JPH068852B2 - Electrical insulation diagnosis method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial application] The present invention relates to a coil insulation of a high-voltage rotating electric machine, a mold coil of a resin mold transformer, a resin mold bushing,
The present invention relates to a method for diagnosing electrical insulation by measuring partial discharge mainly for high-voltage electrical equipment of solid insulation type such as high-voltage power cables and parts thereof.

[Conventional technology]

Solid insulation high voltage electrical equipment, especially electrical, thermal,
There are electrical or material chemical insulation diagnosis methods as insulation diagnosis methods for high-voltage rotating electric machine coils of 6KV or more, which are most exposed to mechanical stress, but the latter material chemical insulation diagnosis method is still at the stage of research. Therefore, the former electrical insulation diagnosis method is generally used because it is difficult to correspond to the actual high-voltage rotating electric machine coil. This electrical insulation diagnosis method includes direct current resistance and dielectric loss tangent (tan δ) as means for detecting voids generated in the insulating layer of the high voltage rotating electric machine coil due to various deterioration stresses such as heat and heat cycles.
And there is a method of measuring partial discharge. The measurement of the DC resistance is to determine the degree of wetting of the void portion of the insulating layer,
The dielectric loss tangent is an average of the moisture absorption, withdrawal and corona discharge of the insulating layer, and the partial discharge is measured by focusing on the local void and corona discharge generated in the void. The discharge is measured and determined.

By the way, the resin that binds the insulating layer of the high-voltage rotating electric machine was an asphalt compound in the old days, but most of the high-voltage rotating electric machines that are currently manufactured or are actually used for operation are polyester or It has been changed to resin such as epoxy resin. Therefore, deterioration in asphalt compound insulation, which has poor heat resistance, begins with blistering of the insulating layer, that is, voids in the insulating layer.It is sufficient to detect this void, and conventional electrical insulation diagnostic methods are effective in this respect. It has been used. However, current resin-based insulation such as polyester or epoxy resin has excellent heat resistance of insulation, and therefore voids are created in the coil insulation layer, and corona discharge in that area corrodes the insulation layer, which rarely leads to an accident. Therefore, the origin of the deterioration is shifted from the inside of the coil insulating layer to another portion, and it is difficult to catch the deterioration according to the type by the electric method so far.

FIG. 6 is a fragmentary cross-sectional view showing a state where the high-voltage rotating electric machine coil is housed in the iron core slot. The coil 2 housed in the slot of the iron core 1 is a shaped coil conductor 3 and a resin-based ground main insulation surrounding the shaped coil conductor 3. The surface of the main insulating layer 4 is provided with an outer corona preventive layer 5 made of a low resistance paint or the like over a length slightly exceeding the slot insertion part, and the outer corona preventive layer 5 is at the same potential as the iron core 1. By being held, the occurrence of partial discharge (called slot discharge) in the gap between the coil and the iron core is prevented. Further, end corona preventive layers 6 made of high resistance paint or the like are applied to both ends of the outer corona preventive layer 5, and a partial discharge in a creeping direction caused by electric field concentration at the ends of the outer corona preventive layer 5 (called end discharge). Is prevented from occurring.

Explaining in detail an example of an accident in the high-voltage rotating electric machine coil formed in this way, first, the start of deterioration in the high-voltage rotating electric machine coil is often damage to the outer corona preventing layer 5 or the end corona preventing layer 6. Next, regarding the content, in the case of damage to the outer protective corona prevention layer, the coil vibrates due to electromagnetic vibration when the coil is loosened due to withdrawal of the wedge that holds the high-voltage rotating electrical machine coil, and the coil surface vibrates. The outer corona preventing layer 5 applied is missing, electrical contact between the outer corona preventing layer 5 and the iron core 1 becomes defective, slot discharge occurs in the iron core slot, and finally the coil insulating layer is eroded. It leads to dielectric breakdown. When the end corona preventive layer 6 is damaged, hygroscopic conductive dust adheres to the surface of the end corona preventive layer 6, and the operating voltage applied to the coil insulating surface is gradually decreased by the end corona preventive layer 6 until now. As a result, the function of suppressing the creeping discharge is deteriorated, and a creeping discharge (end discharge) occurs, and finally, the defect of the end corona preventive layer or the insulating layer is eroded to cause dielectric breakdown.

