Electronics > Power/Renewable Energy/EV's
Help decoding strange V,I behavior in facility
Houseman:
Hi forum. I really need your help decoding a strange Voltage and Current waveform.
I am working in a facility as power quality engineer.
We have several vacuum pumps that sometimes rattle, lights flickers and PC reboots suddenly.
After putting everywhere a power quality meter we have discovered that several times a day also by night, when the pumps are shut down the mains AC 400V power get this typical waveform (typical because it's the same in every moment) as shown in the picture.
Voltage fist goes slightly up then it drops freefall and needs some time to recover to normal value.
Every load connected to it has this peaks in current absorption, as shown in the picture.
We are getting mad trying to understand the cause of this.
Any help would be very appreciated.
Please feel free to ask for more informations
LSP
fourtytwo42:
Looking at the last two in particular this would indicate a large load applied external to your facility as the voltage has changed substantially without a change in current, it could also be a sub-station tap changer so I think you should be talking to your utility to improve your supply quality.
I don't see anything that should cause a PC to re-boot as any SMPS will simply ride over these very short interruptions so that is likely something else, have you tried putting the power quality monitor directly at the PC outlet as that may have another local problem that needs sorting out.
I assume these vacuum pumps are large 3 phase motors, are they driven by inverters or line direct (you don't say) if the latter and they are grumbling there is something much more serious than you have logged on your power monitor such as periodic loss of an entire phase.
capt bullshot:
The last two ones might be sub-station transformer tap changes, as fourtytwo said.
The first one looks like a heavy load being started outside your facility.
The second might be similar, but worse since there's a major imbalance over a short period - three phase motors won't like that.
The third one, heavy load started outside, and something in turn stopped within your facility (current is reduced). As the voltage rises visibly when your current draw falls, your mains feed looks quite high impedance. You should talk to your utility.
Your power quality recorder might be able to record the U and I waveforms, triggering at the voltage dip, maybe these could give some more enlightenment.
Houseman:
I firstly would like to thank very much forty-two and capt bullshot for their reply.
Yes you are both right. The last two pictures are the voltage/current captured directly at the vacuum-pump electrical terminal.
The pumps are small three phase asynchronous motors 2kW/5kW each but apart from grumbling the main problem here is they are spitting drops of lubricating oil through the Anti-Suck Back Isolation Valve on a random time inside the vacuum chamber. This ruins the whole process and all the chamber needs to be cleaned with IPA (three days work) since I learned that oil tends to flow towards the vacuum.
The pumps has been several times retired for revision and the producer has firmly said they has no problems.
Apart from changing the pump with a dry one, my job is to find the cause related to the effect and if really the voltage dip is the real issue.
I honestly have no clue how to move forward..
The strange thing I have noticed is that these dips mostly occurs on Friday morning and on Monday morning on a regular basis (also 10 times in 2/3hours). (not on a regular basis unluckily happens the oil spit).
What could cause on a regular basis external to our facility?? We are near (500mt.) a famous national TV broadcast antenna and we are crossed by 15kV electrical rod transmission lines. (not really a safe place to live...)
@capt bullshot;
- my power quality recorder has a trigger and has recorded U and I waveforms (apart from phase, harmonics and a lot of other parameters.
What should I have to search for?
- do you think the problem is related more to the voltage drop (does 25V dip cause such a issue) or due to other variations?
Thank You again all for your help.
Regards from Italy.
Dundarave:
I’d immediately contact the power provider and try to make it their problem, or if they are not under any contractual obligation to provide clean power, appeal to their knowledge and need to assist you and their other customers who might be similarly affected.
This situation is costing your company significant money, and if it’s caused by the quality of power your provider is sourcing, they likely have some kind of obligation to at least assist in getting to the bottom of it.
[edit] Thinking on this further, if the power anomalies can't be identified and eliminated, perhaps the use of some kind of motor-generator assembly to electrically isolate the production motors from the incoming power would be called for. Notionally, the flywheel effect of the motor-generator would then eliminate the power feed anomalies and provide a "buffered" 3 phase power source.
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