JPS5829873B2 - Method for determining insulation deterioration of rotating machine stator windings - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for determining insulation deterioration of a stator winding of a rotating machine.

In order to protect the stator windings of generators, harmonizers, and other rotating machines connected to the power grid from abnormal voltages that occur in the grid, voltage values that take abnormal voltages into account (in Japan (2E+
1) Defined in KV (E: rated voltage).

), it is necessary to maintain an insulation state that can withstand high temperatures, and for this purpose, it is necessary to constantly monitor whether the desired insulation state is maintained through periodic inspections.

In this case, carrying out the test using the above-mentioned voltage value is actually quite restrictive, so it is desirable to be able to judge the deterioration using a lower test voltage (for example, a maximum voltage of 1.25E/fi). In Japan, a method is widely used in which the degree of insulation deterioration is determined from the results of three types of tests: loss angle test, current characteristic test, and partial discharge test.

By the way, the first method, which uses the loss angle and current, is based on the loss angle, which is based on the increase in loss due to partial discharge, so-called void discharge, that occurs in the gap inside the insulated part of the winding due to insulation deterioration. Rate of increase in alternating current (Jt
and (JI) as the determination items.

In addition, in partial discharge tests, the charge is proportional to the voltage (Q
=CV), the discharge charge Qamax (this is generally referred to as the maximum discharge charge) is calculated from the maximum voltage value of the discharge pulse generated during void discharge, which is a measure of insulation deterioration.

) and use this as the judgment item. These methods calculate the rate of increase in loss angle (Jtanδ), rate of increase in current (JI), and maximum discharge charge (Qamax) for the stator winding under test. Judgment standard value (Jtan δS) obtained for a large number of stator windings of the same insulation class and the same voltage class as the line,
(JIs) and (Qamaxs), and the state of deterioration is determined based on the magnitude relative to the determination standard value.

However, these conventional methods may produce different judgment results, and in particular, the method using the maximum discharge charge often produces differences from the other two methods.

Therefore, a judgment is made by integrating the three types of results, but even this may differ from the results obtained by the dielectric strength test, such as the results for generator C shown in Table 1 (see below), and there are still cases where It has not yet achieved sufficient reliability.

The present invention aims to improve reliability by providing a method for determining insulation deterioration of stator windings with high accuracy using a method using maximum discharge charge as a determination item.

This will be explained in detail next. According to the research conducted by the present inventors, the main reason for the difference between the judgment results of the conventional method and the actual dielectric strength results is due to the so-called creeping discharge that occurs on the surface of the stator winding. revealed.

When the generator was first manufactured, the occurrence of electrical discharge on the stator winding surface was prevented, for example, by applying anti-discharge paint, but as the years passed, this effect gradually faded, and the extent of this was limited by the It varies depending on usage conditions, etc.

For this reason, in a method in which the loss angle and the rate of increase in current are used as judgment items, the loss increases accordingly, tilting the judgment results in a pessimistic direction and causing variations in the judgment results.

In addition, in the partial discharge test method in which the maximum discharge charge determined from the discharge pulse voltage value is used as a judgment item as described above, if the amount of discharge charge due to creeping discharge exceeds the maximum discharge charge amount due to void discharge, The maximum discharge charge detected indicates that due to creeping discharge, so in this case the influence of creeping discharge is much greater than when the increase rate is the criterion item, and the other three factors are not considered when determining deterioration. This results in a difference.

The present invention aims to avoid the influence of creeping discharge and improve the accuracy of the determination by utilizing the difference in the properties of void discharge and creeping discharge in a method of determining deterioration in which the maximum discharge charge is the criterion item. It was conceived and done.

Void discharge occurs in the void inside the winding, that is, in a closed space, which causes insulation deterioration, so once a discharge occurs, the discharge itself will not develop any further even if the test voltage increases. The number of discharges only increases.

Therefore, if the gap lengths of multiple gaps are the same, the relationship between the test voltage and the maximum discharge charge will be as shown by the solid line shown in Figure 1a, and as the gap length becomes smaller, the maximum discharge charge changes as shown by the dotted line in the figure (as the gap length decreases, the discharge voltage decreases, but as the insulator becomes more complete, the voltage shared by the insulator increases, and the discharge starting voltage increases).

Furthermore, in a real winding wire in which there are a plurality of gaps having different gap lengths, discharge occurs from the one with the smallest gap length, so the maximum discharge charge value changes as shown by the dashed-dotted line in FIG. 1a.

- Since the surface discharge is a discharge in an open space, it gradually develops as the test voltage increases, and the maximum discharge charge tends to gradually become smaller as shown in FIG.

Furthermore, discharge generally spreads rapidly as the test voltage increases, and cases in which the maximum discharge charge due to creeping discharge exceeds the maximum discharge charge due to void discharge occur near the highest test voltage.

These facts mean that when making judgments, instead of focusing only on the maximum discharge charge at a point near the highest test voltage value, which is likely to be affected by creeping discharge, as in the past, This suggests that it is possible to reduce the influence of creeping discharge by focusing on the behavior of the maximum discharge charge over the entire voltage range.

The present invention calculates the logarithm of the maximum discharge charge and the test voltage, and plots the relationship between the two on a scale paper, thereby approximating the above relationship curve with a straight line and finding a scale. When the maximum discharge charge at voltage is expressed as 100% and the origin of the relational curve is taken as the highest test voltage point, the relational curve exhibits the tendency shown in Figure 2 due to the difference in the properties of void discharge and creeping discharge as described above, indicating that void discharge The idea is that a highly accurate determination can be made by comparing the slope of the relational curve in the region where the problem occurs with the slope of the determination reference curve.

