RU2384855C1 - Measuring method of insulation resistance in direct current circuits - Google Patents

Abstract

FIELD: measurement equipment.

SUBSTANCE: invention refers to electrical measurement equipment. Namely to measurement of DC circuits insulation. Two resistors are connected to poles of DC circuit. Two other resistors are connected parallel to the load. To connection point of resistors between each other there connected is measurement circuit consisting of in-series connected sources of measurement voltage and current metre. Voltage source is connected in alternatively varying pole polarity. Equivalent measurement current is determined as half the sum of two absolute current values measured successively in time at different polarity of voltage source. Insulation resistance is determined as per the following formula R=E/I_equiv - 0.5 r, where E - source voltage, I_equiv - equivalent current, r - resistance of resistors.

EFFECT: excluding measurement error from unbalance current in circuit of resistors.

3 dwg, 6 cl

Description

Usage: to measure the insulation resistance in DC circuits, in the load elements of DC circuits, in dual-current networks, to determine the place of insulation wear, to improve the control and measuring and protective functions of the automation system.

The inventive method for measuring insulation resistance in DC circuits is based on: connecting to the poles of the DC circuit of a resistor circuit consisting of two series-connected resistors having the same resistance value, including at the junction of the resistors between themselves the first end of the measuring circuit, consisting of in series the connected source of the measuring voltage and current meter, connecting the second end of the measuring circuit to the ground element, determining of the current in the measuring circuit, turning on the source of the measuring voltage either in the same polarity of the poles, then in the opposite polarity of the poles, determining the equivalent measuring current as half the sum of two absolute values of the measuring current, measured sequentially in time, determining the equivalent circuit resistance of two resistors, dividing the voltage of the measuring source by the value of the equivalent measuring current and subtracting from the value obtained as a result of this values, the value of the equivalent resistance of the resistor circuit.

Description of the invention

The invention relates to electrical engineering and can be used in DC networks having elements requiring insulation control and earth fault protection, for example, in excitation systems of electrical machines. At the same time, the following problems were solved: accuracy of measurements, speed, simplicity of the algorithm and ease of use. When implementing the method, the following tasks were additionally solved: determining the location of insulation damage, monitoring the contact joints of the measurement system and improving the reliability of contact joints.

A known method of three samples of a voltmeter [1] for measuring insulation resistance in DC voltage circuits, including measuring between the poles of an electric circuit, alternately shunting the poles of the circuit to ground with the resistor, measuring the steady-state voltage values on the shunt resistor, calculating the equivalent insulation resistance as a product of the value of the shunting resistor on the ratio of the voltage of the measured circuit to the sum of the steady-state voltages on the shunt resistor, reduced by one.

The disadvantages of this method are: the need for voltage between the poles of the electric circuit and the long procedure of three consecutive measurements. Therefore, this method: is deprived of the ability to measure insulation resistance in the absence of voltage between the poles, does not provide measurement accuracy in dynamic modes, requires inertial measuring instruments damping voltage fluctuations in non-stationary modes, does not provide the necessary speed for tripping of protection against earth faults.

The closest in technical essence to the proposed method is a method of measuring insulation resistance according to the "balanced bridge method" [2], which includes connecting two resistors connected in series to the poles of the circuit, determining the absence of unbalance current in the circuit of two series-connected resistors, including two resistors between each other of the measuring voltage source and current meter, connected in series and connected on the other side of this circuit to the ground element, measure the current in the circuit of the measuring voltage source in the absence of an unbalance current in the circuit of series-connected resistors, the determination of the equivalent insulation resistance by the following formula:

R = (E / Iism) -Rd-r1r2 / (r1 + r2),

where R is the equivalent insulation resistance of the network;

E is the voltage of the measuring source;

Iism - current in the circuit of the measuring voltage source;

Rd - limiting resistance;

r1, r2 - two resistors connected to the poles of the circuit.

In the known method [2], selected for the prototype, it is possible to measure the insulation resistance in the absence of voltage between the poles by connecting two resistors 7 and 8 to the poles and turning on the switch 6, the measuring voltage source 5 and the current meter 3 ( see Figure 1).

The disadvantage of the prototype method is that for accurate measurement of insulation, the absence of unbalance current in the circuit of series-connected resistors is necessary. An unbalance current occurs when an asymmetric violation of insulation occurs inside any element of the DC circuit relative to the poles.

