CN111487469B - Electrified detection device for contact resistance of secondary circuit of current transformer - Google Patents
Electrified detection device for contact resistance of secondary circuit of current transformer Download PDFInfo
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- 238000001514 detection method Methods 0.000 title claims abstract description 105
- 238000012360 testing method Methods 0.000 claims abstract description 82
- 230000003750 conditioning effect Effects 0.000 claims abstract description 56
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- 238000006243 chemical reaction Methods 0.000 claims description 7
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- 239000004973 liquid crystal related substance Substances 0.000 claims description 4
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- 238000004364 calculation method Methods 0.000 claims description 3
- 230000003993 interaction Effects 0.000 claims description 3
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- 239000002184 metal Substances 0.000 description 3
- 229910052751 metal Inorganic materials 0.000 description 3
- 238000012790 confirmation Methods 0.000 description 2
- 230000005347 demagnetization Effects 0.000 description 2
- 238000005259 measurement Methods 0.000 description 2
- 239000000203 mixture Substances 0.000 description 2
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- 229910000896 Manganin Inorganic materials 0.000 description 1
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- G—PHYSICS
- 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
- G01R27/20—Measuring earth resistance; Measuring contact resistance, e.g. of earth connections, e.g. plates
- G01R27/205—Measuring contact resistance of connections, e.g. of earth connections
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R1/00—Details of instruments or arrangements of the types included in groups G01R5/00 - G01R13/00 and G01R31/00
- G01R1/30—Structural combination of electric measuring instruments with basic electronic circuits, e.g. with amplifier
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- G—PHYSICS
- 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
- G01R27/08—Measuring resistance by measuring both voltage and current
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Abstract
The invention belongs to the technical field of contact resistance testing, and particularly relates to a secondary circuit contact resistance live detection device of a current transformer. The device comprises a shell and an electric part, wherein the electric part is arranged in the shell and comprises a detection wiring module, a power module, a voltage-controlled current source module, a current signal detection conditioning module, a voltage signal detection conditioning module, an LC alternating current channel module, a loop protection module, a CPU control module, a display/operation module and a direction switching module; the CPU control module is connected with the display/operation module, the voltage-controlled current source module, the current signal detection and conditioning module, the voltage signal detection and conditioning module, the direction switching module and the loop protection module; the voltage-controlled current source module is connected with the LC alternating current path module through the direction switching module, and the LC alternating current path module is connected with the loop protection module; the detection wiring module is connected with the loop protection module, the voltage signal detection conditioning module and the tested junction box loop.
Description
Technical Field
The invention belongs to the technical field of contact resistance testing, in particular to a secondary circuit contact resistance live detection device of a current transformer, which is suitable for power production in various environments, and particularly suitable for detection of metering equipment with high requirements on reliable power supply.
Background
With the overlay application of the electric energy collection system, faults of a large number of electric energy metering are discovered and processed, wherein the phenomenon of current imbalance accounts for a large proportion. At present, the suspected faults can only be checked in a power failure mode, and the normal production and life of power users are seriously affected. Analysis according to the past detection conditions: weak wiring and oxidation of the contacts are the most dominant failure factors. Meanwhile, the circuit is unbalanced due to the fact that the wiring is not firm and the contacts are oxidized, faults are unintentionally removed due to the fact that related screws are disassembled and screwed up again in the conventional power failure detection process, and fault judgment is difficult. Since current transformer operating regulations prescribe that no open circuit is allowed, there are few current studies on transformer live contact resistance testing. If the test of the contact resistance of the current secondary loop can be carried out under the normal electricity utilization condition, the comparison between different phase test values can determine whether the current imbalance is caused by the contact resistance or the normal phase deviation load. The number of times of power failure can be reduced, the electric quantity loss is reduced, and the potential safety hazard of power failure operation is avoided.
Disclosure of Invention
The invention aims to provide the electrified detection device for the contact resistance of the secondary circuit of the current transformer, aiming at the defects, the device can play a role in measuring and judging whether the secondary circuit of the current has poor contact under the condition of no power failure, and is particularly suitable for the test requirement of screening the current unbalance found by an electric energy acquisition system.
