1% AC volt drop

[hduz5]

Hi Guys,

I haven't been on here for a while and was just wondering how most people are interpreting the DTI guide 1% voltage drop recommendation nowadays?

Is the only way to be 100% sure that inverters will not ever drop out to design to 1%?

And when meeting 1% requires enormous cable sizes (eg farm outbuildings with 100m AC run) are people just installing a smaller cable with a slightly higher VD and accepting a risk of some downtime?

To share my experience, I have installed loads of systems where the VD has been a bit above 1%, and 99% of those operate just fine. However, there have been problems with inverter cutouts on a couple.

Thanks in advance for any replies.

 

[Earthstore]

This can depend on supply voltage, if it is on the high side, Say 253V and your volt drop is 3%, then for the inverter to match the voltage it has to go over 260V, which then causes it to shutdown as it is over voltage.

If a system needs a bigger and more expensive cable to work properly, then that is what it needs, simple.

All too often, installers think a high volt drop will be fine, if it is a supply cable to a motor, then the motor will still work, maybe a little slower, but it would not be noticed, however PV is different.

I hope this helps.

 

[rich.250]

It will work yes...... But it will get a tad warm...

And agree with the rest above ^^^

 

[Gavin A]

This can depend on supply voltage, if it is on the high side, Say 253V and your volt drop is 3%, then for the inverter to match the voltage it has to go over 260V, which then causes it to shutdown as it is over voltage.

different between SMA and Aurora - SMA will shut down above 253V for 10 minute average, Aurora only for 264V instantaneous value.

However, if you're pushing things on the aurora and it's regularly breaching the 253V 10 minute average rule, then the DNO would be within their rights to demand the install is cut off, or adjusted if they ever found out what was going on as it would put their system in breach of their regulations.

but I'd certainly be prepared to go over the 1% volt drop mark as long as the local grid voltage was in the 240 range rather than the 250 range prior to the PV being installed as long as the inverter could handle it.

 

[SolarCity]

I like to play things on the safe side, particularly where a 100m cable run is involved. I allow for 1% VD and no more.

 

[hduz5]

Cheers for this guys. It is interesting to hear other people's experiences. We will be designing to 1% on this. Haven't done the calcs yet but I imagine we'll be looking at a 70mm cable, as you say Earthstore, if that is what it needs to work properly then that is what it needs.