CN111337752A - Power cable ground insulation resistance online detection system and application thereof - Google Patents
Power cable ground insulation resistance online detection system and application thereof Download PDFInfo
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- CN111337752A CN111337752A CN202010168892.1A CN202010168892A CN111337752A CN 111337752 A CN111337752 A CN 111337752A CN 202010168892 A CN202010168892 A CN 202010168892A CN 111337752 A CN111337752 A CN 111337752A
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- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R27/00—Arrangements for measuring resistance, reactance, impedance, or electric characteristics derived therefrom
- G01R27/02—Measuring real or complex resistance, reactance, impedance, or other two-pole characteristics derived therefrom, e.g. time constant
- G01R27/16—Measuring impedance of element or network through which a current is passing from another source, e.g. cable, power line
- G01R27/18—Measuring resistance to earth, i.e. line to ground
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- G—PHYSICS
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- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R27/00—Arrangements for measuring resistance, reactance, impedance, or electric characteristics derived therefrom
- G01R27/02—Measuring real or complex resistance, reactance, impedance, or other two-pole characteristics derived therefrom, e.g. time constant
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Abstract
The invention discloses an on-line detection system for insulation resistance of a power cable to the ground, wherein each cable of a three-phase three-wire power cable is respectively connected with a detection circuit, each detection circuit comprises a direct-current stabilized power supply, a safe direct-current voltage-dividing resistor and a voltage-dividing detection resistor module, one end of each safe direct-current voltage-dividing resistor is connected with the anode of the direct-current stabilized power supply, the other end of each safe direct-current voltage-dividing resistor is connected with the voltage-dividing detection resistor module and an alternating-current cable, the other end of each voltage-dividing detection resistor module is electrically connected with the cathode of the. Therefore, the invention can measure the resistance value of the insulation resistor of each cable relative to the ground, thereby quantitatively judging the risk of electric leakage. The invention also discloses various practical applications of the power cable ground insulation resistance online detection system, including a leakage protector and an ohmmeter.
Description
Technical Field
The invention relates to the field of circuit detection, in particular to an on-line detection system for ground insulation resistance of a power cable and application thereof.
Background
The existing power supply system generally supplies power based on a three-phase alternating current mode, and the neutral point of the three-phase alternating current power supply system is grounded for historical reasons. However, in special situations, such as a power system on a ship, the neutral point is not grounded, and particularly when the ship sails in the ocean, the cable is continuously in a bumpy state under the influence of sea waves, so that the cable is abraded, and therefore, the ground insulation condition of the power cable needs to be frequently detected.
As shown in fig. 1, in the conventional detection method, Vc and Gc in fig. 1 are a positive electrode and a negative electrode of a dc power supply, respectively. The anode of the direct current power supply is connected to the upper end of the resistor R1, and the cathode of the direct current power supply is connected to the lower end of the resistor R3. The direct current resistance of the generator winding is very small, and the insulation resistances of the A phase, the B phase, the C phase and the zero line relative to the ground are in parallel connection and exist between the ground and the cable. The direct current circuit is characterized in that the positive electrode of a direct current power supply is connected with one end of the R1, the other end of the R1 is connected with the ground, namely the common end of the insulation resistors of each phase relative to the ground, the other end of each phase of insulation resistor is connected with the upper end of the R2 through a power line, the R2 is connected with the R3 in series, and the other end of the R3 is connected with the negative electrode of the power supply. Namely, after being connected in parallel, the insulation resistors of each phase are connected between Vc and Gc in series with R1, R2 and R3. When a certain insulation resistance is reduced, the total insulation resistance in parallel connection is reduced, and the resistance values of R1, R2 and R3 are constant and unchanged because the total resistance in parallel connection is connected with R1, R2 and R3 in series, so that the voltage value at two ends of R3 is increased.
However, the voltage across R3 increases, which only represents that the resistance of the parallel total resistance of the insulation resistors of the three-phase power line relative to the ground decreases, but the specific resistance of each insulation resistor of the relative ground cannot be determined, and the specific phase of which insulation resistor decreases cannot be determined.
In addition, in order to protect the safety of personnel and equipment, an earth leakage protection device is generally arranged, but the existing earth leakage protection device is basically protected in a 'sheep-killing patch' mode, for example, a three-phase earth leakage protection method with ungrounded neutral line is provided in the Chinese patent with the application number of 200910171177.7, as shown in fig. 2, when three-phase load resistors are unbalanced, the voltage values among phases are unequal, the vector sum of the voltages is not zero, the coupling signals of C1, C2 and C3 are different, signals are generated for a transformer at the moment, only the signals generated at the moment are extremely small, and if tripping is caused at the moment, misoperation is carried out. Only when one phase of the three-phase load is grounded, a large signal is generated for the transformer, and the tripping caused at the moment is the tripping generated by the leakage protection, and although the tripping is generated, a large leakage accident may occur.
