HZ Frequency Variations?

[Craig]

Hi I was on a site yesterday where the Single phase AC Mains supply was at 217Vac but, the HZ Frequency Was jumping around like a Jack rabbit constantly from 48Hz to 52.1Hz, it is supposed to be stable at 50Hz on 230Vac. What I found was that I was getting resets on my microprocessor and the TFT Display would freeze and do strange things. If I test at a different site where the Voltage supply is correct 230Vac @ 50Hz, all works perfectly and everything executes flawlessly.

In my design I am using a Meanwell IRM-30-12 Encapsulated Switch mode supply [Digi-Key Part Number: 1866-3043-ND], Which takes the 230Vac and outputs 12Vdc and then after this unit I have a bank of Electrolytic and Multi layer Ceramic caps, MOV's and TVS Diodes to block and filter.

I have instructed my client to call out the electrician which did the installation to sort this out as there is an obvious issue.
What is the best way to deal with the Frequency Variances, this should never be the case but, here is a site where this is occurring and making nonsense and I cannot afford to have lockups etc by something like this, I will have to take this type of unforeseen issue into account as I suppose these strange things can happen in the future.


I don't think a Ferrite bead will work as that cuts out higher frequencies but, please advise me on the correct path to take as I don't have any experience with this.

Your help and insight is very much appreciated.

Regards
Craig
   

[Gamboa]

Double conversion UPS.
Regards,
Gamboa

[david]

Hi,
That seems like quite a frequency variation but are you sure your meter is not being fooled by waveform distortion or transients on the mains?
If it's in an industrial application, there could be some ugly waveforms present.
Also - why should your circuit be sensitive to mains frequency variation (within reason)?  Does your DC supply to the circuit change in any way?
The ferrite bead won't help you as they come in to play in the 10's to 100s of MHz.
We may need more information to solve this one.

Cheers,
David

[Craig]

Thanks Gamboa .David there is a grid tied solar installation on site as well and the electrician sent me a video from the Sunsync app showing the exact same variance where it shows the frequency on the grid and on the system independently.

[david]

OK - even if there is a frequency variation your supply is rated for input frequency of 47Hz - 440Hz.  Why would this give you random resets? 

David

[trastikata]

Why would this give you random resets? 

Is it possible that the board will pick up EM interference?

If there are some ADC inputs, I've seen them cause resets from voltage jumps despite the clamping diodes and current limiting resistors.

It's a switching power supply - not sure how it would react to fast input waveform changes?

[See_Mos]

I think this is EM interference as well.

The power supply converts the AC to DC and stores energy at around 340V before it is stepped down to 12 volts so very short voltage disturbances will not affect the output.  As David pointed out the input frequency accepted by the PSU has a wide range of 47Hz to 440Hz.

Incidentally, I have also noted the instability of the mains supply frequency since the introduction of solar panels and wind turbines.

Is there any welding equipment at the same location?  AC TIG welding especially creates massive amounts of electrical noise.
 

[Craig]

Thanks Trastikata and See-Mos, I have and ADC reading the Keypad in a Voltage ladder on a single pin. It is working fine so not sure if that is causing any issues the Micro controller is a Pic18F47Q10 running Internal at 64Mhz.

The Problem in South Africa is that we are having major issues with Electricity supply, your electricity gets switched Off and then On again at least four times a day for hours at a time. We have three phase supply on our property and you sometimes get some of the phases that come back at 85v or 125v and your third phase will be correct at 230v and so on, luckely this does not happen often.

It is very possible that the Frequency does drop below the 47Hz range for a second and then go up to 48 - 52hz anything is possible here. When I checked the power at the Lady's residence yesterday I had switched my equipment off and was measuring around her house and then in the street where the Electricity mains supply comes into her property so yes it could dip below the range of the power supply and who knows what that will do?

She had nothing on that would draw excessive current and No there is no welding equipment on her property. I do suspect that there is an issue with her solar installation as in the street the electricity supply was perfect 225Vac @ 50Hz but, in her house where ever I measured the Frequency was jumping all around.

I have been running her two units all night and all day today in my office and they run perfectly without a hicup my electricity comes straight from the grid and is stable at 228Vac @ 50.1Hz.

[DaveS]

As See_Mos said EM interference, dirty mains.
I would fit a 12V Spike Suppressor to your equipment cost about £10, worked for me in the past on various electronic equipment, worth a try.

The problem may not be on her property, could be any property on the same supply line causing an issue.
You would need to monitor the mains power supply over a longer period to find out what is actually happening.
If the voltage drops lower than 85v, I would supply the 12v dc via a 12v boxed power supply with battery backup or use a UPS unit.

Dave

[dnaci]

It may be useful to connect 6.8NF 250V between Smps -V and ground. Just a suggestion. Resetting your processor makes you think that your pcb design may be problematic. Your processor should not be reset even if the voltage frequency changes.

[david]

How close is the supply module to your circuitry?  Is it possible it uses unshielded ferrite cores for filtering that may radiate in to your circuit?  Fast changes on the mains supply may produce considerable magnetic fields in nearby components.

David

[See_Mos]

The description in post 7 suggests to me a bad connection somewhere between the street and the equipment and the erratic voltage and frequency readings are the result of arcing

[david]

The description in post 7 suggests to me a bad connection somewhere between the street and the equipment and the erratic voltage and frequency readings are the result of arcing

It does seem curious that the voltage and frequency are so different between the road and the house. 
I also wonder if the solar equipment is being used to sell power back to the grid.  A neighbour near us does this but he says the price they buy back a kWH is only a fraction of what they charge a consumer for it.  No idea how individual units sync up to the national grid.

David

[Craig]

Thanks Very much DaveS, Dnaci, David and See_Mos for all the help. I think there is defiantly and issue with the electricians solar installation and setup and I am sure there are loose connections also which causes arcing and frequency issues.
regards
Craig

[joesaliba]

Here who install solar panels and sell to the grid must be licenced by the authority to do so to keep things under control.

However, at my fathers house I saw an overvoltage, higher than the permitted 10%. When I called the electrical supplier they told me that currently there is a problem with solar panels which are boosting the grid, but they are adding / taking measures voltage levels back to normal.

Indeed they was the panels at `fault', as as soon a the sun went a bit down, thus generating less power from solar panels, voltage went back to normal. 

[Craig]

Thanks Joe What I noticed when taking more measurements is that the Frequency would suddenly spike from 49Hz to 53Hz in a very quick pulse and the ac voltage would only change by about a volt.

[david]

How does this impact your DC supply to the micro?  How are the frequency changes linked to the micro resetting?

David

[Craig]

Hi David

I had to remove the Brown Out Reset and it then doesn't Reset. Every time this Frequency spike would happen it would cause a reset so I Removed the Brownout Reset and now it is fine.

[david]

Most interesting and I'm glad you have it sorted now but doesn't that imply that your DC supply was dropping below a critical level?  I would be looking at the supply line with a 'scope because the problem seems to be the way the AC-DC power module copes with the frequency changes.

David

[Craig]

A scope will be the way to go thanks for your help David