Transformer Basics and Efficiency

Transformer Definition

• A transformer is a static device that transfers power from one electrical circuit to another without changing frequency.
• It steps up or steps down voltage with a corresponding decrease or increase in current.
• It works on mutual induction.

Static Device and Losses

• Transformers are static devices; they have no moving parts.
• This absence of moving parts eliminates rotational losses.

Rotational Losses

• Windage loss
• Friction loss
• These losses occur only in rotating machines.

Transformer Cooling

• Transformers often include a cooling fan which is an auxiliary part of a transformer.
• Transformers can have low windage and friction losses.
• Transformers usually have a high efficiency, often up to 98%.

Transformer Core Materials

• Transformers have high silicon-steel laminated cores [0.35mm to 0.5mm thickness].
• This reduces eddy current losses.
• Increasing the resistance reduces eddy current loss

Transformer Frequency

• Transformer frequency does not change due to the non-relative movement between primary and secondary windings.

EMF Equation of a Transformer

• The instantaneous EMF induced in the primary is given by
• E₁ = -N₁ (dΦ/dt)
• This is derived from Faraday's law of electromagnetic induction
• Substituting Φ = Im Sinωt gives
• E₁ = N₁ ωm Cosωt = N₁ ωm Sin(ωt - 90°)
• The RMS value is then calculated as
• E₁ = (4.44) f N₁ Φm

Transformer Turn Ratio

The ratio of the number of turns in the secondary to the primary windings defines the transformation ratio or turn ratio

• E₂ = E₁ (N₂ / N₁)

Transformer Construction

• The cross-sectional area of the yoke is always kept 15-20% higher than the limb.
• This arrangement is to reduce core losses.

No-Load Current in Transformers

• No-load current in transformers is 3 to 5% of full-load current.
• This current establishes the flux in the core.
• It is greater than in induction motors due to rotational components and the presence of air gaps.

No Load Power Factor in Transformers

• The no-load power factor of a transformer is typically very low, in the range of 0.2 to 0.3 lagging, due to the presence of an air gap.

Equivalent Circuit of a Transformer at No-Load

• The equivalent circuit exhibits various factors, including Resistance (R₁), leakage reactance (X₁), core loss resistance (R_c), and magnetizing reactance (X_m) for both primary and secondary windings.

This quiz covers the fundamental concepts of transformers, including their operation, components, and efficiency. Learn about the static nature of transformers, the significance of core materials, and the impact of cooling methods on performance. Test your knowledge on how transformers manage voltage changes and losses in electrical circuits.