RU2028634C1 - Method of and device for insulation resistance measurement in alternating-current lines incorporating static converters - Google Patents

Abstract

FIELD: electric measurement technology. SUBSTANCE: method involves superposition of varying-polarity A C measuring voltage onto line under measurement whereupon D C component of current through circuit of D C measurement voltage source is measured upon end of transient process; then insulation resistance is calculated. Transient process is ceased without waiting for its completion and then D C component of voltages across insulation impedance and mentioned current are measured and insulation resistance value is found from equation given in description of invention. EFFECT: improved measurement accuracy. 3 cl, 2 dwg

Description

 The invention relates to electrical engineering.

 A known method of measuring the insulation resistance of electrical AC networks with static converters by superimposing on a controlled network of measuring DC voltage used in the device [1].

 The disadvantage of this method is the low accuracy of measuring the insulation resistance of networks having a large capacity relative to the housing, which is caused by the large time constant of recharging the network capacity relative to the housing each time the measuring DC voltage is connected and disconnected and the state of the controlled network is inconsistent due to switching loads during the measurement cycle.

 A device for implementing this method is known, comprising a measuring voltage source connected by poles to switch terminals and a meter [1].

 The disadvantage of this device is the low accuracy of measuring the insulation resistance of networks having a large capacity relative to the housing.

 The closest proposed in its technical essence is a method for measuring the insulation resistance of AC electric networks with static converters by applying alternating polarity measuring DC voltage to the controlled network and measuring the DC component of the voltage across the measuring resistor connected in series with the measuring DC voltage source and calculating the resistance value insulation used in the device [2].

 However, this method also has drawbacks consisting in the low accuracy of measuring the insulation resistance of networks having a large capacity relative to the housing. This is caused by a large time constant for recharging the network capacity relative to the case (tens of seconds) with each change in the polarity of the measuring DC voltage and the inconsistency of the state of the controlled network due to switching loads during the measurement cycle.

 It is also known a device for implementing this method, containing a measuring voltage source, which is connected to the housing through one of the poles through a switch and a resistor, and the tolerance control unit, indicator [2] is connected to the common terminal of the device, which is its input, through the limiting resistor.

 However, this device also has drawbacks consisting in the low accuracy of measuring the insulation resistance of networks having a large capacity relative to the housing. Low accuracy is caused by a large time constant for recharging the network capacity relative to the housing (tens of seconds) with each change in the polarity of the measuring constant voltage and the inconsistency of the state of the controlled network due to switching loads during the measurement cycle.

 The purpose of the invention is to improve the accuracy of measuring the insulation resistance of electrical networks having a large capacity relative to the housing.

, где К - коэффициент пропорциональности, учитывающий рабочие диапазоны измерения величины сопротивления изоляции;
U₁T₁ и U₂T₂ - постоянные составляющие измеренных напряжений и тока соответственно при обеих полярностях измерительного постоянного напряжения.This goal is achieved by the fact that according to the method for measuring the insulation resistance of electric networks of direct and alternating current with static converters, based on the application of alternating polarity of the measured direct voltage to the controlled network and measuring, at the end of the transition process in the controlled network, the direct current component in the measuring constant circuit voltage source, and calculating the value of the insulation resistance, further stop the transient s in a controlled network, without waiting for it to end, after which the DC component of the voltage is measured at the insulation impedance and the indicated current, and the value of the insulation resistance is calculated by the formula
R _of = K

where K is the coefficient of proportionality, taking into account the operating ranges of measuring the value of insulation resistance;
U ₁ T ₁ and U ₂ T ₂ are the constant components of the measured voltages and current, respectively, at both polarities of the measuring constant voltage.

 Another objective of the invention is to reduce the time between measurements of insulation resistance.

, где n - порядковый номер очередной смены полярности источника измерительного постоянного напряжения.This goal is achieved by the fact that in the proposed method, the calculation of the insulation resistance value is performed with each change in the polarity of the measuring DC voltage source according to the formula
R _of = K

where n is the sequence number of the next polarity change of the source of the measuring constant voltage.

