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November 2013 - Magnetic particle testing, electricity and cosinus φ

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Written by Administrator
Saturday, 12 October 2013 14:45

The phase difference between voltage and current intensity, when using alternative current (AC), shall be kept as low as possible. It is also called the power factor, and is expressed by the cosine of the angle φ, between the moment when the maximum voltage is got and the moment when the maximum current intensity is delivered. Ideally, this angle should be zero.

This power factor is especially important for high-power equipment, such as an MT bench. When coils and other high-impedance items are connected to a main line, the angle may then become significant. The current is late vs the voltage.

The datum generally used to qualify the power factor is the cosine of the angle, as it is an easy-to-remember figure. A cosine may have values between zero and one. Zero means the angle is 90°, while the unit means that the angle is 0°.

The more open (important) angle), the more the consumption of the equipment is high, for a given delivered power.

The electricity utilities try to have this angle as low as possible: this is why some (huge) installations, containing incredibly powerful capacitors, have been installed in some areas, to improve the phase difference.

When an angle is close to zero, its cosine figure is close to one. When the angle figure increases, the cosine φ decreases.

The currently displayed figure for the cosine φ is circa 0.85/0.8, in the vast majority of users’ installations.

All these elements, basic to everyone involved in electricity, made us wonder about the knowledge of a lecturer, during a conference recently held on MT equipment and detection media, in France. The point in question is:

To lower the consumption, it is necessary to diminish the cosine φ of the magnetic bench”.

The right sentence should have been:
To lower the consumption, it is necessary to increase the cosine φ
Or
To lower the consumption, it is necessary to diminish the angle.

Mistakes happen everywhere, and, to be honest, despite a thorough shuttle of the documents between us, sometimes we also published documents with errors.

Last Updated ( Tuesday, 22 October 2013 06:08 )