CN112798903A - Double-shielded cable fault detection method - Google Patents
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- 238000001514 detection method Methods 0.000 title claims abstract description 40
- 238000012544 monitoring process Methods 0.000 claims abstract description 96
- 238000009413 insulation Methods 0.000 claims description 35
- 238000005070 sampling Methods 0.000 claims description 7
- 238000002347 injection Methods 0.000 claims description 6
- 239000007924 injection Substances 0.000 claims description 6
- 239000004020 conductor Substances 0.000 claims description 5
- 239000000463 material Substances 0.000 claims description 5
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- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 description 2
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
- G01R31/08—Locating faults in cables, transmission lines, or networks
- G01R31/081—Locating faults in cables, transmission lines, or networks according to type of conductors
- G01R31/083—Locating faults in cables, transmission lines, or networks according to type of conductors in cables, e.g. underground
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
- G01R31/08—Locating faults in cables, transmission lines, or networks
- G01R31/088—Aspects of digital computing
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
- G01R31/50—Testing of electric apparatus, lines, cables or components for short-circuits, continuity, leakage current or incorrect line connections
- G01R31/52—Testing for short-circuits, leakage current or ground faults
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
- G01R31/50—Testing of electric apparatus, lines, cables or components for short-circuits, continuity, leakage current or incorrect line connections
- G01R31/54—Testing for continuity
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
- G01R31/50—Testing of electric apparatus, lines, cables or components for short-circuits, continuity, leakage current or incorrect line connections
- G01R31/58—Testing of lines, cables or conductors
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Abstract
The invention discloses a double-shielded cable fault detection method, which loads a power supply between a grounding wire and a monitoring wire at the other end of a double-shielded cable to be detected, wherein the grounding wire or the monitoring wire connected with the cathode of a diode is connected with the anode of the power supply; and then measuring the current of the monitoring wire or the grounding wire at the other end of the double-shielded cable to be detected, quickly obtaining the short-circuit condition of the grounding wire and the monitoring wire according to the resistance obtained by dividing the power supply voltage and the detection current and a short-circuit set threshold value, then adopting reverse loading current, obtaining the loop resistance of the monitoring wire and the grounding wire according to the loading voltage values on the monitoring wire and the grounding wire and the voltage values at the two ends of the diode simultaneously, and judging whether the monitoring wire and the grounding wire of the double-shielded cable to be detected have broken wire faults or not.
Description
Technical Field
The invention belongs to the technical field of shielded cable detection, and particularly relates to a double-shielded cable fault detection method.
Background
Due to the special use environment of the mining cable, the mining cable has more severe requirements on the safety and the high reliability of the cable, and the double-shielded cable well solves the problem. The national standard JB/T8739-2015 also gives detailed requirements for insulation monitoring protection between the monitoring line and the ground line of the double-shielded rubber sleeve cable. However, the existing detection means generally adopts passive devices such as a termination resistor or a diode for auxiliary detection, and the termination resistor or the diode has a defect that a loop resistor fault, an insulation resistor fault or even a single fault cannot be accurately judged after an accident occurs, so that the accident handling and rescue are seriously hindered.
Disclosure of Invention
The invention aims to provide a double-shielded cable fault detection method to overcome the defects of the prior art, and the method can accurately judge the type and the position of the system fault and provide powerful guarantee for mine rescue and equipment safety.
