three phase power

[AdamNuhfer]

And here I thought the DC {Thomas Alva Edison} vs AC {Nilola Tesla/George Westinghouse} plight was all over and decided.
Forgetful me, how does that sayin go.. Ah yes, those who forget the past....................

 

[Calin]

One more thing I never saw mentioned here is:
Well, you might live in a perfect world. However, take into account that the power for a neighborhood came from a three-phased power line, and goes thru a three-phase transformer that reduces the 10KV-something used for transport to the 380V triphasic delivered to final users (consumers).
Now, for home users, they all get monophasic current, so the three phases are distributed, every phase to one third of the consumers. In the ideal situation, when all consumers consumes the same, voltage on all lines are identical.
Let's say now you have a short on one of the lines (a resistence high enough to keep the current flowing and the fuses not blowing). For easier understanding, let's say the resistance is close to 0. This means most of the voltage drop occurs in the transformer, and the 0 of the transformer (the common ground, let's call it) moves the that phase's output. Suddenly, you have two phases that have voltage equal to some 380 volts instead of the 220V rated).
What if the fuses blows on one line? You get the 380V of power divided equally on two phases, so you get 170V instead of 220V. Not a good thing

Simple justification for the result: the transformer generates three lines of power. In ideal conditions, the "null" line has no current flowing in it (imagine every phase as a centrifugal force on a circle, equal in size and pulling in three spots at angles of 120 degrees, just like in Mercedes sign. Now, every line's influence in moving the center is in inverse proportion with the resistance on the line. Cut the line, and the null moves between the other forces. Zero it, and the null moves on the third point

 

[AdamNuhfer]

In my not perfect world it's 240,00 or 115,000 volts for transmission with a 345,000 volt line sharing out right of way that belongs to another utility. For our sub tranmission we use 34,500
For the customer use we give them 115,000 feed {Real Big customers}, 34,500 {Big customers}, others get a mix from 12,000-8000-4000 feeders. Regular old everyday folks {smaller customers} get a mix of 480/277{3 Phase}-240/120 {3 Phase or single}-208/120 {3 Phase} It can be one, two or three transformers depending on customer needs. In a perfect senerio where each phase has the same load, there will be little if any current flow on the system netural, in a Wye system. We try and break the single phase customers up so as to balance the load. On paper it looks good, in reality it's not so good. You run a single phase 7.2KV line 6 miles out along a rural road and get a numbler of people buy buliding lots, well then up goes your load. As for fuses blowing, happens all the time. We lose one line of a three phase 12 KV line, it causes problems for the three phase customers, doesn't do a thing to the single phase customers on the other two lines. I'm talking Wye here, not Delta as we have very little Delta Dist..

 

[Delbert]

Originally posted by: Soldier
The drill motor would burn out rather quickly...to put it into computer terms, you'd be overclocking to high.

The charger would most likely fail also because you would be exceeding the input by a large margin.

Feeling like I should have started a new thread about 400Hz vs 60Hz power, sorry for the slight thread deviation.
Mark R said if it?s a universal motor it should work, but not an induction motor. Google says most household vacuum cleaner motors are the universal type. Google for 400Hz aircraft vacuum and you will find several for sale. Are they the same thing (marked up as something special)?
Also, remember we are talking 115 VAC still, only the frequency is different.

AdamNuhfer, laughed at the Edison vs. Westinghouse comment.

 

[PowerEngineer]

Soldier, AC certainly comes out as superior to DC overall because: transformers make it relatively easy to raise voltage for more efficient transmission and then lower it again for actual use by loads, regular current zeros (twice every cycle) make circuit breakers practical, and multiple phases allow self-starting motors without brushes. All that said, the actual efficiency of DC transmission is slightly better than AC at any given voltage.

Your point about currents and conductor size required to transmit bulk power over long distances without stepping up the voltage is a good one, and true for either AC or DC. The fact the AC can be stepped up is crucial. On the other hand, Painkiller's point is valid too.

 

[Calin]

Originally posted by: AdamNuhfer
In my not perfect world it's 240,00 or 115,000 volts for transmission with a 345,000 volt line sharing out right of way that belongs to another utility. For our sub tranmission we use 34,500
For the customer use we give them 115,000 feed {Real Big customers}, 34,500 {Big customers}, others get a mix from 12,000-8000-4000 feeders. Regular old everyday folks {smaller customers} get a mix of 480/277{3 Phase}-240/120 {3 Phase or single}-208/120 {3 Phase} It can be one, two or three transformers depending on customer needs. In a perfect senerio where each phase has the same load, there will be little if any current flow on the system netural, in a Wye system. We try and break the single phase customers up so as to balance the load. On paper it looks good, in reality it's not so good. You run a single phase 7.2KV line 6 miles out along a rural road and get a numbler of people buy buliding lots, well then up goes your load. As for fuses blowing, happens all the time. We lose one line of a three phase 12 KV line, it causes problems for the three phase customers, doesn't do a thing to the single phase customers on the other two lines. I'm talking Wye here, not Delta as we have very little Delta Dist..

If you work in electric energy transmission field, you certainly are correct. However, I remember times when the voltage (single-phase voltage) would go up or down quite a bit compared to the standard voltage. However, once a new transforming station a quarter of mile from our house was functioning, the voltage was more steady. It might have been connected to the fact that we were faaaar from the transforming station

 

[AdamNuhfer]

Delbert: I thought you did good when you asked about 400 hz/ Aircraft APU's.

All: Thanks, this has been a good thread/question/response line. No one posted profainty or insults towards anyone. Just what all these forums should be like. It's nice coming in here and being able to learn from others. Thanks again!!!

 

[Calin]

One more thing I wanted to add: while I was in the high school, we stayed in a building with 100 rooms. During winter, some of the students used hand-made heaters that didn't worked unless you replaced the fuses with nails (ok, I am exagerating a little).
Being an electric profile (Industrial Automation and Computers) faculty, some of us had voltmeters, and I remember that someone said once the bulbs were anormally brights, and at that time there was some 270V on them.
EDIT: power on the building was received from a triphasic transformer that feed another 7 buildings, but every floor had triphasic power distributed as single phase to the rooms (every room had lights and power outlets on different fuses, and I think phases)