Low-frequency Oscillation Suppression Wiring Method and Device for Voltage Transformers Applied to Distribution Networks

Abstract

The present invention discloses a wiring method and device for suppressing low-frequency oscillation of a voltage transformer in a distribution network. The method is applied to a voltage transformer with a double-winding V-V wiring, the voltage transformer includes a first winding and a second winding, the first winding is arranged between a first end and a common end, and the distance between the first end and the common end is a first distance; the second winding is arranged between a second end and the common end, and the distance between the second end and the common end is a second distance; the method includes the following steps: short-circuiting a first short-circuit point of the first winding of the voltage transformer and a second short-circuit point of the second winding, the distance from the first short-circuit point to the common end is 2 / 3 of the first distance, and the distance from the second short-circuit point to the common end is 2 / 3 of the second distance. The technical solution of the present invention realizes the suppression of low-frequency oscillation of an electromagnetic voltage transformer in a distribution network.

Description

Technical Field

[0001] The present invention relates to the technical field of suppressing low-frequency oscillations of voltage transformers, and particularly to a wiring method for suppressing low-frequency oscillations of voltage transformers applied to a distribution network. Background Technique

[0002] In China's 10 kV - 35 kV distribution network, the system neutral point is not directly grounded. According to the load characteristics, it is further divided into main neutral point grounding methods such as an ungrounded neutral point system (a network with a small capacitive current), a neutral point grounded through an arc suppression coil (a network mainly composed of overhead lines), and a neutral point grounded through a small resistor (a network mainly composed of cable lines). In addition, there are also methods such as a neutral point grounded through an arc suppression coil in parallel with a small resistor and a neutral point grounded through a reactor.

[0003] In a distribution network, an electromagnetic voltage transformer (hereinafter referred to as "PT") has non-linear characteristics. When certain disturbances occur in the power grid, overvoltage or overcurrent passes through the high-voltage coil of the PT, causing it to reach the saturation state, and the excitation inductance decreases. When the system inductance (mainly the PT excitation inductance) and the system capacitance parameters match to form a resonant circuit, ferroresonant overvoltage and overcurrent can be excited.

[0004] With the development of the distribution network, the scale of cable lines is getting larger and larger, and the length and quantity of overhead lines have also increased. Especially in composite dense areas, a large number of power cables with a large capacitance to the ground are used, which significantly increases the system capacitance to the ground of the distribution network system. At this time, the system capacitive reactance is small, and it is difficult to form a resonance condition with the PT inductance, that is, the inductance and capacitance parameters are out of the resonance region and enter the low-frequency oscillation region. At this time, ferroresonance no longer constitutes the main contradiction, and the fault form has undergone a qualitative change.

[0005] Low-frequency oscillation refers to that when the distribution network system undergoes operations (such as removing a grounded fault line, normally opening a line, and the recovery process of a single-phase ground fault), the charge accumulated on the capacitance of the non-fault phase line will be discharged through the loop formed by the PT. At this time, the excitation source is the charge accumulated on the line capacitance, which is close to the DC component, that is, the primary current of the PT changes from AC excitation to quasi-DC excitation; due to the very low frequency ω, during the charge discharge process, the windings of the PT present low impedance and a small inductance value, and during the charge discharge process, a non-linear low-frequency oscillation process will be triggered in the discharge loop. At this time, the current passing through the primary side winding and the primary side fuse of the PT body is large, bringing a large operating risk to the PT fuse and even the PT body.

[0006] In a distribution network, there are three types of potential transformers (PTs), namely, Y-Y connection (star three-winding), V-V connection (two windings connected between three phases), and V connection (single winding connected between two phases). For occasions where three-phase voltages need to be measured, the Y-Y connection type is selected; when used for purposes such as voltmeter indication and energy extraction, a PT with a phase connection with fewer coils is chosen, such as V-V connection (two coils for three-phase voltage display) and V connection (one coil for energy extraction), to obtain better technical and economic indicators.

[0007] When the capacitance to ground of a 10 kV - 35 kV distribution network is relatively large, the cooperation with the inductance parameters of the PT has deviated from the resonance region and entered the low-frequency oscillation region. When the system undergoes operations (such as removing a grounded fault line, normally opening a line, and the recovery process of a single-phase ground fault), the charge accumulated by the line capacitance will discharge through the loop formed by the PT. Since the excitation source is close to the DC component and the frequency ω is very low, the PT winding presents a low impedance and a small inductance value, and a non-linear low-frequency oscillation process will be triggered in the discharge loop, resulting in an increase in the PT winding current and frequent problems such as the fuse of the PT on the outgoing line of the phase connection type PT (including V-V connection PT and V connection PT) and even the failure of the PT body. According to operation statistics, the burnout of the primary fuse of the PT during operation mostly occurs in the phase connection PT (V-V connection PT and V connection PT).

[0008] Due to the ferroresonance formed by the matching of inductance and capacitance parameters and the low-frequency oscillation formed by charge discharge, because the formation mechanisms are different, the commonly used and mature anti-resonance measures lack pertinence in suppressing low-frequency oscillations. Therefore, in actual operation, faults such as the fusing of PT fuses, burnout of the PT body, and even explosions still occur frequently; even after optimizing the neutral grounding method of the distribution network (such as grounding through a small resistor), the overvoltage of the non-fault phase is effectively clamped. However, the fusing of PT fuses caused by low-frequency oscillations and even the failure of the PT body are still relatively common. Summary of the Invention

[0009] The present invention provides a low-frequency oscillation suppression wiring method for a voltage transformer applied to a distribution network, which can prevent ferroresonance and suppress the low-frequency oscillation of an electromagnetic voltage transformer in the distribution network to ensure the safe operation of the PT fuse and the body winding under low-frequency oscillation.

[0010] An embodiment of the present invention provides a low-frequency oscillation suppression wiring method for a voltage transformer applied to a distribution network, including the following steps:

[0011] A voltage transformer applied to the V-V connection of a double winding. The voltage transformer includes a first winding and a second winding. The first winding is arranged between a first end and a common end, and the distance between the first end and the common end is a first distance; the second winding is arranged between a second end and the common end, and the distance between the second end and the common end is a second distance; the following steps are included:

[0012] Short-circuit the first short-circuit point of the first winding of the voltage transformer and the second short-circuit point of the second winding. The distance from the first short-circuit point to the common end is 2 / 3 of the first distance, and the distance from the second short-circuit point to the common end is 2 / 3 of the second distance.

[0013] Further, the connection point between the first winding and the first end is a first connection point, the connection point between the first winding and the common end is a second connection point, and the ratio of the winding length from the first short-circuit point to the first connection point to the winding length from the first short-circuit point to the second connection point is 1:2;

[0014] The connection point between the second winding and the common end is a third connection point, the connection point between the second winding and the second end is a fourth connection point, and the ratio of the winding length from the second short-circuit point to the third connection point to the winding length from the second short-circuit point to the fourth connection point is 2:1.

[0015] Further, a first damping resistor is connected at the first short-circuit point, and a second damping resistor is connected at the second short-circuit point.

[0016] Further, the resistance values of the first damping resistor and the second damping resistor range from 60 kΩ to 120 kΩ.

[0017] Another embodiment of the present invention provides a device for suppressing low-frequency oscillation of a voltage transformer applied to a distribution network, which is applied to a voltage transformer with a V-V connection of a double winding. The voltage transformer includes a first winding and a second winding. The first winding is arranged between a first end and a common end, and the distance between the first end and the common end is a first distance; the second winding is arranged between a second end and the common end, and the distance between the second end and the common end is a second distance;

[0018] The device includes a short-circuit line for connecting the first winding and the second winding. The connection point of the short-circuit line and the first winding is a first short-circuit point, the connection point of the short-circuit line and the second winding is a second short-circuit point. The distance from the first short-circuit point to the common end is 2 / 3 of the first distance, and the distance from the second short-circuit point to the common end is 2 / 3 of the second distance.

[0019] The connection point between the first winding and the first terminal is the first connection point, the connection point between the first winding and the common terminal is the second connection point, and the first short - connection point satisfies the following proportional characteristics:

[0020] The ratio between the winding length from the first short - connection point to the first connection point and the winding length from the first short - connection point to the second connection point is 1:2;

[0021] The connection point between the second winding and the common terminal is the third connection point, the connection point between the second winding and the second terminal is the fourth connection point, and the second short - connection point satisfies the following proportional characteristics:

[0022] The ratio between the winding length from the second short - connection point to the third connection point and the winding length from the second short - connection point to the fourth connection point is 2:1.

[0023] Furthermore, a first damping resistor is connected at the first short - connection point, and a second damping resistor is connected at the second short - connection point.

[0024] Furthermore, the resistance values of the first damping resistor and the second damping resistor range from 60 kΩ to 120 kΩ.

[0025] The embodiments of the present invention have the following beneficial effects:

[0026] The present invention provides a wiring method and device for suppressing low - frequency oscillation of a voltage transformer applied to a distribution network. This method short - circuits at the first short - connection point of the first winding of the voltage transformer and the second short - connection point of the second winding. The distance from the first short - connection point to the common terminal is 2 / 3 of the first distance, and the distance from the second short - connection point to the common terminal is 2 / 3 of the second distance. It realizes the targeted increase in the damping of the remaining charge discharge loop on the line capacitance, hits the key point of suppressing the low - frequency oscillation of the PT, achieves the purpose of preventing ferro - resonance and suppressing the low - frequency oscillation of the electromagnetic voltage transformer in the distribution network, and ensures the safe operation of the PT fuse and the body winding under low - frequency oscillation. Therefore, the present invention achieves the purpose of suppressing the low - frequency oscillation of the electromagnetic voltage transformer in the distribution network by increasing the impedance of the charge discharge loop on the distribution network line capacitance, realizes the determination and suppression of the low - frequency non - linear oscillation of the PT, and differentiates the ferro - resonance and low - frequency oscillation of the PT. By adopting different suppression methods for different system over - voltages, it has strong pertinence, can effectively reduce the fuse blowing and burning accidents of the PT, and improve the safety of the distribution network power system. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 is a schematic flow chart of a wiring method for suppressing low - frequency oscillation of a voltage transformer applied to a distribution network provided by an embodiment of the present invention;

[0028] Figure 2It is a schematic diagram of the winding short - circuit circuit in a voltage transformer for a voltage transformer low - frequency oscillation suppression wiring method applied to a distribution network provided by an embodiment of the present invention;

[0029] Figure 3 is provided by an embodiment of the present invention Figure 2 Schematic diagram of the equivalent circuit of the winding short - circuit circuit;

[0030] Figure 4 is a schematic diagram of the circuit of a V - V type voltage transformer without short - circuit during normal operation of the distribution network provided by an embodiment of the present invention;

[0031] Figure 5 is a schematic diagram of the equivalent low - frequency oscillation circuit of a V - V type voltage transformer without short - circuit after the distribution network cuts off a faulty line provided by an embodiment of the present invention;

[0032] Figure 6 is a schematic diagram of the PT excitation curve of a voltage transformer low - frequency oscillation suppression wiring method applied to a distribution network provided by an embodiment of the present invention;

[0033] Figure 7 (a) is a schematic diagram of the circuit of a V - V type voltage transformer with short - circuit after the distribution network cuts off a faulty line for a voltage transformer low - frequency oscillation suppression wiring method applied to a distribution network provided by an embodiment of the present invention;

[0034] Figure 7 (b) is a schematic diagram of the equivalent low - frequency oscillation circuit of a V - V type voltage transformer with short - circuit after the distribution network cuts off a faulty line for a voltage transformer low - frequency oscillation suppression wiring method applied to a distribution network provided by an embodiment of the present invention. Detailed implementation manners

[0035] Next, the technical solutions in the present invention will be clearly and completely described in conjunction with the accompanying drawings in the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments in the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0036] As Figure 1 shown, a voltage transformer low - frequency oscillation suppression wiring method applied to a distribution network provided by an embodiment of the present invention is applied to a V - V type voltage transformer with double windings. The voltage transformer includes a first winding and a second winding. The first winding is arranged between a first end and a common end, and the distance between the first end and the common end is a first distance; the second winding is arranged between a second end and the common end, and the distance between the second end and the common end is a second distance; it includes the following steps:

[0037] Step S101: Short-circuit the first short-circuit point of the first winding of the voltage transformer and the second short-circuit point of the second winding. The distance from the first short-circuit point to the common terminal is 2 / 3 of the first distance, and the distance from the second short-circuit point to the common terminal is 2 / 3 of the second distance.

[0038] As one of the embodiments, the connection point between the first winding and the first end is the first connection point, the connection point between the first winding and the common terminal is the second connection point, and the ratio between the winding length from the first short-circuit point to the first connection point and the winding length from the first short-circuit point to the second connection point is 1:2;

[0039] The connection point between the second winding and the common terminal is the third connection point, the connection point between the second winding and the second end is the fourth connection point, and the ratio between the winding length from the second short-circuit point to the third connection point and the winding length from the second short-circuit point to the fourth connection point is 2:1.

[0040] Step S102: Connect a first damping resistor at the first short-circuit point and a second damping resistor at the second short-circuit point.

[0041] As one of the embodiments, as Figure 2 shown, without changing the existing V-V type wiring PT winding structure, for the phase-interphase double-winding PT with V-V type wiring, for the winding between phases AB, from a distance of from phase A, and for the winding between phases BC, from a distance of from phase C, connect a short-circuit wire. Without changing the existing V-V type wiring PT winding structure, for the phase-interphase double-winding PT with V-V type wiring, for the winding between phases AB, from a distance of from phase A, and for the winding between phases BC, from a distance of from phase C, connect resistors R respectively. When no fault occurs in the line, the PT winding is in the linear region, and the suppression measures have no impact on the normal operating line and PT. When the fault of the distribution network outgoing line is removed, the capacitive charge of the non-faulty phase line to the ground is discharged, a large current flows through the PT winding, and the excitation curve of the winding enters the non-linear region. At this time, low-frequency non-linear oscillation occurs on the PT. When no suppression measures are taken, the overcurrent amplitude caused by the low-frequency oscillation is relatively large, and the large current causes the PT to heat up, so accidents such as fuse burnout or even PT burnout are likely to occur.

[0042] Perform equivalent transformation on Figure 2 to obtain the equivalent circuit schematic diagram as Figure 3 shown. It can be seen that after short-circuiting, the PT can be equivalent to a Y type, and the inductance value of each phase winding after equivalence is Meanwhile, the connected damping resistor does not change the existing V-V type PT winding structure, which is equivalent to changing the wiring method of the PT. The connected damping resistor shares the line voltage applied to the original PT high-voltage winding during a single-phase grounding fault, reducing the charge that needs to be released after the fault is eliminated and minimizing the impact of the capacitive current on the PT after the fault is restored.

[0043] The circuit diagram of the potential transformer without using the short-circuit wiring method of the present invention during normal operation is as Figure 4 shown. During normal operation, the excitation curve of the PT winding is in the linear region, with a relatively large inductance value, and no PT faults occur. The excitation curve of the PT is as Figure 6 shown. The equivalent low-frequency oscillation circuit of the phase-interphase V-V wiring type PT without short-circuiting after the fault line is removed is as Figure 5 shown. At this time, after the fault is removed, the charge stored in the line-to-ground capacitance of the non-fault phase line is redistributed. When a relatively large current flows through the PT winding, magnetic saturation occurs in the PT winding core, the excitation curve enters the non-linear region, the inductance value of the PT winding exhibits non-linear characteristics, and the line-to-ground capacitance and the primary inductive reactance of the electromagnetic potential transformer form a zero-sequence oscillation circuit. Its oscillation frequency is determined by the line-to-ground capacitance and the PT inductance, that is, ultra-low-frequency saturated overcurrent is generated, and low-frequency non-linear oscillation of the PT occurs.

[0044] As Figure 7 (a) shown, Figure 7 (a) is the circuit diagram of the V-V type wiring potential transformer using the short-circuit wiring method of the present invention (i.e., adopting the low-frequency oscillation suppression measure described in the present invention). At this time, the line can be equivalent to the equivalent circuit as Figure 7 (b) shown. It can be obtained that compared with not adopting the low-frequency oscillation suppression measure described in the present invention, the impedance in the line-to-ground capacitance charge discharge loop increases to times the original (i.e., from ωL to ), which can effectively reduce the amplitude of the current flowing through the PT winding during low-frequency oscillation. And due to the connected damping resistor, it shares the line voltage applied to the original PT high-voltage winding during a single-phase grounding fault. By not changing the PT type, the charge that needs to be released after the fault is eliminated is reduced, the impact of the capacitive current on the PT after the fault is restored is minimized, thereby reducing the influence of the overcurrent on the PT, and avoiding the phenomenon of PT fuse blowing or even PT burning. It can be seen that the connected damping resistor of the present invention shares the line voltage applied to the original PT high-voltage winding during a single-phase grounding fault. By not changing the PT type, the charge that needs to be released after the fault is eliminated is reduced, the impact of the capacitive current on the PT after the fault is restored is minimized, the impedance in the loop is increased, thereby suppressing the amplitude of the inrush current. The current flowing through the PT winding during the low-frequency oscillation process will be lower than the rated current of the fuse (0.5 A) and there is a margin, reducing the occurrence of PT accidents.

[0045] In view of the low-frequency oscillation problem brought about by the significant increase in the system's capacitance to the ground during the development of the 10 kV - 35 kV distribution network, based on the mechanism of low-frequency oscillation, this invention specifically increases the damping of the remaining charge discharge loop on the line capacitance, hitting the key point of suppressing the low-frequency oscillation of the PT, achieving the purpose of preventing ferroresonance while suppressing the low-frequency oscillation of the electromagnetic voltage transformer in the distribution network, and realizing the safe operation of the PT fuse and the main body winding under low-frequency oscillation. This invention achieves the purpose of suppressing the low-frequency oscillation of the electromagnetic voltage transformer in the distribution network by increasing the impedance of the charge discharge loop on the distribution network line capacitance, realizes the determination and suppression of the low-frequency non-linear oscillation of the PT, and differentiates the ferroresonance and low-frequency oscillation of the PT. By adopting different suppression methods for different system overvoltages, it has strong pertinence, can effectively reduce the fuse fusing and burning accidents of the PT, and improve the safety of the distribution network power system.

[0046] Based on the above-mentioned invention embodiments, this invention correspondingly provides an embodiment of a wiring device for suppressing the low-frequency oscillation of a voltage transformer applied to a distribution network;

[0047] Another embodiment of this invention provides a wiring device for suppressing the low-frequency oscillation of a voltage transformer applied to a distribution network, which is applied to a voltage transformer with a double-winding V-V connection. The voltage transformer includes a first winding and a second winding. The first winding is arranged between a first end and a common end, and the distance between the first end and the common end is a first distance; the second winding is arranged between a second end and the common end, and the distance between the second end and the common end is a second distance;

[0048] As Figure 2 shown, the device includes a short-circuit line for connecting the first winding and the second winding. The connection point of the short-circuit line and the first winding is a first short-circuit point, and the connection point of the short-circuit line and the second winding is a second short-circuit point. The distance from the first short-circuit point to the common end is 2 / 3 of the first distance, and the distance from the second short-circuit point to the common end is 2 / 3 of the second distance.

[0049] As one of the embodiments, the connection point of the first winding and the first end is a first connection point, and the connection point of the first winding and the common end is a second connection point. The first short-circuit point satisfies the following proportional characteristics:

[0050] The ratio of the winding length from the first short-circuit point to the first connection point to the winding length from the first short-circuit point to the second connection point is 1:2;

[0051] The connection point of the second winding and the common end is a third connection point, and the connection point of the second winding and the second end is a fourth connection point. The second short-circuit point satisfies the following proportional characteristics:

[0052] The ratio between the winding length from the second short contact point to the third connection point and the winding length from the second short contact point to the fourth connection point is 2:1.

[0053] As one of the embodiments, a first damping resistor is connected at the first short contact point, and a second damping resistor is connected at the second short contact point.

[0054] As one of the embodiments, the resistance values of the first damping resistor and the second damping resistor range from 60 kΩ to 120 kΩ.

[0055] For the convenience and brevity of description, the embodiments of the device item of the present invention include all the implementation manners in the above embodiments of the wiring method for suppressing low-frequency oscillation of a voltage transformer applied to a distribution network, and will not be described herein again.

[0056] The above are the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements are also regarded as the protection scope of the present invention.

[0057] Those of ordinary skill in the art can understand that to implement all or part of the processes in the above embodiments, it can be completed by instructing relevant hardware through a computer program. The program can be stored in a computer-readable storage medium. When the program is executed, it can include the processes of the above embodiments. Among them, the storage medium can be a magnetic disk, an optical disc, a read-only memory (ROM), or a random access memory (RAM), etc.

Claims

1. A wiring method for suppressing low-frequency oscillation of a voltage transformer applied to a distribution network, characterized in that A voltage transformer applied to the V-V connection of a double winding. The voltage transformer includes a first winding and a second winding. The first winding is arranged between a first end and a common end, and the distance between the first end and the common end is a first distance; the second winding is arranged between a second end and the common end, and the distance between the second end and the common end is a second distance; the following steps are included: Short-circuit the first short-circuit point of the first winding of the voltage transformer and the second short-circuit point of the second winding. The distance from the first short-circuit point to the common end is 2 / 3 of the first distance, and the distance from the second short-circuit point to the common end is 2 / 3 of the second distance.

2. The voltage transformer low-frequency oscillation suppression wiring method applied to the distribution network according to claim 1, characterized in that, The connection point of the first winding and the first end is the first connection point, the connection point of the first winding and the common end is the second connection point, and the ratio between the winding length from the first short-circuit point to the first connection point and the winding length from the first short-circuit point to the second connection point is 1:2; The connection point of the second winding and the common end is the third connection point, the connection point of the second winding and the second end is the fourth connection point, and the ratio between the winding length from the second short-circuit point to the third connection point and the winding length from the second short-circuit point to the fourth connection point is 2:

1.

3. The voltage transformer low-frequency oscillation suppression wiring method applied to the distribution network according to claim 2, characterized in that, Connect a first damping resistor at the first short-circuit point and connect a second damping resistor at the second short-circuit point.

4. The voltage transformer low-frequency oscillation suppression wiring method applied to the distribution network according to claim 3, characterized in that, The resistance values of the first damping resistor and the second damping resistor range from 60 kΩ to 120 kΩ.

5. A low-frequency oscillation suppression device for a voltage transformer applied to a distribution network, characterized in that, A voltage transformer applied to the V-V connection of a double winding. The voltage transformer includes a first winding and a second winding. The first winding is arranged between a first end and a common end, and the distance between the first end and the common end is a first distance; the second winding is arranged between a second end and the common end, and the distance between the second end and the common end is a second distance; The device includes a short-circuit line for connecting the first winding and the second winding. The connection point of the short-circuit line and the first winding is the first short-circuit point, the connection point of the short-circuit line and the second winding is the second short-circuit point. The distance from the first short-circuit point to the common end is 2 / 3 of the first distance, and the distance from the second short-circuit point to the common end is 2 / 3 of the second distance.

6. The voltage transformer low-frequency oscillation suppression device applied to a distribution network according to claim 5, characterized in that, The connection point of the first winding and the first end is the first connection point, the connection point of the first winding and the common end is the second connection point, and the first short-circuit point satisfies the following proportional characteristics: The ratio between the winding length from the first short-circuit point to the first connection point and the winding length from the first short-circuit point to the second connection point is 1:2; The connection point of the second winding and the common end is the third connection point, the connection point of the second winding and the second end is the fourth connection point, and the second short-circuit point satisfies the following proportional characteristics: The ratio between the winding length from the second short-circuit point to the third connection point and the winding length from the second short-circuit point to the fourth connection point is 2:

1.

7. The voltage transformer low-frequency oscillation suppression device applied to the distribution network according to claim 6, characterized in that, Connect a first damping resistor at the first short-circuit point and connect a second damping resistor at the second short-circuit point.

8. The voltage transformer low-frequency oscillation suppression device applied to a distribution network according to claim 7, characterized in that The resistance values of the first damping resistor and the second damping resistor range from 60 kΩ to 120 kΩ.

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