In conclusion, the existing scheme for detecting the insulation resistance of the three-phase cable to the ground is not perfect, and the existing leakage protection device cannot realize a better protection function.
Disclosure of Invention
The technical problem to be solved by the invention is as follows: an on-line detection system for insulation resistance to ground of a power cable is provided.
In order to solve the technical problems, the technical scheme adopted by the invention is as follows:
a power cable ground insulation resistance on-line detection system comprises a three-phase three-wire power cable, and is characterized in that each cable of the three-phase three-wire power cable is respectively connected with a detection circuit; the detection circuit comprises a direct current stabilized voltage power supply, a safe direct current divider resistor and a voltage division detection resistor module; one end of the safe direct current divider resistor is connected with the anode of the direct current stabilized voltage power supply, and the other end of the safe direct current divider resistor is electrically connected with the voltage division detection resistor module and the alternating current cable; the other end of the voltage division detection resistance module is electrically connected with the cathode of the direct current stabilized power supply; each voltage division detection resistance module is connected with a corresponding ground insulation resistance of the alternating current cable in parallel, and comprises a voltage division resistance and a detection resistance module which are connected together in series; the negative electrode of the direct current stabilized power supply is connected with the ground or connected with the ground after passing through a circuit formed by connecting inductance resistors in series and parallel, so that the safety of each component in the circuit is protected when strong interference signals such as thunder and lightning occur.
The direct current signal external connection point and the alternating current signal external connection point are respectively led out from the detection resistance module.
Compared with the prior art, the invention has the following technical effects:
the scheme can detect the change of the insulation resistance of the alternating current cable to the ground in the power system. Taking phase A as an example, phase A and phase BThe insulation resistance to the ground of the A phase is connected with the voltage division detection resistance module of the A phase in parallel to form rAThe insulation resistance to the ground of the B phase is connected with the voltage division detection resistance module of the B phase in parallel to form rB，rAAnd rBThen connected between A phase power cable and B phase power cable in series, when A phase ground insulation resistance is reduced, then rAThe voltage of the voltage division detection resistor module of the phase A is reduced, and the alternating voltage of the two ends of the detection resistor module corresponding to the phase A is correspondingly reduced on the premise that the alternating voltage between the phase A and the phase B is not changed and the insulation resistor of the phase B is not changed, so that the resistance value of the insulation resistor is reduced; this theory of analysis still holds, according to the superposition theorem, in the case where A, B, C three phases are all present.
In the DC equivalent circuit of the three-phase three-wire system, after the voltage division detection resistance module is connected with the ground insulation resistance of the three-phase AC cable in parallel, the voltage division detection resistance module is connected with the safe DC voltage division resistance in series, when the ground insulation resistance is not reduced, the resistance value of the whole parallel circuit part is kept stable, and the DC voltage division of the DC stabilized power supply on the voltage division detection resistance module is kept unchanged.
Whether the power cable has the risk of electric leakage or not can be judged by detecting the change of the insulation resistance value of the power cable to the ground, and early warning is sent out when the insulation resistance value is lower than a certain threshold value, so that interference can be carried out before an electric leakage accident occurs, and the defect that the existing electric leakage protection equipment can detect the electric leakage accident only after the electric leakage accident occurs is overcome.
On the basis of the technical scheme, the invention can be further improved as follows.
Furthermore, the detection resistance module is connected in parallel with a voltage limiting module for protecting a rear-stage circuit element.
The beneficial effect of adopting the further scheme is that the components of the post-stage circuit are prevented from being damaged under the condition that the detected voltage fluctuation is large.
Furthermore, in the three-phase four-wire power system, the neutral cable is connected with one circuit of the detection circuit.
The method has the advantages that the specific insulation resistance value of each line to the ground can be measured, the total parallel connection value of the insulation resistance of each cable to the ground is not only measured, misjudgment is reduced, and fault location is more accurate.
A leakage protector for a three-phase three-wire power system comprises 3 phase lines, wherein the 3 phase lines are respectively connected with a detection circuit, a direct-current voltage detection circuit, an alternating-current voltage detection circuit, a single chip microcomputer and an electromagnetic switch module;
one end of the direct-current voltage detection circuit and one end of the alternating-current voltage detection circuit are respectively and electrically connected with the voltage division detection resistance module, the other ends of the direct-current voltage detection circuit and the alternating-current voltage detection circuit are respectively and electrically connected with an A/D conversion input port of the single chip microcomputer, and the electromagnetic switch module is electrically connected with an output port of the single chip microcomputer;
the direct-current voltage detection circuit is used for acquiring a divided voltage value of the direct-current voltage in the divided voltage detection resistance module, and the alternating-current detection circuit is used for acquiring a divided voltage value of the alternating-current voltage in the divided voltage detection resistance module;
the single chip microcomputer judges whether the ground insulation resistance of the line is reduced below a set threshold value or not by analyzing the acquired direct-current voltage division value and alternating-current voltage division value, and controls the action of the electromagnetic switch module according to the analysis result.
