WO2014166262A1

WO2014166262A1 - Overvoltage protection device and protection method for alternating-current side of flexible direct-current power transmission system

Info

Publication number: WO2014166262A1
Application number: PCT/CN2013/087804
Authority: WO
Inventors: 荆平; 邱宇峰; 周飞; 陆振纲
Original assignee: 国家电网公司; 国网智能电网研究院
Priority date: 2013-04-09
Filing date: 2013-11-26
Publication date: 2014-10-16
Also published as: CN103296671B; WO2014166130A1; CN103296671A

Abstract

An overvoltage protection device and protection method for an alternating-current side of a flexible direct-current power transmission system. A protection device (7) is connected to the two sides of a grounding resistor (6) at the side of a converter transformer valve in parallel and used for acting to draw away a fault current when a fault occurs in an alternating-current line I (4) or a direct-current line (8) and causes the overvoltage of the alternating-current line or when a valve base controller detects that a short-circuit fault occurs in the alternating-current line I (4), so as to suppress an overvoltage level of the alternating-current line I (4), and protect a valve body (9) of a converter valve. The protection device has rapid action, strong through-flow energy, and large absorbed energy, and can quickly protect the valve body so as to guarantee the secure and stable operation of the flexible direct-current power transmission system.

Description

AC side overvoltage protection device and protection method for flexible direct current transmission system

Technical field

The invention relates to the field of flexible direct current transmission systems, in particular to an alternating current overvoltage protection device and a protection method for a flexible direct current transmission system. Background technique

Flexible DC transmission is a new type of high-voltage direct current transmission technology. It converts traditional alternating current into direct current through a voltage source type converter at a power source such as a hydropower plant or a thermal power plant, and sends the power through a transmission line such as an overhead line or a cable. To the far side of the load. Compared with the traditional high-voltage direct current transmission, it has the advantages of strong controllability, easy trend reversal, and no need for reactive power compensation.

The flexible DC transmission system consists of three parts, including two converter stations at the power supply and load, and a DC cable or overhead line connecting the two stations. The core equipment is a flexible DC converter valve, and its safety needs to pass through the protection system. Get a reliable guarantee.

The converter station has a converter valve 5 switchable between the AC line I and the DC line 8, comprising a power semiconductor valve 9 extending between the AC line I and the DC line 8, through which the power parameters are Conversion between AC and DC. In addition, there is a converter transformer 3 between the AC line I and the AC line II, which is star-connected on the I-valve side of the AC line, and the neutral point is grounded through the resistor 6.

The fault of the flexible DC converter station is generally divided into three types: AC side fault, DC side fault and converter valve fault. The AC and DC side fault protection is protected by the station control system (by voltage transformer, current transformer, AC/DC side filter). , transformer protection and other components are composed).

At present, the DC protection system in the flexible DC converter station mainly judges the DC system fault condition through DC undervoltage and overvoltage protection. When the AC line I single phase or DC line 8 in the converter station has a single pole ground short circuit fault, the AC line I The non-faulty phase voltage may increase to 1.5 to 2 times the normal operating voltage, and the power semiconductor valve 9 may be damaged by excessively high fault voltage.

The conventional power semiconductor valve 9 protection measures are mainly parallel without gap MOV. The protection method generally connects the gapless MOV in parallel at both ends of the power semiconductor valve 9, and utilizes the nonlinear characteristic of the voltage and current of the MOV to consume the energy that may generate an overvoltage through the MOV, thereby protecting the protected device from the overvoltage. However, this method has defects such as difficulty in setting the operating parameters, excessive energy stress, and uncontrollable conduction. And others Traditional line protection devices such as bypass thyristor switches have the disadvantages of complex structure, slow operating time and low overcurrent capability. In view of the above problems, the parallel increase of the protection device of the present invention on the grounding resistance of the converter transformer can effectively reduce the overvoltage of the AC line and avoid damage to the inside of the valve body of the converter valve. Summary of the invention

In view of the deficiencies of the prior art, the object of the present invention is to provide an AC side overvoltage protection device and a protection method suitable for a flexible DC transmission system, and the protection device uses an overvoltage or forced breakdown component to improve overvoltage protection performance, which is good. The problem of over-voltage of the AC line in the station caused by the fault of the flexible DC transmission system is solved.

Usually, when the AC line I has a single-phase ground fault or a DC line has a single-pole ground short-circuit fault, the non-fault phase voltage of the AC line I will rise. According to the predefined voltage, the grounding breakdown gap is adjusted. When the voltage is less than the set breakdown voltage, the protection device is not turned on, the power transmission system can normally transmit power, and once the overvoltage reaches the set value, the protection device is broken down. An electric spark is generated, and a short-circuit current is introduced into the ground through the gap, and the over-voltage of the AC line I is suppressed, and the converter valve body 9 and the AC line I are prevented from being damaged by the overvoltage.

