Overvoltage protection and voltage and current sampling device applied to 10kV system

Abstract

The utility model relates to an overvoltage protection and voltage and current sampling device applied to a 10kV system, which is structurally characterized in that one end of a voltage type non-linear resistance valve plate is connected to a reserved circuit breaker of the 10kV system through a busbar or a cable, and the other end of the voltage type non-linear resistance valve plate is in short-circuit grounding; the other end of the circuit breaker is directly connected to a 10kV system bus; the 10kV voltage transformer samples three-phase secondary voltage and open delta voltage, and the secondary side of the 10kV voltage transformer is connected to the fault recorder; the 10kV current transformer is sleeved at the grounding part of the voltage type non-linear resistor valve plate; the primary side of the 5A current transformer is sleeved on the secondary side of the 10kA current transformer, and the secondary side of the 5A current transformer is connected into the logarithmic current sampling circuit; and the output end of the logarithmic current sampling circuit is connected with the fault recorder. According to the utility model, the problem of damage of system power frequency overvoltage to electrical equipment is solved; and meanwhile, a voltage and current sampling function is realized.

Description

Technical Field

[0001] The utility model belongs to the field of overvoltage detection and protection, and specifically relates to a device for suppressing overvoltage and sampling voltage and current in a 10kV system through a nonlinear resistor valve sheet. Background Art

[0002] For a long time, the main technical measures for power frequency overvoltage protection have been limited to installing various types of lightning arresters or combined overvoltage protectors, which have high starting voltage action values ​​and cannot limit the internal power frequency overvoltage. Since the arc grounding overvoltage lasts for a long time, the energy can easily exceed the arrester's tolerance, causing the arrester to explode; if ferromagnetic resonance occurs, it will cause the voltage transformer to saturate, and when the primary winding has an overcurrent, it may cause the PT to explode or the PT high-voltage fuse to blow.

[0003] Lightning arresters, combined overvoltage protectors, arc suppression coils, active intervention arc suppression devices based on various principles, and PT primary and secondary harmonic eliminators, etc., cannot completely and effectively solve the hazards of system power frequency overvoltage to electrical equipment because they cannot match the protection characteristics of system operating electrical equipment well. Utility Model Content

[0004] In view of the problems existing in the above-mentioned prior art, the utility model provides an overvoltage protection and voltage and current sampling device for 10kV system, which solves the problem that the system power frequency overvoltage harms the electrical equipment; at the same time, the device has both voltage and current sampling functions.

[0005] In order to realize the above functions, the utility model adopts the following technical solutions:

[0006] 10kV system overvoltage protection and voltage and current sampling device, including voltage-type nonlinear resistor valve, fault recorder, 10kV voltage transformer, 10kA current transformer, 5A current transformer and logarithmic current sampling circuit;

[0007] The voltage-type nonlinear resistor valve plate, 10kA current transformer, 5A current transformer and logarithmic current sampling circuit are three independent structures, which are applied to the A, B and C three-phase 10kV system;

[0008] One end of the three voltage-type nonlinear resistor valve plates is connected to the reserved circuit breaker of the 10kV system through a busbar or a cable, and the other end thereof is short-circuited and grounded; the other end of the circuit breaker is directly connected to the 10kV system busbar;

[0009] The 10kV voltage transformer samples the secondary voltage of the three phases A, B, and C and the open triangle voltage. The secondary side of the 10kV voltage transformer leads out the three phases A, B, and C and the open triangle voltage, and directly connects to the idle four-channel PT of the fault recorder to monitor the system voltage.

[0010] Three 10kV current transformers are connected to the grounding points of three groups of voltage-type nonlinear resistor valve plates to detect the operating current and fault current of the voltage-type nonlinear resistor valve plates;

[0011] The primary sides of three 5A current transformers are respectively connected to the secondary sides of three groups of 10kA current transformers, and the secondary sides of the 5A current transformers are connected to the logarithmic current sampling circuit;

[0012] The output end of the logarithmic current sampling circuit is connected to a fault recorder.