Compared with the prior art, the invention has the following technical effects:
the protection device can excite the protection action when the insulation resistance of the line is reduced to a certain threshold value, and the line is disconnected before the leakage accident happens to the line, so that the equipment and personal safety is ensured. Meanwhile, the insulation resistance value of a specific line can be determined to be reduced, and the fault location is accurate.
A leakage protector for a three-phase four-wire power system comprises 3 phase lines, 1 neutral line, a direct-current voltage detection circuit, an alternating-current voltage detection circuit, a single chip microcomputer and an electromagnetic switch module, wherein the neutral line is not grounded, and the phase lines and the neutral line are respectively connected with one path of detection circuit;
one end of the direct-current voltage detection circuit and one end of the alternating-current voltage detection circuit are respectively and electrically connected with the voltage division detection resistance module, the other ends of the direct-current voltage detection circuit and the alternating-current voltage detection circuit are respectively and electrically connected with an A/D conversion input port of the single chip microcomputer, and the electromagnetic switch module is electrically connected with an output port of the single chip microcomputer;
the direct-current voltage detection circuit is used for acquiring a divided voltage value of the direct-current voltage in the divided voltage detection resistance module, and the alternating-current detection circuit is used for acquiring a divided voltage value of the alternating-current voltage in the divided voltage detection resistance module;
the single chip microcomputer judges whether the ground insulation resistance of the line is reduced below a set threshold value or not by analyzing the acquired direct-current voltage division value and alternating-current voltage division value, and controls the action of the electromagnetic switch module according to the analysis result;
compared with the prior art, the invention has the following technical effects:
the protection device can excite the protection action when the insulation resistance of the line is reduced to a certain threshold value, and the line is disconnected before the leakage accident happens to the line, so that the equipment and personal safety is ensured. Meanwhile, the insulation resistance value of a specific line can be determined to be reduced, and the fault location is accurate.
A leakage protector for a single phase power system; the single-phase system comprises a phase line and a zero line, wherein the zero line is not grounded, and the phase line and the zero line are respectively connected with one path of detection circuit;
one end of the direct-current voltage detection circuit and one end of the alternating-current voltage detection circuit are respectively and electrically connected with the voltage division detection resistance module, the other ends of the direct-current voltage detection circuit and the alternating-current voltage detection circuit are respectively and electrically connected with an A/D conversion input port of the single chip microcomputer, and the electromagnetic switch module is electrically connected with an output port of the single chip microcomputer;
the direct-current voltage detection circuit is used for acquiring a divided voltage value of the direct-current voltage in the divided voltage detection resistance module, and the alternating-current detection circuit is used for acquiring a divided voltage value of the alternating-current voltage in the divided voltage detection resistance module;
the single chip microcomputer judges whether the ground insulation resistance of the line is reduced below a set threshold value or not by analyzing the collected direct-current voltage division value and alternating-current voltage division value, and controls the action of the electromagnetic switch module according to an analysis result.
Compared with the prior art, the invention has the following technical effects:
the protection device can excite the protection action when the insulation resistance of the line to the ground is reduced to a certain threshold value, and the line is disconnected before the electric leakage accident happens to the line, so that the safety of equipment and personnel is ensured.
A cable-to-ground insulation ohmmeter for a three-phase, three-wire power system; the three-phase three-wire power system comprises 3 phase wires, wherein the 3 phase wires are respectively connected with one path of detection circuit, and further comprises a direct-current voltage detection circuit, an alternating-current voltage detection circuit, a single chip microcomputer and a display and alarm module;
one end of the direct current voltage detection circuit and one end of the alternating current voltage detection circuit are respectively and electrically connected with the voltage division detection resistance module, the other end of the direct current voltage detection circuit and the alternating current voltage detection circuit are respectively and electrically connected with an A/D conversion input port of the single chip microcomputer, and the display and alarm module is electrically connected with an output port of the single chip microcomputer;
the direct-current voltage detection circuit is used for acquiring a divided voltage value of the direct-current voltage in the divided voltage detection resistance module, and the alternating-current detection circuit is used for acquiring a divided voltage value of the alternating-current voltage in the divided voltage detection resistance module;
the single chip microcomputer calculates the ground insulation resistance value of each power cable by analyzing the acquired direct-current voltage division value and alternating-current voltage division value, and judges whether the ground insulation resistance of the line is reduced below a set threshold value or not;
the display and alarm module is used for displaying the measured ground insulation resistance value of the cable outwards and sending alarm information when the ground insulation resistance value is lower than a set threshold value.
Compared with the prior art, the invention has the following technical effects:
the insulation resistance to ground of each cable can be detected, and accurate basis is provided for troubleshooting.