Figure 2 shows generator A whose dielectric strength cannot withstand operation, generator B which has a higher dielectric strength but still cannot withstand operation, generator C whose dielectric strength can withstand operation, and generator C. Using a D generator with even higher dielectric strength,
This is the result of actually measuring the relationship between the maximum discharge charge and the test voltage.

As is clear from this figure, in the A-related curve where the dielectric strength is poor, that is, the maximum discharge charge due to void discharge is large, the maximum discharge charge due to lineside discharge exceeds it, and the slope of the curve becomes large in some parts. (see A1 section of curve A), the relational curve almost approximates the slope of the straight line connecting the highest test voltage point 01 and the void discharge generation point 02.

Furthermore, this tendency can be said to be true for other curves as well, which indicates that the influence of creeping discharge can be reduced by displaying related curves as in the present invention.

Moreover, the degree of slope of the relational curve tends to become gentler as the maximum discharge charge becomes larger.

Therefore, the degree of this inclination is compared with a judgment standard curve S prepared in advance using a large number of windings, and it can be determined, for example, whether the relational curve of the test generator is located on the right side or the left side of the standard curve. If you know this, you can easily judge the deterioration.

In addition, the degree of inclination Qn of the straight line connecting the origin 01 of the relational curve and the void discharge generation point 02 is expressed as follows: vx: test voltage in the linear region of the relational curve Q a m a x vz: maximum discharge charge at the test voltage vx Therefore, deterioration can be determined by numerically comparing the slope Qn of each relational curve thus calculated with the slope Qs of the determination reference straight line S created in advance and determining the magnitude from Qs.

Table 1 compares the determination results of generators A, B, C, and D according to the method of the present invention described above with the results determined by the dielectric strength test.

As is clear from this, the judgment results are completely consistent with the results of the dielectric strength test.

Incidentally, the slope Qn of the relational curve in Fig. 2 is 0.5 for generator A.
4, B was 1.25, C was 2.8, and D was 3.8, and the slope used as the criterion was 1.5.

Next, an example of a simple determination device based on the principles of the present invention will be explained with reference to FIG.

In Figure 3, 1 is an induced voltage regulator, 2 is a high voltage transformer for testing, 2a is its primary winding, 2b is its secondary winding, and 2c is 3
The next winding, 3 is the stator winding of the generator under test, 4 is the coupling capacitor that detects the pulse voltage due to discharge, 5 is the bypass filter that removes the alternating current component, 6 a > 6 b is the nonlinear amplifier for logarithmic conversion , 7 is an X-Y recorder.

In this device, the primary winding 2 by the induced voltage regulator 1
By adjusting the supply voltage of a, the output voltage of the secondary winding 2b is applied between one end of the stator winding 3 and the ground.

The discharge pulse generated at the end of the winding due to the discharge caused by the application of electricity is detected by the coupling capacitor 4, and the AC component is removed by the bypass filter 5, and then enters the nonlinear amplifier 6a for logarithmic conversion, where it is compressed and amplified to convert it into DC. is converted to

Therefore, a DC output corresponding to the logarithmized maximum discharge charge is sent to the output side, and this output is sent to the X-Y recorder 7.
is added to the Y-axis input terminal of

On the other hand, the tertiary winding voltage of the transformer 2 enters a nonlinear amplifier section for logarithmic conversion, is compressed and amplified in the same way as the discharge pulse, and is further converted into DC.

Therefore, a DC output corresponding to the logarithmized test voltage is sent to the output side of the X-Y recorder 7.
Then, the secondary winding voltage of the transformer 2 is set to the maximum test voltage by the induction voltage regulator 1, and the output adjustment device of the logarithmic conversion nonlinear amplifier 6a + 6b is adjusted to the maximum test voltage. Adjust the maximum discharge charge at the 10% scale on the Y axis of the scale paper 7a of the X-Y recorder 7,
Also, set the maximum test voltage to 1001% on the X-axis scale,
The test voltage is gradually lowered.

Then, a relationship curve between the maximum discharge charge and the test voltage is drawn on the scale paper of the X-Y recorder 7.

Therefore, by comparing the reference line marked on the scale paper in advance, insulation deterioration can be easily determined without the need for troublesome operations such as calculating the degree of inclination.

In this case, it goes without saying that a brown indicator is used.

As is clear from the above description, the present invention has an excellent advantage in that the degree of deterioration of the dielectric strength of the stator winding of a rotating machine such as a generator can be determined with high accuracy through a partial discharge test. The effects on maintenance management are remarkable.

[Brief explanation of drawings]

Figures 1a and b are diagrams showing the relationship between the maximum discharge charge and applied voltage during void discharge and creeping discharge in the generator stator winding, and Figure 2 is a graph on a logarithmic scale for explaining the present invention. FIG. 3 is a diagram illustrating the relationship between the maximum discharge charge and the test voltage displayed in multiple numbers, and is a circuit diagram of the insulation deterioration determination device according to the present invention.

Claims (1)

[Claims] 1 Check whether the winding has the dielectric strength necessary for operation by comparing the slope of the relationship curve between the logarithmically displayed maximum discharge charge and the test voltage with the slope of the judgment standard curve. A method for determining insulation deterioration of a stator winding of a rotating machine.