CN201335870Y - DC circuit fault detection system - Google Patents

Abstract

The utility model discloses a system for detecting DC circuit faults, which comprises a voltage detection unit, a current detection unit, a resistance calculation unit, a discharge unit and a fault analysis unit, wherein the discharge unit inverts a large-capacity storage battery into a high-frequency AC current, and rectify the high-frequency AC current to obtain a discharge DC current, and load the discharge DC current for the measured DC circuit; the resistance calculation unit, for the discharge control unit loaded by the discharge The measured circuit of the direct current uses the voltage determined by the voltage detection unit and the current determined by the current detection unit to calculate the resistance value of the tested circuit; The resistance value of the tested loop calculated by the resistance calculation unit is used to determine whether the tested loop is faulty. The utility model can test the circuit to be tested, and can improve the testing precision.

Description

System for detecting direct current loop fault

Technical Field

The utility model relates to a test measurement technical field especially relates to a detect system of direct current loop fault.

Background

Direct current electric energy has the characteristic of being capable of being stored, so that in a power plant and a transformer substation, an independent direct current power supply system is arranged for providing working power supply for circuits such as a control circuit, a signal circuit, relay protection and an automatic device. The importance of the direct current power supply system is related to the safe and stable operation of the whole power grid and equipment. A dc loop is a conductive circuit used to transmit dc power.

In practical applications, the direct current circuit has a hidden danger of increased resistance of the direct current circuit due to poor contact or burning of contacts of an air switch or a fuse part during operation, which may cause heating and blowing of the poor contact part in the direct current circuit, and in addition, due to abnormal increase of the resistance of the direct current circuit, the voltage drop of the circuit is increased, the voltage drop of a tripping/closing coil of the circuit breaker is reduced, and the circuit breaker is likely to fail. Therefore, detecting the loop resistance becomes the main means for detecting the integrity of the dc loop.

At present, for the resistance abnormity of a direct current loop of an electric power system, only a multimeter test method is easily conceived, however, the test method is basically infeasible through analysis, because firstly, the current applied when the multimeter measures the resistance is very small, generally only in milliampere level, hidden faults cannot be found, and in addition, even if the resistance can be measured, the available measurement result is difficult to obtain due to the fact that the measurement precision of the multimeter is not high. Therefore, most blind fault multimeters with poor contact are untestable.

SUMMERY OF THE UTILITY MODEL

In view of this, the utility model provides a detect system of direct current loop fault to solve the problem that adopts the unable too big direct current loop fault of test resistance of universal meter.

Therefore, the utility model adopts the following technical scheme:

a system for detecting faults of a direct current loop comprises a voltage detection unit, a current detection unit, a resistance calculation unit, a discharge unit and a fault analysis unit, wherein the discharge unit inverts a large-capacity storage battery into high-frequency alternating current through an IGBT (insulated gate bipolar transistor), rectifies the high-frequency alternating current to obtain discharge direct current, and loads the discharge direct current for a detected direct current loop; the resistance calculation unit calculates a resistance value of the measured loop for the measured loop loaded with the discharging direct current by the discharging control unit by using the voltage determined by the voltage detection unit and the current determined by the current detection unit; and the fault analysis unit analyzes the resistance value of the tested loop calculated by the resistance calculation unit according to a preset loop abnormity judgment standard, and determines whether the tested loop is in fault.

The discharging unit changes the value of the discharging direct current through the conduction angle of the IGBT.

The system further comprises: and the constant current control unit is used for controlling the discharge unit to load constant direct current for the tested loop according to a set value, wherein the set value of the direct current refers to the short-time tolerance current of the tested loop and/or the maximum load current setting of the tested loop.

The system further comprises: the retest indicating unit is used for indicating that retest is carried out by adopting larger direct current again when the tested loop is determined to be normal; when the retest indicating unit sends an indication, the constant current control unit controls the discharging unit to increase discharging direct current for the tested loop; and the voltage detection unit, the current detection unit, the resistance calculation unit and the fault analysis unit are restarted to retest whether the tested loop has faults or not.

The voltage detection unit and the current detection unit respectively determine the current voltage and current of the tested loop based on a four-wire system measurement scheme of current inversion.

And the fault analysis unit analyzes the resistance value of the tested loop through a history comparison standard, a similar branch comparison standard or/and a same-cable double-line comparison standard to determine whether the tested loop is in fault.

