unbalanced 3 phase generator load

topgone

Senior Member
Unlikely, but possible. Please see the proposal for single phase operation of three phase generator from one manufacturer in post#77.

The generator is rated for full load capacity with its cooling fan running. So its cooling capacity may not be sufficient to meet about 15% over load on one phase. It is helpful if you quote some standard on this issue. Some standard says only 105% phase overload........
Even if you follow that 105% trip standard of yours, the OC protection relays are fed with 1.0 pu that the CTs pickup on the generator lines.

As I said, don't you just believe me, try it. If you spread out the winding in a plane, you must see that there are areas in the generator, loaded as discussed, to be very cool as those coil slots don't get hot. Remember that the other two coil groups are loaded with 1/3 of their respective currents. With a rotor in between, it isn't hard to understand that the cooling air swirls around the coil slots as it pass from one coil end to the other. The extra heat caused by one coil group with 115% overcurrent you are concerned about is compensated with the large volume of cold iron in the stator.
 

topgone

Senior Member
So you want the generator manufacturer quoted in post#77 to be exonerated? :)
That post #77 of yours quotes a manufacturer specs saying single phase AC generators are taken from 3-phase AC generators wired for single-phase application. I don't see the statement you posted in #77 where the figure "57%" is.

Suffice it to say, the manufacturer made it known that the 3-phase generator is re-wired for single-phase application; making sure that the generator windings share the single-phase load as much as possible. That condition is very much different from the discussion re: applying a single-phase load on two of the three generator lines (delta-connected generator).
 

Smart $

Esteemed Member
Location
Ohio
That post #77 of yours quotes a manufacturer specs saying single phase AC generators are taken from 3-phase AC generators wired for single-phase application. I don't see the statement you posted in #77 where the figure "57%" is.

Suffice it to say, the manufacturer made it known that the 3-phase generator is re-wired for single-phase application; making sure that the generator windings share the single-phase load as much as possible. That condition is very much different from the discussion re: applying a single-phase load on two of the three generator lines (delta-connected generator).
Text on the page says:
SINCLE PHASE A.C. GENERAT0RS
The single phase a.c. generators are obtained from
three-phase a.c. generators, delta-connected and used
between two phases. Therefore they are designed for
only one voltage in single phase.
Annotation of the bottom diagam says:
Single-phase alternators (2 leads)
220 - 380 V - 57 % of three-phase power
Don't see anything to indicate the generator is "rewired". The jumpers are the same as the delta diagram.
 

topgone

Senior Member
Text on the page says:

Annotation of the bottom diagam says:

Don't see anything to indicate the generator is "rewired". The jumpers are the same as the delta diagram.
Well, you are free to interpret what you read there. I only saw the image in post #77 and commented the way one would prep a three-phase generators to be used for single-phase, definitely not "delta connection".

"obtained from three-phase generators" doesn't mean "connected as it is" to me. Why do customers need to call application engineers if they can just hook up what they can buy then?

Those issues mentioned in that post#77 are not the reasons why I commented on this thread in the first place. I just wanted to share what the real world offers to people in the offices, so to speak--> that a three-phase, delta-connected generator can take a single-phase load on two of its three lines 57.74% of the 3-phase generators rating. Been there, done that in the field, and the genny ran well.
 

Smart $

Esteemed Member
Location
Ohio
Well, you are free to interpret what you read there. I only saw the image in post #77 and commented the way one would prep a three-phase generators to be used for single-phase, definitely not "delta connection".

"obtained from three-phase generators" doesn't mean "connected as it is" to me. Why do customers need to call application engineers if they can just hook up what they can buy then?
I didn't agree with it from the get go, so I'm not interpretting it any particular way. Besides, it is only one page of the manual, and could easily be out of context with the entire manual.

Those issues mentioned in that post#77 are not the reasons why I commented on this thread in the first place. I just wanted to share what the real world offers to people in the offices, so to speak--> that a three-phase, delta-connected generator can take a single-phase load on two of its three lines 57.74% of the 3-phase generators rating. Been there, done that in the field, and the genny ran well.
I don't doubt it.

However, say your installation ran fine and another with seemingly identical parameters did not. Many variables would be involved with determining why. A few of the many could be differences in calculated load versus connected loads, when they were energized and not, slightly different operating ambient temperature, ventilation, or exposure to direct sunlight or other weather conditions, one had less voltage drop on the feeders, a difference in power factor... the list could be extensive to say the least.

My point throughout this discussion has not varied: a parameter indicating 57.74% change in available power seemingly indicates a generalization based solely on winding configuration. If the windings were wye configured, I wouldn't have challenged.
 

topgone

Senior Member
However, say your installation ran fine and another with seemingly identical parameters did not. Many variables would be involved with determining why. A few of the many could be differences in calculated load versus connected loads, when they were energized and not, slightly different operating ambient temperature, ventilation, or exposure to direct sunlight or other weather conditions, one had less voltage drop on the feeders, a difference in power factor... the list could be extensive to say the least.

