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  • 1.  Anyone with experience on partial discharge condition monitoring?

    Posted 10-16-2020 02:59 PM

    Hi everyone. 

    I have been watching the development of partial discharge test equipment and software over the last few years, and it seems to me that the technology has finally reached the point where it can be considered for condition monitoring, ie where the equipment is robust and reliable enough for long term field installations, where repeatable measurements can be taken and diagnosed without needing a PhD and the systems can pinpoint sources of PD in transformers, switchgear and cables.

    I am considering putting a proposal together for a PD condition monitoring system for buried EHV cable and GIS switchgear, and would like to hear about other people's experiences and challenges in installing and operating these systems.

    Thanks and regards
    Alexander



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    Alexander Mackenzie-Cameron CRE
    Doha
    Qatar
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  • 2.  RE: Anyone with experience on partial discharge condition monitoring?

    Posted 10-19-2020 07:53 AM
    I just sent you a message, Alexander, I may be able to assist - JB

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    Jeff Beukema
    TEGG Service Consultant
    Transworld Inc. Electrical Contractors
    Charleston SC
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  • 3.  RE: Anyone with experience on partial discharge condition monitoring?

    Posted 10-19-2020 09:43 AM
    Thanks Jeff, contact details sent

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    Alexander Mackenzie-Cameron CRE
    Doha
    Qatar
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  • 4.  RE: Anyone with experience on partial discharge condition monitoring?

    Posted 10-19-2020 09:48 AM
    I have forwarded your email to the SME's, hopefully you will hear from someone very soon.





  • 5.  RE: Anyone with experience on partial discharge condition monitoring?

    Posted 10-19-2020 08:37 AM
    Alexander

    It's actually been well beyond R&D for decades.  We have systems installed (Iris/Qualitrol) for 13kV machines as well as involved in cable to detect treeing/splicing issues.  Over the past 20 years have also been involved in the development of the IEEE standards (with input to IEC via Cigre) related to PD testing of machinery, transformers, cables, etc. and this forum is a good place to have the conversation as it is an overlooked testing methodology for electrical reliability.

    Do you have specific questions?

    Sincerely,
    Howard

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    Howard W Penrose, Ph.D., CMRP
    Random Past SMRP Chair (2018), 2019+ Govt Relations Smart Grid, Infrastructure and Cybersecurity Working Group Chair, and
    President
    MotorDoc LLC
    Lombard, Illinois
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  • 6.  RE: Anyone with experience on partial discharge condition monitoring?

    Posted 10-19-2020 09:42 AM

    Hi Howard

    I have been involved in some partial discharge investigations over the years, and my feeling has always been that it suffers from a few problems that prevent it being really useful for on-site condition monitoring on the sort of equipment I am currently responsible for
    1. Very well suited to offline testing such as laboratory or manufacturing quality control and customer acceptance testing. Conversely it is not as well suited to permanent online connection to a trending / monitoring system. Some systems such as the Omicron MPD series have been available for several years now that seem to meet requirements for permanent online connection, but I haven't heard of any user success stories in this regard, only hype from marketers.
    2. Analysis of the partial discharge activity was the domain of an expert engineer/M.Eng/PhD.Eng up to a few years ago. Nowadays there are some fairly good pattern recognition algorithms, expert systems and not-so-expert analysis toolkits that drop the requirement down to the level of a good electrical engineer with online support from the manufacturer. This meets requirements for a small but fairly high tech condition monitoring group, but again I have not heard of success stories from users. Silence makes me concerned as I am otherwise only relying on the word of sales and marketing gurus...
    3. Plant conditions are fairly aggressive. Brutal is another word for it. Ambient air temperatures between 7degC and 48degC, Humidity varying between 25% and 95%, condensing moisture, frequent fog, wind blown salt spray, high levels of fine abrasive alkaline dust. Most of the equipment can be installed inside air conditioned buildings, but some has to be installed outdoors and the device specifications need match conditions. Again, lots of marketing, but some advice from somebody who has installed and found problems could go a long way to avoiding trouble on a new installation.
    4. Difficult equipment to connect to. I have buried cables in a high saline water table that connect directly onto transformer oil-filled bushings with no capacitor taps. Difficult to connect to, so I am probably restricted to using sheath earthing voltage limiter connections with high frequency CTs. Vendors tell me there is no problem with this, but is there any experience with measurement sensitivity problems.
    5. Time domain reflectometry promises to locate partial discharge "trouble spots" to within a few metres. This has been around for a while in cable fault  location and pinpointing, and I know it works well, as long as the person doing it knows what he is up to. How well does it work for PD, and do the sensitivity issues in the earlier comment cause issues? 
    6. Does anyone have experience with both completely installed and networked systems vs permanently installed sensors and portable data acquisition units? The former is obviously substantially more expensive, but are problems experienced with frequent terminal connection changes in a plant environment? If a permanent installation is available, have problems been experienced with high network traffic or inadequate OEM software development and support to meet changing operating system and cyber security challenges? 
    7. How easily (and expensively) do other PD measurements integrate into the installed system - I would like to extend the monitoring later to 220kV/33kV transformers and a fleet of 3.3kV motors. The transformers have load tap changers which makes gas-in-oil analysis a bit difficult, and we have started picking up end winding defects on the motors. I also have some GIS switchgear without installed sensors that I would like to monitor, but I appreciate that the ultra high designed-in reliability and the difficulty of retro-fitting sensors probably makes this less than economical.

