EET 323 – Electrical System Design Lecture 14: Transformers Radian Belu, PhD

Lecture Objectives

A transformer consists of two or more windings coupled by mutual magnetic flux. - Primary Winding - Secondary Winding(s)

Transformer Equation Faraday’s Law states that, If the flux passes through a coil of wire, a voltage will be induced in the turns of wire. This voltage is directly proportional to the rate of change in the flux with respect of time. If we have N turns of wire, Lenz’s Law

Apparent Power Conservation E1*I1 = E2*I2

Transformer Equation Where, ‘a’ is the Voltage Transformation Ratio; which will determine whether the transformer is going to be step-up or step-down For a > 1 E1 > E2 Step-Down For a < 1 E1 < E2 Step-Up For a = 1 E1 = E2 Impedance Transformer

Low-Voltage Transformers LV Transformers Ratings: 600 V or less for booth primary and secondary windings Typically Transformer Ratings: 480-120/240 V, or 480-208 Y/120 V Indoor installations and dry-type construction

Loading Calculations

Floating Υ – Δ Connections Rule of Thumb – Lighting Transformer Leg Load: 2/3 Single-Phase Load + 1/3 3-Phase Load

Transformer Voltage Taps The taps are made to high-voltage side to adjust for the variations in the supply voltage

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