Medium-voltage switch cabinet

Abstract

The utility model discloses a medium-voltage switch cabinet, which relates to the technical field of medium-voltage switch cabinets, and comprises a shell, a voltage transformer and a primary resonance elimination device, and an inner cavity is formed in the shell; the voltage transformer is mounted in the inner cavity, is used for being connected with an external power supply, and comprises a neutral point; one end of the primary resonance elimination device is electrically connected with the neutral point, the other end of the primary resonance elimination device is grounded, and the internal resistance of the primary resonance elimination device is smaller than or equal to 210 kilohms. Specifically, the primary resonance elimination device is connected in series to a neutral point of a primary winding of the voltage transformer, and then the primary resonance elimination device is grounded, so that the connection is completed; when the specification of the voltage transformer is 10KV, the internal resistance of the primary resonance elimination device is set to be smaller than or equal to 210k omega, so that the neutral point of the voltage transformer can be effectively grounded, the internal resistance can be ensured to be high enough while the resonance is eliminated, and the effect of eliminating the resonance is met.

Description

Technical Field

[0001] The utility model relates to the technical field of electrical equipment, and particularly relates to a medium-voltage switch cabinet. Background Art

[0002] At present, most systems below 40.5 kV adopt the operation mode of non-grounded neutral point of the power supply. The primary winding of the electromagnetic voltage transformer on the bus becomes the only metal channel for the non-grounded neutral point power grid to the ground. The charging and discharging path of the capacitance between the power grid and the ground must pass through the primary winding of the voltage transformer. When a single-phase grounding occurs in the system, a capacitive current will flow through the fault point, and the voltage of the whole phase will rise to the line voltage, and the charge corresponding to the line voltage will be charged on the capacitance between it and the ground. Once the grounding fault disappears, the current path is cut off at this time. The non-grounded phase must instantaneously return from the line voltage to the normal phase voltage level. However, since the grounding fault has been disconnected, the charge that the non-grounded phase has been charged to the line voltage during the grounding period can only pass through the high-voltage winding of the voltage transformer, enter the ground through its originally grounded neutral point, and an inrush current with an amplitude of several amperes will appear in the primary winding of the voltage transformer, fusing the high-voltage fuse of the voltage transformer. During this transient process, a very high-amplitude low-frequency saturation current will flow through the high-voltage winding of the voltage transformer, causing the iron core of the voltage transformer to be severely saturated. After saturation, the excitation inductance of the voltage transformer becomes smaller, and the impedance of the system network to the ground tends to be inductive. At this time, if the inductance of the system network to the ground matches the capacitance to the ground, a three-phase or single-phase resonance circuit will be formed, resulting in various ferromagnetic resonance overvoltages. In addition, for single-phase arc grounding in the power grid, due to lightning strikes or other reasons, the line is instantaneously grounded, causing the voltage of the whole phase to suddenly rise and generating a large inrush current, which will also burn out the voltage transformer.

[0003] In order to protect the voltage transformer from being burned out due to the above reasons, in the current prior art, a voltage-type primary harmonic eliminator is usually connected in series at the neutral point of the voltage transformer. However, when the voltage-type primary harmonic eliminator operates normally, its internal resistance is extremely large, which will cause the neutral point of the voltage transformer to be unable to be effectively grounded, resulting in the problem of three-phase imbalance of the system.

[0004] Therefore, it is necessary to provide a new medium-voltage switch cabinet to solve the above technical problems. Content of the Utility Model

[0005] The main purpose of the utility model is to propose a medium-voltage switch cabinet, aiming to improve the technical problem that the series connection of the primary harmonic eliminator at the neutral point of the voltage transformer in the prior art will cause three-phase imbalance.

[0006] To achieve the above object, the medium-voltage switch cabinet proposed by the utility model includes:

[0007] A housing, an inner cavity is formed in the housing;

[0008] A voltage transformer, the voltage transformer is installed in the inner cavity, the voltage transformer is used to connect to an external power supply, and the voltage transformer includes a neutral point;

[0009] A primary harmonic elimination device, one end of the primary harmonic elimination device is electrically connected to the neutral point, the other end of the primary harmonic elimination device is used for grounding, and the internal resistance of the primary harmonic elimination device is less than or equal to 210 kΩ.

