CN100447575C - Method for identifying abnormal conditions in power transformers - Google Patents

Abstract

A preferred method for identifying an anomaly in a power transformer insulation system includes: measuring dielectric loss in a region of the insulation system; calculating a theoretical dielectric loss for the region based on material properties, geometry, and temperature of the region; and generating the measured Graphical representation of the percent difference between and calculated dielectric loss. The preferred method further includes comparing the shape of the graphical representation to one or more other one or more percentage differences between measured and theoretical dielectric losses within the insulation region known to have a particular type of anomaly.

Description

Method for identifying abnormal conditions in power transformers

This application claims priority under 35 U.S.C §119(e) to U.S. Provisional Patent Application No. 60/369,671, filed April 3, 2002, which is incorporated herein by reference in its entirety.

field of invention

The present invention relates to power transformers, and more particularly to methods for identifying abnormal conditions in power transformers.

Background of the invention

Power transformers typically include insulating material between or around the various conductive paths. Insulation is usually made of paper or cellulose material. Mineral oil is also commonly used as an insulator in power transformers.

Defects or other abnormalities in the insulation material of power transformers can degrade the performance of power transformers and, in extreme cases, can lead to dangerous accidents. For example, moisture and contamination can degrade the insulating performance of oil, paper and cellulose insulation. The performance of an insulator is also degraded if it is exposed to a voltage higher than its rated voltage. In addition, defects such as breaks, voids and other cracks, as well as excessive moisture and carbon stains can degrade the performance of paper and cellulose insulation. The insulating properties of oil can be reduced due to aging, overheating or chemical contamination.

Because of the importance of insulation materials to the overall performance of power transformers, diagnostic inspections of power transformer insulation are often performed. For example, the effectiveness of insulation in new or recently refurbished power transformers is often assessed before the power transformer is put into service. Also, the insulation of power transformers in the art is often periodically inspected in order to ensure that the insulation is functioning in a satisfactory manner.

Most commonly used diagnostic checks for power transformer insulation are suitable for identifying abnormalities such as the occurrence of defects in the insulation system. For example, the so-called "power factor test" defined by the American National Organization for Standardization (described in detail below) is often used for diagnostic checks (the power factor test is essentially the same as the so-called "tan-delta" test). Although diagnostic tests such as power factor tests can indicate the presence of an abnormal condition, such examinations often fail to indicate the type of abnormal condition that has occurred.

Identifying specific types of abnormal conditions often requires draining and at least partial disassembly of the power transformer. For example, excessive resistance in the power transformer core ground circuit is sometimes misdiagnosed as excessive moisture in the power transformer cellulose insulation. In other words, currently used diagnostic tests are able to recognize the presence of these types of abnormalities, but often cannot differentiate them. As a result, power transformers are sometimes subject to time-consuming and expensive drying processes based on false information that there is excessive moisture in the insulation of the power transformer.

Therefore, there is a need for a diagnostic method capable of identifying the occurrence of an abnormal condition in a power transformer insulation system as well as identifying the type of abnormal condition.

Summary of the invention

A preferred method for identifying an anomaly in a power transformer insulation system includes: measuring dielectric loss in a region of the insulation system; calculating the theoretical dielectric loss of the region based on material properties, geometry, and temperature of the region; and generating the measured and Graphical representation of the percent difference between calculated dielectric losses. The preferred method further includes comparing the shape of the graphical representation to one or more other one or more percentage differences between measured and theoretical dielectric losses within the insulation region known to have a particular type of anomaly.

A preferred method includes: measuring a dielectric frequency response in an insulating region of a power transformer; calculating a theoretical dielectric frequency response for the region; and generating a dielectric frequency response signature for the region. The preferred method further includes comparing the dielectric frequency response signature to dielectric frequency response signatures of other insulating regions known to have a particular type of anomaly.

A preferred method for classifying a type of abnormal condition within an insulating region of a power transformer comprising: energizing conductors isolated from the insulating region with an alternating voltage; varying the frequency of the alternating voltage between a plurality of discrete frequencies within a predetermined range; and The dielectric loss in the insulating region is measured at each of the discrete frequencies.