In the conventional insulation diagnosis method, an AC voltage of a commercial frequency is applied to a winding formed of a plurality of coils 2 wound in a slot of an iron core 1 to measure partial discharge, and the maximum discharge charge-voltage characteristic obtained is obtained. The method of discriminating the internal discharge, the slot discharge, and the end discharge by empirically judging the tendency of the curve has been adopted.

[Problems to be solved by the invention]

FIG. 7 is a characteristic diagram showing the maximum discharge charge-voltage characteristic by the conventional method. Curve 10A shows an artificial void in the main insulating layer 4, curve 10B shows an artificial defect in the outer corona preventing layer 5, and curve 10C shows. The characteristics of the coils having artificial defects formed in the end corona preventive layer 6 are shown. Curve 10A,
Although 10B and 10C have different maximum discharge charge amounts, there is almost no difference in the tendency with respect to the applied voltage, and the maximum discharge charge amount may be reversed depending on the size of the defect. It is extremely difficult to empirically identify the partial discharge occurrence site from the curve, and there is a drawback that it is difficult to obtain a reliable diagnostic result.

Further, since the reliability of the insulation diagnosis result is low, there is a problem that the external corona is mistakenly judged to be the internal corona due to the deterioration of the main insulating layer and the winding is rewound. .

An object of the present invention is to enable localization of a partial discharge occurrence site by utilizing a new connection between the type of defect in electrical equipment insulation and the partial discharge characteristic.

[Means for solving problems]

In order to solve the above-mentioned problems, according to the present invention, a method for diagnosing an insulation abnormality by applying a high AC voltage to the insulation of a test electrical device or the like to detect a partial discharge is used. Voltage and a low-frequency alternating voltage of several Hz or less, preferably a few minutes of −Hz or less, and each partial discharge pulse is measured according to its positive or negative polarity. The frequency of the applied voltage, the presence or absence of partial discharge detection, and the partial discharge pulse are measured. The partial discharge occurrence site is determined by collating the combination condition of the discharge pulse polarities with the combination condition determined in advance for each insulating partial discharge occurrence site.

[Action]

The method of the present invention is a process of measuring the maximum discharge charge amount-voltage characteristics of a high voltage rotating electric machine coil having an artificial defect by changing the frequency of the applied voltage from a commercial frequency (50 Hz, 60 Hz) to a low frequency region of about 0.01 Hz. The characteristics obtained by applying an AC voltage of a commercial frequency were created based on the peculiarities of the above-mentioned characteristics found in 1. As described above with reference to FIG. 7, a void was formed in the main insulating layer. Partial discharge is detected in both the coil (internal discharge), the coil with a defect in the outer corona prevention layer (slot discharge), and the coil with a defect in the end corona prevention layer (end discharge), and both positive and negative polarities are detected. Although a partial discharge pulse is detected, in the low frequency region, internal discharge shows almost the same characteristics as commercial frequency voltage, whereas slot discharge has positive polarity. Negative pulse is detected only pulse is not detected, the end discharge is not detected in both the positive and negative bipolar pulse, can result a difference in low frequency partial discharge characteristics revealed by partial generation site. The present invention makes it possible to locate a partial discharge occurrence site, which was almost impossible in the past, by utilizing the combination condition of the above frequency and positive / negative polarity discharge pulse for locating the defect type (partial discharge occurrence site) of insulation diagnosis. It is the one. As a concrete means, a commercial frequency AC voltage and a low frequency AC voltage of several Hz or less, preferably a few minutes of −Hz or less are applied to the electrical equipment under test, and the partial discharge pulses are measured according to their positive and negative polarities. By matching the combination conditions of the presence / absence of positive / negative partial discharge pulse and frequency with the combination condition determined in advance for each partial discharge occurrence site, the combination corresponding to the partial discharge occurrence site for each target electric device If the conditions are known in advance, it is possible to determine the partial discharge occurrence site of the electrical equipment under test by comparing the combination conditions with the measurement results.
Further, since the orientation of the partial discharge starting portion is determined not by comparing the magnitudes of the maximum partial discharge charges but by the presence or absence of the detection of the partial discharge charges, erroneous determinations based on empirical determination errors of the monitoring engineer are avoided, Reliable orientation results are obtained.

Example of Invention

 The method of the present invention will be described below based on examples.