[0010] In one embodiment, the primary harmonic elimination device is a current-sensitive primary harmonic elimination device.

[0011] In one embodiment, the internal resistance of the current-sensitive primary harmonic elimination device is less than or equal to 70 kΩ.

[0012] In one embodiment, the excitation characteristic matching degree of the voltage transformer is less than or equal to 20%.

[0013] In one embodiment, the voltage transformer is a fully insulated voltage transformer.

[0014] In one embodiment, the number of the current-sensitive primary harmonic elimination devices is multiple, and the multiple current-sensitive primary harmonic elimination devices are connected in parallel with each other.

[0015] In one embodiment, the medium-voltage switchgear further includes a microcomputer harmonic elimination device, the microcomputer harmonic elimination device is arranged in the inner cavity, and the microcomputer harmonic elimination device is connected in parallel with the primary harmonic elimination device.

[0016] In one embodiment, the medium-voltage switchgear further includes a fuse, the fuse is used to connect to the external power supply, and the voltage transformer is connected to the fuse.

[0017] In one embodiment, the medium-voltage switchgear further includes two isolating plugs, one of the isolating plugs is arranged between the voltage transformer and the fuse, and the other isolating plug is used to be arranged between the fuse and the external power supply.

[0018] In one embodiment, the medium-voltage switchgear further includes a lightning arrester, and the lightning arrester is connected to the fuse and grounded.

[0019] In the above solution, the medium-voltage switchgear includes a housing, a voltage transformer, and a primary harmonic eliminator. An inner cavity is formed inside the housing; the voltage transformer is installed in the inner cavity and is used to connect to an external power supply. The voltage transformer includes a neutral point; one end of the primary harmonic eliminator is electrically connected to the neutral point, and the other end of the primary harmonic eliminator is used for grounding. The internal resistance of the primary harmonic eliminator is less than or equal to 210 kΩ. Specifically, the primary harmonic eliminator is connected in series to the neutral point of the primary winding of the voltage transformer, and then the primary harmonic eliminator is grounded, thus completing the connection. In the prior art, the internal resistance of the primary harmonic eliminator is extremely large during normal operation, and the internal resistance can reach the megohm level. Since the neutral point of the voltage transformer is grounded through the primary harmonic eliminator, this will cause the neutral point of the voltage transformer to be unable to be effectively grounded, resulting in three-phase imbalance of the entire system. As a result, the energy inside the voltage transformer cannot be effectively released through the neutral point, ultimately leading to an unbalanced output voltage on the secondary side of the voltage transformer, which also causes three-phase imbalance. The present utility model adopts a primary harmonic eliminator with a low internal resistance. In this way, the neutral point of the voltage transformer is grounded through the primary harmonic eliminator with a low internal resistance, which can effectively ground the neutral point of the voltage transformer. Under normal operating conditions, the primary harmonic eliminator presents a low resistance. When a three-phase imbalance occurs in the system, the excess energy can be released through the neutral point of the voltage transformer via the primary harmonic eliminator with a low resistance, thereby balancing the three-phase voltage. When resonance occurs in the system, the primary harmonic eliminator presents a high resistance state, playing a role in eliminating resonance. In this way, it can not only play a role in improving three-phase imbalance, but also eliminate ferroresonance. Description of the Drawings

[0020] In order to more clearly illustrate the technical solutions in the embodiments of the present utility model or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments of the present utility model. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on the structures shown in these drawings.

[0021] Figure 1 Schematic diagram of the internal structure of an embodiment of the medium-voltage switchgear provided by the present utility model;

[0022] Figure 2 Schematic diagram of the connection between the primary harmonic eliminator and the voltage transformer provided by the present utility model;

[0023] Figure 3 Schematic diagram of the connection between the fuse, the disconnecting plug, and the lightning arrester provided by the present utility model.

[0024] Explanation of the reference numerals in the drawings:

[0025] 1. Voltage transformer; 2. Primary harmonic elimination device; 11. Neutral point; 3. Fuse; 4. Isolating plug; 5. Lightning arrester; 101. External power supply.

