Magnet Wire / Winding Wire
The evaluation of magnet/winding wire is conducted to testing described in NEMA, ASTM or IEC. The test methods are as harmonized as any category can be; hence the list of tests below can be presented in a color highlighted format.
The test methods are color coded to make the comparison of the NEMA and ASTM methods easy to find. There are two levels of testing:
- Short term performance properties
- Long Term Thermal Aging (LTTA)
This section presents the Short Term tests conducted by ELTEK Labs. The LTTA tests are presented in the RTI – TI section of this site.
NEMA 1000 – Magnet Wire
Part 1- Dimensions– Using the guidelines outlined in Part 1 of NEMA 1000 technicians are able to confirm build and AWG, which are useful in determining parameters for further testing.
Dimensions: 1.1 Includes dimensions of bare and film insulated magnet wire; to assist with the determination of build; [single-Heavy-Triple-Quad] and the corresponding wire gauge sizes; the increase in diameter of the bare wire to the various builds due to the film coating applied is used in determining the proof test voltage for some long term projects.
Part 2 – Properties and Requirements– A lot of testing requires know the type of magnet wire/winding wire that is being tested, each type of magnet/winding wire listed in the NEMA standard has an outline of requirements that testing must confirm.
Types of Magnet wire / ANSI/ NEMA designations: descriptions of the magnet wire coating insulating material (polyurethane – polyamide- imide, etc…) thermal class assigned, and general requirements.
Part 3 – Test Procedures – The guidelines in part 2 outline the test procedures that need to be followed and the testing to be performed for MW confirmation.
The most common tests are as follows:
1.1 Dimension Chart – outline chart for the confirmation and reporting of dimensional changes due to magnet wire coating
188.8.131.52 Dimensions – procedure for measurement of wire.
3.3.1 Adherence and Flexibility – 20 % elongation of the magnet wire and a mandrel wrap to evaluate the conductor and look for cracks in the film coating due to the stretching of the wire and then the stretched wire being wrapped in a helical manner around a mandrel of a specified size for the gauge.
3.5 Heat Shock – a confirmation of the thermal class rating of the magnet (conducted at 20°C over the thermal class assignment of the magnet wire. Using the specimen of wire from the previous Adherence and Flexibility testing; the coil of wire is placed in an air circulating oven for 30 min, removed, then examined for cracks in the film coating.
3.8.1 Dielectric Breakdown – the average dielectric breakdown of a sampling of magnet wire samples by using [TP] twisted pair specimens, foil wrapping of the conductor, and cylinder (very fine gauge wires) methods. All methods have guidelines for the minimum breakdown outlined in the appropriate sections for that type of testing.
3.9 Continuity – continuity tests are performed to evaluate defects in the insulation of the magnet wire; 100 feet of the magnet wire being evaluated is coiled and placed in a bath of phenolphthalein solution, a low voltage direct current is then applied to the conductor to indicate the number of faults in the film insulation along the length.
3.50 Thermoplastic Flow – test to determine and confirm the cut through” temperature of round film- insulated magnet wire. The temperature at which the insulating film on the specimen of magnet wire deforms sufficiently enough to allow electrical contact.
Short Term Magnet Wire Property Evaluation of Film Insulated Magnet Wire
ASTM D1676 – Standard Test Methods for Film-Insulated Magnet Wire – this Test Method presents different procedures for evaluating given properties of film-insulated magnet wire; these tests are intended primarily for the evaluation of the electrical insulating materials used. The intent is that these test methods can be used, except where modified, by individual specifications for particular applications.
Sec. 62-69 Cut Though “Thermoplastic Flow”- determines the thermoplastic flow or deformation of the film insulation of the magnet wire by determining at what temperature the film coating of the specimen deforms sufficiently to allow electrical contact between tow conductors.
Sec. 70-76 Dielectric Breakdown AC Voltage – test method to determine the dielectric breakdown AC voltage, in air, of insulating media on round, rectangular, or square film-insulated magnet wires at commercial power frequencies. Included are twisted pair and foil wrap.
Sec. 100-106 Dimensional Measurement of Conductor and Film-Insulated Magnet Wire – Film-Insulated magnet wire and conductor dimensions are basic parameters used in the design of electrical machinery. The breakdown voltage and other properties are related to the film thickness.
Sec. 122-128 Elongation- Elongation provides a general measure of the ductility (able to be molded or shaped or stretched without breaking) of film-insulated magnet wire. Useful indications of the flexibility and adherence of film insulation to the conductor may be derived from this test.
Sec. 141-148 Film Adherence and Flexibility – Test method procedure for evaluating the adherence and flexibility of the insulating film on the round, rectangular, or square film-insulated magnet wire. A measurement which indicates the degree to which film-insulated magnet wire may be mechanically stressed without visible cracks in the film or loss of adhesion to the conductor.
Sec. 156-162 Heat Shock – Film insulation of magnet wire is stressed during winding and forming operations. It is further stressed by temperature changes in processing of windings, and normal operation of the apparatus. This test is used to evaluate the resistance to cracking of the film insulation upon exposure to rapid temperature changes.