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Hello!
What's the implications on frequency fluctuations on 3 phase power?
From transformer to feed the lighting dimmer rack. We use Fluke power logger and recorded a frequency fluctuations from 50hz to 0hz in almost every 5 secs interval. It's random, different day and time. What may have caused this and possible solution? Thank you!
 
Hello!
Our Power logger data records that all 3 phases L1,L2,L3 has 230v but the frequency drops from 0Hz to 50hz in 5 seconds randomly.
Is this issue on the transformer? I would assume if there's no frequency there would be no voltage as well. Is this correct? Thank you!
 
Hello!
Our Power logger data records that all 3 phases L1,L2,L3 has 230v but the frequency drops from 0Hz to 50hz in 5 seconds randomly.
Is this issue on the transformer? I would assume if there's no frequency there would be no voltage as well. Is this correct? Thank you!
Hi - weird behaviour ... can you tell us please what is the make and model?
 
Frequency is set at the point of generation and remains constant along the distribution network, have you tried a substitute tester? The last time the frequency fell less than 1.5hz the network automatically began shedding load after 2 power stations failed.
 
The Prime Mover Rotating equipment will have under frequency parameters too which would cause a SD. If it behaved in that manner.
 
Thank you all. Can someone interpret the photo. Obviously, there's a fluctuation of frequency but want to know what can cause this and how to resolve?
 

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Hi - can you post up the other plots too? Thanks
Here's the Good and Bad reading of the Frequency.
 

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I'm struggling a bit to read those plots, but the severity of the plots in your post #10 shows power cuts, not frequency fluctuations! From what I can read of those plots, you're getting 0Hz for minutes at a time. Suggest loose cable on meter?? As @pc1966 asked earlier, what caused you to measure, in the first place?
 
I believe its not the loose connection from the power logger because its stationary and the logger is set to trigger every 10secs. And random readings on different times and days.
Reason for taking the reading is to prove where the issue from our Lighting dimmer with relays acting weird on/off during shows. We suspected that there's issue with the main transformer. But we need evidence where the issue lies.
Is it possible that only the Frequency fluctuations to 0hz and not the power voltage?
 
Is it possible that only the Frequency fluctuations to 0hz and not the power voltage?
If you're connected directly to a tx, yes it's impossible. If you've got other circuitry involved then yes, the power could be rectified somehow. Most switch-mode power supplies would be just as happy with 300V DC, but .... I'd say it's one of the less-likely options :)
 
A transformer cannot output power at 0Hz. If the supply is from the grid (i.e. not a stand-alone generator) then your frequency cannot vary independently. All consumers and generators on the grid operate at the same frequency which is controlled closely by the generation authority - if it varies by more than 1-2 Hz they have to shut down due to possible damage.

The plot showing variation between 49.92 and 50.04Hz represents normal operation of a power network. What appears to be the frequency dropping to zero is probably an artefact of another problem.

Can you give some info about the nature of the supply and distribution wiring up to the point at which the logger is attached?
 
To start off, I noted that when the Power Logger(PL) recorded 0Hz the reporting interval was every 5s, whereas when the power Logger recorded 50Hz the reporting interval was every 10s.

I also looked at page 14 of:

http://assets.fluke.com/manuals/PowerLogumeng0100.pdf

The Fluke PL calculates the True Definition of Voltage Unbalance, viz the ratio of the negative sequence voltage to the positive sequence voltage = Vneg/Vpos. This is called the Voltage Unbalance Factor as defined in IEC 61000-4-30. There is also a simpler less accurate NEMA method which does not take into account phase angles - see for a description of both:


From the voltage and current inputs, the FPL analysis the unbalanced voltages into the two balanced positive and negative sequences plus the zero sequence. If the system is balanced then there is no negative nor zero sequence. A good measure of the percentage of unbalance is then the ratio Vneg/Vpos.

I think - don't know for certain - that when it is selected that the Fluke PL uses the negative sequence waveform eg V1N, it uses it to count zero crossings over a timed interval to then calculate frequency. So, for periods when the system is balanced the negative sequence waveform will be of low amplitude and noise will confuse/interfere with the electronics ability to detect zero-crossings sometimes stopping it taking place - zero frequency is output. Again, I don't know for certain - but I reckon that over the longer interval (10s) noise may be less of a consistent problem and, it may be less likely that the zero sequence is of such a small amplitude throughout the interval for noise to be troublesome and stop frequency estimation.

My wife has just returned home from hospital so I must cut short by saying that it could then be a question of understanding how the Fluke PL works, calculates and displays information to explain the quirky drop to 0Hz every so often. If for example V1P for Positive Seq ( cf V1N for Negative Seq) was selected instead, recorded and displayed I suspect the frequency would not dip to 0Hz because it is always of a decent amplitude for noise not to be a problem.

Or something like this..others can expand or correct.
 
Last edited:
I suppose now my theory in #17 is wrong.

Studying your image 2 in #12 it does not look exactly like the one illustrated on page 14 of

http://assets.fluke.com/manuals/PowerLogumeng0100.pdf

for when the Frequency/Unbalance tab is selected. So your data logger does not appear to me to have the True Unbalance capability. Instead it records and displays max, min and average Voltages and Currents. The reference did say some Fluke DL's don't analyse Unbalance.
 

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