0071] Example 6:

[0072] The steps of comparing the calculated value with the measured value in step f) are:

[0073] f-1) Read the fault current I from the fault recorder f , fault voltage U f .

[0074] f-2) Determine the equations for an ungrounded neutral point system and a grounded arc suppression coil system f-3) Determine whether the equation is true in a system where the neutral point is grounded by a small resistance. Is it true?

[0075] The equations in step f-2) and step f-3) hold true, indicating that the 10 kV distribution system overvoltage transmission test is successful.

[0076] Example 7:

[0077] The maximum ground current after compensation in step a-2) is 10A.

[0078] Example 8:

[0079] In step b-2), the area of ​​the exposed metal portion of the grounding electrode of the distribution transformer is greater than or equal to the area of ​​the clamp of the grounding electrode clamp of the ground resistance tester.

[0080] Example 9:

[0081] In a 10 kV system, U N The value is 6000V.

[0082] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art will be able to modify the technical solutions described in the aforementioned embodiments or substitute equivalents for some of the technical features. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. A 10 kV distribution system overvoltage test method, characterized in that: include: a) Obtain the parameters of the substation neutral point grounding device and 10 kV line based on the substation 10 kV busbar neutral point grounding method; b) Measure the equivalent grounding resistance of the distribution transformer; c) Calculate the ground fault current and voltage on the high voltage side of the distribution transformer; d) Simulate the shell-to-ground fault on the high-voltage side of the distribution transformer; e) Measure the grounding electrode current and voltage of distribution transformer; f) Compare the calculated values ​​with the measured values ​​and complete the 10 kV distribution system overvoltage test; The steps for calculating the ground fault current and voltage of the high-voltage side shell contact of the distribution transformer in step c) are as follows: c-1) For a neutral point ungrounded system, the formula U T0 =I C R Tequ The transfer overvoltage U when the medium and high voltage side touches the shell and is grounded is calculated. T0 ; c-2) For a neutral point grounded arc suppression coil system, the formula U T0 =10R Tequ The transfer overvoltage U when the high voltage side touches the shell and is grounded is calculated. T0 ; c-3) For a neutral point grounded system with a small resistance, the formula The transfer overvoltage U when the high voltage side touches the shell and is grounded is calculated. T0 , where U N is the system phase voltage; The steps of comparing the calculated value with the measured value in step f) are: f-1) Read the fault current I from the fault recorder f , fault voltage U f ; f-2) Determine the equations for an ungrounded neutral point system and a grounded arc suppression coil system Is it true? f-3) Determine whether the equation is true in a system where the neutral point is grounded by a small resistance. Is it true? 2. The 10 kV distribution system overvoltage test method according to claim 1, characterized in that: The parameters of the 10 kV line obtained in step a) include: a-1) Obtaining the system capacitance current I in a system with an ungrounded neutral point C ; a-2) Obtain the maximum grounding current after compensation of the neutral point in the arc suppression coil grounding system; a-3) Obtain the low-resistance value R0 and grounding impedance Z after the neutral point passes through the low-resistance grounding system T0 ; a-4) Obtain the line impedance Z between the 10 kV outgoing line start and the test distribution transformer l .

3. The 10 kV power distribution system transmission overvoltage test method according to claim 1, characterized in that: The steps for measuring the equivalent grounding resistance of the distribution transformer in step b) are as follows: b-1) Determine the grounding method of the distribution transformer low-voltage system based on the grounding method of the distribution transformer safety ground and the work site; b-2) Locate the distribution transformer grounding electrode and treat the above-ground part so that the metal part of the distribution transformer grounding electrode is exposed; b-3) Use the ground resistance tester to clamp the ground electrode clamp to the exposed metal part of the distribution transformer ground electrode and measure the equivalent ground resistance R of the distribution transformer. Tequ .

4. The 10 kV power distribution system transmission overvoltage test method according to claim 1, characterized in that: The steps of simulating the high-voltage side shell-to-ground fault of the distribution transformer in step d) are as follows: d-1) Make an artificial grounding electrode at a straight-line distance of more than 10 meters from the grounding electrode of the distribution transformer as the zero potential reference point; d-2) Connect a pole-mounted circuit breaker between the A-phase incoming line on the high-voltage side of the distribution transformer and the distribution transformer casing, and place the circuit breaker controller on an insulating pad 10 meters away from the distribution transformer grounding electrode; d-3) A 10kV core-through zero-sequence current transformer is placed on the conductor between the distribution transformer housing and the circuit breaker, and the primary side of a 10kV single-phase voltage transformer is connected between the neutral point and the zero potential reference point on the low-voltage side of the distribution transformer; d-4) Disconnect all outgoing air switches on the low-voltage side of the distribution transformer and disconnect all neutral lines connected to users on the low-voltage side of the distribution transformer; d-5) Use a ground resistance tester to measure the grounding electrode resistance value R of the distribution transformer again. T .

5. The 10 kV distribution system overvoltage test method according to claim 4, characterized in that: The steps of measuring the grounding electrode current and voltage of the distribution transformer in step e) are as follows: e-1) Connect the secondary sides of the zero-sequence current transformer and zero-sequence voltage transformer to a portable fault recorder. Set the fault recorder to self-start recording, with the voltage sudden change starting value of 10V. e-2) Connect the secondary sides of the zero-sequence current transformer and zero-sequence voltage transformer to the zero potential reference point with wires; e-3) Modify the settings of the test line protection devices in the substation: change the primary value of the overcurrent stage I setting to 600A and the time to 0s; change the primary value of the overcurrent stage II setting to 300A and the time to 3s; and disable all other protection functions; e-4) The switch is remotely closed through the pole-mounted circuit breaker controller, triggering a shell-to-ground fault. After the fault lasts for 2 seconds, the circuit breaker is remotely opened.

6. The 10 kV power distribution system overvoltage test method according to claim 2, characterized in that: The maximum ground current after compensation in step a-2) is 10A.

7. The 10 kV power distribution system overvoltage test method according to claim 3, characterized in that: In step b-2), the area of ​​the exposed metal portion of the grounding electrode of the distribution transformer is greater than or equal to the area of ​​the clamp of the grounding electrode clamp of the ground resistance tester.

8. The 10 kV power distribution system transmission overvoltage test method according to claim 1, characterized in that: In a 10 kV system, U N The value is 6000V.

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