CN110190590B - A protection optimization method for rectifier station in HVDC transmission system - Google Patents

Abstract

The invention discloses a protection and optimization method for a rectifier station of a high-voltage direct current transmission system. After calculating _km , the faults in and outside the rectifier station are identified by judging the relationship between _km and 0. If km is _greater than 0, it is judged that the fault occurs. The fault is outside the rectifier station area. If k _min is less than 0, it is judged that the fault occurs in the rectifier station area, and on this basis, the optimization of the rectifier station protection is realized: if it is judged that the fault occurs outside the rectifier station area, And the setting value of rectifier station protection is satisfied, then block the rectifier station protection whose setting value is satisfied for m seconds, and unlock the blocked rectifier station protection after m seconds; if it is judged that the fault occurs in the rectifier station area, it is not correct Make any changes to the rectifier station protection. The invention can prevent the protection of the rectifier station from malfunctioning under the fault of the AC line outside the area, and does not affect the quickness and sensitivity of the protection of the rectifier station.

Description

A protection optimization method for rectifier station in HVDC transmission system

technical field

The invention relates to the technical field, in particular to a protection optimization method for a rectifier station of a high-voltage direct current transmission system.

Background technique

HVDC transmission system has large transmission capacity, long transmission distance and low transmission loss, so it occupies an increasingly important position in my country's power structure. The basic principle of HVDC transmission is: the electric energy of the sending end power station is transmitted to the rectifier station of the HVDC transmission system through the AC line, and the three-phase alternating current is converted into direct current by the rectifier station, and the electric energy is transmitted through the HVDC transmission line. The inverter station of the system inverts and converts the direct current into three-phase alternating current, and the electric energy is transmitted to the receiving end grid or power station through the alternating current line connected with the inverter station.

Since the rectifier station is connected to the power transmission terminal, if there is a short-circuit fault inside the rectifier station, a large short-circuit current will occur. Therefore, in order to prevent damage to the rectifier station equipment when a fault occurs in the rectifier station area, the actual project is equipped with multiple types of rectifier stations. Protect. However, the actual engineering operation experience shows that when the AC system outside the rectifier station area of the HVDC transmission system fails, the protection of the three types of rectifier station protection, namely low AC voltage protection, low DC voltage protection and 100Hz protection, will malfunction, causing the HVDC transmission system to malfunction. Outages, interrupting power transmission, and even affecting the safety and stability of the AC power grid. For example, a large power outage occurred in Brazil on March 21, 2018. This accident was mainly caused by the fault of the AC system outside the rectifier station area. The operation and the accidental outage of the HVDC transmission system caused the interruption of the power supply of nearly 20,000MW of the Brazilian power grid, and about a quarter of the country's users were out of power. Therefore, designing an optimization method for the protection of the rectifier station of the HVDC transmission system and improving the adaptability of the rectifier station protection under the fault of the AC system outside the area is of great significance to ensure the safe and stable operation of the power grid.

Existing research shows that there are two main reasons for the misoperation of the three types of rectifier station protections under low AC voltage protection, low DC voltage protection and 100Hz protection under AC system faults outside the rectifier station area: First, these three types of rectifier station protection lack correct The ability to identify faults inside and outside the rectifier station; second, the setting time of the protection of these three types of rectifier stations is less than the longest fault removal time of the AC line protection in the AC system outside the area, that is, less than 2.3 seconds, so these three types of rectifier stations The protection may malfunction under the fault of the AC line outside the rectifier station area.

