JPS6159052B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a stator coil used in rotating electric machines, etc., and particularly relates to a stator coil to which not only commercial frequency AC high voltage, but also DC high voltage and ultra-low frequency high voltage are applied. This invention relates to an improvement in the insulation part of the coil end part to prevent creeping discharge.

In the following text, unless otherwise specified, alternating current refers to alternating current at a commercial frequency of 50 to 60 Hz.

The coil end of the conventional stator coil is equipped with a low-resistance corona shield to prevent creeping discharge during alternating current dielectric strength tests conducted in accordance with the Electrical Standards Committee standard JEC-114 (1964). It has been common practice to provide an alternating current field mitigation layer on the main insulating surface, as shown in FIG. 1, in contact with the ends of the layer. In Fig. 1, 1 is a stator conductor;
2 is the main insulating layer, 3 is the low resistance corona shield layer, 4
5 is an alternating current electric field relaxation layer, and 5 is a slot. As this AC electric field relaxation layer 4, a high resistance paint or an electric field relaxation paint having non-linear resistance characteristics is used, but generally the latter has quick response to AC voltage and has good workability. It is constructed using an electric field relaxing paint that has non-linear resistance characteristics.

Next, the electric field relaxation effect of the conventional AC electric field relaxation layer 4 will be explained, taking as an example the case where the AC electric field relaxation layer 4 is made of one type of paint having nonlinear resistance characteristics. This paint is a paint containing silicon carbide, for example, and generally has voltage resistance characteristics as shown in FIG.
FIG. 3a is a block diagram of a conventional stator coil end, and the same reference numerals as in FIG. 1 indicate the same parts, so the explanation will be omitted. FIG. 3b shows a surface potential distribution on the surface of the stator coil end, and FIG. 3c shows an equivalent circuit of the stator coil end. Curve 6 in FIG. 3b shows the AC potential distribution, and curve 7 shows the DC potential distribution. In Fig. 3c, C is the capacitance per unit length corresponding to the main insulating layer 2, R is the linear high resistance per unit length corresponding to the surface of the main insulating layer 2, and R _N is the capacitance per unit length corresponding to the main insulating layer 2. is the corresponding nonlinear resistance per unit length. In addition, the distance X in the figure is measured from the coated end of the low resistance corona shield 3 toward the stator terminal, and Vs(X)
is the surface potential at distance X. Now, the AC voltage Vo corresponding to the dielectric strength test voltage is applied to the stator conductor 1.
, the surface potential Vs(X) is given by the following equation using the current i(X) flowing into the capacitance C at the position X. Here t is time.

Vs(X)=Vo-1/C∫i(X)dt (1) Here, the current i(X) flowing into the capacitance C is strongly controlled by the resistance value of the stator coil surface.
In the alternating current electric field relaxation layer 4, the surface current is controlled by the nonlinear resistance RN having the characteristics shown in FIG. If the difference between the adjacent surface potentials Vs (X) is large in this part, the resistance value will decrease as shown in Figure 2, the surface current will flow more easily, and the capacitance C will be charged quickly. The potential difference is automatically equalized. This equalization of the potential difference proceeds from the side with the smaller distance X at a speed determined by the equivalent circuit constant.

In the conventional stator coil using the above operating principle, the alternating current electric field relaxation layer 4 quickly responds to time changes in the commercial frequency, and the voltage applied to the coating material is Determining the resistance characteristics and length of application is generally done, and the third
As shown by the curve 6 in FIG. b, the potential distribution is made uniform in the alternating current electric field relaxation layer 4.

On the other hand, as the capacity of single rotating electric machines increases, the test transformers used for AC dielectric strength tests have become larger.
Furthermore, as voltages become higher, stator coil terminal processing, which is performed only during testing, has also become more complicated. Against this background, testing methods using alternating current, direct current, or ultra-low frequency voltage as the voltage for dielectric strength tests are being considered, and some are beginning to be implemented. Although global standards are currently under consideration, switching from alternating current to direct current is a worldwide trend. The breakdown voltage of the main insulation layer is generally 2 to 3 times higher in direct current than in alternating current, so
The DC applied voltage for dielectric strength testing is the same as the AC applied voltage.
A value of about 1.6 to 1.8 times is recommended.

When the above-mentioned DC dielectric strength test is performed on a stator coil provided with a conventional AC electric field relaxation layer using a DC voltage of about 1.6 to 1.8 times, creeping discharge often occurs in the air. This poses a danger during the test, causes significant damage to the stator coil, and reduces the residual dielectric strength of the main insulation layer. It had the disadvantage that it was extremely limited.

