CN104767194B - A kind of high voltage power transmission current conversion station over-pressure safety device - Google Patents

Abstract

An overvoltage protection device for a high-voltage transmission converter station, which suppresses the harm caused by overvoltage in the transmission line by connecting a protection circuit in series on the AC side and a parallel protection circuit at the thyristor valve group, and protects the transmission lines before and after the converter station. The energy generated by the fault can be quickly absorbed to protect the normal operation of the transmission line and realize fault ride-through.

Description

A high voltage transmission converter station overvoltage protection device

technical field

The invention relates to the technical field of overvoltage protection in a high-voltage direct current transmission system, in particular to an overvoltage protection device for a high-voltage transmission converter station.

Background technique

At present, my country's high-voltage direct current transmission system is mainly responsible for the important tasks of long-distance, large-capacity power transmission and regional power grid interconnection. Once the DC transmission system suffers from overvoltage caused by lightning, operation, failure or other reasons, once the equipment insulation breakdown accident causes the DC system to shut down, it may cause the load center to lose large-capacity power supply, and then endanger the regional power grid. The consequences will be very serious, especially the damage to a large-scale AC-DC hybrid system like my country's Southern Power Grid will be unimaginable. In recent years, with the rapid development of domestic DC transmission systems, the number, length and number of converter stations of transmission lines put into operation have increased sharply, and the possibility of accidents caused by DC line overvoltages has also increased. The research on the overvoltage of the DC transmission system is the basis and basis for determining the insulation coordination of the system. The research on the overvoltage characteristics and the verification of the insulation level of the HVDC transmission system that is under construction or has been put into actual operation is of great importance to the safety of the system. Stable operation and reducing system construction and maintenance costs are of great significance, especially for accelerating the localization of overvoltage protection equipment in my country's DC transmission system and improving the reliability of domestic equipment.

When a unipolar conductor is grounded, an induced overvoltage will be induced on the sound pole. At this time, "progressive waves" are generated on the DC line, and these "progressive waves" are refracted and reflected between the fault point and the two ends of the line, which will cause a relatively high overvoltage. If the nature of the connection part of the line is different, the resulting overvoltage is also different. When the line is terminated with an inductive impedance, the overvoltage caused by the middle of the line (near the fault point) is low, but a high overvoltage will appear at both ends of the line; on the contrary, if the line is terminated with a capacitive impedance, the line fault The overvoltage near the point is high, while the overvoltage at both ends is very low. According to the research results of the existing DC transmission system, the operating overvoltage on the DC healthy pole is about 1.7 times when the single-pole conductor is grounded on the bipolar overhead line.

The overvoltage on the DC side of the converter station usually has the AC side operating overvoltage transmitted to the converter through the converter transformer: the short circuit between the outlet of the valve side of the converter transformer and the converter valve to ground, due to the discharge of the DC filter capacitor and The inrush of AC current will generate operating overvoltage on the converter and DC neutral bus; the operating overvoltage of the DC line; when bipolar operation occurs, the grounding of the unipolar wire will generate operating overvoltage on the healthy pole; DC When starting at full voltage, due to the switching action of the converter, the operating overvoltage generated on the DC transmission line and so on.

When the converter is switched on and off, both ends of the converter valve will bear a large operating overvoltage, and the converter valve usually uses a thyristor device, and its voltage tolerance level is limited, so overvoltage damage to the converter will often occur. device.

Contents of the invention

Aiming at the deficiencies in the prior art, the present invention provides an overvoltage protection device for a high-voltage transmission converter station, which suppresses the overvoltage caused by the overvoltage in the transmission line by connecting a protection circuit in series on the AC side and a protection circuit in parallel at the thyristor valve group. harm.

Converter valve, also known as thyristor valve (Thynstor Valve), is the core equipment of direct current transmission, and is a kind of power equipment based on thyristor series technology for electric energy form conversion. Modern large-scale high-voltage direct current transmission projects use thyristors as the main components to form 6-pulse or 12-pulse bridge converters. Each converter bridge arm is generally composed of dozens or even hundreds of thyristors in series, that is, thyristor valves. .

The metal oxide voltage limiter can usually withstand the action of voltage under normal and overload operating conditions; it can withstand the effect of swing current; it can limit the overvoltage at both ends below a certain level; the metal oxide voltage limiter should have enough capacity to withstand the effects of energy and current injected during system faults

The HVDC transmission line is mainly composed of three parts: the sending-end converter station where the rectifier that converts AC to DC is located, the transmission line, and the receiving-end converter station where the inverter that converts DC to AC is located.