According to the cause of the malfunction of the rectifier station protection, the existing technology mainly improves the setting time or setting value of the three types of rectifier station protection that may malfunction, such as low AC voltage protection, low DC voltage protection and 100Hz protection, to prevent it from AC outside the area. Malfunction under line fault. Improving the setting time of rectifier station protection refers to increasing the setting time of rectifier station protection that may malfunction to after the longest fault removal time of the AC line protection outside the zone, that is, to more than 2.3 seconds. However, improving the setting time of the rectifier station protection reduces the rapidity of the rectifier station protection to the fault in the area, and prolongs the impact time of the rectifier station equipment on the rectifier station equipment. Therefore, improving the setting time of the rectifier station protection will increase the rectifier station area. The damage risk of the rectifier station equipment under internal faults; and increasing the setting value of the rectifier station protection will reduce the sensitivity of the rectifier station protection and increase the risk of refusal of the rectifier station protection to operate under internal faults.

To sum up, it is urgent to consider the two major causes of malfunction of the rectifier station protection, and introduce an optimization method that does not affect the sensitivity and quickness of the rectifier station protection to prevent the rectifier station protection from malfunctioning under the fault of the AC line outside the area.

SUMMARY OF THE INVENTION

In view of the above problems, the purpose of the present invention is to provide a protection optimization method for a rectifier station of a high-voltage direct current transmission system, which can realize the optimization of the protection of the rectifier station on the basis of identifying the faults inside and outside the rectifier station, which can not only prevent the rectifier station from being rectified The station protection malfunctions under the fault of the AC line outside the area, and does not affect the quickness and sensitivity of the rectifier station protection. The technical solution is as follows:

A protection and optimization method for a rectifier station of a high-voltage direct current transmission system, comprising the following steps:

Step A: judging whether the control and protection system on the rectifier side of the HVDC transmission system detects a fault, if not, return to continue to judge, if so, record the fault time t ₀ at this time;

Step B: acquire in real time the three-phase voltage signals u _A , u _B , u _C at the converter bus M of the rectifier station collected by the voltage measuring point VT; acquire in real time the primary sides of n converter transformers respectively collected from the n current measuring points Three-phase current signal: i _A1 , i _B1 , i _C1 , i _A2 , i _B2 , i _C2 ,..., i _An , i _Bn , i _Cn ; calculate u _A , u _B , u _C within the s millisecond time window after the fault _{The fault components Δu A , Δu B , Δu C of} components Δi _A1 , Δi _B1 , Δi _C1 , Δi _A2 , Δi _B2 , Δi _C2 , . . . , Δi _An , Δi _Bn , Δi _Cn ;

对Δi_A1、Δi_B1、Δi_C1，Δi_A2、Δi_B2、Δi_C2，…，Δi_An、Δi_Bn、Δi_Cn分别进行相模变换得到相应的模量：

Step C: Perform phase mode transformation on Δu _A , Δu _B , and Δu _C to obtain their moduli

Perform phase mode transformation on Δi _A1 , Δi _B1 , Δi _C1 , Δi _A2 , Δi _B2 , Δi _C2 ,..., Δi _An , Δi _Bn , Δi _Cn respectively to obtain the corresponding moduli:

Step D _: Perform wavelet transform _{on Δu} , _{Δi 1} , Δi ₂ , . The frequency range of the low-frequency coefficients under the scale is approximate power frequency;

计算u与i₂夹角的余弦值

计算u与i_n夹角的余弦值

Step E: Calculate the cosine of the angle between u and i ₁

Calculate the cosine of the angle between u and i ₂

Calculate the _cosine of the angle between u and in

Step F: Calculate the minimum cosine value k _min =min(cosθ ₁ , cosθ ₂ ,...,cosθ _n );

Step G: judge whether k _min <0 is established: if yes, then judge that the fault that occurs is a fault in the rectifier station area, and enter step I; if not, then judge that the fault that occurs is a fault outside the rectifier station area, and enter step H;

Step H: Continue to judge whether the setting value of rectifier station protection is satisfied at this time, if the setting value of rectifier station protection is satisfied, return to step A; if the setting value of rectifier station protection is satisfied, then block the setting value The rectifier station is protected for m seconds, and the fault is removed by the AC line protection action outside the rectifier station area, and the blocked rectifier station protection is unlocked after m seconds;

Step I: Continue to judge whether the setting value of rectifier station protection is satisfied at this time, if the setting value of no rectifier station protection is satisfied, then return to step A; if the setting value of rectifier station protection is satisfied, then the setting value is satisfied. The satisfied rectifier station protection acts according to its original configuration strategy, that is, no changes are made to the rectifier station protection.