A cable ground insulation ohmmeter for a three-phase four-wire power system comprises 3 phase lines and 1 neutral line, wherein the neutral line is not grounded, and the phase lines and the neutral line are respectively connected with a detection circuit, a direct-current voltage detection circuit, an alternating-current voltage detection circuit, a single chip microcomputer and a display and alarm module;
one end of the direct current voltage detection circuit and one end of the alternating current voltage detection circuit are respectively and electrically connected with the voltage division detection resistance module, the other end of the direct current voltage detection circuit and the alternating current voltage detection circuit are respectively and electrically connected with an A/D conversion input port of the single chip microcomputer, and the display and alarm module is electrically connected with an output port of the single chip microcomputer;
the direct-current voltage detection circuit is used for acquiring a divided voltage value of the direct-current voltage in the divided voltage detection resistance module, and the alternating-current detection circuit is used for acquiring a divided voltage value of the alternating-current voltage in the divided voltage detection resistance module;
the single chip microcomputer calculates the insulation resistance value of the line to the ground by analyzing the acquired direct-current voltage division value and alternating-current voltage division value, and judges whether the insulation resistance value of the line to the ground is reduced below a set threshold value or not;
the display and alarm module is used for displaying the measured ground insulation resistance value of the cable outwards and sending alarm information when the ground insulation resistance value is lower than a set threshold value.
Compared with the prior art, the invention has the following technical effects:
the insulation resistance to ground of each cable can be detected, and accurate basis is provided for troubleshooting.
A cable ground insulation ohmmeter for a single-phase power system comprises a phase line, a zero line, a direct-current voltage detection circuit, an alternating-current voltage detection circuit, a single chip microcomputer and a display and alarm module, wherein the phase line and the zero line are not grounded;
one end of the direct current voltage detection circuit and one end of the alternating current voltage detection circuit are respectively and electrically connected with the voltage division detection resistance module, the other end of the direct current voltage detection circuit and the alternating current voltage detection circuit are respectively and electrically connected with an A/D conversion input port of the single chip microcomputer, and the display and alarm module is electrically connected with an output port of the single chip microcomputer;
the direct-current voltage detection circuit is used for acquiring a divided voltage value of the direct-current voltage in the divided voltage detection resistance module, and the alternating-current detection circuit is used for acquiring a divided voltage value of the alternating-current voltage in the divided voltage detection resistance module;
the single chip microcomputer calculates the insulation resistance value of the line to the ground by analyzing the acquired direct-current voltage division value and alternating-current voltage division value, and judges whether the insulation resistance value of the line to the ground is reduced below a set threshold value or not;
the display and alarm module is used for displaying the measured ground insulation resistance value of the cable outwards and sending alarm information when the ground insulation resistance value is lower than a set threshold value.
Compared with the prior art, the invention has the following technical effects:
the value of the insulation resistance to ground of each cable of the power supply system can be detected.
Drawings
FIG. 1 is a schematic circuit diagram of a conventional three-phase cable ground insulation resistance detection circuit;
FIG. 2 is a schematic circuit diagram of a conventional three-phase leakage protection device;
FIG. 3 is a circuit diagram of the detection circuit of the present invention for use in a three-phase, three-wire power system;
FIG. 3-1 is a DC equivalent circuit diagram of FIG. 3;
FIG. 3-2 is an AC equivalent circuit diagram of FIG. 3;
FIG. 4 is a circuit diagram of the detection circuit of the present invention for use in a three-phase four-wire power system;
FIG. 5 is a circuit diagram of the detection circuit of the present invention for use in a single phase power system;
FIG. 6 is a circuit schematic of an ohmmeter of the present invention for a three-phase, three-wire power system;
FIG. 7 is a circuit schematic of an ohmmeter of the present invention for a three-phase four-wire power system;
FIG. 8 is a schematic circuit diagram of an ohmmeter of the present invention for a single phase power system;
fig. 9 is a schematic circuit diagram of the earth leakage protection device of the present invention for use in a three-phase, three-wire power system;
fig. 10 is a circuit schematic of the earth leakage protection device of the present invention for a three-phase four-wire power system;
fig. 11 is a schematic circuit diagram of the earth leakage protection device for a single-phase power system of the present invention.
Detailed Description
The principles and features of this invention are described below in conjunction with the following drawings, which are set forth by way of illustration only and are not intended to limit the scope of the invention.
Example 1:
fig. 3 is a circuit diagram of the on-line detection circuit for insulation resistance to ground of the power cable applied to a three-phase three-wire power system.
In fig. 3, Vc denotes a dc power supply positive electrode of the detection circuit, and Gc denotes a power supply negative electrode.