FIG. 1 is a principle structural diagram showing a partial discharge measuring circuit in the method of the present invention. A test piece 100 such as a high voltage rotating electric machine is shown.
High-voltage power supply 11 for applying an alternating voltage of variable frequency to the capacitor, a coupling capacitor 12 connected in parallel to the sample, and a partial discharge measuring instrument 1 provided on the ground potential side of the coupling capacitor 12.
3 and a monitor 14 for measurement data.
As the high-voltage power supply 11, a high-voltage transformer having a fixed commercial frequency (50 Hz or 60 Hz) is generally used. Here, a variable frequency high-voltage power supply is used to measure the frequency characteristic of partial discharge. As the frequency variable high voltage power source 11, the method of making a sine wave by program control combining positive and negative DC high voltages is the simplest (see JP-A-60-219965), and the variable frequency range is about 0. 0.01 to 100 Hz.
However, a commercial frequency power source and a low frequency power source may be used separately. As the partial discharge detector 13, a commercially available tuned corona measuring device, or a peak hold type corona measuring device or a partial discharge measuring device having a storage device such as a digital memory because the interval of partial discharge pulse generation becomes long in a low frequency region. Used.

In the partial discharge measuring circuit configured as described above, when the voltage supplied from the high-voltage power supply to the winding of the high-voltage rotating electric machine as the test piece 100 is gradually increased, the test piece including the defect will be defective. Partial discharge is generated from the part, and a partial discharge pulse 101 indicated by a solid line arrow and a partial discharge pulse 102 indicated by a broken line arrow in the closed loop of the partial discharge pulse formed by the test object 100 and the coupling capacitor 12 in opposite directions. It is detected by the flow partial discharge measuring instrument 13 and observed by the monitor 14. Here, the partial discharge pulse 101 directed in the direction of the solid arrow is defined as a positive polarity pulse, and the reverse partial discharge pulse 102 is defined as a negative polarity pulse.

Next, an AC high voltage with a constant voltage and varying frequency was applied to a rotating electrical machine coil in which an air gap was intentionally formed in the ground main insulating layer, and the maximum discharge charge-frequency characteristic was measured. As a result, as shown in FIG.
Both the A and the negative polarity internal discharge pulse 102A generate a discharge pulse with a maximum discharge charge amount of 1000 Pc over a wide frequency range from several tens Hz to 0.01 Hz, and a significant difference between the commercial frequency and the low frequency region of several Hz or less I was not able to admit.

FIG. 3 is a maximum discharge charge amount-frequency characteristic diagram obtained by applying the same voltage as the above to a rotating electric machine coil having the same rating as the above, in which the external corona prevention layer is intentionally provided with a missing portion, Although the maximum discharge charge amount of the slot discharge pulse 101B is several ten times larger than that of the internal discharge pulse 101A, the change of the discharge charge amount with respect to the frequency is small. On the other hand, although the negative polarity slot discharge pulse 102B is generated in the commercial frequency region of several Hz or higher, it is not detected in the low frequency region of 1 Hz or lower, showing a characteristic tendency that can be easily distinguished from the characteristic of the internal discharge pulse.

FIG. 4 is a characteristic diagram of an end discharge pulse obtained for a coil having a defect in the end corona preventive layer.
In the low frequency region below z, the positive end discharge pulse 10
Neither 1C nor the negative polarity end discharge pulse 102C was detected, showing a characteristic tendency that could be easily discriminated from the internal discharge pulse and the slot discharge pulse.

FIG. 5 shows the result of summarizing the combination conditions of the presence / absence of positive and negative bipolar pulses and the frequency in the characteristic diagrams shown in FIGS. 2 to 4 by defect type (partial discharge occurrence site),
By comparing the presence / absence of positive / negative bipolar pulses obtained by applying the low-frequency AC voltage with each other, it is possible to easily discriminate the partial discharge occurrence site. Therefore, first, a commercial frequency AC voltage is applied to the test piece to determine the occurrence of partial discharge and its applied voltage, and a low frequency AC voltage of the same voltage value is applied to check for the presence of positive / negative bipolar discharge pulses. By comparing with the combination conditions shown in FIG. 5, the partial discharge occurrence site of the sample can be easily located. Further, since the orientation is performed depending on whether or not the partial discharge pulse in the order of several thousand Pc is detected, compared to the conventional method of empirically discriminating the partial discharge occurrence site from the difference in the magnitude of the partial discharge charge at the commercial frequency. Much more reliable orientation results are obtained.

