JPH01153975A - Monitoring method for insulation deterioration of rotating machine coil - Google Patents

Abstract

PURPOSE:To previously preclude a dielectric breakdown accident by inspecting the electrostatic capacity of the insulating layer of a rotating machine coil and detecting remaining dielectric strength from the quantity C''/C' of variation in electrostatic capacity C'' measured by using a couple of measured frequencies to the electrostatic capacity C'. CONSTITUTION:The insulating layer 2b of the high-voltage rotating machine coil 2 is formed of mica and resin. In this state, the electrostatic capacity of the insulating layer 2b between a conductor 2a and a model slot 1 is measured to obtain a constant value shown by a prescribed expression. Here, when the high-voltage rotating machine is used for a long time, composite stress is applied to the insulating layer 2b, a void and a cavity part 3 for control, etc., are produced between mica tapes in the insulating layer 2b and the conductor 2a and insulating layer 2b. The specific dielectric constant epsilon' of this cavity part 3 is nearly 1, so the electrostatic capacity of the insulating layer 2b at the time of deterioration is different from the value in the initial state. The deterioration like this causes the insulating layer 2b to decrease in dielectric strength and makes it difficult to absorb moisture.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for monitoring insulation deterioration of rotating machine coils, and is intended to enable easy and accurate detection of insulation deterioration.

B1 Summary of the Invention The present invention applies the phenomenon that when the insulating layer of a deteriorated coil absorbs moisture, the capacitance of the insulating layer becomes frequency dependent, and that the capacitance changes depending on the measurement frequency, and calculates the rate of change. Through measurement, the deterioration and moisture absorption ratio can be ascertained and the remaining breakdown strength of the insulating layer can be estimated.

C1 Conventional technology High-voltage rotating machines tend to be smaller and lighter, and their operating temperatures and operating voltages are increasing. Therefore, in order to ensure the long life of the equipment, high reliability is required for the insulation of rotating machine coils.

In high-voltage rotating machines, during operation, in addition to electrical stress, there is thermal stress due to the temperature rise of the conductor.

Combined stress, including thermal stress due to heat cycles associated with startup and shutdown, and mechanical stress due to vibration and bending, is applied to the coil's insulating layer.

D. Problems to be Solved by the Invention From the viewpoint of improving reliability, it is necessary to understand the deterioration state of the coil insulating layer during long-term operation and prevent dielectric breakdown from occurring. However, in the past, there was no means for easily and accurately detecting the state of deterioration. Conventionally, countermeasures have been taken such as warming up the rotary machine with a heater before starting operation to remove moisture that can cause insulation breakdown accidents.

In view of the above-mentioned circumstances, the present invention provides insulation deterioration monitoring that measures the nondestructive characteristics of a high-voltage rotating machine during operation, performs insulation deterioration diagnosis, grasps the deterioration state of the insulating layer, and estimates the remaining strength. The present invention provides a method.

E. Means for Solving Problems The present invention for monitoring insulation deterioration described above inspects the capacitance of the insulating layer of a rotating machine coil, and calculates the capacitance C measured using a certain measurement frequency after the coil deteriorates and absorbs moisture. The method is characterized in that the remaining breakdown strength is detected from the value of the rate of change -C' of the capacitance C' measured using another measurement frequency C' with respect to '.

F example First, the basic principle of the present invention will be explained.

As shown in FIG.
When the rotating machine coil 2 was attached to the , and the conductor 2a and the model slot 1 were used as detection electrodes, the capacitance of the insulating layer 2b was tested using a bridge circuit.

It was found that the capacitance differs depending on the state of deterioration and moisture absorption. This will be explained next.

The insulating layer 2b of the high-voltage rotating machine coil 2 is made of mica and resin, and in the initial state immediately after manufacturing, the mica and resin are tightly integrated, so there is no possibility that it will have a negative impact on the insulation properties and lifespan. No peeling or voids occur inside the insulating layer 2b, and no moisture absorption occurs. Therefore, the dielectric breakdown strength is also large. In this initial state (see Fig. 2(a)), the conductor 2
When the capacitance of the insulating layer 2b between a and the model slot 1 was measured, it showed a certain constant value as shown in the following equation.

