CN111487466A - A live detection device for the DC resistance of the secondary circuit of a current transformer - Google Patents

Abstract

The invention belongs to the technical field of direct current resistance testing, in particular to a live detection device for direct current resistance of a secondary circuit of a current transformer. It consists of a housing and an electrical part, the electrical part is arranged in the housing, and the electrical part includes a detection wiring module, a power supply module, a voltage-controlled current source module, a current signal detection and conditioning module, a voltage signal detection and conditioning module, a CD AC channel module, Loop protection module, CPU control module, display/operation module and direction switching module; CPU control module and display/operation module, voltage-controlled current source module, current signal detection and conditioning module, voltage signal detection and conditioning module, direction switching module and loop protection The voltage-controlled current source module is connected with the CD AC path module through the direction switching module, and the CD AC path module is connected with the loop protection module; the detection wiring module is connected with the loop protection module, the voltage signal detection and conditioning module and the tested junction box loop.

Description

A live detection device for the DC resistance of the secondary circuit of a current transformer

technical field

The invention belongs to the technical field of DC resistance testing, in particular to a live detection device for DC resistance of a secondary circuit of a current transformer, which is suitable for power production in various environments, especially for measuring equipment with high requirements for reliable power supply.

Background technique

With the coverage and application of power acquisition systems, a large number of power metering faults have been discovered and dealt with, among which current imbalance accounts for a large proportion. To deal with such suspected faults, only power outages can be checked, which seriously affects the normal production and life of power users. According to the analysis of the previous detection situation: the wiring is not strong and the contact oxidation is the main failure factor. At the same time, the circuit is unbalanced due to weak wiring and oxidation of contacts. In the past power failure detection, the fault was unintentionally eliminated due to re-disassembly and tightening of the relevant screws, which made it difficult to judge the fault. Since the current transformer operating regulations stipulate that the open circuit is not allowed, there are few researches on the live DC resistance test of the transformer at present. If the DC resistance test of the current secondary circuit can be carried out under normal power consumption, the comparison between the test values of different phases can determine whether the current imbalance is caused by the DC resistance or the normal phase-biased load. It can reduce the number of power outages, reduce power loss, and avoid potential safety hazards in power outage operations.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a current transformer secondary circuit DC resistance live detection device in view of the above shortcomings, which can measure and determine whether there is poor contact in the current secondary circuit under the condition of no power outage. Check the test requirements for current imbalances found by the power harvesting system.

The present invention adopts following technical scheme to realize:

A current transformer secondary circuit DC resistance live detection device is composed of a casing and an electrical part, the electrical part is arranged in the casing, and the electrical part includes a detection wiring module, a power supply module, a voltage-controlled current source module, and a current signal detection module. Conditioning module, voltage signal detection and conditioning module, CD AC channel module, loop protection module, CPU control module, display/operation module and 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 module is respectively connected with the voltage-controlled current source module, the current signal detection module The conditioning module, the voltage signal detection conditioning module and the CPU control module are connected, and provide working power for these connected modules; the voltage-controlled current source module is connected with the CD AC channel module through the direction switching module, and the CD AC channel module is connected in parallel with the loop protection module. ;The detection wiring module is connected with the loop protection module, the voltage signal detection and conditioning module and the circuit of the junction box under test;

The detection wiring module is composed of a current output line and a voltage signal line. The current output line is composed of two soft copper wires with a cross-sectional area greater than 2mm ² . The voltage signal line is composed of a shielded twisted pair. The current output line is drawn from the loop protection module. , the voltage signal line is led out from the voltage signal detection and conditioning module through the direction switching module. When the device of the present invention needs to be used for testing, the current output line and the voltage signal line are respectively connected to the current wiring hole of the metering junction box for testing.

The CPU control module adopts a commercially available ARM single-chip microcomputer as the core, and outputs 0~2.5V analog voltage signal transmitted from the voltage-controlled current source module, and the corresponding voltage-controlled current source outputs 0~10A current. During the measurement process and sequence Set the output of the voltage-controlled current source as: +5A, -4A, +3A, -2A, +1A, -0.5A, +0.2A, 0A, and the measurement time of each value is 2S, so as to verify the DC current under different currents The resistance is distinguished and demagnetized; the digital signals sent by the current signal detection and conditioning module and the voltage signal detection and conditioning module are collected, and the resistance value of the secondary circuit of the current transformer is calculated, and then the circuit state is judged.

