JPH0412432B2 - - Google Patents

Description

Detailed Description of the Invention [Technical Field of the Invention] The present invention relates to a nondestructive insulation testing method for diagnosing the quality of the insulation configuration and insulation performance of electrical equipment by measuring dielectric loss tangent, and in particular, to a method for diagnosing the quality of the insulation structure and insulation performance of electrical equipment. This relates to a non-destructive insulation testing method in which the corona onset voltage is lowered to below the rated voltage of the equipment under test by changing the pressure or type of gas in the pressure vessel.

[Prior art] Conventional non-destructive insulation testing methods of this type include:
For example, there is a method of examining the relationship between the dielectric loss tangent tan δ and the applied voltage in a dielectric loss tangent test. FIG. 1 shows the tan δ-applied voltage characteristic, where the vertical axis shows the dielectric loss tangent tan δ in percentage (%), and the horizontal axis shows the applied voltage in kilovolts (kv). For high voltage dry insulation, tanδ−
Measurement of applied voltage characteristics is generally carried out.
If there is a gap (void) inside the insulator, etc.
As the voltage increases, corona discharge occurs here, so the dielectric loss tangent tan δ increases. Therefore, the value tanδo of the dielectric loss tangent at a relatively low voltage V ₀ where no corona discharge occurs and therefore the dielectric loss tangent tanδ is constant,
Find the increase in dielectric loss tangent Δtanδ due to the voltage rise at voltage Vn, and calculate the deterioration of insulation, the degree of moisture absorption,
Determine the degree of void inclusion and the state of occurrence of corona discharge. In addition, the applied voltage when the dielectric loss tangent tan δ increases from tan δ ₀ by a predetermined value is called the corona starting voltage V1.
Further, if the upper limit voltage at which corona discharge does not occur is V ₀ max, the increase in voltage Vn can be expressed as Δtan δ = tan δ (Vn - V ₀ max). An example of a device for measuring the dielectric loss tangent tan δ is a shearing bridge shown in FIG.
In the Schering bridge shown in FIG. 2, V is the power supply, and Cx and Rx are the equivalent series capacitance and equivalent series resistance of the measurement sample corresponding to the device under test, respectively. Also, Cs is a lossless standard capacitor,
R ₃ is a variable resistor for balancing, C ₄ is a variable capacitor for balancing, R ₄ is a non-inductive resistor, and G is a galvanometer.
An equivalent series capacitance Cx and an equivalent series resistance Rx are connected in series between the bridge connection points a and b, and the connection points b and c
A balancing variable resistor _R3 is connected between them, a balancing variable capacitor _C4 and a non-inductive resistor _R4 are connected in parallel between connection points c and d, and a lossless resistance is connected between connection points d and a. Standard capacitors Cs are connected to each. Further, a galvanometer G is connected between connection points b and d. A power supply V is connected between connection points a and c, and connection point c is grounded. Now, assuming that the bridge balance is obtained by adjusting the values of the variable balancing resistor R ₃ and the variable balancing capacitor C ₄ , the following equation holds true.

Cx＝R4／R3Cs…(1) Rx＝C4／CsR3…(2) Therefore, the dielectric loss tangent tanδx of the measurement sample is tanδx＝ωR4C4 …(3) becomes.

Therefore, the insulation configuration and insulation performance were tested by measuring capacitance changes and resistance changes of the measurement sample while changing the applied voltage, and determining tan δ - applied voltage characteristics.

However, in the conventional test method using dielectric loss tangent,
When the corona onset voltage is higher than the rated voltage of the equipment, as in the case of low-voltage equipment, when the applied voltage is increased to measure the increase in dielectric loss tangent Δtanδ shown in Figure 1, the equipment itself may break down. There was a risk that this method would cause damage to the equipment, making it inappropriate as a non-destructive testing method for equipment, especially after it has deteriorated.

[Summary of the invention]

This invention was made in order to eliminate the drawbacks of the conventional ones as described above. The purpose of the present invention is to provide a non-destructive insulation testing method in which the corona onset voltage is lowered to below the rated voltage by using a gas with a lower minimum spark voltage than air.

