RU2349922C1 - Method of dielectric losses angle measurement - Google Patents

Abstract

FIELD: electricity; physics.

SUBSTANCE: method of dielectric losses angle measurement includes filling of measuring capacitor clearance with the observable dielectric and sinusoidal voltage supply to the capacitor. In addition, alternating electrical voltage V is generated. The above mentioned voltage is proportional to the product of capacitor voltage by the capacitor current. The voltage V is converted into two bipolar voltages V_max and V_min. One voltage value, for example, V_max is equal to the peak value of the positive component, while the other value V_min is equal to the peak value of the negative component of V voltage. Voltages V_max and V_min are converted into two direct voltages V₁ and V₂. One voltage value V₁ is equal to the sum of the absolute V_max and V_min values. On the contrary, the other value V₂ is equal to the difference of the above absolute values. The target value of losses angle sine is derived from the formula

Besides, the unit value (or multiple of a unit) for voltage V₁ is sought while controlling the produced V voltage. In addition, sinδ value is defined directly from voltmeter indications by measuring V₂ voltage.

EFFECT: simple process and increased accuracy of dielectric losses angle measurements within wide frequency interval, possibility of measurements automation.

3 cl, 2 dwg

Description

The invention relates to electrical measurements, is intended to measure the angle of dielectric loss of dielectric materials and can be used in various fields where increased demands are placed on the electrical properties of dielectric materials, for example, in the electronic and electrical industries.

The dielectric loss angle of the dielectric, determined by the phase difference between the active and reactive components of the alternating current of the capacitor with the dielectric in its gap (or between the active and reactive components of the power), is one of the main parameters characterizing the electrical properties of dielectric materials.

Known methods for measuring active power, based on the determination of the phase shift between the active and reactive components of alternating current. The closest in technical essence to the claimed method is the patent RU No. 2296338, IPC. G01R 21/06, 2007 (prototype). In the prototype method for measuring the active power of an alternating current, an electric voltage is generated proportional to the product of the voltage by the load current. From the generated voltage, pulsating voltages of various polarity are isolated. The peak values of these voltages are summarized and the result of the summation is measured with a voltmeter. A limitation of the method is the impossibility of its direct use for measuring the dielectric loss angle.

The technical result of the invention is to simplify the process and improve the accuracy of measuring the angle of dielectric loss of dielectrics in a wide frequency range, as well as the ability to automate measurements.

The technical result achieved is achieved by the fact that in the method for measuring the dielectric loss angle, including filling the gap of the measuring capacitor with the investigated dielectric and applying a sinusoidal voltage to the capacitor, an alternating electric voltage V is generated according to the invention, which is proportional to the product of the voltage across the capacitor and the capacitor current. The generated voltage V is converted into two constant bipolar voltages V _max and V _min , one of which, for example V _max , is equal to the peak value of the positive component, and the other V _min is the peak value of the negative component of voltage V. The voltages V _max and V _{min are} converted into two constant voltage V ₁ and V ₂ , one of which V ₁ is equal to the sum, and the second V ₂ is the difference in absolute values of V _max and V _min . The voltages V ₁ and V _{2 are} measured, and the sought value of the sine of the loss angle is determined by the formula

To simplify the registration of the value of sinδ, adjusting the generated voltage V, achieve a single (or multiple unit) voltage value V ₁ . In this case, the value of sinδ is determined directly by the voltmeter, measuring the voltage V ₂ .

Consider the essence of the claimed method. Let the voltage U across a capacitor with capacity C, the gap between the plates of which is filled with a dielectric, change in time t according to the law

U = U _m sinδ (ωt),

where U _m is the voltage amplitude, ω is the cyclic frequency.

Current in an ideal capacitor circuit without dielectric loss

and taking into account dielectric losses

where δ is the dielectric loss angle.

Instantaneous power taking into account losses, defined as P _t = UI, will be

для мгновенной мощности получимUsing the well-known trigonometry formula

for instant power we get

где

Where

We convert the value of P _t into the electric voltage V so that V linearly changes with the change in P _t , i.e. V = kP _t , where k is the conversion coefficient. We get

V = kA [sinδ + sin (2ωt-δ)].

It follows from the last equation that the voltage V represents sinusoidal oscillations of the doubled frequency 2ω displaced relative to the time axis by ΔV = kAsinδ. Peak bipolar values of V _max and V _{min of} this voltage are achieved at times when sin (2ωt-δ) = ± 1. Their absolute values

Solving the system of equations (1) and (2), we obtain

As follows from (3), to determine sinδ, it suffices to measure the sum of V ₁ and the difference V _{2 of the} absolute values of the peak voltages of the sinusoidal signal.

Moreover, by adjusting the conversion coefficient k, it is possible to achieve that the total voltage V _{1 is} a multiple of unity, i.e. V ₁ = 1 · 10 ^N , where N is an integer, i.e. N = -2, -1, 0, +1, +2, etc. Moreover, the value of sinδ will be a multiple of the difference voltage V ₂ = V _max -V _min , i.e.