Further, the time window is 5 milliseconds.

Further, the frequency range of the approximate power frequency in the step B is between 0 and 200 Hz.

Further, the m seconds is 2.4 to 3 seconds.

The beneficial effects of the present invention are:

1) Malfunction prevention: when the AC line outside the rectifier station area fails, the present invention locks the rectifier protection whose setting value is satisfied for a period of time, avoids the longest fault removal time of the AC line protection outside the area, and avoids the rectifier station. The protection malfunctions under the fault of the AC line outside the zone;

2) Quickness and sensitivity will not be affected: when the present invention fails in the rectifier station area, the rectifier station protection still acts according to its original configuration strategy, and the setting value and setting time are not changed, that is, the rectifier station protection The quickness and agility will not be affected;

3) It is less affected by VT transmission characteristics and noise interference: because the voltage measuring point VT is prone to large errors in the transmission of high-frequency signals, and the high-frequency signals are greatly affected by noise interference, the present invention utilizes the faults of each signal. The approximate power frequency component of the component modulus realizes the optimization of the protection of the rectifier station, and is basically not affected by the VT transfer characteristics and noise interference of the voltage measuring point;

4) Does not rely on long-distance communication: the voltage measuring points and n current measuring points required by the present invention are all in the rectifier station area, and there is no need to rely on long-distance communication to summarize the collected signal data.

Description of drawings

Figure 1 is a flow chart of the protection optimization of the rectifier station of the HVDC transmission system;

Figure 2 is a schematic diagram of the distribution of faults inside and outside the rectifier station of the HVDC transmission system.

Detailed ways

The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. A method for optimizing the protection of a rectifier station in a high-voltage direct current transmission system, the flow chart is shown in Figure 1, and the steps are:

A. Determine whether the control and protection system on the rectifier side of the HVDC transmission system detects a fault, if not, return to continue to judge, if so, record the fault time t ₀ at this time.

B. Real-time acquisition of the three-phase voltage signals u _A , u _B , u _C at the commutation bus M of the rectifier station collected by the voltage measuring point VT, and real-time acquisition of the commutation current collected by the current measuring points CT ₁ , CT ₂ , ..., CT _n The three-phase current signals on the primary side of transformer 1, converter transformer 2, ..., and converter transformer n are i _A1 , i _B1 , i _C1 , i _A2 , i _B2 , i _C2 , ..., i _An , i _Bn , i respectively _Cn ; Calculate the fault components Δu _A , Δu _B , Δu _C of u _A , u _B , u _C within the time window of 5 milliseconds after the fault; calculate i _A1 , i _B1 , i _C1 , i _A2 , The fault components of i _B2 , i _C2 , ..., i _An , i _Bn , i _Cn are Δi _A1 , Δi _B1 , Δi _C1 , Δi _A2 , Δi _B2 , Δi _C2 , ..., Δi _An , Δi _Bn , Δi _Cn , respectively; The sampling frequency of each measuring point is 20kHz.

对Δi_A1、Δi_B1、Δi_C1，Δi_A2、Δi_B2、Δi_C2，…，Δi_An、Δi_Bn、Δi_Cn进行相模变换得到相应的模量分别为

C. Perform phase mode transformation on Δu _A , Δu _B , and Δu _C to obtain their moduli

Perform phase mode transformation on Δi _A1 , Δi _B1 , Δi _C1 , Δi _A2 , Δi _B2 , Δi _C2 ,..., Δi _An , Δi _Bn , Δi _Cn to obtain the corresponding moduli as

D. Do wavelet transform with wavelet base db4 and scale 7 for Δu, Δi ₁ , Δi ₂ , ..., _Δin respectively, and take the low-frequency coefficients under the 7th scale for reconstruction to obtain u, i ₁ , i ₂ , ..., i _n , where the frequency range of the low-frequency coefficients in the seventh scale is 0-78.125 Hz.

