neutral cable burnst on asincronous generator

[181273]

Helloeverybody, I received yesterday an asincronous generator on my office, and It`s comes with the neutral cable burnst.
This generator is from an hydro unit, and the nameplate is 750 Kw, 1000 rpm, 380 V. This is the only problem, the cable that conects the star point with the terminal to ground is burnst.
On my opinion:
- Maybe we got a third harmonic problem.
- Maybe we got a severe unbalance.

There isn`t trend of the currents or some else information. This is a plant that have no so good control.

Please, could somebody tell me if there is other causes that could cause this problem, and how can I avoid it, at this moment I´m thinking about multiply for 2,5 the nominal size.

thank in advance

 

[waross]

I would suspect a bad connection. Over the years the most common cause of burnt cables that I have seen has been poor connections (high resistance, dirty, corroded).
respectfully

 

[whycliffrussell]

waross is probably correct. however, it might be worthwhile to have a look through IEEE C62.92-1989 IEEE Guide to Neutral Grounding in Electrical Utility Systems - Part II - Synchronous Generator Systems to educate yourself on neutral grounding and synchronous machines.

 

[ScottyUK]

The neutral-earth bond is burnt? Then you have current circulating in your earthing system. This is a code violation in most places. The likely cause is you've got the neutral grounded at two locations, and current which should be flowing in the neutral conductor is actually flowing in both the neutral and through the earthing system. The ratio between the two currents depends on the relative impedances of the two paths.

You should ground the neutral at one, and only one location.



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Sometimes I only open my mouth to swap feet...

 

[instrument1717]

If it is a single unit of Power source I Suspect you had bad connection ,which burned by severe ground fault in system.
I my opinion (opinion only ) faults while in a synchronised system may result the same situation if the weakest point( Bad Connection ) was neutral- Ground connection and protections failed or insufficient.