We wait with breath held for the amendment 4. Does it expand on the notes offered up during the consultation period, or leave it for industry to decide what is meant by, and hoe to implement a Customer Limitation Scheme.
In the past those around me have stated “we can just use G100”, but with no further statement on how G100 would work for our installation. While the concept is sound, limit the Solar to ensure the Ina is not exceeded, But how, the same timings 15seconds, 3 times in 24hours….
We think of Limitation and associated with G100, as a system that will cut off/reduce the Solar supply. Could it be by design instead, understanding the characteristics of the installation and see where the current flows. Current supplied from either end of a Bus bar, by the time they meet the will the sum exceed Ina.
15 Seconds above Ina, then maintaining Ina. The thermal equivalent will remain above Ina, diminishing over time but never reaching Ina, until the current falls below Ina. Do we need to set a time. If the overload is cleared by the OCPD as its designed to, the time in overload and the time returned to normal (lower than Ina) will give a thermal equivalent below Ina over time. The 15seconds becoming minutes, do we need a CLS or does the design work naturally.
Initially investigations to see if this Overload of Ina was a thing, as everyone was saying “it will never happen”. Quickly these investigations showed that it could, but they also showed examples where it couldn’t.
While there is only one catch all solution, which is currently defined in 551.7.2 Ina ≥ In + Igs. There are solutions out there that can meet the “as safe or safer”. They just need time and work, an Electrical Designer is unable to just look at a SLD as Yes or No.
Below while I’m unable to give an equation to get a Yes/No, below is my order of investigation work.
Establish Max Demand
½ hour data, Assumed Load
Establish Ieff
T1, the length of time overload can exists without effecting Long duration Ina
Establish Overload Risk
Distribution of current during overload, conditions Ina is not exceeded.
Identify any masked overloads by the solar supply.
Establish actions to be taken by solar during overload conditions.
Minimise the need to reduce/remove the Solar production.
Through control of Solar Supply
Through design
Maintain safe of safer than BS7671 amd 3 551.7.2
There is no guarantee this investigation will produce a desired result, it may just prove for the installation you are looking at Ina ≥ In + Igs is the solution.
If it does produce a solution by design, or the “G100” with a correct set of parameters for your installation. There will be cost savings for the disruption of the installation and the associated additional hardware.
Is it work worth doing, yes. Even if it just proves Ina ≥ In + Igs is the solution, then answer is known. The Design can progress passed all the “what if meetings that tend to stall all good projects”.
Remember Ina ≥ In + Igs will always work.
