why 3-phase power?
 

Alan,

It has to do with efficiency, cost, complexity, etc. It was not a casual
decision. If one uses a delta configuration, instead of a Y, then you only
need three leads, not four.

Evan

Alan,

It has to do with efficiency, cost, complexity, etc. It was not a casual
decision. If one uses a delta configuration, instead of a Y, then you only
need three leads, not four.

Evan

"K9SQG" wrote in message
...
Alan,

It has to do with efficiency, cost, complexity, etc. It was not a casual
decision. If one uses a delta configuration, instead of a Y, then you
only
need three leads, not four.


Unless you are tapping for 120 on a 240 Delta or 240 on a 480 Delta, in
which case a center tap of any of the phases becomes Neutral for a split
phase Edison circuit.

"K9SQG" wrote in message
...
Alan,

It has to do with efficiency, cost, complexity, etc. It was not a casual
decision. If one uses a delta configuration, instead of a Y, then you
only
need three leads, not four.


Unless you are tapping for 120 on a 240 Delta or 240 on a 480 Delta, in
which case a center tap of any of the phases becomes Neutral for a split
phase Edison circuit.

On 31 Dec 2003 00:48:51 GMT, K9SQG wrote:

It has to do with efficiency, cost, complexity, etc. It was not a casual
decision. If one uses a delta configuration, instead of a Y, then you only
need three leads, not four.

IIRC (it's been 50 years since I studied this) a Y-Y circuit
has problems with in-phase circulating third harmonic currents
flowing on the neutral.

--
73 de K2ASP - Phil Kane P.E.

On 31 Dec 2003 00:48:51 GMT, K9SQG wrote:

It has to do with efficiency, cost, complexity, etc. It was not a casual
decision. If one uses a delta configuration, instead of a Y, then you only
need three leads, not four.

IIRC (it's been 50 years since I studied this) a Y-Y circuit
has problems with in-phase circulating third harmonic currents
flowing on the neutral.

--
73 de K2ASP - Phil Kane P.E.

Bill wrote in message ...
wrote:

In sci.electronics.basics Rob Paisley wrote:

| For larger horsepower motors, Three Phases means that they will
| start with no external mechanical assistance.

And, as I understand it, they can then "stand on one leg" although they
will be a bit "shaky".

You can also reverse the rotation by swapping two of the phases. If one
phase is blown you can start it by giving it a spin in the right
direction, 'without' getting your hand caught

Bill Baka

I am not sure if a 3 phase motor would even rotate unloaded on 2
phases but it certainly would not develop a usable amount of
horsepower. I would suspect that running on 1 phase would be out of
the question.

I do know that if a loaded 3 phase motor blows a fuse it will almost
always blow a fuse in one of the other lines due to an overload. Due
to the way the control power for the motor is connected the starter
will then open the circuit if it did not already do so when the first
fuse failed.

Also, there is a number of 1.57 being bandied about in this thread
for the relative horse power of a 3 phase versus single motor for a
given current. This number should be 1.73 (The square root of 3.

Rob.

Bill wrote in message ...
wrote:

In sci.electronics.basics Rob Paisley wrote:

| For larger horsepower motors, Three Phases means that they will
| start with no external mechanical assistance.

And, as I understand it, they can then "stand on one leg" although they
will be a bit "shaky".

You can also reverse the rotation by swapping two of the phases. If one
phase is blown you can start it by giving it a spin in the right
direction, 'without' getting your hand caught

Bill Baka

I am not sure if a 3 phase motor would even rotate unloaded on 2
phases but it certainly would not develop a usable amount of
horsepower. I would suspect that running on 1 phase would be out of
the question.

I do know that if a loaded 3 phase motor blows a fuse it will almost
always blow a fuse in one of the other lines due to an overload. Due
to the way the control power for the motor is connected the starter
will then open the circuit if it did not already do so when the first
fuse failed.

Also, there is a number of 1.57 being bandied about in this thread
for the relative horse power of a 3 phase versus single motor for a
given current. This number should be 1.73 (The square root of 3.

Rob.