A method for determining no-load bus current and a bus connection and disconnection control method using the same

Abstract

This invention discloses a method for determining the unloaded bus current and a busbar switching control method using the same method. The method for determining the unloaded bus current includes the following steps: A1. Installing current sensors on the porcelain bushings of the circuit breakers on the unloaded busbar side of each phase; A2. Connecting each current sensor to a multi-channel waveform recorder to obtain the maximum capacitive current of each phase unloaded busbar through the multi-channel waveform recorder; A3. Obtaining the maximum capacitive current value of the unloaded busbar. The busbar switching control method includes selecting the threshold value for operating the unloaded busbar with the disconnecting switch according to the rated voltage level of the busbar; and selecting the disconnecting switch or the circuit breaker on the unloaded busbar side to control the switching operation of the corresponding unloaded busbar according to the maximum capacitive current and the threshold value. This invention can flexibly adjust the threshold values ​​for operating the unloaded busbar with the current sensors and disconnecting switches according to the rated voltage level of the busbar, which has good engineering adaptability, is more in line with the actual situation on the engineering site, has good performance, and is easy to promote and use.

Description

Technical Field

[0001] This invention belongs to the field of no-load bus current detection and operation technology, specifically relating to a method for determining no-load bus current and a bus switching control method using the same method. Background Technology

[0002] To improve power supply reliability and save investment, large power plants, high-voltage substations, and power distribution facilities with six or more incoming and outgoing circuits mostly adopt the 3 / 2 circuit breaker connection method. In normal power system switching operations and accident handling, the circuit breaker in the 3 / 2 circuit breaker connection method is the main component used to disconnect normal loads and eliminate short-circuit faults. The circuit breaker can normally disconnect and close power equipment such as unloaded transformers, lines and unloaded busbars, and can ensure that the occurrence of conditions that are not conducive to the stable operation of the power system, such as flashover between breaks, breakdown and overvoltage exceeding the specified limit, is avoided, thus ensuring the safety of operation.

[0003] While circuit breakers are safe and reliable to operate, in actual dispatching and operation, especially during the handling of sudden system accidents, sometimes circuit breakers malfunction due to their own inherent problems and become inoperable. It is necessary to isolate the faulty circuit breaker from the system. During this process, equipment on the busbar side of the circuit breaker should be switched to hot standby, and equipment (lines, main transformers) on the other side of the circuit breaker should be shut down. These procedures not only take a long time but also cause unnecessary unplanned power outages. The affected systems or sections may also need to reduce power, posing certain operational risks and delaying emergency response time. To overcome the shortcomings of relying solely on circuit breakers to operate power equipment, disconnecting switches can be used to switch open and close unloaded busbars, preventing forced shutdowns of operating equipment due to circuit breaker malfunctions. This plays a crucial role in dispatching and handling system accidents and emergencies. However, when using disconnecting switches to open and close busbars, if the busbar's capacitive current is large, the opening and closing process can introduce ultra-fast transient overvoltages and overcurrents, potentially causing equipment damage or even short-circuit faults, leading to system accidents. Therefore, relevant substation operation and maintenance management standards specify the maximum capacitive current that disconnecting switches can open and close on unloaded busbars under different voltage levels. However, the magnitude of the busbar capacitive current is much smaller than the rated current, and the current transformer in the circuit breaker connected to it cannot accurately measure it. Furthermore, the busbar capacitive current is affected by various factors such as busbar-to-ground capacitance, phase-to-phase capacitance, and transformers connected to the line. Usually, the main capacitance is measured using a dielectric loss tester to establish a simplified circuit model, and then the capacitive current is calculated. This method is complex and differs from actual operating conditions. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to address the shortcomings of the prior art by providing a method for determining the unloaded bus current and a bus switching control method using the same method. The method has a simple structure, reasonable design, and is easy to implement. The threshold values ​​for operating the unloaded bus can be flexibly adjusted based on the rated voltage level of the bus. It can also be corrected through actual experiments, has good engineering adaptability, is more in line with the actual situation on the engineering site, has good performance, and is easy to promote and use.

[0005] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is: a method for determining the unloaded bus current, comprising the following steps:

[0006] Step A1: Install current sensors on the porcelain bushings of the circuit breakers on the unloaded busbar side of each phase;

[0007] Step A2: Connect each current sensor to the multi-channel recorder and obtain the maximum capacitive current of each phase unloaded bus through the multi-channel recorder.

[0008] Step A3: Obtain the maximum capacitive current value of the unloaded busbar.