    At the end of the day I am excited by the prospect of being able to implement condition monitoring on a highly reliable but mission critical asset that was previously unmonitored. But I am concerned that there does not seem to anybody speaking about PD as an online condition monitoring technology, let alone people speaking about successful implementations. That makes me worried about pushing for a new initiative without any verifiable history, and prompted me to reach out for anybody with user side experience in this.

    Kind regards,



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    Alexander Mackenzie-Cameron CRE
    Doha
    Qatar
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  • 7.  RE: Anyone with experience on partial discharge condition monitoring?

    Posted 10-21-2020 10:48 AM
    Alexander

    Sorry, I did not receive the usual notice from the system that you had responded.  Personally, not involved in the equipment or service for online, just use several services when needed for my clients.

    1. For rotating machinery - I've always used Iris, now Qualitrol, out of Toronto, Ontario for both.  They have a presence in the Middle East.  They do some cable and transformer test technology, but I haven't used them for that.  For continuous monitoring of rotating machines you set a baseline and then the changes are monitored over time and when an alarm is tripped, yes, a little more complicated.  Normally you send the data in for analysis which is a day or two.  Specifics with Qualitrol is that they use a much higher frequency range for fault detection which eliminates noise.  I recently had one at a petro-chem in Illinois where PD measurements were extremely high - the site was using a different system.  What flagged my interest was that the PD coupler and RTD values were exactly the same (usually, depending on where the PD is occurring, values will be up to 10X different between the two).  Appears it was a nearby AM station.

    For continuous monitoring (or 1X measurements) of cables and other electrical equipment, especially to monitor for splice deterioration, Doble.  They have several options for each type of equipment and built-in machine learning for several of their products.  I have not used their continuous monitoring systems, but have been involved in a number of 1X tests of cables and have had feedback from a number of sites.  Not brand new and most utilities and larger plants swear by it.  They have local offices in the Middle East.  I believe they also have a number of options other than capacitive couplers for cables and transformer bushing issues, but capacitive couplers provide the highest degree of accuracy.

    On a side note - I do some offline and advise on it in repair shops (normally use Qualitrol for this), but all my work is in the field and not a lab.

    2.  The Doble, above, is a machine learning system they've had in development for a while.  The PhD level is usually when they want to sell the service so make it appear complicated.  IEEE Std. 1434 covers PD testing of machinery and IEEE Std 400.3 covers cables and systems.  I think the latest version of 1434, which was an almost complete rewrite, has been issued and covers details.  I have not served on the 400.3, other than voting, but seems to be straight forward.  Good narratives on the technology in both.

    3.  Agreed - that's why I recommended Doble, above.  If you don't have a contact, I can reach out to my contacts there and get you one.

    4. (see 1)

    5.  Some claims to location, but have not had any experience there.  Normally my field work involves identifying that the problem actually exists.  There is also a standard related to fault locating in cables - IEEE Std. 1234 which discusses it in more detail.  I'll reach out to Howard Sedding to get his thoughts.  In the meantime, above ground systems I've used either a 'sniffer' such that local AM radio stations can be filtered out or an AM radio (old way) for pinpointing - although it is a little more time intensive scanning across the bands.

    6.  Cyber is always a challenge.  For the cable systems, that's why I recommended Doble.  They have both types of systems and feedback from their users that I've met has been pretty good.  I still defer to Qualitrol for machines.  In the permanently installed systems that I've dealt with, the network load is pretty low for monitoring, which is normally just a numerical value, a full data set for PD mapping would be more network intensive.  However, that's normally used for the analysis portion after changes occur in the trended value.

    7.  I had the Qualitrol (PD Trac IIs) installed on 6 13.8kV motors and one 13.8 kV 30 MW generator.  The motors did require a modification to their connection boxes as the engineers at the site wanted more spacing in the cabinets (unnecessary, but there you are).  Permanent installations at some 33kV wind sites have been pretty straight forward, as well.  Usually requires a shut down for installation of couplers or antennae (basically, picking up AM radiated signals). which are not too intrusive.  With the motors, using RTDs can be done, instead, which can help locate the issue.

    Not an end user, just a user.

    Sincerely,
    Howard

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    Howard W Penrose, Ph.D., CMRP
    Random Past SMRP Chair (2018), 2019+ Govt Relations Smart Grid, Infrastructure and Cybersecurity Working Group Chair, and
    President
    MotorDoc LLC
    Lombard, Illinois
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