The preferred method further comprises calculating a theoretical dielectric loss for the insulating region at each of the discrete frequencies; calculating a percentage difference between the measured dielectric loss and the theoretical dielectric loss at each of the discrete frequencies; and A substantial graphical representation of the percent difference between the measured dielectric loss and the calculated dielectric loss is produced at each. The preferred method further includes comparing the substantially curvilinear shape to one or more predetermined curvilinear shapes of the percentage difference between measured and calculated dielectric losses for insulating regions known to have particular shape anomalies.

Another preferred method comprising: measuring dielectric loss in the region of the power transformer insulation system in response to an alternating voltage varying within a predetermined range of frequencies; calculating a theoretical dielectric loss for the region based on material properties, geometry, and temperature of the insulating region ; and yields a representation of the percentage between the measured and calculated dielectric loss. The preferred method further includes determining whether the shape of the representation is substantially different from the representation of the percentage difference between the measured and calculated dielectric loss in another pre-identified insulating region having a particular type of anomaly.

Another preferred method for identifying an anomaly within a power transformer insulation system comprises: measuring dielectric loss in a region of the insulation system; calculating a theoretical dielectric loss for the region; Theoretical dielectric loss has anomalies when identifying regions. The preferred method further includes generating a graphical representation of the percentage difference between measured and calculated dielectric loss; and comparing the shape of the graphical representation to measurements and theory in one or more other insulating regions known to have a particular type of anomaly The shape of one or more graphical representations of the percentage difference between dielectric losses.

Another preferred method comprises: measuring a dielectric frequency response of an insulating region within a power transformer; calculating a theoretical dielectric frequency response of the region; and identifying a region when there is an anomaly by comparing the measured dielectric response to the theoretical dielectric response. The preferred method further includes generating a dielectric frequency response signature for the zone; and comparing the dielectric frequency response signature to dielectric frequency response signatures of other zones of the insulation system known to have a particular type of anomaly.

Description of drawings

The foregoing Summary, as well as the following Detailed Description of the Preferred Embodiments, will be better understood with reference to the accompanying drawings. For the purpose of illustrating the invention, the drawings show a presently preferred embodiment. However, the invention is not limited to the specific instrumentalities disclosed in the drawings. In the attached picture:

Figure 1 is a flowchart of a preferred method for identifying an abnormal condition in a power transformer insulation system;

Figure 2 is a schematic diagram of a power transformer capable of incorporating the method shown in Figure 1;

Figure 3 is a simplified illustration of the insulation system of the power transformer shown in Figure 2;

Figure 4 depicts a series of dielectric frequency response signatures for an isolated region from a power transformer, where the dielectric frequency response signatures correspond to different values of resistance in the transformer core ground circuit;

Figure 5 depicts the dielectric frequency response signature for the insulating region before and after correction for anomalous conditions affecting the insulating region;

Figure 6 depicts the first dielectric frequency response signature from an isolated region of a first transformer with a higher than normal core-to-ground resistance, and the second dielectric frequency response from an isolated region of a second transformer with a normal core-to-ground resistance sign;

Figure 7 depicts a dielectric frequency response signature for an insulating area with higher than normal levels of humidity; and

Figure 8 depicts the dielectric frequency response signature of an insulating region exhibiting chemical contamination.

Description of the preferred embodiment

A preferred method 10 for identifying anomalies, such as defects, in a power transformer insulation system is partially depicted in FIG. 1 . The method 10 will be described in conjunction with the conventional power transformer 50 depicted in FIG. 2 . Specific details relating to power transformer 50 are shown for exemplary purposes only, and method 10 may be used with virtually any type of power transformer.

The power transformer 50 includes a magnetic core 52 having a leg 52a (the magnetic core 52 includes other legs, not shown in FIG. 1 ). The transformer 50 also includes a low voltage coil 56 surrounding the stem 52 a, and a high voltage coil 54 surrounding the low voltage coil 56 . The magnetic core 52 , the high-voltage coil 54 and the low-voltage coil 56 are housed within the housing 60 . It should be noted that transformer 50 is schematically depicted in FIG. 1 . The various components of transformer 50 are not shown in FIG. 1 , and the spaces between some components are shown exaggerated in FIG. 1 for clarity.

