CN202602252U - Device for suppressing direct current at neutral point of transformer by adjustable resistor method - Google Patents

Abstract

The utility model relates to a device for suppressing the direct current at the neutral point of a transformer in the process of high-voltage power transmission and transformation, in particular to a device for suppressing the direct current at the neutral point of the transformer by an adjustable resistance method. The utility model comprises an adjustable resistance circuit, a state conversion switch circuit and an overvoltage bypass circuit, and the three circuits are connected in parallel and connected in series between the neutral point of the transformer and the grounding pole; the range value of the adjustable resistance circuit is 0 ~4Ω. The utility model adopts a resistor in series at the neutral point of the transformer with direct current to block the direct current of the neutral point, so the resistance value can be set to suppress the direct current of the neutral point of the transformer, ensuring that other equipment does not need to adjust parameters to cooperate with it, especially all relays The electrical protection setting value does not need to be reset. When the state transfer switch is in the breaking state, the neutral point of the transformer is grounded through the adjustable resistance loop, thereby blocking the current of the neutral point of the transformer. The utility model has the advantages of simple structure and high reliability, and improves the reliability of overvoltage bypass startup.

Description

A device for suppressing DC current at neutral point of transformer by adjustable resistance method

technical field

The utility model relates to a device for suppressing the direct current at the neutral point of a transformer in the process of high-voltage power transmission and transformation, in particular to a device for suppressing the direct current at the neutral point of the transformer by an adjustable resistance method.

Background technique

With the development of modern science and technology, especially the breakthrough of high-power power electronic device technology, DC transmission has gained more and more advantages due to its large transmission capacity, low cost, low loss, not easy to aging, long life and unlimited transmission distance. development of. As early as the 1980s, my country had begun to construct DC projects. As of 2010, my country has planned to build a number of DC transmission lines, especially ±800KV UHV DC transmission lines. According to the plan, before 2020, my country will also build a series of high-voltage direct current transmission projects (about 30, including ±500kV, ±660kV, ±800kV, ±1000kV direct current transmission projects). Such as: Xiluodu-West Zhejiang (±800kV/±1000kV), Xiluodu-Zhuzhou (±660kV), Yunnan-Guangdong second round (±800kV), etc. When the DC transmission system operates with a single pole, the ground pole current flows into the AC system through the neutral point of the transformer of the AC system, which has different degrees of influence on the AC transmission system, especially the magnetic bias generated by the DC component superimposed on the neutral point of the AC transformer. It causes magnetic saturation, and generates harmonics, oscillation and noise in the AC system, which affects the safe and stable operation of the AC system. Therefore, the impact of DC power transmission on AC power transmission will become more and more obvious, and the research on the DC current of the neutral point of the transformer will also arise from this.

At present, the main methods for suppressing the DC current at the neutral point of the transformer are: 1. Capacitive blocking method: suppressing the current by connecting a capacitor in series with the neutral point of the transformer. This method can completely suppress the DC current, but at the same time completely repel this current to other grounds. 2. Electrical isolation method: suppress the current by connecting a small resistor in series with the neutral point of the transformer. This method can flexibly configure different resistance resistors to suppress the DC current to varying degrees, and the transformer in the system The neutral point current is configured below the safe level. 3. DC current reverse injection method: apply and generate neutral point DC counter electromotive force around the neutral point of the transformer to suppress the neutral point DC. This method has complicated devices, consumes more power, and cannot completely suppress the DC current. .

The Chinese Invention Patent Application Publication No. CN1625010A describes a "method for limiting DC current at neutral point of transformer by reverse current method". The technical solution is mainly: (1) choose an independent Compensation grounding pole; (2) Connect the "ground" terminal of the DC generating device to an independent compensation grounding pole, and connect the "output" terminal of the DC generating device to the grounded neutral point of the transformer; (3) Transformer neutral point DC current The detection device measures the DC current at the neutral point of the transformer to obtain the value and direction of the DC current at the neutral point; (4) The controller of the DC generator automatically activates the DC generator to inject a current opposite to the DC bias to the neutral point of the transformer. Although this method does not change the original wiring of the transformer, the effect of offsetting the DC bias is obvious, but the device is complicated, the power consumption is large, and the complete suppression of the DC current cannot be realized.

