Device and method for calculating current-carrying capacity of multi-machine arc suppression coil parallel power system

Abstract

The application relates to the technical field of power distribution of an electric power system, and particularly provides a current-carrying capacity calculation device and method for parallel operation of multiple arc suppression coils of an electric power system. In engineering application practice, a transformer substation containing two or more busbars is often required to operate in parallel. In view of the problem of parallel operation of multiple arc suppression coils of a neutral point resonance grounding system, the equivalent principle of Thevenin and the calculation method of the application can be used to measure the difference between the zero sequence capacitance current of the electric power system to the ground and the local compensation capacitance current. The calculation method of the application has high calculation precision of the capacitance current, is simple and easy to implement, and the devices are mutually matched, so that the multiple devices do not need to be adjusted alone, thereby effectively promoting the normal operation of the electric power system. The method can realize real-time online current-carrying capacity measurement and dynamic monitoring of the current-carrying capacity change of the electric power system.

Description

Technical Field

[0001] This invention relates to the field of power system distribution technology, specifically to a device and method for calculating the capacity current of a power system with multiple arc suppression coils in parallel. Background Technology

[0002] With the extension of power grid transmission lines and the parallel use of multiple busbars, the capacitive current of the power system is increasing, exceeding the maximum compensation range of a single arc suppression coil, and the power grid will be in an undercompensated state for a long time.

[0003] Undercompensated power grids are prone to resonance: if the grid asymmetry is large, ferroresonance may be induced during grid operation. After disconnecting some lines, the increase in the grid's capacitive reactance to ground approaches the inductive reactance, leading to linear resonance. Furthermore, as the absolute value of detuning decreases, the rise rate of the arc gap recovery voltage is faster in undercompensated grids than in overcompensated grids, which is detrimental to the extinction of grounding arcs and poses a significant safety hazard.

[0004] Therefore, there is an urgent need to install a multi-machine coordinated arc suppression coil control device in the current power system, which can automatically determine the arc suppression coil devices that need to be coordinated according to the parallel operation of the system, and promote timely and reasonable compensation of the parallel system. Summary of the Invention

[0005] The purpose of this invention is to provide a current-capacity calculation device and method for a power system with multiple arc-suppression coils in parallel. It features high calculation accuracy, simplicity and ease of use, applicability to parallel arc-suppression coils of the same type from different manufacturers, wide applicability, effective maintenance of normal power system operation, real-time online current measurement, dynamic monitoring of power system current changes, and automatic identification of arc-suppression coil devices requiring coordination based on the parallel operation of the system, thereby promoting timely and reasonable compensation of the parallel system.

[0006] To achieve the above objectives, the present invention provides the following technical solution: The present invention provides a method for calculating the capacity current of a power system with multiple arc suppression coils in parallel. The method determines whether the arc suppression coils need to be operated in parallel by checking the status of the bus tie switches in each bus tie section. When not in parallel operation, a single-machine algorithm is used. When in parallel operation, a multi-machine coordination algorithm is used to calculate the system capacity current and the differential capacitance current that the device currently in control needs to compensate. Finally, the tap is adjusted according to the differential capacitance current and the changes in system capacitance current are detected in real time.

[0007] The multi-machine coordination algorithm is based on Thevenin's theorem and uses dual-machine capacitive current calculation as a bridge. It finds the relationship between the system capacitance and the inductive reactance and resistance of the arc suppression branch through impedance transformation, and then obtains the capacitive current of the parallel power system.

[0008] Preferably, it includes the following steps:

[0009] S1. Detect the position status of the corresponding bus tie section switch. When the bus tie switch is in the open position, exit the parallel operation mode. When the bus tie switch is in the closed position, enter the parallel operation algorithm.

[0010] S2. When the arc suppression coils are running in parallel, switch to the multi-machine coordination algorithm;

[0011] S3. Determine whether there are two arc suppression coils operating in parallel. If there are two arc suppression coils operating in parallel, use the dual-machine equivalent impedance algorithm to calculate the impedance. If there are multiple arc suppression coils operating in parallel, use the multi-machine equivalent impedance formula to convert it into dual-machine impedance.

