RU2200329C2 - Insulation resistance measurement technique - Google Patents

Abstract

FIELD: electric measurement technology; computer-aided monitoring systems. SUBSTANCE: proposed technique for measuring insulation resistance of live electric circuits involves connection of known-rating capacitor in parallel with circuit under measurement, measurement of transient time constant, and evaluation of circuit insulation parameters including initial and final values of measured voltages at points under check. EFFECT: facilitated measurement procedure. 2 dwg, 1 tbl

Description

 The method of measuring the electrical insulation resistance in electric harnesses and cables of networks under constant current 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 electronic products.

 A known method of measuring the insulation resistance in electrical harnesses and cables (application 92014756, published 30.04.1995). The inventive method for measuring the insulation resistance provides for two consecutive measurements of the conductivity current with a period of time determined by the speed of the device in which the method is implemented, then the insulation resistance is determined by a known system of equations by comparing the measured resistance with a known divider.

 The disadvantage of this method is the low accuracy, low speed and high performance requirements of the measuring unit, as well as the effect on the controlled circuit.

 A known method of measuring the steady state value of insulation resistance (application 96105043, published 10.01.1998). The measurement method consists in measuring the magnitude of the resistance, its first and second time derivatives, and for the steady-state value of the insulation resistance, take the double value of the insulation resistance at that time when the first derivative has a maximum and the second derivative is zero.

 The disadvantage of this method is the low accuracy and complexity of its implementation.

 The closest in technical essence to the claimed object is a method for determining the insulation of electrical networks (application 5049551, published 02.09.1995).

 The inventive method for determining the insulation resistance of electrical networks is based on alternately shunting the resistors of the poles of the network, sequentially measuring the instantaneous voltage values on it at the time of shunting and then at equal intervals of time determining the equivalent resistance of insulation as the product of the value of the shunt resistor by the ratio of the voltage of the controlled network to the sum of steady-state voltage values on the shunt resistor, reduced by one.

 The disadvantage of this method is a significant effect on the controlled circuit and the lack of the ability to provide galvanic isolation of the measuring circuit from the controlled.

 The task of the invention is to provide a method for measuring the insulation of electrical networks that are energized. This is achieved by reconfiguring the measured circuit 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. This ensures galvanic isolation of the measured and measuring circuits.

 The technical result is achieved through the use of a known capacitance as a shunt element of the capacitor and the simplicity of the method of calculating the parameters of the measured circuit.

 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 a model of a device that implements this method.

The method of measuring the electrical insulation resistance in electric harnesses and cables of networks under constant current voltage is illustrated using the circuit shown in FIG. 1. The following notation is used in the diagram:
V ₁ - voltage source in a controlled circuit,
R _IZ1 , R _IZ2 - insulation resistance of the first and second sections of the circuit with respect to the housing,
C ₁ , C ₂ - parasitic capacitance of the first and second sections of the circuit with respect to the housing,
Сш - a capacitor of known capacity,
R ₃ - resistance in the discharge circuit of the capacitor Сш to zero volts to bring it to its original state before the next measurement cycle.

S ₁ , S ₂ - relay contacts P1 and P2 for the corresponding commutation Сш,
V ₂ , V ₃ - control signal generators for relays.

In the initial state, the capacitor Сш is discharged to zero volts, for example, by closing the contact S ₂ . The potentials of points A and B are measured with respect to point K (the housing). After that, point A or B is shunted (depending on which potential is higher) with capacitor Сш through contact S ₁ , having previously opened contact S ₂ .

Зависимость e(t) приведена на фиг. 2.Measure the parameters of the transient process, which is described by the formula

The dependence e (t) is shown in FIG. 2.

Carrying out constant measurements of the changing potential V _{xi of} point B, we fix the moment t _i when it reaches any value from the table selected for reasons of either the minimum error or the minimum conversion time. This value V _xi corresponds to the coefficient k _i , which determines the relationship between τ _i and t _i .

Зная потенциал V₀ точки В до подключения конденсатора, равный

, значение скачка напряжения V_n в точке В в момент шунтирования, равное

, и постоянную времени переходного процесса τ, легко определить параметры изоляции по формулам

Таким образом, предлагаемый способ позволяет упростить реализацию устройств для измерения электрического сопротивления изоляции и обеспечить гальваническую развязку измерительных цепей.Then τ _i is determined by the formula

Knowing the potential V _{0 of} point B before connecting the capacitor, equal to

, the value of the voltage jump V _n at point B at the time of shunting, equal to

, and the time constant of the transition process τ, it is easy to determine the insulation parameters by the formulas

Thus, the proposed method allows to simplify the implementation of devices for measuring electrical insulation resistance and to provide galvanic isolation of the measuring circuits.

Claims (1)

A method of measuring the electrical insulation resistance of circuits under DC voltage, which consists in changing the configuration of the measured circuit by shunting and making a series of measurements of the measured circuit, characterized in that at the beginning of the measurement the potentials of different sections of the circuits are measured with respect to the case, then they are shunted a section of the circuit having a higher potential, with a capacitor of known capacity, and measure the parameters of the transition process at the bypass points, and according to these parameters in computes values of parasitic capacitances C _Σ circuits and insulation resistance with respect to the housing _IZ1 R and R _ds2 the formulas

where V ₀ , V _n - steady-state and initial voltage values at the measurement point;
τ is the time constant of the transition process;
V ₁ - voltage source in a controlled circuit;
R _IZ1 , R _IZ2 - insulation resistance of the first and second sections of the circuit with respect to the housing;
C ₁ , C ₂ - parasitic capacitance of the first and second sections of the circuit with respect to the housing;
C _w - capacitor of known capacity.

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