Contents of the invention

In order to solve the above technical problems, the utility model provides a device for suppressing the DC current at the neutral point of the transformer by an adjustable resistance method, which is simple in structure, safe and reliable, and can be flexibly configured to suppress the DC current at the neutral point of the transformer.

The technical scheme of the utility model is achieved in that:

A device for suppressing DC current at the neutral point of a transformer by an adjustable resistance method, comprising an adjustable resistance loop, a state transfer switch loop, and an overvoltage bypass loop, and the three loops are connected in parallel and then connected in series between the neutral point of the transformer and the grounding electrode Between; the range of the adjustable resistance loop is 0 ~ 4Ω.

The overvoltage bypass loop includes a rectifier bridge, a first thyristor, a first overvoltage trigger unit, an inductor and a freewheeling diode. The thyristor and the inductor are connected in series, a first overvoltage trigger unit is connected in parallel at both ends of the first thyristor, and a freewheeling diode is connected in parallel at both ends of the inductor.

The inductance is a switch closing inductance and a damping inductance connected in series.

The adjustable resistance loop is an overvoltage gap discharge device connected in parallel at both ends of the resistance.

The adjustable resistance circuit is a zinc oxide overvoltage breakdown discharge circuit connected in parallel at both ends of the resistance.

The adjustable resistance circuit is a zinc oxide overvoltage breakdown discharge circuit connected in parallel at both ends of the resistance.

The first thyristor is two or more thyristors running in parallel.

The thyristor first overvoltage trigger unit is a double set of parallel second overvoltage trigger unit and third overvoltage trigger unit.

The first transfer switch is a double switch or a single switch with multiple contacts.

The beneficial effects of the utility model are as follows:

1. Since the utility model uses a series resistor at the neutral point of the transformer with direct current to block the direct current of the neutral point, the resistance value of the device can be set to suppress the direct current of the neutral point of the transformer, and ensure that other equipment does not need to adjust parameters In conjunction with it, especially all relay protection settings do not need to be reset. When the state transfer switch is in the breaking state, the neutral point of the transformer is grounded through the adjustable resistance loop, thereby blocking the current of the neutral point of the transformer.

2. Since the utility model also utilizes the bypass thyristor and the state changeover switch to cooperate with the resistor, it can quickly realize safe and reliable metallic grounding when the neutral point overvoltage occurs.

3. Since the utility model can add an overvoltage gap discharge device or a zinc oxide overvoltage breakdown discharge circuit at both ends of the resistance, the reliability of the device is high.

4. Since the utility model adopts two sets of thyristor trigger circuits, the reliability of overvoltage bypass startup is improved.

5. Since the state transfer switch of the present invention can adopt double switches or single switch with multiple contacts, the closing fault current capability of the device can be improved.

Description of drawings

Fig. 1 is a block diagram of the utility model;

Fig. 2 is the circuit structure diagram of the utility model embodiment one;

Fig. 3 is the circuit structure diagram of the second embodiment of the utility model;

Fig. 4 is the circuit structure diagram of the utility model embodiment three;

Fig. 5 is a circuit structure diagram of the fourth embodiment of the utility model;

Fig. 6 is a circuit structure diagram of Embodiment 5 of the present utility model.

In the figure: Transformer neutral point 1, adjustable resistance circuit 2, state transfer switch circuit 3, overvoltage bypass circuit 4, DC blocking resistor 5, first transfer switch 6, second transfer switch 61, third transfer switch 62 , rectifier bridge 7, first thyristor 8, second thyristor 81, third thyristor 82, first overvoltage trigger unit 9, second overvoltage trigger unit 91, third overvoltage trigger unit 92, inductance 10, switch closing inductance 101, damping inductance 102, freewheeling diode 11, overvoltage gap discharge device 12, varistor 13.

