JPH0145590B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of measuring dielectric breakdown voltage of an insulated wire. In particular, the present invention relates to a method for measuring dielectric breakdown voltage of windings and lead wires used in various coils of motors, transformers, etc. The key point is to place a needle-like electrode on the surface of an insulated wire, It relates to measuring the dielectric breakdown voltage of a portion by applying a voltage between the electrode and the electrode.

Conventionally, insulated wires used in motors, transformers, etc. have been required to have a thin film and high quality without pinholes or the like in the film.
In order to evaluate the electrical characteristics of insulated wires, the dielectric breakdown characteristics have long been sought using the two-strand method, in which two wires are twisted together, or the dielectric breakdown characteristics of a single wire in water. In recent years, measurements have also been performed in glycerin mixed with saline instead of water.

All of these methods are simple and effective for determining dielectric breakdown values, but they have the following drawbacks. In other words, in the case of a two-stranded sample, the electrically weakest part of the length of the two wires twisted together will be destroyed. Even when measuring in water or glycerin, the weakest part of the length immersed in the liquid bath will be electrically damaged. That is, in the conventional method, it was only possible to understand the characteristics of the defective part, but it was difficult to understand the characteristics of the remaining normal part.
In other words, when discussing insulation properties, it is not possible to separate whether the property values indicate the properties of a local defect or the properties of the entire film, making it difficult to accurately and accurately evaluate the quality. However, I was left with a problem.

However, the present invention provides a method that can determine dielectric breakdown at any one point, which could not be measured using conventional methods. We believe that the combination of the conventional measurement method and the method of the present invention will make it possible to grasp the quality level of insulated wires and to accurately and accurately examine changes in manufacturing conditions, etc.

According to the present invention, it is possible to determine the BDV value of a visually abnormal part, such as a crater occurrence part, a grain occurrence part, a protrusion part, etc., and to compare the quality with that of a normal part. Also, for rectangular wires, the flat surface,
It is also possible to separately determine the dielectric breakdown value at the corner. Further, according to the present invention, the dielectric breakdown voltage value of the coil can be determined without winding the insulated wire.

Conventionally, the needle electrode method has been used to elucidate dielectric breakdown under high electric fields in electric wires that require a high degree of reliability, such as plastic-coated power cables, and a large amount of data has been reported. That is, it has been discussed that the insulating film is destroyed due to the tree that occurs at the tip of the so-called needle electrode.

On the other hand, the effectiveness of the needle electrode method for winding wires used in coils and the like has not been recognized until now. This is because when the winding is wound around a coil and a voltage is applied, the voltage is incomparably lower than that of a power cable, and the dielectric breakdown phenomenon was not given as much importance. Conceivable. In addition, the conductors were thin, the coating was thin, and it seems that there was an awareness that the existence of defects was a given.

However, in recent years, as winding wires have come to be used in coils for small, high-performance devices, defects in the coating have gradually become no longer ignored. In particular, dielectric breakdown voltage characteristics and durability voltage characteristics have become more and more important, and there has been an increasing demand for insulated wires with good characteristics.

In order to produce high-quality insulated wires, the present inventors first conducted intensive research on quality evaluation methods and came to provide the measuring method of the present invention.

The present invention will be explained in detail using the drawings.

The figure shows a method of measuring the breakdown voltage of an insulated wire using the needle electrode method according to the present invention, where 1 is a needle electrode and 2 is an insulated wire to be measured. 3,4
is a lead wire necessary for voltage application. 5 and 6 are
This is a jig that allows the insulated wire to be moved left and right and back and forth, and is effective in easily and accurately setting the needle electrode at any measurement location on the insulated wire.

7 is a movable load, and in the figure, when this load is moved to the left, the force pressing the insulated wire of the needle electrode becomes stiffer, and when it is moved to the right, the force applied to the insulated wire becomes larger. It is what was done. Also, 8 is an arm that supports the needle electrode, and 9
is a jig added to prevent the needle from damaging the insulation film when installing or removing the needle electrode on the surface of the insulated wire.If you turn it to the right, the needle will be attached to the insulated wire. Move away from it and turn it to the left to set the needle on the surface of the wire.

The present invention is capable of determining the dielectric breakdown voltage value or durability voltage characteristic (voltage one hour characteristic) of any arbitrary location by the above-mentioned measurement method. The effects will be explained in detail.

