problems with lights dimming when loads applied (domestic)`

[cypher007]

just had western power out as im fed up of my lights flickering occasionally at night and dimming slightly during the day when we turn say a kettle on.

they put a meter on the supply fuse I went in turned on a 2.2kw kettle and the fan oven result: 242-244v dropping to 232v. this seems a bit high to me. whats the limit?

 

[marconi]

thanks for the reply. I will see what the wp monitor finds. though they didn't seem hopeful that they would be digging up the road any time soon. I get the impression its one of those situations where if not enough people hassle them they hope it goes away.

re. the garage, the light dimming stuff usually happens at night when they are closed. I am wondering as I sit hear if its someone in my road on economy 7 with storage heaters, though Ive seen it do it even at 9 at night.

re. my diverter, its a pretty simple thing on the switching side at least. it uses a triac which is controlled on and off, like a light switch, via an Arduino computer. nothing scary like phase chopping or inverter controlled.

Dear cypher007. I have highlighted two parts of your last post. I will cover the first now and the second after the rugby Barbars - Fiji.

In order to provide some more evidence of line faults to twist WP's arm, so to speak, might you, but ideally WP, measure the PSSC and/or Ze ateach premise and if it is an overhead line supply, note down which phase conductor and pole the supply is connected to.

Then, plot on a piece of paper: along the bottom axis at equal intervals the pole/house number, left-to-right away from the transformer and up the vertical axis the PSSC /Ze by phase (if you can) against each premise/pole. If there is a conductance fault one would expect/might see a change in slope corresponding to the location on the line where it exists. Methinks WP could not argue against that. Other home owners have an interest in cooperating to take the measurements.

if it is a TNS supply and you measure PEFC too you could get maybe a clue on whether it is a line or neutral fault. if your test equipment has the facility also measure neutral-earth loop impedance and plot as well.

 

[marconi]

re. my diverter, its a pretty simple thing on the switching side at least. it uses a triac which is controlled on and off, like a light switch, via an Arduino computer. nothing scary like phase chopping or inverter controlled.

I did some research on the theory and its electrical implementation in PV-Immersion Diverters. I discovered that they are 'quite scary' and infamous for causing troublesome flicker. It is becasue they opereate the triac switch for the immersion heater element in a 'burst fire mode' - so many whole cycles on followed by a number of cycles off. By gradually increasing the length of the on burst to the off burst the diverter regulates the average power consumed by the immersion element. it is significant too that this scheme switches the immersion element on by applying the full mains supply across the element so when switched on there is a step up of 12Amps current drawn dropping suddenly to zero when the triac is switched off. Depending on the algorithm/software of the controller the switching is in the single to low decades of Hertz, and thus within the irritating flicker effect band. It seems, from what research I have done so far, the earlier controllers did not take flicker problems in to account but later and perhaps more expensive diverters do or have an optional 'anti-flicker' mode.

In the same way that switching on your kettle, etcetera is dimming your lighting, the diverter is switching on/off the immersion and causing lower frequency dips to the mains voltage affecting your home and others I suspect. It will also cause harmonics, sub-harmonics and intermodulation currents - and thus a reduction in voltage quality.

Maybe some other folk in your street have PV and diverters which are producing switching current affecting you?

I think that the PV & Diverter switching 'pollution' is made worse by your street's supply having an insufficiently low impedance for some reason yet to be discovered.

Of course this explanation only makes sense when your PV system is generating electricity and thus when there is enough sunlight illuminating the panels.

Do you think this is some explanation if not the whole one? Take a look at the PV diverter literature and let me know the make and model too for me to research it on-line. Probably worth phone call to the Diverter maker's technical team.

 

[cypher007]

wow Marconi, I feel like you take this stuff real serious.

WP are fitting a monitor this Friday. I only have a multimeter.

some interesting ideas. there is maybe 4 houses, at least 2, that have PV in my road and an adjacent road.

the overhead WP think has been buried.
the light flickering dimming is usually at night, apart from the dimming that my diverter causes.
the diverter has an anti flicker function that I have switch on. it only does long on periods or short based on my export, no rapid bursts.

this is the unit I built:
http://mk2pvrouter.co.uk/33001.html

 

[marconi]

I remain suspicious about the diverter because even though it should not be turning the immersion on when the pv installation is not generating it could be doing so spuriously. My reason is that I have taken a quick look at the triac output board for this unit and cannot see any snubber circuit (a series RC network) across A1 and A2 of the triac (see http://mk2pvrouter.co.uk/media/f38a139f4c26bb68ffff809ed4355564.pdf).

Such a snubber circuit reduces the likelihood the triac will turn on as a result of fast rise mains voltage transients above 230V. I am also trying to confirm whether the gate drives are sufficiently filtered to prevent electrical noise across gate-cathode junctions causing false triggering: again I'd expect to see a capacitor in parallel with the a resistor between one of the anodes and the gate to act as a decoupler and twisted pairs or screened wires to make the connections. Also, triacs are best triggered for reliability when A2 and the gate have the same polarity - I have yet to work out if the opto-electronic driver does that. I have the data sheets on the triac and driver to read through and will get back to you.

All this sensitivity to spurious triggering becomes worse as the triac body temperature rises. Is your diverter in a warm location?

 

[marconi]

Once WP have connected up their monitoring equipment Fri 4 Sep 15 and it has been in use for a few weekdays and weekend, could you isolate completely the diverter on the supply side and note when you did? After a few weekdays and weekend, switch it back on again, noting the time and date. Be sure to let WP have this information for their analysis of the records. While it is off see if you notice less or no flickering and dimming of your lighting other than of course that caused by kettles and ovens being turned on.

 

[DPG]

I think this is getting a bit bogged down with triac theory, etc. I still reckon the supplier is going to find a high resistance neutral. Daz

 

[marconi]

I think this is getting a bit bogged down with triac theory, etc. I still reckon the supplier is going to find a high resistance neutral. Daz

Dear Daz, I too think WP will/might find some sort of line fault. I have even suggested how to discover and track it down. But, I think a high resistance conductor/connection mainly explains dimming - low conductance... increased loading... volt drop - not flickering - some sort of brief stimulated undulating change in voltage or current waveforms of the mains supply or domestic installation.

For me this is of great interest and I am trying to be helpful to someone. I like problem solving. I learned so much from electricians and electrical engineers during my 50 odd years interest in electricity who spent time explaining things patiently and making me think and telling me about their experience, trials and tribulations. I find electricity fascinating.

Most knowledge on a subject is not passed on in college - there is not the time. It is books and peoples heads.

 

[DPG]

Absolutely. I admire your interest and the effort you put into your posts. Daz

 

[cypher007]

wp are only going to leave the monitor here for 6-7 days.

he did say when there are a few houses with PV it can cause some issues, there are about 2-4 in my road of maybe 20 houses. I said but at night the inverter is off, his answer is that it isn't entirely off even at night.

 

[marconi]

wp are only going to leave the monitor here for 6-7 days.

he did say when there are a few houses with PV it can cause some issues, there are about 2-4 in my road of maybe 20 houses. I said but at night the inverter is off, his answer is that it isn't entirely off even at night.

Please let us know the outcome of WP's monitoring.

 

[cypher007]

they popped round yesterday. upshot is about what I expected really. nice chap really helpful but ultimately the monitoring shows its within limits. one thing they did notice though was on the flicker measurement there was a regular jagged sign wave up and down below a centre line, which they didn't really explain what it was other than a measurement of flicker. as it is so regular he thinks it might be my PV inverter. I recon it could be the varilight touch dimmers myself.