[0012] S4. Calculate the system capacitor current using the dual-machine capacitor current algorithm;

[0013] S5. The calculated total capacitive current data of the parallel system is shared with all parallel system control devices, and the capacitive current that the control device with current control rights should compensate is calculated.

[0014] S6. Adjust the gear to the required compensation level for the capacitor current. Once adjusted, enter the real-time detection mode for the total capacitive current of the system to dynamically monitor changes in the system capacitor current.

[0015] Preferably, when the initial imbalance of the system is not less than 0.5%, the change in the amplitude and phase of the neutral point current before and after the adjustment is more significant, which is more conducive to improving the calculation accuracy.

[0016] The preferred multi-machine coordination algorithm utilizes Thevenin's equivalent theorem to equate the entire parallel operation system of the arc suppression coils to a series resonant circuit combination system consisting of one power source, one resistor, one inductor, and one capacitor. The equivalent parallel resistance is:

[0017]

[0018] The equivalent capacitance is:

[0019]

[0020] Among them, R c This represents the total resistance of the circuit, and its value is R. p +R1, R p R1 represents the series resistance after the system is connected in parallel, and X represents the series resistance of the original first arc suppression coil. p I represents the capacitive reactance of the system after parallel connection. 11 I represents the neutral point current before gear adjustment. 12 X represents the neutral point current after adjustment. L1 Indicates the gear shift resistance before gear adjustment, X L2 θ represents the inductive reactance of the gear before gear adjustment, and θ represents the phase angle of the neutral point current before and after gear adjustment.

[0021] Preferably, the equivalent impedance is calculated, and a quadratic equation in one variable is established using the relationship between the equivalent resistance and the equivalent capacitive reactance:

[0022]

[0023] Where a = X p / R p .

[0024] Preferably, the established quadratic equation in one variable, according to physical meaning, has a solution where Xc cannot be 0, and the solution has a unique value:

[0025]

[0026] Preferably, when three or more arc suppression coil devices are running in parallel, the multi-machine coordination algorithm, using Thevenin's equivalent theorem, equates the parallel operation system of arc suppression coils to two arc suppression coils running in parallel, which, together with the system's zero-sequence capacitance, form a series resonant circuit with an equivalent resistance of:

[0027]

[0028] The equivalent reactance is:

[0029]

[0030] Where n≥3, by performing (n-2) iterations using the above formula, the equivalent R when the two arc-extinguishing devices are running in parallel can be obtained. pn With X pn Then, the system capacity is calculated using the dual-machine calculation formula.

[0031] The aforementioned current-capacity calculation device for a power system with multiple arc-suppression coils in parallel includes:

[0032] (1) Based on Thevenin's theorem and using dual-machine capacity current calculation as a bridge, the relationship between the system capacitance and the inductive reactance and resistance of the arc suppression branch is found through impedance transformation, and then the capacity current of the parallel power system is obtained.

[0033] (2) The parallel operation system is equipped with master and slave control devices; the master is responsible for receiving, processing and forwarding the damping resistance and current compensation data of the entire parallel operation system, as well as issuing logic instructions; other arc suppression coil control devices are set as slave 1, slave 2 and slave 3, which are responsible for the adjustment, calculation and optimization compensation of the entire arc suppression coil parallel operation system;

[0034] (3) The parallel operation system uses RS485 communication for data interaction, and adopts the host polling method to query the status of the slave and issue control commands.

[0035] (4) Real-time monitoring of changes in the capacitor current of the power system, and adjustment method using residual current control; the residual current is used as a set value to control the residual current within a reasonable range during grounding.

[0036] (5) By detecting the position of the bus tie switch, the single-machine algorithm and the multi-machine algorithm are automatically switched.

[0037] Preferably, it also includes (6) the ability to calculate the capacitive current of the same parallel-operating power system containing arc suppression coil devices from different manufacturers:

[0038] When interconnected with control devices of different types from other manufacturers or our own, this arc suppression coil device is set as the main unit. The damping resistor and the compensation data of the other n arc suppression coils are input from the set value. This device is responsible for the adjustment, calculation and optimization compensation of the entire parallel operation system of arc suppression coils.

