Transformers

What happens to power lost inside transformers?

 It becomes heat that must be dissipated.

Why is cooling needed in large transformers?

 To remove excess heat and prevent transformer damage.

What cooling method do large transformers often use?

 Oil pumps circulate oil inside the transformer for cooling.

Why is ventilation important in transformer installations? 

Ventilation prevents overheating and extends transformer life.

Secondary VA Formula

 VAₛ = Vₛ × Iₛ (secondary voltage × secondary current).

Two Basic Transformer Categories

 Isolation transformers; Autotransformers.

Isolation Transformer

 Transformer with electrically isolated primary and secondary coils; only magnetically coupled.

Benefit of an Isolation Transformer

 Filters voltage spikes that could damage equipment.

Isolation Transformer Example

 Used in electronics like TVs to protect circuits from line spikes.

Autotransformer Use

 Regulates line voltage with small increases or decreases.

Who Uses Autotransformers Most

 Power companies for voltage regulation.

Purpose of a Control Transformer

 Steps 240V or 480V down to 120V for control circuits.

Coils in a Control Transformer

 Two primary coils and one secondary coil.

Why Control Primaries Are Cross-Connected

Allows the same transformer to be used for either 240V or 480V.

Primary Coils in Parallel

 Turns ratio stays the same as a single coil.

Primary Coils in Series

 Turns add together, changing the ratio and increasing voltage capacity.

Secondary Tap

 A connection to part of the secondary coil that provides a different output voltage.

Tap Voltage Example

Tap Voltage Example

Center Tap

 A tap at the midpoint of the secondary coil that creates two equal voltages.

Center-Tap Output Voltages

 240V across full winding; 120V from center tap to either end.

Center Tap Neutral

 Connected to earth ground, becoming the neutral conductor in a home.

Home Service Voltage

 240/120V split-phase power supplied by a center-tap transformer.

Devices That Use 240 VAC

 Water heater, dryer, cooking range, air conditioner.

Why Large Appliances Use 240V

 Higher voltage reduces current, allowing smaller wire size.

120 VAC Use in Homes

 Used for outlets and lighting because it's safer.

Why 120V Is Safer

 Lower voltage reduces shock hazard for household devices.

What are the 3 factors in a Transformer

• Primary Side

• Secondary Side

• Turns Ratio