The object of the present invention is achieved by the following technical solutions:

An AC side overvoltage protection device for a flexible DC transmission system, the protection device being included in a flexible DC converter station 1, comprising a flexible DC converter valve 5 switching between an AC line I and a DC line 8, the AC A converter transformer 3 is disposed between the line I and the AC line II, and the converter transformer 3 is star-connected on the side of the AC line I, wherein the neutral point is grounded through the grounding resistor 6; the converter transformer 3 is in the AC line The II network side is a triangular or star connection;

The improvement is that the protection device 7 is connected in parallel to the grounding resistor 6 of the converter transformer 3 for failure of the AC line 1 or the DC line 8 to cause an overvoltage of the AC line 8 or when the valve base controller detects When a short-circuit fault occurs in the AC line I, the operation causes the fault current to be turned on, the AC line I overvoltage level is suppressed, and the converter valve body 9 is protected.

Preferably, the protection device 7 uses a conduction element of a spark gap; the spark gap is grounded. Preferably, the converter valve 5 is a three-phase six-bridge arm structure; each bridge arm is composed of a converter valve body 9; the converter valve body 9 is realized by a semiconductor switching element, including a switchable A semiconductor device (such as IGBT, IGET, IGCT, or GTO) and a diode in anti-parallel with it.

The invention provides an AC side overvoltage protection for a flexible direct current transmission system based on another object. The method is improved in that the protection device 7 for the method is connected in parallel to the grounding resistor 6 of the converter transformer 3; the method comprises the following steps:

A. Detect whether the AC line is faulty, and the fault includes an AC line I single phase, two phase ground fault, a DC line 8 single pole ground fault and a bipolar short fault;

B. When an AC line I single-phase ground fault or DC line single-pole ground fault occurs, the voltage across the spark gap rises to the breakdown voltage, and the spark gap is broken down;

Or when the control device detects an AC line short circuit fault, the control device sends a trigger command to the freewheeling gap to forcibly trigger the freewheeling gap to break the spark gap;

After the spark gap breaks down, the fault current is led to the earth;

C. After the spark gap is broken down, the return status information is sent to the control device, and a lock signal is sent to the converter valve 5 to protect the valve body 9 of the converter valve.

Preferably, the protection configuration method for detecting the voltage overvoltage of the AC line I is that the voltage of the AC line I exceeds a preset value, and the duration also reaches a preset value, the device is immediately turned on, and the valve base controller is immediately blocked. The trigger pulse of the inverter.

Preferably, the preset self-breakdown voltage is not broken down when the voltage of the AC line I is not overvoltage, and is broken down when the AC line I voltage is overvoltage, and the self-breakdown voltage (self-breakdown voltage magnitude) 1.3 to 1.8 times the rated voltage of the line) Determined by theoretical calculations, computer simulations or tests.

Preferably, the magnitude of the discharge current at the time of breakdown (the discharge current at the time of breakdown is 1.5-20 line rated current) is determined by theoretical calculation, computer simulation or experiment.

Preferably, the amount of energy absorbed during breakdown (the amount of energy absorbed during breakdown is the integral of the product of the voltage and current described above) is determined by theoretical calculations, computer simulations or experiments. Compared with the prior art, the beneficial effects achieved by the present invention are:

1. The protection device proposed by the invention has rapid action, strong flow energy, large absorption energy, and can quickly protect the valve body.

2. The control protection device proposed by the invention does not require complicated structure and function.

3. The protection device proposed by the invention has the advantages of simple structure, low cost and easy realization.

4. Reduce the insulation cost of the AC line and the converter valve;

5. Safeguard the safety of AC lines and converter valves; 6. Improve the anti-fault ability of the converter station;

7. Guarantee the safe and stable operation of the flexible DC transmission system. DRAWINGS

1 is a schematic diagram of an AC side overvoltage protection device for a flexible DC transmission system;

Where: 1-flexible DC converter station; 2-AC line II; 3-converter transformer; 4-AC line I; 5- converter valve; 6-resistor; 7-protection device; 8-DC line; Converter valve body. detailed description

The specific embodiments of the present invention are further illustrated in detail below with reference to the accompanying drawings.

The present invention provides an AC line I and a converter valve overvoltage protection device for a flexible DC transmission system. As shown in FIG. 1, the protection device includes a converter valve 5 that switches between an AC line I and a DC line 8, the AC line. A converter transformer 3 is disposed between the I and the AC line II, and the converter transformer 3 is star-connected on the side of the AC line I valve, and the neutral point is grounded through the grounding resistor 6; the converter transformer 3 is in the AC line II The mesh side is a triangular or star connection.