The insulation resistance to be measured of the A phase refers to the insulation resistance of the A phase power cable relative to the ground in the power system and is marked as RA；
The insulation resistance to be measured of the B phase is the insulation resistance of the B phase power cable relative to the ground in the power system and is marked as RB；
The insulation resistance to be measured of the C phase is the insulation resistance of the C phase power cable relative to the earth in the power system and is marked as RC。
R4 is a safe direct-current divider resistor of the A phase, R3 is a divider resistor in a divider detection resistor module in a measuring branch of the A phase, R2 and R1 form a measuring resistor module, R2 and R1 are connected in series and then used for detecting a direct-current voltage signal, and R1 is used for detecting an alternating-current voltage signal; r1 and R2 can also realize the functions by using the same resistor;
in the dc equivalent circuit, as shown in fig. 3-1, the resistances of the series connection of R3, R2, and R1 and the insulation resistance R of the a-phase power cable with respect to the ground are connected in seriesAConnected in parallel, connected in series with R4, and then connected between the positive pole Vc and the negative pole Gc of the DC power supply; r4 and R3 are large resistors, the resistance values of R2 and R1 are small and are used for detecting signals, in the example, R4 and R3 are 400k omega, R2 is 8.1k omega, R1 is 2.2k omega, voltage signals at two ends of R1 are used for detecting A alternating current signals, and R2 and R1 are connected in series and then at two ends of the voltage signalsThe voltage signal is used for detecting an A-phase direct current signal; d1 and D2 are voltage stabilizing diodes connected back to back and used for protecting a rear-stage circuit element, and the voltage stabilizing diodes form a measuring branch.
Similarly, in the B phase, R8 is a safe DC voltage dividing resistor of the B phase, and the resistor formed by connecting R7, R6 and R5 in series and the insulation resistor R of the B phase power cable relative to the groundBConnected in parallel, connected in series with R8, and then connected between the positive pole Vc and the negative pole Gc of the DC power supply; r8 and R7 are large resistors, the resistance values of R6 and R5 are small and are used for detecting signals, voltage signals at two ends of R5 are used for detecting B-phase alternating current signals, voltage signals at two ends after R6 and R5 are connected in series are used for detecting B-phase direct current signals, and the functions of R5 and R6 can be realized by the same resistor; d3 and D4 are used for protecting the detection circuit.
In the C phase, R12 is the safe DC voltage dividing resistor of the C phase, the resistor after the series connection of R11, R10 and R9 and the insulation resistor R of the C phase power cable relative to the groundCConnected in parallel, connected in series with R12, and then connected between the positive pole Vc and the negative pole Gc of the DC power supply; r12 and R11 are large resistors, the resistance values of R10 and R9 are small and are used for detecting signals, voltage signals at two ends of R9 are used for detecting C-phase alternating current signals, voltage signals at two ends of R10 and R9 which are connected in series are used for detecting C-phase direct current signals, and the functions of R9 and R10 can be realized by the same resistor; d5 and D6 are used for protecting the detection circuit.
For convenience of calculation, the following relationship may be satisfied between the resistances:
R1＝R5＝R9；
R2＝R6＝R10；
R3＝R7＝R11；
R4＝R8＝R12；
the above relationship may not be satisfied.
The working process of the circuit is analyzed in detail as follows:
please refer to fig. 3-1, which is a diagram of the dc equivalent circuit of fig. 3.
Taking phase A as an example, when A, B, C phases have insulation resistance to be measured, namely RA、RB、RCWhen any one of the resistance values is reduced, the resistance value between the points F and Gc in FIG. 3-1 is correspondingly reduced, and the resistance value between the points F and Gc is reducedThe direct current partial pressure between the two will be reduced; the direct current voltage division value measured at the direct current voltage division external contact point H is correspondingly reduced, so that the change of the total parallel resistance value of the insulation resistance to the ground can be judged and calculated by detecting the change of the direct current voltage division, and the change condition of the insulation resistance can be known.
Whether the alternating voltage decreases or increases is determined depending on which phase or which phases have a change in insulation resistance.
The detection voltage of each phase of the alternating current signal is a result of the common action of the three-phase alternating current power supply voltages between the three phases, and in the three-phase three-wire system alternating current equivalent circuit diagram, as shown in fig. 3-2, R1, R2, R3 are connected in series and then connected to the insulation resistance R of a relative groundAR for total resistance in parallelARepresents; r5, R6 and R7 are connected in series and then are connected with the insulation resistor R of B relative to the groundBR for total resistance in parallelBRepresents; the resistor after R9, R10 and R11 are connected in series is further connected with the insulation resistor R of C relative to the groundCR for total resistance in parallelCAnd (4) showing.
rAAnd rBThe power supplies are connected in parallel after being connected in series between A, B phase power supplies; r isBAnd rCThe power supplies are connected in parallel after being connected in series between B, C phase power supplies; r isCAnd rAThe power supplies are connected in parallel after being connected in series between C, A phase power supplies;
rAwhile being affected by the voltage difference between the AB phase and the CA phase.
Insulation resistance R when A is relatively earthedAWhen decreasing, rADecreasing, the ac voltage signal detected across R1 decreases, while the ac voltage signal detected across R5, R9 increases;
similarly, when B is the insulation resistance to ground RBWhen decreasing, rBDecreasing, the ac voltage signal detected across R5 decreases, while the ac voltage signal detected across R1, R9 increases;
insulation resistance R when C is relatively largeCWhen decreasing, rCDecreasing, the ac voltage signal detected across R9 decreases, while the ac voltage signal detected across R5, R1 increases.
