A kind of time domain impulse detection method of crosslinked cable joint water inlet state
Technical field
The present invention relates to a kind of power cable state detection technique field, be specifically related to the time domain impulse detection method of a kind of crosslinked cable joint water inlet state.
Background technology
Crosslinked cable is the abbreviation of cross-linked polyethylene insulated cable.This cable is applicable to power frequency ac voltage 500KV and following electric line.High-tension cable absolutely at present major part all adopts crosslinked polyetylene insulated, cross-linked polyethylene insulated cable utilizes chemical method or physical method, cable insulation polyethylene molecule is made to change main body network molecular structure into by linearity molecular structure, namely thermoplastic tygon changes heat cured crosslinked polyethylene into, thus greatly improve its thermotolerance and mechanical property, reduce its shrinkability, no longer melt after making it be heated, and maintain excellent electric property.
Cross-linked polyethylene insulated cable adopts the method for peroxide crosslinking, polyethylene molecule is made to become tridimensional network from linear molecular structure, become thermosets by thermoplastic, working temperature brings up to 90 DEG C from 70 DEG C, significantly improves the current capacity of cable.Cross-linked polyethylene insulated cable has the following advantages: heat resistance: the XLPE of net vertical body structure has very excellent heat resistance.Can not decompose and carbonization below 300 DEG C, Long-term service temperature can reach 90 DEG C, and the thermal life can reach 40 years; Insulating property: XLPE maintains the original good insulation characteristic of PE, and insulation resistance increases further.Its dielectric loss angle tangent is very little, and temperature influence is little; Mechanical property: owing to establishing new chemical bond intermolecular greatly, the hardness of XLPE, rigidity, wearing quality and impact resistance are improved, thus compensate for PE and be subject to environmental stress and the shortcoming chapped; Chemical-resistant characteristic: XLPE has stronger acid and alkali-resistance and oil resistance, and its products of combustion is mainly water and carbon dioxide, less to the harm of environment, meets the requirement of modern fire safety.
Cross-linked polyethylene insulated cable has the incomparable advantage of PVC insulated cable.Its structure simple, lightweight, heat-resisting good, load capacity is strong, non-fusible, resistance to chemical attack, physical strength is high.Also do not have the Method means of effective detection tabs water inlet defect state in cable site test, after can only applying voltage to cable line, measuring media loss factor or loss current harmonic component are to diagnose in whole cable whether there is the aging of insulation course.But this status flag amount of dielectric dissipation factor is not only intake with cable, joint or insulation course is aging relevant, and affects by other factors such as insulating thermal aging, chemical aging, and can only reflect the ageing level of cable.Loss current harmonic component is as status flag amount, and at the scene during testing inspection, need the multiple device means such as high-voltage test electric power, current comparator bridge to coordinate, testing process is implemented comparatively complicated, loaded down with trivial details.
Therefore in the time domain impulse detection method providing a kind of crosslinked cable joint to intake state, the Detection and diagnosis to cable splice water inlet state need be realized.
Summary of the invention
For the deficiencies in the prior art, the invention provides the time domain impulse detection method of a kind of crosslinked cable joint water inlet state, described crosslinked cable joint is the joint of two crosslinked cables, and described crosslinked cable is made up of conductor thread core and metal screen layer, said method comprising the steps of:
S1, departs from the circuit at described cable place and grid cut-off, and by the metal screen layer phase-splitting short circuit separately of phase cable every in circuit;
S2, records the resistance value at the two ends of described crosslinked cable and the two ends of described crosslinked cable joint with impedance instrument, be from left to right followed successively by cable characteristic impedance Z1, joint characteristics impedance Z 2, joint characteristics impedance Z 3 and cable characteristic impedance Z4;
S3, at the head end of cable line from injecting the known steep rising edge pulse I of polarity between the conductor thread core and described metal screen layer of described crosslinked cable
mp,described steep rising edge pulse I
mprising time≤10nS;
S4, with the described steep rising edge pulse I of high speed oscilloscope device observation
mpand the change of response signal waveform.
Preferably, described crosslinked cable joint is in the centre of described cable line.
Preferably, described joint characteristics impedance Z
2with described cable characteristic impedance Z
1do not mate, described steep rising edge pulse I
mpfrom described cable characteristic impedance Z
1transfer to described joint characteristics impedance Z
2to reflect, produce reflected impulse I
2refreturn.
Preferably, described joint characteristics impedance Z
2with described cable characteristic impedance Z
3do not mate, described steep rising edge pulse I
mpfrom described joint characteristics impedance Z
2transfer to described joint characteristics impedance Z
3to reflect, produce reflected impulse I
3refreturn.
Preferably, described steep rising edge pulse I
mpfrom described joint characteristics impedance Z
3transfer to the cable characteristic impedance Z of line end
4the total reflection that rear generation is positive, reflection coefficient is 1, produces reflected impulse I
4refreturn, polarity of wave is identical with described steep rising edge pulse Imp, and amplitude diminishes.
Preferably, described joint characteristics impedance Z 2 is greater than described cable characteristic impedance Z1, described steep rising edge pulse Imp transfers to described joint characteristics impedance Z 2 from described cable characteristic impedance Z1 and produces normal reflection, reflection coefficient is less than 1, reflected impulse I2ref polarity of wave is identical with described steep rising edge pulse Imp, and amplitude diminishes.
Preferably, described joint characteristics impedance Z 2 is greater than described cable characteristic impedance Z3, described steep rising edge pulse Imp transfers to described cable characteristic impedance Z3 from described joint characteristics impedance Z 2 and produces negative reflection, reflection coefficient is less than 1, reflected impulse I2ref polarity of wave is identical with described steep rising edge pulse Imp, and amplitude diminishes.
Preferably, described joint characteristics impedance Z 2 is less than described cable characteristic impedance Z1, described steep rising edge pulse Imp transfers to described joint characteristics impedance Z 2 from described cable characteristic impedance Z1 and produces negative reflection, reflection coefficient is less than 1, reflected impulse I2ref polarity of wave is contrary with described steep rising edge pulse Imp, and amplitude diminishes.
Preferably, described joint characteristics impedance Z 2 is less than described cable characteristic impedance Z3, described steep rising edge pulse Imp transfers to described cable characteristic impedance Z3 from described joint characteristics impedance Z 2 and produces normal reflection, reflection coefficient is less than 1, reflected impulse I2ref polarity of wave is identical with described steep rising edge pulse Imp, and amplitude diminishes.
Preferably, described in cause conductor thread core and described metal screen layer short circuit, described steep rising edge pulse Imp transfers to Z2 from Z1 and produces negative total reflection, and reflection coefficient is 1, and reflected impulse I2ref polarity of wave is contrary with Imp.
With immediate prior art ratio, beneficial effect of the present invention is:
1. can, when not applying outside test high pressure, utilize the otherness of crosslinked solid isolation cable characteristic impedance and cable splice characteristic impedance to judge whether cable splice exists water inlet to the Different Effects rule that time domain impulsive signals transmits.
2. make up the diagnostic test of existing cable circuit off-line and direct-detection, diagnosing cable joint whether cannot there is the shortcoming of water inlet and water inlet degree, realize the Detection and diagnosis to cable splice water inlet state.
Accompanying drawing explanation
Below in conjunction with the drawings and specific embodiments, the present invention is described in further detail.
Fig. 1 is the time domain impulse detection method detection model figure used of crosslinked cable joint of the present invention water inlet state;
Fig. 2 is the time domain impulse detection waveform characteristic pattern that crosslinked cable joint that the present invention detects is not intake;
Fig. 3 is the time domain impulse detection waveform characteristic pattern of the crosslinked cable joint water inlet that the present invention detects;
Fig. 4 is the time domain impulse detection waveform characteristic pattern that crosslinked cable joint that the present invention detects is intake completely;
Description of reference numerals: 1-crosslinked cable joint; 2-metal screen layer; 3-conductor thread core.
Embodiment
Below in conjunction with accompanying drawing, the specific embodiment of the present invention is described in further detail.
In order to thoroughly understand the embodiment of the present invention, by following description, detailed structure is proposed.Obviously, the execution of the embodiment of the present invention is not limited to the specific details that those skilled in the art has the knack of.Preferred embodiment of the present invention is described in detail as follows, but except these are described in detail, the present invention can also have other embodiments.
With reference to the time domain impulse detection method detection model figure used that Fig. 1, Fig. 1 are crosslinked cable joint of the present invention water inlet state.As shown in Figure 1, in figure, crosslinked cable joint 1 is the joint of two crosslinked cables, described crosslinked cable joint 1 is in the centre of cable line, described crosslinked cable is made up of conductor thread core 3 and the metal screen layer 2 that is enclosed in described conductor thread core outside surface, and the intake time domain impulse detection method of state of the crosslinked cable joint 1 applying this model comprises the following steps:
S1, circuit and the grid cut-off at described cable place depart from, and by the metal screen layer phase-splitting short circuit separately of phase cable every in circuit;
S2, records the resistance value at the two ends of described crosslinked cable and the two ends of described crosslinked cable joint 1 with impedance instrument, be from left to right followed successively by cable characteristic impedance Z1, joint characteristics impedance Z 2, joint characteristics impedance Z 3 and cable characteristic impedance Z4;
S3, at the head end of cable line from injecting the known steep rising edge pulse I of polarity between the conductor thread core 3 and described metal screen layer 2 of described crosslinked cable
mp,described steep rising edge pulse I
mprising time≤10nS;
S4, with the described steep rising edge pulse I of high speed oscilloscope device observation
mpand the change of response signal waveform.
Adopt the method when not applying outside test high pressure, can judge whether the cable splice inside of 10 (6) kV ~ 500kV electric pressures exists water inlet defect.
Be the time domain impulse detection waveform characteristic pattern that crosslinked cable joint that the present invention detects is not intake with reference to Fig. 2, Fig. 2.When described joint characteristics impedance Z
2with described cable characteristic impedance Z
1when not mating, described steep rising edge pulse I
mpfrom described cable characteristic impedance Z
1transfer to described joint characteristics impedance Z
2to reflect, produce reflected impulse I
2refreturn; Now described joint characteristics impedance Z
2be greater than described cable characteristic impedance Z1, described steep rising edge pulse I
mpfrom described cable characteristic impedance Z
1transfer to described joint characteristics impedance Z
2produce normal reflection, reflection coefficient is less than 1, reflected impulse I
2refpolarity of wave and described steep rising edge pulse I
mpidentical, amplitude diminishes, then crosslinked cable joint 1 is not intake.
When described joint characteristics impedance Z
2with described cable characteristic impedance Z
3do not mate, described steep rising edge pulse I
mpfrom described joint characteristics impedance Z
2transfer to described joint characteristics impedance Z
3to reflect, produce reflected impulse I
3refreturn; Now described joint characteristics impedance Z
2be greater than described cable characteristic impedance Z3, described steep rising edge pulse I
mpfrom described joint characteristics impedance Z
2transfer to described cable characteristic impedance Z3 and produce negative reflection, reflection coefficient is less than 1, reflected impulse I
2refpolarity of wave and described steep rising edge pulse I
mpidentical, amplitude diminishes, then crosslinked cable joint 1 is not intake.
Described steep rising edge pulse I
mpfrom described joint characteristics impedance Z
3transfer to the cable characteristic impedance Z of line end
4the total reflection that rear generation is positive, reflection coefficient is 1, produces reflected impulse I
4refreturn, polarity of wave and described steep rising edge pulse I
mpidentical, amplitude diminishes.
Composition graphs 3, Fig. 3 is the time domain impulse detection waveform characteristic pattern of the crosslinked cable joint water inlet that the present invention detects.When described joint characteristics impedance Z
2with described cable characteristic impedance Z
1when not mating, described steep rising edge pulse I
mpfrom described cable characteristic impedance Z
1transfer to described joint characteristics impedance Z
2to reflect, produce reflected impulse I
2refreturn; Now described joint characteristics impedance Z 2 is less than described cable characteristic impedance Z1, described steep rising edge pulse Imp transfers to described joint characteristics impedance Z 2 from described cable characteristic impedance Z1 and produces negative reflection, reflection coefficient is less than 1, reflected impulse I2ref polarity of wave is contrary with described steep rising edge pulse Imp, amplitude diminishes, then crosslinked cable joint 1 exists water inlet.
When described joint characteristics impedance Z 2 is not mated with described cable characteristic impedance Z3, described steep rising edge pulse Imp transfers to described joint characteristics impedance Z 3 from described joint characteristics impedance Z 2 and will reflect, and produces reflected impulse I3ref and returns; Now described joint characteristics impedance Z 2 is less than described cable characteristic impedance Z3, described steep rising edge pulse Imp transfers to described cable characteristic impedance Z3 from described joint characteristics impedance Z 2 and produces normal reflection, reflection coefficient is less than 1, reflected impulse I2ref polarity of wave is identical with described steep rising edge pulse Imp, amplitude diminishes, then cable splice 1 exists water inlet.
Composition graphs 4, Fig. 4 is the time domain impulse detection waveform characteristic pattern that crosslinked cable joint that the present invention detects is intake completely.Described conductor thread core 3 and described metal screen layer 2 short circuit, described steep rising edge pulse Imp transfers to Z2 from Z1 and produces negative total reflection, and reflection coefficient is 1, and reflected impulse I2ref polarity of wave is contrary with Imp, amplitude is close, and now crosslinked cable joint 1 exists serious water inlet.
Adopt detection method of the present invention, can, when not applying outside test high pressure, the otherness of crosslinked solid isolation cable characteristic impedance and cable splice characteristic impedance be utilized to judge whether cable splice exists water inlet to the Different Effects rule that time domain impulsive signals transmits; Make up the diagnostic test of existing cable circuit off-line and direct-detection, diagnosing cable joint whether cannot there is the shortcoming of water inlet and water inlet degree, realize the Detection and diagnosis to cable splice water inlet state.
Finally should be noted that: above embodiment is only in order to illustrate that technical scheme of the present invention is not intended to limit; although with reference to above-described embodiment to invention has been detailed description; those of ordinary skill in the field still can modify to the specific embodiment of the present invention or equivalent replacement; these do not depart from any amendment of spirit and scope of the invention or equivalent replacement, are all applying within the claims awaited the reply.