My point throughout this discussion has not varied: a parameter indicating 57.74% change in available power seemingly indicates a generalization based solely on winding configuration. If the windings were wye configured, I wouldn't have challenged.
Let's agree on some and argue on some, that should be clear. There's no such thing as one solution fits all in the first place.

Assuming electrical equipment manufacturers comply with product standards, it would be safe to hold a brands claim re capabilities of their products on every specific application as truthful and correct. Any stunt they do to short-change customers will impact on their future sales as consumer groups will be quick to spread the bad experiences they'd get on any particular equipment. Still, we learn as we get hold of these units and share the good practices as well as those that are impractical.:)
 

Smart $

Esteemed Member
Location
Ohio
Let's agree on some and argue on some, that should be clear. There's no such thing as one solution fits all in the first place.

Assuming electrical equipment manufacturers comply with product standards, it would be safe to hold a brands claim re capabilities of their products on every specific application as truthful and correct. Any stunt they do to short-change customers will impact on their future sales as consumer groups will be quick to spread the bad experiences they'd get on any particular equipment. Still, we learn as we get hold of these units and share the good practices as well as those that are impractical.:)
I'll agree to that... :D
 

Sahib

Senior Member
Location
India
I'll agree to that... :D
I do not agree to that.

Even though the generator manufacturer may be trusted on the strength of his reputation in the market, I think it is prudent to scrutinize his claim because in the relevant IEEE standard, the maximum value for negative sequence current is 10% only, whereas in the subject generator it is about 60%.

The negative sequence current produces an additional ampereturn wave which rotates at synchronously speed in the opposite direction than the rotor. The eddy currents which are induced in the rotor parts will then have the double network frequency. During this conditions, the temperature of the rotor may reach high levels. This accelerates the ageing of the insulation and originates high mechanical stress.

The generator manufacturer, as many others like him, did not give any details regarding the above.
 
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Smart $

Esteemed Member
Location
Ohio
I do not agree to that.

Even though the generator manufacturer may be trusted on the strength of his reputation in the market, I think it is prudent to scrutinize his claim because in the relevant IEEE standard, the maximum value for negative sequence current is 10% only, whereas in the subject generator it is about 60%.

The negative sequence current produces an additional ampereturn wave which rotates at synchronously speed in the opposite direction than the rotor. The eddy currents which are induced in the rotor parts will then have the double network frequency. During this conditions, the temperature of the rotor may reach high levels. This accelerates the ageing of the insulation and originates high mechanical stress.

The generator manufacturer, as many others like him, did not give any details regarding the above.
I'll agree to that, too! :p

(Must not feel like arguing today :angel:)
 

Besoeker

Senior Member
Location
UK
The generator manufacturer, as many others like him, did not give any details regarding the above.
Personally I'd take the view of the designer, manufacturer, and supplier rather more seriously than that of an internet pundit who has neither designed nor manufactured one.
Which of the two would take pain by getting it wrong?
 

Sahib

Senior Member
Location
India
Personally I'd take the view of the designer, manufacturer, and supplier rather more seriously than that of an internet pundit who has neither designed nor manufactured one.
I think this is not in line with the spirit of the forum.

Our intention is to resolve any conflict between what a standard says and what a generator manufacturer claims.

I hope your further posting would be in line with above rather than personal attacks.
 

Besoeker

Senior Member
Location
UK
I think this is not in line with the spirit of the forum.

Our intention is to resolve any conflict between what a standard says and what a generator manufacturer claims.

I hope your further posting would be in line with above rather than personal attacks.
I'd believe the designer. I don't see any conflict in that. It's just being pragmatic.
If he gets it wrong I have recourse to pursue remedial action.
 

Sahib

Senior Member
Location
India
I don't see any conflict in that. Please don't make it one.
The IEEE Standard C37.102-1995, AC generator protection guide has a maximum of 10% for continuous negative sequence current carrying capability of a generator. For three phase delta connected generator used as a single phase generator the negative sequence current is about 60% when used at 57% of its three phase capacity. But still the generator manufacturer advocates such a use of the generator. This is the conflict to be resolved.
 

iwire

Moderator
Staff member
Location
Massachusetts
The IEEE Standard C37.102-1995, AC generator protection guide has a maximum of 10% for continuous negative sequence current carrying capability of a generator. For three phase delta connected generator used as a single phase generator the negative sequence current is about 60% when used at 57% of its three phase capacity. But still the generator manufacturer advocates such a use of the generator. This is the conflict to be resolved.
Just because a manufacturer decides to produce a product that exceeds the requirements of a standard does not make anything a conflict.
 

Sahib

Senior Member
Location
India
Just because a manufacturer decides to produce a product that exceeds the requirements of a standard does not make anything a conflict.
The dictionary definitions of conflict are below
con?flict (k
n
fl
kt
)n.1. A state of open, often prolonged fighting; a battle or war.
2. A state of disharmony between incompatible or antithetical persons, ideas, or interests; a clash.
3. Psychology A psychic struggle, often unconscious, resulting from the opposition or simultaneous functioning of mutually exclusive impulses, desires, or tendencies.
4. Opposition between characters or forces in a work of drama or fiction, especially opposition that motivates or shapes the action of the plot.

I used the second definition here.
 
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