The magnetic core 52 and the high and low voltage coils 54 , 56 are housed in a sealed casing 60 . The high voltage coil 54 is electrically connected to an AC power source (not shown) through a high voltage bushing 62 mounted on the housing 60 . Each high voltage bushing 62 includes wires that pass through the housing 60 and are capable of conducting electrical current. Each high voltage bushing 62 also includes a ceramic ring capable of sufficiently isolating the shell 60 from the wires and sealing the gap between the shell 60 and the wires.

The low voltage coil 56 is electrically connected to a load (not shown) through a low voltage bushing 64 mounted on the housing 60 . Each low voltage bushing 64 includes a wire capable of conducting electrical current through the housing 60 . Each low-voltage bushing 64 also includes a ceramic ring capable of sufficiently isolating the housing 60 from the wires and sealing the gap between the housing 60 and the wires.

Housing 60 is the common ground connection for transformer 50 . Magnetic core 52 is connected to housing 60 at a single location. More specifically, the magnetic core 52 is connected to the housing 60 by a cable 82 that contacts the outer surface of the housing 60 . The cable 82 extends out of the housing 80 through a core ground bushing 83 attached to the outer surface of the housing 60 . The magnetic core ground bushing 83 includes a magnetic ring capable of sufficiently isolating the housing 60 from the cable 82 and sealing the gap between the housing 60 and the cable 82 . Alternatively, the cable 82 may be affixed directly to the inner surface of the housing 60 .

The high voltage coil 54 is energized by an AC voltage from an AC power source. The AC voltage creates a magnetic flux within the magnetic core 52 . The magnetic flux is proportional to the number of turns of the high voltage coil 54 . Magnetic flux cuts through the low voltage coil 56 and generates a voltage within the low voltage coil 56 proportional to the number of turns of the low voltage coil 56 .

The transformer 50 includes insulating material to electrically isolate the various metallic elements inside the transformer 50 from each other. For example, the transformer 50 includes a barrier 74a and a spacer 72a between the high and low voltage coils 54,56. Barrier 74a and spacer 72a are formed of solid insulating material, such as cellulose laminate or paper, and serve to isolate high voltage coil 54 from low voltage coil 56 .

The transformer 50 also includes a barrier 74b and a spacer 72b between the low voltage coil 56 and the magnetic core leg 52a. The potential barrier 74b and the spacer 72b are used to isolate the low voltage coil 56 and the magnetic core 52 . The transformer 50 also includes a spacer 72c for isolating the magnetic core 52 and the casing 60 . The transformer 50 also includes a potential barrier 74c for isolating the high and low voltage coils 54 , 56 from the housing 60 .

Insulation barriers and spacers are also located between other grounded elements of the transformer 10 .

The casing 60 of the transformer 50 is filled with an insulating liquid such as mineral oil 76 . Mineral oil 76 acts as an insulating and cooling medium within housing 60 . Thus, for example, high and low voltage coils 54 , 56 as well as barrier 74 a and spacer 72 a may be isolated by mineral oil 76 .

Each of the high and low voltage coils 54, 56 has their own internal insulation system formed of a solid material such as cellulose pressboard or paper and an insulating liquid such as mineral oil.

The insulation system of the power transformer 50 (including the internal and external structure of the insulation system) is shown in a simplified schematic form in FIG. 3 .

Specific details concerning method 10 are as follows. Method 10 includes identifying the occurrence of an abnormal condition in the insulation system of power transformer 50 , and the general location of the abnormal condition. This is accomplished by isolating discrete regions of the insulation system within the power transformer 50, and inspecting each isolated region under a set of controlled conditions (steps 12, 13 and 14 in Figure 1). More specifically, individual nodes within the insulation system may be grounded or guarded to isolate node-to-node or node-to-ground regions within the insulation system so that the dielectric loss of each of these regions can be measured. For example, the magnetic core 52 or the high voltage bushing 62 or the low voltage bushing 64 in the power transformer 50 may be guarded to isolate various areas of the insulation system. As a specific example, the insulation area between the high voltage coil 54 and ground can be isolated by providing a shield for the low voltage coil 56 .

