直接通电

protection of direct current supply lines direct current direct current keying direct current supply direct current track circuit direct current selection direct current tachometer direct current axle generator direct current impulsing direct current dynamo direct current regulator passage of current stimulus of direct current direct-current alternating current/ direct current alternating current/direct-current alternating-current/direct-current neutral direct current system direct current beta direct-current inserter direct-current erasing head