[0009] The above-mentioned method for determining the unloaded bus current, specifically the process of obtaining the maximum capacitive current value of the unloaded bus in step A3 includes:

[0010] Step A301: Ground each phase unloaded busbar to discharge;

[0011] Step A302: Disconnect the grounding switch of each phase's unloaded busbar and record the unloaded busbar current i of each phase during the operation. 0px x = A, B, C;

[0012] Step A303: Connect and disconnect the current transformers on each phase busbar respectively, and record the no-load busbar current i' of each phase during the operation. 0px x = A, B, C;

[0013] Step A304, from i 0px and i' 0px The maximum value is selected from the samples to determine the maximum value I of the unloaded bus capacitive current. 0px_max .

[0014] This invention also discloses a busbar switching control method, which applies the above-mentioned method for determining no-load busbar current. The busbar switching control method includes the following steps:

[0015] Step B1: Select the threshold I for operating the unloaded busbar with the disconnecting switch based on the rated voltage level of the busbar. 0px_th ;

[0016] Step B2, when I 0px_max <I0px_th When necessary, disconnect switches are used to control the opening and closing operations of the corresponding unloaded busbars;

[0017] Step B3, when I 0px_max ≥I 0px_th When this is the case, the circuit breaker on the unloaded busbar side is used to control the opening and closing operations of the corresponding unloaded busbar.

[0018] Compared with the prior art, the present invention has the following advantages:

[0019] 1. The method of the present invention has a simple structure, reasonable design, and is easy to implement.

[0020] 2. This invention utilizes an additional current detection device to quickly and intuitively obtain the maximum possible value of the capacitive current of the current unloaded bus, avoiding the need for circuit modeling of the load and calculation and analysis of the capacitive current.

[0021] 3. This invention combines the advantages of operating an unloaded busbar with a disconnector switch and operating an unloaded busbar with a circuit breaker. Within the capacitive current threshold of the unloaded busbar, the disconnector switch is selected to operate the unloaded busbar, simplifying the complexity of busbar operation while ensuring reliability; if the capacitive current of the unloaded busbar is large, a circuit breaker is selected for unloaded busbar operation to ensure the safety of the power supply line.

[0022] 4. Based on the rated voltage level of the busbar, the threshold values ​​of the current sensor and disconnector for operating the unloaded busbar can be flexibly adjusted, and can be corrected through actual tests, thus having good engineering adaptability.

[0023] 5. This invention fully considers the influence of the measuring equipment and working status on the unloaded busbar current, which is more in line with the actual situation on the engineering site.

[0024] 6. This invention can be effectively applied to the determination of no-load bus current and the control of bus switching, with good results and easy to promote and use.

[0025] In summary, the method of the present invention has a simple structure, reasonable design, and convenient implementation. The threshold values ​​for the operation of the current sensor and disconnecting switch on the unloaded bus can be flexibly adjusted according to the rated voltage level of the bus. It can also be corrected through actual tests, has good engineering adaptability, is more in line with the actual situation on the engineering site, has good performance, and is easy to promote and use.

[0026] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0027] Figure 1 This is a flowchart of the method for determining the unloaded bus current according to the present invention.

[0028] Figure 2 This is a schematic diagram illustrating a specific implementation of the present invention.

[0029] Explanation of reference numerals in the attached figures:

[0030] 1—Circuit breaker near the busbar; 2—Connection terminal of the circuit breaker near the busbar;

[0031] 3—Busket of circuit breaker near the busbar; 4—Actuator near the busbar;

[0032] 5—Unloaded bus current sensor; 6—Near-bus side disconnect switch;

[0033] 7—Unloaded busbar; 8—Multi-channel recorder. Detailed Implementation

[0034] like Figure 1 As shown, the method for determining the unloaded bus current of the present invention includes the following steps:

[0035] Step A1: Install current sensors on the porcelain bushings of the circuit breakers on the unloaded busbar side of each phase;

[0036] Step A2: Connect each current sensor to the multi-channel recorder and obtain the maximum capacitive current of each phase unloaded bus through the multi-channel recorder.

[0037] Step A3: Obtain the maximum capacitive current value of the unloaded busbar.

[0038] Step A301: Ground each phase unloaded busbar to discharge;

[0039] Step A302: Disconnect the grounding switch of each phase's unloaded busbar and record the unloaded busbar current i of each phase during the operation. 0px x = A, B, C;

[0040] Step A303: Connect and disconnect the current transformers on each phase busbar respectively, and record the no-load busbar current i' of each phase during the operation. 0px x = A, B, C;

[0041] Step A304, from i 0px and i' 0px The maximum value is selected from the samples to determine the maximum value I of the unloaded bus capacitive current. 0px_max .