The power supply module is connected with a battery connected to the charging module, so as to provide the working power of the device of the present invention in the absence of an external power supply.

A power switch is arranged on the casing, and the power switch is connected with the power module and is used to control the operation and stop of the device of the present invention.

The power supply module converts the DC power supplied by the external power adapter or the 24V voltage supplied by the internal battery into a regulated DC+24V, ±12V, ﹢5V﹢3.3V power supply voltage for use by other modules connected to it. , the power supply module can automatically select the circuit to use the internal battery as the power supply when there is no external adapter power supply, and automatically switch the external power supply when the power adapter is connected, and charge the battery.

The voltage-controlled current source module is used to convert the analog voltage signal sent by the CPU control module into a current signal, and use the current expansion circuit of the voltage-controlled current source module to expand the current, thereby realizing the external output excitation current.

A protection fuse, a sampling resistor and a diode are connected in series between the voltage-controlled current source module and the CD AC path module. The current signal detection and conditioning module uses the sampling resistor to convert the excitation current output by the voltage-controlled current source module into a voltage signal, and passes the current The current detection chip inside the signal detection and conditioning module performs conditioning, and then converts it into a digital signal that can be recognized by the single-chip microcomputer of the CPU control module through the analog-to-digital conversion chip.

The voltage signal detection module converts the voltage signal formed by the excitation current in the secondary circuit of the current transformer through operational amplifier conditioning and power frequency filtering, and then uses the analog-to-digital conversion chip to convert it into a digital signal that can be identified by the single-chip microcomputer of the CPU control module. .

The CD AC path module uses capacitors and diodes to form an AC path and a DC blocking circuit. The capacitor C has the characteristics of blocking DC. The capacitor and the diode connected in series provide a power frequency bypass for the secondary circuit of the current transformer under test, so that the secondary circuit AC current No open circuit to ensure safety; DC excitation can only flow from the tested secondary circuit without being bypassed by the CD AC path module, forming an accurate test DC current excitation response.

The circuit protection module is composed of a normally closed relay with a current capacity greater than 10A and a transient diode in parallel, providing an auxiliary bypass path for the secondary circuit with a current transformer, and providing energy leakage for the capacitive element of the CD AC path module. Channel energy leakage channel; the transient suppression diode is used to prevent damage to the measuring device due to overvoltage in the loop.

The display operation module is composed of a liquid crystal screen and an operation button; the liquid crystal screen is installed on the casing and is used to display the control output, current detection signal, voltage detection signal, relay action state, and current transformer two of the device of the present invention. Secondary loop status and other information; the operation button provides the user with the operation interaction of the device of the present invention; the operation button is connected with the CPU control module through a wire; the operation button includes a confirmation key, a return key, an up key, a down key, and a left key and right click.

The direction switching module is realized by the double-throw relay through wiring. When the CPU controls the low level signal, it is the forward current test mode, and when the CPU controls the high level, it is the reverse excitation current test mode, and then realizes the detection of the loop under test. Positive and negative (±) alternate tests.

The advantages of the device of the present invention include: by putting the CD AC path module into the secondary circuit of the current transformer in a charged and no-load state to ensure that the secondary side of the current transformer is not open, and then stepwise applying a controllable DC current to the secondary circuit Excitation; by measuring the DC voltage of the loop, the DC resistance of the loop is detected by Ohm's law, and then the contact state of the secondary loop is judged by the DC resistance value. The invention is specially designed for the live condition of the primary side of the current transformer, and can detect the secondary circuit of the current transformer without the need for power outage by the power user, and can be generally applied to power production in various environments, especially for high reliability of power supply. measurement equipment testing.

Description of drawings

The present invention will be further described below in conjunction with the accompanying drawings:

Figure 1 is a schematic diagram of the device structure of the present invention

Fig. 2 is the composition principle diagram of the electrical part of the present invention;

3 is a schematic diagram of the detection wiring mode between the device of the present invention and the device to be detected when in use;

Fig. 4 is the composition principle diagram of the voltage signal detection and conditioning module of the present invention;

Fig. 5 is the composition principle diagram of the voltage-controlled current source module of the present invention;

6 is a schematic diagram of the composition of the current signal detection and conditioning module of the present invention;

Fig. 7 is the composition principle diagram of the CD AC path module of the present invention;

Fig. 8 is the composition principle diagram of the loop protection module of the present invention;

Fig. 9 is the working principle diagram of the CPU control module of the present invention;

Fig. 10 is the working principle diagram of the direction switching module of the present invention;

Fig. 11 is the working principle diagram 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. Housing, 2. Touch screen, 3. Operation buttons, 4. Power switch.

