RU2230332C2 - Apparatus measuring electric resistance of insulation - Google Patents

Abstract

FIELD: electrical engineering. SUBSTANCE: apparatus is designed to measure electric resistance of insulation of energized bunched conductors and cables. Invention refers to electric measurement technology, specifically, to automated testing systems. It is utilized to test resistance of insulation in networks of electrical and radio engineering articles. In compliance with invention capacitor of known rating is connected in parallel with measured circuit, time constant of transient process is measured and parameters of insulation of circuit are determined with due account of measured initial and final values of voltage. EFFECT: provision for galvanic isolation of measured and measurement circuits which is achieved thanks to usage of capacitor of known capacitance as shunting element, simplified method to compute parameters of measured circuit. 5 dwg

Description

A device for measuring the electrical insulation resistance of two-wire networks that are under DC voltage relates to electrical engineering, in particular to automated control systems, and is used to control the insulation resistance of electrical circuits of electrical and radio products.

Known devices for monitoring and measuring the insulation resistance of electric lines of direct current, in particular, signaling lowering insulation according to A.S. USSR No. 378776, 1972. The signaling device kit consists of a potentiometer, which composes a DC bridge with insulation resistance of each line of the monitored network, and a servo system including amplifiers, an executive motor, and program relay blocks. These devices do not measure the absolute values of insulation resistance, have a long measurement time and are complex in design.

A device for monitoring insulation and protecting two-pass DC networks according to A.S. USSR No. 353214, 1971, containing a bridge formed by two shoulders of a potentiometer and insulation resistance of the busbars of the line, a comparison circuit included in the diagonal of the bridge, and a sensitive element in the form of a blocking generator.

This device has a large inertia, low sensitivity and does not allow to measure the current value of the insulation resistance of each bus line in the presence of large leakage capacitances between the tire and the housing.

A device for measuring the insulation resistance of a two-wire DC line according to A.S. USSR No. 744339, BI 24, 1980. The device for measuring insulation resistance contains a measuring bridge, which includes the insulation resistance of the monitored buses, a digital-controlled resistor, a line power supply, a compensation voltage source, as well as a comparison circuit, a control unit, a switch, and a digital indicator , a digital-controlled resistor with one pin is connected through a normally open contact of the first group and a normally closed contact of the second group of the switch, respectively, with the plus and minus of the compensation source voltage, another output - with the input of the comparison circuit and ground, and a control terminal - through the control unit with the output of the comparison circuit, the second input of which is connected through a normally closed contact of the third group of the switch with a normally closed contact of the first and minus of the line power source, plus which is connected with normally open contacts of the second and third groups of the switch.

The disadvantage of this device is the large measurement cycle and the presence of influence on the measured circuit by connecting measuring resistors.

The closest in technical essence to the claimed object is a device according to the application No. 5005490, from 1991.07.16, publ. 1995.01.09, authors Banshchikova Yu.A. and Naumina V.A. The essence of the operation of the device is that it is carried out at detectable moments in time that the equivalent insulation resistance of the poles of the controlled network is measured in relation to the housing, before each of which the measuring bridge is balanced, the two shoulders of which represent the insulation resistance components, and the other two are the shoulders of the controlled resistive voltage divider and, for each measurement, a constant voltage source is connected to the diagonal of the bridge with a signal resistor using a switching element th power.

The disadvantage of this device is its low speed, which does not allow its effective use in networks with large capacities with a case, as well as the lack of the ability to provide galvanic isolation of the controlled circuits during the measurement process.

The objective of the invention is the creation of a high-speed device for measuring the insulation of electrical networks (including the housing), which are energized, have large leakage capacities and provide galvanic isolation of the controlled circuits during the measurement process. This is achieved by reconfiguring the measured circuit using an additional capacitor and evaluating the type of transient of the measured parameters.

