CN110609207A - A method for fault distance measurement of T-connection line - Google Patents

Abstract

The invention discloses a T-connection line fault distance measurement method, comprising: when the optical fiber channel is normal, using T-point compensation voltage to identify the faulty branch; when the optical fiber channel is abnormal, using the three-terminal fault distance measurement result to identify the faulty branch ; Then, according to the relationship between the minimum value of the fault current and the set maximum fault current threshold value, determine the three-terminal fault removal time; The distance from point T. The invention is used in the existing line protection device. For the T-connection line, the distance can still be measured normally when the communication of the longitudinal channel is abnormal, and the distance measurement accuracy can be guaranteed especially when the single-phase high-resistance grounding fault occurs.

Description

A method for fault distance measurement of T-connection line

technical field

The invention relates to a T-connection line fault ranging method, which belongs to the technical field of electric power system relay protection.

Background technique

At present, there are two main types of fault location algorithms applied to transmission lines: single-end location algorithm and double-end location algorithm. For the double-ended ranging algorithm, it is only applicable to the double-ended system. For the T-connection line (three-terminal system), the principle of the double-ended ranging algorithm is no longer applicable; for the single-ended fault ranging algorithm, the general metallic fault only has one end The distance of the line can be accurately measured, but the results of fault distance measurement at the other two ends are inaccurate due to the existence of shunt branches. For T-connection line fault location algorithms, some traveling wave methods and wave impedance methods are currently being studied. Generally, the algorithms have a large amount of calculation or complex principles, and are difficult to engineer. In an adaptive fault location method applied to T-connected lines, Yao Liang et al. proposed a method of using T-point compensation voltage to identify the fault branch and then using a single-ended fault location algorithm to determine the fault point. The principle is simple and the amount of calculation is small. It is suitable for engineering, but the ranging result of this method is greatly affected by the transition resistance, and the selection result is heavily dependent on the three-terminal synchronization data.

Contents of the invention

The purpose of the present invention is to provide a T-connection line fault distance measurement method, which is used in the existing line protection device. When the optical fiber channel line is inconsistent, code errors and other abnormal conditions can improve the fault area selection ability, in the case of high-resistance grounding faults It also has high ranging accuracy when measuring distance.

In order to achieve the above object, the technical scheme adopted in the present invention is as follows:

A fault location method for T-connection lines, suitable for lines with a voltage level of 110kV and below, including:

Carry out fault selection, including:

When the fiber optic channel is normal, use the T-point compensation voltage to identify the faulty branch;

When the fiber channel is abnormal, after the fault location is performed, the fault location result of the three terminals is used to identify the faulty branch;

After the fault area is selected, perform fault distance measurement, including:

Exclude the non-power supply side according to the device control word "weak feeder input side";

After the fault protection device operates on the T-connection line, compare the fault currents measured on all power supply sides, and identify the end with the smallest fault current;

According to the relationship between the minimum fault current value and the maximum fault current threshold value, determine the three-terminal fault removal time;

After the fault is removed, calculate the per-unit value of fault distance measurement.

Further, the use of the three-terminal fault distance measurement result to identify the fault branch includes:

When the fault distance per unit value of one end is less than 1.00, and the fault distance per unit value of the other two ends is greater than 1.00, the end with the smallest fault distance per unit value is determined to be the fault branch;

When the minimum fault distance per unit value is greater than 1.00 and the maximum fault distance per unit value is less than 1.05, it is determined that the fault point is at point T;

When none of the above conditions are met, the fault selection fails.

Further, the control word of "weak feeder throwing side" is "1" for the pure load side, and the setting value of "weak feeder throwing side" is "0" for the power supply side.

Further, the maximum fault current threshold value is set according to the maximum fault current that the system can withstand continuously for 200 ms.