Thereby can beCalculating the insulation resistance R of the phase A relative to the ground according to the detected parameter values of the direct current voltage signal and the alternating current voltage signal of each phaseAB insulation resistance to earthBC insulation resistance R relative to earthC。
In summary, by detecting the changes of the dc voltage and the ac voltage of each branch, it can be determined which cable has a reduced insulation resistance to ground.
Through theoretical reasoning, the relation between the alternating current and direct current sampling voltage variation and the insulation resistance value of each path can be obtained: rx＝f(VAA)+f(VBB)+f(VCC)+f(Vaa)+f(Vbb)+f(Vcc) Wherein R isxRepresenting the insulation resistance value of the power cable to the earth, where x is R when A isxIs namely RARepresents the insulation resistance value of A relative to the earth, and R is taken as x is BxIs namely RBDenotes a relatively large ground insulation resistance value of B, and R is R when x is CxIs namely RCRepresents the value of the C relative earth insulation resistance; vAADetecting a component for an A-phase DC voltage, wherein VBBDetecting a component for a B-phase DC voltage, wherein VccDetecting components for the C-phase direct current voltage; vaaDetecting a component for A AC voltage, where VbbDetecting a component for the B-phase alternating voltage, wherein VccDetecting a component for the C-phase alternating voltage; therefore, the insulation resistance value of each phase can be specifically calculated according to the measured direct-current voltage component and alternating-current voltage component of each phase.
And a combined circuit of an inductor and a resistor can be connected between the earth and the Gc and is used for protecting the circuit when strong interference signals such as thunder and lightning occur.
Example 2:
a circuit diagram of the detection circuit of the present invention applied to a three-phase four-wire power system is shown in fig. 4; compared with embodiment 1, the difference is that a neutral wire is added in the system, and each cable is respectively connected with one detection circuit, but the working principle is the same.
Example 3:
the circuit diagram of the detection circuit applied to the single-phase power system of the invention is shown in fig. 5; since the power supply system is a three-phase power supply, although only a single-phase cable can be seen in the embodiment, in an actual system, the L phase is still connected with the other two phases, if the dc sampling voltage drops, it is described that the ground insulation resistance of the cable in the line drops, but if the ac sampling voltages of L and N in the present circuit are not changed, it is described that the fault is the fault of the other phase lines, not the fault of L or N in the present figure.
Example 4:
FIG. 6 shows the principle of ohmmeter circuit for detecting three-phase three-wire insulation resistance;
the power supply in fig. 6 is generated by alternating current on each phase line, and the power supply can be generated in various ways and can also be provided by other independent power supplies. The Vc direct current power supply is used for front end detection, and the Vd is used for power supply of circuits such as a signal processing circuit, a singlechip, a display and the like. In a three-phase three-wire circuit, each acquisition signal of the direct current voltage (see fig. 3) is filtered by a filter integration circuit to remove alternating current components, then passes through a voltage follower, and then passes through an integration filter circuit for the second time to be output to an A/D conversion input port of a single chip microcomputer, the single chip microcomputer reads the value of the A/D converter, and the magnitude of the direct current voltage corresponding to each corresponding point can be calculated.
Each signal (see fig. 3) collected from the ac voltage is output to the a/D conversion input port of the single chip through the voltage follower circuit and the peak detection circuit, and the single chip reads the value of the a/D converter, so that the magnitude of each phase of ac voltage can be calculated.
The singlechip analyzes and calculates the resistance value of the insulation resistor of each phase line and zero line to the earth according to each read signal parameter, and displays the resistance value on the display. When one insulation resistance value is smaller than the critical value, an alarm signal can be output to trigger an external alarm device.
Example 5:
FIG. 7 is a schematic diagram of an ohmmeter applied to a three-phase four-wire circuit;
example 6:
FIG. 8 is a schematic diagram of an ohmmeter applied to a single phase system circuit;
example 7:
fig. 9 is a circuit diagram of a leakage protector applied to a three-phase three-wire power system, and differs from embodiment 4 in that the display and audible and visual alarm circuit in embodiment 4 is replaced with an electromagnetic switch protection circuit. When the single chip microcomputer detects that the insulation resistance of any phase (A, B, C phases) to the ground is reduced to a critical value, trip protection is caused. In fig. 9, a rectifier diode D14, a high resistance resistor R48 and a capacitor C17 are connected in series and then connected in parallel between two phase lines (connected between a phase a and a phase B in fig. 9) through a coil of an electromagnetic switch, D14 is turned on in a positive half cycle (voltage of the phase a is higher than voltage of the phase B), current charges C17 through a large resistor R48, and a voltage stabilizing diode D15 is used for protecting the circuit. When the singlechip detects that the insulation resistance of a certain phase or a plurality of phases relative to the ground is reduced to a critical value, the I/O pin of the singlechip outputs low level, the photoelectric coupler is conducted, and the conduction of the one-way thyristor is controlled. The current generated on the wire instantly passes through the electromagnetic switch, so that the mechanical switch is switched off, and the leakage protection is completed. Because the current is very large only instantaneously, the unidirectional silicon controlled rectifier is safe. When the I/O port outputs high level, the circuit is not conducted, and misoperation cannot be caused.
