Fahad's Electrical Encyclopedia

The Complete Electrical Transformers Guide

A simplified, well-organized educational guide to electrical transformers: operating principle, types, components, testing, faults, and protection — with interview questions and practical tools. 50 focused lessons for students, technicians, and engineers, curated by trainer Fahad Refai.

Transformer Interview Questions

75+ questions with concise, professional answers across five career-stage categories — from fresh graduates to protection engineers.

Start Preparing ←

Transformer Current Calculator

Calculate the rated current of any single-phase or three-phase transformer from its power and voltage, with the formula shown.

Try the Calculator ←

Comprehensive Review

Review questions covering every transformer topic with links to detailed answers — test yourself.

Start Reviewing ←

What Are Electrical Transformers?

Start here: the definition of a transformer, its role in the power system, and its main types.

What Is an Electrical Transformer? The Difference Between a Step-Up and a Step-Down Transformer The Difference Between a Power Transformer and a Distribution Transformer Why Is Transformer Capacity Rated in Kilovolt-Amperes (kVA)?

Transformer Basics & Operating Principle

Electromagnetic induction, turns ratio, and current calculations — the foundation for everything that follows.

The Working Principle of the Electrical Transformer Why Doesn't a Transformer Work on Direct Current? What Does the Turns Ratio Mean in Transformers? How to Calculate Transformer Current

Main Transformer Components

Windings, iron core, and insulation: what's inside the tank and why.

Components of the Electrical Transformer The Function of the Iron Core in a Transformer Why Is the Transformer Core Made of Laminations? The Function of Transformer Windings

Oil, Insulation & Cooling

Transformer oil and its accessories, plus ONAN and ONAF cooling systems.

The Function of Transformer Oil The Difference Between BDV and DGA for Transformer Oil The Function of Transformer Radiators ONAN and ONAF Transformer Cooling Systems The Function of the Conservator Tank The Function of the Breather and Silica Gel

Transformer Nameplate

How to read a transformer's official nameplate and use it to make operating decisions.

Understanding the Transformer Nameplate How to Read a Transformer Nameplate

Connections & Vector Group

Star and delta, vector groups, and phase displacement — the language of three-phase transformers.

The Difference Between Star and Delta Connections in Transformers The Meaning of Vector Group in Transformers The Meaning of Dyn11 in Transformers

Tap Changer

Adjusting output voltage by changing the effective turns: the concept, types, and handling guidelines.

The Function of the Tap Changer The Difference Between OLTC and OCTC

Transformer Testing

From insulation resistance (megger) to TTR and the no-load and short-circuit tests — the complete transformer testing toolkit.

Insulation Resistance (IR) Test for Transformers What Does the Polarization Index (PI) Mean? The TTR Test for Transformers Winding Resistance Test Open-Circuit Test for Transformers Short-Circuit Test for Transformers The BDV Test for Transformer Oil The DGA Test for Transformers

Transformer Faults & Maintenance

Diagnosis and prevention: overheating, noise, leaks, maintenance programs, and safety.

Causes of Transformer Overheating Causes of Humming Noise in Transformers Causes of Transformer Oil Leakage Common Transformer Faults Preventive Maintenance for Transformers Safety Procedures Before Transformer Maintenance

Transformer Protection

The complete protection system: Buchholz relay, pressure relief, differential protection, REF, and inrush current.

Electrical Transformer Protection The Function of the Buchholz Relay The Function of the Pressure Relief Device (PRD) Differential Protection for Transformers Inrush Current in Transformers REF Protection: Restricted Earth Fault Protection for Transformers CTs and VTs and Their Relationship to Power Transformers

Transformer Efficiency & Calculations

Losses, efficiency, and voltage regulation — the numbers that govern selection and operation.

Core (Iron) Loss and Copper Loss in Transformers Electrical Transformer Efficiency Voltage Regulation in Transformers

Comprehensive Review

Test yourself: questions covering every topic, with links to their answers.

Comprehensive Review Questions on Electrical Transformers

Lessons & Courses

For those who want structured, step-by-step learning with videos and practical explanations.

Electrical Transformers Course — Fahad Refai FahadApp Educational Articles Engineering Apps & Tools

Want to master electrical transformers step by step?

Follow trainer Fahad Refai's Electrical Transformers course — a practical walkthrough from the fundamentals to testing and reading catalogs.

Browse Fahad Refai's Courses