StepDown Transformer

STEP DOWN TRANSFORMER

RuncoN distribution transformer is a type of step-down transformer used in the final stage of electrical power distribution to deliver electricity to consumers at usable voltage levels.

What it does

It converts medium voltage (e.g., 11 kV, 33 kV) to low voltage (e.g., 415 V, 230 V) for homes, shops, and industries.

Basic principle

It works on electromagnetic induction:

$\frac{V_s}{V_p}=\frac{N_s}{N_p}$Vp​Vs​​=Np​Ns​​

• Since it is a step-down transformer → Vs < Vp and Ns < Np

Typical ratings

• Voltage:
o Primary: 11 kV / 33 kV
o Secondary: 415 V (3-phase) / 230 V (single-phase)

• Power rating:
o 25 kVA, 63 kVA, 100 kVA, 250 kVA, 500 kVA, etc.

Types of distribution transformers

1. Pole-mounted transformer
   o Installed on electric poles
   o Used in rural and small-load areas
2. Pad-mounted transformer
   o Ground-mounted, enclosed type
   o Used in urban areas for safety

Construction parts

• Core (silicon steel laminations)
• Windings (copper or aluminum)
• Transformer oil (cooling + insulation)
• Tank & conservator
• Breather (silica gel type)
• Buchholz relay (protection in larger units)

Working (simple)

1. High voltage from feeder enters primary winding
2. Magnetic flux is created in the core
3. Voltage is induced in secondary winding
4. Output is supplied to distribution lines at lower voltage

Key features

• Designed for continuous operation (24×7)
• Operates at high efficiency (≈ 95–99%)
• Good voltage regulation
• Low losses (core + copper losses)

Example

An 11 kV / 415 V transformer:

• Input: 11,000 V
• Output: 415 V (3-phase supply for buildings)