A look at 2-phase electrical power (13 - Electricity Distribution)

A complete description of 2-phase electrical power distribution, like the one used at Niagara Falls in the 1800's. This form of electricity distribution where the two phases are ninety degrees is obsolete since three phase electricity is superior, but 2-phase power is still superior to single phase. Here I show mathematically why 2-phase power is better than single phase power.

Full edX course with interspersed practice problems to help you learn:

Aaron Danner is a professor in the Department of Electrical and Computer Engineering at the National University of Singapore.

Video filmed and edited by Cheryl Lim.
@randomcheryl

[marcodelao]

houses in north america use a single split phase system to provide 2 hot legs and a center tapped neutral.

[Hossein]

I look forward to watching your 3phase video. I was curious about why someone may want to use 2phase when we have 3phase system until you said that it is an obsolete system. Anyway, it was a nice video 👏

[mernok]

I heard that Pennsylvani and Philadelphia still has lots of 2 phase equipment and some also exist in new york.Some industries can also have old 25 and 40 Hz equipment.

[Blair]

2 phase power is still used in Philadelphia PA and Hartford CT USA. The provider supplies 3 phase but uses a Scott transformer at old buildings that are wired for 2 phase. It was my understanding that the primary advantage of 2 phase was that it could be used to start motors with no additional starting mechanisms. Also the case for 3 phase.

[adrianspeeder]

Philly electrical work ole son! 2 phase was to get motors turning in 19dickity2 before starting capacitors came around.

[johnnott]

OK, so I ran across a really old 2-phase motor and was working on a replacement. I put an amp meter on the 2 phases I found at the disconnect and took a voltage reading too. I wanted to calculate total motor power to see if the current motor is sized correctly for the load. I put them into a spreadsheet to calc power. However, that spreadsheet used P = V * I * sqft(3). I think that for a 2-phase system that was wrong. Would I actually just add the amps from the 2 wires together to get the power? As is P = V * (Amps1 + Amps2)

[mernok]

Hot doesnt carry current from the load and neutral doesnt return it.There is no direction in AC as polarity swaps at 50 or 60 Hz.

[Jecoopster]

What's the difference between 2-phase power, and basically using 2 hots and a neutral to power a dryer or air conditioner in a normal home?