[0013] The three voltage-type nonlinear valve plates include a first nonlinear resistor element R1, a second nonlinear resistor element R2 and a third nonlinear resistor element R3; the second nonlinear resistor element R2 is connected in parallel with the third nonlinear resistor element R3, one end of the first nonlinear resistor element R1 is connected to the bus, and the other end thereof is connected to a middle lead-out terminal on one side of the second nonlinear resistor element R2 and the third nonlinear resistor element R3 connected in parallel, and the other side lead-out terminal of the second nonlinear resistor element R2 and the third nonlinear resistor element R3 connected in parallel is grounded.

[0014] The first nonlinear resistance element R1 is a PTC thermistor, the second nonlinear resistance element R2 is a low-field strength ZnO valve plate, and the third nonlinear resistance element R3 is a high-energy SiC valve plate.

[0015] The current sampling circuit of the fault recorder is logarithmic amplification.

[0016] The secondary side signal of the 10kV voltage transformer is directly connected to the voltage sampling channel of the fault recorder to realize 0V~180V voltage signal sampling.

[0017] The 10kA current transformer has an insulation level of 10kV and a transformation ratio of 2000:1, and is placed where the second nonlinear resistor element R2 and the third nonlinear resistor element R3 are connected in parallel to the ground.

[0018] The transformation ratio of the 5A current transformer is 1000:1.

[0019] The output end of the logarithmic current sampling circuit is connected to the AD conversion circuit corresponding to the linear current sampling circuit of the fault recorder.

[0020] The logarithmic current sampling circuit is implemented based on the logarithmic relationship between the forward conduction current and the reverse saturation current of the PN junction. The PN junction is the most basic device structure of the semiconductor and has the following formula characteristics:

[0021]

[0022] Where I0 represents the forward current, Is Represents the reverse saturation current, V D Represents the forward voltage of the PN junction, V T represents the thermal voltage, and its value is about 26mV.

[0023] The logarithmic current sampling circuit is implemented by using a triode with an NPN structure and a thermistor to offset the change of thermal voltage, thereby achieving temperature drift compensation.

[0024] Compared with existing products, this application has the following advantages: the current-carrying capacity of the voltage-type nonlinear resistor valve is much larger than that of the lightning arrester and the conventional overvoltage protector, and there is almost no temperature rise in the long-term operation environment of 20mA.

[0025] The clamping voltage is low, with the initial clamping voltage value ≥1.72pu and the maximum clamping voltage value ≤2.20pu, which can effectively protect almost all 10kV system equipment from insulation damage caused by excessive voltage.

[0026] It has a fault recording function, which can record abnormal system voltage fluctuation faults including overvoltage.

[0027] It has the logarithmic current sampling function of the nonlinear resistance valve plate, which can cover the signal sampling of mA-level current under normal system operation conditions and kA-level current under fault conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 It is a schematic diagram of a single-phase nonlinear resistance valve.

[0029] Figure 2 This is a schematic diagram of the volt-ampere characteristics of a nonlinear resistor valve.

[0030] Figure 3 This is a schematic block diagram of the system structure of this device. DETAILED DESCRIPTION

[0031] The following will be combined with the drawings in the embodiments of the utility model to clearly and completely describe the technical solutions in the utility model. Obviously, the described embodiments are the utility model, not all embodiments. Based on the embodiments in the utility model, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the utility model.

[0032] Example

[0033] See also Figure 1 The utility model provides a nonlinear resistor valve plate structure, including a first nonlinear resistor R1, a second nonlinear resistor R2 and a third nonlinear resistor R3.

[0034] The core materials of the nonlinear resistance valve sheet are: the first nonlinear resistance element R1 is a PTC thermistor, the second nonlinear resistance element R2 is a low-field strength ZnO valve sheet, and the third nonlinear resistance element R3 is a high-energy SiC valve sheet.

[0035] The connection relationship of the nonlinear resistance valve plate elements is as follows: the second nonlinear resistance element R2 is connected in parallel with the third nonlinear resistance element R3, one end of which is connected to the ground terminal and the other end is connected to the first nonlinear resistance element R1, and the other end of the nonlinear resistance element R1 is connected to the 10kV system bus.

