Electrical Engineering ⇒ Topic : Utility Factor

Utility Factor. Utility factor is defined as the ratio of the volt-amperes obtained from the rectifier on the output side to volt-amperes supplied from A.C. input side.

Fig. (a) shows the relation between utility factor and m and it is obvious that utility factor is maximum for m = 2.7. Since m has integral values, hence utility factor is maximum for a rectifier which has three phases.The current in a mercury-arc rectifier can be controlled with the help of perforated grids placed between the anode and the cathode.

                                                                  Fig.(a). Relation between utility factor and m

Various grid-control methods can be broadly divided into two classes :

• Soft control method
• Hard control method.

By increasing the relative phase difference between the anode and grid voltages, the establishment of the arc between the anode and cathode can be delayed by any amount and so D.C. output can be controlled. Such method is known as phase-shift control method. The phase-shift can be achieved with the help of an induction regulator or by bias-shift control method