The small grounding current system double-loop wire single-phase ground fault distance measuring method
Technical field
The invention belongs to the electric power system fault distance-finding method, particularly a kind of small grounding current system double-loop wire single-phase ground fault distance measuring method.
Background technology
At present, when electric system is short-circuited fault,, be that parameter has been realized fault localization with electric current, voltage because short-circuit current is very big, the distance of trouble spot as can be known.But, when small grounding current system generation singlephase earth fault, because ground current is very little, it only is the capacitive earth current of system, and its size of current is only relevant with the ground connection degree with the method for operation, and irrelevant with earthing position, therefore is difficult to be grounded fault localization.For this reason, at present still continuing to use traditional patrolling method artificial along the line aspect the earth point searching.
Summary of the invention
The objective of the invention is to overcome the prior art above shortcomings, a kind of small grounding current system double-loop wire single-phase ground fault distance measuring method that can accurately measure the earth fault distance is provided.
Small grounding current system double-loop wire single-phase ground fault distance measuring method of the present invention may further comprise the steps:
1, the double loop with diverse location is numbered and is preset in the microcomputer of ground connection transfer device;
2, gather, calculate phase, line voltage and residual voltage and each circuit zero-sequence current on the substation bus bar in real time by microcomputer, judgement system has or not the separate of ground connection and ground connection, when system's generation singlephase earth fault, provide the split-phase switch reclosing command of ground connection phase by microcomputer, provide the instruction of record ripple simultaneously;
3, after the record ripple was finished, microcomputer carried out the route selection operation in conjunction with the numbering of double loop by residual voltage and the zero-sequence current of measuring;
4, then, calculate to the range equation between the trouble spot by measuring the double loop first line ground current branch flow valuve equation, the measurement double loop second line ground current branch flow valuve equation, measurement inflow trouble spot ground current value equation and measuring circuit end by microcomputer, the position of earth point when trying to achieve some ground connection of double loop, promptly line end is to the distance between the trouble spot;
The described measurement double loop first line ground current branch flow valuve equation is:
U0″/U0′×(I01′-I01)-(I01″-I01)＝A×IJ (1)
The described measurement double loop second line ground current branch flow valuve equation is:
U0″/U0′×(I02′-I02)-(I02″-I02)＝B×IJ (2)
Described measurement flows into trouble spot ground current value equation:
U0″/U0′×(I01′-I01)-(I01″-I01)+U0″/U0′×(I02′-I02)-(I02″-I02)＝IJ (3)
Described measuring circuit end to the range equation between the trouble spot is
X＝L×(A×IJ-B×IJ)/(A×IJ+B×IJ) (4)
Each symbolic representation implication is as follows in the formula:
Indicate " " " value when shifting for ground connection; the value when indicating " ' "; mark " " for ground connection " with " ' " be value when normally moving, I01 is the first-line zero-sequence current of double loop, I02 is the second-line zero-sequence current of double loop, U0 is the residual voltage on the bus, A*IJ is the ground current that the double loop first line fault goes up mutually, B*IJ is the ground current that the double loop second line fault goes up mutually, and wherein A and B are diverting coefficient, A=(L-X)/2L, B=(L+X)/2L, IJ is for flowing into the ground current of earth point, and L is every line length, and X is the distance of line end to the trouble spot.
In above-mentioned equation, measuring double loop line one ground current branch flow valuve equation, measuring the double loop second line ground current branch flow valuve equation is two fundamental equations, is the important equation that is grounded differentiation, ground current measurement, localization of fault.
Two fundamental equations are a zero-sequence current " three is poor " equations, wherein first poor (I01 '-I01) with (I02 '-the zero-sequence current increment that produces during I02) for system earth, second poor (the zero-sequence current increment of I01 " I01) with (I02 "-generation when I02) shifting for ground connection, the 3rd the difference U0 "/U0 ' * (I01 '-I01)-(I01 "-I01) with U0 "/U0 ' * (I02 '-I02)-(I02 "-I02), first difference be multiply by a coefficient of contact U0 "/U0 '; carrying out difference computing of equal value with second difference then; its objective is; because of self capacitive earth current is all arranged; after this three eikonal equation is handled in every circuit first difference and second difference; can eliminate self capacitive earth current influences in order to eliminate in every circuit self capacitive earth current component, and for non-ground loop, the value of three eikonal equations is null, for ground loop, the value of three eikonal equations is the ground current that fault flows through on mutually, makes the proportional relation in position of two circuit every road ground current shunting result and earth point.
The invention has the beneficial effects as follows;
By two fundamental equations and the value of ground current can know system earth the time; The circuit that can know ground connection by the difference of two fundamental equations, when its difference is timing, earth point on circuit 1, otherwise on circuit 2; Can know the distance of earth point by the 4th equation; The route selection result is not subjected to have or not on the double loop circuit the whether influence of factor such as balance of T link and self capacitive earth current; The route selection result is not subjected to the influence of zero sequence CT three-phase imbalance and three impedance unbalances of double loop; The route selection result is not crossed by arc suppression coil to mend and owes to mend and the influence of installation site; The route selection result is not limited by system operation mode, generates corresponding results automatically by the current method of operation; Fault localization requirement when this distance-finding method also is suitable for looped network working line point ground connection.
Description of drawings
Fig. 1 is an elementary diagram of implementing phase-splitting earth protective device of the present invention.