Detailed ways

The present invention will be described in detail below with reference to Figures 1 to 12 and specific embodiments.

Referring to Fig. 1 and Fig. 2 , a current transformer secondary circuit DC resistance live detection device of the present invention is composed of a housing 1 and an electrical part, the electrical part is arranged on the circuit board in the housing 1, and the electrical part is Including detection wiring module, power supply module, voltage-controlled current source module, current signal conditioning detection module, voltage signal conditioning detection module, CD AC path module, loop protection module, CPU control module, display/operation module and direction switching module.

The CPU control module is respectively connected with a voltage-controlled current source module, a current signal detection and conditioning module, a voltage signal detection and conditioning module, a direction switching module 1, a direction switching module 2, a protection module and a display operation module. The voltage-controlled current source module is connected to the direction switching module 1 through a protection fuse and a sampling resistor R9. The current signal detection and conditioning module detects the voltage signal at both ends of the sampling resistor R9 and is connected to the CPU control module. The voltage signal detection and conditioning module is connected to the direction switching module 1 and the CPU control module. The CD AC channel module and the protection module are connected in parallel with the test cable. L2 is connected. The test cable L1 and the test cable L2 are respectively connected to the device body and the junction box of the circuit under test.

As the control core, the CPU control module outputs a controllable DC excitation current to the circuit under test by controlling the voltage-controlled current source module. The current signal detection and conditioning module synchronously detects the excitation current through the sampling resistor R9, and feeds it back to the CPU control module. The conditioning module detects the response voltage of the excitation current in the loop under test through the detection loop, and the CPU control module can calculate the resistance value of the loop under test through the response voltage and the excitation current and draw the excitation response curve.

Since the voltage-controlled current source module can only output unidirectional excitation current, the voltage signal detection and conditioning module is only designed for positive voltage. Switching module 1, the direction switching module 2 is connected in series between the voltage-controlled current source module and the CD AC channel module. The principle of the two direction switching modules is the same; ) outputs a high-level signal, corresponding to the negative excitation current test direction; when outputting a low-level signal at the same time, it corresponds to the positive excitation current test direction, so as to realize the alternate test effect of positive and negative excitation current.

The display operation module adopts a commercially available 5-inch touch screen 2. The display operation module cooperates with the CPU control module to display the voltage and current parameters of the test, display the test process, and display the measurement and judgment results. At the same time, the touch screen 2 is used to operate the user. It is sent to the CPU control module to achieve the function of control interaction. For the convenience of manipulation, the display operation module also adopts an operation button 3, which is connected with the CPU control module through a wire; the operation button 3 includes a power button, an up button, a down button, a left button, a right button, a confirmation button and a return button , the power key turns on and off the device of the present invention, the up key, the down key, the left key and the right key are used to adjust the position of the selected function menu, the confirmation key is used to confirm the selected menu function, and the return key is used to return to the upper level menu.

Referring to Figure 3, in the detection wiring module of the present invention, L1 and L2 are test cables, the test cable L1 is used as a current output cable, S1 and S2 are the end contacts of the test cable L1, and the test cable L2 is used as a voltage signal acquisition cable. S3, S4 is the end contact of the test cable L2, the end contact S1 of the test cable L1 and the end contact S3 of the test cable L2 are connected to the input position of the junction box at the same time, the end contact S2 of the test cable L1 and the end contact S4 of the test cable L2 are connected at the same time The output position of the junction box; the test cable L1 and the test cable L2 are separated for measurement, which avoids the voltage division effect of the test line of the test cable L1 on the voltage signal. To the position shown in Figure 3, there is no need to remove the current transformer and the electric energy meter from the junction box and then test it. The tightness of the original wiring screw is not damaged, and the circuit contact condition is most accurately reflected, and the current transformer circuit for power failure detection is avoided.

