SU1325377A1 - Device for selective measurement of electric network insulation resistance - Google Patents

Abstract

The invention allows to improve the noise immunity of the measurement process. The device contains a source of constant voltage I, switch 2, filter 3, adder 5, memory blocks 7 and 8, subtraction block 9, display block 10, synchronizer 11 and semiconductor converter 12. Introduction of integrator 6 allows by integrating leakage current reduce the effect of the variable component on the output voltage of the leakage current converter, which uses a phase current adder. 1 il. (L P + :: - cL || C | cl Ikiisil t SO you ate oo She L

Description

113253772

The invention relates to the field of earth and impulse electrical measurements, namely to a new voltage U. The leakage current iy (t) is applied.

caused by voltage 1 and voltage Ujj, Uf, caused by the asymmetry of the insulation resistances 13 and 14, respectively, on the AC and DC side of the controlled connection 17, is fed to the input of the adder 5 of the phase currents.

measurements of insulation resistance, and can be used for selective control of insulation resistance of galvanically connected DC and AC electrical networks, insulated from the ground, both de-energized and operating in operating modes.

The purpose of the invention is to increase noise immunity by reducing the effect on the measurement result of an AC disturbance.

The drawing shows a functional diagram of a device for selectively measuring the insulation resistance of electrical networks.

The device contains a voltage source 1, the outputs of which are connected to the first and second inputs of the switch 2, the first output of which through the filter 3 is connected to the phases of the controlled network 4p, the second output of the switch 3 is grounded, the adder 5 of the phase currents whose input is inductively coupled with phases of the monitored network section, the output of the adder is 5 currents; the phases are connected to the first integrator input 6. The output of the first memory block 7 is connected to the first input of the second memory block 8. The input of the subtraction unit 9 is connected to the input of the display unit 10. The first output of synchronizer 1 is connected to the control input of the switch, the second output of synchronizer 11 is connected to the first inputs of the first memory block 7 and the subtraction block 9, the second input of which is connected to the output of the first memory block 7. The output of the second memory block 8 is connected to the third input of the subtraction unit 9 and the second input of the second memory block 8 is connected to the third output of the synchronizer 11, the fourth output of which is connected to the second input of the integrator 6.

In addition, the figure shows the semiconductor converter 12 and the insulation resistances 13 and 14 and capacitance 15 and 16, respectively.

AC and DC side of the controlled connection 17,

The device works as follows.

From source 1 through the switch 2, controlled by the synchronizer 11j and the filter 3 to the controlled network 4 relative to the earth, a pulse voltage U is applied. The leakage current iy (t).

caused by voltage 1 and voltage Ujj, Uf, caused by the asymmetry of the insulation resistances 13 and 14, respectively, on the AC and DC side of the controlled connection 17, is fed to the input of the adder 5 of the phase currents.

iv (t)

and. Up

+ io (t) 5

five

0

0

five

  t К, 1 „+ Igcosujjt, (1)

where ly is the constant leakage current component ivjCt), due to the voltage and the source;

tl is the constant component of the leakage current i (t) due to the constant component of the potential t fn of the network with respect to the earth, the magnitude and sign of which is determined by the ratio of the resistances 14 of the pole insulation behind the semiconductor converter 1 2; ie (t) 1pCOb is the variable component of the leakage current iy {t) (zero sequence current), due to the asymmetry of the insulation resistances 13 on the AC side of the controlled connection I7; w, j: 27rf, is the circular frequency of the variable component i, (t) of the leakage current;

r, is the equivalent insulation resistance of the controlled attachment 17; K ,, Kj are the proportionality coefficients between the currents I Ij, and the voltages U, Up, respectively. The signal iv (t) from the output of the adder 5

50 phase currents are fed to the input of the integrator 6. The voltage Ujy (t) at the output of the integrator 6 is proportional to the integ-. brine from total leakage current iy (t) at its input during T:

BMX (t) - i6K (t) Jt - (K, I «+

oo

+ Kjln + loC08Wet) dt - (KJ.-t-) 1 +

1 IpCosaj, tdt,

(2)

where T is the integration time.

Since the variable component ip (t) of the leakage current is a periodic function, it follows from expression (2) that, compared with the constant component (K, 1 + Kjl), it causes no signal accumulation over time at the output of integrator 6, and only its oscillations. In addition, the signal-to-noise ratio at the output of the integrator 6

0 (KilH + Cr1p) T; t

Ij cosdj tdt

 (K, It + KjInKoi

loSiniu T

-foT

, de p p1 .r. K.I.n. 0 loSinwJ

signal-to-noise ratio at the input of the integrator 6,

shows that the suppression efficiency of the variable component of the leakage current IQ (t) and the output of the integrator 6 depends on the integration time and the frequency u) p of the variable component

The leakage current, the larger they are, the more efficiently.