The converter valve 5 is a three-phase six-bridge arm structure; each of the bridge arms is composed of a converter valve body 9; the converter valve body 9 is realized by a semiconductor switching element, including an IGBT and a diode connected in anti-parallel thereto. Its structural form includes, but is not limited to, modular multi-level, H-bridge chain, IGBT series.

The protection device 7 is connected in parallel with the neutral point grounding resistor 6 of the converter transformer for performing an action when the AC line I, the DC line fault causes an overvoltage, or when the valve base controller detects the AC line I fault short circuit. The fault current is turned on, the AC line I overvoltage level is suppressed, and the converter valve body 9 is protected.

The protection device 7 uses a spark gap conduction element; the spark gap is grounded.

The working principle of the spark gap adopted by the present invention is as follows:

The seal gap is automatically triggered when the spark gap is single-phase grounded by AC line I or the single-pole ground fault of the DC line causes its voltage to exceed the self-trigger voltage.

Or when the converter valve control protection device detects a short-circuit fault of the commutated AC line 1 (4), a forced trigger command is issued through the fiber or cable to force the gap to be turned on, so that the short-circuit current flows quickly through the seal gap.

The preset breakdown voltage is required to ensure that the device will not be broken down when the AC line voltage is not over-voltage, and will be broken down when the AC line voltage is over-voltage. The size is configured by theoretical calculation and computer simulation. Or test to determine. The configuration of the discharge current at the time of breakdown is determined by theoretical calculation, computer simulation or experiment. The configuration method of absorbing energy at the time of breakdown is determined by theoretical calculation, computer simulation or experiment.

(1) According to the theoretical calculation, computer simulation and test of flexible DC short-circuit fault, the breakdown voltage, short-circuit current and absorbed energy of the spark gap are determined as follows:

The theoretical calculation process is as follows: The commutation transformer network side AC bus 2 is equivalent to a voltage source ^ and the internal impedance of the series, according to the converter transformer 3 ratio, and consider the transformer valve side leakage reactance X, the voltage source U _s And the internal impedance Z _{s is} converted to the transformer valve side. The power supply electromotive force equivalent to the transformer valve side is: U _s2 = kU _s ', internal resistance is: Z _s2 = k ² Z _{s +} X _L ; The transformer valve side voltage t/ _s2 in normal operation. As an initial condition, according to the characteristic that the voltage of the DC line (or AC line II single phase) at the fault ground is 0, a mathematical expression reflecting the voltage of the non-fault phase of the AC bus in the ground fault process is established, and is calculated according to the initial conditions and expressions. The fault voltage expression of the AC bus in the station;

After the fault, the AC bus non-fault phase voltage u _acn (t) is a function of the converter side valve side initial voltage U _s20 , line impedance z _s2 and ground impedance ^: _αοι (ο = ^ρ([/ _χ2 。,ζ _χ2 , ζ„, ο ; indicates time. The breakdown voltage of the spark gap is determined according to the voltage of each phase to ensure that the breakdown voltage is higher than the peak value of the AC line voltage in the station during normal operation (preferably 1.2 times), which is lower than the AC bus voltage at the time of failure. The maximum value. Combined with the mathematical model of the spark gap, the discharge current and absorbed energy of the spark gap under the fault voltage can be calculated.

The process of computer simulation is as follows: In the computer simulation software, a simulation model including the equivalent system, transformer, DC line in the station, converter valve and ground fault is established. The fault is obtained by single-phase and two-phase ground fault simulation at different times. The amplitude of the non-fault phase voltage of the AC bus in the station. The breakdown voltage of the spark gap is determined according to the voltage to ensure that the breakdown voltage is higher than the AC bus voltage in the station during normal operation (preferably 1.2 times), which is lower than the maximum value of the AC voltage at the time of failure. A model of the spark gap is established in the simulation software to determine the maximum current allowed by the spark gap based on the maximum current flowing through the spark gap at the fault. The energy that the spark gap needs to absorb is determined based on the highest breakdown voltage and the maximum allowable current. (2) Determine the separation distance of the spark gap according to the breakdown voltage; the breakdown voltage U is a function of the gas pressure P and the distance d between the electrodes and the absolute temperature T: U = f (pd / T).

(3) Install one end of the spark gap in parallel on the neutral side grounding resistor 6 on the valve side of the converter transformer, and the other end is grounded;

(4) As shown in Figure 1, when the AC line I single-phase, two-phase grounding or DC line single-pole ground fault occurs, the voltage across the spark gap rises to the breakdown voltage, thereby breaking the spark gap; or when communicating When a short-circuit fault occurs in the line, the voltage measuring device or the protection device monitors the voltage across the spark gap, triggers a spark gap, and forces the spark-free gap to be triggered by the trigger gap to break the spark gap.