Although the embodiment has been described by taking the case of the rotary electric machine coil as an example, the high voltage conductor is also enclosed in other solid insulation type electric devices such as a resin mold transformer, a resin mold bushing, and a plastic insulated power cable. The main insulating layer has a common insulating structure in that it has a main insulating layer and a ground metal portion arranged outside the main insulating layer, and the electrical insulation diagnosis method according to the present invention can be effectively used.

〔The invention's effect〕

As described above, the method of the present invention applies a commercial frequency AC voltage and a low frequency AC voltage of several Hz or less, preferably -min. It was constructed so that the partial discharge occurrence site could be determined by finding the combination condition and comparing it with the prepared combination condition for each partial discharge occurrence site. As a result, the location of the partial discharge can be determined depending on the presence or absence of the partial discharge pulse, so that it is possible to achieve a significantly more reliable orientation than the conventional method based on the difference in the maximum partial discharge charge, and the insulation diagnosis engineer's experience It is possible to provide an electrical insulation diagnosis method that eliminates the need for judgment and is therefore easy to carry out and has high orientation accuracy. In addition, since it is possible to grasp the insulation abnormality for each defect, it becomes possible to accurately identify the life expectancy, and it is possible to grasp the planned repair plan and the repair contents. A long repair period and economic burden are eliminated, and a high preventive maintenance effect can be obtained. In particular, in rotating electrical machines using resin-based insulated coils, it is possible to clearly distinguish defects in the external corona prevention layer and end corona prevention layer, which have a large effect on the remaining life, from the occurrence of voids due to deterioration of the main insulating layer. The relatively light repair of repairing the corona preventive layer has the advantage of significantly extending the remaining life of the rotating electric machine.

[Brief description of drawings]

FIG. 1 is a principle configuration diagram of a partial discharge measuring circuit for explaining an embodiment method, and FIGS. 2, 3, and 4 show a rotary electric machine coil having an artificial defect which differs depending on the embodiment method. Fig. 5 shows the maximum discharge charge-frequency characteristic diagram obtained from Fig. 5, Fig. 5 shows the combination conditions for each partial discharge generation site obtained from Fig. 2, Fig. 3, and Fig. 4, and Fig. 6 shows the crushing of a rotating electric machine coil. FIG. 7 is a cross-sectional view and FIG. 7 is a maximum discharge charge-voltage characteristic diagram by the conventional method. 1 ... Iron core, 2 ... Coil, 3 ... Adjustable coil conductor, 4 ... Main insulating layer against ground, 5 ... External corona prevention layer, 6 ... End corona prevention layer, 11 ... High voltage power supply, 12 ... Coupling capacitor, 13
... Partial discharge measuring instrument, 100 ... Specimen, 101 ... Positive discharge pulse, 102 ... Negative discharge pulse.

Claims (5)

[Claims] 1. A method for diagnosing an insulation abnormality by applying a high AC voltage to the insulation of a test electrical device or the like to detect a partial discharge, in a commercial frequency AC voltage and several Hz or less, preferably several. Applying a low-frequency AC voltage of 1 Hz or less and measuring partial discharge pulses for each positive and negative polarity,
Characterizing the combination of the frequency of the applied voltage, the presence / absence of partial discharge detection, and the polarity of the partial discharge pulse with the combination condition determined in advance for each partial discharge occurrence part of the insulation to locate the partial discharge occurrence part Electrical insulation diagnosis method. 2. The method according to claim 1, wherein the electric device under test is a high-voltage rotating electric machine, and an outer corona formed on the surface of the ground main insulating layer of the coil housed in the iron core slot. A method for diagnosing electrical insulation, comprising an anti-corrosion layer and an anti-corona prevention layer. 3. The method according to claim 1 or 2, wherein when the predetermined combination condition is a partial discharge under each frequency condition and each positive and negative polarity condition, it is determined to be an internal partial discharge of the ground main insulating layer. A method for diagnosing electrical insulation, characterized in that 4. The method according to claim 2, wherein the predetermined combination condition is a low-frequency negative polarity condition and there is no partial discharge, and there is a partial discharge under other conditions except the above conditions. A method for diagnosing electrical insulation, characterized in that it is determined as slot discharge based on layer abnormality. 5. The method according to claim 2, wherein the predetermined combination condition is low frequency condition without partial discharge and commercial frequency condition with partial discharge. End due to abnormality of end corona preventive layer. A method for diagnosing electrical insulation, characterized in that it is judged as discharge.