Under different sampling frequencies, the frequency ranges of the low-frequency coefficients are also different, but they are all in the approximate industrial frequency band, that is, between 0 and 200 Hz.

计算u与i₂夹角的余弦值

计算u与i_n夹角的余弦值

E. Calculate the cosine of the angle between u and i ₁

Calculate the cosine of the angle between u and i ₂

Calculate the _cosine of the angle between u and in

F. Calculate the minimum cosine value of the approximate power frequency component of the angle between the three-phase voltage fault component modulus of the converter bus M of the rectifier station and the three-phase current fault component modulus of the primary side of each converter transformer k _min =min (cosθ ₁ , cosθ ₂ ,...,cosθ _n ).

G. Judge whether k _min <0 is established, if so, judge that the fault occurred in the rectifier station area, if not, judge that the fault occurred is the fault outside the rectifier station area; the schematic diagram of the distribution of faults inside and outside the rectifier station area of the HVDC transmission system as shown in picture 2.

H. If it is judged in step G that the fault occurred outside the rectifier station area, continue to judge whether the setting value of rectifier station protection is satisfied at this time, and if the setting value of no rectifier station protection is satisfied, return to step A; If the setting value of rectifier station protection is satisfied, the rectifier station protection whose setting value is satisfied will be blocked for 2.7 seconds, the fault will be removed by the AC line protection action outside the rectifier station area, and the blocked rectifier station protection will be unlocked after 2.7 seconds.

I. When step G judges that the fault occurred in the rectifier station area, continue to judge whether the setting value of rectifier station protection is satisfied at this time, and if no rectifier station protection setting value is satisfied, then return to step A; If the setting value of rectifier station protection is satisfied, the rectifier station protection whose setting value is satisfied will act according to its original configuration strategy, that is, no change will be made to the rectifier station protection.

Simulation

Two AC lines L ₁ and L ₂ are built outside the rectifier station area of the international large grid standard HVDC transmission system model in the PSCAD/EMTDC simulation platform. The length of L ₁ is 10km and the length of L ₂ is 15km. There are two converter transformers in the rectifier station area of the standard HVDC transmission system model. The specific simulation results are shown in Table 1. Among them, f ₁ and f ₂ represent two different types of faults in the rectifier station area, and f ₃ -L ₁ and f ₃ -L ₂ respectively represent the faults occurred on the AC line L ₁ and the AC line L ₂ outside the rectifier station area; AG in Table 1 represents the ground fault of phase A, and AB represents the two-phase short-circuit fault of phase A and phase B; the fault distance in Table 1 represents the distance between f ₃ -L ₁ or f ₃ -L ₂ from the converter bus M of the rectifier station distance; the transition resistances of f ₁ , f ₂ , f ₃ -L ₁ and f ₃ -L ₂ are all 100Ω; in Table 1, the faults are judged as "inside" and "outside" respectively means "the fault is judged to be rectification. "Faults within the station" and "The faults that occur are judged to be faults outside the rectifier station area"; the protection satisfaction of "1" and "0" means "the setting value of the rectifier station protection is satisfied" and "the setting without the rectifier station protection" respectively. The value is satisfied"; the action strategy is "1" and "0", which means "block the rectifier station protection whose setting value is satisfied for 2.7 seconds and then unlock the rectifier station protection" and "do not make any changes to the rectifier station protection".