The converter station at the sending end from the AC to the intermediate DC bus has an AC power supply system, a series protection device on the AC side, a converter transformer, a converter valve and a converter valve group protection device.

The series protection device on the AC side consists of a series capacitor, a metal oxide voltage limiter, a spark gap and a bypass switch. The capacitors, the metal oxide voltage limiter, the spark gap and the bypass switch are connected in parallel. The bypass switch can Choose devices with automatic shutdown functions such as circuit breakers and overcurrent protectors.

During normal operation, the bypass switch is closed, that is, the circuit breaker is closed, the AC current flows through the bypass switch, and the electric energy is converted and transmitted through the converter transformer and the converter valve. When there is a large current in the transmission line, such as The overload current caused by the induction current generated by lightning or the short circuit caused by the component failure in the line. At this time, the bypass switch, such as a circuit breaker, automatically disconnects in response to the overload current. At this time, the capacitor and the metal oxide voltage limiter And the spark gap is connected to the circuit. The voltage in the circuit is loaded on both ends of the capacitor. When the voltage loaded on both ends of the capacitor is low at this time, that is, when the conduction voltage of the metal oxide voltage limiter is not reached, the current flows through the capacitor normally. Power supply is provided to the converter transformer and converter valve.

When the voltage loaded on both ends of the capacitor reaches a certain threshold, such as 1.8 times the rated voltage, at this time, the metal oxide voltage limiter reaches the turn-on voltage and turns on, and discharges a large current based on its operating characteristics, thereby eliminating the When the voltage drops below the conduction voltage value of the metal oxide voltage limiter, the metal oxide voltage limiter is not turned on, showing disconnection. At this time, the capacitor works normally, and the power transmission of the load-carrying circuit , when the overvoltage is induced again, work again according to the above process.

When a larger overvoltage occurs in the transmission line, such as 5 times or more than the rated voltage, and lasts for a long time, due to the limitation of the withstand voltage level of the metal oxide voltage limiter, it may not be able to withstand the voltage Or when the speed of high-current discharge cannot eliminate the overvoltage, the spark gap connected in parallel with the capacitor and the metal oxide voltage limiter is turned on, so as to perform rapid discharge, thereby eliminating the overvoltage.

When the voltage level drops to a certain value, such as below 5 times the rated voltage, the spark gap does not conduct, and the metal oxide voltage limiter conducts a large current discharge. When the voltage drops below the conduction of the metal oxide voltage limiter When the voltage value is applied, the metal oxide voltage limiter does not conduct, and it is disconnected. At this time, the capacitor works normally, and the power transmission of the carrying circuit. When the overvoltage is induced again, it will work again according to the above process, so that the The AC side realizes series protection.

The current limiting value of the bypass switch and the capacity of the capacitor, the conduction voltage of the metal oxide current limiter, the withstand voltage level, the conduction voltage of the spark gap, and the gap are set accordingly, for example, at 1.0-1.2 times the rated voltage , the protection device does not operate. When the rated voltage is 1.2-1.8 times, the bypass switch is disconnected. When the rated voltage is 1.8-5 times, the metal oxide voltage limiter is used for large current discharge to eliminate the overvoltage. When 5 When the overvoltage is more than twice or the overvoltage lasts for a certain period of time, the discharge will be carried out by the spark gap.

The protection device for the converter valve group is connected in series with the metal oxide voltage limiter and the spark gap, and at the same time, the metal oxide voltage limiter is connected in series with the spark gap and then connected in parallel with the thyristor.

During normal operation, the thyristor valve group converts electric energy. Since the metal oxide voltage limiter is connected in series with the spark gap, the protection circuit connected in parallel with the thyristor is not conducting and the leakage current is small.

When a short circuit on the DC side or a fault such as lightning strike or grounding occurs, the voltage on the DC side exceeds the rated value, and the voltage across the thyristor rises. When the voltage threshold is reached, the spark gap is turned on. The two ends of the voltage regulator, and the metal oxide voltage limiter enters the inflection point, and discharges with a large current, thereby absorbing the energy of the circuit. At this time, the maximum discharge current is limited by the spark gap, so that the current can be quickly discharged.