Inspection of each isolation area of the insulation system can be accomplished using conventional techniques generally known to those skilled in the art in power transformer insulation system design. For example, the power factor test determined by the American National Standards Organization mentioned above can be used as a check. A power factor test can be performed on an isolated area by placing an AC voltage of eg 10000v on a node or terminal at each end of the area. In other words, a voltage is applied across the wires, such as the high voltage coil 54, separated by the isolation area of the insulation system. The applied voltage typically has a frequency approximately equal to the power supply frequency of the power transformer 50, for example 60 hertz. The resulting capacitive current flowing through the insulation system, and the phase angle between the applied voltage and current can then be measured.

The power factor in the isolated region of an insulation system can be obtained by calculating the cosine of the phase angle between the voltage and current, which represents the dielectric loss (or "tan-delta") there. The power factor is compared with a predetermined value to determine whether there is an abnormal condition in the area. For example, a power factor greater than 0.005 or 0.5% indicates an abnormal situation.

Alternatively, the inspection for anomalies can be carried out by frequency-domain dielectric spectroscopy, that is, by measuring the dielectric loss in isolated regions of the insulation system when the frequency of the applied voltage is set to various values within a predetermined range, i.e., between approximately 0.01 hertz and 1000 hertz . The resulting graphical representation (typically a curve) of "dielectric loss versus frequency for a particular region" is hereinafter referred to as the "dielectric response" of the region.

Dielectric loss can be quantified based on the applied voltage, the measured current, and the measured phase angle between the applied voltage and the measured current, using conventional techniques for power transformer insulation system design known to those skilled in the art. A suitable device for generating the input voltage and measuring the resulting current and phase angle is available from General Electric Company, model no. IDA200. The dielectric response obtained from the measured voltage, current and phase angle for a particular region is hereinafter referred to as the "measured dielectric response" for that region.

The measured dielectric response is compared to the calculated dielectric response for the corresponding region of the insulation system to determine if an anomaly exists in that region. The calculated dielectric response is a theoretical representation of the dielectric response in regions where no anomalies exist. The calculated dielectric response is based on the material properties and geometry of the insulating material in the zone (including the material properties of any oil that acts as an insulating material in the zone). Calculating the dielectric response is also based on the temperature of the insulating material when the measured dielectric response was obtained.

The theoretical dielectric loss was calculated for each frequency at which the dielectric loss was measured based on the above factors using conventional techniques for power transformer insulation system design generally known to those skilled in the art. Calculate the dielectric response curve representing these values as a function of frequency.

A deviation between the measured and calculated dielectric responses greater than a predetermined amount indicates the presence of an anomaly within the corresponding region of the insulation system and thereby provides an indication showing the approximate location of the anomaly.

It should be noted that the above tests for determining the presence and approximate location of abnormalities are described for exemplary purposes only, and that other types of diagnostic tests may also be used in the context of these specific tests.

After identifying the occurrence and approximate location of the abnormal condition, ie after having identified the area of the insulation system with the abnormal condition (step 16 ), the type of the abnormal condition is identified. More specifically, a graphical representation (typically a curve) showing the deviation between the measured and calculated dielectric responses is generated (step 18). This graphical representation is referred to below as the "dielectric frequency response signature" or "DFR signature" of the corresponding region.

The DFR signature is generated by subtracting the calculated dielectric loss at each sampling frequency from the measured dielectric loss at the corresponding frequency. Divide the difference between the calculated and measured dielectric losses at each frequency by the calculated dielectric loss at that frequency and multiply by 100. The sum of these values is plotted as a function of frequency to represent the DFR signature. In other words, the DFR signature is a normalized signature function that tends to vary within the normal dielectric loss frequency spectrum of the insulation system.

Subsequently, the DFR signature is compared with other DFR signatures to determine the type of anomaly that occurred within the test area (step 20). Applicants have discovered that particular types of anomalies are often DFR signatures with unique or distinctive characteristics. A "library" or database of each DFR signature corresponding to a particular type of anomaly can be obtained from DFR signatures of power transformers with known anomalies or assembled from laboratory tests.

