Supply of Direct Current

If a coil such as that imagined above carries an alternating current, and if a second coil is placed alongside, a varying electromagnetic field is produced in the second coil as well as in the first. A current then flows in the second coil if it is not open-circuit. This is the phenomenon of mutued inductance, and it is the basis of the transformer. 

If the secondary coil is connected to a load, a current I2 flows in the load and a corresponding current I flows in the primary coil. Since energy is conserved, the current transformation ratio is the inverse of the voltage transformation ratio  

The total supply current to the transformer is in fact + I, but Iq normally is small enough to be ignored. 

In the A-arrangement, phase voltages and line voltages are equal. Each line current is equal to the vector difference between the currents in the two phases to which the line is connected, and so in this case the line current is equal to /3 times the phase current. With either arrangement, the power output is the same for a given phase angle  

The choice of either of two arrangements on both the primary and secondary gives four possibilities in a transformer. The wye-delta connection is a common one in chlor-alkali plants, as it is in many industrial installations. It is favored in step-down transformers partly because of the neutral connection that is available and the consequent relative ease of grounding the high-voltage side. For the same reason, the delta-wye hookup is common in step-up transformers. 

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When it comes to rectification of an electrical signal for supply of direct current to the cells, thyristors are generally the preferred devices (Section 10.3.1.2). One of their deficiencies is a low power factor, particularly when operating well below the design current. New devices for reconfiguring DC signals (DC choppers) can overcome this... 

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