[0039] The beneficial effects of this invention are:

[0040] (1) The current calculation device and method for a power system with multiple arc suppression coils in parallel according to the present invention have high calculation accuracy, are simple and easy to implement, and can be applied to the parallel operation of arc suppression coils of the same type from different manufacturers, effectively maintaining the normal operation of the power system; it can realize real-time online current measurement, dynamically monitor the changes in the current of the power system, and can automatically determine the arc suppression coil devices that need to be coordinated according to the parallel operation of the system, promoting timely and reasonable compensation of the parallel system.

[0041] It relies on the fixed data transmitted from the complete set of measuring CT, measuring PT and other control devices. The current calculation is accurate, does not increase investment, is easy to modify, and there is no situation where multiple devices adjust the gear independently.

[0042] (2) The current calculation device and method for multi-machine arc suppression coil parallel power system of the present invention automatically switches between single machine operation and coordinated operation mode by detecting the bus tie signal. It does not require manual operation, has a high degree of automation, and the compensation current distribution ratio depends on the structure of the arc suppression coil body. It is not affected by the fluctuation of system voltage and current or ambient temperature, and has high reliability. Attached Figure Description

[0043] Figure 1 This is a schematic diagram of the parallel operation system of multiple arc suppression units of the present invention;

[0044] Figure 2 This is the zero-sequence equivalent diagram of multiple arc-extinguishing units operating in parallel according to the present invention;

[0045] Figure 3 This is an equivalent diagram of two arc suppression coils side by side according to the present invention;

[0046] Figure 4 This is an equivalent vector diagram of the arc suppression coil before and after adjustment according to the present invention;

[0047] Figure 5 This is a flowchart of the multi-machine coordinated operation capacity calculation of the present invention;

[0048] Figure 6 This is a schematic diagram of multi-machine coordinated RS485 communication according to the present invention. Detailed Implementation

[0049] To facilitate understanding of the technical means, inventive features, and achieved effects of this invention, the technical solutions in the embodiments of this invention will be further described clearly and completely below with reference to the accompanying drawings. Obviously, the described embodiments are merely some embodiments of this invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0050] Example 1

[0051] A current-capacity calculation device for power systems with multiple arc-suppression coils in parallel, such as Figure 5 As shown, it includes:

[0052] (1) Based on Thevenin's theorem and using dual-machine capacity current calculation as a bridge, the relationship between the system capacitance and the inductive reactance and resistance of the arc suppression branch is found through impedance transformation, and then the capacity current of the parallel power system is obtained.

[0053] (2) The parallel operation system is equipped with master and slave control devices; the master is responsible for receiving, processing and forwarding the damping resistance and current compensation data of the entire parallel operation system, as well as issuing logic instructions; other arc suppression coil control devices are set as slave 1, slave 2 and slave 3, which are responsible for the adjustment, calculation and optimization compensation of the entire arc suppression coil parallel operation system;

[0054] (3) Figure 6 As shown, the parallel operation system uses RS485 communication for data interaction, and adopts a master polling method to query the slave status and issue control commands.

[0055] (4) Real-time monitoring of changes in the capacitor current of the power system, and adjustment method using residual current control; the residual current is used as a set value to control the residual current within a reasonable range during grounding.

[0056] (5) By detecting the position of the bus tie switch, the single-machine algorithm and the multi-machine algorithm are automatically switched.

[0057] (6) It can calculate the capacitive current of the same parallel-running power system containing arc suppression coil devices from different manufacturers: When interconnected with control devices of different types from other manufacturers or this manufacturer, this arc suppression coil device is set as the host, and the damping resistor and the compensation data of the other n arc suppression coils are input from the set value. This device is responsible for the adjustment, calculation and optimization compensation of the entire parallel-running arc suppression coil system.

[0058] Example 2

[0059] Methods for calculating capacitive current in power systems with multiple arc suppression coils in parallel, such as Figure 5 As shown, it includes the following steps:

[0060] S1. Detect the position status of the corresponding bus tie section switch. When the bus tie switch is in the open position, exit the parallel operation mode. When the bus tie switch is in the closed position, enter the parallel operation algorithm.

[0061] S2. When the arc suppression coils are running in parallel, switch to the multi-machine coordination algorithm;

[0062] S3. Determine whether there are two arc suppression coils operating in parallel. If there are two arc suppression coils operating in parallel, use the dual-machine equivalent impedance algorithm to calculate the impedance. If there are multiple arc suppression coils operating in parallel, use the multi-machine equivalent impedance formula to convert it into dual-machine impedance.

[0063] S4. Calculate the system capacitor current using the dual-machine capacitor current algorithm;

[0064] S5. The calculated total capacitive current data of the parallel system is shared with all parallel system control devices, and the capacitive current that the control device with current control rights should compensate is calculated.

[0065] S6. Adjust the gear to the required compensation level for the capacitor current. Once adjusted, enter the real-time detection mode for the total capacitive current of the system to dynamically monitor changes in the system capacitor current.

[0066] Example 3

[0067] In the method for calculating the capacitive current of a power system with multiple arc suppression coils in parallel, when the arc suppression coil system is running with multiple units, the neutral point voltage and neutral point current are changed by adjusting the reactance of a single arc suppression coil, thereby calculating the system capacitive current.

[0068] When multiple arc suppression coils are connected in series, to avoid mutual interference caused by isolated calculations and adjustments of multiple devices, a main unit needs to control the adjustment actions of other devices, and the capacitance current is calculated through the adjustment of the main unit. Using an equivalent circuit diagram, the multi-machine coordination circuit can ultimately be transformed into a resonant circuit consisting of an arc suppression coil, an equivalent resistance, and an equivalent capacitance connected in series. Then, by changing the reactance of the main unit's arc suppression coil, the total capacitance current to ground of the system can be solved based on the change in the electrical quantity of the main unit's neutral point.

[0069] A schematic diagram of a parallel arc suppression coil system is shown below. Figure 1 As shown, four arc suppression coils are operating in parallel. This schematic diagram can be expanded to N arc suppression coils.

[0070] The equivalent circuit diagram of the dual-machine parallel operation circuit, simplified using Thevenin's theorem, is as follows: Figure 3 The parameters of each electrical appliance are explained below:

[0071] L1: Inductive reactance of the first arc suppression coil; R1: Resistance of the first arc suppression coil; Z p : System equivalent impedance; U0: System equivalent unbalanced voltage.

[0072] After the system's zero-sequence capacitance and the impedance transformation of one of its arc suppression coils are equivalent, the electrical parameters have the following quantitative and calculation relationships:

[0073]

[0074]

[0075] The ratio of equivalent capacitive reactance to equivalent impedance is

[0076]

[0077] Change the inductive reactance of arc suppression coil No. 1 (with range adjustment control), and plot the neutral point current vector change before and after range adjustment as shown in the figure. Figure 4 The system capacitor current is calculated based on its changes. The electrical parameters are explained as follows: AB represents the voltage across the equivalent resistance of arc suppression coil 1 before adjustment; BD represents the voltage between the arc suppression coil and its equivalent capacitance before adjustment; AC represents the voltage across the equivalent resistance of arc suppression coil 1 after adjustment; CD represents the voltage between the arc suppression coil and its equivalent capacitance after adjustment; R... c I represents the total series resistance of the circuit after the circuit is equivalent. 11 I represents the neutral point current before gear adjustment. 12 X represents the neutral point current after adjustment. L1 Indicates the gear shift resistance before gear adjustment, X L2 Let θ represent the inductive reactance before gear adjustment, and let θ represent the phase angle of the neutral point current before and after gear adjustment. Based on the vector diagram, and utilizing the fact that the geometric lengths within line segment AC and line segment BD are equal, R is established. c With X P The system of equations can be solved to obtain...

[0078]

[0079]

[0080]

[0081] From the expression, we get

[0082]

[0083] Analyze and substitute the variables in the above equation to calculate, since X C If it is not 0, we get X. C As the only unknown quantity, we get

[0084]

[0085] This leads to the system capacitor current.

[0086]

[0087] Example 4

[0088] When multiple machines are operating in coordination, taking the parallel operation of four arc suppression coils as an example, the equivalent circuit diagram is as follows: Figure 2 Then, the multi-machine system is equivalent to a two-machine model, such as... Figure 3 Then calculate the system capacitance current.

[0089] (X L1 +R L1 ) / / … / / (X Li +R Li ) / / … / / (X Ln +R Ln )

[0090] Four arc suppression coils are connected in parallel. Assume the capacitor current of the first coil is calculated, and all other arc suppression coils are equivalently represented by Thevenin as a series circuit of one inductor and one resistor. Let the series resistance be... The inductive reactance of a series inductor is Then, the capacity calculation is performed according to the algorithm of running two machines in parallel.

[0091] The current-capacitance calculation steps are the same as in Example 1, and the final system impedance is obtained as follows:

[0092]

[0093] In the formula, a' is the ratio of inductive reactance to impedance after being equivalent to a dual-machine system;

[0094] Assuming the first unit calculates the system current capacity, and we need to calculate the impedance of the second, third, and fourth units connected in parallel, the circuit is equivalent to an inductor and resistor connected in series, which is then connected in parallel with another branch of an inductor and resistor connected in series. The following formula can be derived:

[0095] Z p2 = (R2 + jX2) / / (R3 + jX3)

[0096] The equivalent impedance can be obtained

[0097]

[0098]

[0099] The obtained R p2 and X p2 As new R2 and X2, iterative calculations are performed with another parallel branch (R4+jX4) to obtain the required equivalent R. p3 and X p3 Then, using the dual-machine calculation formula, the system capacity can be obtained.

[0100] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

[0101] Other embodiments of this disclosure will readily occur to those skilled in the art upon consideration of the specification and practice of the disclosure herein. This application is intended to cover any variations, uses, or adaptations of this disclosure that follow the general principles of this disclosure and include common knowledge or customary techniques in the art not disclosed herein. The specification and examples are to be considered exemplary only, and the true scope of this disclosure is indicated by the following claims.

Claims

1. A method for calculating the capacitive current in a power system with multiple arc suppression coils in parallel, characterized in that, The status of the bus tie switch in each bus tie section determines whether the arc suppression coil needs to be operated in parallel. When not in parallel operation, a single-machine algorithm is used. When in parallel operation, a multi-machine coordination algorithm is used to calculate the system current capacity and the differential capacitor current that the device currently in control needs to compensate. Finally, the gear is adjusted according to the differential capacitor current and the changes in the system capacitor current are detected in real time. The multi-machine coordination algorithm is based on Thevenin's theorem and uses dual-machine capacity current calculation as a bridge. It finds the relationship between the system capacitance and the inductive reactance and resistance of the arc suppression branch through impedance transformation, and then obtains the capacity current of the parallel power system. Includes the following steps: S1. Detect the position status of the corresponding bus tie section switch. When the bus tie switch is in the open position, exit the parallel operation mode. When the bus tie switch is in the closed position, enter the parallel operation algorithm. S2. When the arc suppression coils are running in parallel, switch to the multi-machine coordination algorithm; S3. Determine whether there are two arc suppression coils operating in parallel. If there are two arc suppression coils operating in parallel, use the dual-machine equivalent impedance algorithm to calculate the impedance. If there are multiple arc suppression coils operating in parallel, use the multi-machine equivalent impedance formula to convert it into dual-machine impedance. S4. Calculate the system capacitor current using the dual-machine capacitor current algorithm; S5. The calculated total capacitive current data of the parallel system is shared with all parallel system control devices, and the capacitive current that the control device with current control rights should compensate is calculated. S6. Adjust the gear according to the required capacitor current compensation. After adjustment, enter the real-time detection mode of the total capacitive current of the system to dynamically monitor the changes in the system capacitor current. When three or more arc suppression coil devices are running in parallel, the multi-machine coordination algorithm, using Thevenin's equivalent theorem, equates the parallel operation system of arc suppression coils to two arc suppression coils running in parallel, and then forms a series resonant circuit with the system's zero-sequence capacitance. Its equivalent resistance is: ； The equivalent reactance is: ; Where n≥3, by performing (n-2) iterations using the above formula, the equivalent operation of two arc-extinguishing devices running in parallel can be obtained. and Then, the system capacity is calculated using the dual-machine calculation formula.