Comparing DFR signatures from regions of power transformers 50 with abnormal conditions with DFR signatures in the database can simplify the identification of the type of abnormal conditions occurring in the region. In other words, matching the contours of the DFR signature of the test area with the contours of the reference DFR signatures corresponding to known anomalies can simplify the identification of the anomalies (steps 22, 24). Conversely, if no matching of the profile of the DFR signature of the test area with the profile of the reference DFR signature can be obtained, the type of anomaly cannot be identified (step 25) (it should be noted that the DFR signature varies with the geometry of the corresponding area. Thus, The reference DFR signature must correspond to the geometry of the particular area of the insulation system being evaluated).

The above steps can be repeated until the abnormal conditions of all areas of the insulation system in the power transformer are checked (step 26).

Method 10 may be performed as an inspection on a newly manufactured, newly repaired, or newly refurbished power transformer such as power transformer 10 . The method 10 can also be performed as a daily inspection when the power transformer 10 is in use, that is, when the power transformer 10 is installed in a field operation location. Furthermore, method 10 may be performed after the occurrence of an abnormal condition is identified using standard power factor tests or indeed other types of diagnostic tools in order to classify the specific type of abnormal condition.

Typically, other types of diagnostic tests for power transformers such as power transformer 50 can identify the presence of an abnormal condition, but cannot distinguish the specific type of abnormal condition. The method 10 is capable of identifying specific types of abnormal conditions, and in particular can be performed without dismantling the power transformer 50 and draining the insulating oil of the power transformer 50 . Method 10 is particularly advantageous when a power transformer 10 is used. More specifically, by simplifying the identification of specific types of abnormal conditions, method 10 can prevent unnecessary removal and disassembly of transformer 10 when the abnormal conditions are of a type that can be corrected in situ. Thus, the effort, expense and downtime often associated with removing the power transformer from the operating location or disassembling the power transformer in order to diagnose an abnormal condition can be avoided by using the method 10 . Furthermore, method 10 can be performed using readily available, off-the-shelf equipment, and the time, effort, and skill required to implement method 10 is relatively low.

Furthermore, the method 10 is capable of identifying abnormalities that conventional diagnostic tests would normally misdiagnose. For example, one common cause of high power factor in transformers such as transformer 50 is excessive resistance in the core ground circuit. This particular anomaly can be caused by a higher than normal resistance between the core and the core ground bar or by a higher than normal resistance between layers in the core. Routine diagnostic tests such as power factor tests often cannot distinguish between excessive resistance in the core-to-ground circuit and moisture within the cellulose insulation of the power transformer. As a result, power transformers exhibiting high power factor due to excessive resistance in the core ground circuit can sometimes undergo unnecessary bakeout processes based on the false information that moisture is present in the transformer's cellulose insulation.

In contrast, method 10 is able to clearly identify a higher than normal resistance in the core-to-ground circuit of a transformer such as transformer 10 . For example, FIG. 4 depicts a series of experimentally determined DFR signatures for a core-ground circuit of a two-coil power transformer similar to power transformer 50 . By connecting resistors of varying resistance to the ground strip of the power transformer, the resistance of the core ground circuit is varied within a value range. The DFR signatures for the corresponding areas of the insulation system were measured with the resistance of the core ground circuit set to each of the values shown in Figure 4.

Figure 4 shows that the DFR signature at different values of the core ground resistance is substantially the same as the resistance at the low frequency input voltage. However, the profile of the DFR signature varies substantially at high frequency input voltages. More specifically, the DFR signature corresponding to each different value of resistance has a unique profile at high frequency input voltages. The specificity of the DFR signature corresponding to each value of resistance can be used to identify higher than normal resistance in the transformer core ground circuit, making it less likely to misdiagnose higher than normal resistance as an abnormality related to insulation materials.

Also, the power factor test is performed at one frequency of the input voltage, so the power factor test cannot diagnose anomalies that manifest themselves at frequencies other than the test frequency. Instead, the DFR signature is obtained over a range of input voltage frequencies, so the DFR signature is able to identify anomalies that manifest themselves at frequencies other than the single test frequency of the power factor test.

