Epstein frame or Epstein square is a standardised measurement device for measuring the magnetic properties of soft magnetic materials, especially used for testing of electrical steel

Electrical steel

Electrical steel, also called lamination steel, silicon electrical steel, silicon steel, relay steel or transformer steel, is specialty steel tailored to produce certain magnetic properties, such as a small hysteresis area and high permeability.The material is usually manufactured in the form of...

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In Europe

Europe

Europe is, by convention, one of the world's seven continents. Comprising the westernmost peninsula of Eurasia, Europe is generally 'divided' from Asia to its east by the watershed divides of the Ural and Caucasus Mountains, the Ural River, the Caspian and Black Seas, and the waterways connecting...

 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. BS EN 60404-2:1998+A1 contains an updated version of IEC 60404-2.

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 1 N (see photo).

The power losses are measured by means of a wattmeter

Wattmeter

The wattmeter is an instrument for measuring the electric power in watts of any given circuit.An instrument which measures electrical energy in watt hours is essentially a wattmeter which accumulates or averages readings; many such instruments measure and can display many parameters and can be...

 method in which the primary current and secondary voltage are used. During the measurement the Epstein frame behaves as an unloaded transformer

Transformer

A transformer is a device that transfers electrical energy from one circuit to another through inductively coupled conductors—the transformer's coils. A varying current in the first or primary winding creates a varying magnetic flux in the transformer's core and thus a varying magnetic field...

.

Power loss, P_c, is calculated as:



where:
- number of turns of primary winding

- number of turns of secondary winding

- reading of the wattmeter in watt

Watt

The watt is a derived unit of power in the International System of Units , named after the Scottish engineer James Watt . The unit, defined as one joule per second, measures the rate of energy conversion.-Definition:...

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- total resistance of the instruments in the secondary circuit in ohm

Ohm

The ohm is the SI unit of electrical resistance, named after German physicist Georg Simon Ohm.- Definition :The ohm is defined as a resistance between two points of a conductor when a constant potential difference of 1 volt, applied to these points, produces in the conductor a current of 1 ampere,...

s

- average secondary voltage in volt

Volt

The volt is the SI derived unit for electric potential, electric potential difference, and electromotive force. The volt is named in honor of the Italian physicist Alessandro Volta , who invented the voltaic pile, possibly the first chemical battery.- Definition :A single volt is defined as the...

s

Specific power loss, P_s, are calculated as:



where:
- length of the sample in metres

- average magnetic path length = 0.94 (constant value)

- mass of the sample in kilograms

If all conditions are as defined in the standard the standard deviation

Standard deviation

Standard deviation is a widely used measure of variability or diversity used in statistics and probability theory. It shows how much variation or "dispersion" there is from the average...

 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.