dumb question - 200 amp, 3 phase, 208 volt

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winnie said:
The power factor placed on the _entire_ transformer secondary is unity.
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Jon,

I agree with jghrist... the power factor placed on the system, your "_entire_ transformer secondary", is not unity.

If you were to nominally power just the one 208V 20A resistive-only load, the minimum size wye-secondary transformer would need to be 7.2kVA (2400VA per secondary winding). Yet if you were to nominally power three such balanced loads, the minimum size would be 12.48kVA (4160VA per secondary winding)... putting a beancounter spin on that, it would be an output rating of only 73% more (ratio is 1.73:1, minus the 1), but sufficient enough to increase the load by 200% (300% total minus existing 100% load).
 
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Besoeker said:
Smart $ said:
The power factor of the load on the system is not unity. That is the whole point of the discussion.
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My response was based on your comment about the load:
The current of said load will be 30? out-of-phase with the applied voltage
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OK, I'll give you that... but you're taking the statement outside the context of the discussion (...and you know it :)).

Perhaps I should have wrote "...applied voltages". Yet I still have to wonder ;)
 
081206-1003 EST

If I have a three wire 3 phase source and load this with a Y resistive load of 9 KW, and compare this with a delta load of 9 KW, then is there any difference in the magnitude and phase angle in the three wires relative to a fixed phase reference?

The answer is no. It also does nor matter whether the source is Y or delta.

.
 
gar said:
081206-1003 EST

If I have a three wire 3 phase source and load this with a Y resistive load of 9 KW, and compare this with a delta load of 9 KW, then is there any difference in the magnitude and phase angle in the three wires relative to a fixed phase reference?

The answer is no. It also does nor matter whether the source is Y or delta.

.
Click to expand...

OK.


...but if you are attempting to make a point relative to the discussion I've been involved with in this thread, I just don't see it :confused:
 
081206-2047 EST

Smart $:

Now consider two sources. One Y to Y and the other Y to delta.

An ideal transformer's secondary voltage is identical to the primary except as modified by the turns ratio. The primary current is exactly the same as the secondary except for the turns ratio effect.

If the secondary has a Y resistive load, then all of the following are equal primary KW, KVA, and secondary KW, KVA. This one is very obvious.

Change the secondary to a delta with a delta resistive load. Select phase 1 with terminals A and B and disconnect it from the other two phases and relabel the disconnected terminals A' and B'. The instantaneous voltage between A and A' is zero. Same for B and B'. Thus, nothing has changed for the phase 1 secondary. Put a wire between A and A', and one between B and B'. Measure the current in each of these wires and it is 0.

The primary to phase 1 and its secondary have exactly the same values for KW and KVA.

Every thing is unity power factor because the KWs and KVAs are all equal.

.
 
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I know I'm in way above my head you talking power factor and all that.

But excluding power factor isn't the answer as simple as the conductors are good for 200 amps. and the full capacity of the system would be 200 amps. x 1.73 or 346 amps? :)
 
gar said:
081206-2047 EST

Smart $:

Now consider...
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Considered... and OK, again. I understand all that, so I still don't see your point.

Now consider the scenario of a wye secondary with a delta connnected resistive load. No line to neutral loads. Wye or delta primary is of no concern (at this point, anyway). Assume each leg of the load is independently variable. Unbalance the load. The transformer will see the power factor value drop as load imbalance is increased. In the extreme unbalanced case, the power factor will be .866 (for theoretically ideal conditions).
 
Zog,

You wrote:
"Infinite resistance" is the one that gets me going, should also be banned."

Reminds me that all "Insulators" are also "Semi-Conductors",
depending on how you measure them.
Also depends on whether the passing of current is:
(1) undesirable 'leakage'
(2) 'under biased control'
(3) 'approaching the limits (of infinite resistance)'!

Sorry, wasn't supposed to use the banned wording!

Your comments are always welcome.

...
 
Thought I was smart until I came to this site. My father taught me 2, 4, and 8. He said "can you rember that"? You have 2 amps per KW at 480V, 4 amps per KW at 240V, and 8 amps per KW at 120V. I know I admit this is over simplified but my father was a farm boy.
 
Wow

Wow

1st off, I wanted to thank you for everyones input. I have not checked this post lately, and now to find it 9 pages long, wow.

Anyway, we have been getting our power bill from our power company, and it keeps increasing about $100/month. Long story short, we keep adding more gear in our data center and I think we have figured out where the power is going.

But I am running into a problem with the KWHr calculations. Granted the power company is in the power company, so I am certain they are correct and I am doing something wrong. I just used my amp meter to measure each of our phases, here is what they show:
Phase 1 - 24 AMPS
Phase 2 - 46 AMPS
Phase 3 - 35 AMPS

The power company is billing us for 327 KWhr's per day for this last month (34 days worth)
How do you get 327? If I do some quick math I get roughly:

Total amps of each phase:
24+46+35 = 105

Amps X volts = total watts
105 X 208 = 21840

Watts / 1000 = KWatts
21840 / 1000 = 21.84

KWatts X 24 hours per day = KWhr per day
21.84 X 24 = 524

So, by my figures (which I am pretty confident are wrong) I show 524 KWhr usage per day, a bit off from 327 KWhr.

Now, please note, our loads are very stable and do not change. We have a data center of 100+ servers, switches, routers, UPS's, etc... that run 24/7/365 The only load I have found that changes much is a fan on our AC unit that kicks on/off every 10 seconds or so.

So, using the above as an example, how do I properly calculate our power usage?
 
081211-1226 EST

richard.bessey:

Use 120 V instead of 208 in your calculation, and I get 302 KWH which correlates with your power company value. Looks like you have close to a resistive load.

.
 
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