Transformers Inrush Current

The inrush current originates at a time when the polarity and magnitude of the residual magnetic flux do not equal the polarity and magnitude of the flux generated by the power connected to the transformer terminals.

The energization of a transformer is an old case of the appearance of these currents. It causes the inrush current to the reset voltage, and energizes one transformer in parallel when the other is already in service.

The inrush current has as characteristics to contain a DC component and odd and even harmonics and to have the time constant much greater than the exponential decay of the DC component of a short circuit current.

Inrush current, which can be mistaken for an internal fault, may have spikes in the order of 8 to 30 times the rated current.

The factors that control the duration and magnitude of this current are:

– The size of the transformer;

– The size of the power system connected to the transformer;

– The type of iron used in the transformer core, as well as the saturation density;

– The residual iron flux;

– The type of transformer energization.

Esta entrada foi publicada em agosto 11, 2017, em Uncategorized.

Shaded Poles Engine Principles

The shaded poles electric motor, also called as distorted field motor, upon start-up, is simplified, reliable and economical for all types of single-phase induction motors. Several types can be found, although the most common is that of protruding poles, each pole being present, containing a part received by a shorted copper loop.

What can be expected is a process that is similar to a rotating field capable of moving in the direction of the uncaged portion of the pole, causing the torque to achieve nominal rotation, causing the motor to rotate and may vary According to the side in which the clamped part of the pole is located.

In this way, the distorted field motor may have a single direction of rotation, which can be reversed by changing the position of the rotor shaft tip relative to the stator. There are a few other methods to get rotation reversal. In terms of performance, distorted field motors rely on low starting torque, yield and reduced power factor.

Esta entrada foi publicada em agosto 7, 2017, em Uncategorized.