FIG. 5 depicts actual DFR signatures obtained before and after diagnosing and correcting abnormal conditions in a main transformer similar to power transformer 50 . The presence of abnormal conditions is initially detected based on high power factor readings (higher than 0.5%). Subsequently, when the inspection of the main transformer was traced back to the auxiliary transformer used in the load tap changer which is electrically grounded to the main transformer, based on the comparison between the measured DFR signature and the reference DFR signature corresponding to the high core ground resistance, abnormal conditions Identified as a higher than normal resistance in the main transformer core ground circuit.

Figure 5 depicts the DFR signature of the affected area of the insulation system measured before and after tuning the auxiliary transformer in order to reduce the high core-to-ground resistance in the main transformer. Figure 5 shows that the DFR signature before this anomaly correction has a unique profile relative to the DFR signature after repair (the profile of the DFR signature after repair is typically that particular geometrically shaped insulating region without any anomaly).

Figure 6 depicts a first dielectric frequency response signature from an isolated region of a first transformer having a higher than normal core resistance to ground. Figure 6 also depicts a second dielectric frequency response signature from an isolated region of a second transformer with normal core-to-ground resistance. As shown in Figure 6, it is clear that this particular type of condition can be identified by the unique profile of the dielectric frequency response signature of the affected area.

Figure 7 depicts a DFR signature obtained from an insulating area with a relatively higher level of humidity, and a second DFR signature obtained from an insulating area with a relatively lower level of humidity. Figure 8 depicts the DFR signature obtained from an insulating region exhibiting chemical contamination. The unique profiles of these DFR signatures are each substantially consistent with a specific type of insulation anomaly and can therefore be used to identify such anomalies in other areas of the insulation system.

It is to be understood that while the foregoing description has set forth many of the features and advantages of the invention, such disclosure is illustrative only and that changes may be made in the invention within the broad meaning defined in the appended claims, within the scope of the principles of the invention.

Claims (20)

1. a method is used for a kind of abnormal conditions of insulation system identification at power transformer, comprising:

In the area inner measuring dielectric loss of insulation system, wherein before described area inner measuring dielectric loss, isolate described zone electrically;

Theoretical dielectric loss based on the described zone of temperature computation in material behavior, geometric configuration and zone;

Produce the diagrammatic representation of the percentage difference between the measurements and calculations dielectric loss; With

Relatively the diagrammatic representation that is produced is with the predetermined reference diagrammatic representation of percentage difference between measurement and the theoretical dielectric loss, and each described predetermined reference diagrammatic representation is corresponding to specific abnormal conditions type.

2. the method for claim 1, wherein in the zone, measure dielectric loss and be included in execution dielectric frequency response test on the zone.

3. method as claimed in claim 2, wherein, be included in and carry out a plurality of power factors tests on the zone carrying out dielectric frequency response test on the zone, use the input voltage frequency that is different from the input voltage frequency that is used for other power factor test to implement each power factor test.

4. the diagrammatic representation that the method for claim 1, wherein produces the percentage difference between measurement and the theoretical dielectric loss comprises the dielectric response frequency signature that produces the zone.

5. method as claimed in claim 4, wherein, the dielectric response frequency signature that produces the zone comprises and calculates each a theoretical dielectric loss and a corresponding difference of measuring between the dielectric loss, and by calculating merchant between a described difference and the corresponding theoretical dielectric loss with described difference divided by a corresponding theoretical dielectric loss.

6. method as claimed in claim 5, wherein, the dielectric response frequency signature that produces the zone also comprises with 100 takes advantage of described merchant.

7. the method for claim 1, wherein also comprise the measurement of from database, reading in one or more known other insulating regions with particular type abnormal conditions and one or more diagrammatic representations of the percentage difference between the theoretical dielectric loss.

8. the method for claim 1, the shape of one of the measurement that the figured shape that also comprises the percentage difference between the coupling measurements and calculations dielectric loss and one or more known other insulating regions with particular type abnormal conditions are interior and one or more diagrammatic representations of the percentage difference between the theoretical dielectric loss.