[0026] The realization, functional features and advantages of the purpose of the present utility model will be further described with reference to the embodiments and the accompanying drawings. Detailed implementation manners

[0027] The technical solutions in the embodiments of the present utility model will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present utility model. Obviously, the described embodiments are only a part of the embodiments of the present utility model, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present utility model without creative efforts shall fall within the protection scope of the present utility model.

[0028] It should be noted that if there are directional indications (such as up, down, left, right, front, back,...) in the embodiments of the present utility model, the directional indications are only used to explain the relative positional relationship and movement conditions between components in a specific posture. If the specific posture changes, the directional indications will also change accordingly.

[0029] In addition, if there are descriptions such as "first" and "second" in the embodiments of the present utility model, the descriptions of "first" and "second" are only for descriptive purposes and cannot be understood as indicating or implying their relative importance or implicitly indicating the quantity of the indicated technical features. Thus, the features defined with "first" and "second" may explicitly or implicitly include at least one such feature. In addition, if "and / or" or "and / or" appears throughout the text, its meaning includes three parallel solutions. Taking "A and / or B" as an example, it includes solution A, solution B, or a solution that satisfies both A and B at the same time. In addition, the technical solutions between the embodiments can be combined with each other, but it must be based on the ability of those of ordinary skill in the art to implement. When the combination of technical solutions results in contradictions or cannot be implemented, it should be considered that such a combination of technical solutions does not exist and is not within the protection scope required by the present utility model.

[0030] Please refer to Figure 1 and Figure 2, the present utility model proposes a medium voltage switchgear, which includes a housing, a voltage transformer 1 and a primary harmonic eliminator 2. An inner cavity is formed inside the housing; the voltage transformer 1 is installed in the inner cavity, and the voltage transformer 1 is used to connect to an external power supply 101. The voltage transformer 1 includes a neutral point 11; one end of the primary harmonic eliminator 2 is electrically connected to the neutral point 11, and the other end of the primary harmonic eliminator 2 is used for grounding, and the internal resistance of the primary harmonic eliminator 2 is less than or equal to 210 kΩ. Specifically, the primary harmonic eliminator 2 is connected in series to the neutral point 11 of the primary winding of the voltage transformer 1, and then the primary harmonic eliminator 2 is grounded, thus completing the connection; in the prior art, the internal resistance of the primary harmonic eliminator 2 is extremely large during normal operation, and the internal resistance can reach the megohm level. Since the neutral point 11 of the voltage transformer 1 is grounded through the primary harmonic eliminator 2, this will cause the neutral point 11 of the voltage transformer 1 to be unable to be effectively grounded, resulting in the three-phase imbalance of the entire system. In this way, the internal energy of the voltage transformer 1 cannot be effectively released through the neutral point 11, ultimately leading to the imbalance of the output voltage on the secondary side of the voltage transformer 1, which also causes the three-phase imbalance. This medium voltage switchgear adopts a primary harmonic eliminator 2 with a low internal resistance. In this way, the neutral point 11 of the voltage transformer 1 is grounded through the primary harmonic eliminator 2 with a low internal resistance. When the specification of the voltage transformer 1 is 10 KV, the internal resistance of the primary harmonic eliminator 2 is set to be less than or equal to 210 kΩ. In this way, it can not only effectively ground the neutral point 11 of the voltage transformer 1, but also ensure that the internal resistance is high enough to eliminate resonance under the condition of eliminating resonance; under normal operating conditions, the primary harmonic eliminator 2 presents a low resistance. When the system has a three-phase imbalance, the excess energy can be released through the neutral point 11 of the voltage transformer 1 through the low-resistance primary harmonic eliminator 2, thereby balancing the three-phase voltage. When the system has resonance, the primary harmonic eliminator 2 presents a high-resistance state, playing the role of eliminating resonance. In this way, it can not only play the role of improving the three-phase imbalance, but also eliminate the ferroresonance.

[0031] In one embodiment, the primary harmonic eliminator 2 is a current-sensitive type primary harmonic eliminator. The current-sensitive harmonic eliminator can continuously and quickly eliminate the ferroresonance overvoltage, which means that no matter how the amplitude of the resonance overvoltage changes, the current-sensitive type primary harmonic eliminator can respond in time and process it; the larger the amplitude of the resonance overvoltage, the shorter the harmonic elimination time of the current-sensitive type primary harmonic eliminator, which ensures the stability and safety of the power system, especially under extreme conditions; the current-sensitive type primary harmonic eliminator can also ensure that the voltage transformer 1 is not burned out and the fuse of the voltage transformer 1 is not blown, thus protecting the key equipment in the power system from the influence of overvoltage.