[Embodiments of the invention]

Therefore, one embodiment of the test method of the present invention will be described with reference to the drawings. FIG. 3 shows a measurement sample 10 used in the test according to the present invention, where 1 is a conductor, 2 is a conductor, and 2 is a conductor.
is the insulator of the conductor 1, and the main insulating material is aromatic polyamide fiber. Further, reference numeral 3 denotes an electrode attached closely around the insulator 2. FIGS. 4 and 5 show cross-sectional views of the measurement sample 10 before deterioration and the measurement sample 10' after deterioration, respectively. In the measurement sample 10 before deterioration in FIG. However, in the measurement sample 10' shown in FIG. 5, which was heat-degraded at 250° C. for 48 hours, a gap 4 was formed between the conductor 1 and the heat-deteriorated insulator. FIG. 6 shows a longitudinal cross-sectional view of the measurement sample 10' after deterioration in FIG. 5, and a voltage V is applied between the conductor 1 and the electrode 3. In the figure, d indicates the thickness of the insulator 2, and lg indicates the distance of the gap 4. Also, the seventh
The figure shows the electrical equivalent circuit of Figure 6, and Ca
is the capacitance of insulator 2 in the part without void 4, Cg
is the capacitance of the air gap 4, and Ci is the capacitance of the insulator 2 in series with the air gap 4. At this time, if the corona starting voltage in the gap 4 is Vg, the applied voltage V that can generate corona in the gap 4 is as follows: V=(1+Cg/Ci)Vg (4). The corona starting voltage Vg is proportional to the product of the atmospheric pressure and the distance lg of the air gap 4 according to the well-known Paschen's law, and the capacitance Cg of the air gap 4 is proportional to the relative dielectric constant of the atmosphere and the air gap. 4
Determined by Furthermore, equation (4) can be expressed as a function of pressure P as shown in equation (5).

V=(1+Cg/Ci)Vg(P)...(5) From equation (5), it is expected that in a reduced pressure atmosphere, the applied voltage V that can generate corona will decrease up to a certain reduced pressure value, and the dielectric loss tangent tanδ Naturally, it can be expected that the corona start voltage during measurement will be lower than atmospheric pressure. Further, if similar measurements are performed in an atmosphere with a lower minimum spark voltage than air, it is expected that the applied voltage V that can generate corona will be further reduced.

FIG. 8 shows an actual test device. In FIG. 8, 10 is the measurement sample shown in FIGS. 3 to 5 (actually 10, 10') 20 is a pressure vessel, 21 is a pressure gauge that indicates the pressure inside the pressure vessel 20, and 22 is a pressure gauge. A tan δ measuring device such as the Schering Bridge shown in Figure 2, 23 a vacuum pump, 24
is a valve installed in a pipe connecting the vacuum pump 23 and the pressure vessel 20, 25 is a helium gas cylinder,
Further, 26 is a valve provided in a pipe connecting the helium gas cylinder 25 and the pressure vessel 20.
The measurement sample 10 is placed in a pressure vessel 20,
The tanδ measuring device 22 measures the conductor 1 and electrode 3 (third to third
(See Figure 6), a voltage is applied between them, and the tan δ-applied voltage characteristic is measured. The air pressure inside the pressure vessel 20 can be adjusted to a desired pressure by a vacuum pump 23. In addition, when performing a similar test in, for example, helium gas, which has a lower spark generation voltage than air, it is necessary to use a helium gas cylinder 25 to exchange the air in the pressure vessel 20 with helium gas and bring it to the desired pressure. I can do it. Note that helium gas is often used for pressure leakage tests of the pressure vessel 20 and the like. Therefore, inside the pressure vessel 20, as shown in FIG.
The test samples 10 and 10' before and after deterioration shown in FIG. The tanδ-applied voltage characteristics were determined for each when the helium gas pressure was reduced. The results are as follows. Note that the atmospheric pressure is expressed in units of millimeter Hg (mmHg).

First, Figure 9 shows tanδ− when the air pressure is reduced.
It is an applied voltage characteristic curve diagram. Curves A ₁ , A ₂ , and A ₃ are for the measurement sample 10 before deterioration at 765 mmHg (atmospheric pressure), 100 mmHg, and 10 mmHg, respectively, and curves B ₁ , B ₂ , and B ₃ are for the measurement sample 10' after deterioration. 765mmHg (atmospheric pressure), 100mmHg, 10mm respectively
This is in Hg. The rise of tanδ is
The pressure is 100% lower than that of 765tmmHg (atmospheric pressure).
It can be seen that as the pressure decreases from mmHg to 10 mmHg, it becomes steeper, and that the corona start voltage decreases as the pressure decreases. Also, when comparing the tanδ curve patterns before and after deterioration, the pattern becomes compressed in the axial direction of the applied voltage as the pressure decreases, but the respective trends are the same. You can see the significant difference afterward.

