Unless it is designed for that: sometimes a three phase generator is configured to work as a single phase generator by a manufacturer.
unbalanced 3 phase generator load
- Thread starter PLR
- Start date
- Status
Unless it is designed for that: sometimes a three phase generator is configured to work as a single phase generator by a manufacturer.
- Location
- Massachusetts
All three phase generators in the US can supply single phase loads of various percentages of the rating.
Please provide a link to a three phase generator that cannot supply a single phase load.
Phil Corso
Senior Member
- Location
- Boca Raton, Fl, USA
Smart $...
PLR stated that the generator was 3-ph, delta. You stated in your 29-Apr (12:28) reply, "One thing many forget is that in a delta configuration, 1/3 of a single-phase load's current is handled by the two indirectly-connected windings."
I've been in this business quite a while, and I'm eager to learn something new! So what I would like you to explain is, how? Specifically, if the single-phase load is connected to, say, phase A-B, then how do the indirectly-connected phases, say, B-C and C-A, carry 1/3 each?
Phil
PLR stated that the generator was 3-ph, delta. You stated in your 29-Apr (12:28) reply, "One thing many forget is that in a delta configuration, 1/3 of a single-phase load's current is handled by the two indirectly-connected windings."
I've been in this business quite a while, and I'm eager to learn something new! So what I would like you to explain is, how? Specifically, if the single-phase load is connected to, say, phase A-B, then how do the indirectly-connected phases, say, B-C and C-A, carry 1/3 each?
Phil
Last edited:
Not only in the US, but all three phase generators in other parts of the world can supply single phase loads of various percentages of the rating with negative sequence current limited: 10 % is the maximum negative sequence current. So what is the percentage of negative sequence current in the OP's case?
Phil:
In delta connection line current=1.732 times phase current. Suppose the load is connected between any two terminals in a delta connected generator. Then VA supplied to load is line currentxvoltage=1.732xphase currentxvoltage. So 1.732 times individual phase supply capacity of the delta connected generator. But this comes with a prize.
In delta connection line current=1.732 times phase current. Suppose the load is connected between any two terminals in a delta connected generator. Then VA supplied to load is line currentxvoltage=1.732xphase currentxvoltage. So 1.732 times individual phase supply capacity of the delta connected generator. But this comes with a prize.
I drew up the following for a discussion regarding a transformer with 480V delta-configured secondary, but the principle is the same...
The easiest way to understand is to look at the windings as two separate power sources connected in parallel, each having a different source impedance (z for one winding, 2z for two).
Phil Corso
Senior Member
- Location
- Boca Raton, Fl, USA
Sahib...
You are dead wrong! Please consult any 3-ph power text!
Regards, Phil
You are dead wrong! Please consult any 3-ph power text!
Regards, Phil
Phil Corso
Senior Member
- Location
- Boca Raton, Fl, USA
Smart $
You too, are dead wrong. The line-current is the vector-sum of both legs connected to that line. You can't add them arithmetically!
Phil
You too, are dead wrong. The line-current is the vector-sum of both legs connected to that line. You can't add them arithmetically!
Phil
- Location
- Placerville, CA, USA
- Occupation
- Retired PV System Designer
Phil, you are the one who is right in general but wrong in this particular case.
The voltage between the two connection points (corners of the delta) from the two sources are identical vectorially, since they are normally connected to each other. If you open the corners you still have the same voltage difference at both the two-coil and one-coil side.
As a result, any currents flowing into a (for simplicity resistive) load from the two sources will be in phase also.
In the special case that two vector currents are in exactly the same direction, you are completely justified in adding the amplitudes.
The winding current has the same angle (phase) on all three windings, only the magnitude differs.
For example, using the previously posted depictions, what is the current's angle on the two-winding power source? The one-winding power source? Are not the vector sum and arithmetic the same?
He's not wrong, he just hasn't thought it through completely... yet.
Phil Corso
Senior Member
- Location
- Boca Raton, Fl, USA
Smart $...
I want be very clear about your aassertion... that is, the winding to which the load is connected, say A-B, carries two-thirds of the load, while the indirectly-connected windings, B-C and C-A (in series) carry a third of the load!
Sahib...
I thought the SQRT(3) factor appled only to balanced loads? Do you mean to say that Sqrt(3) x 20 = 30?
Phil
I want be very clear about your aassertion... that is, the winding to which the load is connected, say A-B, carries two-thirds of the load, while the indirectly-connected windings, B-C and C-A (in series) carry a third of the load!
Sahib...
I thought the SQRT(3) factor appled only to balanced loads? Do you mean to say that Sqrt(3) x 20 = 30?
Phil
Phil Corso
Senior Member
- Location
- Boca Raton, Fl, USA
Goldigger...
I pose a 3rd question to you. Are you saying if the delta were opened so that the 30A load remained connected to A-C, the voltage across winding A-C is only 2/3, of what it normally is, so the load-current now drops to20A?
Phil
I pose a 3rd question to you. Are you saying if the delta were opened so that the 30A load remained connected to A-C, the voltage across winding A-C is only 2/3, of what it normally is, so the load-current now drops to20A?
Phil
Phil Corso
Senior Member
- Location
- Boca Raton, Fl, USA
Smart $, Sahib; Goldigger...
When you reply please discount excitation or circulating-currents!
Phil
When you reply please discount excitation or circulating-currents!
Phil
- Location
- Placerville, CA, USA
- Occupation
- Retired PV System Designer
The load current does not change at all, nor does the voltage. The source from which that current is supplied does change though.
And the reason that two thirds of the current comes from the direct winding and one third from the series pair is, as was stated, that the source impedance of the double winding is twice that of the single winding. (To a very good first approximation anyway!)
Last edited:
That is correct....!!!
PS: Since Golddigger is starting to add nuances, I suppose I should state that each single winding is of equal impedance.
To help, what is a purely resistive load current's phase angle when connected across the missing winding of an open delta compared to the phase angle of each individual winding's voltage?
Last edited:
- Location
- Placerville, CA, USA
- Occupation
- Retired PV System Designer
I notice that you have also not specified whether it is a gas or diesel generator, nor whether it is rated for use as a prime mover. :angel:
That is correct...!!!
Phil Corso
Senior Member
- Location
- Boca Raton, Fl, USA
Smart $ ...
Rather than play your "Who's on First" game, I can recommend an excellent text on 3-phase generators!
Regards Phil Corso
Rather than play your "Who's on First" game, I can recommend an excellent text on 3-phase generators!
Regards Phil Corso
- Status