Further, according to the relationship between the minimum fault current value and the maximum fault current threshold value, determining the three-terminal fault removal time includes:

If the minimum value of the fault current is less than the maximum fault current threshold value, the side with the minimum value of the fault current is the back-cut side, and the back-cut side delays to remove the fault, and the other two ends cut off the fault instantaneously after the differential protection action of the T-connected line;

If the minimum fault current value is greater than the maximum fault current threshold value, the three terminals will trip quickly after the T-connection line differential protection operates.

Further, the time for the delay cut-off fault on the trailing cut side is: +20 ms after the fault current at the other two ends disappears.

Further, the single-ended ranging method is used to calculate the per unit value of fault ranging, including:

Among them, k is the per unit value of fault distance measurement, is the fault phase voltage on side m of the transmission line, is the fault phase current on side m of the transmission line, is the fault zero-sequence current on side m of the transmission line, for Conjugate of , Z _l is the full-length positive-sequence impedance of the transmission line, and Z _0l is the full-length zero-sequence impedance of the transmission line.

The beneficial effects achieved by the present invention are:

The invention provides a T-connection line fault distance measurement method, which is used in the existing line protection device. For the T-connection line, when the communication of the longitudinal channel is abnormal, the distance can still be measured normally, especially for single-phase high-resistance grounding faults. The distance measurement accuracy can be guaranteed.

Description of drawings

Fig. 1 is a schematic diagram of T-connection line partitions in the present invention;

Fig. 2 is a fault selection technology roadmap in the present invention;

Fig. 3 is a roadmap of fault location technology in the present invention;

Fig. 4 is the RTDS simulation model in the embodiment of the present invention.

Detailed ways

The present invention will be further described below. The following examples are only used to illustrate the technical solution of the present invention more clearly, but not to limit the protection scope of the present invention.

The embodiment of the present invention provides a method for fault distance measurement of a T-connection line, which is mainly divided into two parts, the first part is a fault area selection method, and the second part is a fault distance measurement method.

Fault selection is to determine which section of the line the fault point is in. As shown in Figure 1, line M-T is zone 1, line N-T is zone 2, and line P-T is zone 3. Here, M, N, P are three substations on the T line, and T point is the intersection point of the three lines.

The fault selection area of the T-connection line mainly depends on the electrical quantity of the three terminals, so it is closely related to the communication status of the fiber channel. The fault selection method is shown in Figure 2:

When the fiber channel is normal, use the T-point compensation voltage to identify the faulty branch, specifically:

Calculate the positive sequence voltage at point T along the three branch lines of MT, NT and PT respectively

in: are the positive sequence voltage and current of each side, and Z _mt , Z _nt , Z _pt are the positive sequence impedance values of each side branch.

The absolute value after subtracting the positive sequence voltages of the three T contacts in pairs is taken as the voltage difference, expressed as:

If MIN(ΔU _mnt ,ΔU _mpt ,ΔU _npt )=ΔU _mnt , then the branch PT is a faulty branch, and the current injected into the faulty branch at point T is

If MIN(ΔU _mnt ,ΔU _mpt ,ΔU _npt )=ΔU _mpt , then branch NT is a faulty branch, and the current injected into the faulty branch at point T is

If MIN(ΔU _mnt ,ΔU _mpt ,ΔU _npt )=ΔU _npt , then the branch MT is a faulty branch, and the current injected into the faulty branch at point T is

If ΔU _mnt ≈ ΔU _mpt ≈ ΔU _npt , then it is judged as T point fault.

The technical scheme of T-point compensation voltage identification fault branch comes from: Yao Liang, Chen Fufeng, Chen Qi. An adaptive fault location method applied to T-connected lines. Power System Protection and Control, 2012, 40(3): 26-30.

When the fiber channel is abnormal (routing inconsistency, serious bit error occurs in the channel), directly use the single-end ranging algorithm to calculate the fault distance length, and then identify the fault branch through the three-terminal fault distance measurement results:

When the fault distance per unit value (fault distance measurement length/line setting length) of one end is less than 1.00, and the other two ends are greater than 1.00, the end with the smallest fault distance per unit value is determined to be the fault branch;

When the minimum fault distance per unit value is greater than 1.00 and the maximum fault distance per unit value is less than 1.05, it is determined that the fault point is near point T;

When none of the above conditions are met, report fault selection failure.

