Enameled wire is a main variety of winding wire. It is composed of conductor and insulating layer. After the bare wire is annealed and softened, it is painted and baked several times. However, it is not easy to produce products that meet both standard requirements and customer requirements. It is affected by factors such as raw material quality, process parameters, production equipment, and the environment. Therefore, the quality characteristics of various enameled wires are different, but they all have Mechanical properties, chemical properties, electrical properties, thermal properties four major properties. Today we will take a look at electrical performance.
Electrical properties include: breakdown voltage, paint film continuity and DC resistance test. The breakdown voltage refers to the ability of the enameled wire paint film to withstand the voltage load. The main factors affecting the breakdown voltage: (1) the thickness of the paint film; (2) the roundness of the paint film; (3) the degree of curing; (4) the external impurities in the paint film
This test method is suitable for determining the breakdown voltage resistance of the paint film of enameled flat wire under normal or high temperature conditions.
The provisions of this standard are consistent with the provisions of the International Electrotechnical Commission (IEC) 251-3 (1978).
1 Test equipment
1.1
The main components of the breakdown voltage test bench shall meet the following requirements.
1.1.1 Test transformer
Rated capacity: >500VA
Output waveform: approximate sine wave
Output current: >5mA
Maximum pressure drop: 2%
1.1.2i
Test voltage
Frequency: 50Hz or 60Hz
Waveform: Approximate sine wave
Bee value coefficient: √2±5%(1.34~1.48)
1.1.3
When the action current of the high-voltage circuit current relay is equal to or greater than 5mA, it can cut off the power supply and indicate the breakdown.
1.2
The surface of the test bar is polished.
1.8
The diameter of the electrode steel ball is not more than 2mm, and it should be cleaned with appropriate solvent regularly to prevent rust.
1.4 Electric heating blast box 0~300℃.
2 Sample preparation
2.1 The length of the sample is 350mm, and 5 samples should be sampled for each test of ancestry conditions.
2.2 Remove the insulation from one end of the specimen. On the test rod of the diameter specified in Table 1, bend the broad side of the test piece to form a “U” shape.
3 test steps
3.1 Room temperature test
3.1.1 According to the regulations in the figure, place the sample in the electrode tank filled with beads, and the two ends of the sample must protrude for a considerable length.
3.1.2 Between the steel ball and the sample conductor, apply a voltage at the boosting speed specified in Table 2 until it breaks down.
3.1.3
The test can also be performed in a cuff-filled electrode tank. The type of sleeve and the breakdown voltage value are determined by the manufacturer and the user through negotiation.
3.2 High temperature test
3.2.1 Put the steel ball and electrode tank into the electric heating blast box, and preheat to the temperature specified in the product standard.
3.2.2 Put the U-shaped sample into the electrode tank as specified in the figure, and heat it to the specified temperature.
8.2.3
Within 15 minutes after the sample reaches the specified temperature, the test shall be carried out according to the provisions of Section 4.1.2.
3.2.4
The total time of the sample in the electric blast box should not exceed 30mn.
4 Test results and calculations
The breakdown voltage values of the 5 samples measured at room temperature or high temperature must meet the requirements of the product standard.
The paint film continuity test is also called the pinhole test. Its main influencing factors are: (1) raw materials; (2) operating process; (3) equipment. DC resistance refers to the resistance value measured per unit length. Its main influencing factors: (1) degree of annealing; (2) enameled equipment.
Therefore, the enameled wire has a high resistance to softening and breakdown temperature, excellent mechanical strength, good solvent resistance and refrigerant resistance, and its weakness is that it is easy to hydrolyze under closed conditions, and is widely used in motors, electrical appliances, instruments, and power tools that require high heat resistance. , Windings such as dry-type power transformers.