Hi Slavag,
Yes the parallelling is for a short time at the moment but we hope to secure a permanent grid connection some time in the future so we need to disconnect the generator star point to meet the requirements of G59/1.
Regards
Scotty, Slavag,
I have to come clean here. I have specified a 1600A Neutral Earthing Breaker (no resistor in neutral circuit) for this occaisionally parallelled 1MVA DG set. The panel builder has not allowed sufficient space for the NEB and is looking for technically sound reasons for reducing...
Andross,
I would concur with Marmite but tell me, how has the generator neutral CB been sized? There does not appear to be a resistor in circuit so is the current rating of the neutral switch the same as the phase circuit breaker ?
Regards
Mr Slavag,
You got it! Now how would you determine the rating of the switch you describe ?
Take neutral cables for example. It is common practice to install half size neutrals from a transformer or generator star point. Could this logic be extended to the rating of a neutral switch ? What do...
DPC,
To comply with G59/1 it is necessary to open the generator neutral earthing breaker when operating in parallel with the grid so as to prevent circulating currents. The breaker becomes closed when the generator is islanded.
Now, could we stick to the point here. What factors (apart from...
Scotty,
Thank you for your post. I appreciate the withstand capability of the breaker should be as you describe but my question related to the service rating of the breaker under normal operating conditions.
For example for a 1MVA generator would the rating be 1600A?
Gents,
Best practice would suggest that a DG Neutral Earthing Breaker would be sized as the Phase circuit breaker but is this really necessary given the low neutral current which will flow in service ?
Are there any factors which would justify derating the device and what might be a sensible...
Gentlemen,
Thanks for your posts. We seemed to have moved away from the 2 neutrals question to the power system configuration.
Firstly on neutral changeovers; When the generator is being used in the TRIAD mode and becomes sychnronised and the generator breaker closes the NEB will not OPEN...
Dear Hoxton and Rbulsara,
Perhaps I should have explained. The generator has 2 functions.
Firstly TRIAD or peak lopping. At the beginning of a TRIAD period the generator will start and run up to synchronism against the mains with the NEB closed. At the moment of synchronism the NEB will open...
Hello,
I am designing a power system which comprises a 11/0.4kV 1000kVA grid connected transformer feeding an LV switchboard. In addition a 1000kVA generator will be used in parallel with the transformer for occaisional peak lopping (TRIAD operation). To meet the requirements of G59 and in...
Gentlemen,
Thank you for your responses but I think I have answered my own question.
The reason that an arbitary number has been abandoned is that no matter what that number is it is no subsitute for good design up front.
It is a bit like the old 500 lux on the working surface in an office...
