generator fault?

[Max1882]

Hi all. my problem is, i had to wire a generator up to a mobile phone last. In a nut shell i have checked all 3 phases against earth and nuetral while they are in a connector block and i get 415 on all 3 phases, however when i hard wire it into the isolator and turn the changeover switch from mains to generator the voltage drops on 2 of the phases (i get 230v,200v,180v) some thing obviously is wrong in the data/control cabinet? And if there is somehting wrong why does it not affect it when there is mains power on it? The voltage dropping only happens when the mast is powered by the generator? Im going back out to the job at 6am so any help appreciated!lol. Thanks in advance....

 

[Marvo]

i have checked all 3 phases against earth and nuetral while they are in a connector block and i get 415 on all 3 phases,

If you're getting 415v between phase and earth or phase and neutral this is a massive overvoltage. Why did you connect it up to the equipment and perform live tests in that case??

......when i hard wire it into the isolator and turn the changeover switch from mains to generator the voltage drops on 2 of the phases (i get 230v,200v,180v)

Are you testing to earth or to neutral to get those phase voltages?

 

[Sintra]

Is the generator correctly rated for the load?

 

[Max1882]

when all 5 wires were in onnector blocks i tested all 3 phases to earth and nuetral

 

[Max1882]

When it was wired into the isolator i checked it against nuetral and earth and it drops on both. There is even a voltmeter switch on the generator what allows me to check the voltage. I dont know the rating of the generator but they are deployed to masts all over the country so i presume it will be big enough, The physical size of it sits on a trailer so its not a small thing id expect it to be big enought to power x2 control/comms cabinets.

 

[snowhead]

Has the Generator side of the changeover switch got fuses in?
180v is that magical figure you get back from a 3 phase load when 1 phase is missing.

 

[Marvo]

when all 5 wires were in onnector blocks i tested all 3 phases to earth and nuetral

You should not have seen 415v between phases and neutral. 240 or maybe 250 volts maximum would be the expected voltage L1-N, L2-N and L3-N.

 

[Max1882]

Sorry just read back, my bad..... When i was testing to earth and Nuetral i was getting 230v and across all 3 i was getting 400v. Everything was electriacally sound until i hard wire it in and turn the changeover switch to generator

 

[Max1882]

theres no fuses, nothing trips and its hard wired into the same place on the isolator as what the mains power tails are and it works fine with mains

 

[Richard Burns]

So effectively you are saying that you have full voltage supplied from the generator when under no load and when the generator is placed under load you are getting significantly reduced voltage. The generator is not being overloaded, though you could have a fault in the load that is drawing excess current.
This sounds more like a lot of loose phase connections in the generator.

 

[Lucien Nunes]

Possibly high resistance neutral connection to the star point? Has the same effect as a duff neutral on the mains.

 

[tazz]

I think you have just answered your own question...."it ok on mains".....tends to suggest the generator is not beef enough.

 

[Max1882]

Im 99% sure the generator is big enough like i say its only powering x2 control/data cabinets cant see those taking a big load. So would you say gett anoth generator deliver to site is the best bet?

 

[Marvo]

I'd also go with the overload theory from the info given. If it was a high impedance neutral at the star point you'd probably see some phases testing high and some testing low WRT the neutral, not all 3 phase at 230v or less.

 

[UKMeterman]

Hi,
Get a clamp ammeter out and see what current is being drawn on all three phases and what current is in N. If you are feeling posh you could even try a power analyser.

 

[davesparks]

Have you confirmed the continuity of the neutral back to the star point?
What does the engine do when it is put under load? Does it labour or hunt or does it continue to maintain speed within reason?
What does the generators control panel have to say about it? Are there any errors reported? Does it trip/shutdown through undervoltage or underfrequency?

 

[Max1882]

the generator continues running but you can hear a difference in the engine. Thinking about it, there is a voltmeter/ HZ meter and an ampmeter on the generator. you can turn a little knob to see the readings of all 3 phases. When the change over switch has been turned to generartor and the voltage drops the ampmeter shows 0 so its not pulling any current.

 

[davesparks]

They sound like analogue meters from the way you describe it, if they are then I wouldn't trust them!

 

[Clive P]

Hi,

Does your switch have knife blades, quite often if they are not aligned properly you can lose a phase or two. Especially if it's a new one and hasn't been used before.

Worth a check.

Regards.

 

[elevate]

Are the Commutator brushes ok