Low frequency transients, sometimes called Utility Switching Transients or Power Factor Correction Capacitor Switching Transients, can be pretty hard to identify. Traditional power monitoring equipment has never done a particularly good job at spotting these – folks of a certain age will recall that the BMI-4800 power monitor would throw a frequency error (either 61.9 Hz or 64.0 Hz) if the transient caused an extra zero-crossing – sometimes that was the only way to detect the transient, and savvy engineers would use these frequency faults as a diagnostic tool.
Looking through a lot of Fluke 1750 data sets over the years (we’re looking at Site #4472 this week), we’ve gotten pretty good at pulling these transients out of the 100s or 1000s of transient events captured. Some detection tools:
- Some transients do indeed trigger a voltage transient event, but need to be carefully reviewed because the reported magnitude is often that of the higher frequency leading edge
- Many transients are accompanied by a rise in RMS voltage, so carefully adjusting the voltage swell threshold can often help to spot these.
- In Wye systems, many transients cause a Neutral-Ground swell event, which can often be spotted.
In a recent data set; none of these indicators worked out. We were very fortunate that the first current event captured (with a current swell threshold set to 10 Amps, a typical threshold for our reports) was a transient event – so we happened to notice it.
Current Triggered Event #1
Then, identifying the duration of the current swell event (~ 17 msec, much shorter than the normal equipment loading) and the amplitude (between 15-20 Arms, normal equipment current swells were much higher) we were able to sort through 100s of current triggered events to find nine (9) low frequency transients in the data.
Normally, we would not be so concerned about these transients, which are comparatively minor, simply looking at the voltage waveforms, with no significant overvoltage nor multiple voltage zero-crossings, However, the associated current swell (70-100 A peak) indicates something in the equipment under test is sensitive to or reacting to these transients, and drawing a slug of current. So they are worth looking into….
Current Triggered Event #646
I found out this morning that Joe Briere of Computer Power Northeast passed away back in March – obituary.
Joe and I go back a long ways. When I worked at Philips Medical in Shelton (pre-1995) he stopped in a few times to see if there was any business there; he was plying his trade as a power quality consultant in the medical imaging field, doing a lot of work with Siemens Medical, so it was natural that our paths would cross. He was one of those “I’ll help you with your power quality issues and maybe sell a transformer, voltage regulator, power conditioner, Uninterruptible Power Supply, or Surge Protective Device along the way” kind of consultants that inevitably made a lot more money than me (who chose not to sell or rep products, just provide technical services). He was always a straight-shooter, never found him to oversell or over-promise, and was a hands-on guy who knew his way around grounding, the electrical code, isolation transformers, etc. We did not agree on everything, but I always respected his opinions and experience.
For a few years there (2001 – 2003) Joe and I would often find ourselves meeting at Siemens trouble sites across the country as the service organization tried to get a handle on power and grounding issues, so I got to know him pretty well, poking around hospital electrical systems and sharing a beer and a meal afterwards.
Have not been in contact for many years (my last contact with Joe was 2003, and with Computer Power Northeast was 2009) but I’d pop over to the website now and then to see if they were still in business. Joe was probably retirement age when I started working closely with him, and reportedly kept busy well into his 80’s. His business partner called for a little consulting project this morning and shared the news.
Was a long time ago in a galaxy far, far away. Power Quality Consulting was kind of the wild west back then and the folks who knew what they were doing, were not afraid to open an electrical panel and make some measurements, and could sort out technical issues that left others scratching their heads were a rare breed. RIP, old friend.
I just sent a client a document from a seminar that I created and led in 1996. (The seminar client is long out of business).
It’s nice to be (a) the old dog who was around back in the day, and (b) a bit of a digital pack rat. Also interesting that the technical issues of 2017 are no so different from the technical issues of 1996.
Here’s a snapshot of that document (pretty slick for 1996, no?) – and no guarantees that the IEC / UL references or requirements are still valid. But the concept – that measuring ground resistance with a low current ohmmeter is going to give you sketchy results – remains valid.
Power Quality for Diagnostic Medical Imaging Systems by South Carolina Electric & Gas (SCE&G)
Normally these sorts of utility “power quality” documents are fairly cursory, but this one is comprehensive and well done. Recommended!
Yes, these things can be glorified sales pitches. But hey, FREE and CONTINENTAL BREAKFAST.
When: November 10, 2016
Where: Radisson Hotel
50 Morgan Street
Hartford, Connecticut 06120
1 (860) 549-2400
More Info (PDF)
Heard yesterday on Fresh Air: Aging And Unstable, The Nation’s Electrical Grid Is ‘The Weakest Link’
In her new book, The Grid, Gretchen Bakke argues that the under-funded power grid is incapable of taking the U.S. into a new energy future. She explains the challenges to Fresh Air‘s Dave Davies.
Just ordered a copy online; was a great interview and sounds like a wonderful book, dealing with the realities of balancing nearly unlimited, yet inconsistent renewable power sources (solar, wind, etc.) with the reality of consumer and commercial demand.
I confess to being a little curmudgeonly about issues of power usage, renewable energy sources, attempts to encourage consumer energy savings, etc. and this book gets to the heart of a lot of that. Really looking forward to this read!
Popped upon my social media feed this afternoon.
Price Chopper is running a sponsored ad touting their support of Riverfest, at the same time the cancellation of said event is all over most social media feeds.
It’s one of the reasons I’m a bit hesitant to embrace scheduled, planned social media posts, and have a more hands-on, direct approach. Because one never knows – some sort of political incident, tragic accident, hilarious meme, or other news story could crop up and the juxtaposition of a social media post (sponsored or otherwise) with a problematic news story could result in a social media fail. Even if there’s no direct connection (as there is here), promoting a fun and games event in the wake of a crime, attack, or natural disaster is at best, tone deaf.
I do schedule some things, but I do so judiciously, and keep an eye on things – ready to pull the plug at any time. And I notice what companies and organizations seem to be managing their social media somewhat robotically or blindly – and make some assumptions about the entity’s customer service accordingly.
We’ve spent some time recently putting together a spreadsheet for a client to review advance reservations for a local Dinner Train. It is intended to help management and marketing look down the road to fine-tune marketing and social media efforts.
The magic is the use of templates and macros – the spreadsheet is designed to quickly and easily import data obtained from an eCommerce platform (Shopify), and with the push of a button, to sort, filter, and copy the data so that the charts are automatically produced – in less than a minute, and by users who are not spreadsheet gurus.
Step-by-step instructions embedded into the spreadsheet to ensure non-expert users and/or new users can work with the spreadsheet.
We set the spreadsheet and graphs up just once – and through macros, paste new data into the spreadsheet, so that the graphs are updated and ready for use without touching them at all.
Just one of our many skills and services – if you have data that you’re having trouble making good use of, or are spending too much time on repetitive tasks to get your data into useful form, give us a shout. A few hours of work setting up an automated spreadsheet can yield huge savings down the road.
Siemens Healthcare Becomes Siemens Healthineers
We’ve been working with Siemens since 2001. Somewhere along May 2009, we transitioned reports and templates from being branded as Siemens Medical Solutions to Siemens Healthcare. So I suppose it’s about time for a bit of rebranding. Pretty minor change for us (the word “Healthcare” appears a grand total of 2x in the report templates we start from.
The new name embodies the company’s pioneering spirit and engineering expertise in the healthcare industry. It is unique and bold and gives a new identity to the organization and to the people – the people accompanying, serving and inspiring healthcare providers worldwide – the people behind outstanding products and solutions.
Makes me think of Walt Disney and the Imagineers (I’ve recently watched a PBS biography of Uncle Walt).