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<p>power was not entirely displaced by alternating current and was useful in railway and electrochemical processes. Prior to the development of <a href="page.php?w=mercury-arc_valve">mercury-arc valve</a> <a href="page.php?w=rectifier">rectifier</a>s, rotary converters were used to produce DC power from AC. Like other commutator-type machines, these worked better with lower frequencies.</p>

<p><big>Transmission and transformers</big></p>
<p>With AC, <a href="page.php?w=transformer">transformer</a>s can be used to step down high transmission voltages to</p><p>
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