Clean output waveform of a 24kW STC head

[rcavictim]

I just bought a identical pair of big 24kW, 30 kVA STC, 277-480 volt 3-phase heads from Tom Osborne.  I have been able to belt one up to my Changfa 1115 engine on a test stand but due to only having a really small pulley on the generator head and only two belts I have to run the Changfa at just 1400 RPM to achieve 1800 RPM on the gen head. This engine handles a 6 kW (2 kW per leg) load with ease at this low speed and makes absolutely colorless exhaust at this power with exhaust temp around 500 F.  I could not get enough traction from the small pulley to run 6 kW continuously so I dialed back the load to 5 kW and it ran reliably for four hours straight in my test last night.

I have determined that the AVR which is fed from the harmonic winding appears to operate rather well and was extremely pleased to see what the actual output power waveform looks like.  Picture grab off my o-scope is attached.  All three phases look identical.  This is a very nice, clean looking power waveform IMO.  Note the total absense of that narly harmonic step that is present on the single phase ST heads.

The 24k head is easy to spin.  I have a 100% oversize using this head on a 22 HP diesel but I like overkill for the added reliability and stiffer power that I should see. 

[rl71459]

That looks like quite a good waveform! You must be pleased... Have you spun up both heads? do they
both look that good? Congrat's!

Rob

[rcavictim]

That looks like quite a good waveform! You must be pleased... Have you spun up both heads? do they
both look that good? Congrat's!

Rob

Only had a chance to test one so far.  I'm trying to get a 4 shieve pulley the same size (5-7/8" or 6" OD) as the one on the engine (5-7/8" OD) before I go any further.

[BruceM]

It's nice to see a confirming o'scope image, RCAvictim; the 3 phase ST's waveform really don't have the single phase "harmonic hump".  Thank you for capturing this data!

As I mentioned before- the bigger ST heads have too much field coil inductance to respond much to AVR attempts at flicker reduction, so there is no flicker performance penalty for series harmonic regulation AVRs (like Tom's at Georgia Generator) on large 3 phase ST heads.  On smaller or single phase heads I think AVR's should  be wired externally to use the AC output as the excitation source.

Best Wishes,
BruceM

[rcavictim]

It's nice to see a confirming o'scope image, RCAvictim; the 3 phase ST's waveform really don't have the single phase "harmonic hump".  Thank you for capturing this data!

As I mentioned before- the bigger ST heads have too much field coil inductance to respond much to AVR attempts at flicker reduction, so there is no flicker performance penalty for series harmonic regulation AVRs (like Tom's at Georgia Generator) on large 3 phase ST heads.  On smaller or single phase heads I think AVR's should  be wired externally to use the AC output as the excitation source.

Best Wishes,
BruceM

Bruce,

Send me your contact email addy and i'll fire off a video of my test run to you.