At the same time, based on the series structure of the metal oxide voltage limiter and the spark gap, the discharge between the two DC busbars is avoided, that is, when the voltage drops to a certain level, the metal oxide voltage limiter shows a certain impedance value , so that the discharge voltage can change smoothly.

At the same time, part of the circuit energy is consumed by the metal oxide voltage limiter to improve the withstand voltage level of the parallel structure. After discharging, the DC voltage drops, the voltage at both ends of the metal oxide voltage limiter returns to the residual voltage, and the spark gap stops discharging , at this time the energy absorption ends and normal operation resumes.

When carrying out the energy absorption protection of the converter valve group, according to the withstand voltage level of the thyristor, the metal oxide voltage limiter and the spark gap, the corresponding settings are made, for example, the protection voltage of the metal oxide voltage limiter and the spark gap can be set At 1.5 times the rated voltage, the voltage change at both ends of the thyristor can be carried by the metal voltage limiter and the spark gap in series to prevent malfunction. At the same time, when the overvoltage comes, the two can work at the same time to quickly absorb the overvoltage energy. .

Through the setting of the series protection device on the AC side and the protection device of the converter valve group, the energy generated by the fault in the transmission line before and after the converter station can be quickly absorbed, the normal operation of the transmission line is protected, and the fault ride-through is realized.

Description of drawings

Figure 1 is the structure diagram of HVDC transmission line

Figure 2 is a structural diagram of the HVDC transmission station

Figure 3 is a structural diagram of the series protection device on the AC side

Fig. 4 is a structural diagram of a converter valve protection device.

Detailed ways

An overvoltage protection device for a high-voltage transmission converter station, which suppresses the harm caused by overvoltage in a transmission line by connecting a protection circuit in series on the AC side and a protection circuit in parallel at a thyristor valve group.

Converter valve, also known as thyristor valve (Thynstor Valve), is the core equipment of direct current transmission, and is a kind of power equipment based on thyristor series technology for electric energy form conversion. Modern large-scale high-voltage direct current transmission projects use thyristors as the main components to form 6-pulse or 12-pulse bridge converters. Each converter bridge arm is generally composed of dozens or even hundreds of thyristors in series, that is, thyristor valves. .

The metal oxide voltage limiter can usually withstand the action of voltage under normal and overload operating conditions; it can withstand the effect of swing current; it can limit the overvoltage at both ends below a certain level; the metal oxide voltage limiter should have enough capacity to withstand the effects of energy and current injected during system faults

As shown in Figure 1, the HVDC transmission line is mainly composed of three parts: a rectifier that converts AC to DC, a transmission line, and an inverter that converts DC to AC.

As shown in Figure 2, the converter station at the sending end of the AC-DC bus has an AC power supply system, an AC side series protection device A, a converter transformer, a converter valve and a converter valve group protection device V.

As shown in Figure 3, the series protection device on the AC side consists of a series capacitor, a metal oxide voltage limiter, a spark gap, and a bypass switch, and the capacitors, metal oxide voltage limiters, spark gaps, and bypass switches are connected in parallel Connection, bypass switch can choose such as circuit breaker, over-current protector and other devices with automatic shutdown function.

During normal operation, the bypass switch is closed, that is, the circuit breaker is closed, the AC current flows through the bypass switch, and the electric energy is converted and transmitted through the converter transformer and the converter valve. When there is a large current in the transmission line, such as The overload current caused by the induction current generated by lightning or the short circuit caused by the component failure in the line. At this time, the bypass switch, such as a circuit breaker, automatically disconnects in response to the overload current. At this time, the capacitor and the metal oxide voltage limiter And the spark gap is connected to the circuit. The voltage in the circuit is loaded on both ends of the capacitor. When the voltage loaded on both ends of the capacitor is low at this time, that is, when the conduction voltage of the metal oxide voltage limiter is not reached, the current flows through the capacitor normally. Power supply is provided to the converter transformer and converter valve.

When the voltage loaded on both ends of the capacitor reaches a certain threshold, such as 1.8 times the rated voltage, at this time, the metal oxide voltage limiter reaches the turn-on voltage and turns on, and discharges a large current based on its operating characteristics, thereby eliminating the When the voltage drops below the conduction voltage value of the metal oxide voltage limiter, the metal oxide voltage limiter is not turned on, showing disconnection. At this time, the capacitor works normally, and the power transmission of the load-carrying circuit , when the overvoltage is induced again, work again according to the above process.

