Day 2 ECET 2026 Night – 1-Φ Transformer: Construction & EMF Equation

Concept Notes

🔹 What is a Transformer?

A transformer is a static electrical machine which transfers AC power from one circuit to another without change in frequency but with change in voltage level, using the principle of mutual induction.

• Input side → Primary winding
• Output side → Secondary winding
• Core → Provides low reluctance path for flux

---

🔹 Construction of a 1-Φ Transformer

1. Magnetic Core
   • Made of laminated silicon steel sheets to reduce eddy current losses.
   • Two types:
     • Core-type (windings on two limbs)
     • Shell-type (windings on central limb, flux divides in side limbs).
2. Windings
   • Primary winding: connected to input AC supply.
   • Secondary winding: connected to load.
   • Made of copper/aluminum, insulated.
3. Insulation
   • Between windings and core to avoid short-circuit.
4. Cooling System
   • Air-cooled for small transformers.
   • Oil-cooled (transformer oil) for larger ones.
5. Other Parts
   • Tank, bushings, conservator, breather, tap changer (for voltage control).

---

🔹 Principle of Operation

When AC is supplied to the primary winding:

• AC current → alternating flux in core → induces EMF in both primary & secondary.
• According to Faraday’s Law of Electromagnetic Induction.

---

🔹 EMF Equation of Transformer

Let,

• = Number of primary turns
• = Number of secondary turns
• = Maximum flux (Weber)
• = Frequency (Hz)

By Faraday’s Law,
Induced EMF per turn =

• Primary induced EMF:

Secondary induced EMF:

Turns ratio (K):

---

🔹 Example

A 1-Φ transformer has 500 turns on primary, flux = 0.01 Wb, frequency = 50 Hz.

---

⚙️ Formulas

• EMF per turn:
• Primary EMF:
• Secondary EMF:
• Turns ratio:

---

🔟 10 MCQs

Q1. A transformer works on the principle of:
a) Self-induction
b) Mutual induction
c) Coulomb’s law
d) Ohm’s law

Q2. In a transformer, frequency of primary and secondary is:
a) Different
b) Same
c) Half
d) Double

Q3. A 1-Φ transformer is classified as:
a) Rotating machine
b) Static machine
c) Semi-rotating machine
d) None

Q4. The EMF per turn in transformer is given by:
a)
b)
c)
d)

Q5. For 100 turns in primary, 400 turns in secondary, turns ratio is:
a) 0.25
b) 4
c) 40
d) 25

Q6. The core of a transformer is laminated to reduce:
a) Hysteresis loss
b) Eddy current loss
c) Copper loss
d) Stray loss

Q7. In ideal transformer:
a) No copper loss
b) No core loss
c) Efficiency = 100%
d) All of the above

Q8. A transformer has , . If , find .
a) 100V
b) 200V
c) 400V
d) 1000V

Q9. The EMF equation is derived from:
a) Lenz’s Law
b) Faraday’s Law
c) Coulomb’s Law
d) Newton’s Law

Q10. The transformer does NOT change:
a) Voltage
b) Current
c) Frequency
d) Power

---

✅ Answer Key

Q.No	Answer
1	b
2	b
3	b
4	b
5	b
6	b
7	d
8	c
9	b
10	c

---

🧠 Explanations

• Q1: Transformer works on mutual induction → (b).
• Q2: Frequency remains same in primary & secondary → (b).
• Q3: Transformer is static → (b).
• Q4: Standard formula → (b).
• Q5: → (b).
• Q6: Laminations reduce eddy current losses → (b).
• Q7: In ideal case → no loss → efficiency 100% → (d).
• Q8: → (c).
• Q9: Derived from Faraday’s Law → (b).
• Q10: Transformer does not change frequency → (c).

---

🎯 Motivation / Why Practice Matters

Transformers are the backbone of power systems. From power plants to our mobile chargers, transformers are everywhere. ECET 2026 will test your ability to apply EMF equations and concepts like turns ratio, losses, and efficiency. If you master this now, you’ll solve future AC machines & power systems problems with ease.

---

📲 CTA

👉 Join our dedicated ECET 2026 WhatsApp Group for daily notes, MCQs & preparation updates:
🔗 Join Now