Generator Megger Testing

[EEbyChoice]

I am installing a new 480 Volt, 1825 KW standby generator (its predecessor suffered a generator bearing failure during an extended run). The new unit sat outside at the dealer for a couple of weeks in almost constant rain/wind and high humidity. It was wrapped in plastic sheeting for part of the time. It was megger tested upon arrival at the dealership, and tested OK.

The unit has since been delivered to our customer's site (they pay us to operate and maintain their standby system, and it is considered of critical importance to them) and set back into the enclosure. The phase cabling has been terminated. We are asking the vendor to repeat the megger test prior to operating the engine since the unit sat outside and was transported since the original test, just as a safety precaution.

My vendor's engineer insists that this is a complete waste of time since it was tested upon arrival at their shop. In my opinion, it is a good final check to assure that no moisture remains in the windings, and that no damage was done during transport and installation. It is quick, cheap and easy to repeat and may also show problems with sensing instruments and/or phase cabling between the switchgear and the engine.

Am I out of line insisting that this test be repeated? Is their really nothing to be gained?

Just looking for opinions.

Thanks

 

[DanDel]

A full set of Acceptance tests (not just megger) are always recommended for any new device after it is installed in place. The idea behind these tests is to verify that the device is 'acceptable' to the buyer before they take ownership of the equipment.

How else do you know nothing was damaged during installation, or some part of the installation was not performed correctly?

Previous tests, including factory tests, are not applicable.

 

[dpc]

Seems appropriate and reasonable to me. If I were the owner, there's no way I would energize it without doing a megger and polarization index on site. Also helps establish a baseline for future maintenance testing.

 

[ScottyUK]

Is this a packaged generator in an enclosure or a bare skid-mounted unit? If it is a skid-mounted unit which is not designed for outdoor service then you have reasonable grounds to reject the unit outright if it has been stored inappropriately, something you might gently remind the vendor of.

The tests you are proposing sound entirely reasonable. I assume the vendor is providing a warranty against any failure due to poor storage? You might consider making that a condition of not rejecting the unit.


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

 

[EEbyChoice]

Clarification. This is a Skid mounted generator set designed to be housed in some type of container or building.

Thanks for the replies. I apprceciate your feedback!

 

[JBinCA]

Vendor's engineer is WAY out of line.

Tell him to megger it or get it off your site - cordially, of course.

And DanDel is right, megger is the bare minimum test. There are a whole host of other's you should be considering.


Regards,

JB

 

[dpc]

I think I'd ask for another field engineer. If this guy wants to skip something simple such as a megger test, I would be concerned about what else he might be cutting corners on.

 

[waross]

Don't forget to short the diodes and test the rotating windings. If the rotor responds slower than the stator to increases in ambient temperature it may be more susceptible to condensation than the stator.
respectfully

 

[Zogzog]

Plus acceptance testing gives you baseline data for future maintenance testing to be conpared to for trend analysis.

 

[Bekza]

Ya I agree, it is important to atleast have some finger print that you can base your mainatance and life of the insulation on before, this should form part of the commissioning requirements.Its easy and it does not take time to perform the test, i think that engineer is way out of line and will be charged for negligence or he might be in the wrong field somehow

 

[TheBlacksmith]

I hope you're kidding. If my supplier's engineer suggested skipping common acceptance tests, I couldn't be rid of him, the supplier and the equipment fast enough. But some people think I'm a bit brash and lack social graces.