Three-Phase Transformers Lecture

Introduction

• Sponsor: Madox Transformer, a transformer superstore.
• This lecture covers three-phase transformers, focusing on Delta primary and Y secondary configurations with a rating of 2 KVA.

Basics of Transformers

• Purpose: Converts AC voltage to another voltage without moving parts or direct wire connections between primary and secondary.
• Primary Coil: Connects across the phase and neutral.
• Secondary Coil: Completely separate, connects hot wires to ends and neutral to the center.
• Output: 240V between two hot wires; 120V between neutral and hot wire (using half of the secondary coil).
• Waveform: AC sine wave observed using oscilloscope.

Single Phase vs. Three-Phase

• Single-Phase for Homes: Typically pole-mounted, connects to phase and neutral of the distribution grid.
• Three-Phase for Commercial: Provides power to commercial buildings; generated by power stations spinning magnets past coils.

Power Transmission and Distribution

• Efficiency: Increase voltage for long distances to reduce power loss; step up and step down transformers used.
• Substations: Reduce voltage at various points before distribution to homes and commercial buildings.

Transformer Construction

• Coils and Cores: Two coils of wire around a steel core; electromagnetic field induces voltage in secondary coil.
• Laminated Steel Sheets: Used to minimize energy waste (eddy currents) and heat generation.
• Voltage and Turns Ratio: Output voltage is dependent on the ratio of turns in primary and secondary coils.
• Step Up/Down Transformers: Primary to secondary turns ratio determines whether voltage is increased or decreased.

Types of Transformers

• Single-Phase Transformers: Basic construction with primary and secondary coils.
• Three-Phase Transformers: Consist of three single-phase transformers, typically for commercial applications.
• Configurations: Delta-Delta, Y-Y, Y-Delta, and Delta-Y; influences voltage and current distribution.

Practical Examples

• Small Commercial Building: Pad-mounted transformer with 12,470V Delta primary and 208/120V Y secondary, rated 150 KVA.
• Large Commercial Building: Supplies 480V 3-phase motors, 277V fluorescent lighting, and 120V outlets with a 500 KVA transformer.
• Taps: Allow adjustments for supply voltage variations to maintain the designed output voltage.

Special Configurations

• Open Delta: Uses two transformers, provides reduced capacity but cheaper to install.
• High Leg Delta: Creates a high voltage leg; dangerous for 120V appliances if improperly connected.

Calculations and Formulas

• Voltage Calculations: Use trigonometry and the square root of 3 to relate line voltage to phase voltage.
• Current Calculations: Simplified formulas for both Y and Delta configurations.
• Power Conversion: Power transferred remains the same; voltage and current are transformed.

Transformers in Practice

• Commercial and Industrial Use: Configurations for specific voltage requirements; importance of proper connection and load management.
• Efficiency and Capacity: Understanding transformer ratings, voltage, current, and safety limits.

Conclusion

• Madox Transformer: Supplier of various transformer types, supporting quick delivery and offering educational resources.
• Further Learning: References to available resources, such as mugs with formulas and diagrams, and PDF sheets for study.

Acknowledgments

• Supporters: Patreon and channel members thanked for contributions.