The invention is realized by adopting the following technical scheme:
The secondary circuit contact resistance live detection device of the current transformer comprises a shell and an electric part, wherein the electric part is arranged in the shell and comprises a detection wiring module, a power supply module, a voltage-controlled current source module, a current signal detection conditioning module, a voltage signal detection conditioning module, an LC alternating current channel module, a circuit protection module, a CPU control module, a display/operation module and a direction switching module;
The CPU control module is respectively connected with the display/operation module, the voltage-controlled current source module, the current signal detection and conditioning module, the voltage signal detection and conditioning module, the direction switching module and the loop protection module; the power supply module is respectively connected with the voltage-controlled current source module, the current signal detection conditioning module, the voltage signal detection conditioning module and the CPU control module, and provides working electric energy for the connected modules; the voltage-controlled current source module is connected with the LC alternating current path module through the direction switching module, and the LC alternating current path module is connected with the loop protection module in parallel; the detection wiring module is connected with the loop protection module, the voltage signal detection conditioning module and the tested junction box loop;
The detection wiring module consists of a current output line and a voltage signal line, the current output line consists of two soft copper wires with the sectional area larger than 2mm 2, the voltage signal line consists of twisted pair wires with shielding, the current output line is led out from the loop protection module, the voltage signal line is led out from the voltage signal detection conditioning module through the direction switching module, and when the device is required to be used for testing, the current output line and the voltage signal line are respectively connected to the current wiring holes of the metering wiring box for testing.
The CPU control module adopts a commercial ARM single chip microcomputer as a core, outputs 0-2.5V analog voltage signals transmitted by the voltage-controlled current source module, outputs 0-10A current to the corresponding voltage-controlled current source, and sets the voltage-controlled current source output as follows in the measuring process and sequence: +5A, -4A, +3A, -2A, +1A, -0.5A, +0.2A, 0A, each value measuring time is 2S, thereby verifying the contact resistance difference under different currents and realizing demagnetizing effect; the digital signals transmitted by the current signal detection conditioning module and the voltage signal detection conditioning module are collected, the resistance of the secondary loop of the current transformer is calculated, and then the loop state is judged.
The power module is connected with a storage battery connected with the charging module so as to provide working electric energy of the device under the condition of no external power supply.
The shell is provided with a power switch which is connected with the power module and used for controlling the work and stop of the device.
The power module converts 24V voltage transmitted by a direct current power supply or an internal storage battery sent by an external power adapter into stabilized direct current of plus 24V, minus 12V and plus 5V plus 3.3V power voltage for other modules connected with the power module to use, and the power module can automatically select the internal storage battery as a power supply when the external adaptive power supply is not available, automatically switch the external power supply for power supply when the external power adapter is connected, and charge the storage battery.
The voltage-controlled current source module is used for converting the analog voltage signal sent by the CPU control module into a current signal, and expanding the current by utilizing the current expanding circuit of the voltage-controlled current source module, so that the excitation current is output to the outside.
The current signal detection conditioning module converts exciting current output by the voltage-controlled current source module into a voltage signal by utilizing the sampling resistor, conditions the exciting current by a current detection chip in the current signal detection conditioning module, and then converts the exciting current into a digital signal which can be identified by a singlechip of the CPU control module by an analog-to-digital conversion chip.
The voltage signal detection module is used for converting a voltage signal formed by exciting current in a secondary circuit of the current transformer into a digital signal which can be identified by a singlechip of the CPU control module by utilizing an analog-to-digital conversion chip after operational amplifier conditioning and power frequency filtering.
The LC alternating current path module utilizes the principle of capacitive inductance series resonance, the power frequency impedance is zero during LC resonance, meanwhile, the capacitor has the characteristic of blocking direct current, a power frequency bypass is provided for a secondary loop of the current transformer, the safety of the secondary loop is ensured, direct current excitation can only circulate from the secondary loop, and an accurate current excitation response is formed.
The loop protection module consists of a normally closed relay with the current capacity larger than 10A and a transient diode which are connected in parallel, and provides an auxiliary bypass path for a secondary loop of the current transformer and an energy leakage path for an LC resonance loop of the LC alternating current path module; the transient suppression diode is used for preventing the damage to the measuring device caused by overvoltage of the loop.
The display/operation module consists of a liquid crystal screen and operation buttons; the liquid crystal screen is arranged on the shell and used for displaying information such as control output, current detection signals, voltage detection signals, relay action states, secondary circuit states of the current transformer and the like of the device; the operation buttons provide operation interaction of the device for a user; the operation button is connected with the CPU control module through a wire; the operation buttons include a confirm key, a return key, an up key, a down key, a left key, and a right key.
The direction switching module is realized by a double-throw relay through wiring, and is in a forward current test mode when the CPU controls a low-level signal, and is in a reverse excitation current test mode when the CPU controls a high-level signal, so that positive and negative (. + -.) alternate test of a tested loop is realized.
Advantages of the device of the invention include: the secondary circuit of the current transformer is put into an LC alternating current channel module under the electrified no-load state to ensure that the secondary side of the current transformer is not opened, and then a controllable direct current excitation is applied to the secondary circuit step by step; and detecting the loop contact resistance by measuring the direct-current voltage of the loop and utilizing ohm law, and judging the secondary loop contact state by the direct-current resistance value. The invention is designed specifically for the primary side electrification condition of the current transformer, can detect the secondary circuit of the current transformer without power failure of a power user, can be widely applied to power production in various environments, and particularly can detect metering equipment with high requirements on reliable power supply.