9. the method for claim 1 also comprises by the theoretical dielectric loss of the measurement dielectric loss in the comparison domain with the zone, identified region when having abnormal conditions.

10. the method for claim 1, wherein, the diagrammatic representation that is relatively produced with measure and theoretical dielectric loss between the predetermined reference diagrammatic representation of percentage difference comprise determine figured shape whether and the measurement in one or more known other insulating regions with particular type abnormal conditions and the one or more figured shape of the percentage difference between the theoretical dielectric loss be different in essence.

11. the method for claim 1, wherein be included in theory of computation dielectric loss under the situation of any abnormal conditions influence in the consideration of regional not based on the theoretical dielectric loss in the temperature computation zone in material behavior, geometric configuration and zone.

12. a method is used for the type of the abnormal conditions in the transformer insulated zone of labeled power supply, comprising:

The lead that utilizes alternating voltage excitation insulating regions to isolate;

In preset range, change the frequency of the alternating voltage between a plurality of discrete frequencies;

Dielectric loss in each place's measurement insulating regions of discrete frequency wherein, was isolated described zone electrically before described area inner measuring dielectric loss;

The theoretical dielectric loss of calculating insulating regions at each place of discrete frequency;

The percentage difference of measuring between dielectric loss and the theoretical dielectric loss is calculated at each place in discrete frequency;

Each place in discrete frequency produces the essence curve representation of measuring dielectric loss and calculating the percentage difference between the dielectric loss; With

The essence curve representation that is relatively produced is represented with the measurement dielectric loss that is used for known insulating regions with particular type abnormal conditions and one or more predetermined curves of the percentage difference between the calculating dielectric loss.

13. method as claimed in claim 12 also is included in excitation wire and before other wire for power ground in this lead and the power transformer is isolated.

14. method as claimed in claim 12 also comprises by comparing and measuring at least one and the corresponding theoretical dielectric loss in the dielectric loss, identification insulating regions when having abnormal conditions.

15. method as claimed in claim 12, wherein, the frequency that changes the alternating voltage between a plurality of discrete frequencies in preset range is included in the frequency that changes alternating voltage between 0.01hertz and the 1000hertz.

16. method as claimed in claim 12 also comprises and reads the measurement dielectric loss that is used for known insulating regions with particular type abnormal conditions and the one or more predetermined curves that calculate the percentage difference between the dielectric loss represented from database.

17. method as claimed in claim 12 comprises that also coupling one of represents in the measurement dielectric loss at each place of discrete frequency and the essence curve representation that calculates the percentage difference between the dielectric loss and the measurement dielectric loss that is used for known insulating regions with particular type abnormal conditions and one or more predetermined curves of the percentage difference between the calculating dielectric loss.

18. method as claimed in claim 13 wherein, is included under the situation of considering any abnormal conditions in the insulating regions each place's theory of computation dielectric loss in discrete frequency in each place's theory of computation dielectric loss of discrete frequency.

19. a method is used for a kind of abnormal conditions of identification in the power transformer insulation system, comprising:

In the area inner measuring dielectric loss of insulation system, wherein, before described area inner measuring dielectric loss, isolate described zone electrically;

The theoretical dielectric loss of zoning;

When having abnormal conditions, the theoretical dielectric loss by measurement dielectric loss in the comparison domain and zone discerns described zone;

Produce the diagrammatic representation of the percentage difference between the measurements and calculations dielectric loss; With

Relatively the diagrammatic representation that is produced is with the predetermined reference diagrammatic representation of percentage difference between measurement and the theoretical dielectric loss, and each described predetermined reference diagrammatic representation is corresponding to specific abnormal conditions type.

20. a method comprises:

In power transformer, measure the dielectric frequency response of insulating regions, wherein, before described area inner measuring, isolate described zone electrically;

The theoretical dielectric frequency response of zoning;

When discerning described zone when dielectric response and the response of theoretical electrolyte have abnormal conditions by comparing and measuring;

Produce the dielectric frequency response signature in zone; With

Relatively dielectric frequency response signature is signed with known dielectric frequency response with other insulating regions of particular type abnormal conditions.

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