In order to achieve the purpose, the invention adopts the following technical scheme:
a double-shielded cable fault detection method comprises the following steps:
s1, connecting a diode between the grounding wire at one end of the double-shielded cable to be detected and the monitoring wire; loading a power supply between a grounding wire at the other end of the double-shielded cable to be detected and the monitoring wire, and connecting the grounding wire connected with the cathode of the diode or the monitoring wire to the anode of the power supply;
s2, measuring the current of the monitoring wire or the grounding wire at the other end of the double-shielded cable to be detected, if the resistance obtained by dividing the power supply voltage and the detection current is less than the short-circuit set threshold value, indicating that the double-shielded cable to be detected is in voltage loss short circuit or electric leakage, and alarming; if the resistance obtained by dividing the power supply voltage and the detection current is greater than or equal to the short circuit setting threshold, the double-shielded cable to be detected has no voltage loss short circuit or electric leakage;
s3, if the double-shielded cable to be detected has no voltage loss short circuit or electric leakage, the detected resistance value is the insulation resistance between the grounding wire and the monitoring wire, the reverse current of the step S2 is loaded on the monitoring wire and the grounding wire at the other end of the double-shielded cable to be detected, the loaded voltage values on the monitoring wire and the grounding wire and the voltage values at two ends of the diode are detected at the same time, the difference between the loaded voltage values on the monitoring wire and the grounding wire and the voltage values at two ends of the diode is divided by the current flowing through the diode, and then the loop resistance of the monitoring wire and the grounding wire can be obtained, if the loop resistance is larger than the set threshold value of open circuit, the monitoring wire and the grounding wire of the double-shielded cable to be detected have a fault of open.
Furthermore, a power supply is loaded between the grounding wire at the other end of the double-shielded cable to be detected and the monitoring wire, and an alternating square wave constant current source is adopted.
Furthermore, the alternating square wave constant current source signal is provided with a square wave constant current source with dead time.
Further, the voltage of the alternating square wave constant current source is +/-24V, and the limiting current is constant current of 2-10 mA; the positive and negative half-cycle single pulses are the same: t-40 mS, dead time: ts is 10 mS.
Furthermore, the sampling resistor is connected in series with the grounding wire or the monitoring wire, and the voltage at two ends of the sampling resistor is detected, so that the current flowing through the grounding wire or the monitoring wire can be obtained.
Furthermore, the anode of the diode is connected with one end of the monitoring wire, and the cathode of the diode is connected with one end of the grounding wire: a forward current is input at the other end of the grounding wire, and the diode ZD is connected with the loop resistor RK in series and then is connected with the insulation resistor RD in parallel;
detecting the voltage Uin 'between the monitoring line and the grounding line, wherein IPL' is a reverse injection current signal, the forward voltage drop UD of the diode,
then:
Uin’＝RD*(IPL’-IK’)
namely: RD ═ Uin '/(IPL ' -IK ')
The diode leakage current IK' is negligible, the insulation resistance is:
RD≈Uin’/IPL’
if the monitoring wire and the grounding wire are damaged and short-circuited, the insulativity between the monitoring wire and the grounding wire is reduced, and the insulation resistance value is reduced, so that the short-circuit fault between the monitoring wire and the grounding wire can be judged.
Furthermore, the anode of the diode is connected with one end of the monitoring wire, and the cathode of the diode is connected with one end of the grounding wire: inputting forward current at the other end of the monitoring line, and connecting a diode ZD and a loop resistor RK in series and then connecting an insulation resistor RD in parallel;
detecting a voltage Uin between the monitoring line and the grounding line, wherein IPL is a forward injection current signal, the forward voltage drop UD of the diode is approximately equal to 0.7V, and the resistance value of the insulation resistor RD is obtained in the above step;
then there are: IPL ═ ID + IK;
ID＝Uin/RD
IK＝(Uin-UD)/RK
namely: IPL ═ Uin/RD + (Uin-UD)/RK
RK＝(Uin-UD)/(IPL-Uin/RD)
ID is the current flowing through the insulation resistor RD, IK is the current flowing through the diode; UD is the voltage at two ends of the diode;
the loop resistance is then: RK is approximately equal to (Uin-UD)/(IPL-Uin/RD);
if the loop resistance is larger than the set threshold value of the broken circuit, the monitoring line and the grounding line of the double-shielded cable to be detected have broken line faults, alarming is carried out, and otherwise, the monitoring line and the grounding line are normal.
Further, according to the insulation resistance value obtained in the step 2), the position of the short circuit from the detection end can be obtained by combining the resistivity and the cross section of the material of the double-shielded cable to be detected and according to a conductor resistance formula.
