CN106602523A - Zero-sequence current differential phase selection element - Google Patents

Abstract

The invention relates to a zero-sequence current differential phase selection element, which includes a phase selection criterion I for distinguishing a single-phase ground fault phase from a two-phase ground fault phase, and a phase selection criterion I for distinguishing a single-phase ground fault phase from a two-phase metallic ground fault phase Phase selection criterion II and phase selection criterion III of three-phase short-circuit unbalanced zero sequence outside the defense zone; AND gate output between the phase selection criterion I, phase selection criterion II and phase selection criterion III, and single-phase output ground fault phase. The sensitivity of the homodyne protection phase selection element proposed by the technical solution of the present invention is higher than that of the homodyne protection, and it is not affected by the load current. When a single-phase high-impedance ground fault occurs, the fault phase can still be selected accurately, and it can be used in conjunction with the homodyne protection to realize When a single-phase high-resistance grounding fault occurs, the phase-selection tripping of the homodyne protection prevents the occurrence of three-phase tripping due to minor faults.

Description

A zero-sequence current differential phase selection element

Technical field:

The invention relates to the field of electric power system relay protection, and more specifically relates to a zero-sequence current differential phase selection element.

Background technique:

Zero-sequence current differential protection is an important transmission line protection, which is used to cut off single-phase high-impedance grounding faults in transmission lines, but zero-sequence current differential protection does not have a phase selection function, and phase selection components are required to cooperate with it to achieve phase separation Tripping, the existing phase selection element is mainly used as the phase selection element of homodyne protection by reducing the braking coefficient of the current differential protection criterion, but the phase selection element is greatly affected by the load current. When a high-impedance ground fault occurs, the phase selection of the phase selection element fails, and the result is a slight fault (single-phase through a high-impedance ground fault) that jumps three phases, so the operating performance of the phase selection element directly affects the operating performance of the zero-sequence current differential protection.

In view of the above problems, the present invention proposes a phase selection element for zero-sequence current differential protection.

Invention content:

The purpose of the present invention is to provide a zero-sequence current differential phase-selection element, which can realize phase-selection tripping of homodyne protection when a single-phase high-resistance ground fault occurs, and prevent the occurrence of three-phase tripping of homodyne protection for minor faults.

In order to achieve the above object, the present invention adopts the following technical solutions: a zero-sequence current differential phase selection element, including a phase selection criterion I for distinguishing a single-phase ground fault phase and a two-phase ground fault phase, distinguishing a single-phase ground fault phase The phase selection criterion II of the two-phase metallic ground fault phase and the phase selection criterion III of the three-phase short-circuit unbalanced zero sequence outside the defense zone; the phase selection criterion I, the phase selection criterion II and the phase selection criterion III Between AND gate output, output single-phase ground fault phase.

The phase selection criterion I is determined by using the amplitude relationship between the negative sequence differential current and the zero sequence differential current.

The phase selection criterion I is determined by the following formula:

in, for The negative sequence current on both sides of the phase line, is the zero-sequence current on both sides of the line,

The phase selection criterion II is determined by using the phase relationship between the positive sequence differential current and the negative sequence differential current.

The phase selection criterion II is determined by the following formula:

in, for Positive sequence current on both sides of the phase line

The phase selection criterion III is determined using a low brake coefficient differential criterion.

The phase selection criterion III is determined by the following formula:

in,, on both sides of the line phase current, for The corresponding current phasor, for The corresponding current phasor (if

When a single-phase ground fault occurs, the faulty phase Satisfy the phase selection criterion I; when two-phase ground fault occurs, The phase selection criterion I is not satisfied.

When a single-phase ground fault occurs, the faulty phase Satisfy the phase selection criterion II; when two phases are grounded metallically, the non-faulty phase The phasing criterion II is not met.

When criteria I, II, and III are all satisfied, the single-phase-to-ground fault phase is output.