The essence of the invention lies in the fact that a capacitor of known nominal is connected in parallel to the measured circuit, the time constant of the transient process is measured, and taking into account the measured initial and final voltage values at the controlled points, the insulation parameters of the circuit are determined. That is, to measure the leakage resistance between one of the wires and the casing, a measuring capacitor of known capacitance is connected (hereinafter, all considerations are given for the case of measurement with respect to the casing), as a result of which the charge is redistributed between the leakage capacitances and the measuring capacitance. The transient parameters calculate the values of the leakage resistance and leakage capacitance. This ensures galvanic isolation of the measured and measuring circuits. If it is necessary to clarify the results with relatively small values of leakage capacities, determined as described above, the method of alternately connecting the measuring resistors to the positive and negative circuits of the bus is used and the adjusted leakage resistances are calculated by the deviation of the housing potential.

The technical result is achieved through the use of a set of capacitors switched with a demultiplexer in the device and accurate measurement of the transient parameters with the help of a differential amplifier and an analog storage device with the subsequent calculation of the result.

The possibility of carrying out the invention is confirmed by the fact that the authors conducted a simulation of the measurement processes and have already developed and tested the device layout.

Figure 1 shows the equivalent measurement circuit; figure 2 - transients resulting from the switching of measuring capacitors.

In the diagram (figure 1) the following notation:

E - voltage source in a controlled circuit,

R ₁ , R ₂ - insulation resistance of the first and second sections of the circuit with respect to the housing,

C ₁ , C ₂ - leakage capacitance of the first and second bus wires in relation to the housing,

C ₀ - measuring capacitor of known capacity,

S ₁ , S ₂ - keys for the corresponding switching With ₀ ,

R _p - discharge resistor

U _UPR1 , U _UPR2 - key management signals S ₁ and S _2, respectively,

R _d1 , R _d2 - the resistance of the divider, providing the potential for comparison,

U _k is the potential difference between the comparison point and the chassis bus.

In figure 2, the following notation:

U _k1 (t) = F (R ₁ , R ₂ , C ₁ , C ₂ and C ₀₁ ) and U _k2 (t) = F (R ₁ , R ₂ , C ₁ , C ₂ and C ₀₂ ) are transition functions processes at point K, characterized by the capacitance of the measuring capacitors C ₀₁ and C ₀₂ ,

U ₁₁ , U ₁₂ and U ₂₁ , U ₂₂ are the potential values U _{k0 of the} point K with respect to point A, taken at the corresponding time instants t ₁₁ , t ₁₂ , and t ₂₁ , t ₂₂ for C ₀₁ and C _02, respectively.

In the initial state, the capacitor C _{0 is} discharged to zero volts, for example, by closing the contact S ₂ . Measure the potential of point A with respect to point K (housing). After that, a capacitor C _{0 is} connected to one of the wires (depending on what sign of the potential of point A is) through contact S ₁ , after opening contact S ₂ , and the parameters of the transition process are measured. This ensures the absence of DC coupling of the controlled circuit with the housing.

The transition process (figure 2) is described by the expression:

Two pairs of measurements U ₁₁ (t ₁₁ ), U ₁₂ (t ₁₂ ) and U ₂₁ (t ₂₁ ), U ₂₂ (t ₂₂ ) for C ₀₁ and C ₀₂ , respectively, and the voltage before switching U _k0 can be determined:

Transient time constants for C ₀₁ and C ₀₂ :

Then the expressions for R ₁ , R ₂ and C ₁ + C ₂ take the form:

Initial Leap:

Figure 3 shows the equivalent circuit for measuring leakage resistances using a measuring resistor R ₀ . The leakage resistances R ₁ and R ₂ are measured using two measurements U _K. In the case when the resistor R _{0 is} connected by the key S ₂ to the positive bus wire, the steady-state value U _{K1 is} measured, and when the resistor R _{0 is} connected by the key S ₁ to the negative bus wire, U _{K2 is} measured. The difference value is calculated

Δ = U _K1 -U _K2

and according to known U _K and E, R ₁ and R ₂ are calculated by the formulas that are obtained from the following expressions.

