EVSE questions

I am not talking about that kind of management.

Ah, but we were - and more to the point I suspect the EVSE manufacturers were as well. For the likes office carparks or even domestics with a limited supply and a heavy existing peak demand, I see a market for such things (in the same way that load shedding relays sell in France/Spain, where supplies tend to be small).

 

There is no point whatever in running an electric car unless it is solely charged from "renewables"

Certainly the more renewables the better, but I don't think it's has to be 100% to 'break even' as it were. Conventional internal combustion engines in vehicles are notoriously inefficient - the need to match engine output to road conditions means it runs very poorly much of the time (certainly in urban areas). Burning fuel in large scale plant running at peak efficiency almost all the time claws back a lot of efficiency that can compensate for the distribution and charging/discharging losses. So something like 50% renewables and 50% fossil generated electricity may well be more efficient that say a 100% petrol engine. Don't forget the advantages in local air quality too (a growing issues in many of our cities now).

 

All of this assumes that EV drivers would be happy that they had no control of the charge in their car

I see it more as co-operation rather than totally relinquishing all control. A couple of buttons on the charge point - press one for 'have it fully charged by a certain time in the cheapest way possible' another for 'charge as fast as possible (even if that incurs a higher cost)' sort of thing.


 

Detecting that a CNE connection has failed is very difficult because there is no reference potential available, and using a TT type connection as reference has many problems which we have discussed many times. IF the supply is 3 phase, we may use the 3 phase/neutral voltages to recognise a break under some fairly ideal conditions, but load power factors and powers may seriously sway the results so as to make them unreliable. With a single phase supply there is no isolated Earth reference available, and thus it is probably impossible to detect a CNE break. If someone comes up with a non-TT method I would be interested to analyse it fully and the Patent application would be unlikely to succeed if it could not be shown to work under any possible conditions, by demonstration.

As I understand it, the idea is to use the line voltage as the reference - as that remains reliably referenced to Earth at the source even during a broken CNE event - albeit offset by Uo.


So on a simple entirely single phase system any voltage rise on the CNE due to a broken CNE could be deteected as a corresponding voltage drop in the L-N (or L-PE) voltages.


On a completely 3-phase system (having checked that the L-L-L voltages are normal) you can create an artificial N point that should replicate the voltage at the source's star point (i.e. Earth potential) - and use that as a reference.


The tricky one is where the distribution is polyphase but the installation is single phase - where the single phase L-N voltage measurement approach will work most of the time, but can under some conditions be fooled into thinking all is well when it really isn't. I guess you're into probabilities there - if it works 99.99% of the times the rest is probably an acceptable risk, if it was only 50% of the time it's probably not going to be acceptable. If it's presumed that the severed CNE voltage is going to swing about significantly during the fault as single phase loads switch on and off (or fry) and if having once detected the break EVSE will remain latched in the disconnected state, then the risks are likely to be reduced further. I gather that some manufacturers are adding current monitoring to the EV c.p.c. to disconnect should it reach 30mA or similar - rather like using an RCD to provide direct shock protection - to mitigate any remaining risk.


  - Andy.

I am not talking about that kind of management.

Ah, but we were - and more to the point I suspect the EVSE manufacturers were as well. For the likes office carparks or even domestics with a limited supply and a heavy existing peak demand, I see a market for such things (in the same way that load shedding relays sell in France/Spain, where supplies tend to be small).

 

There is no point whatever in running an electric car unless it is solely charged from "renewables"

Certainly the more renewables the better, but I don't think it's has to be 100% to 'break even' as it were. Conventional internal combustion engines in vehicles are notoriously inefficient - the need to match engine output to road conditions means it runs very poorly much of the time (certainly in urban areas). Burning fuel in large scale plant running at peak efficiency almost all the time claws back a lot of efficiency that can compensate for the distribution and charging/discharging losses. So something like 50% renewables and 50% fossil generated electricity may well be more efficient that say a 100% petrol engine. Don't forget the advantages in local air quality too (a growing issues in many of our cities now).

 

All of this assumes that EV drivers would be happy that they had no control of the charge in their car

I see it more as co-operation rather than totally relinquishing all control. A couple of buttons on the charge point - press one for 'have it fully charged by a certain time in the cheapest way possible' another for 'charge as fast as possible (even if that incurs a higher cost)' sort of thing.


 

Detecting that a CNE connection has failed is very difficult because there is no reference potential available, and using a TT type connection as reference has many problems which we have discussed many times. IF the supply is 3 phase, we may use the 3 phase/neutral voltages to recognise a break under some fairly ideal conditions, but load power factors and powers may seriously sway the results so as to make them unreliable. With a single phase supply there is no isolated Earth reference available, and thus it is probably impossible to detect a CNE break. If someone comes up with a non-TT method I would be interested to analyse it fully and the Patent application would be unlikely to succeed if it could not be shown to work under any possible conditions, by demonstration.

As I understand it, the idea is to use the line voltage as the reference - as that remains reliably referenced to Earth at the source even during a broken CNE event - albeit offset by Uo.


So on a simple entirely single phase system any voltage rise on the CNE due to a broken CNE could be deteected as a corresponding voltage drop in the L-N (or L-PE) voltages.


On a completely 3-phase system (having checked that the L-L-L voltages are normal) you can create an artificial N point that should replicate the voltage at the source's star point (i.e. Earth potential) - and use that as a reference.


The tricky one is where the distribution is polyphase but the installation is single phase - where the single phase L-N voltage measurement approach will work most of the time, but can under some conditions be fooled into thinking all is well when it really isn't. I guess you're into probabilities there - if it works 99.99% of the times the rest is probably an acceptable risk, if it was only 50% of the time it's probably not going to be acceptable. If it's presumed that the severed CNE voltage is going to swing about significantly during the fault as single phase loads switch on and off (or fry) and if having once detected the break EVSE will remain latched in the disconnected state, then the risks are likely to be reduced further. I gather that some manufacturers are adding current monitoring to the EV c.p.c. to disconnect should it reach 30mA or similar - rather like using an RCD to provide direct shock protection - to mitigate any remaining risk.


  - Andy.