CN112653080A

CN112653080A - Self-adaptive reclosing method and controller for mechanical direct-current circuit breaker

Info

Publication number: CN112653080A
Application number: CN202011300825.7A
Authority: CN
Inventors: 郭彦勋; 王要强; 王明东; 李海锋; 王钢
Original assignee: Zhengzhou University
Current assignee: Zhengzhou University
Priority date: 2020-11-19
Filing date: 2020-11-19
Publication date: 2021-04-13
Anticipated expiration: 2040-11-19
Also published as: CN112653080B

Abstract

The invention provides an adaptive reclosing method and controller for a mechanical DC circuit breaker, wherein the method includes the following steps: preparing for reclosing, identifying the nature of the fault after the preparation is completed, and if it is judged that the line has a permanent fault, executing: opening The isolation switch RB2 isolates the faulty line and waits for the next reclosing; if it is judged that the line has a transient fault, execute: open the isolation switch RB2 and the isolation switch RB3, close the switch S1, and the capacitor C quickly discharges to 0 voltage through the resistor R1; After the capacitor C is discharged, the switch S1 is turned off; the isolation switch RB1, the isolation switch RB2 and the fast mechanical switch MS are closed, and the DC grid charges the fault line through the resistor R3; after the fault line is charged to the system voltage, the isolation switch RB3 is closed to connect the resistor R3 Bypass, DC circuit breaker completes reclosing.

Description

Self-adaptive reclosing method and controller for mechanical direct-current circuit breaker

Technical Field

The invention relates to the field of direct-current power transmission of a power system, in particular to a self-adaptive reclosing method and a controller of a mechanical direct-current circuit breaker.

Background

After a direct-current line fault occurs in a direct-current power grid, the direct-current circuit breaker can quickly isolate a fault area, and normal operation of a non-fault area is guaranteed. After fault isolation is completed, the timely reclosing of the direct-current circuit breaker can effectively reduce adverse effects caused by transient line faults, and the power transmission efficiency of the direct-current circuit is improved.

To the characteristics of direct current circuit breaker, current reclosing strategy is: 1) fully discharging the capacitor of the direct current breaker after isolating the fault; 2) the direct current power grid charges a circuit through a capacitor; 3) the fault nature is identified using the capacitor voltage steady state value. However, when the reclosing is in a permanent fault, the system still has a large fault current; when reclosing occurs in a transient fault, the line will experience significant voltage oscillations.

Therefore, there is a need for an adaptive reclosing strategy that can effectively suppress the surge of fault current and the oscillation of line voltage during reclosing.

Disclosure of Invention

In order to solve the above problems, it is necessary to provide an adaptive reclosing method for a mechanical dc circuit breaker and a controller.

The invention provides a self-adaptive reclosing method of a mechanical direct-current circuit breaker, which comprises the following steps:

step 1, closing a switch S2 to discharge a capacitor C through a resistor R2, and opening the switch S2 when the voltage of the capacitor C is reduced to uc 0;

step 2, waiting for the fault line to dissociate; during this time, the disconnector RB1, the disconnector RB2, the fast mechanical switch MS, the switch S1, the switch S2 and the switch S' are in an off state, and the disconnector RB3 is in a closed state;

step 3, after the line is dissociated, closing an isolating switch RB1 and an isolating switch RB2, and charging the fault line by the direct-current power grid through a series branch formed by an inductor L and a capacitor C;

step 4, in a preset time delta tth, if the low-pass filtering value delta ucf of the voltage increment delta uc of the capacitor C exceeds a threshold value delta uth, judging that a permanent fault occurs in the line, and executing step 5; if the delta ucf is always smaller than the delta uth, judging that the transient fault occurs in the line, and executing the step 6-9;

step 5, opening an isolating switch RB2, isolating the fault line, and waiting for the next reclosing;

step 6, opening an isolating switch RB2 and an isolating switch RB3, closing a switch S1, and rapidly discharging the capacitor C to 0 voltage through a resistor R1;

step 7, after the capacitor C finishes discharging, the switch S1 is switched off;

step 8, closing an isolating switch RB1, an isolating switch RB2 and a quick mechanical switch MS, and charging the fault line through a resistor R3 by the direct-current power grid; closing the switch S ', and charging the capacitor C' to a preset voltage;

and 9, after the fault line is charged to the system voltage, closing the isolating switch RB3 to bypass the resistor R3, and completing reclosing by the direct-current circuit breaker.

