CN203811728U - Single-core power cable sheath earth fault detecting system based on circulation measurement - Google Patents

Abstract

The utility model relates to the single-core power cable sheath earth fault detecting field and especially relates to a single-core power cable sheath earth fault detecting system based on circulation measurement. The system comprises three phases, specifically, a phase a, a phase b, and a phase c. The system is characterized in that a plurality of sheaths are respectively arranged on the three phases a, b, c; the front end and the tail end of each phase (a, b, c) are grounded; adjacent sheaths of the three phases a, b, c are interconnected in a crossed way through leading-out wires; and power switchgears are serially connected among the adjacent sheath leading-out wires and a copper terminal before the adjacent sheath leading-out wires are grounded. The system can acquire circulation characteristics on different fault ground points according to a circuit theory model of a fault sheath circulation loop with a single-end grounding means and experimental data, and then perform fault determination and positioning. The whole detection process is simple. The calculation amount is small. On-line detection can be further realized.

Description

The single-core power cables sheath ground-fault detection system of measuring based on circulation

Technical field

The utility model relates to a kind of single-core power cables sheath Earth Fault Detection field, particularly a kind of single-core power cables sheath ground-fault detection system of measuring based on circulation.

Background technology

The cable of single cored structure, electromagnetics principle, this must cause that induced voltage appears in protective metal shell, if earthing mode is improper, this induced voltage can form very large induction current on protective metal shell, the ability that causes cable transfer electric power is reduced greatly, and cause that protective metal shell heating reduces major insulation, shortens the normal operation life of cable.Some Domestic operation power department has rule of thumb formulated the standard of controlling separately circulation, conventionally circulation need to be controlled at load current 10% with interior or below 10A.

Generally, for short-term road, protective metal shell should adopt the direct ground connection in one end, and the other end is through overvoltage protection device ground connection; If circuit is slightly long, the first earthing mode induced potential cannot meet code requirement, and underwater cable, cable that transmission capacity is less etc. can be taked the direct ground connection in circuit two ends; For long transmission line, protective metal shell should be in isolating joint place rule in accordance with regulations by the coordinated transposition of cable cross-connect case, the direct ground connection of two terminals.

The earthing mode of the above three kinds of single core cable protective metal shells more at least reliable ground that is in operation, but because the external insulation of cable metal screen layer meets with after mechanical damage or long operational time in the time laying, stinging of chemical corrosion, mouse and ant worm is bad etc. causes protective metal shell multipoint earthing, causes its circulation to increase rapidly so that threatens personal safety, infringement cable insulation, shortens cable life and reduce cable power transmission ability.The monitoring method of cable metal sheath multipoint earth faults has impulse method, HVDC flashover m ethod and the impulse HV flashover method etc. surveyed under protective metal shell insulation resistance method, off-line, but all not bery desirable and can not on-line measurement.Ring current method is to judge by the variation of monitoring cable protective metal shell circulation whether it occurs earth fault and can position Single Point of Faliure, is On-line Measuring Method.

Utility model content

According to above the deficiencies in the prior art, the technical problems to be solved in the utility model is: provide one can overcome above-mentioned defect, can carry out the single-core power cables sheath ground-fault detection system of measuring based on circulation of cable earth fault detection and location.

The utility model solves the technical scheme that its technical matters adopts:

The described single-core power cables sheath ground-fault detection system of measuring based on circulation, comprise a, b, c three-phase, it is characterized in that: on a, b, c three-phase, multiple sheaths are set respectively, the head end of a, b, c three-phase and end ground connection, the adjacent sheath of a, b, c three-phase is cross interconnected by extension line, ground connection after the power switchgear of connecting between adjacent sheath extension line and copper tip.

Preferred further, the end of a, b, c three-phase is respectively by switch k _a3, switch k _b3, switch k _c3ground connection.

Preferred further, a phase sheath comprises sheath l _a1, sheath l _a2with sheath l _a3, b phase sheath comprises sheath l _b1, sheath l _b2with sheath l _b3, c phase sheath comprises sheath l _c1, sheath l _c2with sheath l _c3, a phase sheath l _a1extension line and b phase sheath l _b2extension line connect, a phase sheath l _a1extension line by switch k _b1with ground connection after copper tip series connection, b phase sheath l _b1extension line and c phase sheath sheath l _c2extension line connect, b phase sheath l _b1extension line by switch k _c1with ground connection after copper tip series connection, c phase sheath l _c1extension line and a phase sheath l _a1extension line connect, c phase sheath l _c1extension line by switch k _a1with ground connection after copper tip series connection.