So, with an asymmetric violation of insulation inside an element of the DC circuit 9 having a resistance Rн (see Figure 1) and connected between the poles, an unbalance current appears in the chain of series-connected resistors 7 and 8, which distorts the value of the measured insulation resistance. In this case, the formula for measuring the current in the circuit of the measuring voltage source 5 will have the following form:

Iism = {E + Unb} / {R + Rd + r1r2 / (r1 + r2)},

where U is the voltage between the poles of the DC circuit;

Unb = U (R1r2-R2r1) / [(r1 + r2) (R1 + R2)] is the unbalance voltage in the chain of series-connected resistors 7 and 8;

R1, R2 - insulation resistance 1 and 2 between the poles and ground.

The essence of the invention lies in the fact that, as in the prototype method, a method for measuring insulation resistance, comprising connecting two resistors 7 and 8 connected in series to the circuit poles, including a measuring voltage source 5 and a current meter 3 at the junction of the two resistors, connected in series and connected on the other side of this circuit to the grounding element 10, current measurement in the circuit of the measuring voltage source 5, but unlike the prototype, two identical wires are connected to the poles of the circuit Stores 7 and 8, include a source of measuring voltage 5, then in the same polarity of the poles, then in the opposite polarity of the poles (see Figure 2), two current values I1 and I2 are measured according to these positions of the source and the insulation resistance is determined by the following formula:

R = (E / Ieq) -Req,

where Ieq = {| I1 | + | I2 |} / 2 = {| (E + Unb) / (R + Req) | + | (-E + Unb) / (R + Req) |} / 2 = E / (R + Req) - equivalent measuring current;

Req = r1r2 / (r1 + r2) = r / 2 is the equivalent resistance of the circuit of resistors 7 and 8, r = r1 = r2.

The proposed method allows to exclude the account of the unbalance current in the circuit of resistors connected in series between the poles and this ensures:

- automation of insulation measurement by excluding the procedure for pre-setting the unbalance current to zero;

- improving the accuracy of measurements of insulation resistance in all emergency situations;

- acceleration of the process of measuring insulation;

- expanding the functionality of the implementation of this method.

In the study of patent and other scientific and technical information, the applicant did not find sources that would provide information on technical solutions containing the totality of the distinguishing features of the proposed method, although technical solutions are known that contain individual features of the claimed object, however, the properties and effect that these signs inform these objects other than in the proposed solution, therefore, these differences are significant.

A method of measuring insulation in DC circuits is implemented in a device (see Figure 2), containing: 1 - insulation resistance between + pole and earth, 2 - insulation resistance between-pole and earth, 3 - current sensor in the measuring circuit I1, I2 5 - measuring voltage source, 7, 8 - series-connected resistors, 11 - fuse, 12 ... 15 - optocouplers for switching the polarity of the measuring voltage source, 16 - zener diodes, 17 - load resistor (with resistance r3), 18 - controller (for calculation of insulation resistance and control Lenia switching the measuring voltage source poles) with the analog input module, 19 - reset button 20 - power supply, 21 - signal relays 22 - isolating terminals 23 - automatic switch.

In order to compensate for the internal resistance of the measuring circuit and to improve the accuracy of measurement at low measuring currents, a load resistor 17 is additionally connected to the junction of the two resistors (see Figure 2). The current of the load resistor I3 will not affect the determination of the equivalent measuring current, so it can be ignored:

Ieq = {| I1-I3 | + | I2-I3 |} / 2 = {| (E + Unb) / (R + Req) -I3 | + | (-E + Unb) / (R + Req) -I3 |} / [2 = E / (R + Req),

where I3 is the current of the load resistor 17.

In order to determine the direction of the displacement of the asymmetric violation of the load insulation relative to the position of the middle of the load resistance, it is established that the voltage in the DC circuit is not equal to zero. The unbalance current is determined as the difference between two absolute values of the measuring current, measured sequentially in time:

Inb = | I1 | - | I2 | = | (E + Unb) / (R + Req) | - | (-E + Unb) / (R + Req) | = 2Ub / (R + Req) = {U ( R1-R2) / (R1 + R2)} / (R + Req) - unbalance current;

R1 is the value of the insulation resistance between the + pole and the ground;

R2 is the value of the insulation resistance between the-pole and the ground.

It is determined that the displacement of the asymmetric violation of the load insulation relative to the position of the middle of the load resistance occurred towards the positive pole if the unbalance current is negative. It is determined that the displacement of the asymmetric violation of the load insulation relative to the position of the middle of the load resistance occurred towards the negative pole if the unbalance current is positive.

If the condition Inb <0 (or Inb <- Iust, where Ist is the specified minimum current value Inb) is satisfied, i.e. R1 <R2, then there is a signal "Closing the positive pole". If the condition Inb> 0 (or Inb> Iust) is satisfied, i.e. R1> R2, then there is a signal "Short circuit of the negative pole." If U = 0, then Inb = 0 and there will be no signal.

