Epstein frame

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Epstein frame
Epstein frame

Epstein frame or Epstein square - standardised measurement device for measuring the magnetic properties of soft magnetic materials, especially used for testing of electrical steels.

In Europe the measurement configuration and conditions are defined by a standard: IEC 60404-2:1996 Magnetic materials - Part 2: Methods of measurement of the magnetic properties of electrical steel sheet and strip by means of an Epstein frame.[1]

Epstein frame comprises a primary and a secondary winding. The sample under test should be prepared as a set of a number of strips (always multiplicity of 4) cut from electrical steel sheet or ribbon. Each layer of the sample is double-lapped in corners and weighed down with a force of 10 N (see photo).

The power losses are measured by means of a wattmeter method in which the primary current and secondary voltage are used. During the measurement the Epstein frame behavas as an unloaded transformer.

Power loss, Pc, is calculated as:

P_c = \frac {N_1}{N_2} \cdot P_m - \frac {\left( 1,111 \cdot |\bar{U_2}| \right)}{R_i}

where: N_1~ - number of turns of primary winding
N_2~ - number of turns of secondary winding
P_m~ - reading of the wattmeter in watts
R_i~ - total resistance of the secondary winding in ohms
|\bar{U_2}| - average secondary voltage in volts

Specific power loss, Ps, are calculated as:

P_s = \frac {P_c \cdot 4 \cdot l}{m \cdot l_m}

where: l~ - length of the sample in metres
l_m~ - average magnetic path length = 0,94 (constant value)
m~ - mass of the sample in kilograms

If all conditions are as defined in the standard the standard deviation of the reproducibility of the values is not greater than 1.5 % up to 1.5 T for non-oriented electrical steel and up to 1.7 T for grain-oriented electrical steel.

[edit] References

  1. ^ IEC Web Store | Publication Detail > IEC 60404-2 Ed. 3.0 Bilingual
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