Earthing neutral and frequency of 40 Kw generator.

[John Rumm]

A reasonable description here for those who are interested:

[John Rumm]

Indeed - making you genny spin at something about equal to mains frequency is one thing, making it "grid tied" is something quite different!

Well it does rather depend on the application. For small portable gensets just running individual power tools etc, then an IT[1] configuration (i.e. both sides of the output windings isolated from earth) will remain safe even if there is a live to chassis fault since any indirect contact by an operator to the tools live would simply drag the "live" side of the generator output to earth potential.

For large three phase gensets running fixed tooling etc, that is a less desirable setup. Its also no good if you want to power stuff that expects to have a earth referenced neutral, like a boiler for example where the flame detection will typically fail without.

[1] Not Information Technology in this case, but a less commonly used (non) earthing system:

[George]

se devices in my workshop.

as a problem starting a couple of my machines in the winter when the oil is very thick. I have been trying to rig up a phase comparison device to dete rmine if the frequency of the set is correct, by connecting the alternator output of one phase to the incoming mains supply via two 240 volt bulbs in series. this has worked on several generators over the years and the lights beat against the mains voltage and when the speed is correct to give 50 He rtz the beating stops and the lights stay on or off. It works very well, h owever when I tried to connect one phase from the Lister to the mains throu gh my two bulb box, the earth leakage trip tripped. I cannot see why this should be unless there is a neutral to earth leak somewhere. A chase aroun d with a meter did not reveal anything that I did not expect but I am wonde ring if the neutral wire from the alternator should be strapped to the fram e and / or run to an earth pole in the outside ground. The incoming mains is earthed by a copper rod below the electric meter.

which has an earth wire out just connected to it's chassis, performs perfe ctly and as I can also test this against the Lister with no problem I have set the little engine as accurately as I can to the mains frequency and the n connect this to the Lister set and re-synchronized it. I want to mount t he frequency setting facility permanently so I would rather fix the problem . Would it be better to run an earth wire across the workshop or bang a gal vanized earth pole into the ground outside adjacent to the generator. set

30 HP motor, (22Kw) that I am thinking of scrapping. It can be seen runnin g and is really too good to scrap.

So much traffic and I am sorry to say that I have had a computer problem an d also a domestic one, (two kids moving schools, one to University and the other to 6th. Form College) At the moment the generator is connected earth to earth, neutral to neutral and one phase out of the three on the generat or to the one phase in my distribution box. It is a RCD in the mains distr ibution box and trips when I start the alternator and switch it on.

The 30 HP motor and the 400 Hertz alternator were coupled together on a big frome and provided I think it was a medium sized computer Mainframe, that I was once the resident engineer looking after it. I used to do everything "technical" like installations all sorts of maintenance to just about ever thing and I was also told to dispose of kit no longer used. For most peopl e this meant get rid of it and I acquired a stack of useful kit like this,

- a hundred or so 2 volt lead acid cells that were time expired, even thoug h they were in excellent condition which I washed out, sealed and boxed up and sent back to UK when I came on leave. Most years I used to send a big c rate home, weighing several tons and then hired a lorry to pick them up at Felixstowe.

I do not know what device it was that required 400 Hz at 22 Kw, as this cam e from another center up the road that I had little to do with, but I got t he job of taking it out and getting rid of it. One machine we had was drive n by a 65 Kw diesel generator and I ended up with this alternator too, It i s standard three phase and a quality product. There are a few pictures of this on my website in the Old Engines section in Part two as I had some pro blems getting it to excite.

Incidentaly I did not like Sulphuric acid much and in the search for a less dangerous electrolyte I found out that lead acid cells can be filled with an Alum solution with very little change in the characteristics Alum or Alu minum Sulphate is used in large crystal form as an underarm deodorant so in dication that it is less harmful than sulphuric! Idealy the cells should b e thoroughly washed out before the change, but apart from a slight lowering of the cell voltage the work OK.

Regards George.