The beneficial effect that the utility model has is:

The described single-core power cables sheath ground-fault detection system of measuring based on circulation will be for single-end earthed, cable cover(ing) under three kinds of earthing modes of two sides earth and cross interconnected ground connection carries out circulation detection, make every kind of earthing mode can be converted to easily and safely mode single-end earthed in the time measuring by the various grounding boxes of cable being installed additional to on-off element, then under this state, measure circulating current in sheath value, obtain the circulation characteristic under different faults earth point according to the Circuit theory Model and experiment data in the fault circulating current in sheath loop under mode single-end earthed, and then carry out fault judgement location.

Brief description of the drawings

Fig. 1 is the cable under test exemplary plot under cross interconnected earthing mode of the present utility model;

Fig. 2 is the sheath l of example cable of the present utility model _a2circulation loop equivalent-circuit model;

Wherein, l _a1, l _a2, l _a3, l _b1, l _b2, l _b3, l _c1, l _c2, l _c3, sheath; k _a1, k _b1, k _c1, k _a2, k _b2, k _c2, k _a3, k _b3, k _c3, switch.

Embodiment

Below in conjunction with accompanying drawing, embodiment of the present utility model is described further:

As shown in Figure 1, the single-core power cables sheath ground-fault detection system of measuring based on circulation described in the utility model, comprise a, b, c three-phase, it is characterized in that: on a, b, c three-phase, multiple sheaths are set respectively, the head end of a, b, c three-phase and end ground connection, the adjacent sheath of a, b, c three-phase is cross interconnected by extension line, ground connection after the power switchgear of connecting between adjacent sheath extension line and copper tip.The end of a, b, c three-phase is respectively by switch k _a3, switch k _b3, switch k _c3ground connection.A phase sheath comprises sheath l _a1, sheath l _a2with sheath l _a3, b phase sheath comprises sheath l _b1, sheath l _b2with sheath l _b3, c phase sheath comprises sheath l _c1, sheath l _c2with sheath l _c3, a phase sheath l _a1extension line and b phase sheath l _b2extension line connect, a phase sheath l _a1extension line by switch k _b1with ground connection after copper tip series connection, b phase sheath l _b1extension line and c phase sheath sheath l _c2extension line connect, b phase sheath l _b1extension line by switch k _c1with ground connection after copper tip series connection, c phase sheath l _c1extension line and a phase sheath l _a1extension line connect, c phase sheath l _c1extension line by switch k _a1with ground connection after copper tip series connection.

The single-core power cables sheath earth-fault detecting method of measuring based on circulation, comprises the following steps:

Step 1, the direct grounding box in one end to the cable under the direct ground connection in two ends and cross interconnected earthing mode makees following processing: the electric power Switch equipment of connecting between cable cover(ing) extension line and junction box's copper tip, switch closure at ordinary times, sheath is at this reliable ground, in the time detecting single-core power cables sheath earth fault, disconnect all switches, sheath extension line is unsettled at this, and the cable under mode single-end earthed is not done to similar processing;

Step 2, all cross interconnected protective ground casees are done to following processing: an on-off element in parallel on each alternating layers protector, switch disconnects at ordinary times, in the process that detects single-core power cables sheath earth fault whenever necessary, Closing Switch, makes corresponding cross interconnected extension line reliable ground;

Step 3, make wherein one end earth terminal of the direct ground connection in two ends and cross interconnected ground connection unsettled, can on the basis of step 1, disconnect the earth terminal that adds switch, so the two ends of the cable of three kinds of earthing modes can be divided into earth terminal and ungrounded end, and to make cable grounding end be head end, ungrounded end is end;

Step 4, measures each time each phase head end circulating current in sheath value, and measures each phase running current value simultaneously each time at cable grounding end place;

Step 5, observes each phase circulation value, and under normal circumstances, each phase circulation should be close to 0, if certain occurs the larger situation of circulation mutually, establishing this is that n returns x phase mutually, i.e. this phase head end circulating current in sheath I _snx1>0, can judge that the sheath of this phase sheath and series connection with it exists earth fault, can and then judge its abort situation, and judgment mode is as follows:

1) for mode single-end earthed, comprise the two sides earth mode that an earth terminal is unsettled, can be directly by experiment or the method for simulation calculation find the I under current running current _snx1with relation and then the failure judgement point position of trouble spot to the distance of earth terminal;

2) need to do further detection judgement for cross interconnected earthing mode, to fault phase sheath and series connection sheath thereof totally three sections of sheaths by being numbered respectively l by earth terminal to the order of ungrounded end _nx1, l _nx2, l _nx3, it is as follows that it detects determining step:

A, at l _nx1with l _nx2cross interconnected protective ground point measurement l _nx2circulation I _snx2if, I _snx2≈ 0, can failure judgement point at l _nx1upper, by sheath l _nx1equivalence is considered as mode single-end earthed, according to judgment mode 1), find I _snx1with relation and then the failure judgement point position of trouble spot to the distance of earth terminal, if I _snx2>0 enters step B;

B, short circuit l _nx1with l _nx2sheath extension line and the grounding copper terminal of cross interconnected protective ground point, make its reliable ground, be made as new earth terminal, remeasure now l _nx2circulation I _snx2, and note down, then at l _nx1with l _nx2cross interconnected protective ground point measurement l _nx3circulation I _snx3if, I _snx3≈ 0, can failure judgement point at l _nx2upper, by sheath l _nx2equivalence is considered as mode single-end earthed, according to judgment mode 1), find I _snx2with relation and then the failure judgement point position of trouble spot to the distance of earth terminal, if I _snx3>0 enters step C;

C, now with the localization of faults at l _nx3upper, short circuit l _nx2with l _nx3sheath extension line and the grounding copper terminal of cross interconnected protective ground point, make its reliable ground, be made as new earth terminal, remeasure now l _nx3circulation I _snx3, and note down, by sheath l _nx3equivalence is considered as mode single-end earthed, according to judgment mode 1), find I _snx3with relation and then the failure judgement point position of trouble spot to the distance of earth terminal.

Judgment mode 1 described in described step 5) in emulated computation method as follows:

A, first obtain total induction electromotive force E that each return cable core running current produces in fault sheath unit length _s;

The induction electromotive force E of the core running current in loop of first obtaining a certain m of being numbered in fault sheath unit length _sm, establish threephase load balance, i.e. I every time _ma+ I _mb+ I _mc=0, this time each phase core center is respectively D to the distance at fault sheath center _sma, D _smb, D _smcif (or b, c) phase core center is 0 to the distance at fault sheath center to a, makes D _sma(or D _smb, D _smc)=R _s, wherein R _sfor sheath external radius, so E _smsolving equation is as follows:

E _sm＝jωμ/(2π)*[ln(D _sma/D _smb)I _mb+ln(D _sma/D _smc)I _mc]

In like manner, can obtain as stated above the induction electromotive force of each loop line core running current in fault sheath unit length, establishing total feeder number is M, total induction electromotive force that each return cable core running current produces in fault sheath unit length:

$E_s=\underset{m=1}{\overset{M}{\mathrm{\Σ}}}{E}_{\mathrm{sm}}$

B, measure and calculate sheath resistance per unit length value ρ _swith self-inductance L _s, the earth EU Equivalent Unit length leak resistance ρ _e, earth terminal grounding resistance r ₀, fault ground resistance value r _f;

C, to establish earth terminal be l to the distance of trouble spot _f, by following relational expression:

1/I _s＝(r ₀+r _f)/E _s*l _f+(ρ _s+jωL _s+ρ _e)/E _s

Obtain l _fwith fault circulating current in sheath I _schanging Pattern, and then according to I _sobtain l _f.

Judgment mode 1 described in described step 5) in experimental technique as follows:

A, choose representative experiment sheath, measure the core running current of certain stable operation period on this sheath, and then try to achieve the induction electromotive force E of core running current in fault sheath unit length _svalue;

B, in this stable operation period, the actual artificial manufacturing fault point of incorporation engineering is in different l _fsheath ground fault condition, and its circulation value I that samples _s;

C, recording different l _fand corresponding I _safter, following formula is done to parameter estimation:

1/I _s＝α/E _s*l _f+β/E _s

Try to achieve after parameter alpha and β known I _sand E _sjust can try to achieve l by above formula _f.