 The sign “stop the transient” in the controlled network is known in the method used in the device [3], when the measurement begins at the end of the transient in the controlled network. However, in the proposed method, to reduce the time of the transient process, the transient process is stopped without waiting for its end, which, in combination with the measurement of the constant components of the voltage at the insulation impedance and current in the measuring DC voltage circuit, provides a reduction in the time between measurements at different polarities of the measuring voltage source, and, therefore, it increases the accuracy of calculating the equivalent insulation resistance value.

 Thus, the proposed method has the property of improving the performance of the measurement, which coincides with the properties shown by the signs in the known solutions, and which is not equal to the sum of these properties, which allows us to conclude: the proposed method meets the criterion of "significant differences".

 In the device that implements the proposed method, containing a measuring voltage source, which is connected to the housing through one switch through a switch and a resistor, and an access control unit (threshold device connected to with an indicator), an indicator (recording device), a load resistor, an analyzer, two meters, a control unit, a computer connected by two outputs respectively with the inputs of the tolerance control unit and indicator, two information inputs with the corresponding information outputs of the meters, and four controlled inputs respectively with the four control outputs of the control unit, the other three outputs of which are connected respectively to the controlled inputs of the meters and the switch, the common terminal of the device is connected to measuring input of the first meter and through the analyzer with the input of the control unit, a common connection point of the limiting resistor and switch I am connected to one terminal of the load resistor, the other terminal of which is connected to the measuring input of another meter and to a common point of connection of the resistor and switch.

 The sign “analyzer introduced” is known in the device [4], where it manifests itself as a fixator for the end of the transition process in a controlled network.

 However, in the proposed device, in conjunction with the introduction of a load resistor, it is possible to stop the transient process in the presence of any value of the DC component of the voltage of the controlled network relative to the housing, i.e. keep this voltage constant with a predetermined degree of accuracy.

 The sign "entered control unit" is known in the device [5], where it manifests itself as a transmission link, issuing a signal to the control input of the inductor and the control input of an adjustable resistor upon receipt of a mismatch signal at the input of the control unit.

 However, in the proposed device, in conjunction with the analyzer, it is possible to set the program of the device and stop this program at the moment when a transient occurs during the measurement of electrical quantities.

 Communication: "the common connection point of the limiting resistor and the switch is connected to one terminal of the load resistor, the other terminal of which is connected to the measuring input of another meter and to the common connection point of the resistor and switch" allow you to simultaneously measure the DC components of the measuring constant voltage and voltage impedance isolation.

 Thanks to such an embodiment of the analyzer of the control unit and the load resistor, the transient is stopped in the controlled network, which allows the implementation of the device to achieve a reduction in the measurement time of the insulation resistance of the controlled network.

 Figure 1 shows a diagram of a device that implements the proposed method.

 The device contains a measuring voltage source 1, which is connected via one of the poles through switch 2 and resistor 3 to the housing, and the tolerance control unit 6 (connected in series with the threshold) is connected to the common terminal 5 of the device, which is its input, through the switch 2 and the resistor 3 to the other pole device and indicator), indicator 7 (recording device), load resistor 8, analyzer 9, meters 10 and 11, control unit 12, calculator 13 connected to two inputs respectively OK 6 and indicator 7, two information inputs - with the corresponding information outputs of meters 10 and 11, and four control inputs - respectively, with four control outputs of the control unit 12, the other three outputs of which are connected respectively to the controlled inputs of the meters 9 and 10 and switch 2, the common terminal 5 of the device is connected to the measuring input of the meter 10 and through the analyzer 9 with the input of the control unit 12, the common connection point of the limiting resistor 4 and switch 2 is connected to one output ohm load resistor 8, the other terminal of which is connected to the measuring input of the meter 11 and with a common connection point of the resistor 3 and switch 2. The device also contains a calculator 13.

