CN106972476A - A kind of DC converter station divider secondary side overvoltage protection system and method - Google Patents

Abstract

The invention discloses a secondary side overvoltage protection system of a voltage divider in a DC converter station, comprising: a resistance-capacitance voltage dividing unit, a gas discharge tube and a piezoresistor, and the resistance-capacitance voltage dividing unit is used to The ratio divides the high voltage into a low voltage; the gas discharge tube is used to transmit the low voltage of the system on the secondary side of the DC voltage divider together with the varistor when the system is operating normally; In the state, the overvoltage at both ends of the gas discharge tube exceeds the discharge voltage of the gas discharge tube. When the gap breaks down, a leakage channel is provided for the circuit; the piezoresistor is used to communicate with the The low voltage of the gas discharge tube common transmission system on the secondary side of the DC voltage divider; it is used to generate a residual voltage when the overvoltage at both ends of the gas discharge tube exceeds the discharge voltage of the gas discharge tube under transient conditions. Voltage drop, to ensure that the voltage value of the low-voltage circuit is greater than or equal to the minimum working voltage of the secondary circuit side of the DC voltage divider.

Description

A secondary side overvoltage protection system and method of a voltage divider in a DC converter station

technical field

The present invention relates to the field of overvoltage protection of converter stations, and more specifically, to a secondary side overvoltage protection system and method of a voltage divider of a DC converter station.

Background technique

The converter station is the hub of the DC power system. Once a lightning damage accident occurs, it may cause a large-scale power outage and the impact will be very serious. Therefore, the converter station requires reliable lightning protection measures. The lightning damage of the converter station comes from two aspects. One is that the lightning directly strikes the converter station and causes damage to the equipment in the station, which is referred to as direct lightning strike; the other is that the lightning strikes the tower and lightning protection line of the transmission line, causing insulator flashover ( Counterattack), or the lightning wave generated by directly hitting the wire (shielding), the wave is transmitted to the converter station along the transmission line, and the lightning overvoltage is generated on the converter station equipment, causing the insulation damage of the equipment, which is referred to as intrusion wave. If the converter station is subjected to direct lightning strikes or lightning intrusion waves generated by nearby lightning strikes, it may cause the voltage of the grounding grid in the station to rise, causing the secondary side protection of the equipment in the station to operate, affecting the safe operation of the system. Let's take a real accident as an example to illustrate.

September 19, 2015 at 21:58:00:206, Jinsu DC Jinping Station OWS reported "Line Fault Undervoltage Protection InitDown", 21:58:00:233, pole I DC line protection tripped at startup logic, 21 :58:00:247, pole II DC line protection restart logic trip, pole I and pole II are blocked successively. The fault inspection shows that the pole control fault recording shows that the DC voltage of pole I and pole II drops to 0 instantaneously. After about 4ms, the low-voltage current limiting function makes the α angle increase, and the DC current decreases. After about 80ms, the DC undervoltage protection action; The fault location device is activated but there is no ranging result. The preliminary analysis results show that there was continuous lightning and rainstorm in Jinping Station when the fault occurred, and the DC current did not change significantly when the DC voltage suddenly changed. It can be judged that the DC line and DC primary equipment did not fail. After checking the DC partial voltage of pole I and pole II There is no common link part of the converter, only the common part of the grounding system exists. Therefore, the analysis judged that lightning caused the voltage of the grounding grid in the station to rise, and at the same time caused the breakdown of the overvoltage protection in the gap of the DC voltage divider circuit of pole I and pole II, and failed to extinguish the arc, so that the DC voltage could not be established at all, and then caused DC line undervoltage protection action, resulting in pole I, pole II bipolar blocking.

Therefore, it is necessary to conduct research and analysis on the overvoltage condition of the DC voltage divider in the converter station and the action characteristics of the protection device under the action of the overvoltage, and design an overvoltage protection system for the DC voltage divider in the converter station to solve the problem of commutation The problem that the station cannot operate reliably.

Contents of the invention

The invention provides an overvoltage protection system for the secondary side of a voltage divider of a DC converter station to solve the problem that the converter station cannot operate reliably.