Compared with the closest prior art, the technical solution provided by the present invention has the following excellent effects

1. The sensitivity of the homodyne protection phase selection element proposed by the technical solution of the present invention is higher than that of the zero-sequence current differential protection, and is not affected by the load current. When a single-phase high-impedance ground fault occurs, the fault phase can still be accurately selected, which is different from the homodyne protection With the use of;

2. The technical solution of the present invention protects important transmission lines more reliably, and is used to remove single-phase high-resistance grounding faults of transmission lines;

3. The technical solution of the present invention improves the operating performance of the line zero-sequence current differential protection.

Description of drawings

FIG. 1 is an action logic diagram of a phase selection element according to an embodiment of the present invention;

Fig. 2 is a schematic diagram of fault lines in an embodiment of the present invention;

3 is a schematic diagram of three-phase current sampling values on both sides of line MN in Embodiment 1 of the present invention;

Fig. 4 is the schematic diagram of simulation result of criterion I of embodiment 1 of the present invention;

Fig. 5 is the schematic diagram of the simulation result of criterion II of embodiment 1 of the present invention;

Fig. 6 is a schematic diagram of the simulation results of criterion III of Embodiment 1 of the present invention;

7 is a schematic diagram of three-phase current sampling values on both sides of the line MN in Embodiment 2 of the present invention;

Fig. 8 is the schematic diagram of simulation result of criterion 1 of embodiment 2 of the present invention;

Fig. 9 is a schematic diagram of the simulation results of criterion II of the second embodiment of the present invention;

FIG. 10 is a schematic diagram of the simulation results of criterion III of Embodiment 2 of the present invention.

detailed description

The invention of this example provides a zero-sequence current differential phase selection element, which consists of three parts, as shown in Figure 1:

(1) Using the similar principle of negative-sequence current differential current and zero-sequence differential current, distinguish single-phase ground fault phase and two-phase ground fault phase. Phase selection criterion I is as follows:

(2) Using the phase relationship between the positive-sequence differential current and the negative-sequence differential current, distinguish single-phase ground fault phases from two-phase metallic ground fault phases. Phase selection criterion II is as follows:

(3) Use the differential criterion of low braking coefficient to judge the unbalanced zero-sequence current of the three-phase short-circuit outside the defense zone. Phase selection criterion III is as follows:

Criterion I, II, III is "AND" gate output, and the single-phase ground fault phase is output.

When a single-phase ground fault occurs, the faulty phase Criterion I is satisfied, when two-phase high-impedance ground fault occurs, Criterion I is not met.

When a single-phase ground fault occurs, the faulty phase Criterion II is satisfied, when two phases are grounded metallically, the non-faulty phase Criterion II is not met.

If F1 at the middle point of line MN in Figure 2 fails, the system voltage level is 1000kV, the line length is 200km, and the protection is installed at 1 and 2 in the figure.

(1) Collect the three-phase current at protection 1 and 2 Calculate differential flow The values are A, B, C. Calculate the positive, negative and zero-sequence difference currents, respectively

(2) Calculation criterion 1,

(3) Calculation criterion 2,

(4) Calculation criterion 3, in

(5) When the criteria I, II, and III are satisfied at the same time, it is judged that the single-phase ground fault phase

(6) Simulation verification:

Example 1:

1) Phase A ground fault through 800Ω transition resistance

Figure 3 shows the sampling values of the three-phase currents on both sides of the line MN. It can be seen that when the 800 Ω transition resistance fails, the current change is very small.

The simulation results of criterion I are shown in Fig. 4. Criterion 1 uses the relationship between negative sequence current differential current and zero sequence differential current amplitude. The solid line in the figure is the fixed value curve, and the dotted solid line is the three-phase action curve , it can be seen that phase A satisfies criterion I.

The simulation results of criterion II are shown in Figure 5. Criterion 2 uses the phase relationship between the positive sequence differential current and the negative sequence differential current to select phases. The straight lines in the figure are 45° and 75° fixed value curves respectively. , the solid line with dots is the three-phase action curve, it can be seen that phase A satisfies criterion II.

The simulation results of criterion III are shown in Figure 6. The solid line in the figure is the braking curve, and the solid line with dots is the three-phase action curve. As shown in the figure, phase A satisfies criterion III.

Criteria I, II, III are output through the "AND" gate, and the single-phase ground fault phase A is output.

