Learn all about single phase transformer including its working, diagram, construction, advantages, applications, types, and more. Understand how a single phase transformer operates in power systems.
A single phase transformer is a static electrical device designed to transfer alternating current (AC) electrical energy between two separate circuits without a direct electrical connection. It operates on the principle of electromagnetic induction, allowing it to either step up or step down voltage levels while maintaining the same frequency. The transformer consists of two windings—primary and secondary—wound around a common iron core. When alternating current flows through the primary winding, it creates a magnetic field that induces a voltage in the secondary winding, enabling the transfer of electrical power.
The working principle of a single phase transformer is based on Faraday’s Law of Electromagnetic Induction, where the change in magnetic flux induces an electromotive force (EMF) across the windings. This mutual induction process makes it possible to alter voltage levels efficiently and safely.
Single phase transformers are widely used in residential, commercial, and light industrial power distribution systems, where they play a crucial role in stepping down high transmission voltages to usable levels for household and office equipment.
What is a Single Phase Transformer?
A single phase transformer is an electrical device that converts alternating current (AC) voltage from one level to another using electromagnetic induction. It is designed to operate with single-phase AC power and is commonly used in residential and light commercial electrical systems. Also referred to as 1 phase transformers or one phase transformers, they serve as a critical component in voltage regulation and energy distribution.
Faraday’s Law of Electromagnetic Induction
The working of a single-phase transformer is fundamentally based on Faraday’s Law of Electromagnetic Induction, which states that a changing magnetic field within a closed loop induces an electromotive force (EMF) in the loop. This principle is the foundation of all transformer operations.
Single-Phase Transformer Construction and Working Principle
The construction and working principle of a single-phase transformer are simple but highly efficient. It consists of primary and secondary windings wound on a laminated magnetic core, where energy is transferred through electromagnetic induction.
Construction of Single Phase Transformer
The key components of a single phase transformer are:
- Core: Made of laminated silicon steel to reduce eddy current losses.
- Windings: Consist of insulated copper or aluminum wires, including primary and secondary coils.
- Insulation: Electrical insulation separates windings and the core.
- Enclosure: A protective casing that shields the transformer.
- Cooling system: May include air natural or oil-immersed cooling depending on the rating.
Construction of Single Phase Transformer with Neat Diagram
Here is a single phase transformer diagram showing the core, windings, and terminals:
This simplified transformer diagram helps in understanding the layout and physical design.
A single phase transformer is constructed with two main windings—the primary winding and the secondary winding—wound on a laminated iron core. The core provides a low-reluctance path for magnetic flux and minimizes eddy current losses. The windings are made of insulated copper or aluminum conductors and are carefully layered to reduce leakage reactance.
The primary winding is connected to the AC supply, and the secondary winding is connected to the load. Both windings are electrically isolated but magnetically linked through the core. The entire assembly is placed inside a robust metallic tank filled with insulating oil for cooling and electrical insulation. The tank is also equipped with bushings for safe electrical connections and radiators to dissipate heat.
Additional parts may include tap changers (for voltage regulation), temperature gauges, and breather units. The transformer is designed for high efficiency and low maintenance.
Working Principle of Single Phase Transformer
When the primary winding of a transformer is connected to an alternating current (AC) source, it produces a changing magnetic field around it. This magnetic field links to the secondary winding, which is placed nearby on the same magnetic core. As the AC continuously changes direction, the magnetic field also changes accordingly.
According to Faraday’s Law of Electromagnetic Induction, a changing magnetic field induces an electromotive force (EMF) in the secondary winding. If the secondary circuit is closed, this EMF drives a current through it, allowing electrical energy to be transferred from the primary to the secondary circuit—without any direct electrical connection.
A typical transformer consists of two windings—primary and secondary—wound around a laminated iron core. The laminations help reduce energy losses due to eddy currents. The core forms a closed magnetic path that improves magnetic coupling between the windings.
In most cases, the primary winding receives the higher voltage, while the secondary winding delivers the required output voltage. The magnetic field created in the primary is transferred through the core and induces voltage in the secondary, effectively transforming the voltage level for safe and efficient power usage.
Principle of operation of single phase transformer:
- When AC voltage is applied to the primary winding, it generates a varying magnetic field in the core.
- This varying flux induces an EMF in the secondary winding through electromagnetic induction.
- The voltage induced in the secondary winding depends on the turns ratio between the primary and secondary windings.
EMF Equation Of a Single Phase Transformer
The induced EMF (electromotive force) in a transformer winding is derived from Faraday’s Law of Electromagnetic Induction, which states:
The magnitude of the induced EMF in a coil is directly proportional to the rate of change of magnetic flux linkage.
Let,
- Sinusoidal flux in the core
- N₁ = Number of turns in primary winding
- N₂ = Number of turns in secondary winding
- Φₘ = Maximum magnetic flux in Weber (Wb)
- f = Frequency of the AC supply in Hz
- E₁ = RMS value of induced EMF in primary
- E₂ = RMS value of induced EMF in secondary
Assume the magnetic flux in the core is sinusoidal:
where ω=2πf
According to Faraday’s law, the instantaneous EMF induced in a coil of N turns is:
Substitute Φ(t):
This can also be written as:
So, the peak value of EMF is:
RMS Value of Induced EMF
Therefore, the EMF equation becomes:
For the primary winding:
For the secondary winding:
The RMS value of the induced EMF in any winding of a transformer is given by:
This is the standard EMF equation used in designing and analyzing single-phase transformers.
