Are Over Voltage Problems widespread

[matthunt]

Are any of you seeing High voltage problems in houses with Solar/PV installed in same street?

I attended a call out a few weeks ago due to the fuse board apparently smoking. When i arrived it transpired it was the shower circuit, the voltage measured was 246v and the current 36 amps meaning a 7.5kw shower drawing 8.8kw through a cartridge type Wylex db. The fuse was rated at 30amps and you just could not touch it due to the heat. We all know of the inherant problems with this type of fuse whilst continuing to operate on steady over current. Has anyone else seen this type of problem? as i am aware that multiple PV installs in a street on the same phase will obviously boost the voltage due to the nature of the invertors.

 

[JD6400]

You do have a fair point , and to be honest when we install showers i do first see what the incoming supply is like and if the place is near a transformer when out in the sticks we do tend to up the cable to allow for the fact that 9 times out of 10 it will be running at the higher end of the limit !

 

[JD6400]

Matt hunt / Mike hunt , am i the only one that waisted at least some of my youth watching the Simpsons !??
A little like Seymour butts .:joker:

 

[BillyTheSparks]

yes, you've forgotten about applying ohms law as the load is a resistive load, so the rated output only applies at a specific voltage. At higher voltages the ampage and wattage drawn also increases.

I used ohms law to work these figures out. So how can the higher voltage increase the ampage or wattage of the load.

I'm sorry if I'm coming across as a bit dim but I can't fathom this out at the moment. It's probably very simple.

 

[plugsandsparks]

Assume R is fixed, so I=V/R, so if V rises so does I

 

[Sintra]

Ok we will go simple with a 10 ohm fixed resistance load like a small shower at a voltage of 230V and 250V

@230V
I = V/R
I = 230/10
I = 23A

W = V x I
W = 230 x 23
W = 5290W or 5.29 KW

@250V
I = V/R
I = 250/10
I = 25A

W = V x I
W = 250 x 25
W = 6250W or 6.25 KW

hope this helps

 

[Gavin A]

I used ohms law to work these figures out. So how can the higher voltage increase the ampage or wattage of the load.

I'm sorry if I'm coming across as a bit dim but I can't fathom this out at the moment. It's probably very simple.

it's a resistive load, so you have to calculate the resistance value from the rated figures for V & I first.

calculate ampage at the rated voltage eg for 230V
I = 7500W / 230V = 32.6A

Calculate resistance
R = 230V/32.6A = 7.06ohms


then calculate the ampage at a given voltage, eg 253V
I = 253/7.06 = 35.8A

W = 35.8A x 253V = 9066W

for example.

 

[matthunt]

I used ohms law to work these figures out. So how can the higher voltage increase the ampage or wattage of the load.

I'm sorry if I'm coming across as a bit dim but I can't fathom this out at the moment. It's probably very simple.

Hi Billy, work your figures back using ohms law, remember ohms are constant so voltage and current will reduce proportionally, so if you have a smaller voltage but resistance is constant use V squared R, try it with 1kw at 250v

 

[poppag]

Hi first post, relevant topic, I feel overvoltage presents as many issues as undervoltage. I have been to many jobs where i have encountered a significant overvoltage that has caused damage to electronic equipment & motors ie. boiler pcb/mira shower pcb & fridge/freezers. "The shower manufacturers will have tested its units well beyond voltages expected in domestic supply" They may be tested at a higher voltage than 230v but surley it would still be within the safe working limit 253V max. I find 265V is a common reading i get at jobs like above and a TP-N lift stopped working, L2 - N 337V L2 - E 337V L1&L3 to N&E 241V L1 - L2 400V L1 - L3 400V L2 - L3 400v readings taken at TP-N isolator at incoming head all normal ? Lift motor completley burnt out but im not a lift engineer.

