Fluke 1750 PQM data loss after utility switching operations

[SecondGen]

Data from a 30-day power quality recording was completely wiped out after the utility company de-energized the feeder being monitored, causing a flood of events.

This was a dual source 15kV switchgear that was being evaluated for 90 days because the gear was to be completely replaced. A Fluke 1750 recording meter had been set up on the secondary circuits inside both of the main breaker cubicles for weeks prior to utility operations.

This is a customer owned switchgear but the utility company has access to a switchyard just behind the substation and also the main breakers in the 15kV switchgear. PQM voltage probes were connected to the secondary of the PT and current at the protective relays.

When I came in for a routine checkup of the meter (now 3 weeks into recording), I noticed one of the breakers was racked out. At first I didn’t think it would be a big deal but once I got into things it was a shock to see I only two days’ worth of data.

To make a long story short, by pulling the PT drawer, the PQM recognized a loss of voltage and started to log events. After about 5 days of recording nothing but events, it appears that the memory had reached capacity and older data from weeks ago was being overwritten to make space for new data.

Under normal circumstances, opening and removing the main breaker would not affect the recording meter as line bus voltage would still be present (unless the feeder was de-energized). It would be expected to see current drop off when the breaker was opened.

However, since the PT drawer was also racked out, voltage sensed by the recording meter was lost as the meter was connected to the secondary side of the PT to monitor voltage levels that exceed the rating of the unit. This caused a loss of line voltage condition on the meter, triggering events.

Needless to say the recorded data for the weeks prior to my arrival was wiped from the memory, leaving me with nearly 20,000 events and no usable data over the course of only a couple days. It’s still unclear why the feeder was taken out (could have been emergency) but had we been notified the data could have been downloaded before having a chance to overwrite.

[ElectricalTestTech]

Data from a 30-day power quality recording was completely wiped out after the utility company de-energized the feeder being monitored, causing a flood of events.

This was a dual source 15kV switchgear that was being evaluated for 90 days because the gear was to be completely replaced. A Fluke 1750 recording meter had been set up on the secondary circuits inside both of the main breaker cubicles for weeks prior to utility operations.

This is a customer owned switchgear but the utility company has access to a switchyard just behind the substation and also the main breakers in the 15kV switchgear. PQM voltage probes were connected to the secondary of the PT and current at the protective relays.

When I came in for a routine checkup of the meter (now 3 weeks into recording), I noticed one of the breakers was racked out. At first I didn’t think it would be a big deal but once I got into things it was a shock to see I only two days’ worth of data.

To make a long story short, by pulling the PT drawer, the PQM recognized a loss of voltage and started to log events. After about 5 days of recording nothing but events, it appears that the memory had reached capacity and older data from weeks ago was being overwritten to make space for new data.

Under normal circumstances, opening and removing the main breaker would not affect the recording meter as line bus voltage would still be present (unless the feeder was de-energized). It would be expected to see current drop off when the breaker was opened.

However, since the PT drawer was also racked out, voltage sensed by the recording meter was lost as the meter was connected to the secondary side of the PT to monitor voltage levels that exceed the rating of the unit. This caused a loss of line voltage condition on the meter, triggering events.

Needless to say the recorded data for the weeks prior to my arrival was wiped from the memory, leaving me with nearly 20,000 events and no usable data over the course of only a couple days. It’s still unclear why the feeder was taken out (could have been emergency) but had we been notified the data could have been downloaded before having a chance to overwrite.

Very interesting. We install meters to collect data. We spend time thinking about routing extension cords out of the way to avoid being inplugged. We come up with clever ways of duct taping cords to be plugged into receptacles, or tie-wrapping them to receptacles.

We come up with ways of keeping the temporary installation electrically safe, to those who may wander into the electrical room. All of this thought goes into signage and installation that I never thought about putting signage on the breaker being monitored to call my cell if the circuit is to be de-energized.

Thanks for making me aware of another scenario to look out for.