In order to solve the above problems, according to one aspect of the present invention, a secondary side overvoltage protection system of a voltage divider in a DC converter station is provided, the system includes: a resistance-capacitance voltage division unit, a gas discharge tube and a piezoresistor,

The resistance-capacitance voltage dividing unit is used to divide the high voltage into a low voltage according to the voltage division ratio, and the resistance-capacitance voltage dividing unit includes: a high-voltage arm terminal composed of a first resistor and a first capacitor connected in parallel, a second resistor and a The low-voltage arm end formed by the parallel connection of the second capacitor, and the high-voltage arm end and the low-voltage arm end are connected in series;

The gas discharge tube is connected in series with the piezoresistor and then connected in parallel with the low-voltage arm end to form a low-voltage circuit, which is used to transmit the system with the piezoresistor in the secondary voltage of the DC voltage divider when the system is in normal operation. The low voltage on the side; it is used to provide a leakage channel for the circuit when the overvoltage at both ends of the gas discharge tube exceeds the discharge voltage of the gas discharge tube under transient conditions, and the gap breaks down;

The varistor is used to jointly transmit the low voltage of the system on the secondary side of the DC voltage divider with the gas discharge tube when the system is in normal operation; it is used for the overvoltage at both ends of the gas discharge tube under transient conditions When the discharge voltage of the gas discharge tube is exceeded, a residual voltage drop is generated when the gap breaks down, ensuring that the voltage value of the low-voltage circuit is greater than or equal to the minimum working voltage of the secondary circuit side of the DC voltage divider.

Preferably, the minimum working voltage is 35V.

Preferably, the piezoresistor whose absolute value of the difference between the residual voltage drop value and the minimum operating voltage at the secondary circuit side of the DC voltage divider is not less than a preset threshold is selected in series with the gas discharge tube.

Preferably, the preset threshold is at least 1V.

Preferably, the system further includes: a low-voltage voltage measurement unit and a protection trigger unit,

The low-voltage measurement unit is connected in parallel with the gas discharge tube and the branch of the piezoresistor in series, and is used to measure the low voltage after the DC voltage divider divides the voltage, and obtain the low voltage measurement value;

The protection triggering unit is connected with the low-voltage measuring unit, and is used for triggering an under-voltage protection action of the system when the measured low-voltage value is lower than the minimum working voltage of the secondary circuit side of the DC voltage divider.

According to another aspect of the present invention, a secondary side overvoltage protection method of a voltage divider of a DC converter station is provided, the method comprising:

The input end of the secondary circuit side of the DC voltage divider receives high voltage;

The DC voltage divider divides the high voltage into a low voltage according to the voltage division ratio;

When the system is working normally, the gas discharge tube and the piezoresistor jointly transmit the low voltage of the system on the secondary side of the DC voltage divider; under transient conditions, the overvoltage at both ends of the gas discharge tube exceeds the discharge voltage of the gas discharge tube , When the gap breaks down, the gas discharge tube provides a leakage channel for the circuit, and uses the residual voltage drop generated on the varistor to ensure that the voltage value of the low-voltage circuit is greater than or equal to the minimum working voltage of the secondary circuit side of the DC voltage divider.

Preferably, the minimum working voltage is 35V.

Preferably, the piezoresistor whose absolute value of the difference between the residual voltage drop value and the minimum operating voltage at the secondary circuit side of the DC voltage divider is not less than a preset threshold is selected in series with the gas discharge tube.

Preferably, the preset threshold is at least 1V.

Preferably, wherein said method further comprises:

Measure the low voltage after the DC voltage divider is divided to obtain the low voltage measurement value;

Judging whether to trigger the undervoltage protection action of the system according to the low voltage measurement value, if the low voltage measurement value is less than the minimum operating voltage of the secondary circuit side of the DC voltage divider, then trigger the undervoltage protection action of the system; otherwise , does not trigger.

The beneficial effects of the present invention are:

In the present invention, the varistor is connected in series in the branch where the gas discharge tube is located. Under transient conditions, when the overvoltage at both ends of the gas discharge tube exceeds its discharge voltage and the gap breaks down, a certain residual voltage can be generated on the varistor. Voltage drop, the voltage of the gas discharge tube plus varistor branch will not drop to 0, so it will not cause the DC line undervoltage protection action, which can effectively avoid the occurrence of bipolar blocking accidents; at the same time, effectively realize the DC voltage divider When the secondary side is subjected to the overvoltage of the same polarity, the rapid release of the overvoltage and the rapid recovery of the loop voltage ensure the stable operation of the DC voltage divider.

