Neutral Grounding

Simple: when the generator is energised, the main breaker is experiencing a current that exceeds its trip setting.

As the installation cannot be seen from here, get a qualified local electrician to check the system and eliminate the fault that the breaker is proving is there before trying again. Has the installation had an insulation and continuity proving test before energising, for example _{<rhetorical question - NNTR>}?

The generator breaker is tripping when the neutral of the generator is connected to ground or earth point. if i remove the grounding of the neutral it is fine. But as you know it is better to hold the neutral at earth potential to have uniform single phase voltages on all the 3 phases.

Megger and continuity test have been done before enegising and it is fine.

Please describe the breaker and its rating(s).

It is preferred to use TNCS type earthing system with seperate PN and E conductor. Generator neutral should be connected to earth electrodes directly which should be different from electrodes of equipment earth bus. However, they may be interconnected at the electrode terminal end to bring down the overall earth resistance. You may like to monitor the neutral current of the generator by providing a neutral CT and use a earth fault relay for generator protection. This relay will not sense the unbalance current of the single phase loads.

Thanks for the suggestion.I agree . Any how i have a question again. what difference it makes if the generator neutral grounding and distribution board ground is common. pls can you explain me in detail.

Are you sure what the "root cause" for the generator load breaker trip actually is?

It may not be due an overload condition at all and it very well could be that the machine has ground fault protection on-board which is tripping the load breaker via the "shunt" trip circuit due to improper ground/earth connection(s) or other fault(s).

You really need to de-energize the system and check wiring continuity for correct connections and for any earth/ground fault conditions with a VOM.

Once the conductor continuity is verified you need to meggar the conductors and system at the rated voltage of the generator to eliminate and/or identify any insulation failures/faults.

If you are not thoroughly competent with performing these procedures, seek professional electrical help.

If the generator neutral grounding and the distribution board grounding is common then there will be current in the neutral bus both in case of ground fault and unbalance in single phase load. Thus it will be difficult to differentiate between the two and trip the circuit breaker only in case of ground fault.

Hence the neutral should be isolated from the earth bus and should be connected to earth only at one point near the generator and no multipoint earthing should be provided. This can be done like this - the generator neutral should be branched out at the terminal box, one branch should be connected to earth electrodes and a CT should be provided in this circuit, the other branch will be connected to the neutral bus of the distribution board. With this type of neutral bifurcation, the CT will sense only the ground fault current and not the unbalance current in the circuit. Hope I have cleared your doubt.

I have seen reputed manufacturer connecting neutral to generator metal work.

i wanted to have separate earth point for the Ground-cum-neutral bus of generator. you are right. if we separate the ground-cum neutral earth point from the DB earth point , it should be ok.

thanks for the clarity.

Get yourself a clamp on current meter and measure what is going on

Does the main breaker still trip if the single phase branch circuit breakers are open(off)?

Is this a back up for a mains connected installation or a standalone generator?

Is the distribution board ground also neutral bonded?

Can you table a sketch of your installation please?

Isollate the load from grid this may be the couse

Could be......

Need OP's input here.

No need to guess if we have all or at least more information.

Don't connect neutral/ground bus to earth but use it as neutral. At the load end use an earth electrode for grounding/earth. Tell us whether it works now.

Then it becomes ungrounded neutral system. In that case if there is any fault, the other phase voltages will rise. i want to connect the generator neutral to ground point, so that even in case of fault other phase voltages are held at their normal value.

Ground the frame of the generator and connect the neutral to neutral in the dist board, if the supply to the distribution board or mains switch is fed by an armoured cable earth to that, but if it isn't an underground cable then you need to put in an earthing spike.

Bazzer

I brought a Diesel generator 3 ph 4 wire 380v 60 Hz. The neutral terminal was connected to ths ground bus. I connected the 3 phases with neutral to different single phase loads. I connected the neutral/ground bus of generator to earth and distribution board ground also to the same earth point. When I energise the generator main breaker is tripping. Why?

Disconnect the neutral from the ground at the generator. If its ok, then one of the phase loads is connected to a local ground and wired the wrong way!

, you may need to go back to the basics.

What is the capacity of the generator,what is the load.when the generator is running. is the utility power isolated effectively.

do you have a dedicated earthing for the genset.

is your genset earthing effectively seperated from the rest of the earthing pits...i.e 6/7 meters apart.

sometimes obvious issues are left unattaended

regards

SAK

is your genset earthing effectively seperated from the rest of the earthing pits...i.e 6/7 meters apart.

Huh?

Care to provide a model. citation or personal anecdote to support this?

The MEN connection in the generator is pretty standard from what I have seen of many sets coming into Australia from overseas. Apart from the standard questions about competencies and qualifications, you need to be aware that once you change the manufacturer's design you become personally liable for any damage caused when/if things go BANG. These same gensets have the MEN conductor running through the earth leakage relay's toroid. Is it the circuit breaker or the earth leakage relay tripping?

For myself I am still attempting to work out how to manage the liability issues as they conflict with the Australian Standards that state the MEN must be in the main distribution board...anyone? (& my apologies for hijacking this thread)

From post 2: The generator breaker is tripping when the neutral of the generator is connected to ground or earth point. if i remove the grounding of the neutral it is fine. Which cables are you disconnecting exactly - the MEN in the genset, or from DB earth bar?

Drawings would be extremely useful right about 15 days ago

The requirement for E-N bonding inside the genset is dependent on whether or not an RCD device is installed.

Have a look at section 5.2.2 and ensuing paragraphs.