Taking into account that the frequency Lp of the variable component of the leakage current (interference) in the monitored network is always known, depending on the desired signal-to-interference ratio f at the output of the integrator 6, you can always select the required integration time T and, therefore, reduce the variable component ig (t) of the leakage current at the output of integrator 6 to such a degree that expression (2) takes the form

and

6HX

(t) (K, I, KjIn) T -b

T

+ i (t) dt X (K, 1, + Kjl)., (4)

B

At the end of the time t T, passed from the beginning of the integration and necessary to suppress the variable component IQ (t) of the leakage current, the signal from the fourth output of the synchronizer 11 is fed to the second input of the integrator 6 and transfers it from the Integration mode to the Storage mode. After that, on a signal si-.

G325377

5), About

20

25

Oq

35 45

40

chronizer 11, coming from its second output to the first input of the first memory block 7, voltage U. ti:

U; UBM. (T) (K, 1 and K.IJT.

After the time required to write the voltage to the first memory block 7, from the first output of the synchronizer 11, a signal is sent to the control input of the switch 2, which changes the polarity of the voltage Uj of source 1 to the opposite polarity in the previous i-th half-cycle, and the next (1-st) 1-th voltage period U, and a new leakage current measurement cycle iy (t) begins.

After the time elapsed after the start of the (i + l) -ro half-period and necessary for recharging the capacities 15 and 16 of the monitored network D, the signal from the fourth output of the synchronizer 11 goes to the second input of the integrator 6 and puts it into the integration mode, having previously set it in the initial state. After a time t T elapsed from the beginning of the integration and necessary to suppress the variable component of the leakage current, the signal from the fourth output of the synchronizer I1 transfers the integrator 6 from the Integration mode to the Storage mode. According to the synchronizer signals from the third output to the second input of the second memory block 8 and from the second output to the first input of the first memory block 7, the voltage and. from the first memory block 7 is rewritten to the second memory block 8, after which the voltage Uj, proportional to the average leakage current t ,, (t) for the current (1 + 1) th half period, is written from the output of the integrator 6 to the first block 7 memories:

and

MIC 1 + 1

(t) - (K, 1, -t-) T ..

Upon completion of the writing of the voltage Ui to the first memory block 7 in the subtraction block 9, an algebraic operation is performed by the command of the synchronizer 11;

whether - and ,, -and, "(to ,, + to, 1") - (-K, 1 "Kjln) lT - K1", (5)

where K is the proportionality coefficient between the leakage current component 1 and the voltage 11 (, at the output of the subtraction unit 9. The result of the subtraction is fed to the input of the display unit 10 and, as can be seen from (5), is proportional to the leakage current component 1 the voltage U of the source and, consequently, the resistance r of the insulation of the controlled network.

After the time elapses, dp writes voltage U, and U. respectively to the second and first memory blocks and the block 9 subtracts the algebraic subtraction operation, the first output of syncro 11 receives a signal to the control input of switch 2, which changes The polarity of the source I voltage is opposite to its polarity in the previous (i + l) -M half period and the next () and half voltage period U and the new leakage current measurement cycle begin.

Thus, the introduction of an integrator's insulation resistance into the selective measurement device allows, by integrating the leakage current, to reduce the influence of the variable component on the output voltage of the leakage current measuring transducer.

as which is used sum- 35 is connected to the second input of the first

the current phase maker, and, as a result.

Editor E, Papp

Compiled by B. Togunov Tehred V. Kadar Corrector, E, Roshko

Order 3102/39 Circulation 730 Subscription

VNIIPI USSR State Committee for Inventions and Discoveries 113035, Moscow, Zh-35, Raushsk nab. e.A / 5

Production and printing company, Uzhgorod, st. Project, 4

improve the noise immunity of the device.

Claims (1)

Invention Formula A device for selectively measuring the insulation resistance of electrical networks, containing a constant voltage source, the outputs of which are connected to the first and second inputs of the switch, the first output of which through the filter is connected to the phases of the controlled network, the second switch output is grounded, and the control input of the switch is connected to 5 with the first output of the synchronizer, the second output of which is connected to the first inputs of the first memory block and the subtractor, the second input of which is connected to the output of the first memory block and the first input of the second memory block, the second input of which is connected to the third output of the synchronizer, and the output of the second the memory unit - with the third input of the subtraction unit, the output of which is connected to the input of the display unit, the phase current adder, the input of which is inductively connected to the phases of the monitored network, characterized in that, in order to increase noise immunity, the integrator is entered into it, the first input of which is connected to the output of the phase current adder, the second input is connected to the fourth output of the synchronizer, and the integrator output 0 five memory block.