Table 1 Simulation results

According to the results in Table 1, when different types of faults occur in the rectifier station area, k _min is less than 0, and the fault identification results are all faults in the rectifier station area; When different types of faults occur at different distances, k _min is greater than 0, and it is judged that the fault occurs outside the rectifier station area. Therefore, it can be known that the present invention can accurately identify the fault regardless of whether the fault occurs in the rectifier station area or outside the rectifier station area. Moreover, the present invention can take accurate action strategies according to the satisfaction of the protection setting value of the rectifier station when _a fault occurs in the rectifier station area or outside the area. When the A-phase grounding fault occurs at 1km, the present invention accurately judges that the fault occurs outside the rectifier station area, and judges that the setting value of the rectifier station protection is satisfied at this time, and adopts the “blocking rectifier station protection whose setting value is satisfied”. The action strategy of "unlocking the rectifier station protection after 2.7 seconds" is consistent with the purpose to be achieved by the present invention.

Claims (4)

1. A protection optimization method for a rectification station of a high-voltage direct-current transmission system is characterized by comprising the following steps:

step A: judging whether the control protection system on the rectifying side of the high-voltage direct-current power transmission system detects a fault, if not, returning to continuous judgment, and if so, recording that the fault is at the momentTime of failure t₀；

And B: three-phase voltage signal u acquired by voltage measuring point VT in real time at commutation station commutation bus M_A、u_B、u_C(ii) a Acquiring n primary side three-phase current signals of the converter transformers respectively acquired from n current measuring points in real time: i.e. i_A1、i_B1、i_C1，i_A2、i_B2、i_C2，…，i_An、i_Bn、i_Cn(ii) a Calculating u in s millisecond time window after fault_A、u_B、u_CFault component Δ u of_A、Δu_B、Δu_C(ii) a Calculating i in s millisecond time window after fault_A1、i_B1、i_C1、i_A2、i_B2、i_C2，…，i_An、i_Bn、i_CnFault component Δ i of_A1、Δi_B1、Δi_C1，Δi_A2、Δi_B2、Δi_C2，…，Δi_An、Δi_Bn、Δi_Cn；

And C: for Δ u_A、Δu_B、Δu_CPerforming phase-mode conversion to obtain modulus

For Δ i_A1、Δi_B1、Δi_A2、Δi_B2、Δi_C2，…，Δi_An、Δi_Bn、Δi_CnRespectively carrying out phase-mode conversion to obtain corresponding moduli:

step D: for Δ u, Δ i respectively₁，Δi₂，…，Δi_nPerforming wavelet transformation, and reconstructing low-frequency coefficients under the e-th scale to respectively obtain u and i₁，i₂，…，i_nWhere the frequency of the low frequency coefficient at the e-th scaleThe range is approximate power frequency;

step E: calculating u and i₁Cosine value of included angle

Calculating u and i₂Cosine value of included angle

…, calculating u and i_nCosine value of included angle

Step F: calculating the minimum cosine value k of the included angle between the fault component modulus of the M three-phase voltage of the converter bus of the rectifier station and the approximate power frequency component of the fault component modulus of the three-phase current on the primary side of each converter transformer_min＝min(cosθ₁,cosθ₂,...,cosθ_n)；

Step G: judgment of k_min<Whether 0 holds: if yes, judging that the fault is a fault in the rectifying station area, and entering the step I; if not, judging that the fault is an external fault of the rectifier station, and entering the step H;

step H: continuously judging whether the setting value of the rectifier station protection is met or not, and returning to the step A if the setting value of the rectifier station protection is not met; if the setting value of the rectifier station protection is met, locking the rectifier station protection with the setting value met for m seconds, removing the fault by the protection action of the alternating current line outside the rectifier station area, and unlocking the locked rectifier station protection after m seconds;

step I: continuously judging whether the setting value of the rectifier station protection is met or not, and returning to the step A if the setting value of the rectifier station protection is not met; if the setting value of the rectifier station protection is met, the rectifier station protection with the setting value met acts according to the original configuration strategy, namely, the rectifier station protection is not changed.

2. The method of claim 1, wherein the time window is 5 milliseconds.

3. The method according to claim 1, wherein the frequency of the approximate power frequency is in the range of 0-200 Hz.

4. The method according to claim 1, wherein the m seconds is 2.4-3 seconds.

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