Resonance elimination device of voltage transformer for medium and low voltage distribution network

Abstract

The utility model relates to a voltage transformer resonance elimination device for a medium and low voltage power distribution network. The voltage transformer resonance elimination device comprises a non-linear fixed value resistor used for primary side resonance elimination, an adjustable damping resistor module used for secondary side resonance elimination, and a controller used for controlling the synergistic effect of the non-linear fixed value resistor and the adjustable damping resistor module. The nonlinear fixed-value resistor is connected in series with a neutral point at the primary side of the voltage transformer, and the damping resistor is connected in parallel with an opening at the secondary side of the voltage transformer; and the nonlinear fixed-value resistor and the adjustable damping resistor module are also in communication connection with the controller. The device has the advantages that primary and secondary side collaborative resonance elimination can be carried out on ferromagnetic resonance, and energy generated by resonance can be quickly eliminated.

Description

Technical Field

[0001] The utility model relates to the technical field of electromagnetic voltage transformer resonance elimination in distribution networks, and particularly relates to a resonance elimination device for voltage transformers in medium and low voltage distribution networks. Background Art

[0002] In medium and low voltage distribution networks operating with ungrounded neutral points, electromagnetic voltage transformers (abbreviation: PT) are generally connected to the busbars of substations. When the power system suffers from certain disturbances, overvoltage is likely to occur, resulting in a decrease in the inductance value of the PT, and the iron core of the PT changes from a linear unsaturated state to a saturated state in one, two, or three phases. When recovering from the saturated state, it is easy to form a resonance with the ground capacitance. Under different system ground capacitance parameters and PT parameters, the system may exhibit subharmonic, fundamental frequency, or high-frequency resonance. The overvoltage generated during ferromagnetic resonance in medium and low voltage distribution networks poses a threat to the safety of power system operation. The long-term ferromagnetic resonance overvoltage may cause the breakdown of the insulation of primary equipment, trigger a short-circuit fault, and then lead to a power outage accident. In addition, the heating phenomenon caused by the persistent overcurrent during ferromagnetic resonance may cause serious damage to lines and equipment.

[0003] Currently, the resonance elimination in medium and low voltage distribution networks mainly includes primary resonance elimination and secondary resonance elimination, and mostly uses microcomputer resonance elimination protection devices. The microcomputer resonance elimination device cyclically detects the open delta voltage of the PT. When the system is in a steady state, the resonance elimination element in the device is in an open state and has no impact on the system operation. When the open delta voltage of the PT is greater than the rated value, a fault occurs in the system. The resonance elimination device analyzes the detected data to obtain the fault type. If it is currently ferromagnetic resonance, the system immediately activates the resonance elimination circuit to quickly eliminate the ferromagnetic resonance under the damping effect. In some harsh plateau environments where thunderstorms and strong winds often occur, intermittent arc grounding often occurs in the system. If only a primary-side microcomputer resonance elimination device or only a secondary-side microcomputer resonance elimination device is installed in the system, its resonance elimination ability is not very good in such situations. If microcomputer resonance elimination devices are installed on both the primary and secondary sides, since the microcomputer resonance elimination for the primary and secondary sides of the voltage transformer is a separate independent system and the primary and secondary sides cannot cooperate in resonance elimination, its suppression effect is also not satisfactory. Therefore, it is necessary to invent a resonance elimination system device for voltage transformers in medium and low voltage distribution networks to control the cooperative resonance elimination on the primary and secondary sides. Summary of the Utility Model

[0004] In order to solve the above problems, the purpose of the utility model is to provide a resonance elimination device for voltage transformers in medium and low voltage distribution networks, which can perform cooperative resonance elimination on the primary and secondary sides for ferromagnetic resonance and quickly eliminate the energy generated by resonance.

[0005] To achieve the above purpose, the utility model adopts the following technical solutions:

[0006] A harmonic elimination device for a medium and low voltage distribution network voltage transformer, comprising a non-linear fixed value resistor for primary side harmonic elimination, an adjustable damping resistor module for secondary side harmonic elimination, and a controller for controlling the coordinated action of the non-linear fixed value resistor and the adjustable damping resistor module; the non-linear fixed value resistor is connected in series to the neutral point of the primary side of the voltage transformer, and the damping resistor is connected in parallel to the opening of the secondary side of the voltage transformer; the non-linear fixed value resistor and the adjustable damping resistor module are also communicatively connected to the controller; the controller controls the sequence of the non-linear fixed value resistor and the adjustable damping resistor module being put into the power system circuit and the resistance value of the adjustable damping resistor module put into the circuit.

[0007] More preferably, the conditions for the controller to judge ferromagnetic resonance are: abnormal three-phase voltage, or abnormal three-phase voltage and the zero-sequence voltage amplitude is greater than the rated phase voltage and persists for a preset time length.

[0008] More preferably, the adjustable damping resistor module is formed by at least two damping resistor units connected in parallel, each damping resistor unit includes a switch and a branch damping resistor connected in series, and each switch is controlled by the controller; the resistance value of each branch damping resistor ≤ 100Ω.