In order to determine the ratio of the magnitude of the displacement of the place of asymmetric violation of the load insulation relative to the position of the middle of the load resistance, it is established that the voltage in the DC circuit and the equivalent measuring current are not equal to zero, divide the unbalance current by the value of the equivalent measuring current and the voltage in the constant current, multiplied by the magnitude of the voltage of the measuring source:

(R1-R2) / (R1 + R2) = (Inb / Ieq) (E / U) - the ratio of the offset value of the asymmetric violation of the load insulation relative to the position of the middle of the load resistance.

In order to control the contacts (or brushes) connecting the measuring circuit and the circuit of resistors 7 and 8 with DC circuits, load circuits 9 and ground circuits 10, an additional control circuit is introduced, consisting of a control signal source 29 and an alarm element 26 and connected at its ends to contacts 27 and 28 (see Figure 3).

In order to increase the contact forces in contacts 27 and 28 connecting the measuring circuit and the circuit of resistors 7 and 8 with DC circuits, load circuits 9 and ground circuits 10 that occur when contact 27 or 28 is broken, an element of electromagnetic energy storage is additionally introduced into the control circuit (see Figure 3).

LITERATURE

1. Ivanov E.A., Kudryavtsev V.P. et al. Evaluation of errors in measuring the insulation resistance of ship DC networks. M .: Shipbuilding, 1974, No. 7, p. 37-38.

2. News of electrical engineering. No. 4 (52), 2008. "How to correctly measure the insulation resistance of electrical installations." (subsection "The method of balanced bridge".) // E. Ivanov, A. Dyachkov.

Claims (6)

1. The method of measuring the insulation resistance in DC circuits, based on connecting to the poles of the DC circuit of a resistor circuit consisting of two series-connected resistors, including at the connection point of the resistors between themselves the first end of the measuring circuit, consisting of a series-connected measuring voltage source and a meter current, connecting the second end of the measuring circuit to the ground element, determining the measuring current in the measuring circuit, characterized in that, in order to use the measurement error from the unbalance current in the resistor circuit, connect two resistors with the same resistance to the poles of the DC circuit, turn on the source of the measuring voltage, either in the same polarity or in the opposite polarity of the poles, determine the absolute values of the measuring current, determine the equivalent measurement current, as half the sum of two absolute values of the measuring current, measured sequentially in time at different polarity of the source ritelnogo voltage, determine the equivalent circuit resistance of resistors of equal magnitude as half the value of one resistor divide value measuring voltage source by an amount equivalent to the measuring current and is subtracted from the value obtained by this division, the equivalent resistance value of the resistor chain. 2. The method according to claim 1, characterized in that, in order to compensate for the internal resistance of the measuring circuit and improve the accuracy of measurement at low measuring currents, a load resistor is additionally connected to the junction of the two resistors. 3. The method according to claim 1, characterized in that, in order to determine the direction of the displacement of the asymmetric violation of the load insulation relative to the position of the middle of the load resistance when the voltage in the DC circuit is not equal to zero, the unbalance current is determined as the difference between two absolute values of the measurement current, measured sequentially in time at different polarity of the measuring voltage source, determine that the displacement of the asymmetric violation of the insulation of the load relative to the position among s the load resistance was towards the negative pole, if the current imbalance is positive. 4. The method according to claim 1, characterized in that, in order to determine the ratio of the magnitude of the displacement of the location of the asymmetrical violation of the load insulation relative to the position of the middle of the load resistance when the voltage in the DC circuit is not equal to zero, the unbalance current is determined as the difference of two absolute values measuring current, measured sequentially in time at different polarity of the measuring voltage source, divide the value of the unbalance current by the equivalent measuring current and the voltage eniya the DC link, is multiplied by the value of the measuring voltage source. 5. The method according to claim 1, characterized in that it additionally introduces a control circuit of the brush contact connecting the measuring circuit and the ground circuit to a rotating shaft on which DC circuits are located, consisting of a control signal source, an alarm element and a second brush contact, connected in series connecting at one end to the place of the brush contact connecting the measuring circuit and the ground circuit to the rotating shaft, and the second end and the brush contact to this rotating shaft. 6. The method according to claim 1, characterized in that it further introduces a circuit to increase the contact forces that occur when the brush contact ruptures, connecting the measuring circuit and the ground circuit with a rotating shaft, on which there are direct current circuits, consisting of a control signal source connected in series, element of the accumulation of electromagnetic energy and the second brush contact, connected at one end to the place of the brush contact connecting the measuring circuit and the ground circuit with a rotating shaft, and the second m and the brush contact end - to this rotating shaft.

Images