C= -X 8.855 X 10-" [F] ・
...(1) However, C: Capacitance in the initial state ε: Relative permittivity of the insulating layer 2b in the initial state (ε〉〉1) S: Area of the detection electrode (area of the inner groove of the model slot 1) d: Insulating layer (between conductor 2a and model slot) When a high-voltage rotating machine is used for a long period of time, the above-mentioned complex stress is applied to the insulating layer 2b, causing deterioration. A void 3 such as a void or peeling occurs between the insulating layer 2b and the insulating layer 2b (see FIG. 2(b)). Since the relative permittivity ε' of the cavity 3 is approximately 1, the capacitance of the insulation 52b when deteriorated differs from the value in the initial state. If such deterioration occurs, the insulating layer 2b will fail.
The yield strength decreases and moisture absorption becomes more likely. Furthermore, even during deterioration when the absolute R proof strength decreases, moisture evaporates during operation due to the rise in temperature caused by the heat of the conductor 2a, and moisture absorption does not occur. Therefore, when we measured the capacitance after deterioration and when no moisture was absorbed, we found the following equation.

However, C1: Capacitance ε when not absorbing moisture after deterioration,: Relative permittivity of the insulating layer 2b (including voids) when not absorbing moisture after deterioration ε〉ε 〉〉ε′=1 If the operation is stopped in a deteriorated state The insulating layer 2b absorbs moisture, and when it absorbs moisture, the dielectric strength of the insulating layer 2b decreases significantly. If operation is started in such a deteriorated and moisture-absorbed state, there is a high risk of an insulation breakdown accident. The relative permittivity of the entire frame edge layer 2b is the relative permittivity ε2 at the time of moisture absorption (see FIG. 2(e)).
is larger than the relative dielectric constant ε when moisture is not absorbed. Therefore, when we measured the capacitance after deterioration and during moisture absorption, we found the following equation.

However, C2: Capacitance when the film is wet after deterioration (C2>C,) C2: Relative dielectric constant of the insulating layer 2b when the film is wet after deterioration (C2>C,
1) It has been found that the capacitance of the insulating layer 2b that has further deteriorated and absorbed moisture shows frequency dependence, and that the capacitance changes depending on the measurement frequency.

Experimental data on this frequency dependence is shown in FIG. In this experiment, the frequency characteristics of the capacitance in the normal state before moisture absorption and the frequency characteristics of the capacitance after moisture absorption were measured using an impedance measuring device over the range of 70H2 to IOMH for the coil that had deteriorated due to complex stress. It was measured. From the measurement data, especially when deterioration and moisture absorption occurs,
It has been found that the capacitance increases and frequency dependence appears on the relatively low frequency side below KH2.

Next, each coil with different residual fracture strength is allowed to absorb moisture, and the first
The measurement frequency was 1000 H2 using the experimental equipment shown in the figure.
The capacitance at C4°. . When the capacitance C12° was examined at a measurement frequency of 120 H2, the characteristics were as shown by the solid line in FIG.

It can be seen that the residual fracture strength decreases as the strength increases.

I know what will happen. Note that E is the rating (KVI) of the rotating machine, and the proof strength (2E + 1) KVlf is based on the "Generator Winding Insulation Deterioration Judgment Criteria" (Report & 67001) of the Central Research Institute of Electric Power Industry, which is adopted by electric power companies and manufacturers. It is compliant.

Capacitance using an actual SKV class turning machine. From this, it is possible to track the frequency characteristics of capacitance in actual rotating machines, and determine, for example, that the capacitance is at a certain point. Dielectric breakdown accidents can be prevented.

G. Detailed Description of the Invention As described above, according to the present invention, residual dielectric strength can be easily and accurately detected from the value of the rate of change of frequency characteristics of capacitance, and dielectric breakdown accidents can be prevented.

[Brief explanation of the drawing]

Figure 1 is a perspective view showing an example of measuring the capacitance of a rotating machine coil, Figure 2 (a) is a sectional view showing various states of the insulating layer, and Figure 3 is a cross-sectional view showing various states of the insulating layer. Figure 4 is a characteristic diagram showing the relationship between capacitance and frequency, and Figure 4 is a characteristic diagram showing the relationship between residual breakdown strength and the rate of change in the frequency characteristics of capacitance.In the diagram, 1 is a model slot) 2 is a rotating machine 2a is a conductor, 2b is an insulating layer, and 3 is a gap.

Claims (1)

[Claims] The capacitance of the insulating layer of the rotating machine coil was inspected, and the rate of change in capacitance C'' measured using another measurement frequency with respect to the capacitance C' measured using a certain measurement frequency after the coil deteriorated and absorbed moisture. A method for monitoring insulation deterioration of a rotating machine coil, characterized by detecting residual breakdown strength from the value C″/C′.