Embodiment 1:

Exist the list of sheath earth fault to return three-phase single core cable as example taking certain, as shown in Figure 1, detecting step is as follows:

1, be cable end piece ground connection tandem tap, remain closed at ordinary times, for the cross interconnected protective ground paralleling switch of cable, remain open at ordinary times, the numbering of all switches as shown in Figure 1.

2, cut-off switch k _a3, k _b3, k _c3, respectively by sheath l _a1, l _b1, l _c1extension line at head end is measured at sheath l _a1, l _b1, l _c1on electric current I _sa1, I _sb1, I _sc1, observe three current value sizes, find wherein I _sb1, I _sa1no better than 0, I _sc1obviously be greater than 0, can judge sheath l _c1, l _a2, l _b3on may there is earth fault.

3, pass through l _a2with l _c1connected extension line is measured l _a2on electric current I _sa2, I _sa2obviously be greater than 0, illustrate that trouble spot is not at l _c1on.

4, Closing Switch k _a1, again measure l _a2on electric current I _sa2, and cover former record.Pass through l _b3with l _a2connected extension line is measured l _b3on electric current I _sb3, I _sb3no better than 0, illustrate that trouble spot is at l _a2on.

5, to sheath l now _a2equivalent-circuit model is set up as shown in Figure 2 in circulation loop, and its equivalent-circuit model is with sheath is identical single-end earthed.

Wherein:

E _sb＝jωμ/(2π)*[ln(R _s/D _sab)I _b+ln(R _s/D _sac)I _c]

E _sbfor b phase sheath unit length induction kinetic potential, I _a, I _b, I _cbe respectively a, b, c three-phase core electric current, and I _a+ I _b+ I _c=0, R _sfor sheath external radius, D _sabfor a phase sheath center is to the distance at b phase core center, D _sacfor a phase sheath center is to the distance at c phase core center.ρ _sfor sheath resistance per unit length value, L _sfor self-inductance, ρ _efor the earth EU Equivalent Unit length is leaked resistance, r ₀for earth terminal grounding resistance, r _ffor fault ground resistance value.

Finally try to achieve trouble spot to switch k _a1distance:

l _f＝E _sa/(r ₀I _sa2+r _fI _sa2)-(ρ _s+jωL _s+ρ _e)/(r ₀+r _f)

The transformation that the utility model installs on-off element additional to the various grounding boxes of cable makes every kind of earthing mode can be converted to easily and safely mode single-end earthed in the time measuring, then under this state, measure circulating current in sheath value, obtain the circulation characteristic under different faults earth point according to the Circuit theory Model and experiment data in the fault circulating current in sheath loop under mode single-end earthed, and then carry out fault judgement location.Whole process detects simple, and calculated amount is little, belongs to online detection.

Claims (3)

1. a single-core power cables sheath ground-fault detection system of measuring based on circulation, comprise a, b, c three-phase, it is characterized in that: on a, b, c three-phase, multiple sheaths are set respectively, the head end of a, b, c three-phase and end ground connection, the adjacent sheath of a, b, c three-phase is cross interconnected by extension line, ground connection after the power switchgear of connecting between adjacent sheath extension line and copper tip.

2. the single-core power cables sheath ground-fault detection system of measuring based on circulation according to claim 1, is characterized in that: described a, b, the end of c three-phase are respectively by switch k _a3, switch k _b3, switch k _c3ground connection.

3. the single-core power cables sheath ground-fault detection system of measuring based on circulation according to claim 1, is characterized in that: described a phase sheath comprises sheath l _a1, sheath l _a2with sheath l _a3, b phase sheath comprises sheath l _b1, sheath l _b2with sheath l _b3, c phase sheath comprises sheath l _c1, sheath l _c2with sheath l _c3, a phase sheath l _a1extension line and b phase sheath l _b2extension line connect, a phase sheath l _a1extension line by switch k _b1with ground connection after copper tip series connection, b phase sheath l _b1extension line and c phase sheath sheath l _c2extension line connect, b phase sheath l _b1extension line by switch k _c1with ground connection after copper tip series connection, c phase sheath l _c1extension line and a phase sheath l _a1extension line connect, c phase sheath l _c1extension line by switch k _a1with ground connection after copper tip series connection.