Referring to Figure 4, the voltage signal detection and conditioning module of the present invention, the test cable L2 shown in Figure 3 transmits the voltage signal of the circuit under test to the precision operational amplifier AD629 in Figure 4, the precision operational amplifier AD629 has a high common mode voltage measurement The characteristics of differential signal, through the precision op amp AD629, the common mode interference of the external test loop can be minimized, and the external loop can be isolated at the same time. The middle resistor R1, resistor R2, resistor R3, capacitor C1, capacitor C2, capacitor C3 and the power frequency band rejection filter composed of the operational amplifier OP1 and the operational amplifier OP2, further filter out the power frequency interference obtained in the voltage signal; The blocking filter filters out the power frequency interference in the voltage signal transmitted by the precision operational amplifier AD629 and sends it to the sampling module, converts the analog voltage signal into a 16-bit digital signal that can be processed by the CPU control module, and transmits the digital voltage signal to the CPU. control module for processing. Among them, the value of resistor R1 and resistor R2 is 318.4kΩ, the value of capacitor C1 and capacitor C2 is 0.01uF, the value of resistor R3 is 159.2kΩ, and the value of capacitor C3 is 0.02uF; resistor R4 is a potentiometer, used for Adjust the quality of the industrial frequency band rejection filter; the operational amplifier OP1 and operational amplifier OP2 are operational amplifiers, generally select the OP77 type operational amplifier with high gain and low offset; the sampling module adopts the high-precision 16-bit AD7606 type digital-to-analog conversion chip.

Referring to Figure 5, it is a voltage-controlled current source module, which converts the 0-2.5V voltage sent by the single-chip microcomputer of the CPU control module into a current output of 0-10A, and the voltage-controlled current source module adopts an operational amplifier OP3 as a pre-operational amplifier , a field effect transistor IRF530 is connected in series after the operational amplifier OP3; the non-inverting input terminal of the operational amplifier OP3 is connected in series with the resistor R5 and the capacitor C5 in sequence and then grounded; the drain (D pole) of the field effect transistor IRF530 is grounded through the resistor R6, so The resistor R6 is a sampling resistor; the source (S pole) end of the FET IRF530 is connected in series with a capacitor C4 and a resistor R7; the operational amplifier OP3 adopts the OP77 model of low-load regulation, high-gain, and low-bias operational amplifiers, using sampling resistors R6 converts the voltage analog signal sent by the CPU control module into a current signal, and uses the field effect transistor IRF530 as a current expansion loop to increase the current output power and output it to the outside world. Among them, resistor R5 selects 470Ω ordinary metal film resistor; resistor R6 selects four 12Ω precision metal film resistors with an accuracy of 0.1% and a temperature drift coefficient of 25ppm in parallel to form a sampling resistor with a resistance value of 3Ω. The chip is used as a current spreading element, the resistor R7 is a metal film resistor with a resistance value of 3Ω and a power of 2W, and the capacitor C5 is a 0.1uF capacitor.

Referring to Figure 6, the current signal detection and conditioning module adopts a current detection chip, the VCC end of the current detection chip is grounded through a capacitor C6, and an operational amplifier OP4 is connected in series with the OUT end of the current detection chip; The detection terminal A and detection terminal B are connected to the two ends of the sampling resistor R9 in the middle; the current signal detection and conditioning module detects the excitation current by measuring the voltage signal generated at both ends of the sampling resistor R9 when the excitation current flows through the sampling resistor R9 in Figure 2. Purpose. The sampling resistor R9 in Fig. 2 adopts the low temperature coefficient manganin sampling resistor with a typical value of 10mΩ. The voltage signal at both ends of the manganin sampling resistor has the characteristics of potential suspension and small potential difference. The current signal detection and conditioning module selects the special current detection chip MAX4173T/F/H type chip, and cooperates with the follower circuit composed of the operational amplifier OP4 to convert and condition the floating excitation current signal into a measurable voltage signal and send it to the digital-to-analog conversion sampling. The chip is then converted into a digital current signal that can be processed by the CPU control module.

Referring to Figure 7, the CD AC path module is composed of capacitors, Zener diodes, and common diodes. Zener diode DW1 is connected in parallel with polar capacitor C7, and then connected in series with common diode D1 to form a positive-phase branch. Zener diode DW2 and polarity The capacitor C8 is connected in parallel with the ordinary diode D2 to form an anti-phase branch, and the positive-phase branch and the anti-phase branch are connected in parallel to form an all-phase conduction CD AC path module. Has isolation. The typical value of C7 and C8 is 1F, and the typical value of D1 and D2 is 10A. D1 and D2 are arranged in the reverse direction. When the power frequency current in the tested loop is forward half-wave, C7 and D1 are conducting, and the reverse half-wave When C8 and D2 are turned on, DW1 and DW2 are zener diodes that limit the voltage when the voltage rises due to excessive charge accumulation in C7 and C8 to protect the capacitor from breakdown. Finally, the AC path and DC isolation are realized.

