As an aside, I toured the Veolia Steam Plant in Philadelphia, yesterday. Th is plant has been in continuous operation since it opened in 1909, and is q uite a remarkable place. I got to be up-close-and-personal with the equipme nt, including the steam and gas turbines, the boilers, pumps, controls, swi tchgear, powerhouse and uplink.
Standing under the main step-up transformer (2,300 VAC to 23,000 VAC) is a truly visceral experience. Once one feels that level of "HUM", one will nev er mistake 60 for 120 ever again.
Relevance:
60 HZ hum suggests a bad or failing rectifier.
120 HZ hum suggests bad or failing filter caps.
50 & 100 for our Euro and Asian friends.
Amazing amount of mechanical-feedback devices in use in these plants - it s eems that VFDs and great many "modern" grid-tie devices are simply not suf ficiently reliable or rugged at this scale.
Peter Wieck Melrose Park