Detailed ways

The utility model is a device for suppressing the DC current at the neutral point of a transformer by an adjustable resistance method, as shown in Figure 1, the utility model includes three adjustable resistance loops 2, a state conversion switch loop 3, and an overvoltage bypass loop 4 The basic circuit, these three circuits are connected in parallel, one end is connected in series to the neutral point 1 of the transformer, and the other end is grounded. When the state transfer switch is in the breaking state, the neutral point of the transformer is grounded through the adjustable resistance loop 2, thereby blocking the current of the neutral point of the transformer, and the range value of the adjustable resistance loop 2 is 0 ~ 4Ω. The state transfer switch circuit 3 is composed of a switch that can be controlled to close/break, and its state determines the operating state of the device; when the switch is closed, all devices of the device are bypassed, and the neutral point of the transformer is grounded metallically through the switch contact. In the case of resistor grounding, a voltage is developed across the resistor due to the fact that the DC current at the neutral point 1 of the transformer is suppressed by the resistor. When the voltage across the resistor is higher than a certain voltage limit—the voltage threshold, the overvoltage bypass circuit 4 is turned on, and at the same time, the conduction current is used to drive the state changeover switch to close—to enter the direct grounding state. Since the voltage threshold is much higher than the highest voltage formed across the resistor in the DC system, only when a three-phase unbalanced fault occurs in the AC system, the voltage across the resistor can exceed the voltage threshold.

Example 1:

As shown in Fig. 2, Fig. 2 is a circuit structure diagram of Embodiment 1 of the present utility model. In the figure, the bypass circuit is composed of a rectifier bridge 7, a first thyristor 8, a first overvoltage trigger unit 9, an inductor 10 and a freewheeling diode 11, and the two arms of the rectifier bridge 7 are connected with the adjustable resistance circuit 2 and the state conversion switch circuit 3 in parallel, the rectifier bridge 7 is connected in series with the first thyristor 8 and the inductor 10, the first overvoltage trigger unit 9 is connected in parallel at both ends of the first thyristor 8, and the freewheeling diode 11 is connected in parallel at both ends of the inductor 10.

The bypass circuit 4 is connected in parallel with the DC blocking resistor 5 and the first transfer switch 6 and then connected in series to the neutral point of the transformer. Wherein, the DC blocking resistor 5 plays a role of suppressing the DC neutral point of the transformer, and at the same time grounds the AC neutral point with low impedance. When the first transfer switch 6 is in the closed state, it is the direct grounding operation state; when the first transfer switch 6 is in the open state, it is the resistance operation state. The rectifier bridge 7 plays the role of voltage polarity conversion, regardless of the polarity of the voltage on both sides of the resistor 5 and the state first changeover switch 6, the rectifier bridge 7 ensures that the voltage applied to the first thyristor 8 is connected positively to the anode and negatively to the cathode; When the voltage applied to the first thyristor 8 is higher than the trigger threshold, the first overvoltage trigger unit 9 is turned on and triggers the first thyristor 8 to be turned on; when the first thyristor 8 is turned on, the conduction current excites the inductor 10 And drive the state transfer switch 6 to trip and close; when the current of the first thyristor 8 drops, the freewheeling diode 11 releases the current of the inductor 10 rapidly.

The inductor 10 in FIG. 2 may be a switch closing inductor 101 and a damping inductor 102 connected in series, wherein the switch closing inductor 101 is used to drive the first transfer switch 6 to close by using the first thyristor 8 to conduct current when the fast bypass is started; The damping inductor 102 is used to suppress the rising rate of the conduction current of the first thyristor 8 and protect the first thyristor 8 .

Example 2:

As shown in Fig. 3, Fig. 3 is a circuit structure diagram of Embodiment 2 of the present utility model. It is embodiment 2 of the resistance method suppressing transformer neutral point direct current device. On the basis that other structures are the same as in Embodiment 1, in order to increase the reliability of the device, an overvoltage gap discharge device 12 or a zinc oxide overvoltage breakdown discharge circuit can be added at both ends of the resistor 5, such as at both ends of the resistor 5 A varistor 13 is connected in parallel.