Referring to Figure 8, the loop protection module is composed of a transistor Q1, a relay and a TVS. The input end of the transistor Q1 is connected to the control signal of the CPU control module, the emitter of the transistor Q1 is connected to the resistor R8 and the relay coil, and the relay contact is connected in parallel with the TVS. In order to prevent overvoltage in the test circuit, the circuit protection module connects TVS in parallel at both ends of the current output terminal; the normally closed relay is driven by a triode, and is usually in a closed state. When the device of the present invention is connected to the circuit under test, the current is guaranteed. The transformer is in the closed state. During the test phase, the high-level output of the transistor is driven by the CPU control module to drive the relay to open. At this time, the CD AC path module in Figure 7 can still provide an AC channel for the external current transformer to avoid the open-circuit state of the current transformer. , After the test, the CPU control module outputs a low level and the relay is closed to ensure that the external current transformer under test is in a short-circuit state.

Referring to accompanying drawing 9, the CPU control module as the control core outputs a controllable DC excitation current to the circuit under test by controlling the voltage-controlled current source module, and the current signal conditioning detection module synchronously detects the excitation current size through the sampling resistor, and feeds back to the CPU control module. , Voltage signal conditioning detection module, detects the response voltage of the excitation current in the circuit under test through the detection circuit, the CPU control module can calculate the DC resistance value of the circuit under test through the response voltage and excitation current and draw the circuit excitation response curve. The CPU control module controls the relay action of the protection module by outputting control signals to the protection module, thereby strengthening the protection control. The CPU control module realizes the switching of the positive and negative directions of the excitation current of the loop under test by outputting control signals to the direction switching module 1 and the direction switching module 2.

The CPU control module adopts ARM chip model STM32F407, with low power consumption, high computing performance CPU chip, with GPIO interface, can drive the relay of the protection module to open and close, drive the direction switching module relay to open and close, and can read the voltage signal conditioning module and The current signal adjusts the voltage signal and current signal transmitted from the detection module, and calculates the DC resistance of the circuit under test. The CPU control module has an analog-to-digital conversion interface, which can output a DC control voltage signal to the voltage-controlled current source module, and then output a controllable current to the circuit under test. The typical value and sequence are set as: +5A, -4A, +3A, -2A, +1A, -0.5A, +0.2A, 0A, in order to verify the difference of DC resistance under different currents and realize demagnetization.

Referring to Figure 10, the direction switching module includes two double throw relays, a transistor Q2 and a resistor R18, the relay coil is connected to the emitter of the transistor Q2, the relay JDQ1 terminal J11 is connected to the relay JDQ2 terminal J23, and the relay JDQ1 terminal J13 is connected to the relay JDQ2 terminal J21. The direction switching module uses a triode to drive the double-throw relay to conduct and close, switch the contact position, and then follow the wiring method shown in Figure 10 to realize the forward current when the low-level signal sent by the CPU control module Stimulus test mode. When the CPU control module sends a high level signal, it is the reverse current excitation test mode.

Referring to Figure 11, the power supply module includes a battery, a DC/DC±12V DC power supply module, a DC/DC5V DC power supply module, a voltage regulator (AMS1117 chip) and a transistor Q13, and the 24V input of the power adapter passes through the diode D11 and the transistor Q13. The battery is connected, the battery is connected to DC/DC±12V and DC/DC5V through the power switch, and the DC/DC5V is converted into 3.3V voltage through the AMS1117 chip to supply power to the CPU control module, and the power switch is arranged on the casing. The power supply module can automatically select the commercial power or the storage battery as the power supply of the device of the present invention, and the output to each module is stable at +24V, ±12V, +5V, +3.3V. The power adapter selects a commercially available AC220 to DC24V power adapter, and uses a transistor Q13 and a diode D11 to form a power supply selection circuit. When the mains has electricity, Q13 is turned on, and the battery is charged at this time, and the device is powered. When the mains has no electricity , Q13 is closed, the battery supplies power to the device, and the power supply module adopts commercially available DC/DC±12V, DC/DC5V and chip AMS1117 chip to convert the power supply voltage of each module and supply power.

Referring to Figure 12, the timing diagram of the excitation current test, the CPU control module uses the voltage-controlled current source module to output an excitation current of 0 to 10A by outputting a voltage analog signal of 0 to 2.5V, and the direction switching module to achieve -10A to +10A current Excitation, specifically using the excitation current sequence test shown in Figure 12, which is characterized by a gradual decrease in positive and negative staggered to achieve the demagnetization effect of the current transformer (CT) while testing, to avoid the remanence of the CT core caused by unidirectional current excitation, and the transformation ratio inaccurate question.

