Transformers Explained - How transformers work
Understanding Transformers: How They Work and Their Importance
Introduction to Transformers
- Transformers are essential devices that connect homes to electrical power stations, playing a crucial role in modern lifestyles.
- They transfer electrical energy and can change voltage and current, but only function with alternating current (AC), not direct current (DC).
Types of Transformers
- Transformers are rated in volt-amperes (VA) or kilovolt-amperes (kVA), unlike most appliances which are rated in watts or kilowatts.
- There are various sizes of transformers, from small ones used in doorbells to large ones supplying entire cities.
Transformer Construction
- A transformer consists of two coils of wire wrapped around an iron core; the primary side connects to the power source while the secondary side connects to the load.
- The basic construction involves two separate coils and sheets of iron, emphasizing safety when handling electricity.
Voltage Transformation Process
- Step-up transformers increase voltage for efficient long-distance transmission, while step-down transformers reduce it for local distribution.
- For example, power stations may produce 12,000 volts which is stepped up to 400,000 volts for transmission and then reduced back down for home use.
Efficiency in Power Transmission
- Higher voltage reduces energy loss during transmission due to lower current; losses can be significant at lower voltages.
- An example illustrates that sending power at high voltage results in minimal losses compared to low voltage scenarios.
Electrical Systems Overview
- North America uses a three-wire system allowing both 120V and 240V outputs; most other regions utilize a simpler two-wire system providing around 230V.
Magnetic Fields and AC Generation
- Passing an electric current through a wire generates a magnetic field; reversing the current reverses this field.
- Connecting an AC generator creates alternating electron movement within a closed loop wire due to constantly reversing magnetic fields.
Frequency Characteristics
- The frequency input into a transformer equals the output frequency; transformers adjust voltage but do not alter frequency.
- The sine wave pattern observed on oscilloscopes reflects this alternating nature of AC supply frequencies (50Hz or 60Hz).
Induction Principles
- Wrapping wires into coils strengthens magnetic fields; insulation is necessary for effective operation by ensuring proper current flow.
Understanding Transformers and Electromagnetic Induction
The Basics of Electromagnetic Induction
- A transformer operates on the principle of electromagnetic induction, where moving a magnet past a coil induces voltage due to changing magnetic fields that disturb free electrons.
- This process generates electromotive force (EMF), which is effective only with alternating current (AC); direct current (DC) does not induce EMF consistently due to its constant polarity.
Direct Current vs. Alternating Current
- In DC circuits, EMF is generated only momentarily when the switch is opened or closed, causing brief changes in the magnetic field.
- With AC supply, a consistent output voltage is achieved as the magnetic field continuously fluctuates.
Transformer Efficiency and Design
- Using two separate coils without a core wastes much of the magnetic field; introducing a ferromagnetic iron core enhances efficiency by concentrating the magnetic field towards the secondary coil.
- However, this design leads to eddy currents that generate heat and waste energy; laminated sheets are used in cores to minimize these losses.
Losses in Transformers
- Transformers experience copper losses from resistance in wires and iron losses from vibrations within laminated sheets, contributing to energy loss.
- The humming sound produced by transformers results from tiny expansions and contractions caused by alternating current.
Step-Up and Step-Down Transformers
- A step-up transformer increases voltage with more turns on the secondary side while decreasing current; conversely, a step-down transformer reduces voltage but increases current.
- Power conservation is maintained: if inputting 240 volts results in 120 volts output, then current doubles while power remains constant across both sides.
Understanding Apparent Power and Power Factor
- Transformers use volt-amperes (VA), not kilowatts (kW), because they transfer power without knowing connected loads; apparent power must remain constant regardless of load variations.
- Reactive power represents wasted energy that does no work but contributes to total apparent power; it’s analogous to foam atop beer—unwanted yet present.
Practical Applications of Transformers
- Manufacturers specify transformers based on their capacity for apparent power rather than true power since actual usage varies widely depending on connected devices.
- In rectifier circuits, transformers first reduce voltage before diodes convert AC into rough DC, followed by capacitors smoothing out fluctuations for clean power supply.
Calculating Transformer Outputs
- For example calculations: with 1,000 primary turns at 120 volts input leading to an output of 12 volts indicates it's a step-down transformer.
Understanding Transformer Currents and Voltages
Calculating Primary and Secondary Currents
- The primary current can be calculated using a specific formula if the secondary current is known (1.2 amps), resulting in a primary current of 0.12 amps.
- Power conservation in transformers is verified by multiplying voltage and current on both sides, ensuring they are equal.
Step-Up Transformer Examples
- In a step-up transformer with 100 turns on the primary and 200 on the secondary, supplying it with 120 volts results in a secondary voltage of 240 volts.
- If only the output voltage and number of turns are known, formulas can be used to determine input voltage or number of turns on either side.
Finding Current Relationships
- For a secondary current of 1 amp, the corresponding primary current can be found using another formula, yielding an answer of 2 amps.