Insulated wires are generally long objects, and are naturally required to have uniform quality in the length direction. For example, local defects in the insulation coating are caused by impurities contained in the insulation paint, burnt spots on the conductor, dents, copper powder, dust such as burnt residue in the baking oven, and the quality of the insulation coating deteriorates due to the presence of these. I'll come. Furthermore, defects in the insulation film over the entire film often result from insufficient baking. Also,
This occurs when an unsuitable curing agent or the like is mixed into the insulating film, which deteriorates the electrical properties. With the conventional method, it was not possible to distinguish whether the dielectric breakdown was caused by a local defect or whether the entire film was at that dielectric breakdown value level. However, in the case of local defects, when measured using the method of the present invention, the dielectric breakdown voltage of a normal area is often measured, and the measured value shows a high level. Furthermore, when defects exist in the entire film, even when measured by the method of the present invention, the measured values show almost the same low level as those determined by the conventional method.

Next, according to the present invention, the dielectric breakdown value of the defective portion of the coating film can be determined. For example, it is possible to know how much the dielectric breakdown value of a defective part such as a crater part or a grain generation part compares with the dielectric breakdown value of a normal part. In addition, insulated wires using rectangular conductors are said to have a low dielectric breakdown value because the coating thickness tends to be thin at the corners. However, this cannot be confirmed using conventional methods.

By using the present invention, since the flat portion and the corner portion can be measured separately, the characteristics of the corner portion can be accurately recognized. The data obtained from this will also serve as basic data for applying and baking the required film thickness. This prevents the film from being unnecessarily thick or too thin, and allows the film thickness to be designed to meet the required insulation properties. This ultimately leads to improved reliability of the equipment or miniaturization of the equipment.

Additionally, if there is an abnormality in a coil wound with insulated wire, a dielectric breakdown test of the wire is often required.In this case, the coil is wound up and measured using the conventional method. When unwinding the coil, force is applied to the wire, and the coating is subject to processing deterioration. It is recognized that the influence of this unwinding greatly influences the measured values. It is particularly difficult to unwind a coil that has been treated with impregnated varnish, and it is almost impossible to unwind the wire without damaging the wire. However, with the present invention, a needle electrode can be placed at any location on the coil before unwinding, and measurement can be performed. If you want to take further measurements, simply unwind the tape after taking the measurements and place the needle electrode at the location you want to measure.

The above description has been made in detail regarding the case of determining the dielectric breakdown voltage value, but the present invention also exhibits great power in measuring durable voltage characteristics.

A needle electrode is installed at one point on any insulated wire or coil, a predetermined voltage is applied, and the voltage-time characteristics can be determined.

The conductive needle used in the present invention may be made of any metal, for example,
Things like iron wire, stainless steel wire, piano wire, chrome wire, nickel wire, copper wire, and aluminum wire can be used. Additionally, commercially available bead needles can also be used and are suitable for the present invention. The conductor diameter of the conductive needle is preferably 0.1 to 2 mm. If it is less than 0.1 mm, it will be too thin and the contact with the insulated wire will be unstable, and if it is more than 2 mm, it will be too thick and workability will be poor. Further, the needle angle at the tip of the conductive needle is preferably 5° to 120°. If the angle is less than 5 degrees, the tip of the needle will be too sharp and may damage and break through the insulation film. At temperatures above 120°C, the tip of the needle becomes rounded, making it impossible to determine dielectric breakdown at any one point, which is a feature of the present invention.

The tip of the needle only needs to be strong enough not to damage the insulation film, and the load on the needle tip should be approximately 1g to 50%.
around g is good. If the load exceeds 50 g, the tip of the needle will penetrate into the film, which is undesirable. Furthermore, in the present invention, it is preferable to attach the needle electrode each time a measurement is made. This is because the tip of the needle melts, bends, and deforms due to the overcurrent that flows during dielectric breakdown.

Next, the present invention will be explained using examples.

In the following examples, the conductor diameter is 1 mm and the tip angle is
A 10° bead needle was used as the conductive needle.

Example 1 Two types of insulating paints, namely a polyester insulating paint and a polyester insulating paint containing copper powder with an average particle size of 20 μm, were separately applied and baked on a copper wire having a conductor diameter of 1.0 mm to produce an insulated wire.

The number of times of coating and baking was 6 times. The film thickness is the same
It was 35 μm. (In addition, copper powder is based on the weight of the coating,
After that, dielectric breakdown voltage measurement in glycerin using the conventional method and dielectric breakdown voltage measurement using the needle electrode of the present invention were performed. I got the following results.