Further, the position of the short circuit from the detection end:
namely: and L is RD S/rho, RD insulation resistance, S is a sectional area, and rho is the resistivity of the double-shielded cable material to be detected.
Further, the short circuit setting threshold is 3K, and the open circuit setting threshold is 1.5K.
Compared with the prior art, the invention has the following beneficial technical effects:
the invention relates to a double-shielded cable fault detection method, which is characterized in that a diode is connected between a grounding wire and a monitoring wire at one end of a double-shielded cable to be detected; loading a power supply between a grounding wire at the other end of the double-shielded cable to be detected and the monitoring wire, and connecting the grounding wire connected with the cathode of the diode or the monitoring wire to the anode of the power supply; and then measuring the current of the monitoring wire or the grounding wire at the other end of the double-shielded cable to be detected, quickly obtaining the short-circuit condition of the grounding wire and the monitoring wire according to the resistance obtained by dividing the power supply voltage and the detection current and a short-circuit set threshold, then adopting reverse loading current, and simultaneously detecting the loading voltage values on the monitoring wire and the grounding wire and the voltage values at the two ends of the diode to obtain the loop resistance of the monitoring wire and the grounding wire, wherein if the loop resistance is greater than the open circuit set threshold, the condition that the monitoring wire and the grounding wire of the double-shielded cable to be detected have a broken wire fault is shown.
Furthermore, the alternating square wave constant current source signal is provided with the square wave constant current source with dead time, so that the reverse quick response continuous monitoring can be realized, and the detection precision is improved.
Furthermore, the invention can accurately judge whether the circuit fault or the insulation fault occurs according to the fault on the monitoring line, and calculate the approximate position of the fault point on the whole section of the line.
Drawings
Fig. 1 is a cross-sectional view of a double shielded cable to be tested according to an embodiment of the present invention.
Fig. 2 is a schematic diagram of the waveform structure of an alternating square wave constant current source signal in the embodiment of the invention.
FIG. 3 is a schematic diagram of a positive half-cycle current loop analysis for cable detection according to an embodiment of the present invention.
FIG. 4 is a schematic diagram of a cable detection negative half-cycle current loop analysis according to an embodiment of the present invention.
In the figure, 1, a cable main line; 2. detecting lines; 3. a ground line; 4. an outer jacket; 5. a wire core; 6. an insulating layer; 7. monitoring a line; 8. an inner sheath layer.
Detailed Description
The invention is described in further detail below with reference to the accompanying drawings:
as shown in fig. 1, wait to detect double shielded cable and monitor line structure, including cable thread 1 and detection line 2, cable thread 1 and detection line 2 outer lane are equipped with outer shielding layer (earth connection) 3, and the outside parcel of outer shielding layer (earth connection) 3 has outer jacket 4, and cable thread 1 includes sinle silk 5, and the sinle silk 5 outside has wrapped insulating layer 6, split-phase shielding layer 7 (monitoring line) and interior sheath 8 by interior outer in proper order.
A double-shielded cable fault detection method comprises the following steps:
s1, connecting a diode between the grounding wire at one end of the double-shielded cable to be detected and the monitoring wire; loading a power supply between a grounding wire at the other end of the double-shielded cable to be detected and the monitoring wire, and connecting the grounding wire connected with the cathode of the diode or the monitoring wire to the anode of the power supply;
s2, measuring the current of the monitoring wire or the grounding wire at the other end of the double-shielded cable to be detected, if the resistance obtained by dividing the power supply voltage and the detection current is less than the short-circuit set threshold value, indicating that the double-shielded cable to be detected is in voltage loss short circuit or electric leakage, and alarming; if the resistance obtained by dividing the power supply voltage and the detection current is greater than or equal to the short circuit setting threshold, the double-shielded cable to be detected has no voltage loss short circuit or electric leakage;
s3, if the double-shielded cable to be detected has no voltage loss short circuit or electric leakage, the detected resistance value is the insulation resistance between the grounding wire and the monitoring wire, the reverse current of the step S2 is loaded on the monitoring wire and the grounding wire at the other end of the double-shielded cable to be detected, the loaded voltage values on the monitoring wire and the grounding wire and the voltage values at two ends of the diode are detected at the same time, the difference between the loaded voltage values on the monitoring wire and the grounding wire and the voltage values at two ends of the diode is divided by the current flowing through the diode, and then the loop resistance of the monitoring wire and the grounding wire can be obtained, if the loop resistance is larger than the set threshold value of open circuit, the monitoring wire and the grounding wire of the double-shielded cable to be detected have a fault of open.
