D.c. voltage sources

A converter unit is used for the control of d.c. machines and also to provide a d.c. source to an inverter unit controlling an a.c. machine. In d.c. drives the d.c. voltage after tlie converter unit should be variable, whereas for in a.c. drive it is kept fixed. The voltage is varied by the invener unit. A convener unit is the basic power conversion scheme to convert an a.c. supply to a d.c. supply. Conventionally they are also known us rectifier units and c in be arranged in four different modes to suit dilTerent applications of a motor as follows ... 

This is Ihe most commonly used inverter for Ihe control of a.c. motors and is shown in Figure 6.28(a). The fixed d.c. voltage from the uncontrolled rectifier converter acts as a voltage source to the inverter. The voltage in Ihe inverter unit is varied to Ihe required level by using a pulse width modulation, as noted earlier. Through Ihe switching circuit of Ihe inverter Ihe frequency of the... 

Smoothing circuit To obtain a near-constant voltage source for the inverter circuit a smoothing capacitance across the d.c. link is used to smooth the a.c. ripples present in the d.c. link after cotiversion. The capacitor retains the charge and provides a near-constant d.c. voltage output. 

After sjnoothing the d.c. voltage may contain moderate ripples not desirable when a constant voltage d.c. source is needed. To achieve this, a charging capacitor C is also provided across the d.c. link for all sizes of drives as show n in Figures 6.24(a) and 6.28(a). 

Using the impressed-current technique the driving voltage for the protec-ive current comes from a d.c. power source. The sacrificial anode technique... 

Several self-healing processes, in the early stages, of 2 cm of a chemical of the TD type, including every oxidatively-heating substance, have been simulated by generating the electric heat at several rates, by means of a constant voltage D.C. power source, in a resistor-thermocouple composite, in place of 2... 

Busbars. Fitting the tank for d-c power is usually accompHshed usiag round copper busbars, both for supporting the anodes and the work or cathodes. Size of the copper bus is determined by the amount of current flow expected 1000 amperes requires about 6.5 cm of cross-sectional area. The bus is iasulated from the tank, and any other sources of grounding, and coimected to the d-c power supply. Shorter distances from the tank as well as fewer electrical connections keeps the voltage drop to a minimum. 

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