The invention provides a controller for a mechanical direct current breaker, which comprises a processor, a memory and an adaptive reclosing control program stored in the memory, wherein when the adaptive reclosing control program is operated by the processor, the steps of the adaptive reclosing method for the mechanical direct current breaker are realized.

In the method, when the mechanical direct current breaker is reclosed in a permanent fault, the capacitor C has certain initial voltage, so that the fault current impact is limited; when the mechanical direct current breaker is reclosed in a transient fault, a direct current power grid charges a line through a closing resistor, so that the voltage oscillation of the line is limited; by the method, the line outage time caused by transient line faults can be reduced, and the power transmission efficiency of the direct-current line is improved.

Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention.

Drawings

The above and/or additional aspects and advantages of the present invention will become apparent and readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings of which:

FIG. 1 is a flow chart of the method of the present invention.

Fig. 2 is a topological diagram of a mechanical dc breaker in the method of the invention.

Fig. 3 is a diagram of the connection mode of a four-terminal bipolar dc power grid constructed in embodiment 3 of the present invention.

Detailed Description

In order that the above objects, features and advantages of the present invention can be more clearly understood, a more particular description of the invention will be rendered by reference to the appended drawings. It should be noted that the embodiments and features of the embodiments of the present application may be combined with each other without conflict.

In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention, however, the present invention may be practiced in other ways than those specifically described herein, and therefore the scope of the present invention is not limited by the specific embodiments disclosed below.

Example 1

As shown in fig. 1 and fig. 2, the present embodiment provides an adaptive reclosing method for a mechanical dc circuit breaker, wherein the mechanical dc circuit breaker includes a disconnector RB1, a disconnector RB2, a disconnector RB3, a coupling inductor L ', a capacitor C ', a resistor R1, a resistor R2, a resistor R3, a switch S ', a switch S1, a switch S2, a fast mechanical switch MS, a lightning arrester, and a pre-charging circuit;

the isolating switch RB1, the quick mechanical switch MS, the isolating switch RB2 and the isolating switch RB3 are sequentially connected in series; the lightning arrester is connected with the rapid mechanical switch MS in parallel; the coupling inductor L and the capacitor C form a series branch and then are connected with the rapid mechanical switch MS in parallel; the switch S1 and the resistor R1 are connected in series and then connected in parallel with the capacitor C, and the switch S2 and the resistor R2 are connected in series and then connected in parallel with the capacitor C; the resistor R3 is connected with the isolating switch RB3 in parallel; the pre-charging circuit is connected with the capacitor C 'in parallel, and the capacitor C', the coupling inductor L 'and the switch S' form a series loop. The switch S1 is an isolating switch or a thyristor, and the switch S2 is an insulated gate bipolar transistor IGBT.

The self-adaptive reclosing method comprises the following steps:

preparation stage of reclosing

fault nature identification phase

Step 3, after the circuit is dissociated, closing the isolating switch RB1 and the isolating switch RB2, and charging the fault circuit through a series branch formed by the inductor L and the capacitor C;

line recovery phase

Specifically, the calculation method of the voltage increment Δ uc of the capacitor C includes:

Δuc(t)＝uc(t)-uc(t0) (1)

the value of Δ uc at time t is Δ uc (t), the value of the capacitor voltage uc at time t is uc (t0), and the value of the capacitor voltage uc at the time of starting reclosing is uc (t 0).

