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Low (<1kV) grid transients - worst seen? 1

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Skogsgurra

Skogsgurra

Electrical
Mar 31, 2003
11,815
Hello world!

I am trying to get a good picture of the worst transients one can expect on normal low voltage grids in different parts of the world.

Personally, I have met one transient that tripped drives and other equipment in a whole region. It was caused by 39 Mvar phase compensation capacitors being switched (unsynchronized) to a 130 kV transmission line and generated a dip-plus-peak-ringing that made the 500 V grid peak at 940 V. See attached recording. The upper trace shows VFD DC link voltage being pumped up by the transient so inverter trips.

That is the worst I have seen in about 40 years, this was in 1991. I guess that I have been lucky - there must be much worse transients. I am not asking about lightning hits or indirect hits, they are usually in the microseconds range, but transients with lots of energy. The width of such transients is usually one or two milliseconds - perhaps more.

It would also be interesting how you handle such potential threats. What protection is used?


Gunnar Englund
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
 
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LOL Gunnar... you are proving something I have tried to make a point of for a while. Most of our utilities SWEAR that this does not happen! They also swear that they don't use capacitors for line compensation.

At one industrial installation where all of their VFDs kept tripping on OV even though the display would read normal. I suspected they had caps that were ringing on grid switches and even found the caps out near the highway where their service came in. The utility denied it even after I told them I had pictures of the caps on their pole, they just denied the devices were caps! Unfortunately I could never get anyone to pay for renting a recording meter so I could wave it in the face of the utility engineer, but instead, they just took my recommendation to pay the utility to install a series reactor down stream from the caps (that were NOT caps) and lo and behold, the problem miraculously went away! Before that, they would just keep switching brands of VFDs, hoping that someday someone would create a magic one that could withstand their peaks.
 
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That's great Jeff. As you probably guessed, I am trying to anticipate what a drive can be exposed to when installed anywhere on this globe.

There are horror stories about three time sine peak voltage and milliseconds wide. But I have yet to see one of them. Please, send all links, graphs, reports that you have available or may know about.

Gunnar Englund
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
 
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"Please, send all links, graphs, reports that you have available or may know about"

This was meant for all visitors - not only Jeff.

Gunnar Englund
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
 
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Very few answers, so far.

The subject was supposed to be "Low voltage (<1kV) grid transients - worst seen?"

Would that make the question any clearer?

There must be hundreds or thousands of recorded transients out there - please share with the rest of the world.

Use the Attachment function (step 3 below) to attach any jpg, pdf, doc, tif or other document you have available.

Gunnar Englund
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
 
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Gunnar, I have hungreds recorders, but only on MV side, we havent's recorders on the LV sides.
Regards.
Slava
 
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Hi Slava!

MV would also be interesting since we always derive our LV grid from MV. Also when running from a GT in islanding mode.

It would be very interesting to see some of your worst recordings. Especially generator output voltage when running at full load and a large part of the load trips.

Of course, any capacitor switching or other reason for fast transients is also interesting.

Gunnar Englund
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
 
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No Problem Gunnar. It's take time, I need sort all recorders. Trip of generator on full load and Capasitor switching, I need check.
On this moment,on my desktop I have intresting recordings of XFR inrush and BB ,with induction motors, load voltage in case of infeed trips.
Are you have recorder viewr for COMTRADE format?
Regards.
Slava
 
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No, sorry. I don't have it - I think. Or is that the Siemens disturbance recorder format? I can get a viewer for that.

Gunnar Englund
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
 
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SIGRA ( SIEMENS) is good viewer.
Possible TOP, is free of charge.
Are you intresting only in voltage recorders or current also?
Regards.
Slava
 
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Voltage first hand, but current could be interesting, too.

Would it be possible to make pdf copies? Or bmp by using PrtSc?

Gunnar Englund
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
 
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Here are some interesting recordings on a fairly large 600VAC service (I think it was 2kA or 3kA). All recording are +/-1.5kv and +/-1kA even though only one scale is shown. The voltage measurement is phase-ground so 347Vrms nominal or 490V peak. The plant was running at a low time so the load was varying about 100A to 200A.

A 50kVAR capacitor was switching onto this service and it was causing >1kA ringing between the capacitor and the utility. Computers and VFD's on the service were tripping when this was happening. Unfortunately, I don't have info on the transformer or utility.

I probably have others but this was a recent one I remember.
 
 http://files.engineering.com/getfile.aspx?folder=c3622315-777b-4545-895d-c9c670749d82&file=Capacitor_Switching_Events.doc
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Thanks, Lionel!

This one is very much like the one I got back in 1991. It is interesting that the looks of them are similar even if yours was caused by a capacitor switching on the 600 V side and mine was on the 130 kV side. There are "sharper" spikes (higher frequency contents) in yours. The lower frequencies seem to travel through a couple of transformers from 130 kV to 10 kV and from 10 kV to 500 V rather unaffected.

Gunnar Englund
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
 
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Hi.
Please find attached file, it's more current recorder.
1.File it's diff protection unwanted trip ( 161kV 1-ph AR result), from report with Harmonic analysis
2.File it's diff protection unwanted trip ( XFR inrush result), from report with Harmonic analysis.
3. Intresting inrush.
Only in first file showed Voltages.
Regards.
Slava
 
 http://files.engineering.com/getfile.aspx?folder=a4b85e51-06bc-48e0-843e-8a96a23bb733&file=New_WinZip_File.zip
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Thanks Slava,

I have to dig into that.

Gunnar Englund
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
 
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Hi, Gunnar,
I have some data from a plant in India which has transient events around 850-900V Line to Line on it. I was sent 10-20 of this type of thing, which we could then feed into the mains source for testing purposes.
The site was a Jute manufacturing plant, and was blowing up drives (mainly 11~15kW) with alarming regularity, and "extreme prejudice". This caused an almighty panic and a lot of investigation. Peak volts seen was typically 850V-ish, which of course caused large current surges into the bridge diodes. As you know, a VFD that has blown its IGBT's/input bridge cannot tell you a lot.
It turned out to be cauesd by the facory chimney next door, throwing carbon fibre slivers straight into the "air conditioning for the drives" system.
It appears that our IT thought police won't allow me to upload to engineeringfiles.com, but if you are interested I will find a way of publishing this data.
Regards,
Mort
 
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Hi scum,

Was that a 400 V or a 500 V grid?

I could always come and get the recordings. I know where you live :)

There are other means, though. It is not difficult to find my mailing address from my www. Hint: "contact" is spelt "kontakt" in Swedish.



Gunnar Englund
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
 
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