Specifically, the alternating square wave constant current source is adopted for loading the power supply between the grounding wire at the other end of the double-shielded cable to be detected and the monitoring wire, and the current can be input in a forward and reverse cycle, so that forward and reverse cycle detection is formed, whether the double-shielded cable to be detected has a fault or not and the type of the fault can be quickly detected, and the method is simple, convenient and quick. As shown in fig. 2, the alternating square wave constant current source has a schematic structural diagram of the waveform of the signal, and the alternating square wave constant current source has a square wave constant current source with dead time.
By connecting the sampling resistor in series with the grounding wire or the monitoring wire, the voltage at two ends of the sampling resistor is detected, and the current flowing through the grounding wire or the monitoring wire can be obtained.
Establish the roof fall accident and lead to the cable damaged, monitor line and earth connection and at first can take place the short circuit, or can arouse insulating decline when damaged cable falls into the aquatic to lead to monitoring the insulating decline between line and the earth connection, if monitor the insulating resistance less than or equal to short circuit between line and the earth connection and set for the threshold value, then require the line protection, this application short circuit is set for the threshold value and is 3K. When the cable is broken completely, the loop resistance is larger than or equal to the set open-circuit threshold value, and the action is also reliable, and the set open-circuit threshold value is 1.5K.
As shown in fig. 2: the limiting voltage of Uin + and Uin-of the alternating square wave constant current source is within +/-24V, and the limiting current is constant current of 2-10 mA; the positive and negative half-cycle single pulses are the same: t-40 mS, dead time: ts is 10 mS;
the loop resistance is RK (resistance value of the loop formed by the monitoring line and the connecting line), the insulation resistance is RD (insulation between the monitoring line and the connecting line), the sampling resistance is RPL, and the terminal diode is ZD (forward voltage drop is about 0.7V, reverse leakage current is less than or equal to 10Ua/75 ℃). The AC line is a monitoring line, and the BD line is a grounding line. The AB end is a detection end, namely a loading power supply end, and the CD end is connected with a terminal diode.
The insulation resistance RD is a fault that whether the whole double-shielded cable to be detected has insulation damage or not, and may cause electric leakage or short circuit seriously. As shown in fig. 3, the anode of the diode is connected to the monitor line, the cathode of the diode is connected to the ground line: injecting negative half-cycle current from a port B of a grounding wire, connecting the negative half-cycle current in series with a loop resistor RK through a diode ZD, and then connecting an insulation resistor RD in parallel to flow to a port A of a monitoring wire to form a complete loop;
the voltage Uin 'between the monitoring line and the ground line is detected, while the reverse injection current signal IPL' is known, the diode forward voltage drop UD ≈ 0.7V (leakage current IK '≈ 10uA/75 ℃) is negligible here, i.e. the current IK' ≈ 0 flowing through the diode.
Then:
Uin’＝RD*(IPL’-IK’)
namely: RD ═ Uin '/(IPL ' -IK ')
The insulation resistance is then:
RD≈Uin’/IPL’
if the monitoring wire and the grounding wire are damaged and short-circuited, the insulativity between the monitoring wire and the grounding wire is reduced, and the insulation resistance value is reduced, so that the short-circuit fault between the monitoring wire and the grounding wire can be judged.
