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05/13/15 |
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Epstein
device is used for iron loss measurement in laminated iron cores
under sinusoidal and non-sinusoidal excitation that are used in electrical machines and transformers. The main components of
the device are four pairs of coils, as shown in the figure below. These four
pairs of coils are connected in series, creating a primary and a
secondary winding. The leakage between these two windings is very small.
The specimens are placed inside the coils in
crosswise order, creating a one-pole transformer. Magnetic
flux in the air produces part of output voltage which is corrected by M windings
(see the figure). The magnetizing waveforms are generated by a
waveform generator, which can generate a range of waveforms with
high accuracy. A number of standard voltage waveforms are
available including sine, square, triangle, ramp and pulse. When a
sinusoidal flux density is developed in the specimen in order to obtain
measurements, the source voltage
is adjusted so that the average rectified value of the secondary voltage
U2 becomes U2 = 4*f*N2*S*B where f is the frequency (Hz); N2 the number of turns of the secondary winding; S the cross-section area of the test specimen (m2); and B is the peak value of the magnetic flux density (T). Even if the AC flux density is not sinusoidal, it can be demonstrated that the peak flux density B can be calculated from previous equation, provided that no even harmonics are present. The control over the secondary voltage magnitude and wave form is achieved by using a standard analogue proportional feedback circuit. This feedback is used for improvement of sine waveform in order to comply with IEC-404-2 standard. The B-H curve of the specimen is obtained on the oscilloscope screen. One can also measure the maximum flux density, residual flux, and core losses using this curves. |
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Epstein Device connected to a waveform generator. |
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Circuit connection of the Epstein device for core loss measurements. |
This site was last updated 05/13/15