The following FIG. 10 is a tan δ-applied voltage characteristic curve diagram when the pressure of helium gas is reduced. Curves A ₁ and B ₁ are the same as curves A ₁ and B ₁ in Fig. 9, respectively, that is, the measurement samples were measured at 765 mmHg (in the atmosphere) before and after deterioration in the air, and the curves Ah ₁ and Ah ₂ is the helium gas pressure 765 of each measurement sample 10 before deterioration in helium gas
mmHg (atmospheric pressure) and 100 mmHg, and curves Bh1 and Bh2 are for measurement sample 1 after deterioration.
0' at a helium gas pressure of 765 mmHg (atmospheric pressure) and 100 mmHg, respectively. The corona starting voltage in air and helium gas is 765, respectively.
Comparing in mmHg, it can be seen that the corona initiation voltage is considerably lower when helium gas is used. Furthermore, even in helium gas, the curve patterns of tan δ before and after degradation have the same tendency.

Further, FIG. 11 shows the relationship between gas pressure and corona start voltage when the gas pressure is reduced in air and helium gas using the measurement sample 10 before deterioration. In the figure, the vertical axis shows the corona onset voltage in kilovolts (kV), and the horizontal axis shows the gas pressure in millimeter etchings (mm).
Curve A is in air, and curve Ah is in helium gas. Note that gas pressure is measured on a logarithmic scale. 76.5mmH in air
Compared to the corona onset voltage at g (atmospheric pressure),
The corona starting voltage at 100 mmHg in air is approximately 1/2,
And at 765 mmHg in helium gas, it is about 1/3.

From the above, by reducing the pressure inside the pressure vessel or changing the type of gas, it is possible to lower the corona initiation voltage and measure the tanδ-applied voltage characteristic, and the pattern of the tanδ curve can be changed. Since it is similar to the case of atmospheric pressure in air,
It has been proven that this method can be used as a non-destructive insulation testing method.

Note that the gas used is not limited to helium.

〔Effect of the invention〕

As described above, according to the present invention, in a non-destructive insulation test method for diagnosing the quality of the insulation configuration and insulation state, the corona initiation voltage can be adjusted by changing the pressure and type of the atmosphere of the equipment under test. It is possible to lower the voltage below the rated voltage of the equipment, and it is possible to easily perform non-destructive insulation tests on low-voltage electrical equipment.

[Brief explanation of drawings]

Fig. 1 is a tan δ-applied voltage characteristic curve diagram, Fig. 2 is a circuit diagram of a Schering bridge, and Fig. 3 is a perspective view of a measurement sample used in an insulation test according to the present invention.
Figure 4 is a sectional view of the measurement sample before deterioration, Figure 5 is a sectional view of the measurement sample after deterioration, Figure 6 is a longitudinal sectional view of the measurement sample after deterioration, and Figure 7 is the same as in Figure 6. Fig. 8 is a schematic diagram of a test device according to an embodiment of the present invention, and Fig. 9 is an electrical equivalent circuit diagram of a measurement sample.
FIG. 10 is a tan δ-applied voltage characteristic curve diagram in helium gas, and FIG. 11 is a diagram showing the relationship between gas pressure and corona starting voltage. 10...Measurement sample, 20...Pressure vessel, 22...tanδ
Measuring instrument, 23...vacuum pump, 25...helium gas cylinder. In addition, in the figures, the same reference numerals indicate the same or corresponding parts.

Claims (1)

[Claims] 1. In a nondestructive insulation testing method for diagnosing the quality of the insulation configuration and insulation performance of electrical equipment by measuring the dielectric loss tangent, the equipment under test is placed in a pressure vessel, and the pressure of the air in the pressure vessel is measured. A non-destructive insulation testing method in which the corona onset voltage is lowered to below the rated voltage of the equipment under test by reducing the pressure of the air or changing the air to a gas having a minimum spark voltage lower than the minimum spark voltage. 2. The non-destructive insulation testing method according to claim 1, wherein the gas having a lower minimum spark voltage than air is helium gas.