Ground fault active full compensation device using frequency conversion signal line selection

Abstract

The utility model discloses a ground fault active full compensation device using frequency conversion signal line selection, which comprises a grounding transformer, a controller and an active power compensator, the output end of the active power compensator is connected with an injection transformer, one end of the primary side of the injection transformer is grounded, and the other end of the primary side of the injection transformer is grounded. The other end of the primary side is connected with a grounding transformer primary side through a high-voltage switch; the active power compensator is also connected with a secondary side neutral point of the grounding transformer; the controlled end of the active power compensator is connected with the output end of a controller, the input end of the controller is connected with a synchronization unit, and the input end of the synchronization unit is connected with a voltage transformer arranged on a system bus; and the input end of the controller is also respectively connected with the signal ends of the current transformers arranged on the lines. According to the utility model, the active power compensator is adopted to output voltage signals with different frequencies to carry out disturbance line selection, the proportion of an active current component to a reactive current component is improved through harmonic frequency adjustment, and the line selection accuracy is improved.

Description

Technical Field

[0001] The utility model relates to the technical field of single-phase grounding protection of distribution networks, in particular to an active full compensation device for grounding faults. Background Art

[0002] An active full ground fault compensation device typically consists of a power transformer, a step-up transformer, a vacuum contactor, an active power compensator (APC), and a controller, and requires an arc suppression coil for use. In the event of a single-phase ground fault, the controller adjusts the APC's output voltage, compensating the voltage and current at the fault point to near zero. This completely eliminates arcing during a single-phase ground fault and allows for precise line selection using a disturbance method, making it the optimal solution for resolving single-phase ground faults.

[0003] When using the transient method to select lines, the zero-sequence current of all lines when the fault occurs is recorded and then the waveform is analyzed. However, since the recording process is easily disturbed and the fault cannot be reproduced, there is a certain degree of randomness in line selection.

[0004] When only arc suppression coil compensation is used (no full compensation device is used), the main differences between the fault line and the non-fault line are: ① The zero-sequence current flowing through the fault line is the system residual current, while the zero-sequence current of other lines is their own capacitive current to ground. Since the residual current is uncertain, the capacitive current of a certain line may be equal to the system residual current, so this cannot be used as a basis for line judgment; ② The fault line has an additional grounding resistance compared to other lines, so line selection can be based on this resistance.

[0005] In a system equipped with an active full-compensation device for ground faults, the full-compensation controller can easily adjust the output voltage, causing disturbances to the system to select the faulty grounded line. During the line selection process, some patents distinguish between faulty and non-faulty lines by comparing the change in zero-sequence current of the line in the fully compensated state and other states, or by comparing the phase of the zero-sequence current. Both methods introduce reactive current components with large amplitudes, resulting in a small proportion of the current change in the collected current and a less obvious characteristic. In addition, judging through only a single comparison increases randomness and also affects the accuracy of line selection. Utility Model Content

[0006] The technical problem to be solved by the utility model is to provide an active full compensation device for ground faults using variable frequency signals for line selection, which improves the accuracy of line selection by outputting voltage signals of different frequencies for disturbance line selection.

[0007] In order to solve the above technical problems, the technical solutions adopted by the present invention are as follows.

[0008] An active full-compensation device for ground faults using variable frequency signals for line selection comprises a grounding transformer, a controller, and an active power compensator. The output end of the active power compensator is connected to an injection transformer, one end of the primary side of the injection transformer is grounded, and the other end of the primary side is connected to the primary side of the grounding transformer via a high-voltage switch. The active power compensator is also connected to the neutral point of the secondary side of the grounding transformer. The controlled end of the active power compensator is connected to the output end of the controller, the input end of the controller is connected to a synchronization unit that generates a square wave synchronization signal, and the input end of the synchronization unit is connected to a voltage transformer provided on a system bus. The input end of the controller is also connected to the signal ends of current transformers provided on each line. The controller controls the active power compensator to output a disturbance signal superimposed with harmonics of different frequencies to the system based on the square wave synchronization signal sent by the synchronization unit, and then selects the line using the harmonic currents of each frequency collected by the current transformer.

[0009] The above-mentioned active full compensation device for ground faults using variable frequency signal line selection, the synchronization unit includes a step-down transformer, a voltage divider circuit and a comparison circuit connected in series, the input end of the step-down transformer is connected to the output end of the voltage transformer, the output voltage of the step-down transformer is divided by the voltage divider circuit and enters the comparison circuit, and the comparison circuit outputs a square wave synchronization signal and sends it to the input end of the controller.

[0010] In the above-mentioned active full compensation device for ground faults using variable frequency signal line selection, the main chip of the comparison circuit is the comparator LM393.

[0011] Due to the adoption of the above technical solution, the technical progress achieved by the present invention is as follows.

[0012] The utility model adopts an active power compensator to output voltage signals of different frequencies for disturbance line selection. By adjusting the harmonic frequency, the ratio of active current component to reactive current component is improved, the characteristic quantity is more obvious, and the accuracy of line selection is improved. In addition, multiple injection calculations with different frequencies can be performed, which increases the number of samples, eliminates accidental factors, and further ensures the accuracy of line selection. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 This is the system wiring diagram of the utility model;

[0014] Figure 2 This is the electrical schematic diagram of the synchronization unit;

[0015] Figure 3 This is the equivalent circuit diagram of the zero-sequence circuit when the full compensation device is compensated after the system grounding occurs.

[0016] Figure 4 This is a flow chart of line selection for the utility model.

[0017] Figure 1 In Chinese: JDB, grounding transformer; APC, active power compensator; KM, high-voltage switch; KZQ, controller; TBDY, synchronization unit; ZRB, injection transformer; PT, voltage transformer; CT1-CTn, current transformers 1-n; L1-Ln, line equivalent impedance; Rd, grounding resistance. DETAILED DESCRIPTION

[0018] The present invention will be further described in detail below with reference to the accompanying drawings and specific implementation methods.

[0019] An active full-compensation device for ground faults using variable frequency signal line selection includes a grounding transformer JDB, a controller KZQ, an active power compensator APC, an injection transformer ZRB, and a synchronization unit TBDY. The device is used in a system with n lines. A voltage transformer PT is connected to the system busbar to measure the system voltage. Each line is equipped with a current transformer CT1-CTn to measure the zero-sequence current of each line. The system wiring of the aforementioned electrical equipment is as follows: Figure 1 As shown, the details are as follows.

[0020] The grounding transformer JDB is connected to the system bus, and the active power compensator APC is connected to the controller KZQ and the neutral point of the secondary side of the grounding transformer JDB respectively; the output end of the active power compensator APC is connected to the secondary side of the injection transformer ZRB, one end of the primary side of the injection transformer ZRB is grounded, and the other end of the primary side is connected to the primary side of the grounding transformer JDB through the high-voltage switch KM.

[0021] The input end of the controller is connected to the synchronization unit TBDY that generates a square wave synchronization signal, and the input end of the synchronization unit TBDY is connected to the signal end of the voltage transformer PT; the synchronization unit converts the system three-phase voltage sinusoidal signal collected by the voltage transformer into a square wave synchronization signal, which facilitates the controller to calculate the voltage frequency. After the square wave signal enters the controller, the controller calculates the period and frequency of the voltage signal, and divides or multiplies the frequency according to this frequency, and then controls the active power compensator APC to generate voltage signals of different frequencies and output them to the injection transformer ZRB.

[0022] The input end of the controller is also connected to the signal end of each current transformer respectively.

[0023] In the present utility model, the electrical schematic diagram of the synchronization unit TBDY is as follows: Figure 2As shown, it includes a step-down transformer PT1, a voltage divider circuit and a comparison circuit connected in series. The input end of the step-down transformer PT1 is connected to the output end of the voltage transformer PT. The output voltage of the step-down transformer is divided by the resistors R1 and R2 of the voltage divider circuit and enters the comparator LM393 of the comparison circuit. A voltage signal greater than 0 is output as a high level, and a voltage signal less than 0 is output as a low level, thereby converting the sinusoidal wave signal into a square wave signal and sending it to the input end of the controller.

[0024] The controller selects lines by taking advantage of the different ground impedances between normal lines and grounded lines and the different voltage impedance changes at different frequencies. It can perform multiple frequency injection calculations, increase the ratio of active current components to reactive current components, and improve line selection accuracy.

[0025] The utility model is applied in the system. When a single-phase grounding fault occurs in the system, its equivalent circuit is as shown in the figure. Figure 3 As shown, the controller performs phase judgment and controls the active power compensator APC to output a compensation signal to the grounding transformer JDB to compensate for the system's active current, reactive current and harmonic current, and the system enters a fully compensated state.

