No Current? No Problem!

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.

Ultrasound OutageFirst, 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.

Ultrasound TransientsNext 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.

Ultrasound Switch-onRMS 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…..