When a larger overvoltage occurs in the transmission line, such as 5 times or more than the rated voltage, and lasts for a long time, due to the limitation of the withstand voltage level of the metal oxide voltage limiter, it may not be able to withstand the voltage Or when the speed of high-current discharge cannot eliminate the overvoltage, the spark gap connected in parallel with the capacitor and the metal oxide voltage limiter is turned on, so as to perform rapid discharge, thereby eliminating the overvoltage.

When the voltage level drops to a certain value, such as below 5 times the rated voltage, the spark gap does not conduct, and the metal oxide voltage limiter conducts a large current discharge. When the voltage drops below the conduction of the metal oxide voltage limiter When the voltage value is applied, the metal oxide voltage limiter does not conduct, and it is disconnected. At this time, the capacitor works normally, and the power transmission of the carrying circuit. When the overvoltage is induced again, it will work again according to the above process, so that the Series protection is implemented on the AC side.

The current limiting value of the bypass switch and the capacity of the capacitor, the conduction voltage of the metal oxide current limiter, the withstand voltage level, the conduction voltage of the spark gap, and the gap are set accordingly, for example, at 1.0-1.2 times the rated voltage , the protection device does not operate. When the rated voltage is 1.2-1.8 times, the bypass switch is disconnected. When the rated voltage is 1.8-5 times, the metal oxide voltage limiter is used for large current discharge to eliminate the overvoltage. When 5 When the overvoltage is more than twice or the overvoltage lasts for a certain period of time, the discharge will be carried out by the spark gap.

As shown in Figure 4, the protection device of the converter valve group is connected in series with the metal oxide voltage limiter and the spark gap, and at the same time, the metal oxide voltage limiter is connected in series with the spark gap and then connected in parallel with the thyristor.

During normal operation, the thyristor valve group converts electric energy. Since the metal oxide voltage limiter is connected in series with the spark gap, the protection circuit connected in parallel with the thyristor is not conducting and the leakage current is small.

When a short circuit on the DC side or a fault such as lightning strike or grounding occurs, the voltage on the DC side exceeds the rated value, and the voltage across the thyristor rises. When the voltage threshold is reached, the spark gap is turned on. The two ends of the voltage regulator, and the metal oxide voltage limiter enters the inflection point, and discharges with a large current, thereby absorbing the energy of the circuit. At this time, the maximum discharge current is limited by the spark gap, so that the current can be quickly discharged.

At the same time, based on the series structure of the metal oxide voltage limiter and the spark gap, the discharge between the two DC busbars is avoided, that is, when the voltage drops to a certain level, the metal oxide voltage limiter shows a certain impedance value , so that the discharge voltage can change smoothly.

At the same time, part of the circuit energy is consumed by the metal oxide voltage limiter to improve the withstand voltage level of the parallel structure. After discharging, the DC voltage drops, the voltage at both ends of the metal oxide voltage limiter returns to the residual voltage, and the spark gap stops discharging , at this time the energy absorption ends and normal operation resumes.

When carrying out the energy absorption protection of the converter valve group, according to the withstand voltage level of the thyristor, the metal oxide voltage limiter and the spark gap, the corresponding settings are made, for example, the protection voltage of the metal oxide voltage limiter and the spark gap can be set At 1.5 times the rated voltage, the voltage change at both ends of the thyristor can be carried by the metal voltage limiter and the spark gap in series to prevent malfunction. At the same time, when the overvoltage comes, the two can work at the same time to quickly absorb the overvoltage energy. .

Through the setting of the series protection device on the AC side and the protection device of the converter valve group, the energy generated by the fault in the transmission line before and after the converter station can be quickly absorbed, the normal operation of the transmission line is protected, and the fault ride-through is realized.

The above description is only the preference of the present invention and is not intended to limit the present invention. Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalent technologies, the present invention also intends to include these modifications and variations.

