Power factor correction

Correct power factor by using energy-efficient motors or capacitors. 

The drive converter normally operates at unity power factor. If the drive converter and inverter are the same frame size (current rating), the converter will have additional capacity after supplying the hoist drive current. This additional capacity can be used in the form of leading VAR s. The converter can be programmed to provide either fixed or variable leading VAR s, and if connected to the site power management system, could be used to dynamically correct power factor at the mine site. 

Power Supplies and Controls. Induction heating furnace loads rarely can be connected directiy to the user s electric power distribution system. If the load is to operate at the supply frequency, a transformer is used to provide the proper load voltage as weU as isolation from the supply system. Adjustment of the load voltage can be achieved by means of a tapped transformer or by use of a solid-state switch. The low power factor of an induction load can be corrected by installing a capacitor bank in the primary or secondary circuit. 

Approximate length of wire for each feeder up to the power factor correction relay (PFCR) 35 m. 

Automatic correction is always recommended to eliminate manual dependence and to achieve better accuracy. It also elimintites the risk of a leading power factor by a human error that may cause an excessive voltage at the motor and the control gear terminals. 

Assume the plant p.f. before the power factor correction to be 0.65. (We have provided in Table 23.8 the likely operating power factors for different types of industries, as a rough guide.) It this p.f. is to be improved to say, 0.95. then from Table 23.6,... 

Figure 23.38 Typical front views of automatic power factor correction relays...

For a capacitor bank of 500 kVAr in 10 units of 50 kVAr each, for an automatic power factor correction the rating of components would be... 

Power factor correction circuits are intended to increase the conduction angle of the rectifiers and to make the ac input current waveform sinusoidal and in phase with the voltage waveform. The input waveforms can be seen in Figure C-2. This means that all the power drawn from the power line is real power and not reactive. The net result is that the peak and RMS current drawn from the line is much lower than that drawn by the capacitive input Alter circuit traditionally used. 

Active power factor correction circuits can take the form of nontransformer isolated switching power supply topologies, such as buck, boost, and buck/boost. The buck topology in Figure C-3 produces an output dc voltage lower than found at its input, whenever the PFC stage is operating (F > Fom). In other... 

C.1 A Universal Input, 180W, Active Power Factor Correction Circuit... 

The resulting schematic of the power factor correction circuit is given in Figure C-9. 

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