# Three Phase Transformers

#### kool_dude_blr

Joined Oct 31, 2006
2
Hello, can some recommed some good and standard books for three phase transformers? Also I am trying to understand the V-I relations in three phase transformers in time domain. can anyone explain this with diagram or point to some URL explaining this.

#### mrmeval

Joined Jun 30, 2006
833

#### kuyoli

Joined Nov 3, 2006
1
step down 240v to 12v using solid state device

#### kool_dude_blr

Joined Oct 31, 2006
2
Thanks for the reply but it does not explain the time domain relationships. I would be thankful if someone can point out to a resource in time domain.

#### EngineerJoe

Joined Nov 4, 2006
15
The V-I relationships for three phase circuits are nearly the same as for single phase circuits with some special considerations. Perhaps you are trying to understand why three phase power is used or made? With respect to the time domain, think of three generators on a common drive shaft. Each generator produces a positive and negative half of a sine wave. If the generators are attached to the common shaft in an identical fashion, then all three generators cross through zero (from positive to negative to positive again) at exactly at the same time.

If you tilt the first generator 120° clockwise and lock it back onto the shaft and then tilt the last generator 120° counter clockwise and lock it back onto the shaft, then power will be available on any 2 of the three phases at any point in time. When one A/C sine wave is crossing through zero, the other two are 120° ahead or behind. Try plotting out 3 sine waves of any magnitude where the first one crosses over (from negative to positive) at 0° while the other two identical sine waves do the same thing at 120° and 240° respectively. This relationship between phases remains fixed at all frequencies. Does this help?

#### subtech

Joined Nov 21, 2006
123
A super good book just to have in general is Delmar's Standard Textbook of Electricity by Stephen L. Herman.
It covers many, many aspects of things electrical from basic ac and dc properties to larger 3 phase ac generators and motors. I carry a copy every day at work as a reference and I use it as a teaching aid for apprentice linemen. It not only explains things in very simple language, but it includes diagrams and color coded pictures for more complex issues. It can be had at times from Amazon.com in the used book section for reasonable money, or if you,re not financially challenged like me, you could splurge for the new shiny edition(\$). I think you would find it most helpful.

#### fanta_hanu

Joined Mar 9, 2009
8
Electrical Machines by Dr.P.S.Bhimbra

#### here2learn

Joined Mar 6, 2009
2
i guess for the basics "generalized theory of electical machines by P.S bhimbhra" would help........