The loop resistance is an important parameter for detecting whether the cable is broken or not or has poor contact, and when the cable is cut off due to a roof fall accident or artificial dragging, protection action needs to be timely performed to ensure personal safety and complete equipment. The detection structure is shown in fig. 4: injecting positive half-cycle current from the port A, connecting the positive half-cycle current in series with the loop resistor RK through the diode ZD, and then connecting the positive half-cycle current in parallel with the insulation resistor RD to flow to the port A of the monitoring line to form a complete loop;
detecting a voltage Uin between the monitoring line and the grounding line, wherein IPL is a forward injection current signal, the forward voltage drop UD of the diode is approximately equal to 0.7V, and the resistance value of the insulation resistor RD is obtained in the above step;
then there are: IPL ═ ID + IK;
ID＝Uin/RD
IK＝(Uin-UD)/RK
namely: IPL ═ Uin/RD + (Uin-UD)/RK
RK＝(Uin-UD)/(IPL-Uin/RD)
ID is the current flowing through the insulation resistor RD, IK is the current flowing through the diode; UD is the voltage at two ends of the diode;
the loop resistance is then: RK ≈ (Uin-UD)/(IPL-Uin/RD)
It can be seen that the error of the test result is mainly derived from the voltage UD across the diode and the leakage current IK', i.e. the parameters of the diode. If the monitoring line and the grounding line are disconnected, the resistance of the monitoring line and the resistance of the connecting line are wirelessly increased, the loading voltage and the current of the measuring line, namely the current generated by the insulation resistance between the monitoring line and the connecting line, are loaded, and the condition of the line can be obtained by quickly calculating the resistance value of the loop.
And (3) judging the fault position of the cable:
according to the conductor resistance formula: r ═ ρ × l/s (ρ -resistivity; l-conductor length; s-cross-sectional area). Taking copper as an example, the resistivity ρ of copper is 0.01851 Ω · mm2/m (normal temperature), and the insulation resistance RD is measured to be the conductor resistance R when the cable is short-circuited at a certain position due to a roof fall accident; after the cable material is selected, the cross-sectional area S of the monitoring wire is constant. The position of the short circuit from the detection end can be deduced according to known conditions:
namely: and L is RD S/rho.
The scheme has the advantages that the alternating constant current signal is injected to analyze different loops, so that the faults of the insulation resistance and the loop resistance can be distinguished, the parameters meet the monitoring requirements of national standards on the double-shielded cable, and the function of roughly judging fault points is also provided.
Claims (10)
1. A double-shielded cable fault detection method is characterized by comprising the following steps:
s1, connecting a diode between the grounding wire at one end of the double-shielded cable to be detected and the monitoring wire; loading a power supply between a grounding wire at the other end of the double-shielded cable to be detected and the monitoring wire, and connecting the grounding wire connected with the cathode of the diode or the monitoring wire to the anode of the power supply;
s2, measuring the current of the monitoring wire or the grounding wire at the other end of the double-shielded cable to be detected, if the resistance obtained by dividing the power supply voltage and the detection current is less than the short-circuit set threshold value, indicating that the double-shielded cable to be detected is in voltage loss short circuit or electric leakage, and alarming; if the resistance obtained by dividing the power supply voltage and the detection current is greater than or equal to the short circuit setting threshold, the double-shielded cable to be detected has no voltage loss short circuit or electric leakage;
s3, if the double-shielded cable to be detected has no voltage loss short circuit or electric leakage, the detected resistance value is the insulation resistance between the grounding wire and the monitoring wire, the reverse current of the step S2 is loaded on the monitoring wire and the grounding wire at the other end of the double-shielded cable to be detected, the loaded voltage values on the monitoring wire and the grounding wire and the voltage values at two ends of the diode are detected at the same time, the difference between the loaded voltage values on the monitoring wire and the grounding wire and the voltage values at two ends of the diode is divided by the current flowing through the diode, and then the loop resistance of the monitoring wire and the grounding wire can be obtained, if the loop resistance is larger than the set threshold value of open circuit, the monitoring wire and the grounding wire of the double-shielded cable to be detected have a fault of open.