Example 8:
as shown in fig. 10, the leakage protector of the present invention is applied to a three-phase four-wire circuit;
example 9:
fig. 11 is a schematic circuit diagram of the leakage protector applied to a single-phase system.
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents, improvements and the like that fall within the spirit and principle of the present invention are intended to be included therein.
Claims (9)
1. A power cable ground insulation resistance on-line detection system comprises a three-phase three-wire power cable, and is characterized in that each cable of the three-phase three-wire power cable is respectively connected with a detection circuit; the detection circuit comprises a direct current stabilized voltage power supply, a safe direct current divider resistor and a voltage division detection resistor module; one end of the safe direct current divider resistor is connected with the anode of the direct current stabilized voltage power supply, and the other end of the safe direct current divider resistor is electrically connected with the voltage division detection resistor module and the alternating current cable; the other end of the voltage division detection resistance module is electrically connected with the cathode of the direct current stabilized power supply; the voltage division detection resistance module comprises a voltage division resistance and a detection resistance module which are connected in series; the detection resistance module also comprises two external contacts which are respectively an external contact of a direct current voltage signal and an external contact of an alternating current voltage signal; and the negative electrode of the direct current stabilized power supply is connected with the ground.
2. The on-line detection system for insulation resistance to ground of power cable of claim 1, wherein the voltage limiting module is connected in parallel to the detection resistance module.
3. An on-line detection system for insulation resistance to ground of a power cable according to claim 1 or 2, characterized in that a neutral cable is further provided at a common end of the three phase lines to form a three-phase four-wire power supply system, and a detection circuit is connected to the neutral cable.
4. A earth leakage protector for a three-phase three-wire power system, which comprises 3 phase lines, characterized in that 3 phase lines are respectively connected with a detection circuit as claimed in any one of claims 1-2, and further comprises a direct voltage detection circuit, an alternating voltage detection circuit, a single chip microcomputer and an electromagnetic switch module;
one end of the direct-current voltage detection circuit and one end of the alternating-current voltage detection circuit are respectively and electrically connected with the voltage division detection resistance module, the other ends of the direct-current voltage detection circuit and the alternating-current voltage detection circuit are respectively and electrically connected with an A/D conversion input port of the single chip microcomputer, and the electromagnetic switch module is electrically connected with an output port of the single chip microcomputer;
the direct-current voltage detection circuit is used for acquiring a divided voltage value of the direct-current voltage in the divided voltage detection resistance module, and the alternating-current detection circuit is used for acquiring a divided voltage value of the alternating-current voltage in the divided voltage detection resistance module;
the single chip microcomputer judges whether the ground insulation resistance of the line is reduced below a set threshold value or not by analyzing the acquired direct-current voltage division value and alternating-current voltage division value, and controls the action of the electromagnetic switch module according to the analysis result.
5. A leakage protector for a three-phase four-wire power system comprising 3 phase wires and 1 neutral wire, said neutral wire being ungrounded, characterized in that said phase wires and neutral wire are electrically connected to a detection circuit as claimed in any one of claims 1-2, respectively, and further comprising a dc voltage detection circuit, an ac voltage detection circuit, a single-chip microcomputer and an electromagnetic switch module;
one end of the direct-current voltage detection circuit and one end of the alternating-current voltage detection circuit are respectively and electrically connected with the voltage division detection resistance module, the other ends of the direct-current voltage detection circuit and the alternating-current voltage detection circuit are respectively and electrically connected with an A/D conversion input port of the single chip microcomputer, and the electromagnetic switch module is electrically connected with an output port of the single chip microcomputer;
the direct-current voltage detection circuit is used for acquiring a divided voltage value of the direct-current voltage in the divided voltage detection resistance module, and the alternating-current detection circuit is used for acquiring a divided voltage value of the alternating-current voltage in the divided voltage detection resistance module;
the single chip microcomputer judges whether the ground insulation resistance of the line is reduced below a set threshold value or not by analyzing the acquired direct-current voltage division value and alternating-current voltage division value, and controls the action of the electromagnetic switch module according to the analysis result.