The selection method of the delta uth and uc0 comprises the following steps:

1) enabling the direct current breaker to be reclosed at the slightest permanent fault, recording a voltage increment low-pass filtering value of the capacitor C as delta umin at a delta tth moment after reclosing, and satisfying the following relation:

Δuth≤Δumin＝k2×(us-uc0)＝k2×Δu (2)

wherein us is a rated voltage of the system, and Δ u ═ us-uc0, and k2 ═ Δ umin/Δ u;

2) enabling a direct current breaker to be reclosed at an instantaneous fault, recording the equivalent capacitance to the ground of the whole line as Cline, sharing the system voltage by the equivalent capacitance of the capacitor C and the line, and enabling the low-pass filtering value of the capacitor voltage increment to be equal to the steady-state value delta ucs of the capacitor voltage increment:

wherein k1 ═ Cline/(C + Cline).

3) When the direct current breaker is reclosed in a transient fault, the delta ucs is smaller than the delta uth, and a certain safety margin umar is reserved:

Δuth≥Δucs+umar＝k1×Δu+umar (4)

by combining the formulae (2), (3) and (4), the compounds are obtained

Then the selection principle of uc0 is:

after a proper delta tth is selected, values of k1 and k2 are obtained through parameter calculation, the values are substituted into the formula (6) to obtain the value range of uc0, and then the value range of delta uth is obtained according to the formula (2) and the formula (4).

In order not to increase the time required for the reclosing preparation period, the time required for the capacitor C voltage to discharge from the maximum cut-off voltage of 1.5us to uc0 does not exceed the line deionization time. The selection principle of the resistor R2 is as follows:

in the formula, t_disThe maximum time allowed for the capacitor to discharge.

Example 2

This embodiment proposes a controller for a mechanical dc circuit breaker, including a processor, a memory, and an adaptive reclosing control program stored in the memory, where the adaptive reclosing control program is executed by the processor:

step 1, controlling a switch S2 to be closed, discharging a capacitor C through a resistor R2, and controlling a switch S2 to be opened when detecting that the voltage of the capacitor C is reduced to uc 0;

step 2, waiting for the fault line to dissociate;

step 3, after the circuit is free, timing is started after the isolating switch RB1, the isolating switch RB2 and the switch S' are controlled to be closed, and the fault circuit is charged through a series branch formed by the inductor L and the capacitor C;

step 4, in a preset time delta tth, if the low-pass filtering value delta ucf of the voltage increment delta uc of the capacitor C is detected to exceed a threshold value delta uth, judging that a permanent fault occurs in the line, and executing step 5; if detecting that the delta ucf is always smaller than the delta uth, judging that the transient fault occurs in the line, and executing the step 6-9;

step 5, controlling an isolation switch RB2 to be opened, isolating the fault line, and waiting for the next reclosing;

step 6, controlling an isolation switch RB2 and an isolation switch RB3 to be opened, closing a switch S1, and rapidly discharging the capacitor C to 0 voltage through a resistor R1;

step 7, after the capacitor C is detected to be discharged, controlling the switch S1 to be switched off;

step 8, controlling the isolation switch RB1, the isolation switch RB2 and the rapid mechanical switch MS to be closed, and charging the fault line through a resistor R3 by the direct current power grid; closing the switch S ', and charging the capacitor C' to a preset voltage;

and 9, after the fault line is charged to the system voltage, controlling the isolation switch RB3 to be closed to bypass the resistor R3, and completing reclosing by the direct current breaker.

The cut-off frequency fc of the low-pass filter for calculating the low-pass filtering value by the processor is designed to be smaller than the main frequency fz of the oscillation component of the capacitor voltage when the direct-current circuit breaker is reclosed in the transient fault. Specifically, during design, a low-pass filter may be built on the processor to perform low-pass filtering value calculation, or a low-pass filter may be designed separately, and after low-pass filtering, the processor performs line fault property identification.