Drawings
The invention will be further described with reference to the accompanying drawings in which:
FIG. 1 is a schematic view of the apparatus of the present invention;
FIG. 2 is a schematic diagram of the components of the electrical portion of the present invention;
FIG. 3 is a schematic diagram of the detection wiring mode of the device of the present invention and the device to be detected when in use;
FIG. 4 is a schematic diagram of the components of the voltage signal detection conditioning module of the present invention;
Fig. 5 is a schematic diagram of the composition of the voltage controlled current source module of the present invention;
FIG. 6 is a schematic diagram of the components of the current signal detection conditioning module of the present invention;
FIG. 7 is a schematic diagram of the composition of the LC alternate current path module of the present invention;
FIG. 8 is a schematic diagram of the circuit protection module of the present invention;
FIG. 9 is a schematic diagram of the operation of the CPU control module of the present invention;
FIG. 10 is a schematic diagram of the operation of the direction switch module of the present invention;
FIG. 11 is a schematic diagram of the operation of the power module of the present invention;
FIG. 12 is a timing diagram of the excitation current test of the present invention.
In the figure: 1. the touch display screen comprises a shell, 2, a touch display screen, 3, an operation button, 4 and a power switch.
Detailed Description
The present invention will be described in detail with reference to fig. 1 to 12 and the specific examples.
Referring to fig. 1 and 2, the secondary circuit contact resistance live detection device of the current transformer is composed of a shell 1 and an electric part, wherein the electric part is arranged on a circuit board in the shell 1 and comprises a detection wiring module, a power supply module, a voltage-controlled current source module, a current signal conditioning detection module, a voltage signal conditioning detection module, an LC alternating current channel module, a circuit protection module, a CPU control module, a display/operation module, a direction switching module I and a direction switching module II.
The CPU control module is respectively connected with the voltage-controlled current source module, the current signal detection and conditioning module, the voltage signal detection and conditioning module, the direction switching module I, the direction switching module II, the protection module and the display/operation module. The voltage-controlled current source module is connected with the direction switching module I through a protection fuse and a sampling resistor R9. The current signal detection and conditioning module detects voltage signals at two ends of the sampling resistor R9 and then is connected with the CPU control module, the voltage signal detection and conditioning module is connected with the control module of the direction switching module I, CPU, and the LC alternating current channel module is connected with the test cable L2 after being connected with the protection module in parallel. The test cable L1 and the test cable L2 are respectively connected with the device body and the junction box of the tested loop.
The CPU control module is used as a control core to output controllable direct current excitation current to the tested loop through controlling the voltage-controlled current source module, the current signal detection conditioning module synchronously detects the excitation current through the sampling resistor R9 and feeds back the excitation current to the CPU control module, the voltage signal detection conditioning module detects the response voltage of the excitation current in the tested loop through the detection loop, and the CPU control module can calculate the resistance value of the tested loop through the response voltage and the excitation current and draw an excitation response curve.
Because the voltage-controlled current source module can only output unidirectional excitation current, the voltage signal detection conditioning module is designed only for positive voltage, in order to achieve the purpose of live test for testing negative-direction excitation current, the voltage signal detection module and the test cable L1 are connected in series with a direction switching module I, the voltage-controlled current source module and the LC alternating current channel module are connected in series with a direction switching module II, and the principles of the two direction switching modules are the same; the CPU control module outputs high-level signals to two modules (a direction switching module I and a direction switching module II) simultaneously, and the high-level signals correspond to a negative excitation current test direction; when the low-level signals are output at the same time, the positive excitation current testing direction is correspondingly adopted, so that the positive and negative excitation current alternating testing effect is realized.
The display/operation module adopts a commercially available 5-inch touch display screen 2, and the display/operation module and the CPU control module are matched to display tested voltage and current parameters, display testing process and display measurement judgment results, and simultaneously, the touch display screen 2 is utilized to convey the operation of a user to the CPU control module to achieve the interaction control effect. For convenient operation, the display/operation module also adopts an operation button 3, and the operation button 3 is connected with the CPU control module through a wire; the operation buttons 3 comprise a power key, an upper key, a lower key, a left key, a right key, a confirmation key and a return key, wherein the power key is used for starting and stopping the device, the upper key, the lower key, the left key and the right key are used for adjusting the menu position of the selection function, the confirmation key is used for confirming the selected menu function, and the return key is used for returning to the upper menu.
Referring to fig. 3, in the detection wiring module of the present invention, L1 and L2 are test cables, the test cable L1 is a current output cable, S1 and S2 are terminal contacts of the test cable L1, the test cable L2 is a voltage signal acquisition cable, S3 and S4 are terminal contacts of the test cable L2, the terminal contacts S1 and S3 of the test cable L1 and L2 are simultaneously connected to an input position of the junction box, and the terminal contacts S2 and S4 of the test cable L1 and L2 are simultaneously connected to an output position of the junction box; the branching measurement of the test cable L1 and the test cable L2 avoids the voltage division effect of the test wire self resistance of the test cable L1 on the voltage signal, when the external loop contact resistance is detected, the junction box pulling sheet is pulled to the position shown in the figure 3, the current transformer and the electric energy meter are not required to be detached from the junction box and then detected, the tightness degree of the original wiring screw is not damaged, the loop contact condition is reflected most accurately, and meanwhile, the current transformer loop is prevented from being detected in power failure.