Example: A single-phase transformer has 500 turns on the primary winding and is connected to a 230 V, 50 Hz AC supply. Calculate the number of turns required on the secondary winding to get 115 V output. Assume 100% efficiency and neglect losses.
EMF Equation:
Where:
- E1== Primary voltage = 230 V
- E2== Secondary voltage = 115 V
- N1= Primary turns = 500
- N2= Secondary turns = ?
The number of secondary turns required is 250 turns.
Turn Ratio of Single Phase Transformer
The turn ratio of a single-phase transformer is the ratio of the number of turns in the primary winding to the number of turns in the secondary winding. It is a critical parameter that determines how the voltage changes between the primary and secondary sides. Mathematically, it is expressed as:
Turn Ratio (K) = N₁ / N₂
Where,
N₁ = Number of turns in the primary winding
N₂ = Number of turns in the secondary winding
If the turn ratio is greater than one (N₁ > N₂), the transformer is a step-down transformer, reducing voltage. If it is less than one (N₁ < N₂), it is a step-up transformer, increasing voltage.
The voltage ratio follows the turn ratio directly, assuming ideal conditions:
V₁ / V₂ = N₁ / N₂
Understanding the turn ratio is essential for ensuring the proper voltage is supplied to the load while maintaining efficiency and safety in electrical systems.
Example: A single-phase transformer has N₁ = 1000 turns on the primary and N₂ = 200 turns on the secondary. The primary voltage is 230 V. calculate:
(1)The secondary voltage
(2) The turn ratio
Turn Ratio (n):
Secondary Voltage (E₂)
Classification of Single Phase Transformer
- Based on Purpose:
- Step-down Transformer: Decreases the voltage from primary to secondary. Widely used in residential and commercial power supply.
- Step-down Transformer: Decreases the voltage from primary to secondary. Widely used in residential and commercial power supply.
- Based on Construction:
- Core Type Transformer: Windings surround the core limbs. Easier to cool and maintain; often used in high-voltage applications.
- Shell Type Transformer: Core surrounds the windings. Offers better short-circuit strength and compact design.
- Depending on Winding Configuration:
- Two Winding Transformer: Has separate primary and secondary windings; used when voltage difference is significant.
- Auto-transformer: A single winding acts as both primary and secondary. Compact and cost-effective for small voltage differences.
- Depending on Cooling Method:
- Air Natural (AN): Cooled by natural air circulation; suitable for low-capacity indoor transformers.
- Oil Immersed Natural (ONAN): Uses insulating oil and natural convection for cooling; commonly used in outdoor transformers.
- Forced Air or Oil Cooling (OFAF): Uses external fans or pumps for faster heat dissipation in high-capacity transformers.
- Based on Installation Location:
- Indoor Transformers: Installed inside buildings with environmental protection and suitable for controlled spaces.
- Outdoor Transformers: Built to withstand weather conditions, often housed in enclosures or mounted on poles.
- Based on Insulating Medium
- Oil-Immersed Transformer: Uses insulating oil for cooling and insulation, suitable for high-power outdoor installations with better heat dissipation.
- Dry Type Transformer: Uses air or solid insulation; ideal for indoor use due to enhanced safety and fire resistance.
Load Test on Single Phase Transformer
A load test is conducted by applying rated voltage and load to a single-phase transformer to determine its voltage regulation and efficiency under actual working conditions. This test helps evaluate how the transformer performs when supplying power to a real load, giving insights into output voltage stability and energy loss. It also provides valuable data to calculate full-load efficiency.
Losses in Transformer
Single phase transformers experience two main types of losses: iron losses (also called core losses) and copper losses.
Iron losses occur in the transformer’s magnetic core and consist of two components: hysteresis loss and eddy current loss. Hysteresis loss happens due to repeated magnetization and demagnetization of the core as alternating current flows through the windings. Eddy current loss is caused by circulating currents induced within the core material itself. To minimize these losses, the core is made of laminated sheets with high magnetic permeability.
Copper losses, also known as I²R losses, occur due to the resistance in the primary and secondary windings. As current flows through the windings, electrical energy is lost in the form of heat. These losses depend on the load current and increase with the square of the current.
Both losses affect the overall efficiency of the transformer and must be minimized through proper design and material selection.
Efficiency of Transformer
The efficiency of a transformer is the ratio of its output power to the input power, expressed as a percentage. It indicates how effectively the transformer converts input energy into usable output.
A transformer operates at maximum efficiency when its copper losses are equal to its iron (core) losses. This balance ensures minimal energy wastage. High-efficiency transformers are essential for power systems to reduce losses and improve performance. Modern single-phase transformers typically achieve efficiency levels between 95% and 99%, depending on their design and operating conditions.
Advantages of Single Phase Transformer
- Simple design and robust construction
- Cost-effective for low power applications
- Easy installation and maintenance
- High efficiency in light load conditions
- High reliability
Disadvantages of Single Phase Transformer
- Not suitable for heavy industrial loads
- Poor load balancing in 3-phase systems
- Less efficient in high power applications
Applications of Single Phase Transformer
- Household power distribution
- AC adapters and chargers
- Industrial control circuits
- HVAC systems
- Medical and testing equipment
- Welding transformers
- Battery chargers
- Street lighting
- UPS system
A single phase transformer is a vital component in various electrical and electronic systems. Its efficiency, simplicity, and reliability make it an essential tool for stepping up or stepping down voltages in single-phase AC networks.
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