The reason why the AC field relaxation layer 4 of the conventional stator coil does not work effectively against DC voltage application is that the surface potential distributions of AC and DC are completely different, as shown in Figure 3b. . In this figure, the AC curve 6 shows the state where the applied voltage has reached its peak value, and the DC curve 7 shows the state about 1 minute after the application of the DC voltage, which is about 1.6 times the effective value of the AC voltage.
In the direct current curve 7, most of the applied voltage is distributed near the coating end of the alternating current electric field relaxation layer 4, and this electric field concentration causes direct current creeping discharge. The explanation of the electric field concentration caused by this direct current is as follows using FIG. 3c. Nonlinear resistance RN in the diagram
has a resistance value range that allows the capacitance C to be quickly charged and discharged in response to changes in the commercial frequency, that is, changes on the order of milliseconds, but unlike direct current, the time required for voltage changes is approximately 10 ⁴ to 10 ⁵ times longer, non-linear resistance
The resistance range is such that the surface current necessary to charge the capacitance C in contact with RN can sufficiently flow to the coating end. Therefore, the capacitance C at the application terminal of the AC field relaxation layer 4 is sufficiently charged during DC application and about 1 second to 1 minute after the application, and the surface potential Vs(X) at that point is equal to the applied voltage. It is sufficiently smaller than Vo. On the other hand, since the surface resistance R of the main insulating layer 2 outside the AC electric field relaxation layer 4 is extremely high, the surface current is extremely small and the capacitance C of this part
The charging time is extremely long. This time varies depending on the dimensions of the stator coil and the state of moisture absorption on the stator coil surface, but generally it takes several tens of minutes to several hours, and within the one minute period normally applied in dielectric strength tests, the surface The potential Vs(X) is almost equal to the applied voltage Vo.
For the above reasons, the curve 7 of the DC potential distribution of the conventional stator coil causes significant electric field concentration at the coated end of the AC field relaxation layer 4, causing creeping discharge.

This invention was made to eliminate the above-mentioned drawbacks, and it can provide a DC electric field relaxation effect without interfering with the AC electric field relaxation effect in the slightest, and does not cause creeping discharge due to electric field concentration even at DC voltage. The purpose is to provide stator coils.

An embodiment of the present invention shown in FIG. 4 will be described below. In FIG. 4, the same reference numerals as those in FIG. 1 indicate the same or corresponding parts, so the explanation will be omitted.
Reference numeral 8 denotes a DC electric field relaxation layer provided in contact with the end of the AC electric field relaxation layer 4, and is composed of a linear high resistance having a value lower than the surface resistivity of the main insulating layer 2. Generally, the resistivity of the surface of the main insulating layer 2 when dry is about 10 ¹² to 10 ¹⁴ Ω, and the resistivity of the DC electric field relaxing layer 8 is selected to be in the range of about 10 ⁹ to ^{10 13} Ω. Further, the selection can be made appropriately by anticipating the dimensions of the stator coil and the moisture absorption conditions of the test.
If the resistivity is 10 ⁸ Ω or less, the DC electric field relaxation effect ends within a very short time, and the electric field will concentrate again during about 1 minute of direct current application, so the resistance used for the DC electric field relaxation layer 8 is 10 ⁹ Ω. It is limited to high resistances above. In addition to applying a high-resistance paint, the DC electric field relaxation layer 8 can be fabricated by any method, such as wrapping a tape with a predetermined high resistance value around the stator coil, or wrapping a wrapper in the same way. May be used. The length of the DC electric field relaxation layer 8 is appropriately determined depending on the stator coil dimensions, the resistivity used, the applied DC voltage value, and the applied time.

Next, the specific structure and operation of the present invention will be explained using FIG. 5. FIG. 5a is a sectional view showing details of the coil end portion of the stator coil shown in FIG. 4, and the same reference numerals as in FIG. 4 indicate the same or corresponding parts. FIG. 5b is a diagram showing the surface potential distribution of the stator coil end corresponding to FIG. shows the potential distribution at

Here, the DC applied voltage value is approximately the AC voltage effective value.
1.6 times the value, and the DC potential distribution of curve 9 shows the state about 1 minute after voltage application. The conventional stator coil end DC potential distribution shown by curve 7 in FIG. 3 is shown in FIG. 5a. By introducing the DC electric field relaxation layer 8, the voltage distribution changes as shown by the curve 9 in FIG. 5b. Most of the voltage that was conventionally borne only on a part of the surface of the main insulating layer 2 is transferred to the DC electric field relaxation layer 8.
, and its potential gradient is also alleviated. This principle will be explained using the equivalent circuit shown in FIG. 5c. The surface resistance RDC per unit length of the linear high resistance layer forming the DC electric field relaxation layer 8 is slightly smaller than the surface resistance R of the main insulating layer 2. Therefore, Figure 5c
In the equivalent circuit of , the surface current flowing through the surface resistance RDC is larger than the surface current flowing through the surface resistance R,
The capacitance C in contact with the linear high-resistance layer is appropriately charged, and for this reason, the extreme voltage distribution as shown by curve 7 in Figure 3 is dispersed as the surface potential Vs (X), and the DC electric field A relaxing effect takes place.