[0009] More preferably, the adjustable damping resistor module is formed by four damping resistor units connected in parallel.

[0010] More preferably, an input threshold is set for each damping resistor unit one by one, the effective value of the secondary side open delta voltage is compared with each input threshold, and the damping resistor units that reach the input threshold are all put into the circuit.

[0011] More preferably, the resistance value of the non-linear fixed value resistor ≥ 10KΩ.

[0012] More preferably, the controller includes a main control chip, the non-linear fixed value resistor and the adjustable damping resistor module are respectively connected to the I / O of the main control chip; the non-linear fixed value resistor is connected to the main control chip through a switch.

[0013] Based on the same utility model concept, the present utility model also provides a voltage mutual

[0014] The present utility model has the following beneficial effects:

[0015] The present utility model simultaneously sets resistors for harmonic elimination on the primary side and the secondary side of the voltage transformer, and the controller controls different working modes of the primary and secondary side harmonic elimination resistors to cooperate for harmonic elimination according to the intensity of ferromagnetic resonance, quickly eliminates the resonance energy while optimizing the working performance of the voltage transformer, and improves the stability and reliability of the power system. Description of the Drawings

[0016] Figure 1 Schematic diagram of the ferromagnetic resonance circuit in the harmonic elimination device of the present utility model;

[0017] Figure 2 Schematic diagram of the wiring of the harmonic elimination resistor of the voltage transformer of the present utility model;

[0018] Figure 3 Integrated system control diagram of the present utility model;

[0019] Figure 4 Schematic diagram of the adjustable damping resistor module of the present utility model;

[0020] Figure 5 Schematic diagram of the control of the harmonic elimination resistor of the present utility model; Specific implementation manners

[0021] The following further describes the present utility model in detail with reference to the accompanying drawings and specific embodiments:

[0022] Embodiment 1

[0023] Refer to Figures 1 to 3 , a harmonic elimination device for a voltage transformer in a medium and low voltage distribution network, including a non-linear fixed value resistor R for primary side harmonic elimination 1 , an adjustable damping resistor module R for secondary side harmonic elimination 2 and a controller for controlling the coordinated action of the non-linear fixed value resistor R 1 and the adjustable damping resistor module R 2 . The non-linear fixed value resistor R 1 is serially connected to the neutral point of the primary side of the voltage transformer, and the damping resistor is shunt-connected to the open end of the secondary side of the voltage transformer; the non-linear fixed value resistor R 1 and the adjustable damping resistor module R 2 are also communicatively connected to the controller. The controller can control the non-linear fixed value resistor R 1 and the adjustable damping resistor module R 2 to be simultaneously put into the power system circuit, or can control the non-linear fixed value resistor R 1 to be put into the power system circuit first, the adjustable damping resistor module R 2 to be put into the power system circuit later, or can also only put the adjustable damping resistor module R 2 . In short, with the controller, the way of putting the non-linear fixed value resistor R 1 and the adjustable damping resistor module R 2 into the circuit and their resistance values can be set according to actual needs, and the harmonic elimination methods on the primary and secondary sides are more flexible.

[0024] The controller mainly includes a main control chip, and the non-linear fixed value resistor R 1and the adjustable damping resistor module R 2 are respectively connected to the I / O of the main control chip, and the non-linear fixed-value resistor R 1 and the adjustable damping resistor module R 2 are controlled by the signal output by the main control chip to determine whether they are put into the circuit. Exemplarily, the non-linear fixed-value resistor R1 and the adjustable damping resistor module R2 are respectively connected to the main control chip through switches, and the main control chip controls the on-off of the switches, so as to control whether the non-linear fixed-value resistor R1 and the adjustable damping resistor module R2 are put into the circuit. Two IGBTs connected in reverse can be used as switches. At the same time, the main control chip is also used to receive the power parameters monitored in the power system, such as phase voltage, zero-sequence voltage, and the effective value of the open-delta voltage, etc.

[0025] The controller can judge whether ferromagnetic resonance occurs according to parameters such as three-phase voltage abnormality, the amplitude of zero-sequence voltage being greater than the rated phase voltage, and the amplitude of neutral point current. For example, during a fault, the phase voltage of the fault phase will drop to zero, and the non-fault phase becomes the line voltage. Preferably, when ferromagnetic resonance occurs, the neutral point of the primary side of the voltage transformer is connected in series with the non-linear fixed-value resistor R 1 , Exemplarily, a signal is sent by the controller to trigger the conduction of a switch (not shown) connected to the non-linear fixed-value resistor. The non-linear fixed-value resistor R 1 should be selected with a large resistance. In this embodiment, a non-linear fixed-value resistor with a resistance value of 10KΩ is preferably used. When a resistor of 5KΩ or more is used, it can also be used as a large resistor in the low-voltage distribution network. Therefore, the resistance value of the non-linear fixed-value resistor R 1 ≥5KΩ are all equivalent replacements of the 10KΩ resistor of the present invention and belong to the protection scope of the present invention. The present invention can quickly suppress the overvoltage of neutral point resonance by connecting a large resistor at one time. When the voltage harmonic signal passes through the non-linear fixed-value resistor R 1 , it will encounter a large impedance, which will cause the energy of the voltage harmonic to be quickly consumed, thereby reducing the amplitude of the voltage harmonic. The connection of the large resistor will also destroy the original resonance parameter matching of the system, so that the original possible resonance will not occur and multiple resonances will not occur at the same time, reducing the system resonance probability. The harmonic elimination method of the non-linear fixed-value resistor R 1 is simple and direct, does not require frequent adjustment, and has the characteristics of stability and reliability. At the same time, the cost of the fixed-value resistor itself is relatively low, and the installation and maintenance costs are also relatively reduced.

[0026] Please refer to Figures 3 to 5 , the adjustable damping resistor module R 2 can be put into the circuit together with the non-linear fixed-value resistor R 1 , or can be put into the system circuit only when the ferromagnetic resonance intensity is large. The adjustable damping resistor module R 2The adjustable damping resistor module R is composed of at least two damping resistor units connected in parallel, each of which includes a switch and a branch damping resistor connected in series, and each of the switches is controlled by the controller. Preferably, the resistance of each branch damping resistor is ≤100Ω. 2 It is composed of four damping resistor units connected in parallel. Each damping resistor unit can be put into the circuit at the same time under the control of the controller, or the appropriate number of damping resistor units can be selected according to the ferromagnetic resonance strength. Generally speaking, the larger the effective value of the open triangle voltage, the greater the ferromagnetic resonance strength, the more damping resistor units are put into the circuit, and the smaller the damping resistance value after parallel connection, the current flowing through the adjustable damping resistor module R 2 The larger the current, the shorter the detuning time. In this embodiment, the switch is composed of two IGBTs connected in reverse parallel, and the number of damping resistor units and the value of the damping resistor are controlled by controlling the opening and closing of the IGBTs.

[0027] The utility model discloses a voltage transformer detuning device for medium and low voltage distribution networks. Resistors for detuning are arranged on the primary and secondary sides of the voltage transformer at the same time, and a controller can control the cooperative detuning mode of the detuning resistors on the primary and secondary sides, thereby realizing rapid elimination of resonant energy, optimizing the working performance of the voltage transformer, and improving the stability and reliability of the power system.

[0028] The above description is only a specific implementation method of the utility model, and does not limit the patent scope of the utility model. Any equivalent structural transformation made using the contents of the utility model specification and drawings, or directly or indirectly used in other related technical fields, are also included in the patent protection scope of the utility model.

Claims

1. A voltage transformer detuning device for medium and low voltage distribution networks, characterized in that: It comprises a nonlinear fixed-value resistor for primary-side detuning, an adjustable damping resistor module for secondary-side detuning and a controller for controlling the coordinated action of the nonlinear fixed-value resistor and the adjustable damping resistor module; the nonlinear fixed-value resistor is connected in series to the neutral point of the primary side of the voltage transformer, and the damping resistor is connected in parallel to the opening of the secondary side of the voltage transformer; the nonlinear fixed-value resistor and the adjustable damping resistor module are also connected to the controller for communication.

2. A voltage transformer detuning device for medium and low voltage distribution networks according to claim 1, characterized in that: The controller determines that the conditions for ferromagnetic resonance to occur are: the three-phase voltage is abnormal, or the three-phase voltage is abnormal and the zero-sequence voltage amplitude is greater than the rated phase voltage and lasts for a preset time length.

3. A voltage transformer detuning device for medium and low voltage distribution networks according to claim 1, characterized in that: The adjustable damping resistor module is formed by at least two damping resistor units connected in parallel, each of the damping resistor units comprises a switch and a branch damping resistor connected in series, each of the switches is controlled by the controller; the resistance value of each branch damping resistor is ≤100Ω.

4. A voltage transformer detuning device for medium and low voltage distribution networks according to claim 3, characterized in that: The adjustable damping resistor module is formed by connecting four damping resistor units in parallel.

5. A voltage transformer detuning device for medium and low voltage distribution networks according to claim 3 or 4, characterized in that: An input threshold is set for each damping resistor unit in a one-to-one correspondence, the effective value of the secondary side open triangle voltage is compared with each input threshold, and the damping resistor units that reach the input threshold are all put into the circuit.

6. A voltage transformer detuning device for medium and low voltage distribution networks according to claim 1, characterized in that: The resistance of the nonlinear fixed-value resistor is ≥10KΩ.

7. A voltage transformer detuning device for medium and low voltage distribution networks according to claim 1, characterized in that: The controller includes a main control chip, and the nonlinear fixed value resistor and the adjustable damping resistor module are respectively connected to the I / O of the main control chip; the nonlinear fixed value resistor is connected to the main control chip through a switch.

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