Classic direct current systems
Conventional direct current applications constitute a substantial portion of the
portfolio of ABB Switzerland. The group-wide center of competence for
rectifiers and for excitation systems is located in Turgi.
Rectifiers supply electrolysis plants with high-voltage direct currents, which they transform
from alternating current using power semiconductors. In an aluminum mill in Oman, for
example, five rectifier groups from Turgi ensure that direct current of 360 000 amperes flows
at a level of 1650 volts through 360 melting furnaces connected in series. Electrolytic
processes also play a role in the production of copper, nickel and zinc, so rectifiers are used
there accordingly – just as they are in the electrolysis of chlorine from brine. Another area in
which rectifiers are used is heavy industry, in electric arc furnaces for the melting of scrap.
Static excitation systems constitute a further group of important and classic DC applications.
Remo Lütolf, Head of the Global Business Unit ATE elaborates: “They serve as pacemakers
in the heart of the power plant, if you will, providing the generator with variable direct current
to excite the magnetic field in the rotor.” The generator voltage and the power factor can
therefore be controlled, which is crucial for the quality of the electrical energy the power plant
feeds into the grid. Excitation systems therefore have to be able to regulate very quickly so
the power grid remains stable. As with rectifiers, excitation systems release huge outputs, up
to several megawatts. Lütolf: “ABB is world market leader for rectifiers and for excitation
systems. Product responsibility and development are located here in Turgi.”
For further information contact:
ABB Switzerland
Lukas Inderfurth
Melanie Nyfeler
Press Office
5400 Baden
+ 41 58 585 00 00
www.abb.ch
ABB Switzerland, May 2012
AC/DC
Unlike alternating current (AC), direct current (DC) cannot simply be stepped up to a
different voltage level with a transformer. Transformers are based on the principle of
induction. That requires alternating current. The two types of current can also be converted
into each other (rectification/inversion). With the use of modern semiconductors, this process
is highly efficient, achieving levels of efficiency of up to 99 percent at high voltages.