[0026] In the full compensation state, the controller controls the active power compensator to output the fundamental voltage and output the harmonic voltage of different frequencies, and then collects the harmonic current of the frequency of all lines to calculate the active component I of each line. R and the ratio of reactive components The line with the largest proportion is the ground line.

[0027] The specific harmonic injection line judgment process of the utility model is as follows Figure 4 The detailed method is as follows.

[0028] (1) Calculate the ratio of each line impedance and capacitive reactance in the first frequency conversion state

[0029] The controller controls the active power compensator to output the fundamental voltage and superimpose the 1 / 2 harmonic voltage to the injection transformer, and then collects the 1 / 2 harmonic current of all lines through the current transformer of each line, and extracts the active component I R and reactive component I C ,

[0030] Calculate the active power component I of each line R and reactive component I C Proportion (Under industrial frequency conditions, the ratio of the active current component to the reactive current component of the non-grounded line is roughly equal, about 2% to 3%).

[0031] The grounding line has the largest impedance to capacitive reactance ratio due to the presence of grounding resistance. Since the harmonic voltage frequency is adjusted to 1 / 2 of the original frequency, the ratio of active current component to reactive current component is also increased by 2 times.

[0032] Repeat the harmonic injection and calculation three times. If the line with the highest proportion is greater than or equal to 2, then this line is the grounded line. If the lines with the highest proportion in the three calculations are all different lines, perform the second frequency conversion.

[0033] (2) Calculate the ratio of impedance and capacitive reactance of each line in the second frequency conversion state

[0034] The controller controls the active power compensator to output the fundamental voltage and superimpose the 1 / 5 harmonic voltage to the injection transformer, and then collects the 1 / 5 harmonic current of all lines through the current transformer of each line, and extracts the active component I R and reactive component I C ,

[0035] Calculate the active power component I of each line R and reactive component I C Proportion The grounding line has the largest impedance to capacitive reactance ratio due to the presence of grounding resistance. Since the harmonic voltage frequency is adjusted to 1 / 5 of the original frequency, the ratio of active current component to reactive current component also increases by 5 times.

[0036] Repeat the harmonic injection and calculation three times. If the line with the highest proportion is greater than or equal to 2, then this line is the grounded line. If the lines with the highest proportion in all three calculations are different lines, line selection fails.

[0037] In this utility model, the frequency, number of harmonic injections, and number of judgments can all be modified to other values ​​based on actual conditions. This utility model utilizes the adjustable voltage frequency of the active full compensation device to enable multiple harmonic injections and calculations, increasing the ratio of active to reactive current components. Multiple injections and calculations can also be performed, increasing the number of samples, eliminating some accidental factors, and effectively improving line selection accuracy.

[0038] The above embodiments are only preferred implementation methods of the present invention. It should be pointed out that ordinary technicians in this technical field can make several improvements and modifications without departing from the technical principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. An active full compensation device for ground faults using variable frequency signal line selection, comprising a grounding transformer (JDB), a controller (KZQ) and an active power compensator (APC), characterized in that: The output end of the active power compensator (APC) is connected to an injection transformer (ZRB), one end of the primary side of the injection transformer (ZRB) is grounded, and the other end of the primary side is connected to the primary side of the grounding transformer (JDB) via a high-voltage switch (KM); the active power compensator (APC) is also connected to the neutral point of the secondary side of the grounding transformer (JDB); the controlled end of the active power compensator (APC) is connected to the output end of the controller (KZQ), the input end of the controller is connected to a synchronization unit (TBDY) that generates a square wave synchronization signal, and the input end of the synchronization unit (TBDY) is connected to a voltage transformer (PT) arranged on the system bus; the input end of the controller is also connected to the signal end of the current transformer arranged on each line; the controller controls the active power compensator to output a disturbance signal superimposed with harmonics of different frequencies to the system according to the square wave synchronization signal sent by the synchronization unit, and then selects the line through the harmonic currents of each frequency collected by the current transformer.

2. The active full compensation device for ground faults using variable frequency signal line selection according to claim 1, characterized in that: The synchronization unit (TBDY) includes a step-down transformer, a voltage divider circuit and a comparison circuit connected in series. The input end of the step-down transformer is connected to the output end of the voltage transformer (PT). The output voltage of the step-down transformer enters the comparison circuit after being divided by the voltage divider circuit. The comparison circuit outputs a square wave synchronization signal and sends it to the input end of the controller.

3. The active full compensation device for ground faults using variable frequency signal line selection according to claim 1, characterized in that: The main chip of the comparison circuit is the comparator LM393.

Images