Description of drawings

A more complete understanding of the exemplary embodiments of the present invention can be had by referring to the following drawings:

Fig. 1 is the structural representation of the connection of the gas discharge tube on the secondary side of the existing DC voltage divider;

2 is a schematic structural diagram of a DC voltage divider secondary side overvoltage protection system according to an embodiment of the present invention; and

Fig. 3 is a flow chart of a secondary side overvoltage protection method 300 of a DC voltage divider according to an embodiment of the present invention.

detailed description

Exemplary embodiments of the present invention will now be described with reference to the drawings; however, the present invention may be embodied in many different forms and are not limited to the embodiments described herein, which are provided for the purpose of exhaustively and completely disclosing the present invention. invention and fully convey the scope of the invention to those skilled in the art. The terms used in the exemplary embodiments shown in the drawings do not limit the present invention. In the figures, the same units/elements are given the same reference numerals.

Unless otherwise specified, the terms (including scientific and technical terms) used herein have the commonly understood meanings to those skilled in the art. In addition, it can be understood that terms defined by commonly used dictionaries should be understood to have consistent meanings in the context of their related fields, and should not be understood as idealized or overly formal meanings.

Accidents of both poles being blocked and out of service due to lightning strikes in the vicinity of DC converter stations occur from time to time. The analysis results show that the voltage of the ground grid in the station is raised, and at the same time, it causes the secondary protection gap of the DC voltage divider of pole 1 and pole 2, that is, gas discharge The tube was broken down and failed to extinguish the arc, so that the DC voltage could never be established, which in turn caused the DC line undervoltage protection action, resulting in bipolar blocking of pole I and pole II. FIG. 1 is a schematic structural diagram of a gas discharge tube connection on a secondary side of a conventional DC voltage divider. As shown in Figure 1, when the DC voltage divider in the converter station suffers from overvoltage, the gas discharge tube (i.e., the protective gap) shown will be broken down and cannot be extinguished, so that the DC voltage cannot be established all the time, and then Cause DC line undervoltage protection action. Based on this, research and analysis are carried out on the overvoltage condition of the DC voltage divider in the converter station and the action characteristics of the protection device under the action of the overvoltage, and a new protection measure for the DC voltage divider using a gas discharge tube plus a varistor is proposed.

Fig. 2 is a schematic structural diagram of a secondary side overvoltage protection system of a DC voltage divider according to an embodiment of the present invention. As shown in Figure 2, the secondary side overvoltage protection system of the DC voltage divider is used to protect the secondary side voltage circuit of the DC voltage divider. When the system is operating normally, the secondary side voltage of the DC voltage divider is determined by The gas discharge tube and the varistor share the load, but because the current is very small, the varistor presents a high resistance characteristic, the voltage that the varistor bears is very small, and the voltage is almost all applied to the gas discharge tube; in the transient state, when The overvoltage at both ends of the gas discharge tube exceeds its discharge voltage. When the gap breaks down, a current flows and a certain residual voltage drop is generated on the varistor. The voltage of the gas discharge tube plus the varistor branch will not be less than the specified The minimum working voltage of the secondary circuit side of the DC voltage divider is 0, so it will not cause the DC line undervoltage protection action, which can effectively avoid the occurrence of bipolar blocking accidents. The new protection measures of the gas discharge tube and the varistor can effectively realize the rapid release of the overvoltage and the rapid recovery of the circuit voltage when the secondary side of the DC voltage divider is subjected to the overvoltage of the same polarity, and ensure the stable operation of the DC voltage divider. At the same time, when protecting the secondary side of the DC voltage divider in the converter station, it can ensure that the secondary side voltage of one of the DC voltage dividers in the converter station can quickly recover to the normal voltage value when the converter station is subjected to overvoltage, avoiding damage caused by protection. The bipolar blocking accident caused by malfunction is of great significance to ensure the reliable operation of the converter station. The secondary side overvoltage protection system of the DC voltage divider includes: a resistance-capacitance voltage division unit, a gas discharge tube and a piezoresistor.

Preferably, the resistance-capacitance voltage dividing unit is used to divide the high voltage into a low voltage according to the voltage division ratio, and the resistance-capacity voltage division unit includes: a high-voltage arm end composed of a first resistor and a first capacitor connected in parallel, and a second Two resistors and a second capacitor are connected in parallel to form a low-voltage arm end, and the high-voltage arm end and the low-voltage arm end are connected in series.

