TRANSFORMER • A DEVICE THAT HAS THE ABILITY TO CHANGE THE VOLTAGE & CURRENT WITHOUT CHANGING THE FREQUENCY • AC/HEATING TRANSFORMERS ARE ISOLATION TRANSFORMERS • MADE UP OF A PRIMARY & A SECONDARY
Step-down Transformer L 1 240 volt Primary T 1 Induced voltage 24 v Secondary T 2 L 2 Ratio 10 : 1 Voltage 240 : 24
PRINCIPLE OF OPERATION • OPERATES ON THE PRINCIPLE OF MAGNETIC INDUCTION – WHEN CURRENT FLOWS THROUGH THE PRIMARY, IT INDUCES A CURRENT FLOW IN THE SECONDARY – THAT NEW CURRENT FLOWS IN THE OPPOSITE DIRECTION – VOLTAGE IN THE SECONDARY IS DETERMINED BY THE PRIMARY VOLTAGE & THE WINDINGS RATIO
PRINCIPLE OF OPERATION • TRANSFORMERS CAN BE STEP-UP OR STEP-DOWN • STEP-DOWN TRANSFORMERS ARE COMMON IN MODERN AC/HEATING APPLICATIONS • 120 VAC TO 24 VAC IS A VERY COMMON CONTROL TRANSFORMER – 5: 1 RATIO OF PRIMARY TO SECONDARY WINDINGS – 5: 1 RATIO OF PRIMARY TO SECONDARY VOLTAGES
VOLTAGE & CURRENT RELATIONSHIPS • TRANSFORMERS ARE VERY EFFICIENT DEVICES • OPERATE AT 95% – 98% EFFICIENCY • CONSIDERED TO BE WORKING AT 100%I. E. POWER IN = POWER OUT
TESTING THE TRANSFORMER 1. CHECK FOR VOLTAGE TO IT 2. CHECK FOR VOLTAGE FROM IT 3. OHM PRIMARY: 1. OPEN (OL) 2. SHORT (0 OHMS) 3. GROUNDED (ANY OHMS TO GROUND) 4. OHM SECONDARY: 1. OPEN (OL) 2. SHORT (0 OHMS) 3. GROUNDED (ANY OHMS TO GROUND)