The potential U _K without connecting R ₀ is

the potential difference with different connections R ₀ will be:

after transformations

then

a

or

- нормированное значение перепада разности потенциалов,Where

- the normalized value of the difference in potential difference,

- нормированное значение потенциала корпуса до коммутации R₀.

- the normalized value of the potential of the housing before switching R ₀ .

Figure 4 presents the structural diagram of the device, which includes:

1 - node dividers UD, providing the formation of the potential for comparison of each of the N tires, containing N pairs of resistors,

2 - the first bus multiplexer MS1,

3 - the second multiplexer of the potential comparison bus MS2,

4 - polarity switch MS3 (third multiplexer),

5 - switch measuring input MS4 (fourth multiplexer) of the differential amplifier, providing a circuit for measuring either the voltage between the positive and negative wire n of the _i-th bus, or between the housing and the bus of the middle potential,

6 - differential amplifier remote control,

7 - the first demultiplexer DMS 1 for connecting one of the L resistors (forms a digital-controlled resistor),

8 - analog storage device AZU,

9 - analog-to-digital Converter ADC,

10 - block calculation results BVR measurement

11 - the second demultiplexer DMS2 for connecting one of the M capacitors (forms a digital-controlled capacitor),

12 - node indicating the results of UIR measurement,

13 ₁ -13 _L - measuring resistors R ₁ -R _L ,

14 ₁ -14 _M - keys K ₁ -K _M ,

15 ₁ -15 _M - discharge resistors R _p1 -R _RM ,

16 ₁ -16 _M - measuring capacitors C ₁ -C _M ,

17 - control unit BU

18 ₁₁ and 18 ₁₂ -18 _N1 and 18 _N2 - pairs of resistors of the node dividers R ₁₁ and R ₁₂ -R _N1 and R _N2 ,

19 ₁₁ and 19 ₁₂ -19 _N1 and 19 _N2 - pairs of wires for tires F ₁₁ and F ₁₂ -F _N1 and F _N2 ,

20 - bus "Start",

21 - tire housing object.

The outputs of node 1 of the dividers are connected respectively to the inputs of the first bus multiplexer MS ₁ 2 and to the inputs of the second multiplexer of comparison potentials MS ₂ 3. The pair of outputs of multiplexer 2 is connected to the inputs of the polarity switch MS ₃ 4 and the pair of inputs of the switch for measuring inputs MS ₄ 5 of the differential amplifier DY 6 The output of the MS ₂ 3 multiplexer and the object housing bus 21 are connected to the second pair of inputs of the MS ₄ 5 multiplexer. The MS ₃ 4 output is connected to the inputs of the DMS ₁ 7 and DMS ₂ 11 demultiplexers, and the pair of MS4 5 outputs through DY 6 to the input of the RAM 8. The output of the RAM 8 ADC 9 is connected to the calculator BSB 10, whose output is connected to the ODS 12. Outputs DMS _{July 1} are connected to respective inputs of the measuring resistors, whose outputs are connected to the bus body object 21. Outputs ₂ DMS 11 are connected to the inputs of respective measuring condenser 16 ₁ ... 16 _M and through the keys 14 ₁ ... 14 _M to the inputs of the discharge resistors 15 ₁ ... 15 _M. The outputs of the resistors 15 ₁ ... 15 _M and the capacitors 16 ₁ ... 16 _{M are} connected to the bus of the housing 21. In the division node 1 to the input buses 19 ₁ and 19 ₁₂ ... 19 _N1 and 19 _N2 respectively connected in series resistors 18 ₁ and 18 ₁₂ ... 18 _N1 and 18 _N2 . The outputs of the control unit BU 17 are connected to the corresponding control inputs of the following nodes: MS ₁ 2, MS ₂ 3, MS ₃ 4, MS ₄ 5, DMS ₁ 7, DMS ₂ 11, AZU8, ADC 9 and BVR 10, a bus is connected to the input of BU17 "START" 20.

