Testing a 3 phase generator

[Guineafowl]

A mate of mine has bought a Pramac GSL30 generator (30kVA) ‘as seen’, and of course there is no output.

Inside the connection box of the Stamford alternator unit, someone has been fiddling - the output wires have been disconnected and taped, and the AVR has also been unplugged.

Now, it’s a 12-wire stator, corresponding to six coils. It was hooked up as a series star, giving 415V ph-ph and 240V ph-n. This is the configuration we want.

I’ve isolated the 12 wires, and identified how they relate to each coil. Using a Megger at 500V, I’ve found that some coils are >3Gohm apart, while others are less than 10k. Have I done enough to call the alternator dead?

 

[jim hardy]

Using a Megger at 500V, I’ve found that some coils are >3Gohm apart, while others are less than 10k. Have I done enough to call the alternator dead?

I wouldn't call it dead yet.
Sounds to me like moisture in the insulation .

In the plant we 'dried' electric motors to get their resistance readings up to snuff..
Sometimes by covering them and placing big incandescent light bulbs underneath
sometimes by connecting a welder and applying somewhat less than full load current(there's no cooling airflow when it's stationary so feel the windings often)
sometimes simply by energizing the built in "heater" resistors.
We'd plot resistance readings every hour or so.

Brush out any carbon dust and grime. A soap and distilled water wash is strong but permissible medicine , follow by a good long heated dry.

I’ve isolated the 12 wires, and identified how they relate to each coil.

I find a Boy Scout compass and small DC source (D-cell battery or wall-wart) handy for that check but it's easier with the rotor out..

Good Luck !

 

[Guineafowl]

I wouldn't call it dead yet.
Sounds to me like moisture in the insulation .

In the plant we 'dried' electric motors to get their resistance readings up to snuff..
Sometimes by covering them and placing big incandescent light bulbs underneath
sometimes by connecting a welder and applying somewhat less than full load current(there's no cooling airflow when it's stationary so feel the windings often)
sometimes simply by energizing the built in "heater" resistors.
We'd plot resistance readings every hour or so.

Brush out any carbon dust and grime. A soap and distilled water wash is strong but permissible medicine , follow by a good long heated dry.


I find a Boy Scout compass and small DC source (D-cell battery or wall-wart) handy for that check but it's easier with the rotor out..

Good Luck !

Brilliant.

Its most likely use was as a standby generator, so it could have sat for a while, condensating.

Looks like I’ll have to pull it from the engine and have a look inside. Pics to follow.

Many thanks, Jim.

 

[Guineafowl]

I find a Boy Scout compass and small DC source (D-cell battery or wall-wart) handy for that check but it's easier with the rotor out..

Thankfully I discovered a diagram of the wire connections under the top plate (after I’d cleverly worked out the configuration).

 

[jim hardy]

Thankfully I discovered a diagram of the wire connections under the top plate (after I’d cleverly worked out the configuration).

Sounds like the wire markers were still there. That's Good Luck - whoever disconnected it didn't cut them off .