2. The method for calculating the capacitive current of a power system with multiple arc-suppression coils in parallel, as described in claim 1, is characterized in that... When the initial imbalance of the system is not less than 0.5%, the changes in the amplitude and phase of the neutral point current before and after the adjustment are more significant, which is more conducive to improving the calculation accuracy.

3. The method for calculating the capacitive current of a power system with multiple arc-suppression coils in parallel, as described in claim 1, is characterized in that... The multi-machine coordination algorithm utilizes Thevenin's equivalent theorem to equate the entire parallel operation system of the arc suppression coils to a series resonant circuit combination system consisting of one power source, one resistor, one inductor, and one capacitor. The equivalent parallel resistance is: ； The equivalent capacitance is: ； in, This represents the total resistance of the circuit, and its value is... , This represents the series resistance after the system is connected in parallel. This represents the series resistance of the original first arc suppression coil. This represents the capacitive reactance after the system is connected in parallel. This indicates the neutral point current before gear adjustment. X represents the neutral point current after adjustment. 11 Indicates the gear shift resistance before gear adjustment, X 12 θ represents the inductive reactance of the gear after gear adjustment, and θ represents the phase angle of the neutral point current before and after gear adjustment.

4. The method for calculating the capacitive current of a power system with multiple arc-suppression coils in parallel, as described in claim 3, is characterized in that... Find the equivalent impedance, and use the relationship between the equivalent resistance and the equivalent capacitive reactance to establish a quadratic equation in one variable: ； in, .

5. The method for calculating the capacitive current of a power system with multiple arc-suppression coils in parallel, as described in claim 4, is characterized in that... The established quadratic equation in one variable, according to physical meaning, has a solution where Xc cannot be 0, and the solution has a unique value: 。 6. A current-capacity calculation device for a power system with multiple arc-suppression coils in parallel, characterized in that, The method for calculating the capacitive current of a power system with multiple arc-suppression coils in parallel, as described in any one of claims 1-5, includes: (1) Based on Thevenin's theorem and using dual-machine capacitive current calculation as a bridge, the relationship between the system capacitance and the inductive reactance and resistance of the arc suppression branch is found through impedance transformation, and then the capacitive current of the parallel power system is obtained. (2) The parallel operation system is equipped with master and slave control devices; the master is responsible for receiving, processing and forwarding the damping resistance and current compensation data of the entire parallel operation system, and issuing logic instructions; other arc suppression coil control devices are set as slave 1, slave 2 and slave 3, which are responsible for the adjustment, calculation and optimization compensation of the entire arc suppression coil parallel operation system; (3) The parallel operation system uses RS485 communication for data interaction, and adopts the host polling method to query the status of the slave and issue control commands; (4) Monitor the changes in the capacitor current of the power system in real time, and adjust it by residual current control; use the residual current as a set value to control the residual current within a reasonable range during grounding. (5) By detecting the position of the bus tie switch, the single-machine algorithm and the multi-machine algorithm are automatically switched.

7. The current-capacity calculation device for a power system with multiple arc-suppression coils in parallel according to claim 6, characterized in that, It also includes (6) the ability to calculate the capacitive current of the same parallel-operating power system containing arc suppression coil devices from different manufacturers: When interconnected with control devices of different types from other manufacturers or our own, this arc suppression coil device is set as the main unit. The damping resistor and the compensation data of the other n arc suppression coils are input from the set value. This device is responsible for the adjustment, calculation and optimization compensation of the entire parallel operation system of arc suppression coils.

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