[0032] In one embodiment, the internal resistance of the current-sensitive primary harmonic elimination device is less than or equal to 70 kΩ. When the specification of the voltage transformer 1 is 35 KV, setting the internal resistance of the primary harmonic elimination device 2 to be less than or equal to 70 kΩ can effectively ground the neutral point 11 of the voltage transformer 1. At the same time, when eliminating resonance, it can ensure that the internal resistance is high enough to play the role of eliminating resonance; under normal operating conditions, the primary harmonic elimination device 2 presents a low resistance. When the system has a three-phase imbalance, the excess energy can be released through the neutral point 11 of the voltage transformer 1 via the low-resistance primary harmonic elimination device 2, thereby balancing the three-phase voltage. When resonance occurs in the system, the primary harmonic elimination device 2 presents a high-resistance state, playing the role of eliminating resonance. In this way, it can not only improve the three-phase imbalance but also eliminate ferroresonance.

[0033] In one embodiment, the excitation characteristic matching degree of the voltage transformer 1 is less than or equal to 20%. Considering the stability and economy of the power system. In a parallel operating power system, especially for equipment such as generators and transformers, the excitation characteristic matching degree directly affects the distribution of reactive power and the stability of the system voltage. The excitation characteristic matching degree of the voltage transformer 1 being less than or equal to 20% can balance technical and economic factors and achieve reliable and effective operation at low cost.

[0034] In one embodiment, the voltage transformer 1 is a fully insulated voltage transformer 1. The fully insulated voltage transformer 1 uses completely insulating materials and is not directly grounded, which makes them more reliable in various harsh environments, especially in areas with severe pollution or environments with chemical corrosion; due to its comprehensive insulation design, the fully insulated voltage transformer 1 can better resist lightning strikes, preventing the high voltage caused by lightning from being transmitted to the secondary side, thereby improving the safety of the system; and because of the fully insulated design, the fully insulated voltage transformer 1 reduces the environmental impact on internal components. The fully insulated voltage transformer 1 has a longer service life and higher accuracy, reduces the frequency of maintenance and replacement, and greatly reduces the use cost.

[0035] In one embodiment, the number of current-sensitive primary harmonic elimination devices is multiple, and multiple current-sensitive primary harmonic elimination devices are connected in parallel. Connecting multiple current-sensitive primary harmonic elimination devices in parallel can increase the total harmonic elimination current capacity, thereby more effectively suppressing resonant overvoltage. When ferroresonance occurs in the system, multiple current-sensitive primary harmonic elimination devices work simultaneously, which can absorb and disperse overvoltage energy faster and shorten the harmonic elimination time; moreover, when one or more of the current-sensitive primary harmonic elimination devices fail or need maintenance, the other current-sensitive primary harmonic elimination devices can still continue to work, ensuring the continuous harmonic elimination ability of the system, improving the stability and reliability of the overall system, and preventing the system from losing the harmonic elimination function due to a single-point failure.

[0036] In one embodiment, the medium-voltage switchgear further includes a microcomputer harmonic elimination device. The microcomputer harmonic elimination device is disposed in the inner cavity and is connected in parallel with the primary harmonic elimination device 2. The microcomputer harmonic elimination device monitors the voltage and current parameters in the power system in real time through sensors, and quickly analyzes the collected data through the built-in microprocessor to determine whether there are harmonics or ferromagnetic resonance. When harmonics are detected, the controller will immediately adjust the operating state of the harmonic elimination device and suppress the harmonic current by changing the impedance of the device. The microcomputer harmonic elimination device can automatically adjust the harmonic elimination strategy according to the changes in the system load and grid conditions to ensure the best harmonic elimination effect. By connecting the microcomputer harmonic elimination device in parallel with the primary harmonic elimination device 2, they can cooperate with each other to further improve the harmonic elimination effect, and the real-time data can be observed from the display screen of the microcomputer harmonic elimination device.