Referring to fig. 4, the voltage signal detection conditioning module of the invention, a voltage signal of a detected loop is transmitted to a precision operational amplifier AD629 in fig. 4 by a test cable L2 shown in fig. 3, the precision operational amplifier AD629 has the characteristic of measuring differential signals under a high common mode voltage, common mode interference of an external test loop can be reduced to the maximum extent by the precision operational amplifier AD629, meanwhile, the external loop is isolated once, the precision operational amplifier AD629 responds to the differential voltage signal, namely the detected loop, by a power frequency band elimination filter consisting of a resistor R1, a resistor R2, a resistor R3, a capacitor C1, a capacitor C2, a capacitor C3, an operational amplifier OP1 and an operational amplifier OP2 in fig. 4, and further filters the power frequency interference obtained in the voltage signal; the band-stop filter filters the power frequency interference in the voltage signal transmitted by the precise operational amplifier AD629, and then transmits the voltage signal to the sampling module, converts the analog voltage signal into a 16-bit digital signal which can be processed by the CPU control module, and transmits the digital voltage signal to the CPU control module for processing. Wherein, the values of the resistor R1 and the resistor R2 are 318.4kΩ, the values of the capacitor C1 and the capacitor C2 are 0.01uF, the value of the resistor R3 is 159.2kΩ, and the value of the capacitor C3 is 0.02uF; the resistor R4 is a potentiometer and is used for adjusting the quality of the industrial frequency band-stop filter; the operational amplifiers OP1 and OP2 are operational amplifiers, and are generally selected from OP77 type operational amplifiers with high gain and low bias; the sampling module adopts a high-precision 16-bit AD7606 model number digital-analog conversion chip.
Referring to fig. 5, the voltage-controlled current source module is used for converting 0-2.5V voltage sent by a singlechip of the CPU control module into 0-10A current output, the voltage-controlled current source module adopts an OP3 as a front-end OP, and a field effect transistor IRF530 is connected in series after the OP 3; the non-inverting input end of the operational amplifier OP3 is sequentially connected with a resistor R5 and a capacitor C5 in series and then grounded; the drain electrode (D pole) of the field effect tube IRF530 is grounded through a resistor R6, and the resistor R6 is a sampling resistor; the source electrode (S electrode) end of the field effect tube IRF530 is connected in series with a capacitor C4 and a resistor R7; the operational amplifier OP3 adopts an OP77 model operational amplifier with low load adjustment rate, high gain and low bias, converts a voltage analog signal transmitted by a CPU control module into a current signal by utilizing a sampling resistor R6, and simultaneously utilizes a field effect tube IRF530 as a current expansion loop to boost current output power and output the current. Wherein, the resistor R5 is 470 omega common metal film resistor; the resistor R6 is a sampling resistor with a resistance value of 3 omega formed by connecting 4 precise metal film resistors with a precision of 12 omega and a temperature drift coefficient of 25ppm in parallel, the field effect transistor IRF530 is a type IRF530 chip which is used as a current spreading element, the resistor R7 is a metal film resistor with a resistance value of 3 omega and a power of 2W, and the capacitor C5 is a capacitor of 0.1 uF.
Referring to fig. 6, the current signal detection conditioning module adopts a current detection chip, a VCC terminal of the current detection chip is grounded through a capacitor C6, and an OUT terminal of the current detection chip is connected in series with an operational amplifier OP4; a detection end A and a detection end B which are connected with two ends of a sampling resistor R9 in FIG. 2 are respectively led out from a current detection chip; the current signal detection conditioning module achieves the purpose of detecting the excitation current by measuring voltage signals generated at two ends of the sampling resistor R9 when the excitation current flows through the sampling resistor R9 in FIG. 2. The sampling resistor R9 in fig. 2 is a low temperature coefficient manganin sampling resistor having a typical value of 10mΩ. The voltage signals at two ends of the manganese-copper sampling resistor have the characteristics of potential suspension and small potential difference. The current signal detection and conditioning module selects a special current detection chip MAX4173T/F/H model chip, and simultaneously cooperates with a follower circuit formed by an operational amplifier OP4 to convert and condition the suspended excitation current signal into a voltage signal which can be measured, and the voltage signal is sent to the digital-to-analog conversion sampling chip and then is converted into a digital current signal which can be processed by the CPU control module.