The ranging algorithm of the embodiment of the present invention is mainly applicable to lines with a voltage level of 110kV and below. On the premise of ensuring system stability and not damaging the primary equipment, an improved T-connection line ranging algorithm is proposed, see Figure 3, the details are as follows :

Set a maximum fault current threshold value I _{delay_set} , which is set according to the maximum fault current that the system can withstand continuously for 200ms.

Before fault location, exclude the non-large power supply side according to the device control word "weak feeder input side": the control word "weak feeder input" is "1" for the pure load side, and the value for the weak feeder input side is "0" for the power supply side.

After the line fault protection device operates, compare the fault currents measured on all power supply sides, and identify the end with the smallest fault current.

Judging whether the minimum value of the fault current is less than the maximum fault current threshold (I _{delay_set} ),

If the judgment conditions are not satisfied, the probability of a grounding fault through a large excessive resistance is small, and the three-terminal protection device trips quickly after the differential protection action of the T-connected line, and the distance is directly measured by the single-end distance measurement method.

If the judgment conditions are met, it is determined that this side is the back cut side, and the back cut side delays to remove the fault, and the other two ends isolate the fault instantaneously after the differential protection action of the T-connected line; the time for the back cut side to delay the removal of the fault is: the other two ends +20ms after the fault current disappears.

After the differential protection action of the T-connected line, the fault isolation time of the fast switching side is: protection action time 30ms + switch tripping time 60ms;

The fault isolation time of the rear switching side is: the fault isolation time of the fast switching side is 90ms + the protection delay action time is 20ms + the switch tripping time is 60ms.

Finally, the off-time of the trailing side switch is 170ms, which is less than the set 200ms.

Among them, the quick-cut side refers to the side that isolates the fault immediately after the protection device operates, and the back-cut side refers to the side that isolates the fault after a delay for a period of time after the protection device operates.

After the fault is removed on the back cut side, the single-ended ranging method is used to calculate the per unit value of fault distance measurement on the back cut side:

Since the fast-cut side has already isolated the fault, the integrated zero-sequence current flowing through R _g is shown in formula (2):

Both sides of equation (1) are multiplied by (vector Conjugate of ), take the imaginary part and calculate the fault distance per unit value k:

in, is the fault phase voltage on side m of the transmission line, is the fault phase current on side m of the transmission line, is the fault zero-sequence current on side m of the transmission line, Z is the fault zero-sequence current on the n-side of the transmission line, Z _l is the full-length positive-sequence impedance of the transmission line, Z _0l is the full-length zero-sequence impedance of the transmission line, and R _g is the transition resistance of the fault point.

Example

Establish the RTDS simulation model shown in Figure 4, and the model parameters are shown in Table 1:

Table 1 Model parameters

project parameter unit Positive sequence resistance 0.147 Ω/km Positive sequence reactance 0.430 Ω/km Positive sequence parallel capacitive reactance 0.530 MΩ*km Zero sequence resistance 0.500 Ω/km Zero sequence inductive reactance 1.200 Ω/km Zero sequence parallel capacitive reactance 0.786 MΩ*km Line length MT (zone 1) 20 km Line length NT (Zone 2) 30 km Line length PT (Zone 3) 40 km

If the simulated fault point K1 is 50% away from the M side, the theoretical T point distance measurement result is 20*0.5=10kM; the simulated fault point K2 is 50% away from the N side fault, and the theoretical T point distance measurement result is 30*0.5=15kM; simulated fault The point K3 is 30% away from the fault on the P side, and the theoretical ranging result of point T is 40*0.7=28kM.