BDV in glycerin, n = 100, (immersion length was 1 m) Polyester wire average = 4.5kV Variation σ = 0.7kV Copper powder-containing polyester wire average = 1.5kV Variation σ = 0.6kV Needle electrode method BDV, n = 100, Polyester wire average = 4.9kV Variation σ = 0.5kV Copper powder-containing polyester wire Average = 4.8kV Variation σ = 0.4kV From this example, it can be seen that copper powder causes partial defects in the insulation film. I can understand.

Example 2 Everything is the same as in Example 1 except as described below.

An insulated wire was manufactured using a polyamide-imide insulating paint and a polyamide-imide insulating paint to which carbon black with an average particle size of 1 μm was added as an insulating paint. Carbon black is 1% per film weight
Contained.

I got the following results.

2-strand BDV, n = 100, polyamide-imide wire average = 8.5kV Variation σ = 0.9kV Carbon black-containing polyamide-imide wire average = 1.8kV Variation σ = 0.4kV Needle electrode method BDV, n = 100, polyamide-imide wire Average = 5.1kV Variation σ = 0.6kV Polyahodoimide wire containing carbon black Average = 1.9kV Variation σ = 0.4kV From this example, it can be understood that carbon black causes overall defects in the insulation film. .

Example 3 The dielectric breakdown characteristics of the flat part and corner part of a rectangular insulated wire with a conductor of 3 mm x 6 mm coated with polyvinyl formal insulation paint and baked were measured using the method of the present invention. I got the result. The number of times the insulating paint was applied and baked was 7 times, and the film thickness on the flat part was 40 μm.

The number of measurements was n=100.

Flat section corner average = 5.5kV Average = 3.2kV Variation σ = 0.7kV Variation σ = 0.8kV From this example, as has been conventionally said,
It has been proven that the dielectric breakdown properties of the corner portions are inferior to those of the flat portions.

Example 4 Everything is the same as in Example 3 except as described below.

In a flat section of a rectangular insulated wire, dielectric breakdown voltage was measured at a crater-generated section and a normal section using the method according to the present invention.

The number of measurements was n=100.

Average of normal area and crater area = 5.5 kV Average = 4.1 kV Variation σ = 0.7 kV Variation σ = 0.9 kV From this example, it was confirmed that the crater generated area had inferior dielectric breakdown characteristics compared to the normal area.

Example 5 A copper wire with a conductor diameter of 0.5 mm was coated with polyester imide insulating paint and baked, and then wound 100 turns around a ferrite rod with a diameter of 20 mm to form a coil.
Thereafter, an impregnating varnish treatment was performed using two types of impregnating varnish, namely, an epoxy-modified alkyd varnish and an unsaturated polyester varnish.

The film thickness was 20 μm, and the thickness of the impregnated varnish was approximately 20 μm. After this coil was thermally degraded at 240° C. for 24 hours, the dielectric breakdown voltage characteristics of this coil were measured by the method of the present invention.

The number of coils used was one for each, and the measurements were made on the wires on the surface of the coils without unwinding. The number of measurements was n=20.

Coil treated with epoxy-modified alkyd unsaturated polyester varnish Coil treated with varnish Average = 1.5kV Average = 3.8kV Variation σ = 0.4kV Variation σ = 0.7kV From this example, epoxy-modified alkyd varnish is used as the impregnation varnish. It can be seen that the use of unsaturated polyester varnish has better dielectric breakdown characteristics.

[Brief explanation of drawings]

The figure shows an apparatus for measuring the breakdown voltage of an insulated wire using a needle electrode according to the present invention. 1... Needle electrode, 2... Insulated wire of the object to be measured,
3, 4...Lead wire, 5, 6...Jig with the function of moving the object to be measured back and forth, left and right, 7...Movable load, 8...Arm, 9...Arm 8 with a needle electrode attached A jig that functions when raising and lowering.

Claims (1)

[Claims] 1. A method of measuring dielectric breakdown voltage or durable voltage characteristics by installing a conductive needle on the surface of an insulated wire and applying a voltage between the insulated wire and the needle. . 2. The measuring method according to claim 1, characterized in that a winding wire is used as the insulated wire. 3. The measuring method according to claim 1, wherein a conductive needle having a conductor diameter of 0.1 to 2.0 mm is used, and the needle angle at the tip is 5° to 120°. 4. The measuring method according to claim 1, wherein the amount of load applied to the tip of the needle can be varied from 1 to 50 g.