The device operates according to an algorithm determined by BU17. An enlarged block diagram of the algorithm is shown in figure 5, where the following notation:

1 - "Getting Started"

2 - n = 0, m = 0, 1 = 0 (bringing the counter of bus numbers n, numbers of measuring capacitors m and numbers of measuring resistors 1 to zero),

3 - n _{i + 1} : = n _i +1 (increase the number of the measured tire by one),

4 - n _i > N, where N is the number of tires,

5 - to measure the value of the potential of the housing in relation to the potential comparison bus U _k ,

6 - Uk <Ukdop., Where Ukdop. - minimum jump Uk sufficient to provide the required measurement sensitivity,

7 - m _{i + 1} : = m _i +1,

8 - to measure the maximum deviation U _{n the} potential of the body after mutation With _{o oi} ,

9 - Un <Umax, where Umax is the max. a value sufficient to measure the resistance and leakage capacitance,

10 - measurements and calculations of R _1,2 and C _1,2 using switchable capacitors,

11 - m _i > M, where M is the number of measuring capacitors,

12 - σ _ci <σ _{with add} , where σ _ci and σ _{with add} - current and permissible measurement errors,

13 - l _{i + 1} : = l _i +1,

14 - measurement of R using switchable resistors,

15 - σ _Ri <σ _{R add} , where σ _Ri and σ _{R add} - current and permissible measurement errors,

16 - l _i > L, where L is the number of measuring resistors,

17 - indication of the results,

18 - check for the presence of the command "STOP",

19 - the end.

In the initial state, N buses of the two-wire network are connected to the input of the device, and all multiplexers and demultiplexers are in the zero state, i.e. all switched circuits are broken. By the “Start” command, the BU17 connects through the MS ₁ 2 a pair of wires of the first bus to the inputs of MS ₃ 4 and MS ₄ 5. At the same time, the MS potential of the divider 18 ₁₁ and 18 _{12 is} connected to the third input of MS ₄ 5 through MS ₂ 3. At the command BU17, MS ₄ 5 connects to the measuring inputs of DN6 a pair of wires of the measured bus. ADC9 measures the potential difference between the wires of the bus E ₁ and enters the result of the conversion in BVR10. Each measurement is carried out in the following sequence. The measured signal through the differential amplifier ДУ6, which suppresses the common-mode component of the noise, is fed to the input of the AZU8, which fixes the input signal for the duration of the measurement. After that, the ADC9 takes a measurement. The result obtained with a delay at the output of the ADC9 exactly corresponds to the input signal at the moment the AZU8 transitions from the tracking state to the storage mode, which eliminates the dynamic component of the measurement error.

After measuring the voltage between the wires of the pair of the first bus, MS ₄ 5 switches the measuring inputs of ДУ6 to the output MS2 (where the comparison potential of the first bus is connected) and the housing bus, and the ADC measures the potential difference U ₀ between them. In BVR10, an assessment of the level of U _{01 is} carried out and, if it is within the permissible U _{0 add} (this is determined by the ratio of R ₁ , R ₂ and R _{1,2 add} ), then by the appropriate command BU17 MS ₁ 2 will provide connection to the measurement of the pair of wires of the second bus network.

Measurements of E ₂ and U ₀₂ as well as E _i and U _{0i of the} remaining N-1 tires are made in the same sequence.