6. A earth leakage protector for a single-phase system, the single-phase system comprising a phase line and a zero line, the zero line being ungrounded, characterized in that the phase line and the zero line are respectively connected to a detection circuit as claimed in any one of claims 1-2, further comprising a direct voltage detection circuit, an alternating voltage detection circuit, a single chip microcomputer and an electromagnetic switch module;
one end of the direct-current voltage detection circuit and one end of the alternating-current voltage detection circuit are respectively and electrically connected with the voltage division detection resistance module, the other ends of the direct-current voltage detection circuit and the alternating-current voltage detection circuit are respectively and electrically connected with an A/D conversion input port of the single chip microcomputer, and the electromagnetic switch module is electrically connected with an output port of the single chip microcomputer;
the direct-current voltage detection circuit is used for acquiring a divided voltage value of the direct-current voltage in the divided voltage detection resistance module, and the alternating-current detection circuit is used for acquiring a divided voltage value of the alternating-current voltage in the divided voltage detection resistance module;
the single chip microcomputer judges whether the ground insulation resistance of the line is reduced below a set threshold value or not by analyzing the acquired direct-current voltage division value and alternating-current voltage division value, and controls the action of the electromagnetic switch module according to the analysis result.
7. A cable-to-ground insulation ohmmeter for a three-phase, three-wire power system; the three-phase three-wire power system comprises 3 phase wires, and is characterized in that the 3 phase wires are respectively connected with a detection circuit as claimed in any one of claims 1-2, and further comprises a direct-current voltage detection circuit, an alternating-current voltage detection circuit, a single chip microcomputer and a display and alarm module;
one end of the direct current voltage detection circuit and one end of the alternating current voltage detection circuit are respectively and electrically connected with the voltage division detection resistance module, the other end of the direct current voltage detection circuit and the alternating current voltage detection circuit are respectively and electrically connected with an A/D conversion input port of the single chip microcomputer, and the display and alarm module is electrically connected with an output port of the single chip microcomputer;
the direct-current voltage detection circuit is used for acquiring a divided voltage value of the direct-current voltage in the divided voltage detection resistance module, and the alternating-current detection circuit is used for acquiring a divided voltage value of the alternating-current voltage in the divided voltage detection resistance module;
the single chip microcomputer calculates the insulation resistance value of the line to the ground by analyzing the acquired direct-current voltage division value and alternating-current voltage division value, and judges whether the insulation resistance value of the line to the ground is reduced below a set threshold value or not;
the display and alarm module is used for displaying the measured ground insulation resistance value of the cable outwards and sending alarm information when the ground insulation resistance value is lower than a set threshold value.
8. A cable-to-ground insulated ohmmeter for a three-phase four-wire power system comprising 3 phase wires, 1 neutral wire, said neutral wire not being grounded, characterized in that said phase wires and neutral wire are connected to a detection circuit according to any of claims 1-2, respectively, and further comprising a dc voltage detection circuit, an ac voltage detection circuit, a single-chip microcomputer and a display and alarm module;
one end of the direct current voltage detection circuit and one end of the alternating current voltage detection circuit are respectively and electrically connected with the voltage division detection resistance module, the other end of the direct current voltage detection circuit and the alternating current voltage detection circuit are respectively and electrically connected with an A/D conversion input port of the single chip microcomputer, and the display and alarm module is electrically connected with an output port of the single chip microcomputer;
the direct-current voltage detection circuit is used for acquiring a divided voltage value of the direct-current voltage in the divided voltage detection resistance module, and the alternating-current detection circuit is used for acquiring a divided voltage value of the alternating-current voltage in the divided voltage detection resistance module;
the single chip microcomputer calculates the insulation resistance value of the line to the ground by analyzing the acquired direct-current voltage division value and alternating-current voltage division value, and judges whether the insulation resistance value of the line to the ground is reduced below a set threshold value or not;
the display and alarm module is used for displaying the measured ground insulation resistance value of the cable outwards and sending alarm information when the ground insulation resistance value is lower than a set threshold value.
9. A cable ground insulation ohmmeter for a single-phase system, the single-phase system comprising a phase line and a zero line, the zero line being ungrounded, characterized in that the phase line and the zero line are respectively connected to a detection circuit as claimed in any one of claims 1-2, further comprising a direct voltage detection circuit, an alternating voltage detection circuit, a single chip microcomputer and a display and alarm module;
one end of the direct current voltage detection circuit and one end of the alternating current voltage detection circuit are respectively and electrically connected with the voltage division detection resistance module, the other end of the direct current voltage detection circuit and the alternating current voltage detection circuit are respectively and electrically connected with an A/D conversion input port of the single chip microcomputer, and the display and alarm module is electrically connected with an output port of the single chip microcomputer;
the direct-current voltage detection circuit is used for acquiring a divided voltage value of the direct-current voltage in the divided voltage detection resistance module, and the alternating-current detection circuit is used for acquiring a divided voltage value of the alternating-current voltage in the divided voltage detection resistance module;
the single chip microcomputer calculates the insulation resistance value of the line to the ground by analyzing the acquired direct-current voltage division value and alternating-current voltage division value, and judges whether the insulation resistance value of the line to the ground is reduced below a set threshold value or not;
the display and alarm module is used for displaying the measured ground insulation resistance value of the cable outwards and sending alarm information when the ground insulation resistance value is lower than a set threshold value.
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| CN112816784A (en) * | 2020-12-31 | 2021-05-18 | 广电计量检测（成都）有限公司 | Resistance test circuit and system |
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