Example 3:

As shown in Fig. 4, Fig. 4 is a circuit structure diagram of Embodiment 3 of the present utility model. When the device is applied to a system with a large neutral point fault current, on the basis of other structures being the same as in Embodiment 1, two or more first thyristors 8 can be operated in parallel to improve the current capability of the device. As shown in FIG. 4 , it is the device for suppressing the neutral point DC current of the transformer when two thyristors, the second thyristor 81 and the third thyristor 82 operate in parallel.

Example 4:

As shown in FIG. 5, FIG. 5 is a circuit structure diagram of Embodiment 4 of the present utility model. On the basis that other structures are the same as in Embodiment 1, a double set of thyristor trigger circuit is adopted, that is, the first overvoltage trigger unit 9 of the thyristor is a double set of second overvoltage trigger unit 91 and a third overvoltage trigger unit 92 connected in parallel, so as to Improve the reliability of overvoltage bypass start.

Example 5:

As shown in FIG. 6, FIG. 6 is a circuit structure diagram of Embodiment 5 of the present utility model. On the basis that other structures are the same as in Embodiment 1, the state changeover switch, that is, the first changeover switch 6, can adopt double switches or single-switch multi-contact switches, that is, the second changeover switch 61 and the third changeover switch 62, to improve the device ability to close fault currents. As shown in Figure 6, it is the device for suppressing the neutral point DC current of the transformer when double switches are used.

Claims (9)

1. an adjustable resistance method suppresses the device of transformer neutral point direct current; It is characterized in that: comprise adjustable resistance loop (2), state switch loop (3) and overvoltage bypass loop (4), be connected between transformer neutral point (1) and the earth electrode after said three loop parallel connections; Described adjustable resistance loop (2) value range is 0 ~ 4 Ω.

2. a kind of adjustable resistance method according to claim 1 suppresses the device of transformer neutral point direct current; It is characterized in that: said overvoltage bypass loop (4) comprises rectifier bridge (7), first thyristor (8), the first overvoltage trigger element (9), inductance (10) and fly-wheel diode (11); Two arms of rectifier bridge (7) and adjustable resistance loop (2), state switch loop (3) are parallelly connected; Rectifier bridge (7) is connected with first thyristor (8), inductance (10); First thyristor (8) two ends are parallel with the first overvoltage trigger element (9), and inductance (10) two ends are parallel with fly-wheel diode (11).

3. a kind of adjustable resistance method according to claim 2 suppresses the device of transformer neutral point direct current, it is characterized in that: said inductance (10) is the switch closure inductance (101) and the damping circuit (102) of series connection.

4. according to the device of claim 2 or 3 described a kind of adjustable resistance methods inhibition transformer neutral point direct currents, it is characterized in that: said adjustable resistance loop (2) is resistance (5) two ends parallel connection overvoltage gap discharge devices (12).

5. according to the device of claim 2 or 3 described a kind of adjustable resistance methods inhibition transformer neutral point direct currents, it is characterized in that said adjustable resistance loop (2) is zinc oxide over-voltage breakdown discharge loops of resistance (5) two ends parallel connection.

6. a kind of adjustable resistance method according to claim 4 suppresses the device of transformer neutral point direct current, it is characterized in that: said adjustable resistance loop (2) is zinc oxide over-voltage breakdown discharge loop of resistance (5) two ends parallel connection.

7. suppress the device of transformer neutral point direct current according to the described a kind of adjustable resistance method of each claim in the claim 1,2,3,6, it is characterized in that: said first thyristor (8) is the thyristor of two or two above parallel runnings.

8. suppress the device of transformer neutral point direct current according to the described a kind of adjustable resistance method of each claim in the claim 1,2,3,6, it is characterized in that: the said thyristor first overvoltage trigger element (9) is the second overvoltage trigger element (91) and the 3rd overvoltage trigger element (92) of two cover parallel connections.

9. a kind of adjustable resistance method according to claim 7 suppresses the device of transformer neutral point direct current, and it is characterized in that: said first change over switch (6) is biswitch or the multifinger switch of single switch.

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