3-Phase circuits Chpt 12 INEL 4075 Dr. Sandra Cruz-Pol Professor Electrical Engineering UPRM

Three-phase circuits The 3-  circuits can be motors or generators and are the ones used nowadays to distribute electric power through all cities. They consists of: –3 sources –3 transmission lines (3 or 4 wires) –3 loads We use the frequency domain to work with 3-  –Impedances& phasors Advantages: –Total power is constant with time, which is necessary to keep large generators and motors running smoothly –More efficient and economic

Nikola Tesla 3-  motor

Line voltages for positive phase sequence abc: Assuming T.L. are lossless Line currents are I a, I b and I c

For Delta connection: Compute the line-to-line voltages:

Connections:  Y to Y   to    to Y Systems is balanced when the loads, currents, voltages are equal in all 3 phases. Then can do a per-phase equivalent circuit.

For balanced Y-Y systems;

Conversion  to Y

Conversion Y to 

References Wikipedia! Univ Zagreb