[0042] The busbar switching control method of the present invention includes the following steps:

[0043] Step B1: Select the threshold I for operating the unloaded busbar with the disconnecting switch based on the rated voltage level of the busbar. 0px_th ;

[0044] Step B2, when I 0px_max <I 0px_thWhen necessary, disconnect switches are used to control the opening and closing operations of the corresponding unloaded busbars;

[0045] Step B3, when I 0px_max ≥I 0px_th When this is the case, the circuit breaker on the unloaded busbar side is used to control the opening and closing operations of the corresponding unloaded busbar.

[0046] like Figure 2 As shown, to demonstrate the feasibility of the invention, for the A-phase no-load busbar closing operation process of the 750kV system, a no-load busbar current detection method is adopted, and a no-load busbar current sensor 5 is installed on the bushing 3 of the circuit breaker near the busbar side; wherein the circuit breaker 1 near the busbar side adopts an SF6 tank-type circuit breaker LW55-800, the disconnecting switch 6 near the busbar side adopts a high-voltage disconnecting switch GW-800DW, the no-load busbar current sensor 5 adopts a flexible Rogowski coil ETCR300FA, and the multi-channel recorder 8 adopts an oscilloscope recorder DL950.

[0047] In practice, first install the ETCR300FA on terminal 2 of the circuit breaker near the busbar of the LW55-800, and connect the output of the ETCR300FA to one channel of the DL950; then disconnect the measuring equipment on the unloaded busbar 7 and short-circuit the unloaded busbar 7 to ground; start the waveform recording function of the DL950, disconnect the grounding of the unloaded busbar 7, and record the capacitive current i of the unloaded busbar 7. 0pA After the no-load bus current reaches a steady state, close the measuring device on the no-load bus 7, and the DL950 will record the no-load bus current value i' of the device. 0pA After the current waveform returns to a steady state, stop recording; then, check the recording data of one channel of the DL950, from i 0pA and i' 0pA The maximum value of the current waveforms at both ends is selected as the maximum value I of the unloaded bus capacitive current. 0px_max For a rated voltage of 750kV, a threshold voltage of 2A is selected. When I 0px_max When the voltage is <2A, the no-load bus voltage is operated by using the disconnecting switch GW-800DW to switch on and off the no-load bus; when I 0px_max When the voltage is ≥2A, the no-load bus voltage is operated by using circuit breaker LW55-800 to switch the no-load bus on and off.

[0048] Through the above process, the capacitive current of the unloaded busbar can be quickly obtained under actual operating conditions, simplifying the existing process for determining the capacitive current of the unloaded busbar. Simultaneously, determining the switching operation mode of the unloaded busbar based on the measurement results and the rated voltage level of the busbar balances operational safety and convenience compared to existing unloaded busbar operation methods.

[0049] The above description is merely a preferred embodiment of the present invention and does not constitute any limitation on the present invention. Any simple modifications, alterations, or equivalent structural changes made to the above embodiments based on the technical essence of the present invention shall still fall within the protection scope of the present invention.

Claims

1. A method for determining the unloaded bus current, characterized in that, Includes the following steps: Step A1: Install current sensors on the porcelain bushings of the circuit breakers on the unloaded busbar side of each phase; Step A2: Connect each of the current sensors to the multi-channel recorder, and obtain the capacitive current of each phase unloaded bus through the multi-channel recorder; Step A3: Obtain the maximum capacitive current value of the unloaded busbar; The specific process for obtaining the maximum capacitive current value of the unloaded busbar in step A3 includes: Step A301: Ground each phase unloaded busbar to discharge; Step A 302, open the phase no-load bus grounding switches respectively, and record the phase no-load bus current i during the operation 0px x = A, B, C; Step A303: Connect and disconnect the current transformers on each phase busbar respectively, and record the no-load busbar current i' of each phase during the operation. 0px x = A, B, C; Step A304, from i 0px and i' 0px The maximum value is selected from the samples to determine the maximum value I of the unloaded bus capacitive current. 0px_max .

2. A busbar switching control method, characterized in that, The method for determining the no-load bus current according to claim 1, wherein the bus switching control method includes the following steps: Step B1: Select the threshold I for operating the unloaded busbar with the disconnecting switch based on the rated voltage level of the busbar. 0px_th ; Step B2, when I 0px_max <I 0px_th When necessary, disconnect switches are used to control the opening and closing operations of the corresponding unloaded busbars; Step B3, when I 0px_max ≥I 0px_th When this is the case, the circuit breaker on the unloaded busbar side is used to control the opening and closing operations of the corresponding unloaded busbar.

Images