In FIG. 1 also indicates the equivalent capacitance C _of and the equivalent insulation resistance R _{of the} controlled network relative to the housing.

 The device operates as follows.

In the first measurement of insulation resistance, the measuring cycle contains four operating cycles, shown in figure 2:
1) the transition process associated with connecting to the measuring circuit of the device a measuring voltage source of a certain polarity and measuring at the end of a specified period of time the value of the DC component of the voltage U ₁ between the phase (pole) and the housing of the controlled network;
2) stabilization of the DC component of the voltage between the phase (pole) and the housing and measuring the value of the DC component of the current I ₁ in the measuring circuit;
3) a transition process associated with switching the polarity of the source of the measuring voltage and re-measurement at the end of a specified period of time the value of the DC component of the voltage U ₂ between the phase (pole) and the housing of the controlled network;
4) stabilization of the DC component of the voltage between the phase (pole) and the housing and measuring the value of the DC component of the current I ₂ in the measuring circuit.

,
, (1) где К - коэффициент пропорциональности, учитывающий рабочие диапазоны измерения величины сопротивления изоляции;
U₁ и U₂ - величины напряжений между фазой (полюсом) и корпусом контролируемой сети, измеренные в первом и третьем тактах работы устройства соответственно;
I₁ и I₂ - величины токов измерительной цепи, измеренные во втором и четвертом тактах работы устройства соответственно.At the end of the fourth clock cycle, using the measured voltage values U ₁ , U ₂ and currents I ₁ , I ₂ , the equivalent insulation resistance R is calculated _{from the} formula
R _of = K

,
, (1) where K is the coefficient of proportionality, taking into account the operating ranges of measuring the value of insulation resistance;
U ₁ and U ₂ - the magnitude of the voltage between the phase (pole) and the housing of the monitored network, measured in the first and third clock cycles of the device, respectively;
I ₁ and I ₂ - the magnitude of the currents of the measuring circuit, measured in the second and fourth clock cycles of the device, respectively.

_,
, (2) где n - порядковый номер очередного цикла работы устройства после подключения к данной контролируемой сети.In subsequent cycles of operation of the device, the calculation of the value of insulation resistance is performed at the end of each even cycle of the device using information from the last four measurements, according to the formula

_,
, (2) where n is the sequence number of the next cycle of the device after connecting to this controlled network.

At the first cycle of the device (Fig. 1) to its measuring circuit (controlled network, limiting resistor 4, load resistor 4, load resistor 8, resistor 3, case, equivalent insulation resistance R _equiv , controlled network) by command from control unit 12 connected by a certain polarity using switch 2, the source 1 of the measuring voltage. In the measuring circuit, a transition process begins, caused by the presence of the capacity of the controlled network C _from relative to the housing. After a predetermined period of time (about 2 s), at the command of the control unit 12, the meter 10 measures the instantaneous value of the DC component of the voltage between the phase (pole) of the controlled network and the housing, as well as records this voltage in the first register of the computer 13.

 At the second clock cycle, the device of the control unit 12 acts on the switch 2 in such a way that the constant component of the voltage between the phase (pole) of the controlled network and the housing remains unchanged (stabilized). This is achieved by periodically disconnecting and connecting the measuring voltage source 1 to the measuring circuit. At the same time, upon a command from the control unit 12, with the help of a meter 11, the DC component of the current in the measuring circuit is measured (removed from the resistor 3), and this current is also recorded in the second register of the calculator 13.

At the end of the fourth clock cycle of the device in the calculator 13, at the command of the control unit 12, the value of the equivalent insulation resistance R _{from the} monitored network is calculated using formula (1) and this value is displayed on indicator 7. At the same time, the insulation resistance value is compared with the alarm setpoint in block 6 tolerance control.

Information on the indicator 7 and on block 6 is stored until the next calculation of the insulation resistance R _from .