The specific testing method of the device of the present invention comprises the following steps:

(1) Test wiring;

Connect one end of the test cable L1 to the voltage detection terminal of the device, the S1 contact of the other end of the test cable L1 to the terminal A of the incoming line of the junction box of the electric energy meter (empty terminal on the CT side), and the S2 contact of the test cable L1 to the connection of the electric energy meter The position of the terminal B of the box outgoing line (vacant terminal on the meter side); connect one end of the test cable L2 to the current output terminal of the device, and the S3 contact of the other end of the test cable L2 to the position of the terminal A of the incoming line of the power meter junction box (vacant terminal on the CT side) , the S4 contact at the other end of the test cable L2 is connected to the terminal b of the junction box of the electric energy meter (the vacant terminal on the electric meter side);

(2) Turn on the power switch to make the device start to work. The CPU control module controls the protection module relay to close by default, and turns the paddle of the tested junction box to the open connection position, that is, it is not short-circuited. At this time, the current mutual inductance is realized by closing the relay. The device is still in a short-circuit state;

(3) The relay of the CPU control module controls the protection module to be disconnected. At this time, the CD AC path module is in a resonant state. For the power frequency, the tested current transformer is still in a short-circuit state, and for DC, it is in an open-circuit state.

(4) The CPU control module controls the voltage-controlled current to output an excitation current of 5A for 2 seconds, the current signal detection and conditioning module tests the output current 5A to be consistent with the set value, and the voltage signal detection and conditioning module tests to obtain the circuit under test under the excitation current of +5A. Responding to the voltage signal and sending it to the CPU control module for calculation, the CPU control module obtains the DC resistance of +5A excitation through calculation;

(5) The CPU control module controls the output 4A excitation current, controls the direction switching loop, and realizes the DC resistance test and recording of the -4A excitation current;

(6) Sequentially adjust the size of the excitation current controlled by the CPU control module and adjust the direction switching circuit, and test the corresponding excitation currents of +5A, -4A, +3A, -2A, +1A, -0.5A, +0.2A, and 0A at this time. DC resistance; excitation current +5A, -4A, +3A, -2A, +1A, -0.5A, +0.2A, and 0A, the corresponding sequences are 0~2s, 2~4s, 4~6s, 6~8s , 8～10s, 10～12s, 12～14s, 14～16s;

(7) The CPU control module controls the relay of the protection circuit to close, and displays the DC resistance of the circuit under test, the measurement sequence and the size curve of the excitation current, and then judges the state of the circuit under test.

(8) After turning off the power switch, restore the junction box pick and remove the test wiring to complete the test.

The invention is composed of two sets of test lines, using the junction box to connect to minimize the changes to the circuit under test. loop effect. The power module can automatically determine whether to use commercial power or battery to supply power to the present invention, provide power supply for the device when connected to commercial power and charge the battery at the same time, and use the battery to power the device of the present invention when there is no commercial power. The voltage signal conditioning and detection module uses a differential operational amplifier to avoid common-mode interference, uses a double-T power frequency band rejection filter circuit to filter out power frequency interference, and converts it into a digital signal that can be processed by the CPU through a high-precision digital-to-analog converter. The typical value and sequence of excitation mode are set as: +5A, -4A, +3A, -2A, +1A, -0.5A, +0.2A, 0A, so as to verify the difference of DC resistance under different currents and realize demagnetization. The voltage-controlled current source module is characterized by using a voltage-controlled current composed of a high-precision operational amplifier and a moss tube, which can convert the voltage signal output by the CPU into a current to excite the circuit under test. The current signal detection module uses a dedicated current detection chip and a sampling resistor to form a current detection loop that can measure the current with the characteristics of potential suspension. The CPU control module controls the voltage-controlled current source to output different torrent currents, collects the response voltage and real output current value of the tested loop, and uses Ohm's law to calculate different excitation currents (typical values +5A, -4A, +3A, -2A , +1A, -0.5A, +0.2A, ) to measure the DC resistance of the circuit under test to judge the contact status of the secondary circuit of the current transformer. By comparing the test values of different phases, it can be determined whether the three-phase current imbalance is caused by DC resistance or normal phase-biased load. The CD AC path module uses capacitors to isolate the unidirectional conductivity of DC and diodes, and forms an AC path loop with capacitors and diodes to provide a power frequency circuit for the circuit under test to ensure that the current transformer under test is in a non-open circuit and low resistance state. The circuit protection module is characterized by using TVS to protect the wiring terminals from overvoltage to prevent the overvoltage in the circuit from damaging the components of the present invention, and at the same time using the CPU to control the on-off of the relay, providing a short-circuit path for the current transformer of the loop under test, reducing the risk of open circuit . At the same time, after the test is completed, the resonant circuit is provided with a channel for discharging energy by turning on the relay.