[0037] Please refer to Figure 1 and Figure 3 , in one embodiment, the medium-voltage switchgear further includes a fuse 3. The fuse 3 is used to connect to the external power supply 101, and the voltage transformer 1 is connected to the fuse 3. By connecting the fuse 3 to the voltage transformer 1, when a high-voltage situation occurs, the fuse 3 can be disconnected to disconnect the connection between the voltage transformer 1 and the external power supply 101, protecting the voltage transformer 1 from being damaged and increasing the lifespan of the voltage transformer 1.

[0038] Please refer to Figure 1 and Figure 3 , in one embodiment, the medium-voltage switchgear further includes two isolating plugs 4. One isolating plug 4 is disposed between the voltage transformer 1 and the fuse 3, and the other isolating plug 4 is used to be disposed between the fuse 3 and the external power supply 101. By setting the disconnecting switch, the fuse 3, the voltage transformer 1 and the external power supply 101 can be completely separated to form an obvious disconnection point, which can ensure that the equipment is in a safe power-off state, avoid current leakage and other electrical risks, and protect the safety of the staff. When maintenance, repair or replacement of electrical equipment is required, the disconnecting switch can cut off the connection between the equipment and the power supply, providing a safe working environment for the staff to prevent injuries caused by accidental contact with the power supply. Only by connecting and disconnecting the disconnecting switch can the operation efficiency be greatly improved.

[0039] Please refer to Figure 1 and Figure 3 , in one embodiment, the medium-voltage switchgear further includes a lightning arrester 5. The lightning arrester 5 is connected to the fuse 3 and grounded. The lightning arrester 5 is a device that can protect the equipment in the power system from lightning strikes or internal overvoltage damage. When the medium-voltage switchgear is subjected to an abnormally high voltage (overvoltage), the lightning arrester 5 will quickly guide this part of the voltage energy to the ground, thereby limiting the voltage peak value and protecting the insulation system of the power equipment from being damaged, which can increase the lifespan of the medium-voltage switchgear.

[0040] The above are only exemplary embodiments of the present utility model, and do not limit the patent scope of the present utility model accordingly. Any equivalent structural transformation made under the technical concept of the present utility model by using the content of the specification and drawings of the present utility model, or any direct / indirect application in other related technical fields is included in the patent protection scope of the present utility model.

Claims

1. A medium voltage switch cabinet, characterized in that: include: a housing, wherein an inner cavity is formed in the housing; A voltage transformer, the voltage transformer is installed in the inner cavity, the voltage transformer is used to connect to an external power supply, and the voltage transformer includes a neutral point; A primary detuning device, one end of which is electrically connected to the neutral point, the other end of which is grounded, and the internal resistance of which is less than or equal to 210 kΩ.

2. The medium voltage switchgear according to claim 1, characterized in that: The primary detuning device is a flow-sensitive primary detuning device.

3. The medium voltage switchgear according to claim 2, characterized in that: The internal resistance of the current-sensitive primary detuning device is less than or equal to 70 kΩ.

4. The medium voltage switchgear according to any one of claims 1 to 3, characterized in that: The excitation characteristic matching degree of the voltage transformer is less than or equal to 20%.

5. The medium voltage switchgear according to any one of claims 1 to 3, characterized in that: The voltage transformer is a fully insulated voltage transformer.

6. The medium voltage switchgear according to any one of claims 2 or 3, characterized in that: There are multiple flow-sensitive primary detuning devices, and the multiple flow-sensitive primary detuning devices are connected in parallel.

7. The medium voltage switchgear according to any one of claims 1 to 3, characterized in that: The medium voltage switch cabinet further comprises a microcomputer detuning device, which is arranged in the inner cavity, and the microcomputer detuning device and the primary detuning device are connected in parallel with each other.

8. The medium voltage switchgear according to claim 1, characterized in that: The medium voltage switch cabinet further includes a fuse, which is used to be connected to the external power supply, and the voltage transformer is connected to the fuse.

9. The medium voltage switchgear according to claim 8, characterized in that: The medium voltage switch cabinet further comprises two isolation plugs, one of which is arranged between the voltage transformer and the fuse, and the other of which is arranged between the fuse and the external power supply.

10. The medium voltage switchgear according to claim 8, characterized in that: The medium voltage switch cabinet further comprises a lightning arrester, which is connected to the fuse and grounded.

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