If during the measurement of the parameters of the i-th bus the condition U _K0i <U _{Kdop is} not fulfilled, then БУ17 puts the device into the measurement mode R _1,2i using measuring capacitors. To do this, the measuring capacitors are connected alternately with DMS2, for example, in ascending order of nominal value. In this case, before connecting the next capacitor 16, the key 14 _i disconnects the discharge resistor R _Pi . According to the above-described algorithm, transient measurements of the case potential with respect to the comparison potential of the i-th bus are taken. In BVR10, a comparison is made of the initial jump in the potential U _n associated with the charge redistribution between C _1i , C _2i and C ₀ . If it exceeds U _max , this means that connecting the next measuring capacitor of a higher nominal value provides a transient, the measurement of which is in accordance with the schedule in figure 2, and the calculation of R _1i and R _2i according to formulas (1), (2) and (3) provide the required accuracy of the result. If the leakage capacitance of the bus is so large that the capacitance of the maximum measuring capacitor is not enough to provide a jump of the corresponding magnitude, then the calculation of R _i and C _i is carried out according to the actual transient. The results of calculating the leakage parameters R _1i , R _2i, and C _i both in the first case (when connecting the measuring C _i provides the required accuracy) and in the second are output to the result indication unit.

If the leakage capacitance of the wires is small and the leakage resistance is also small and therefore the transient process from connecting the measuring capacitance is short, then the measurement is carried out by connecting the measuring resistor 13 ₁ ... 13 _L. BU17 through DMS1 connects the first measuring resistor 13 _{1 of} maximum nominal value first to the positive wire through MS ₃ 4, and then to the negative one. BVR10 evaluates the sufficiency of Δ to ensure the required accuracy of calculation (condition 15 of Fig. 5), and if it is not satisfied, then BU17 continues to connect the next lower value resistor, which also checks condition 15. If the condition is satisfied, then R ₁ and R ₂ are calculated by formulas 4 and 5. The results are displayed on UIR12.

After that, if the "STOP" command has not been received, the bus monitoring process starts again.

Thus, the proposed device allows you to measure the leakage parameters of controlled two-wire networks in the presence of large leakage capacitance for a significantly shorter time. For example, in order to wait for a measurement result of the order of 1%, using a bridge circuit, it will take 2-3τ, and in our case, 0.1-0.2τ. It should be borne in mind that τ = R ₁ · C ₁ can be: at R ₁ = 10 ⁴ -10 ⁵ Ohms and C ₀ = 10 ^-3 -10 ^-2 Ф approximately - 10-10 ² seconds.

Claims (1)

A device for measuring the electrical insulation resistance of two-wire DC networks under voltage, comprising a first multiplexer, N pairs of inputs of which are connected to the corresponding pairs of network wires, and whose outputs are connected through the third multiplexer and the first demultiplexer to the first inputs of L measuring resistors, the outputs of which are connected with a housing, an analog-to-digital converter, a display of results, a Start bus, a second multiplexer, the inputs of which are connected to integrated inputs odes of the corresponding pairs of resistors of dividers, the outputs of which are connected to the corresponding pairs of wires of the network, characterized in that a control unit, a fourth multiplexer, a differential amplifier, M measuring capacitors with keys and discharge resistors, an analog storage device, a result calculation unit and a second demultiplexer are inserted into it the input of which is connected to the output of the third multiplexer, and the outputs to the inputs of the measuring capacitors and through the corresponding keys to the inputs of the discharge resis tori, the outputs of which, as well as the outputs of the measuring capacitors, are connected to the housing, the first pair of inputs of the fourth multiplexer connected to the first output of the first multiplexer and the output of the second multiplexer, respectively, and the second pair of inputs connected to the second output of the first multiplexer and the housing, respectively, and the outputs of the fourth the multiplexer through a differential amplifier and analog storage device to the input of the analog-to-digital converter, the output of which is connected to the input of the computing unit I am the result, the first output of which is connected to the node indicating the results, and the second - to the first input of the control unit, to the second input of which the Start bus is connected, and the outputs of the control unit are connected to the corresponding control inputs of four multiplexers, two demultiplexers, an analog storage device, analog-to-digital converter and results calculation unit.

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