Example 3

In the embodiment, a four-terminal bipolar direct-current power grid system is built in the PSCAD/EMTDC, and the wiring mode of the system is shown in FIG. 3. The rated voltage of the direct current power grid is +/-200 kV, 0.05H current-limiting inductors are arranged at two ends of a line and at an outlet of the converter station, and direct current circuit breakers shown in the figure 2 are arranged at two ends of the line. A butterworth low pass filter of order 3 is used to obtain a Δ ucf with a cut-off frequency of 100 Hz. The detailed model of the MMC is taken from a standard model provided by the international large power grid conference working group submitted by the national grid intelligent power grid research institute, and a line adopts a frequency-dependent parameter model. The relevant parameters of the dc circuit breaker and the reclosing are shown in table 1. Taking the reclosing of the line 5 as an example, the dc breaker DCB1 connected to the bus 3 recloses first. The main parameters of the system are shown in table 1.

TABLE 1 DC CIRCUIT BREAKER AND RE-CLOSING PARAMETERS

The self-adaptive reclosing method of the mechanical direct-current breaker in the embodiment comprises the following steps:

(1) closing the switch S2 to discharge the capacitor through the resistor R2, and disconnecting S2 when the voltage of the capacitor is reduced to 150 kV;

(2) waiting for the fault line to dissociate, wherein the waiting time is 300 ms;

(3) after the circuit is dissociated, the isolating switch RB1 and the isolating switch RB2 are closed, and a direct-current power grid charges a fault circuit through a series branch formed by an inductor L and a capacitor C in the direct-current circuit breaker;

(4) within 10ms of closing RB2, if the low-pass filtered value delta ucf of the capacitor voltage increment delta uc exceeds the threshold value 27kV, the line has a permanent fault, and then step 5 is executed; if Δ ucf is always less than 27kV, a transient fault occurs on the line, and then steps 6-9 are executed;

(5) the direct current breaker opens a disconnecting switch RB2, isolates a fault line and waits for the next reclosing;

(6) the isolation switch RB2 and the isolation switch RB3 are opened, then the switch S1 is turned on, and the capacitor C is rapidly discharged to 0 voltage through the resistor R1;

(7) after the capacitor C finishes discharging, the switch S1 is turned off;

(8) closing an isolating switch RB2 and a quick mechanical switch MS, and charging a line by a direct current power grid through a resistor R3;

(9) after the line is charged to the system voltage, the isolating switch RB3 is closed to bypass the resistor R3, and the direct current breaker completes reclosing.

The above description is only for the specific embodiments of the present invention, but the scope of the present invention is not limited thereto, and any person skilled in the art can easily conceive of the changes or substitutions within the technical scope of the present invention, and all the changes or substitutions should be covered within the scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the appended claims.

Claims

1. An adaptive reclosing method for a mechanical DC circuit breaker, comprising the following steps:

Step 1. Close the switch S2 to discharge the capacitor C through the resistor R2. When the voltage of the capacitor C drops to uc0, turn off the switch S2;

Step 2, wait for the fault line to go free; during this period, the isolation switch RB1, the isolation switch RB2, the fast mechanical switch MS, the switch S1, the switch S2 and the switch S' are in an off state, and the isolation switch RB3 is in a closed state;

Step 3. After the line is de-dissociated, the isolation switch RB1 and the isolation switch RB2 are closed, and the DC power grid charges the faulty line through the series branch composed of the inductor L and the capacitor C;

Step 4. During the preset Δtth time, if the low-pass filter value Δucf of the voltage increment Δuc of the capacitor C exceeds the threshold value Δuth, it is judged that the line has a permanent fault, and step 5 is performed; if Δucf is always smaller than Δuth, the circuit is judged If a transient fault occurs, go to steps 6-9;

Step 5. Turn on the isolation switch RB2, isolate the faulty line, and wait for the next reclosing;

Step 6. Open the isolation switch RB2 and the isolation switch RB3, close the switch S1, and the capacitor C is rapidly discharged to 0 voltage through the resistor R1;

Step 7. After the capacitor C is discharged, turn off the switch S1;

Step 8, close the isolation switch RB1, the isolation switch RB2 and the fast mechanical switch MS, and the DC grid charges the fault line through the resistor R3; close the switch S', and the capacitor C' is charged to the preset voltage;

Step 9. After the fault line is charged to the system voltage, close the isolation switch RB3 to bypass the resistor R3, and the DC circuit breaker completes the reclosing.