(5) The short-circuit fault current flows through the spark gap, suppressing the over-voltage level of the AC line in the station, and avoiding the over-pressure of the valve body of the converter valve;

(6) After the spark gap breaks down, return the status information to the control protection device, and the control protection device detects the spark gap breakdown, and sends a blocking signal to the converter valve.

The invention further relates to a converter valve protection method for an AC line fault, the protection device 7 for the method being connected in parallel to the valve side neutral point grounding resistor 6 of the converter transformer; the method comprising the steps of:

A. Detecting whether the protection device has a fault, the fault includes an AC line I single-phase grounding 10, a direct current line unipolar ground fault 10, and a bipolar short-circuit fault;

B. When the AC line I is single-phase grounded or the DC line is single-pole ground fault, the voltage across the spark gap rises to the breakdown voltage and breaks the spark gap;

In the step B, when the AC line single pole ground fault occurs, that is, the voltage of the spark gap exceeds its self-trigger voltage, the spark gap is automatically triggered.

Or when an AC line short circuit fault occurs, the protection device sends a trigger command to the spark gap to force trigger the freewheeling gap to break the spark gap;

It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not limited thereto. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that the present invention can still be The invention is to be construed as being limited to the scope of the appended claims.

Claims

Rights request

1. An overvoltage protection device for the AC side of a flexible DC transmission system. The protection device is included in a flexible DC converter station (1) and includes a flexible switch between the AC line I (4) and the DC line (8). DC converter valve (5), a converter transformer is provided between the AC line I (4) and the AC line II (2)

(3), the converter transformer (3) is star-connected on the valve side of the AC line I (4), and its neutral point is grounded through the grounding resistor (6); the converter transformer (3) is connected on the AC line II ( 2) The network side is a delta or star connection;

It is characterized in that the protection device (7) is connected in parallel to both ends of the grounding resistance (6) of the converter transformer (3), and is used to protect the AC line (8) when a fault occurs in the AC line (4) or the DC line (8). 8) Overvoltage or when the valve base controller detects a short circuit fault in the AC line I (4), it takes action to divert the fault current, suppress the overvoltage level of the AC line I (4), and protect the converter valve body (9) .

2. The AC side overvoltage protection device according to claim 1, characterized in that the protection device (7) adopts a conductive element such as a spark gap; the spark gap is grounded.

3. The AC side overvoltage protection device according to claim 1, characterized in that the converter valve (5) has a three-phase six-arm structure; each bridge arm is composed of a converter valve body (9) Composition; The converter valve body (9) is implemented using semiconductor switching elements, including a turn-off semiconductor device and a diode connected in anti-parallel with it.

4. A method for overvoltage protection on the AC side of a flexible DC transmission system, characterized in that the protection device (7) used in the method is connected in parallel to both ends of the grounding resistor (6) of the converter transformer (3); The method includes the following steps:

A. Detect whether there is a fault in the AC line. The fault includes AC line I (4) single-phase, two-phase ground fault, DC line (8) single-pole ground fault and bipolar short-circuit fault;

B. When a single-phase ground fault occurs on the AC line I (4) or a single-pole ground fault on the DC line, the voltage at both ends of the spark gap rises to the breakdown voltage, causing the spark gap to breakdown;

Or when the control device detects a short-circuit fault in the AC line, the control device sends a trigger command to the freewheeling gap to forcefully trigger the freewheeling gap and breakdown the spark gap;

After the spark gap breaks down, the fault current is led to the earth;

C. After the spark gap breaks down, return status information is sent to the control device, and a locking signal is sent to the converter valve (5) to protect the converter valve body (9).

5. The AC side overvoltage protection method according to claim 1, characterized in that the protection configuration method for detecting the voltage overvoltage of AC line 1 (4) is that the voltage of AC line 1 (4) exceeds a preset value, and When the duration also reaches the preset value, the protection device will be turned on immediately, and at the same time, the valve base controller will immediately block the trigger pulse of the inverter.

6. The AC side overvoltage protection method according to claim 1, characterized in that the preset self-breakdown voltage is not broken down when the voltage of the AC line I (4) is not overvoltage. 4) It is broken down when the voltage is overvoltage, and the self-breakdown voltage is determined through theoretical calculation, computer simulation or experiment.

7. The AC side overvoltage protection method according to claim 1, characterized in that the size of the discharge current during breakdown is determined through theoretical calculation, computer simulation or experiment.

8. The AC side overvoltage protection method according to claim 1, characterized in that the amount of energy absorbed during breakdown is determined through theoretical calculation, computer simulation or experiment.