For example, at N = 0 (V ₁ = 1) the readings of a voltmeter measuring voltage V ₂ will be numerically equal to the measured value of sinδ

(при V₁=1).

(with V ₁ = 1).

Given that for small angles sinδ = tanδ = δ, the voltmeter readings in volts will correspond to the measured angle δ in radians.

Figure 1 shows the characteristic time dependence of various electrical signals that explain the claimed method. In Fig. 1, the voltage U across the capacitor changes sinusoidally with time (solid curve). The capacitor current i without dielectric loss leads the phase voltage U by π / 2 (dashed line). The current I of the capacitor with dielectric losses lags in phase from the current i by an angle δ of dielectric losses (dash-dot). In Fig. 1, b, the sinusoidally changing voltage V (solid curve 1), proportional to the product of the voltage U by the current I of the capacitor, is shifted relative to the time axis ot by the value V ₂ (dashed line 4). Dotted line 2 corresponds to a constant voltage V _max equal to the peak voltage of the positive component of the alternating voltage V. Dotted line 3 corresponds to a constant voltage -V _min equal to the peak voltage of the negative component of the voltage V. The total voltage V ₁ is the sum of the absolute values of the voltages V _max and V _min , and the differential constant voltage V ₂ - the difference of these voltages.

Figure 2 as an example shows a circuit diagram of a device that allows you to implement the claimed method. The capacitor 1, the gap between the plates of which is filled with the investigated dielectric 2, is connected to the generator 3 of the voltage of the audio frequency. A current amplifier 4 is included in the capacitor circuit, which linearly converts the capacitor current to voltage. The output voltage of the generator 3 and the output voltage of the amplifier 4 are supplied to the inputs of the multiplier 5, the output voltage of which is proportional to the product of the voltage across the capacitor by the current of the capacitor. The voltage on the capacitor can be quite large and significantly exceed the voltage allowed for the multiplier, because at the input of the multiplier this voltage is reduced by a voltage divider formed, for example, by resistors R ₁ and R ₂ .

An alternating voltage from the output of the multiplier 5 is supplied to the inputs of the converters 6 and 7. One of the converters, for example 6, converts this voltage into a constant constant voltage + V _max , numerically equal to the peak value of the positive component of the alternating voltage. The second converter 7, similar to converter 6, generates a constant stabilized voltage -V _{min of} opposite polarity, numerically equal to the second peak value of the alternating voltage.

The inverter 8 connected at the output of the converter 7 changes the polarity of the output voltage -V _{min of the} converter 7 to the opposite, i.e. on V _min . The voltages from the outputs of the converters 6 and 7 are fed to the inputs of the differential amplifier 9, for example, to the non-inverting and inverting inputs of a differential operational amplifier with a unity gain. In this case, at the output of amplifier 9, a voltage V ₁ = V _max + V _{min is formed} . The voltage from the output of the converter 6 and from the output of the inverter 8 is supplied to the inputs of the differential amplifier 10, similar to the amplifier 9 so that the voltage V ₂ = V _max -V _min is generated at the output of the amplifier 10. Voltages V ₁ and V ₂ are measured by DC voltmeters 11 and 12. To achieve a voltage V _{1 of a} multiple of 1 · 10 ^N (for example, 10.1 or 0.1 V), an adjustable voltage divider is included at the output of the multiplier 5, for example, a potentiometer R ₃ .

Thus, in the claimed method, the dielectric loss angle δ (for small losses sinδ = tanδ = δ) is converted to a directly measured constant electric voltage, numerically equal to (or multiple) the value of sinδ. This allows you to simplify time-consuming measurements, for example, when studying the influence of the frequency or amplitude of the voltage on the measuring capacitor. Long-term measurements are also simplified, for example, when studying the temperature dependence of the dielectric loss angle, which allows the use of automatic recording, for example, recording the measurement results on a recorder.

Claims (2)

1. The method of measuring the dielectric loss angle, including filling the gap of the measuring capacitor with the investigated dielectric and applying a sinusoidal voltage to the capacitor, characterized in that an alternating electric voltage V is formed proportional to the product of the voltage across the capacitor and the capacitor current, the generated voltage V is converted into two constant bipolar voltages V _max and V _min, one of which is V _max is equal to the peak value of the positive component and the other V _min - peak value otritsat noy component of voltage V, the voltage V _max and V _min are converted into two constant voltages V ₁ and V _2, one of which V ₁ is the sum and the second V ₂ - difference absolute values V _max and V _min, measured voltage V ₁ and V ₂ , and the desired value of the sine of the loss angle is determined by the formula

. 2. The method according to claim 1, characterized in that by adjusting the generated voltage V, they achieve a single (or multiple unit) voltage value V ₁ , while the value of sinδ is determined directly from the voltmeter, measuring voltage V ₂ .

Images