ASTM A804/A804M-04(2009)e1

Materials Evaluation—These test methods were developed to supplement the testing of Epstein specimens for applications involving the use of flat, sheared laminations where the testing of Epstein specimens in either the as-sheared or stress-relief-annealed condition fails to provide the most satisfactory method of predicting magnetic performance in the application. As a principal example, the test methods have been found particularly applicable to the control and evaluation of the magnetic properties of thermally flattened, grain-oriented electrical steel (Condition F5, Specification A876) used as lamination stock for cores of power transformers. Inasmuch as the test methods can only be reliably used to determine unidirectional magnetic properties, the test methods have limited applicability to the testing of fully processed nonoriented electrical steels as normally practiced (Specification A677).

Specification Acceptance—The reproducibility of test results and the accuracy relative to the 25-cm [250-mm] Epstein method of test are considered such as to render the test methods suitable for materials specification testing.

Interpretation of Test Results—Because of specimen size, considerable variation in magnetic properties may be present within a single specimen or between specimens that may be combined for testing purposes. Also, variations may exist in test values that are combined to represent a test lot of material. Test results reported will therefore, in general, represent averages of magnetic quality and in certain applications, particularly those involving narrow widths of laminations, deviations in magnetic performance from those expected from reported data may occur at times. Additionally, application of test data to the design or evaluation of a particular magnetic device must recognize the influence of magnetic circuitry upon performance and the possible deterioration in magnetic properties arising from construction of the device.

Recommended Standard Tests—These test methods have been principally applied to the magnetic testing of thermally flattened, grain-oriented electrical steels at 50 and 60 Hz. Specific core loss at 15 or 17 kG [1.5 or 1.7 T] and peak permeability (if required) at 10 Oe [796 A/m] are the recommended parameters for evaluating this class of material.

1.1 These test methods cover the determination of specific core loss and peak permeability of single layers of sheet-type specimens tested with normal excitation at a frequency of 50 or 60 Hz.

Note 1—These test methods have been applied only at the commercial power frequencies, 50 and 60 Hz, but with proper instrumentation and application of the principles of testing and calibration embodied in the test methods, they are believed to be adaptable to testing at frequencies ranging from 25 to 400 Hz.

1.2 These test methods use calibration procedures that provide correlation with the 25-cm [250-mm] Epstein test.

1.3 The range of test magnetic flux densities is governed by the properties of the test specimen and by the available instruments and other equipment components. Normally, nonoriented electrical steels can be tested over a range from 8 to 16 kG [0.8 to 1.6 T] for core loss. For oriented electrical steels, the normal range extends to 18 kG [1.8 T]. Maximum magnetic flux densities in peak permeability testing are limited principally by heating of the magnetizing winding and tests are limited normally to a maximum ac magnetic field strength of about 150 Oe [12 000 A/m].

1.4 These test methods cover two alternative procedures as follows:
Test Method 1—Sections 6-12
Test Method 2—Sections 13-19

1.4.1 Test Method 1 uses a test fixture having (1) two windings that encircle the test specimen, and (2) a ferromagnetic yoke structure that serves as the flux return path and has low core loss and low magnetic reluctance.

1.4.2 Test Method 2 uses a test fixture having (1) two windings that encircle the test specimen, (2) a third winding located inside the other two windings and immediately adjacent to one surface of the test specimen, and (3) a ferromagnetic yoke structure which serves as the flux-return path and has low magnetic reluctance.

1.5 The values and equations stated in customary (cgs-emu and inch-pound) units or SI units are to be regarded separately as standard. Within this standard, SI units are shown in brackets except for the sections concerning calculations where there are separate sections for the respective unit systems. The values stated in each system may not be exact equivalents; therefore, each system shall be used independently of the other. Combining values from the two systems may result in nonconformance with this standard.

1.6 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.