The test device of the present invention is found through practical use that the wiring is simple and the test is accurate, because the secondary circuit of the current transformer can be detected without the need for a power outage by the power user, so it is convenient to use and can be generally applied to power production in various environments, especially for power supply. Reliable and demanding metering equipment testing.

Claims (10)

1. a current transformer secondary circuit DC resistance live detection device, is characterized in that: be made up of shell and electric part, electric part is arranged in shell, and described electric part comprises detection wiring module, power module, voltage-controlled current Source module, current signal detection and conditioning module, voltage signal detection and conditioning module, CD AC path module, loop protection module, CPU control module, display/operation module and 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 module is respectively connected with the voltage-controlled current source module, the current signal detection module The conditioning module, the voltage signal detection conditioning module and the CPU control module are connected, and provide working power for these connected modules; the voltage-controlled current source module is connected with the CD AC channel module through the direction switching module, and the CD AC channel module is connected in parallel with the loop protection module. ;The detection wiring module is connected with the loop protection module, the voltage signal detection and conditioning module and the circuit of the junction box under test; The voltage-controlled current source module is used to convert the analog voltage signal sent by the CPU control module into a current signal, and use the voltage-controlled current source module current expansion circuit to expand the current, thereby realizing the external output excitation current; A protection fuse, a sampling resistor and a diode are connected in series between the voltage-controlled current source module and the CD AC path module. The current signal detection and conditioning module uses the sampling resistor to convert the excitation current output by the voltage-controlled current source module into a voltage signal, and passes the current The current detection chip inside the signal detection and conditioning module performs conditioning, and then converts it into a digital signal that can be recognized by the single-chip microcomputer of the CPU control module through the analog-to-digital conversion chip; The voltage signal detection module converts the voltage signal formed by the excitation current in the secondary circuit of the current transformer through operational amplifier conditioning and power frequency filtering, and then uses the analog-to-digital conversion chip to convert it into a digital signal that can be identified by the single-chip microcomputer of the CPU control module. ; The CD AC path module uses capacitors and diodes to form an AC path and a DC blocking circuit. The capacitor C has the characteristics of blocking DC. The capacitor and the diode connected in series provide a power frequency bypass for the secondary circuit of the current transformer under test, so that the secondary circuit AC current No open circuit to ensure safety; DC excitation can only flow from the tested secondary circuit without being bypassed by the CD AC path module, forming an accurate test DC current excitation response; The circuit protection module is composed of a normally closed relay with a current capacity greater than 10A and a transient diode in parallel, providing an auxiliary bypass path for the secondary circuit with a current transformer, and providing energy leakage for the capacitive element of the CD AC path module. Channel energy leakage channel; the transient suppression diode is used to prevent damage to the measuring device due to overvoltage in the loop. 2. The current transformer secondary circuit DC resistance live detection device according to claim 1, is characterized in that: the detection wiring module is made up of a current output line and a voltage signal line, and the current output line is composed of two cross-sectional areas greater than ^2mm . It is composed of soft copper wires, the voltage signal wire is composed of shielded twisted pair wires, the current output wire is drawn from the loop protection module, and the voltage signal wire is drawn from the voltage signal detection and conditioning module through the direction switching module. 3. The current transformer secondary circuit DC resistance live detection device according to claim 1, wherein the CPU control module adopts an ARM single-chip microcomputer as a core, and outputs 0 to 2.5 to the output of the voltage-controlled current source module. V analog voltage signal, the corresponding voltage-controlled current source outputs 0~10A current. During the measurement process and sequence, the output of the voltage-controlled current source is set as: +5A, -4A, +3A, -2A, +1A, -0.5A, +0.2A, 0A, the measurement time of each value is 2S, in order to verify the difference of DC resistance under different currents and realize the demagnetization effect; collect the digital signals sent by the current signal detection and conditioning module and the voltage signal detection and conditioning module, and Calculate the resistance of the secondary circuit of the current transformer, and then judge the state of the circuit. 