single phase off a three phase genny

[SparkyTris]

what are the implications of using a 3 phase generator to deliver a single phase load?
ie, just using one of the phases.

 

[SUNRAY]

It's not ideal but frequently done. Don't expect to use the full power capability of the genny on just one phase - IE 10KVA genny cannot run 10KVA on just one phase, it would be 3.33KVA max

Potentially it could run less smoothly (shake) or use more fuel but these days I'd hope neither of those are a problem.

 

[ericmark]

The zigzag config was done a lot at one time, it was common for a generator to have 12 windings, these could be arranged to give 55-0-55, 230, or 380 volt phase to phase.

The use of just one phase, would depend on which phase the regulator monitors. That is if you have a regulator, control varies a lot, I have worked on generators which used voltage and current to power the field windings, and at a set output the voltage was spot on, but under or over that output, it could vary a lot.

Today we see a lot of inverter generators, the output voltage and frequency may vary a lot, but the inverter corrects it to 50 Hz and 230 volts. This allows a generator to run at reduced revs with a light load.

So a 1 kVA generator may not work in the same way as a 250 kVA generator, and no one can give an answer without knowing how the generator being talked about is controlled, I have worked with generators which were really car alternators converter, to 750 MW. And they don't work in the same way.

So I can't comment on Honda etc, but some idea of the internal wiring would help.

Of course, you could feed all into an inverter and get a smooth AC output.

 

[briwire]

Sunray's interpretation of the kVA rating differs from mine. I worked installing and testing diesel generators for 10 years and in my experience, a 10kVA generator will be able to supply 10kVA per phase. When calculating the test current, we applied 0,8 power factor to the kVA so a 10kVA would be able to supply 8kW. With a little maths involving root 3 it gives a rule of thumb of 1.4 amps per kW so a 10kVA set should be fine for 11.2 amps per phase.
Loading one phase should be avoided in an ideal world as it tries to raise the neutral voltage above earth potential. In reality, it doesn't cause any long term damage. Just make sure you have adequately sized earth conductors.

 

[SUNRAY]

Sunray's interpretation of the kVA rating differs from mine. I worked installing and testing diesel generators for 10 years and in my experience, a 10kVA generator will be able to supply 10kVA per phase.

That's interesting, we were once provided with a 12KVA to run a sound stage. Our rig was ~6KW and single phase on 32/1, ie in we weren't set up for 3ph, no way could it run a 6KW rig, the voltage just dropped off to the point the amplifiers dropped out and took seconds to self test and start TBH it struggled with 3KW with the varying load.

When calculating the test current, we applied 0,8 power factor to the kVA so a 10kVA would be able to supply 8kW. With a little maths involving root 3 it gives a rule of thumb of 1.4 amps per kW so a 10kVA set should be fine for 11.2 amps per phase.
Loading one phase should be avoided in an ideal world as it tries to raise the neutral voltage above earth potential. In reality, it doesn't cause any long term damage. Just make sure you have adequately sized earth conductors.

Obviously I'm not taking power factor into consideration and I'm a user of such devices not a provider so I don't have the same detailed knowledge.

As to calculations my fag packet method would be 8000/3/230 = 11.59A and 8000/230/3 = 11.11A without root 3 so I'd see the rule of thumb figure of 11.2A as perfectly acceptable.

 

[ericmark]

I would also consider 12 kW to be 4 kW per phase.

 

[SUNRAY]

I would also consider 12 kW to be 4 kW per phase.

I'm personally not aware of it being anything else but as I said the nitty gritty of this has not been my bag.
In fact the standby gensets we had at work were tightly fused, the 75KVA for example IIRC fused at 100A and later the monthly routines stated to check at 100 or 125A... 75000/240/3=104A
The small trailer mounted 15KVA has 20A fuses. One of the fetes I did for a number of years hired a barrow mounted genset (ie it looked like a 2 wheel wheelbarrow) the OCPD was a 7.5A 3ph breaker, this was a few years back now but I'm convinced it was 5.5KVA. The organisers never did understand it was not suitable for running urn as it regularly tripped. I ran a long cable from the church (C 150m) for the PA system after the first year.

 

[bernardgreen]

A three phase motor, a fly wheel and a single phase generator is an option.

 

[mikehammer69]

It doesn't make much sense to me that a 3P generator could be fully loaded on only 1 phase

That would mean that the generator would need to be very much over-engineered to allow for this possibility

 

[ericmark]

A three phase motor, a fly wheel and a single phase generator is an option.

Inverters be they static or rotary have been used for years, who remembers the Lincoln welding sets. Be them electric or diesel powered?

But the thing which matters, is how the unit is controlled. It all hinges around the AVR.

 

[JohnW2]

Sunray's interpretation of the kVA rating differs from mine. I worked installing and testing diesel generators for 10 years and in my experience, a 10kVA generator will be able to supply 10kVA per phase.

I would also consider 12 kW to be 4 kW per phase.

I'm personally not aware of it being anything else but as I said the nitty gritty of this has not been my bag.

Having had a very quick look around, I suspect that marketing people are inconsistent in their 'top-line'descriptions - such that a 3-phase generator capable of delivering 4 kW per phase may be described as either "4 kW" or "12 kW". However, if one looks at the actual spec., one discovers 'the truth'

 

[ericmark]

Single phase, split phase, or three-phase, in the main there is one exciting coil, so the AVR (automatic voltage regulator) can monitor all and take an average, or one and hope even load. Or it can turn the output to DC then back into AC and control each phase with an inverter generator.

Until one looks at the schematic diagram, it is guess work as to what method is used.

 

[endecotp]

Sunray's interpretation of the kVA rating differs from mine. I worked installing and testing diesel generators for 10 years and in my experience, a 10kVA generator will be able to supply 10kVA per phase. When calculating the test current, we applied 0,8 power factor to the kVA so a 10kVA would be able to supply 8kW. With a little maths involving root 3 it gives a rule of thumb of 1.4 amps per kW so a 10kVA set should be fine for 11.2 amps per phase.

I don't follow your thinking, could you please clarify?

At the end you conclude with "11.2 A per phase", which (at 240 V) is 2688 VA. Three of those is 2688 x 3 = 8 kVA, which is kinda 10 kVA allowing for your 0.8 power factor. So that's 10 kVA *total*, not 10 kVA *per phase*. But you say "a 10kVA generator will be able to supply 10kVA per phase". What have I missed?

 

[JohnW2]

At the end you conclude with "11.2 A per phase", which (at 240 V) is 2688 VA. Three of those is 2688 x 3 = 8 kVA, which is kinda 10 kVA allowing for your 0.8 power factor. So that's 10 kVA *total*, not 10 kVA *per phase*. But you say "a 10kVA generator will be able to supply 10kVA per phase". What have I missed?

Quite so. I don't think it's you who is missing anything

 

[ericmark]

If you need to work out the loads allowing for power factors, then in the main you are sailing too close to the wind. This Is not ideal, but it does seem to work. The generators actually had 12 coils, allowing 400 volt three-phase, 230 volt single phase and 110 volt centre tapped. And were designed to be configured to give variable outputs.

We expect some imbalance, but to have zero load on two phases is really going too far.