1) Three-terminal system (large power supply side, small power supply side, load side), using the traditional impedance distance measurement and the impedance distance measurement comparison of the method of the present invention, the results are shown in Table 2 below:

Table 2 Comparison of Impedance Ranging Results-1

2) For the three-terminal system (large power supply side, small power supply side, and small power supply side), the comparison between the traditional impedance ranging and the impedance ranging of this patent is used, and the results are shown in Table 3 below:

Table 3 Comparison of Impedance Ranging Results-2

Compare the ranging results of simulation results table 2 and table 3, for different system wiring modes (the three terminals of table 2 are the load mixed three-terminal system of power supply system and table 3), the ranging method proposed by the present invention can all be accurate Ranging, compared with the traditional single-ended ranging method and the ranging method proposed by the present invention, the ranging accuracy is basically the same when metallic faults (white background data), but when high-resistance grounding faults (gray background data), this measurement The distance measurement method can accurately measure the distance, and the traditional single-ended distance measurement method has a large ranging error or even cannot measure the distance (the result is represented by /).

The above is only a preferred embodiment of the present invention, and it should be pointed out that for those of ordinary skill in the art, without departing from the technical principle of the present invention, some improvements and modifications can also be made. It should also be regarded as the protection scope of the present invention.

Claims (7)

1. A T-connection line fault location method, suitable for 110kV and below voltage level lines, is characterized in that, comprising: Carry out fault selection, including: When the fiber optic channel is normal, use the T-point compensation voltage to identify the faulty branch; When the fiber channel is abnormal, after the fault location is performed, the fault location result of the three terminals is used to identify the faulty branch; After the fault area is selected, perform fault distance measurement, including: Exclude the non-power supply side according to the device control word "weak feeder input side"; After the fault protection device operates on the T-connection line, compare the fault currents measured on all power supply sides, and identify the end with the smallest fault current; According to the relationship between the minimum fault current value and the maximum fault current threshold value, determine the three-terminal fault removal time; After the fault is removed, calculate the per-unit value of fault distance measurement. 2. A kind of T-connection line fault location method according to claim 1, is characterized in that, described adopting three-terminal fault location result to identify fault branch, comprises: When the fault distance per unit value of one end is less than 1.00, and the fault distance per unit value of the other two ends is greater than 1.00, the end with the smallest fault distance per unit value is determined to be the fault branch; When the minimum fault distance per unit value is greater than 1.00 and the maximum fault distance per unit value is less than 1.05, it is determined that the fault point is at point T; When none of the above conditions are met, the fault selection fails. 3. A method for distance measurement of a T-connection line fault according to claim 1, characterized in that the control word of "throwing the weak feeder side" is "1" for the pure load side, and the fixed value of the weak feeder throwing side is " 0" is the power side. 4 . The fault location method of a T-connection line according to claim 1 , wherein the maximum fault current threshold is set according to the maximum fault current that the system can withstand for 200 ms in a row. 5. A kind of T-connection line fault location method according to claim 1, is characterized in that, described according to the relation of fault current minimum value and maximum fault current threshold value, determines three-terminal fault removal time, comprises: If the minimum value of the fault current is less than the maximum fault current threshold value, the side with the minimum value of the fault current is the back-cut side, and the back-cut side delays to remove the fault, and the other two ends cut off the fault instantaneously after the differential protection action of the T-connected line; If the minimum fault current value is greater than the maximum fault current threshold value, the three terminals will trip quickly after the T-connection line differential protection operates. 6 . The fault location method of a T-connection line according to claim 5 , wherein the delayed fault removal time of the back-cut side is +20 ms after the fault current at the other two ends disappears. 6 . 7. A kind of T-connection line fault ranging method according to claim 1, is characterized in that, adopts single-ended ranging method to calculate fault ranging per unit value, comprising: Among them, k is the per unit value of fault distance measurement, is the fault phase voltage on side m of the transmission line, is the fault phase current on side m of the transmission line, is the fault zero-sequence current on side m of the transmission line, for Conjugate of , Z _l is the full-length positive-sequence impedance of the transmission line, and Z _0l is the full-length zero-sequence impedance of the transmission line.