[0036] The second nonlinear resistor element R2 has very excellent nonlinear characteristics. It is close to the insulating state under normal working conditions, and the power frequency continuous current is only in the microampere level. When overvoltage occurs, it has a strong current-carrying capacity and quickly returns to the high-resistance state after energy release.

[0037] The third nonlinear resistance element R3 has higher thermal stability and chemical stability. It can still maintain excellent mechanical properties at high temperatures and has a lower thermal expansion coefficient, which enables it to have better performance in high temperature applications.

[0038] The first nonlinear resistor element R1 combines the advantages of the second nonlinear resistor element R2 , low residual voltage and large current discharge, and the third nonlinear resistor element R3 , high thermal stability, and is a mixed material of SiC and ZnO.

[0039] According to the different characteristics of the second nonlinear resistor element R2 and the third nonlinear resistor element R3, different 1mA working voltages are set so that when a weak current appears in the system, it first flows through the third nonlinear resistor element R3. As the voltage increases, the effect of the second nonlinear resistor element R2 gradually increases. When the voltage is high enough, almost all the energy is discharged in the second nonlinear resistor element R2.

[0040] Under normal operating voltage, the current flowing through the device is mainly capacitive current, which is equivalent to an insulator and will not cause the device to heat up. There is no need to use a series gap to isolate the operating voltage.

[0041] When a single-phase grounding fault occurs in the system, mA-level current flows through the first nonlinear resistance element R1 and the third nonlinear resistance element R3. Since the elements have high thermal stability, they can operate for a long time.

[0042] When the voltage applied to the device exceeds the starting value of the clamping voltage, the transient voltage is suppressed, and "near conduction" occurs, with most of the energy being discharged through the first nonlinear resistor element R1 and the second nonlinear resistor element R2. When the applied voltage drops below the continuous operating voltage, the valve plate is equivalent to an insulator, so there is no power frequency freewheeling.

[0043] See also Figure 2, the nonlinear resistor valve sheet volt-ampere characteristic, it can be found that the curve can be divided into three areas, the first is the small current area, the second is the voltage limiting working area, and the third is the overload protection area.

[0044] In normal operation, (Figure 1.pu) the valve plate is in a high resistance state, and the current is very small, below 1mA;

[0045] When a single-phase grounding fault occurs in the system (Figure 1.44.pu), the phase voltage becomes the line voltage and the protection current is less than 10mA;

[0046] When overvoltage occurs in the system (Figure 1.72.pu), the valve starts to act according to the voltage amplitude. When it is subjected to impact overvoltage, the valve conducts, discharges energy to the ground, and maintains a certain voltage to the ground.

[0047] Depend on Figure 2 It is found that the system discharge current range is wide, and the current amplitude range is 0.1mA to 10kA, or even higher. If you want to ensure that the circuit covers the upper and lower limits without reducing performance, switching the acquisition range is the simplest working method, but this method does not have a large enough dynamic range. The use of a logarithmic operation circuit can solve the above problem.

[0048] For the signal to be collected, 10uA to 10kA, after logarithmic transformation with base 10, it is -5 to 4, and then the corresponding level conversion can be performed to be sampled by ADC. Therefore, this device changes the original current signal sampling to logarithmic signal sampling.

[0049] See also Figure 3 This is the system structure diagram of the 10kV system overvoltage protection and voltage and current sampling device. The device consists of a voltage-type nonlinear resistor valve, a fault recorder, a 10kV voltage transformer, a 10kA current transformer, a 5A current transformer, and a logarithmic current sampling circuit.

[0050] The voltage-type nonlinear resistor valve plate, 10kA current transformer, 5A current transformer and logarithmic current sampling circuit are three independent structures and are applied to A, B, C three-phase 10kV system.