Furthermore, the introduction of the linear high resistance layer forming the DC electric field relaxation layer 8 is as shown by curve 6 in FIG. 5b.
Another feature is that it has no effect on the AC electric field relaxation effect. The reason for this is that in the equivalent circuit shown in Figure 5c, when AC current is applied, no surface current flows through the surface resistances RDC and R, so the action of the AC electric field is affected by the response principle of the surface current of the conventional AC electric field relaxation layer 4 alone. Therefore, the AC potential distribution 6 in FIG. 5b becomes exactly the same as the AC potential distribution curve 6 in FIG. 3b.

Furthermore, the present invention can be applied to all applied voltage waveforms in which the voltage changes slowly over time; for example, the same effect can be applied to ultra-low frequency AC of 0.1 Hz and low-period quasi-triangular wave voltage. be.

In addition, as the AC electric field relaxation layer 4, although a single nonlinear resistance layer has been described in the conventional example, an AC electric field relaxation layer that is a combination of several different types of nonlinear resistance layers can also be used for DC electric field relaxation by the same operation. Since it has no effect,
By applying this DC electric field relaxation layer 8, DC electric field relaxation becomes possible.

Further, as an embodiment of the DC electric field relaxation layer 8 of the present invention, in addition to the case where it is formed of a single layer of linear high resistance layer shown in FIG. If a configuration is adopted in which the AC electric field relaxation layer 4 is applied from the terminal in ascending order, the DC electric field relaxation effect is further promoted. Figure 6a shows three different types of linear high resistance layers 8 for DC electric field relaxation layer 8.
Fig. 6b is a diagram showing the surface potential distribution of the stator coil end corresponding to Fig. 6a. Curve 6 in the figure shows the AC potential distribution, and curve 10 shows the DC potential distribution.
Compared to the DC potential distribution 9 in the case of a single layer structure, the curve 10 further disperses the electric field concentration by finely dividing the applied voltage to each resistance layer. The AC potential distribution 6 is the same as the curve 6 in Figures 3b and 5b, regardless of the implementation method of the DC field relaxation layer 8, for the reasons mentioned above.The number, resistivity and implementation of the linear high-resistance layers used The length is appropriately determined based on the stator coil dimensions and DC test conditions.

As described above, according to the present invention, since the DC electric field relaxation layer is provided in contact with the AC electric field relaxation layer and is configured to have an electric field relaxation effect on the DC electric field,
Creeping discharge is also prevented for direct current, and the application of DC dielectric strength testing can be expanded to high voltage ranges without damaging the stator coil or reducing dielectric strength due to creeping discharge. Moreover, since it does not affect the AC electric field relaxation effect at all, it has the advantage of having an electric field relaxation effect that is optimal for DC and AC.

[Brief explanation of the drawing]

Figure 1 is a side view showing a conventional stator coil, Figure 2 is a characteristic curve diagram showing the voltage characteristics of a non-linear resistor,
Figure 3a is a sectional view of the coil end of the stator coil shown in Figure 1, Figure 3b is a surface potential distribution diagram corresponding to Figure 3a, and Figure 3c is an equivalent circuit of Figure 3a. FIG. 4 is a side view showing an embodiment of the present invention.
Figure 5a is a sectional view of the coil end of the stator coil shown in Figure 4, Figure 5b is a surface potential distribution diagram corresponding to Figure 5a, and Figure 5c is an equivalent circuit of Figure 5a. FIG. 6a is a sectional view showing a main part of another embodiment of the present invention, and FIG. 6b is a surface potential distribution diagram corresponding to FIG. 6a. In the figure, 1 is a conductor, 2 is a main insulating layer, 3 is a resistive corona shield layer, 4 is an AC electric field relaxation layer, and 8 is a DC electric field relaxation layer. Note that the same reference numerals in the figures indicate the same or corresponding parts.

Claims (1)

[Scope of Claims] 1. A conductor having the property that when one end of the insulating layer is left in contact with the end of a low-resistance corona shield layer that covers the insulating layer and the electric field strength increases, the resistivity decreases. In the device equipped with an AC electric field relaxation layer, a DC electric field relaxation layer made of a linear high-resistance layer having a lower surface resistivity than the insulating surface of the insulating layer is provided in contact with the other end of the AC electric field relaxation layer. A stator coil characterized by: 2. The linear high resistance layer is composed of a plurality of high linear resistance layers having different resistivities, and is arranged in order of decreasing resistivity from the AC electric field relaxation layer side in contact with the AC electric field relaxation layer. A stator coil according to claim 1, characterized in: