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Ruggedscot, I agree with dpc and others suggest. Check that CT and let us know what happens, Regards

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...

Dear Hoxton, Thanks for your post. If the generator does not have a neutral earthing breaker how does it run islanded ? CJ

Hi, Thanks for your post. What is the ENA website ?

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...

Thank you Isquardr, Are you aware of a document which relates to requirements for earth nests ? CJ

Hello, I work in the water industry where the standard earth nest resistance for an LV transformer is usually specified as 1 ohm. We have a site which where the ground conditions make it very difficult to get anywhere near that figure which has prompted a debate about where the requirement for...

Gentlemen, How would you size this particular cable ? Service - 400V AC 50HZ TPN Load 1666A Power factor .91 Cable:- Single core XLPE AWA armour to BS5467 laid up in trefoil. Installation - Direct buried in soil at 500mm below surface groups spaced 600mm apart I have referred this to Pirelli...

Hi, I read about this very application at an airfield where 415V at a high kVA was required about a mile from the main substation. The designers installed two distribution transformers back-to-back and thus avoided all the volt drop problems associated with LV distribution. A neat solution.

cuky2000. Thanks, I thought that was it but wasn't sure. Having checked Pirelli data I note that they actually state the inductance in trefoil for SC cables.

Could anyone advise why power cables are arranged in trefoil groups ? I suspect it is to negate induced or circulating currents but are there any publications which deal with the subject ?