Example 2:

2) Phase-to-phase fault of BC phase via 25Ω transition resistance

Figure 7 shows the sampling values of the three-phase currents on both sides of the fault line MN on both sides of the BC phase through the 25Ω transition resistance between phases.

The simulation results of criterion I are shown in Fig. 8. Criterion 1 uses the relationship between negative-sequence current differential current and zero-sequence differential current amplitude. The solid line in the figure is the fixed value curve, and the solid line with dots is the three-phase action curve. , it can be seen that the three phases A, B, and C do not satisfy criterion I.

The simulation results of criterion II are shown in Figure 9. Criterion 2 uses the phase relationship between the positive sequence differential current and the negative sequence differential current to select phases, and the straight lines in the figure are 45° and 75° fixed value curves respectively , the solid line with dots is the three-phase action curve, and the B and C phases meet the criterion II;

The simulation results of criterion III are shown in Figure 10. The solid line in the figure is the braking curve, and the solid line with dots is the three-phase action curve. As shown in the figure, phases B and C meet the criterion in some time periods.

Criteria I, II, and III are output through the "AND" gate, which does not satisfy the phase selection output of single-phase grounding.

Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Those of ordinary skill in the art should understand with reference to the above embodiments that the specific implementation methods of the present invention can still be modified or equivalent. Replacement, any modifications or equivalent replacements that do not depart from the spirit and scope of the present invention are within the protection scope of the claims of the present invention pending application.

Claims (9)

1. A zero sequence current differential phase selection element, characterized by: the method comprises a phase selection criterion I for distinguishing a single-phase earth fault phase from a two-phase high-resistance earth fault phase, a phase selection criterion II for distinguishing a single-phase earth fault phase from a two-phase metallic earth fault phase and a phase selection criterion III for preventing three-phase short circuit unbalance zero sequence outside a region; and the output of the AND gate among the phase selection criterion I, the phase selection criterion II and the phase selection criterion III outputs a single-phase earth fault phase.

2. A zero sequence current differential phase selection element as claimed in claim 1, characterized in that: and the phase selection criterion I is determined by utilizing the amplitude relation of the negative sequence differential current and the zero sequence differential current.

3. A zero sequence current differential phase selection element as claimed in claim 2, characterized in that: the phase selection criterion I is determined by the following formula:

wherein,is composed ofThe negative-sequence current is conducted on the two sides of the phase line, ${\stackrel{\·}{I}}_{0\mathrm{\Σ}}={\stackrel{\·}{I}}_{0M}+{\stackrel{\·}{I}}_{0N},$ is a zero sequence current at two sides of the line, $I_{0\mathrm{\Σ}}=\left|{\stackrel{\·}{I}}_{0\mathrm{\Σ}}\right|.$

4. a zero sequence current differential phase selection element as claimed in claim 1, characterized in that: and the phase selection criterion II is determined by utilizing the phase relation between the positive sequence differential current and the negative sequence differential current.

5. A zero sequence current differential phase selection element as claimed in claim 4, characterized in that: the phase selection criterion II is determined by the following formula:

wherein,is composed ofAnd positive sequence currents are arranged at two sides of the phase line.

6. A zero sequence current differential phase selection element as claimed in claim 1, characterized in that: the phase selection criterion III is determined by a low braking coefficient differential criterion.

7. A zero sequence current differential phase selection element as claimed in claim 6, characterized in that: the phase selection criterion III is determined by the following formula:

wherein,are respectively two sides of the circuitThe phase current is supplied to the phase current,is composed ofThe corresponding current phasor is calculated from the current phasor,is composed ofCorresponding current phasor, ifThen

8. A zero sequence current differential phase selection element as claimed in claim 3, characterized in that: when a single-phase earth fault occurs, the fault phaseMeeting the phase selection criterion I; when the two-phase high-resistance earth fault occurs,the phase selection criterion I is not fulfilled.

9. A zero sequence current differential phase selection element as claimed in claim 5, characterized in that: when a single-phase earth fault occurs, the fault phaseMeeting the phase selection criterion II; non-faulted phases when two phases are metallically earthedThe phase selection criterion II is not satisfied.