With further operation of the device, the first two cycles of its operation are repeated and the measured voltages and current are recorded in the recording registers of the calculator 13, and at the end of the second cycle, the calculator 13 calculates the equivalent insulation resistance R _{from the} controlled network according to formula (2) and displays this value on the indicator 7 and block 6.

 The subsequent operation of the device is similar to that described above, moreover, the calculation of the equivalent insulation resistance is performed according to the formula (2).

 The analyzer 9 blocks the device from issuing false signals during switching loads and overvoltages in a controlled network.

 The control unit 12 operates as follows. The clock generator gives four control signals in succession, which are supplied to the calculator 13. At the same time, on I and III clocks, the first logic circuit OR issues a control signal to meter 10 to enable the measurement of voltage, and on II and IV clocks it outputs another logic circuit OR resolution for measuring current magnitude.

 On the second and third clocks from the third logic circuit OR, a signal is issued to change the polarity of the operational voltage using switch 2.

 The signal from the analyzer 9 stops the operation of the control unit 12 in the presence of transients in a controlled network.

 The calculator 13 operates as follows.

.Upon receipt of control signals from the control unit 12 and the resolution of the measurement of voltage and current, a recording is made (voltage values U ₁ and U ₂ and current values I ₁ and I _2. In one subtraction unit, the difference is calculated (U ₂ - U ₁ ), and in another block of subtraction, the difference is calculated (I ₁ - I ₂ ). In the division block, the numerical value of the insulation resistance value K is calculated

.

 The proposed method and device can improve the accuracy of measuring the insulation resistance of networks with static converters having a large capacity relative to the housing, as well as reduce the measurement time. In addition, the method and device are also suitable for measuring the insulation resistance of direct current networks.

 The reliability of the implementation of the goal is confirmed by the manufacture of a prototype device and its testing.

Claims (4)

 METHOD FOR MEASURING RESISTANCE OF INSULATION OF AC ELECTRIC NETWORKS WITH STATIC CONVERTERS AND DEVICE FOR ITS IMPLEMENTATION. 1. The method of measuring the insulation resistance of AC electric networks with static converters, based on the application of alternating polarity measuring DC voltage to the controlled network, measuring at the end of the transition process in the controlled network a constant current component in the measuring constant voltage source circuit and calculating the insulation resistance value, which differs the fact that, in order to improve the accuracy of measuring the insulation resistance of electrical networks having a large capacitance relative to the case, stop the transient in a controlled network, without waiting for it to end, then measure the constant component of the voltage at the insulation impedance and the specified current, and the value of R _{and s} of the insulation resistance is calculated by the formula

where K is the coefficient of proportionality, taking into account the operating ranges of measuring the value of insulation resistance;
U ₁ , I ₁ and U ₂ , I ₂ are the constant components of the measured voltage and current, respectively, at both polarities of the measuring constant voltage. 2. The method according to claim 1, characterized in that, in order to reduce the time between measurements of insulation resistance, the calculation of the value of insulation resistance is performed with each change of polarity of the measuring DC voltage source according to the formula

where n is the sequence number of the next polarity change of the source of the measuring constant voltage.  3. A device for measuring the insulation resistance of electrical AC networks with static converters, comprising a measuring voltage source, which is connected to a common bus via a switch and a resistor connected in series with one pole, and connected to a common terminal of the device through a switch and a limiting resistor, which is its input, tolerance control unit, indicator, characterized in that, in order to improve the accuracy of measurement, a load resistor is introduced into it, an analyzer, two meters, a control unit, a computer connected by its two outputs respectively to the inputs of the tolerance control unit and indicator, two information inputs - with the corresponding information outputs of the meters, and four control inputs - respectively, with four control outputs of the control unit, the other three outputs of which connected respectively to the controlled inputs of the meters and the switch, the common terminal of the device is connected to the measuring input of the first meter and through a alizator - to the input of the control unit, the general conclusions limiting resistor and a switch connected to one terminal of the load resistor, the other terminal of which is connected to a measuring input of another meter and with common terminals of the resistor and the switch.

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