4. The current transformer secondary circuit DC resistance live detection device according to claim 1, characterized in that: the power supply module is connected with a battery connected with the charging module, in order to provide this power supply when there is no external power supply. The working power of the invention device. 5. The current transformer secondary circuit DC resistance live detection device according to claim 1, wherein the power module converts the DC power supplied by the external power adapter or the 24V voltage delivered by the internal storage battery into a 24V voltage. The regulated DC﹢24V,±12V,﹢5V﹢3.3V power supply voltage is supplied to other modules connected to it. The power supply module can automatically select the circuit to use the internal battery as the power supply when there is no external adapter power supply. When the power adapter is connected Automatically switch the external power supply and charge the battery. 6. The current transformer secondary circuit DC resistance live detection device according to claim 1, characterized in that: a power switch is provided on the casing, and the power switch is connected with the power module, and is used for the operation of the control device and the stop. 7. The current transformer secondary circuit DC resistance live detection device according to claim 1, characterized in that: the display operation module is composed of a liquid crystal screen and an operation button; the liquid crystal screen is installed on the casing and is used for Display the control output, current detection signal, voltage detection signal, relay action status, and current transformer secondary circuit status of the device of the present invention; the operation button provides the user with the operation interaction of the device of the present invention; the operation button passes the wire It is connected with the CPU control module; the operation buttons include a confirmation key, a return key, an up key, a down key, a left key and a right key. 8. The current transformer secondary circuit DC resistance live detection device according to claim 1, wherein: the direction switching module is realized by the double-throw relay through wiring, and is positive when the CPU controls the low-level signal In the current test mode, when the CPU controls a high level, it is a reverse excitation current test mode, and then realizes the positive and negative alternating test of the circuit under test. 9. A test method of the secondary circuit DC resistance live detection device of a current transformer as claimed in claim 1, characterized in that, comprising the steps: (1) Test wiring; Connect one end of the test cable L1 to the voltage detection terminal of the device, the S1 contact of the other end of the test cable L1 to the vacant terminal on the CT side of the incoming line of the electric energy meter junction box, and the S2 contact of the test cable L1 to the outgoing terminal of the electric energy meter junction box. Terminal; connect one end of the test cable L2 to the current output terminal of the device, the S3 contact of the other end of the test cable L2 to the vacant terminal on the CT side of the incoming line of the electric energy meter junction box, and the S4 contact of the other end of the test cable L2 to the electric energy meter junction box Empty terminals on the outgoing meter side; (2) Turn on the power switch to make the device start to work. The CPU control module controls the protection module relay to close by default, and turns the paddle of the tested junction box to the open connection position, that is, it is not short-circuited. At this time, the current mutual inductance is realized by closing the relay. The device is still in a short-circuit state; (3) The relay of the CPU control module controls the protection module to be disconnected. At this time, the CD AC path module is in a resonant state. For the power frequency, the tested current transformer is still in a short-circuit state, and for DC, it is in an open-circuit state; (4) The CPU control module controls the voltage-controlled current to output an excitation current of 5A for 2 seconds, the current signal detection and conditioning module tests the output current 5A to be consistent with the set value, and the voltage signal detection and conditioning module tests to obtain the circuit under test under the excitation current of +5A. Responding to the voltage signal and sending it to the CPU control module for calculation, the CPU control module obtains the DC resistance of +5A excitation through calculation; (5) The CPU control module controls the output 4A excitation current, controls the direction switching loop, and realizes the DC resistance test and recording of the -4A excitation current; (6) Sequentially adjust the size of the excitation current controlled by the CPU control module and adjust the direction switching circuit, and test the corresponding excitation currents of +5A, -4A, +3A, -2A, +1A, -0.5A, +0.2A, and 0A at this time. DC Resistance; (7) The CPU control module controls the relay of the protection circuit to close, and displays the DC resistance of the circuit under test, the measurement sequence and the size curve of the excitation current, and then judges the state of the circuit under test; (8) After turning off the power switch, restore the junction box pick and remove the test wiring to complete the test. 10. The test method of the current transformer secondary circuit DC resistance live detection device according to claim 9, wherein: the excitation current +5A, -4A, +3A, -2A, +1A, -0.5A The corresponding timings of , +0.2A, and 0A are 0～2s, 2～4s, 4～6s, 6～8s, 8～10s, 10～12s, 12～14s, 14～16s respectively.

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