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Phase difference between primary and secondary voltage of transform is

180 degree

90 degree

45 degree

30 degree

Correct Answer

⚙️ TE • Technical Concept & PrincipleElectricalMachine

Option A

180 degree

Quick Summary:

In an ideal single-phase transformer, the induced secondary EMF is 180° out of phase with the primary terminal voltage (or primary induced EMF) according to Faraday's law of electromagnetic induction and Lenz's law. Lenz's law states that the induced voltage opposes the cause producing it (the alternating flux), resulting in a phase shift of 180°.

⚙️TETechnical SolutionConcept & Principle

💡 Explanation

🔢 Key Formulas

$e_1 = -N_1 \frac{d\Phi}{dt}$ — Primary induced EMF by Faraday's/Lenz's Law

$e_2 = -N_2 \frac{d\Phi}{dt}$ — Secondary induced EMF

$\frac{V_1}{V_2} = \frac{N_1}{N_2} = K$ — Transformer voltage transformation ratio

⚙️ Working Principle

An alternating voltage applied to the primary winding sets up a sinusoidally varying magnetic flux $\Phi$ in the core. According to Faraday's law, this alternating flux induces an EMF in both primary ( $e_1 = -N_1 \frac{d\Phi}{dt}$ ) and secondary ( $e_2 = -N_2 \frac{d\Phi}{dt}$ ) windings. The minus sign in Lenz's law signifies that the induced EMF opposes the flux variation, establishing a 180° phase displacement between the primary supply voltage and the secondary induced voltage.

📌 Key Points

▸
The primary induced EMF $E_1$ and secondary induced EMF $E_2$ are in phase with each other because both are produced by the same mutual flux $\Phi$ .
▸
The primary applied voltage $V_1$ is equal and opposite to $E_1$ , creating a 180° phase difference between $V_1$ and $V_2$ (or $E_2$ ).
▸
Mutual core flux $\Phi$ lags the primary voltage $V_1$ by 90° and leads induced EMFs ( $E_1, E_2$ ) by 90°.

📄 Additional Information

▸
Option B (90 degree) represents the phase angle difference between the main working flux $\Phi$ and the primary voltage $V_1$ (or induced EMF $E_1$ ).
▸
Option C (45 degree) and Option D (30 degree) refer to typical phase shifts observed in specific 3-phase transformer connections (e.g., Star-Delta or Delta-Star connections), but not a standard 1-phase transformer voltage phase relation.

📊 Diagram / Illustration

✅

A is correct — The secondary voltage of a transformer is 180° out of phase with the primary voltage due to Lenz's law.

Core Concepts Used

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Faraday's Law of Electromagnetic Induction Lenz's Law Transformer Phasor Diagram

💡 EXAM TIP

Always remember: $E_1$ and $E_2$ are in phase with each other, but both lag the main flux $\Phi$ by 90° and are 180° out of phase with the primary applied voltage $V_1$ .

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