[0051] One end of the three voltage-type nonlinear resistor valve plates is connected to the reserved circuit breaker of the 10kV system through a busbar or a cable, and the other end thereof is short-circuited and grounded; the other end of the circuit breaker is directly connected to the 10kV system busbar.

[0052] The 10kV voltage transformer samples the secondary voltage of the three phases A, B, and C and the open triangle voltage. The secondary side of the 10kV voltage transformer leads out the three phases A, B, and C and the open triangle voltage, and directly connects to the idle four-channel PT of the fault recorder to monitor the system voltage.

[0053] Three 10kV current transformers are connected to the grounding points of three groups of voltage-type nonlinear resistor valve plates to detect the operating current and fault current of the voltage-type nonlinear resistor valve plates;

[0054] The primary sides of three 5A current transformers are respectively connected to the secondary sides of three groups of 10kA current transformers, and the secondary sides of the 5A current transformers are connected to the logarithmic current sampling circuit;

[0055] The output end of the logarithmic current sampling circuit is connected to the AD conversion circuit corresponding to the linear current sampling circuit of the fault recorder.

[0056] The secondary side signal of the 10kV voltage transformer is directly connected to the voltage sampling channel of the fault recorder to achieve 0V~180V voltage signal sampling. The 10kV voltage transformer can use the PT in the station to sample the secondary voltage and open triangle voltage of the three phases A, B, and C, or configure an independent PT for voltage detection;

[0057] The 10kA current transformer has an insulation level of 10kV and a transformation ratio of 2000:1, and is placed where the second nonlinear resistor element R2 and the third nonlinear resistor element R3 are connected in parallel to the ground.

[0058] The transformation ratio of the 5A current transformer is 1000:1.

[0059] The original structure of the fault recorder consists of: multi-channel PT and its sampling circuit, multi-channel CT and its sampling circuit, multi-channel AD conversion circuit and data processing and display control unit, etc.

[0060] Disconnect the three-way CT sampling circuit from the AD and replace it with three sets of 5A current transformers and corresponding logarithmic current sampling circuits;

[0061] The fault recorder displays the voltage signal as a secondary original signal of 0 to 180V, and displays the current signal as a current logarithmic signal of -5 to 4, the unit of which is ampere. Based on these two signals, the volt-ampere characteristics of the nonlinear resistor valve plate can be intuitively displayed.

[0062] The current sampling circuit of the fault recorder is changed from the linear amplification in the prior art to the logarithmic amplification.

[0063] The logarithmic current sampling circuit is implemented based on the logarithmic relationship between the forward conduction current and the reverse saturation current of the PN junction. The PN junction is the most basic device structure of the semiconductor and has the following formula characteristics:

[0064]

[0065] Where I0 represents the forward current, I s Represents the reverse saturation current, V DRepresents the forward voltage of the PN junction, V T represents the thermal voltage, and its value is about 26mV.

[0066] Affected by the slow dynamic response speed of a single PN junction and the fact that the reverse saturation current is temperature-dependent, the logarithmic current sampling circuit of the device is implemented using a transistor with an NPN structure (two PN junctions) and a thermistor to offset the change in thermal voltage and achieve temperature drift compensation.

[0067] This device is used in the 10kV system of the substation and is installed on the busbar in the station to suppress overvoltage inside the system, with an emphasis on suppressing arc grounding overvoltage. The working principle is similar to that of a lightning arrester, and both use metal oxide composite materials to make valve plates. However, the current capacity of the valve plates used in the device is much higher than that of a zinc oxide lightning arrester (400A / 2ms). The structure and installation form of each phase valve plate group are different from those of a zinc oxide lightning arrester.

[0068] At the same time, the device has voltage and current sampling functions, which can collect the voltage and current amplitudes of normal operation and fault status in real time, providing an accurate reference basis for the overvoltage range and nonlinear resistance valve capacity.