Embodiment
As shown in Figure 1; small connect ground electricity phase-splitting earth protective device has extinguishing arc, overvoltage, human body electrification defencive function; simultaneously accurate identification ground loop and double loop earth fault distance measurement function being arranged again, is a kind of protective device that promotes to improve the small grounding current system safe and reliable operation.Specifically split-phase switch 1, zero sequence current mutual inductor 3 and the microcomputer 2 by quick phase-splitting operation constitutes.Wherein split-phase switch 1 one ends are by disconnecting link connected system A, B, C three-phase supply, and the other end seals star after zero sequence current mutual inductor 3 directly links to each other with the grounded screen of transformer station.Owing to be provided with machinery and program locking between the split-phase switch 1, only allow single-phase on/off switch, so its device is a phase-splitting earth protective device.During work, gather, calculate phase, line voltage and residual voltage on the substation bus bar in real time by microcomputer 2, judgement system has or not the separate of ground connection and ground connection, when system's generation singlephase earth fault, provide the split-phase switch reclosing command of ground connection phase by microcomputer 2, provide the instruction of record ripple simultaneously, (50ms) and fault before the fault on the bus are shifted phase, line voltage, residual voltage and each line zero-sequence current of back (150ms) and record ripple.The split-phase switch 1 of ground connection phase directly gets up ground connection and the earth equipotential after closing a floodgate, and allows the ground current of system transfer to this protective ground point fully to come up, and the ground current of fault ground point goes to zero.Because the responsiveness of device is very fast; from system take place touchdown time play with ground connection mutually time of 100% multiple grounding less than 50 milliseconds; the ground current of the trouble spot ground current that also do not blaze up has just been disappeared; thereby after installing this phase-splitting ground protection additional; when system's generation singlephase earth fault, do not produce electric arc, for preventing that the ground arc arcing from developing into phase fault good protective effect is arranged.If system earth is intermittent, intermittent ground connection can be become a kind of stable state ground connection through this protective device, for preventing that intermittent grounding surge from also having the protective effect of good energy.If ground connection owing to human body electrification causes, has as touch on the electrified body of ground wire, can make the electric shock personnel hightail power supply, to alleviating electric shock personnel extent of injury good protective effect is arranged also.
After the record ripple is finished, microcomputer is in conjunction with the numbering of double loop, the zero-sequence current I0 of single loop line during with the normal operation of measuring, the first-line zero-sequence current I01 of double loop, the second-line zero-sequence current I02 of double loop, the zero-sequence current I0 ' of single loop line during ground connection, residual voltage U0 ' on the bus, the first-line zero-sequence current I01 ' of double loop, the second-line zero-sequence current I02 ' of double loop, the residual voltage U0 when ground connection is shifted on the bus "; the first-line zero-sequence current I01 of double loop ", the second-line zero-sequence current I02 of double loop "; the zero-sequence current I0 of single loop line is " according to double loop ground connection transfer characteristic formula
U0″/U0′×(I01′-I01)-(I01″-I01)+U0″/U0′×(I02′-I02)-(I02″-I02)
And single loop line ground connection transfer characteristic formula
U0″/U0′×(I0′-I0)-(I0″-I0)
Calculate, and flow into earth point when shifting with the ground connection that records by zero sequence current mutual inductor 3
The ground current IJ of (split-phase switch 1 through the ground connection phase flows through) compares;
When result of calculation be positioned at ± the 0.1IJ scope (promptly 〉=-0.1IJ or≤0.1IJ), illustrate that circuit is a non-fault line; When result of calculation in (1 ± 0.1) IJ scope (promptly 〉=0.9IJ or≤1.1IJ), illustrate that circuit is a faulty line.
Then, by microcomputer by measuring the double loop first line ground current branch flow valuve equation, measure the double loop second line ground current branch flow valuve equation, measuring and flow into trouble spot ground current value equation and the measuring circuit end calculates to the range equation between the trouble spot, the position of earth point when trying to achieve certain some ground connection of double loop (looped network);
The described measurement double loop first line ground current branch flow valuve equation is:
U0″/U0′×(I01′-I01)-(I01″-I01)＝A×IJ (1)
The described measurement double loop second line ground current branch flow valuve equation is:
U0″/U0′×(I02′-I02)-(I02″-I02)＝B×IJ (2)
Described measurement flows into trouble spot ground current value equation:
U0″/U0′×(I01′-I01)-(I01″-I01)+U0″/U0′×(I02′-I02)-(I02″-I02)＝IJ (3)
Described measuring circuit end to the range equation between the trouble spot is
X＝L×(A×IJ-B×IJ)/(A×IJ+B×IJ) (4)
Each symbolic representation implication is as follows in the formula:
Indicate " " " value when shifting for ground connection; the value when indicating " ' "; mark " " for ground connection " with " ' " be value when normally moving, I01 is the first-line zero-sequence current of double loop, I02 is the second-line zero-sequence current of double loop, U0 is the residual voltage on the bus, A * IJ is the ground current that the double loop first line fault goes up mutually, B * IJ is the ground current that the double loop second line fault goes up mutually, and wherein A and B are diverting coefficient, and IJ is for flowing into the ground current of earth point, A=(L-X)/2L, B=(L+X)/2L, L are every line length, and X is the distance of line end to the trouble spot.