It is thus clear that the utility model discloses in owing to adopt external battery's heavy current excitation to be surveyed the return circuit, consequently can make to be surveyed the concealed fault point of return circuit and expose, can test to being surveyed the return circuit then. Furthermore, the test precision can be improved by the four-wire system measurement technology and the current inversion technology. In addition, the situation of the tested loop can be determined more accurately by repeatedly testing the tested loop for a plurality of times through various loop abnormity judgment standards.

Drawings

FIG. 1 is a flow chart of a method for detecting a fault in a DC circuit according to the present invention;

fig. 2 is a schematic diagram of the system structure for detecting dc loop fault according to the present invention;

FIG. 3 is a schematic diagram of a four wire system measured resistance;

FIG. 4 is a schematic diagram of a current reversal measurement resistor;

fig. 5 is a circuit diagram of an embodiment of a system for detecting dc loop faults according to the present invention;

fig. 6 is a flowchart of a specific example of the method for detecting dc loop fault implemented with respect to fig. 5.

Detailed Description

The field person can understand, the integrity that detects direct current loop is exactly whether detect direct current loop resistance and exceed standard, consequently the utility model discloses start from loop resistance, strive for accurately to gather on-the-spot loop resistance value. Because the increase of the loop resistance is an internal cause, and the flowing of a large current through the loop is an external cause causing a fault, the external cause action needs to be amplified by impacting the direct current loop to be detected with a large current so as to promote the exposure of potential defects and obtain a detection result.

Referring to fig. 1, it is the present invention provides a method for detecting dc loop fault, including:

s101: inverting a large-capacity storage battery into high-frequency alternating current through an Insulated Gate Bipolar (IGBT) power tube, and rectifying the high-frequency alternating current to obtain discharging direct current;

s102: loading the discharging direct current for a direct current loop to be tested;

s103: determining the current loop current and the current loop voltage, and calculating the resistance value of the direct current loop to be measured according to the current loop current and the current loop voltage;

s104: and analyzing the resistance value of the direct current loop to be tested according to a preset loop abnormity judgment standard to determine whether the direct current loop is in fault.

It is visible, the utility model discloses an external large capacity battery can provide for direct current loop and apply enough big direct current as the power to guarantee can carry out accurate test to the very strong return circuit trouble of disguise. In addition, for making the test result more accurate, the utility model discloses the preferred four-wire system measuring method that adopts based on the electric current is to obtain accurate resistance value, improve measurement accuracy.

In order to fully understand the present invention, the embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

Referring to fig. 2, for the system schematic diagram of the present invention for detecting dc loop fault, the system includes the detected loop

The circuit 201, the discharge unit 202, the voltage detection unit 203, the current detection unit 204, the resistance calculation unit 204, and the fault analysis unit 206.

The functions of the respective sections will be summarized and specifically described below.

The discharging unit 202 inverts a large-capacity storage battery into high-frequency alternating current through an IGBT (insulated gate bipolar transistor), rectifies the high-frequency alternating current to obtain discharging direct current, and loads the discharging direct current for the tested loop 201;

the voltage detection unit 203 is used for detecting the voltage of the tested loop 201 loaded with the discharging direct current generated by the discharging unit 202 and determining the current voltage of the tested loop;

the current detection unit 204 is used for performing current detection on the detected loop 201 loaded with the discharging direct current generated by the discharging unit 202 and determining the current of the detected loop;

a resistance calculation unit 205 for calculating a resistance value of the circuit to be measured by using the voltage determined by the voltage detection unit 203 and the current determined by the circuit current detection unit 204;

the fault analysis unit 206 determines whether the tested loop 201 is faulty or not by analyzing the resistance value of the tested loop calculated by the resistance calculation unit 205 according to a preset loop anomaly judgment criterion.

Preferably, the discharging unit 202 changes the value of the discharging direct current by the conduction angle of the IGBT.

Preferably, the fault analysis unit 206 analyzes the resistance value of the tested loop according to the history comparison judgment standard, the similar branch comparison standard, or/and the same-cable double-line comparison standard, and determines whether the tested loop 201 is faulty.

Preferably, the system further comprises a constant current control unit 207 for controlling the discharging unit 202 to load a constant direct current to the tested loop 201 according to a set value, wherein the set value of the direct current refers to the short-time withstand current of the tested loop and/or the maximum load current setting of the tested loop.

Preferably, the system may further include a retest indication unit 208, configured to indicate that, when it is determined that the tested loop is normal, the retest is performed again by using a larger direct current; when the retest instruction unit sends an instruction, the constant current control unit 207 controls the discharge unit 202 to increase the discharge direct current for the tested loop 201; at this time, the voltage detection unit 203, the current detection unit 204, the resistance calculation unit 204, and the failure analysis unit 206 are all restarted to retest whether the circuit 201 under test has failed. For example, the discharge current is increased by 50% and the test is continued. It should be noted that different loop anomaly determination criteria are adopted, and the obtained test results may be inconsistent, so that different anomaly determination criteria can be selected during repeated tests to obtain a more comprehensive test conclusion.

Preferably, the voltage detection unit 203 and the current detection unit 204 obtain the current voltage and current of the tested loop 201 based on a current-oriented four-wire measurement scheme.

The important parts are analyzed and explained in detail below.

The discharge unit 202 mainly functions to provide a discharge current, and in particular, an external large-capacity storage battery can be used to provide a direct current, and the storage battery can be 12 v and 100AH in capacity. The direct current is inverted into high-frequency alternating current through an IGBT high-power electronic device and a PWM (Pulse Width Modulation) control technology, the high-frequency alternating current is rectified to obtain direct current, and the direct current is used for discharging a load resistor of a tested loop. In addition, the current is changed by controlling the conduction angle of the IGBT, so that the discharging direct current can be adjusted in a large range, and the constant current precision is higher. The control mode can provide large discharge current, can accurately control the magnitude of the discharge current by setting the conduction angle through a program, and can safely turn off the large discharge current.

The constant current control unit 207 is mainly used for controlling the discharge unit 202 to load a constant direct current to the tested loop 201 according to a set value. When the loop is normal, the magnitude of the discharge current has little influence on the measured resistance, but when a fault point with poor contact exists in the loop, the measured resistance is not obviously abnormal when the discharge current is small, and the measured value of the loop resistance also shows an increasing trend along with the increase of the discharge current. In general, the discharge current Ig is chosen not to exceed the short-time withstand current Ipem of the circuit under test, taking into account the maximum load current Imax of the circuit possible in normal and accident conditions. Factors influencing the magnitude of Imax include extreme conditions such as bus differential protection action, three-phase tripping and closing action, full-power operation of a transceiver, full-lighting of a signal indicator lamp and the like. Therefore, the discharge current Ig is selected according to: ig is less than or equal to Imem, and Ig is less than or equal to KxImax, wherein Ig is discharge current, Imem is a loop allowing short-time discharge current, and is related to the material and the sectional area of the wire, the direct current loop generally adopts a copper wire, and the safe current-carrying capacity of the copper wire is 5-8A/mm²And the utility model discloses an experimental preferred Ipiem adopts 10 ~ 15A/mm²(ii) a And Imax is an estimated value of the maximum load current of the loop, wherein K is a natural number, and preferably, K is 8-15.

For the fault analysis unit 206, the resistance value of the tested loop may be analyzed according to a history comparison judgment standard, a similar branch comparison standard, or/and a same-cable double-line comparison standard, so as to determine whether the tested loop 201 is faulty.

(1) Historical alignment criteria: the process of determining whether the dc loop is faulty through the history comparison determination criteria can be described as follows: storing historical normal resistance values and standard exceeding amplitudes; and comparing the resistance value of the tested direct current loop with the historical normal resistance value, judging whether the difference value of the resistance value of the tested direct current loop and the historical normal resistance value is larger than the standard exceeding amplitude, if so, determining that the tested direct current loop has a fault, otherwise, determining that the tested direct current loop is normal. For example, if the circuit resistance is greater than the normal value (past history value) by 4 milliohms or more, it is indicated that the circuit is abnormal, and if the circuit resistance is greater than the normal value by 10 milliohms or more, it is determined that the circuit has a defective point of contact failure.

(2) Comparison standard of similar branches: the determination of whether the dc loop is faulty or not by the comparison criteria of the adjacent branches can be described as follows: storing reference resistance values of adjacent branches; and comparing the resistance value of the direct current loop to be tested with the reference resistance value of the adjacent branch, if the difference amplitude exceeds a threshold value, determining that the direct current loop to be tested is in fault, and otherwise, determining that the direct current loop to be tested is normal. For example, a 1 meter long 2.5mm2 copper wire has a resistance of 7 milliohms and a 1 meter long 4mm2 copper wire has a resistance of 4.4 milliohms. According to the data, when the line length difference between the adjacent screen cabinet and the direct current feeder screen is about 1 meter, the line length difference can be reflected by the tester, if the measured value difference is too large or the situation that the loop resistance with a short distance is larger on the contrary occurs, the reason is to find out whether the distance is increased or the phenomenon of poor contact exists due to too much cable coiling.

(3) The same-cable double-line comparison standard is alternatively called as a positive-negative branch comparison standard: the determination of whether the dc loop is faulty or not by the on-cable and two-wire comparison standard can be described as follows: for the circuits with the same cable and the positive and negative power supplies supplying power in pairs, when the difference of the resistance values of the two tested circuits is greater than a threshold value, the fault of the tested direct current circuit is determined, otherwise, the normal of the tested direct current circuit is determined. For example, for a circuit powered by a pair of co-cable positive and negative power sources, when the resistance value deviation of the two circuits is measured to be more than 3 milliohms, the fault point of poor contact of the circuits can be determined.

As described above, the resistance of the circuit under test 201 is calculated from the voltage determined by the voltage detection unit 203 and the current determined by the current detection unit 204, and therefore, how to improve the accuracy of the voltage detection unit 203 and the current detection unit 204 plays a more critical role in the overall test result. Therefore, the utility model discloses a four-wire system test method based on the electric current is to improving the measuring accuracy. The four wire test principle and method, and the current reversal test principle and method will be described first.

Referring to fig. 3, a schematic diagram of a four-wire system measuring resistor is shown, in which 2 wires are connected to two ends of a measured resistor respectively for a current wire and a voltage wire, Rx is the measured resistor, R1, R2, R3 and R4 are total resistors on the wires respectively,

it is shown that the voltage meter is,

an ammeter is shown. When the input resistance of the voltmeter is large enough, the voltage drop across R3 and R4 is zero, and the reading U of the voltmeter is the voltage drop across the resistor Rx. Rx, R1 and R2 are connected in series with an ammeter which reads the current I flowing through Rx. The resistance value calculated by ohm's law is the resistance value of the resistor Rx, thus eliminating the systematic error in the circuit caused by the lead wire resistance and the contact resistance. I.e., Rx ═ U/I.

Referring to fig. 4, a schematic diagram of the current inversion measurement resistor is shown. The most fundamental principle for measuring resistance is based on ohm's law, the method of measuring voltage with current.

Because the resistance value of the resistor to be tested is very weak, the voltage generated by the test current passing through the resistor is also very weak inevitably, and therefore the influence of the direct current error source cannot be ignored. The DC error source mainly comprises: thermoelectric potential, electrochemical potential, detuning and temperature drift of the amplification circuit itself, etc. Experiments show that an error source in weak resistance measurement does not change along with the magnitude and direction of the test current basically, so that the direction of the test current flowing through the test resistor is changed (current inversion technology), two times of voltage measurement are carried out, and finally, the two times of measurement results are subtracted to eliminate errors.

Let the combination of the thermoelectric potential from the outside of the measuring circuit and the thermoelectric potential from the measuring circuit itself be Eemf, the electrochemical potential from the outside of the measuring circuit and the electrochemical potential from the inside be Ec, and the offset voltage of the amplifying circuit itself converted to the input of the amplifying circuit is Uoffset.

And setting the direct current error signal converted to the input end of the amplifying circuit as delta U:

ΔU＝Eemf+Ec+Uoffset

although the dc error signal is also amplified by the amplifying circuit, when the direction of the test current changes (reverses), the magnitude and polarity of the amplified dc error signal do not change, so that the amplified dc error signal can be distinguished from the signal to be measured by only performing two measurements and subtracting the results.

The following is a detailed description: when the test current Is + Is, the current flows through the resistor Rx to be tested from top to bottom, and at the moment: uo1 ═ AIsRx + a Δ U, where a is the operational amplifier amplification. When the testing current Is inverted to-Is, the current flows through the resistor Rx to be tested from bottom to top, and at the moment: uo2 ═ AIsRx + a Δ U, and the two measurements were subtracted to give: so that the effect of the dc error source is eliminated, Uo1-Uo 2-2 AIsRx.

It is thus clear that four-wire system measurement technique and current fall to the technique and all can effectively improve measurement accuracy, consequently, the utility model discloses an use these two kinds of techniques in the test system to improve the degree of accuracy of test by the loop resistance.

Referring to fig. 5, a circuit diagram of an embodiment of the system for detecting a dc loop fault according to the present invention is shown, in which a four-wire system measurement technique and a current inversion technique are applied. Rx is a tested direct current loop resistor, R1, R2, R3 and R4 represent four conducting wires measured in a four-wire system, E is discharging direct current provided by a discharging circuit, a constant current control circuit is responsible for controlling the discharging circuit to discharge constant current according to a set value, and a current reversing circuit controls the battery to perform polarity reversal after each discharging, so that the reverse discharging is prepared for the next time. The current detection circuit and the A/D conversion measure the magnitude of the discharge current, the operational amplifier and the A/D conversion measure the magnitude of the voltage at two ends of Rx, and the loop resistance value is obtained through the operation of a Digital Signal Processor (DSP). The DSP is connected with peripheral equipment, and provides test results for testers, and the peripheral equipment comprises a communication circuit, a display, a FLASH (FLASH memory) and an SRAM (Static RAM, Static memory) memory and the like.

Referring to fig. 6, a flowchart of a specific example of the method for detecting a dc loop fault implemented in relation to fig. 5 includes:

s601: the method includes initializing a system, specifically including configuration, pin configuration, variable setting and the like of each unit of the system, for example, setting a value of a discharging direct current loaded to a tested loop by a discharging unit through a constant current control circuit;

s602: function selection, for example, selecting a value of a discharge current;

s603: outputting a discharging direct current through a discharging unit;

s604: is it judged whether the discharging dc current exceeds the system range? If yes, returning to execute S602, and reselecting a new discharging direct current, otherwise, executing S604;

s605: selecting a proper amplification factor to amplify the discharging direct current;

s606: starting a sample/hold function;

s607: is the forward and reverse discharge completed? If so, executing S607, otherwise, reversing the current, and then returning to execute S603;

s608: starting an A/D conversion function;

s609: calculating the resistance value of the tested loop;

s610: and analyzing whether the tested loop is in fault or not according to the preselected loop abnormity judgment standard, and displaying the test result to a tester.

It is thus clear that the utility model discloses in owing to adopt external battery's heavy current excitation to be surveyed the return circuit, consequently can make to be surveyed the concealed fault point of return circuit and expose, can test to being surveyed the return circuit then. Furthermore, the test precision can be improved by the four-wire system measurement technology and the current inversion technology. In addition, the situation of the tested loop can be determined more accurately by repeatedly testing the tested loop for a plurality of times through various loop abnormity judgment standards.

The foregoing is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, a plurality of modifications and decorations can be made without departing from the principle of the present invention, and these modifications and decorations should also be regarded as the protection scope of the present invention.

Claims (6)

1. A system for detecting the fault of a direct current loop comprises a voltage detection unit, a current detection unit and a resistance calculation unit, and is characterized by also comprising a discharge unit and a fault analysis unit,

wherein,

the discharging unit inverts a large-capacity storage battery into high-frequency alternating current through an insulated bipolar power tube IGBT, rectifies the high-frequency alternating current to obtain discharging direct current, and loads the discharging direct current for a detected direct current loop;

the resistance calculation unit calculates a resistance value of the measured loop for the measured loop loaded with the discharging direct current by the discharging control unit by using the voltage determined by the voltage detection unit and the current determined by the current detection unit;

and the fault analysis unit analyzes the resistance value of the tested loop calculated by the resistance calculation unit according to a preset loop abnormity judgment standard, and determines whether the tested loop is in fault.

2. The system of claim 1, wherein the discharging unit changes the value of the discharging direct current through a conduction angle of an IGBT.

3. The system of claim 2, further comprising:

and the constant current control unit is used for controlling the discharge unit to load constant direct current for the tested loop according to a set value, wherein the set value of the direct current refers to the short-time tolerance current of the tested loop and/or the maximum load current setting of the tested loop.

4. The system of claim 3, further comprising:

the retest indicating unit is used for indicating that retest is carried out by adopting larger direct current again when the tested loop is determined to be normal;

when the retest indicating unit sends an indication, the constant current control unit controls the discharging unit to increase discharging direct current for the tested loop;

and the voltage detection unit, the current detection unit, the resistance calculation unit and the fault analysis unit are restarted to retest whether the tested loop has faults or not.

5. The system of claim 1,

the voltage detection unit and the current detection unit respectively determine the current voltage and current of the tested loop based on a four-wire system measurement scheme of current inversion.

6. The system according to any one of claims 1 to 5,

and the fault analysis unit analyzes the resistance value of the tested loop through a history comparison standard, a similar branch comparison standard or/and a same-cable double-line comparison standard to determine whether the tested loop is in fault.

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