Preferably, the gas discharge tube is connected in series with the piezoresistor and then connected in parallel with the low voltage arm end to form a low voltage circuit, which is used to transmit the voltage in the DC voltage divider of the system together with the piezoresistor when the system is in normal operation. Low voltage on the secondary side; it is used to provide a leakage channel for the circuit when the overvoltage at both ends of the gas discharge tube exceeds the discharge voltage of the gas discharge tube under transient conditions, and the gap breaks down. Wherein, when the system is in normal operation, the voltage on the secondary side of the voltage divider is almost all applied to the gas discharge tube, so as to avoid accelerated aging of the varistor due to long-term operating voltage.

Preferably, the piezoresistor is used to jointly transmit the low voltage of the system on the secondary side of the DC voltage divider with the gas discharge tube when the system is in normal operation; When the overvoltage exceeds the discharge voltage of the gas discharge tube, when the gap breaks down, a residual voltage drop is generated to ensure that the voltage value of the low-voltage circuit is greater than or equal to the minimum working voltage of the secondary circuit side of the DC voltage divider. Preferably, the minimum working voltage is 35V. Preferably, the piezoresistor whose absolute value of the difference between the residual voltage drop value and the minimum operating voltage at the secondary circuit side of the DC voltage divider is not less than a preset threshold is selected in series with the gas discharge tube. Preferably, the preset threshold is at least 1V. When the system is running normally, the voltage is almost all applied to the gas discharge tube, and the varistor presents a high resistance characteristic and withstands a small voltage. In a transient state, the gap breaks down, and a current flows, causing a certain residual voltage drop on the varistor, and the voltage of the gas discharge tube plus the varistor branch will not be less than the secondary circuit of the DC voltage divider Therefore, it will not cause the DC line undervoltage protection action, which can effectively avoid the occurrence of bipolar blocking accidents. Considering the operation mode of the single valve group of the DC system, the normal minimum working voltage of the secondary circuit of the DC voltage divider is 35V, and the varistor should be matched with it, and the component with a residual voltage value greater than 35V should be selected and the protection gap, that is, the gas discharge tube should be installed in series .

Preferably, the system further includes: a low-voltage voltage measurement unit and a protection trigger unit,

The low-voltage measurement unit is connected in parallel with the branch circuit after the gas discharge tube and the varistor are connected in series, and is used to measure the low voltage after the voltage division of the DC voltage divider to obtain a low-voltage measurement value; the protection trigger unit , connected to the low-voltage measurement unit, and used to trigger the under-voltage protection action of the system when the low-voltage measurement value is lower than the minimum working voltage of the secondary circuit side of the DC voltage divider.

Fig. 3 is a flow chart of a secondary side overvoltage protection method 300 of a DC voltage divider according to an embodiment of the present invention. As shown in FIG. 3, the DC voltage divider secondary side overvoltage protection method 300 is used to protect the system when an overvoltage occurs on the DC voltage divider secondary side. The method 300 starts from step 301, and Step 301: The input end of the secondary circuit side of the DC voltage divider receives a high voltage.

Preferably, in step 302, the DC voltage divider divides the high voltage into a low voltage according to a voltage division ratio.

Preferably, in step 303, when the system is running normally, the gas discharge tube and the piezoresistor jointly transmit the low voltage of the system on the secondary side of the DC voltage divider; under transient conditions, the overvoltage at both ends of the gas discharge tube exceeds the The discharge voltage of the gas discharge tube, when the gap breaks down, the gas discharge tube provides a discharge channel for the circuit, and uses the residual voltage drop generated on the piezoresistor to ensure that the voltage value of the low-voltage circuit is greater than or equal to the secondary circuit side of the DC voltage divider minimum working voltage. Preferably, the piezoresistor whose absolute value of the difference between the residual voltage drop value and the minimum operating voltage at the secondary circuit side of the DC voltage divider is not less than a preset threshold is selected in series with the gas discharge tube. Preferably, the preset threshold is at least 1V. Preferably, the minimum working voltage is 35V.

Preferably, the method further includes: measuring the low voltage after the voltage division of the DC voltage divider to obtain a low voltage measurement value; judging whether to trigger the undervoltage protection action of the system according to the low voltage measurement value, if the If the low voltage measurement value is less than the minimum working voltage of the secondary circuit side of the DC voltage divider, the undervoltage protection action of the system is triggered; otherwise, it is not triggered.

The secondary side overvoltage protection system 200 of the DC voltage divider in the embodiment of the present invention corresponds to the method 300 for protecting the secondary side of the DC voltage divider in another embodiment of the present invention, and will not be repeated here.

