1. Summary of Polyphase
The first slide gives the definitions for polyphase configurations.
The following 2 slides summarize the Y- and -Y connections. They are not intended to be memorized.
How to use them:
Look at each diagram to decide which voltages (Line voltage and Phase voltage) are equal and which currents (Line currents and Phase currents) are equal.
Those that are not equal are related by either  3 or 1/ 3.
Use Ohm’s Law to find V from I and Z, or, I from V and Z.
For phasors: V = I Z or I = V / Z
For magnitudes only: | V | = | I | * | Z | or | I | = | V | / | Z |

2. Definitions Phase voltage of the load Phase current of the generator
Line current
Phase voltage
of the generator
Line voltage

3. Y-Delta and Delta-Y

4. Y-Y and Delta-Delta