Claims

1. Applied to 10kV system overvoltage protection and voltage and current sampling device, characterized in that: It includes voltage type nonlinear resistor valve plate, fault recorder, 10kV voltage transformer, 10kA current transformer, 5A current transformer and logarithmic current sampling circuit; The voltage-type nonlinear resistor valve plate, 10kA current transformer, 5A current transformer and logarithmic current sampling circuit are three independent structures, which are applied to the A, B and C three-phase 10kV system; One end of the three voltage-type nonlinear resistor valve plates is connected to the reserved circuit breaker of the 10kV system through a busbar or a cable, and the other end thereof is short-circuited and grounded; the other end of the circuit breaker is directly connected to the 10kV system busbar; The 10kV voltage transformer samples the secondary voltage of the three phases A, B, and C and the open triangle voltage. The secondary side of the 10kV voltage transformer leads out the three phases A, B, and C and the open triangle voltage, and directly connects to the idle four-channel PT of the fault recorder to monitor the system voltage. Three 10kV current transformers are connected to the grounding points of three groups of voltage-type nonlinear resistor valve plates to detect the operating current and fault current of the voltage-type nonlinear resistor valve plates; The primary sides of three 5A current transformers are respectively connected to the secondary sides of three groups of 10kA current transformers, and the secondary sides of the 5A current transformers are connected to the logarithmic current sampling circuit; The output end of the logarithmic current sampling circuit is connected to a fault recorder.

2. The overvoltage protection and voltage and current sampling device for 10kV system according to claim 1 is characterized in that: The three voltage-type nonlinear valve plates include a first nonlinear resistor element R1, a second nonlinear resistor element R2 and a third nonlinear resistor element R3; the second nonlinear resistor element R2 is connected in parallel with the third nonlinear resistor element R3, one end of the first nonlinear resistor element R1 is connected to the bus, and the other end thereof is connected to a middle lead-out terminal on one side of the second nonlinear resistor element R2 and the third nonlinear resistor element R3 connected in parallel, and the other side lead-out terminal of the second nonlinear resistor element R2 and the third nonlinear resistor element R3 connected in parallel is grounded.

3. The overvoltage protection and voltage and current sampling device for 10kV system according to claim 2 is characterized in that: The first nonlinear resistance element R1 is a PTC thermistor, the second nonlinear resistance element R2 is a low-field strength ZnO valve plate, and the third nonlinear resistance element R3 is a high-energy SiC valve plate.

4. The overvoltage protection and voltage and current sampling device for 10kV system according to claim 1 is characterized in that: The current sampling circuit of the fault recorder is logarithmic amplification.

5. The overvoltage protection and voltage and current sampling device for 10kV system according to claim 1 is characterized in that: The secondary side signal of the 10kV voltage transformer is directly connected to the voltage sampling channel of the fault recorder to realize 0V~180V voltage signal sampling.

6. The overvoltage protection and voltage and current sampling device for 10kV system according to claim 1 is characterized in that: The 10kA current transformer has an insulation level of 10kV and a transformation ratio of 2000:1, and is placed where the second nonlinear resistor element R2 and the third nonlinear resistor element R3 are connected in parallel to the ground.

7. The overvoltage protection and voltage and current sampling device for 10kV system according to claim 1 is characterized in that: The transformation ratio of the 5A current transformer is 1000:

1.

8. The overvoltage protection and voltage and current sampling device for 10kV system according to claim 1 is characterized in that: The output end of the logarithmic current sampling circuit is connected to the AD conversion circuit corresponding to the linear current sampling circuit of the fault recorder.

9. The overvoltage protection and voltage and current sampling device for 10kV system according to claim 1 is characterized in that: The logarithmic current sampling circuit is implemented based on the logarithmic relationship between the forward conduction current and the reverse saturation current of the PN junction. The PN junction is the most basic device structure of the semiconductor and has the following formula characteristics: Where I0 represents the forward current, I s Represents the reverse saturation current, V D Represents the forward voltage of the PN junction, V T represents the thermal voltage, and its value is about 26mV.

10. The overvoltage protection and voltage and current sampling device for 10kV system according to claim 9, characterized in that: The logarithmic current sampling circuit is implemented by using a triode with an NPN structure and a thermistor to offset the change of thermal voltage, thereby achieving temperature drift compensation.

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