AZFlyer

Simple question....do jet/turbine powered transports typical use 3 phase AC generators?

thanks.

rickair7777

The CRJ is 3-phase and I assume any others would be too.

Using 3 phases gets about three times the power out of a given size and weight of generator case. For that reason almost any industrial or weight critical gen will be 3 phase.

But except for motors, most electrical and electronic devices can only use one or two phases, so the phases are usually split off to different subsystems. An exception would be powerful electric motors, like a hydraulic pump...that would probably use all three phases.

Grid power is the same way...it is generated with three phases at a very high voltage. The voltage is stepped down along the way and only two of three phases are delivered to your house. Most circuits (lights, 120 outlets) use one phase at 120V. The second phase might only be used by large 240V appliances such as central AC, washers, and dryers. The plug for those has an extra pin for the extra phase. These devices are not actually two phase devices, they just use the higher voltage available between two phases (240 vice 120).

Twin Wasp

If you were looking along the shaft of a generator that had a winding from 1 o'clock to 4, 5 o'clock to 8 and 9 o'clock to 12, each rotation would give three pulses. In a 115 volt system, each pulse is not 115 volts but they're not 38 volts either. There's a formula to figure them out but effectively you get 115 volts.

Now all I recall is one synchronizing light is one phase, the meter is another and the other synchronizing light is the third phase. And don't close the bus tie unless the lights are out.

rickair7777

When we talk AC voltages, we use root-mean-square (RMS) since the actual voltage is constantly changing. The RMS gives you a phase "average".

You get about 115V phase-to-neutral, and a about 230V phase-to-phase.

I saw somebody do that once...I also saw a 3,000Kw turbine generator jump about four feet into the air

HSLD

Yep, you've gotta turn the KVARs knob until the light stops blinking - THEN throw the bus tie.

UAL T38 Phlyer

The Lear 35, 31, and I assume all the 20-series are not 3-phase. In fact, they weren't AC, they are DC generators. There is a heavy-duty solid-state Inverter that converts it to AC, although most of the plane was DC-powered. T-34C and OV-10; same deal. So, not all jet aircraft (or turboprop) are 3-phase.

But any other jet I have flown was 3-phase.

3-phase is more effective for weight and space considerations, and electrically, it is much easier to turn AC into DC (a rectifier unit) than to go DC to AC (Inverter). Rectifiers are pretty small and cheap; the Inverter in the Lear was huge and expensive, and failed on a semi-regular basis.

Phantom Flyer

Thanks HSLD for providing the correct response. Gosh...what ever happened to the good old days with real Flight Engineers, the requirement to synch the buss and oh well.... (Please don't respond folks. I know the answer to the question !)

For AZFlyer; most electrical systems in large transport category aircraft have 3 phase AC generators. As T38 Phlyer said, it's easy and efficient to convert AC into DC power through Transformer-Rectifiers (TR) units. From the B-727 and after, Boeing used this technology and it's works well and lasts a long time.

Have a bodaceous day Mates

AZFlyer

Exactly what I was wanting to know. Thank you, gentlemen.

IluvRNP

As I recall the 707 (preceded the 727) was about the same.

Dougdrvr

If you couldn't get a generator on line as a new, wet behind the ears, FE and you turned to the left seat and said " Cap'n, we have a Phase Un-balance!"......... I guarantee you the response would be, "What the he11 is that?"