The invention has been described with reference to a small number of embodiments. However, it is clear to a person skilled in the art that other embodiments than the invention disclosed above are equally within the scope of the invention, as defined by the appended patent claims.

Generally, all terms used in the claims are to be interpreted according to their ordinary meaning in the technical field, unless explicitly defined otherwise therein. All references to "a/the/the [means, component, etc.]" are openly construed to mean at least one instance of said means, component, etc., unless expressly stated otherwise. The steps of any method disclosed herein do not have to be performed in the exact order disclosed, unless explicitly stated.

Claims (10)

1. A DC converter station voltage divider secondary side overvoltage protection system, characterized in that the system includes: a resistance-capacitance voltage division unit, a gas discharge tube and a piezoresistor, The resistance-capacitance voltage dividing unit is used to divide the high voltage into a low voltage according to the voltage division ratio, and the resistance-capacitance voltage dividing unit includes: a high-voltage arm terminal composed of a first resistor and a first capacitor connected in parallel, a second resistor and a The low-voltage arm end formed by the parallel connection of the second capacitor, and the high-voltage arm end and the low-voltage arm end are connected in series; The gas discharge tube is connected in series with the piezoresistor and then connected in parallel with the low-voltage arm end to form a low-voltage circuit, which is used to transmit the system with the piezoresistor in the secondary voltage of the DC voltage divider when the system is in normal operation. The low voltage on the side; it is used to provide a leakage channel for the circuit when the overvoltage at both ends of the gas discharge tube exceeds the discharge voltage of the gas discharge tube under transient conditions, and the gap breaks down; The varistor is used to jointly transmit the low voltage of the system on the secondary side of the DC voltage divider with the gas discharge tube when the system is in normal operation; it is used for the overvoltage at both ends of the gas discharge tube under transient conditions When the discharge voltage of the gas discharge tube is exceeded, a residual voltage drop is generated when the gap breaks down, ensuring that the voltage value of the low-voltage circuit is greater than or equal to the minimum working voltage of the secondary circuit side of the DC voltage divider. 2. The system according to claim 1, wherein the minimum operating voltage is 35V. 3. The system according to claim 1, characterized in that the absolute value of the difference between the residual voltage drop value and the minimum operating voltage on the secondary circuit side of the DC voltage divider is selected to be not less than a preset threshold. A resistor is connected in series with the gas discharge tube. 4. The system according to claim 2, wherein the preset threshold is at least 1V. 5. The system according to claim 1, further comprising: a low-voltage voltage measurement unit and a protection trigger unit, The low-voltage measurement unit is connected in parallel with the gas discharge tube and the branch of the piezoresistor in series, and is used to measure the low voltage after the DC voltage divider divides the voltage, and obtain the low voltage measurement value; The protection triggering unit is connected with the low-voltage measuring unit, and is used for triggering an under-voltage protection action of the system when the measured value of the low voltage is lower than the minimum working voltage of the secondary circuit side of the DC voltage divider. 6. A secondary side overvoltage protection method for a voltage divider in a DC converter station, characterized in that the method comprises: The input end of the secondary circuit side of the DC voltage divider receives high voltage; The DC voltage divider divides the high voltage into a low voltage according to the voltage division ratio; When the system is working normally, the gas discharge tube and the piezoresistor jointly transmit the low voltage of the system on the secondary side of the DC voltage divider; under transient conditions, the overvoltage at both ends of the gas discharge tube exceeds the discharge voltage of the gas discharge tube , When the gap breaks down, the gas discharge tube provides a leakage channel for the circuit, and uses the residual voltage drop generated on the varistor to ensure that the voltage value of the low-voltage circuit is greater than or equal to the minimum working voltage of the secondary circuit side of the DC voltage divider. 7. The method according to claim 6, wherein the minimum operating voltage is 35V. 8. The method according to claim 6, characterized in that the absolute value of the difference between the residual voltage drop value and the minimum operating voltage on the secondary circuit side of the DC voltage divider is selected to be not less than a preset threshold. A resistor is connected in series with the gas discharge tube. 9. The method according to claim 8, wherein the preset threshold is at least 1V. 10. The method of claim 6, further comprising: Measure the low voltage after the DC voltage divider is divided to obtain the low voltage measurement value; Judging whether to trigger the undervoltage protection action of the system according to the low voltage measurement value, if the low voltage measurement value is less than the minimum operating voltage of the secondary circuit side of the DC voltage divider, then trigger the undervoltage protection action of the system; otherwise , does not trigger.