Claims (2)

1. a kind of high voltage power transmission current conversion station over-pressure safety device, which is characterized in that HVDC transmission line is mainly by three parts It forms, is respectively：Exchange is converted into the rectifier of direct current, transmission line of electricity and the inverter that direct current is converted to exchange；Its The sending end current conversion station of middle exchange to intermediate dc bus has ac power supply system, exchange side serial protective device, change of current transformation Device, converter valve and change of current valve group protective device；Exchange side serial protective device has series capacitor, metal oxide pressure limiting Device, spark gap and by-pass switch are constituted, between capacitor, metal oxide pressure-limiting device, spark gap and by-pass switch It is connected in parallel two-by-two；Change of current valve group protective device is connected in series with by metal oxide pressure-limiting device and spark gap, meanwhile, metal oxygen Compound voltage limiter is connected in parallel after being connected in series with spark gap with thyristor；

Exchange side serial protective device is closed by-pass switch in normal work, and alternating current is circulated by by-pass switch, And the transformation that electric energy is carried out by converter power transformer, converter valve is transmitted, when larger electric current occurs in transmission line of electricity, such as lightning stroke is produced Overload current caused by short circuit caused by element fault in raw induced current or circuit, at this point, by-pass switch, in response to the mistake It carries electric current to disconnect automatically, with metal oxide pressure-limiting device and spark gap access circuit, the voltage in circuit adds capacitor Capacitance both ends are loaded in, the voltage at capacitance both ends is relatively low when loading at this time, i.e. the not up to electric conduction of metal oxide pressure-limiting device When pressure, electric current carries out normal power supply by capacitor, is supplied to converter power transformer and converter valve,

When voltage of the load at capacitance both ends reaches certain threshold value V1, at this point, metal oxide pressure-limiting device reaches conducting voltage To be connected, and be large current discharge based on its working characteristics, to eliminate the overvoltage in circuit, when voltage drop to it is low When the turn-on voltage of metal oxide pressure-limiting device, metal oxide pressure-limiting device is not turned on, and shows as disconnecting, at this point, capacitance Device works normally, the electric energy transmission of bearer circuit,

When occurring overvoltage V2 in transmission line of electricity, V2 is more than V1, and when the duration is longer, due to metal oxide pressure-limiting device Stress levels limitation, when can not necessarily bear the speed of the voltage or heavy-current discharge can not eliminate the overvoltage, The spark gap being connected in parallel with capacitor and metal oxide pressure-limiting device is connected, should to eliminate to carry out repid discharge Overvoltage,

When voltage class drops to overvoltage V2 or less, spark gap is not turned on, and metal oxide pressure-limiting device conducting carries out big Current discharge, when voltage drops below the turn-on voltage of metal oxide pressure-limiting device, metal oxide pressure-limiting device is not led It is logical, it shows as disconnecting, at this point, capacitor works normally, the electric energy transmission of bearer circuit,

The cut-off current of by-pass switch and the capacity of capacitor, the conducting voltage of metal oxide current limiter, stress levels, spark The conducting voltage in gap, gap are accordingly arranged；

The threshold value V1 is 1.8 times of rated voltage, and the overvoltage V2 is 5 times or more of rated voltage.

2. a kind of high voltage power transmission current conversion station over-pressure safety device as described in claim 1, which is characterized in that change of current valve unit protection Device is carried out the transformation of electric energy by thyristor controlled series compensation, due to metal oxide pressure-limiting device and spark gap string in normal work Connection, therefore show the protection circuit in parallel with thyristor and be not turned on, and leakage current is smaller,

When dc-side short-circuit or lightning stroke, earth fault occurs, DC voltage overrate, thyristor both end voltage liter Height, when reaching voltage threshold, spark gap conducting, thyristor both end voltage load at this time is the two of metal oxide pressure-limiting device End, and metal oxide pressure-limiting device enters inflection point, and be large current discharge, to absorption circuit energy, at this point, maximum electric discharge Electric current is limited by spark gap, thus allows for quickly releasing for electric current,

Meanwhile the cascaded structure based on metal oxide pressure-limiting device and spark gap so that between two busbares for avoiding direct current It discharges, i.e., when metal oxide pressure-limiting device drops to a certain degree under voltage, certain impedance value is shown, to make Discharge voltage can smooth change,

Meanwhile partial circuit energy is consumed by metal oxide pressure-limiting device, the stress levels of the parallel-connection structure are improved, are being carried out After electric discharge, DC voltage declines, and metal oxide pressure-limiting device both end voltage returns to residual voltage, and spark gap stops electric discharge, inhales at this time It can terminate, restore normal operation,

In the energy-absorbing protection for carrying out change of current valve group, according to the stress levels of thyristor, metal oxide pressure-limiting device and spark Gap is accordingly arranged,

The protection voltage of the metal oxide pressure-limiting device and spark gap is 1.5 times of rated voltages.