History of 3-phase Electricity & Distribution

Thread Starter

nsaspook

Joined Aug 27, 2009
9,435

https://en.wikipedia.org/wiki/Mikhail_Dolivo-Dobrovolsky
As one of the founders (the others were Nikola Tesla, Galileo Ferraris and Jonas Wenström) of polyphase electrical systems, he developed the three-phase electrical generator and a three-phase electrical motor (1888) and studied star and delta connections. The triumph of the three-phase system was displayed in Europe at the International Electro-Technical Exhibition of 1891, where Dolivo-Dobrovolsky used this system to transmit electric power at the distance of 176 km with 75% efficiency. In 1891 he also created a three-phase transformer and short-circuited (squirrel-cage) induction motor.[1][2] He designed the world's first three-phase hydroelectric power plant in 1891.
 

crutschow

Joined Mar 14, 2008
29,466
One thing I find very interesting about 3-phase power is that, although the voltage and current fluctuates in each phase, the total power delivered from the 3-phases is constant, the same as a DC system.
That is the reason 3-phase motors are usually quieter that single-phase motors as there is no fluctuation in their torque as they rotate.
 

crutschow

Joined Mar 14, 2008
29,466
That apparently states that a 3-phase motor has torque ripple but, according to this near bottom of page, "The magnetic field is maintaining a constant magnitude while rotating in a counterclockwise direction." , so there should be no torque ripple (other than perhaps caused by the windings not producing a perfect rotating field).

Just for grins, below is the simulation of a 3-phase source driving three equal loads (R4 is needed to resolve a simulator complaint about voltage sources in a loop).
The sum of the instantaneous power into the three loads (yellow, purple, and red traces) is a constant as expected (blue trace), which would imply that the ideal 3-phase motor torque is also a constant.

1641440498449.png
 

Thread Starter

nsaspook

Joined Aug 27, 2009
9,435
You can get torque ripple from the produced and/or induced magnetic field asymmetries in winding and rotor stator slot flux. A physical 3-phase induction motor is more than just coils, the electrical torque is the cross product of the rotor and stator flux vectors.
The ideal 3-phase motor is a mathematical model vs the reality of building a practical, high efficiency 3-phase motor with losses.
 

Thread Starter

nsaspook

Joined Aug 27, 2009
9,435
The entire Kathy loves Physics series is excellent and well worth watching. She does a great job combining the physics and the human history. I really enjoy her work.
She is great and I'm very glad to hear of her recovering from Covid quickly.
 

Ramussons

Joined May 3, 2013
1,227
A bit surprising that there is no mention of Charles F. Scott, the one behind the famous Scott Connection (1890), first used to convert the 2 Phase to 3 Phase. We were told that this was first used to convert the original 2 phase Niagara Falls power station generators to 3 phase.
 
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