2. The self-adaptive reclosing method of a mechanical DC circuit breaker according to claim 1, wherein the calculation method of the capacitor C voltage increment Δuc is:

Δuc(t)=uc(t)-uc(t0) (1)

Among them, Δuc(t) is the value of Δuc at time t, uc(t) is the value of capacitor voltage uc at time t, and uc(t0) is the value of capacitor voltage at the start of reclosing.

3. The self-adaptive reclosing method of mechanical DC circuit breaker according to claim 1, is characterized in that, the selection method of described Δuth and uc0 is:

1) To reclose the DC circuit breaker at the slightest permanent fault, at the moment Δtth after the reclosing, the low-pass filter value of the voltage increment of the capacitor C is recorded as Δumin, and the following relationship is satisfied:

Δuth≤Δumin=k2×(us-uc0)=k2×Δu (2)

where us is the rated voltage of the system, Δu=(us-uc0), k2=Δumin/Δu;

2) Reclose the DC circuit breaker for a transient fault, record the ground-equivalent capacitance of the entire line as Cline, the capacitance C and the line equivalent capacitance share the system voltage together, and the low-pass filter value of the capacitor voltage increment is equal to the capacitor voltage Incremental steady-state value Δucs:

where k1=Cline/(C+Cline).

3) When the DC circuit breaker is reclosed in a transient fault, Δucs should be less than Δuth and a certain safety margin umar is reserved:

Δuth≥Δucs+umar=k1×Δu+umar (4)

Combining formulas (2), (3) and (4), we can get

Then the selection principle of uc0 is:

After selecting the appropriate Δtth, calculate the values of k1 and k2 according to the parameters, and substitute them into formula (6) to obtain the value range of uc0, and then obtain the value range of Δuth according to formula (2) and formula (4).

4. The self-adaptive reclosing method of mechanical DC circuit breaker according to claim 1, is characterized in that, the selection principle of described resistance R2 is:

In the formula, t _dis is the maximum time allowed to discharge the capacitor.

5 . The method for self-adaptive reclosing of a mechanical DC circuit breaker according to claim 1 , wherein the mechanical DC circuit breaker comprises an isolation switch RB1 , an isolation switch RB2 , an isolation switch RB3 , a coupled inductor L, and a coupled inductor. 6 . L', capacitor C, capacitor C', resistor R1, resistor R2, resistor R3, switch S', switch S1, switch S2, fast mechanical switch MS, arrester and pre-charging circuit;

The isolating switch RB1, the fast mechanical switch MS, the isolating switch RB2, and the isolating switch RB3 are connected in series in sequence;

The arrester is connected in parallel with the fast mechanical switch MS;

The coupled inductor L and the capacitor C form a series branch and are connected in parallel with the fast mechanical switch MS;

The switch S1 and the resistor R1 are connected in series with the capacitor C, and the switch S2 and the resistor R2 are connected in parallel with the capacitor C;

The resistor R3 is connected in parallel with the isolation switch RB3;

The precharge circuit is connected in parallel with the capacitor C', and the capacitor C', the coupled inductor L' and the switch S' form a series loop.

6 . The adaptive reclosing method of a mechanical DC circuit breaker according to claim 5 , wherein the switch S1 is an isolation switch or a thyristor, and the switch S2 is an insulated gate bipolar transistor (IGBT). 7 .

7. A controller for a mechanical DC circuit breaker, characterized by comprising a processor, a memory, and an adaptive reclosing control program stored in the memory, the adaptive reclosing control program being When the processor is running, it implements the steps of the method for self-adaptive reclosing of the mechanical DC circuit breaker according to any one of claims 1-6.

8 . The controller for a mechanical DC circuit breaker according to claim 7 , wherein the cutoff frequency fc of the low-pass filter for calculating the low-pass filter value by the processor is designed to be smaller than the DC circuit breaker coincidence. 9 . The dominant frequency fz of the oscillatory component of the capacitor voltage during transient faults.