Referring to fig. 7, an LC ac path module is an LC resonant circuit with a power frequency of 50Hz formed by an inductance L8 and a capacitance C7, and a filter capacitance C9 and a filter capacitance C8 are connected in parallel beside the LC resonant circuit; the LC resonant circuit only provides a passage for power frequency and high frequency and has isolation effect on exciting current and direct current voltage. Wherein, the value of the inductance L8 is 0.001H, and the value of the capacitance C7 is 0.01014F; the LC alternating current path module provides a power frequency path for an external tested loop, in particular to a current transformer, so that the open-circuit state of the current transformer is avoided when the tested loop is opened. The capacitors C9 and C8 are BP capacitors of 1uF and 0.01uF respectively, and provide high-frequency and sub-high-frequency paths for the loop.
Referring to fig. 8, the loop protection module is composed of a triode Q1, a relay and a TVS, the input end of the triode Q1 is connected with the control signal of the CPU control module, the emitter of the triode Q1 is connected with a resistor R8 and a relay coil, and the relay contact is connected with the TVS in parallel. The circuit protection module is used for preventing overvoltage in the test circuit, and TVS is connected in parallel to two ends of the current output terminal; the normally closed relay is driven by the triode and is normally in a closed state, when the device is connected into the tested loop, the current transformer is ensured to be in a closed state, the high-level drive relay is output to the triode by the CPU control module in the testing stage, the LC power frequency resonant circuit in the figure 7 still can provide an alternating current channel for the external current transformer, the open state of the current transformer is avoided, after the testing is finished, the CPU control module outputs a low level, the relay is closed, and the external tested current transformer is ensured to be in a short circuit state.
Referring to fig. 9, a CPU control module is used as a control core to output controllable direct current excitation current to a measured loop through controlling a voltage-controlled current source module, a current signal conditioning detection module synchronously detects the excitation current through a sampling resistor and feeds back the excitation current to the CPU control module, a voltage signal conditioning detection module detects the response voltage of the excitation current in the measured loop through detecting the loop, and the CPU control module can calculate the contact resistance value of the measured loop through the response voltage and the excitation current and draw a loop excitation response curve. The CPU control module controls the relay of the protection module to act by outputting a control signal to the protection module, so that the protection control is enhanced. The CPU control module outputs control signals through the direction switching module I and the direction switching module II to realize the positive and negative direction switching of the exciting current of the tested loop.
The CPU control module adopts an ARM chip model STM32F407, has low power consumption and high calculation performance, is provided with a GPIO interface, can drive the relay of the protection module to open and close, and can drive the relay of the direction switching module I and the direction switching module II to open and close, can read the voltage signals and the current signals transmitted by the voltage signal conditioning module and the current signal conditioning detection module, and calculates the contact resistance of the tested loop. The CPU control module is provided with an analog-to-digital conversion interface and can output a direct-current control voltage signal to the voltage-controlled current source module, and then controllable current is output to the tested loop. Typical values and sequences are set as: +5A, -4A, +3A, -2A, +1A, -0.5A, +0.2A, 0A, thereby verifying the contact resistance difference at different currents and realizing demagnetization.
Referring to fig. 10, the direction switching module I and the direction switching module II each include two double-throw relays, a triode Q2 and a resistor R18, a relay coil is connected to an emitter of the triode Q2, a relay JDQ1 terminal J11 is connected to a relay JDQ2 terminal J23, and a relay JDQ1 terminal J13 is connected to a relay JDQ2 terminal J21. The direction switching module I and the direction switching module II can realize a forward current excitation test mode when the CPU control module sends a low-level signal by using a triode to drive the double-throw relay to be conducted and closed and switching the contact positions and then according to the wiring mode shown in FIG. 10. The test mode is stimulated by reverse current when the CPU control module sends a high level signal.
Referring to fig. 11, the power module includes a battery, a DC/DC 12V DC power module, a DC/DC5V DC power module, a voltage regulator (AMS 1117 chip) and a transistor Q13, the power adapter 24V input is connected to the battery through a diode D11 and the transistor Q13, the battery is connected to the DC/DC 12V and the DC/DC5V through a power switch, the DC/DC5V is converted into a 3.3V voltage through the AMS1117 chip to supply power to the CPU control module, and the power switch is disposed on the casing. The power supply module can automatically select commercial power or a storage battery as a power supply of the device, and output and stabilize the power supply of plus 24V, plus 12V, plus 5V and plus 3.3V to each module. The power adapter is a commercial AC 220-DC 24V power adapter, a power selection circuit is formed by utilizing a triode Q13 and a diode D11, when mains supply is powered on, the Q13 is conducted, a storage battery is charged at the moment and supplies power to the device, when the mains supply is not powered on, the Q13 is closed, the storage battery supplies power to the device, and the power module converts commercial DC/DC +/-12V, DC/DC and a chip AMS1117 chip into power supply voltage of each module and supplies power.
Referring to fig. 12, the exciting current test time sequence relation diagram, the CPU control module realizes 0-10A exciting current output by using the voltage-controlled current source module through outputting 0-2.5V voltage analog signals, realizes-10A to +10A current excitation by using the direction switching module I (or the direction switching module II), and specifically adopts the exciting current time sequence test shown in fig. 12.
The specific testing method of the device comprises the following steps:
(1) Testing wiring;
One end of a test cable L1 is connected to a device voltage detection terminal, an S1 contact at the other end of the test cable L1 is connected to a position (CT side empty terminal) of an incoming line A terminal of the junction box of the electric energy meter, and an S2 contact of the test cable L1 is connected to a position (electricity meter side empty terminal) of an outgoing line b terminal of the junction box of the electric energy meter; one end of a test cable L2 is connected to a device current output terminal, an S3 contact at the other end of the test cable L2 is connected to a position (CT side empty terminal) of an incoming line A terminal of the junction box of the electric energy meter, and an S4 contact at the other end of the test cable L2 is connected to a position (electricity meter side empty terminal) of an outgoing line b terminal of the junction box of the electric energy meter;
(2) The power switch is turned on to enable the device to start working, the CPU control module defaults to control the relay of the protection module to be closed, the pulling sheet of the junction box to be tested is pulled to an empty connection position, namely, a state of no short circuit is achieved, and at the moment, the current transformer is still in a short circuit state through closing of the relay;
(3) The CPU control module controls the relay of the protection module to be disconnected, at the moment, the LC alternating current path module is in a resonance state, the tested current transformer is still in a short circuit state for power frequency, and is in an open circuit state for direct current.
(4) The CPU control module controls the voltage-controlled current to output exciting current 5A for 2 seconds, the current signal detection conditioning module tests that the output current 5A is consistent with a set value, the voltage signal detection conditioning module tests to obtain a response voltage signal of the tested loop under the exciting current of plus 5A and sends the response voltage signal to the CPU control module for calculation, and the CPU control module calculates the contact resistance of plus 5A during excitation;
(5) The CPU control module controls and outputs 4A exciting current, controls a direction switching loop, and realizes contact resistance test and record of-4A exciting current;
(6) Sequentially adjusting the CPU control module to control the excitation current and the direction switching circuit, and testing the contact resistance corresponding to the excitation current of +5A, -4A, +3A, -2A, +1A, -0.5A, +0.2A and 0A at the moment; the excitation currents +5A, -4A, +3A, -2A, +1A, -0.5A, +0.2A, and 0A are respectively 0-2 s, 2-4 s, 4-6 s, 6-8 s, 8-10 s, 10-12 s, 12-14 s, and 14-16 s;
(7) The CPU control module controls the protection loop relay to be closed, displays the curve of the contact resistance of the tested loop, the measuring time sequence and the exciting current, and further judges the state of the tested loop.
(8) And after the power switch is turned off, recovering the terminal box pulling piece, and removing the test wiring to finish the test.
The invention consists of two groups of test wires, the change of a tested loop is reduced to the greatest extent by using the wiring box to connect, and the S1, the S3 and the S2 and the S4 of the test cables L1 and L2 are connected at the wiring terminals, so that the influence of the current output cables on the tested loop is avoided. The power module can automatically judge and select to use the commercial power or the storage battery to supply power for the device, when the commercial power is accessed, the power module supplies power for the device and simultaneously charges the storage battery, and when the commercial power is not available, the storage battery is used for supplying power for the device. The voltage signal conditioning detection module utilizes a differential operational amplifier to avoid common mode interference, utilizes a double-T power frequency band-stop filter circuit to filter power frequency interference, and converts the power frequency interference into a digital signal which can be processed by a CPU through a high-precision digital-to-analog converter. The excitation pattern typical value and sequence are set as follows: +5A, -4A, +3A, -2A, +1A, -0.5A, +0.2A, 0A, thereby verifying the contact resistance difference at different currents and realizing demagnetization. The voltage-controlled current source module is characterized in that voltage-controlled current of a high-precision operational amplifier and a Morse tube is utilized, and the voltage signal output by a CPU can be converted into current to excite a tested loop. The current signal detection module utilizes a special current detection chip and a sampling resistor to form a current detection loop with potential suspension characteristics. The CPU control module is used for controlling and outputting different exciting currents to the voltage-controlled current source, collecting response voltage and real output current value of the tested loop, and calculating the contact resistance of the tested loop under different exciting currents (typical values of +5A, -4A, +3A, -2A, +1A, -0.5A, +0.2A) by using ohm's law so as to judge the contact condition of the secondary loop of the current transformer. And comparing between different phase test values can determine whether the three-phase current imbalance is caused by contact resistance or normal phase bias load. The LC alternating current path module utilizes the LC resonance principle to form a series power frequency resonance loop to provide a power frequency loop for a tested loop, and the current transformer is ensured to be in a non-open-circuit low-resistance state. The loop protection module is characterized in that the TVS is used for carrying out overvoltage protection on the terminal, so that the damage of overvoltage in a loop to the components is prevented, meanwhile, the CPU is used for controlling the on-off of the relay, a short circuit path is provided for a tested loop current transformer, and the open circuit risk is reduced. And meanwhile, after the test is finished, an energy-discharging channel is provided for the resonant circuit by conducting the relay.
The testing device is found through actual use, wiring is simple, testing is accurate, and because the secondary circuit of the current transformer can be detected without power failure of a power user, the testing device is convenient to use, and can be widely applied to power production in various environments, and particularly, the testing device is used for detecting metering equipment with high requirements on reliable power supply.
Claims (10)
1. The utility model provides a current transformer secondary circuit contact resistance live detection device which characterized in that: the device comprises a shell and an electric part, wherein the electric part is arranged in the shell and comprises a detection wiring module, a power module, a voltage-controlled current source module, a current signal detection conditioning module, a voltage signal detection conditioning module, an LC alternating current channel module, a loop protection module, a CPU control module, a display/operation module and a direction switching module;
The CPU control module is respectively connected with the display/operation module, the voltage-controlled current source module, the current signal detection and conditioning module, the voltage signal detection and conditioning module, the direction switching module and the loop protection module; the power supply module is respectively connected with the voltage-controlled current source module, the current signal detection conditioning module, the voltage signal detection conditioning module and the CPU control module, and provides working electric energy for the connected modules; the voltage-controlled current source module is connected with the LC alternating current path module through the direction switching module, and the LC alternating current path module is connected with the loop protection module in parallel; the detection wiring module is connected with the loop protection module, the voltage signal detection conditioning module and the tested junction box loop;
the voltage-controlled current source module is used for converting the analog voltage signal sent by the CPU control module into a current signal, and expanding the current by utilizing a current expanding circuit of the voltage-controlled current source module so as to realize the external output of excitation current;
A protection fuse, a sampling resistor and a diode are connected in series between the voltage-controlled current source module and the LC alternating current channel module, the current signal detection conditioning module converts exciting current output by the voltage-controlled current source module into a voltage signal by using the sampling resistor, conditioning is carried out by a current detection chip in the current signal detection conditioning module, and then the digital signal is converted into a digital signal which can be identified by a singlechip of the CPU control module by an analog-to-digital conversion chip;
The voltage signal detection module is used for conditioning and filtering the voltage signal formed by exciting current in the secondary circuit of the current transformer through an operational amplifier and converting the voltage signal into a digital signal which can be identified by a singlechip of the CPU control module through an analog-to-digital conversion chip;
The LC alternating current path module utilizes the principle of capacitive inductance series resonance, the power frequency impedance is zero during LC resonance, meanwhile, the capacitor has the characteristic of blocking direct current, a power frequency bypass is provided for a secondary loop of the current transformer, the safety of the secondary loop is ensured, and direct current excitation can only circulate from the secondary loop, so that accurate current excitation response is formed;
the loop protection module consists of a normally closed relay with the current capacity larger than 10A and a transient diode which are connected in parallel, and provides an auxiliary bypass path for a secondary loop of the current transformer and an energy leakage path for an LC resonance loop of the LC alternating current path module; the transient suppression diode is used for preventing the damage to the measuring device caused by overvoltage of the loop.
2. The current transformer secondary circuit contact resistance live detection device according to claim 1, wherein: the detection wiring module consists of a current output line and a voltage signal line, the current output line consists of two soft copper wires with the sectional area larger than 2mm 2, the voltage signal line consists of twisted pair wires with shielding, the current output line is led out from the loop protection module, and the voltage signal line is led out from the voltage signal detection conditioning module through the direction switching module.
3. The current transformer secondary circuit contact resistance live detection device according to claim 1, wherein: the CPU control module adopts an ARM single chip microcomputer as a core, outputs 0-2.5V analog voltage signals transmitted by the voltage-controlled current source module, outputs 0-10A current to the corresponding voltage-controlled current source, and sets the voltage-controlled current source output as follows in the measuring process and sequence: +5A, -4A, +3A, -2A, +1A, -0.5A, +0.2A, 0A, each value measuring time is 2S, thereby verifying the contact resistance difference under different currents and realizing demagnetizing effect; the digital signals transmitted by the current signal detection conditioning module and the voltage signal detection conditioning module are collected, the resistance of the secondary loop of the current transformer is calculated, and then the loop state is judged.
4. The current transformer secondary circuit contact resistance live detection device according to claim 1, wherein: the power module is connected with a storage battery connected with the charging module so as to provide working electric energy of the device under the condition of no external power supply.
5. The current transformer secondary circuit contact resistance live detection device according to claim 1, wherein: the power module converts 24V voltage transmitted by a direct current power supply or an internal storage battery sent by an external power adapter into stabilized direct current of plus 24V, minus 12V and plus 5V plus 3.3V power voltage for other modules connected with the power module to use, and the power module can automatically select the internal storage battery as a power supply when the external adaptive power supply is not available, automatically switch the external power supply for power supply when the external power adapter is connected, and charge the storage battery.
6. The current transformer secondary circuit contact resistance live detection device according to claim 1, wherein: the shell is provided with a power switch which is connected with the power module and used for controlling the operation and the stop of the device.
7. The current transformer secondary circuit contact resistance live detection device according to claim 1, wherein: the display/operation module consists of a liquid crystal screen and operation buttons; the liquid crystal screen is arranged on the shell and used for displaying information such as control output, current detection signals, voltage detection signals, relay action states, secondary circuit states of the current transformer and the like of the device; the operation buttons provide operation interaction of the device for a user; the operation button is connected with the CPU control module through a wire; the operation buttons include a confirm key, a return key, an up key, a down key, a left key, and a right key.
8. The current transformer secondary circuit contact resistance live detection device according to claim 1, wherein: the direction switching module is realized by a double-throw relay through wiring, and is in a forward current test mode when the CPU controls a low-level signal, and is in a reverse excitation current test mode when the CPU controls a high-level signal, so that positive and negative alternate tests on a tested loop are realized.
9. A method for testing a secondary circuit contact resistance live detection device of a current transformer as claimed in claim 1, comprising the steps of:
(1) Testing wiring;
One end of a test cable L1 is connected to a device voltage detection terminal, an S1 contact at the other end of the test cable L1 is connected to an empty terminal at the incoming line CT side of the junction box of the electric energy meter, and an S2 contact of the test cable L1 is connected to an empty terminal at the outgoing line ammeter side of the junction box of the electric energy meter; one end of a test cable L2 is connected to a device current output terminal, an S3 contact at the other end of the test cable L2 is connected to an empty terminal at the incoming line CT side of the junction box of the electric energy meter, and an S4 contact at the other end of the test cable L2 is connected to an empty terminal at the outgoing line ammeter side of the junction box of the electric energy meter;
(2) The power switch is turned on to enable the device to start working, the CPU control module defaults to control the relay of the protection module to be closed, the pulling sheet of the junction box to be tested is pulled to an empty connection position, namely, a state of no short circuit is achieved, and at the moment, the current transformer is still in a short circuit state through closing of the relay;
(3) The CPU control module controls the relay of the protection module to be disconnected, at the moment, the LC alternating current channel module is in a resonance state, the tested current transformer is still in a short circuit state for power frequency, and is in an open circuit state for direct current;
(4) The CPU control module controls the voltage-controlled current to output exciting current 5A for 2 seconds, the current signal detection conditioning module tests that the output current 5A is consistent with a set value, the voltage signal detection conditioning module tests to obtain a response voltage signal of the tested loop under the exciting current of plus 5A and sends the response voltage signal to the CPU control module for calculation, and the CPU control module calculates the contact resistance of plus 5A during excitation;
(5) The CPU control module controls and outputs 4A exciting current, controls a direction switching loop, and realizes contact resistance test and record of-4A exciting current;
(6) Sequentially adjusting the CPU control module to control the excitation current and the direction switching circuit, and testing the contact resistance corresponding to the excitation current of +5A, -4A, +3A, -2A, +1A, -0.5A, +0.2A and 0A at the moment;
(7) The CPU control module controls the protection loop relay to be closed, displays the curve of the contact resistance of the tested loop, the measuring time sequence and the exciting current, and further judges the state of the tested loop;
(8) And after the power switch is turned off, recovering the terminal box pulling piece, and removing the test wiring to finish the test.
10. The method for testing the secondary loop contact resistance live detection device of the current transformer according to claim 9, wherein the method comprises the following steps of: the excitation currents +5A, -4A, +3A, -2A, +1A, -0.5A, +0.2A, and 0A correspond to the time sequences of 0-2 s, 2-4 s, 4-6 s, 6-8 s, 8-10 s, 10-12 s, 12-14 s, and 14-16 s respectively.
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| CN111487466B (en) * | 2020-06-04 | 2024-06-07 | 国网江苏省电力有限公司宿迁供电分公司 | Electrified detection device for direct-current resistor of secondary loop of current transformer |
| CN112433180A (en) * | 2020-11-04 | 2021-03-02 | 国网北京市电力公司 | Intelligent wiring detector for electric energy meter |
| CN112731259B (en) * | 2021-01-22 | 2023-10-10 | 浙江万胜智能科技股份有限公司 | Open-short circuit detection method for current transformer |
| CN114062841B (en) * | 2021-11-10 | 2022-08-12 | 无锡诚勇自动化技术有限公司 | Testing equipment for wire break alarm |
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