2. The double-shielded cable fault detection method according to claim 1, wherein a power supply is applied between a ground line at the other end of the double-shielded cable to be detected and the monitoring line by using an alternating square wave constant current source.
3. The double-shielded cable fault detection method of claim 2, wherein the alternating square-wave constant current source signal is a square-wave constant current source with dead time.
4. The double-shielded cable fault detection method according to claim 2 or 3, wherein the voltage of the alternating square wave constant current source is +/-24V, and the limiting current is 2-10 mA; the positive and negative half-cycle single pulses are the same: t-40 mS, dead time: ts is 10 mS.
5. The method as claimed in claim 1, wherein the voltage across the sampling resistor is detected by connecting the sampling resistor in series with the ground line or the monitoring line, so as to obtain the magnitude of the current flowing through the ground line or the monitoring line.
6. The double-shielded cable fault detection method according to claim 1, wherein the anode of the diode is connected to one end of the monitoring line, the cathode of the diode is connected to one end of the grounding line: a forward current is input at the other end of the grounding wire, and the diode ZD is connected with the loop resistor RK in series and then is connected with the insulation resistor RD in parallel;
detecting the voltage Uin 'between the monitoring line and the grounding line, wherein IPL' is a reverse injection current signal, the forward voltage drop UD of the diode,
then:
Uin’＝RD*(IPL’-IK’)
namely: RD ═ Uin '/(IPL ' -IK ')
The diode leakage current IK' is negligible, the insulation resistance is:
RD≈Uin’/IPL’
if the monitoring wire and the grounding wire are damaged and short-circuited, the insulativity between the monitoring wire and the grounding wire is reduced, and the insulation resistance value is reduced, so that the short-circuit fault between the monitoring wire and the grounding wire can be judged.
7. The double-shielded cable fault detection method according to claim 6, wherein the anode of the diode is connected to one end of the monitoring line, the cathode of the diode is connected to one end of the grounding line: inputting forward current at the other end of the monitoring line, and connecting a diode ZD and a loop resistor RK in series and then connecting an insulation resistor RD in parallel;
detecting a voltage Uin between the monitoring line and the grounding line, wherein IPL is a forward injection current signal, the forward voltage drop UD of the diode is approximately equal to 0.7V, and the resistance value of the insulation resistor RD is obtained in the above step;
then there are: IPL ═ ID + IK;
ID＝Uin/RD
IK＝(Uin-UD)/RK
namely: IPL ═ Uin/RD + (Uin-UD)/RK
RK＝(Uin-UD)/(IPL-Uin/RD)
ID is the current flowing through the insulation resistor RD, IK is the current flowing through the diode; UD is the voltage at two ends of the diode;
the loop resistance is then: RK is approximately equal to (Uin-UD)/(IPL-Uin/RD);
if the loop resistance is larger than the set threshold value of the broken circuit, the monitoring line and the grounding line of the double-shielded cable to be detected have broken line faults, alarming is carried out, and otherwise, the monitoring line and the grounding line are normal.
8. The double-shielded cable fault detection method according to claim 6, wherein the position from the short circuit occurrence position to the detection end can be obtained according to the insulation resistance value obtained in the step 2) and a conductor resistance formula by combining the resistivity and the cross section of the material of the double-shielded cable to be detected.
9. The double-shielded cable fault detection method according to claim 8, wherein the position of the short circuit from the position of the detection end is:
namely: and L is RD S/rho, RD insulation resistance, S is a sectional area, and rho is the resistivity of the double-shielded cable material to be detected.
10. The method of claim 1, wherein the short circuit setting threshold is 3K and the open circuit setting threshold is 1.5K.
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
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| CN115144791A (en) * | 2022-09-06 | 2022-10-04 | 浙江新图维电子科技有限公司 | Method and system for online detection of high-voltage cable armor grounding state |
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