We recently looked at Fluke 1750 data from an ultrasound site. As is often the case with these 120 VAC, 1 Phase monitoring, it’s voltage only (due to the need to use a break-out cable to monitor current on a manufactured power cord; even if they are made up and sent with the monitoring equipment, they tend to disappear from the power analyzer kits over time.
A lack of current data can be a real handicap when analyzing data, but we go back a few years, to the days before current monitoring was ubiquitous. Here’s a few things we were able to determine, even without current data.
First, an outage was captured, identified by the service engineer as “hospital power went out”. We’re not so sure; the rapid loss of voltage, with no significant decay, points to a local event (not facility wide), and the neutral-ground voltage swell and phase voltage collapse points to a high current event. Our best guess – equipment fault caused an overload and a subsequent breaker trip.
Next some voltage transients, captured a few times during monitoring, on both phase-neutral and neutral-ground. Without current data, it’s hard to make much of a guess regarding the source of these. But zooming out a bit provides additional evidence.
RMS voltage logs show some small drops in voltage immediately after the transient – typical of a load switch-on (neutral-ground data, not shown, also supports this). We’re sure the transients are associated with load switch-on; probably switch bounce of a circuit breaker, relay, or contactor.
Power analysis without current data. Kicking it old school…..