 

[matthunt]

wow, away 5 minutes and the chance of explaining a formula comes up and we have 1000 posts

 

[matthunt]

Hi poppag and welcome, indeed undervoltage is also a major issue, i too have encountered major issue with brown outs on back up generators and indeed Emergency lighting energising. Wow interesting readings on the lift supply

 

[Gavin A]

Hi first post, relevant topic, I feel overvoltage presents as many issues as undervoltage. I have been to many jobs where i have encountered a significant overvoltage that has caused damage to electronic equipment & motors ie. boiler pcb/mira shower pcb & fridge/freezers. "The shower manufacturers will have tested its units well beyond voltages expected in domestic supply" They may be tested at a higher voltage than 230v but surley it would still be within the safe working limit 253V max. I find 265V is a common reading i get at jobs like above and a TP-N lift stopped working, L2 - N 337V L2 - E 337V L1&L3 to N&E 241V L1 - L2 400V L1 - L3 400V L2 - L3 400v readings taken at TP-N isolator at incoming head all normal ? Lift motor completley burnt out but im not a lift engineer.

If you're finding anything over 253V regularly then it's the DNO's responsibility to correct it, and quite possibly their liability for any damaged equipment.

Brief occasional blips above 253 but below 264V are allowed as long as the 10minute average is below 253V, anything over 265 isn't allowed full stop, and should definitely be reported to the DNO straight away to correct, and IME they're pretty quick to correct it (unless there's a dispute over whether it's solar induced, in which case they'll monitor it for 2 weeks first).

Correctly operating solar systems will not cause voltages outside these limits either btw, and if it is a solar installation to blame then the DNO has the power to order the system to be disconneted, or to disconnect their supply as it's obviously not complying with the G83 or G59 regs, which ultimately makes that installer responsible for any resulting damage.

 

[poppag]

Indeed had to take pics of readings to prove to boss. Was asif the neutral had become a phase only in relation to L2. As for the formula
I=V/R so P=I x V so true power rating of equipment P=v2/R resistance is constant heating water isnt.

 

[poppag]

readings at head were perfect I called edf who got there suprisingly fast probably the reason you said. "then it's the DNO's responsibility to correct it, and quite possibly their liability for any damaged equipment"

 

[matthunt]

If you're finding anything over 253V regularly then it's the DNO's responsibility to correct it, and quite possibly their liability for any damaged equipment.

Brief occasional blips above 253 but below 264V are allowed as long as the 10minute average is below 253V, anything over 265 isn't allowed full stop, and should definitely be reported to the DNO straight away to correct, and IME they're pretty quick to correct it (unless there's a dispute over whether it's solar induced, in which case they'll monitor it for 2 weeks first).

Correctly operating solar systems will not cause voltages outside these limits either btw, and if it is a solar installation to blame then the DNO has the power to order the system to be disconneted, or to disconnect their supply as it's obviously not complying with the G83 or G59 regs, which ultimately makes that installer responsible for any resulting damage.

Hi Gavin, this is a question not a statement! if an invertor needs to export to the grid at a couple of volts for example above grid voltage and a few other houses on the same phase on the same street also have solar, would each invertor have to up the voltage above the other to export causing the local grids voltage to rise?

 

[Gavin A]

Hi Gavin, this is a question not a statement! if an invertor needs to export to the grid at a couple of volts for example above grid voltage and a few other houses on the same phase on the same street also have solar, would each invertor have to up the voltage above the other to export causing the local grids voltage to rise?

erm, sort of.

it's a bit hard to explain, but it's not exactly that they all have to kick out at X V higher than the grid, they more just keep raising the voltage slightly until they're able to export power, so you don't (or shouldn't) get some sort of cascade voltage rise going on, and on top of the actual inverter outputs, how much higher the voltage goes depends on resistances and loads within the low voltage grid, then the resistance in pushing the power backwards through the transformer... but that's around the point where my knowledge ends as I'm still yet to get a totally straight answer out of the DNO's about how their transformers operate in that respect.

There could well be situations where mulitple <16amp installations have been installed on the same street which result in voltages being pushed up to the point where inverters end up tripping in and out regularly in full sunlight, which I referred to before, which depending on the impedance, loads etc could result in 2-4V voltage swings per inverter cutting in and out, so if there are several cutting in and out in quick succession due to having the same settings, that could result in some fairly hefty localised voltage swings. It's partly why I and many other installers are starting to push for a more gradual output reduction around the limits, as we can see this being an issue, and the solution proposed by Ofgem and the DNO's will have minimal impact on it (theirs is based on complex pre-notification rules, but it won't work).