E1 – Electrical Fundamentals # 2 – AC and DC Current

© 2005 Refrigeration Training Services - E1#2 AC and DC Current v1.1 Direct Current Moves in one direction Negative to positive Can be produced through chemical action Chemical electrolyte produces electrons Negative cathode gives away electrons Positive cathode collects electrons © 2005 Refrigeration Training Services - E1#2 AC and DC Current v1.1

© 2005 Refrigeration Training Services - E1#2 AC and DC Current v1.1 Direct Current (DC) Electrolyte Zinc Case (Negative Electrode) Carbon Rod (Positive Electrode) Dry Cell Battery When load is attached, the chemical reaction in the electrolyte causes current flow © 2005 Refrigeration Training Services - E1#2 AC and DC Current v1.1

Alternating Current (AC) Moves in one direction, then the other Produced by a generator © 2005 Refrigeration Training Services - E1#2 AC and DC Current v1.1

Alternating Current (AC) Generator Generators produce Alternating Current First, the current goes in one direction Then it reverses, or alternates, in the opposite direction © 2005 Refrigeration Training Services - E1#2 AC and DC Current v1.1

Alternating Current (AC) Generator In the U.S. there are 60 complete cycles per second © 2005 Refrigeration Training Services - E1#2 AC and DC Current v1.1

© 2005 Refrigeration Training Services - E1#2 AC and DC Current v1.1 Cycles and Frequency Cycle: One complete electrical alternation Frequency Number of cycles in a second Measurement of frequency: Hertz (Hz) Cycles U.S. frequency is 60 hertz, or 60 cycles © 2005 Refrigeration Training Services - E1#2 AC and DC Current v1.1

Generating Alternating Current (AC) Passing a conductor through a magnetic field A generator uses many conductors and a large magnetic field to produce electrical current © 2005 Refrigeration Training Services - E1#2 AC and DC Current v1.1

Generating Alternating Current Magnet NORTH Passing a conductor between two magnets causes electrons to flow in the wire. This produces electrical current in the wire. SOUTH Magnet Conductor © 2005 Refrigeration Training Services - E1#2 AC and DC Current v1.1

Expressing AC with a Sine Wave A sine wave shows how alternating current flows in one direction, then reverses to flow in the opposite direction © 2005 Refrigeration Training Services - E1#2 AC and DC Current v1.1

Sine Wave of Alternating Current Magnet 0º 90º 180º 270º 360º NORTH Positive Negative SOUTH Magnet One cycle Conductor © 2005 Refrigeration Training Services - E1#2 AC and DC Current v1.1

© 2005 Refrigeration Training Services - E1#2 AC and DC Current v1.1 Effective voltage Alternating current starts at 0, reaches a peak, then returns to 0 Peak voltage at 90° (electrical degrees) Effective voltage is .707 times peak voltage © 2005 Refrigeration Training Services - E1#2 AC and DC Current v1.1

© 2005 Refrigeration Training Services - E1#2 AC and DC Current v1.1 Effective Voltage 0º 90º 180º Peak Voltage 170 v Effective Voltage 120 v .707 x 170 = 120 v 0 v Effective voltage = .707 x Peak voltage Note: Meters measure effective voltage © 2005 Refrigeration Training Services - E1#2 AC and DC Current v1.1

Generating 3 Phase Alternating Current 3Ø current is generated by passing three conductors through a magnetic field © 2005 Refrigeration Training Services - E1#2 AC and DC Current v1.1

© 2005 Refrigeration Training Services - E1#2 AC and DC Current v1.1 Generating 3Ø Current Magnet NORTH Current is generated in each conductor as it passes through the magnetic field. SOUTH Magnet © 2005 Refrigeration Training Services - E1#2 AC and DC Current v1.1

Sine Wave of 3 Phase Current Magnet 0º 120º 240º 360º NORTH 90º 180º 270º SOUTH Magnet Each sine wave starts 120° after the other. © 2005 Refrigeration Training Services - E1#2 AC and DC Current v1.1

Sine Wave of 3 Phase Current Magnet 0º 120º 240º 360º NORTH 90º 180º 270º SOUTH Magnet Windings 120° out of phase give 3Ø motors their high starting torque. © 2005 Refrigeration Training Services - E1#2 AC and DC Current v1.1

Inductance & Reactance The out-of-phase condition between voltage and amperage Reactance: The resistance voltage encounters when it changes flow Inductive reactance: A combination of inductance and reactance Necessary for the starting and running of an induction motor © 2005 Refrigeration Training Services - E1#2 AC and DC Current v1.1

Inductive Reactance Induction: When voltage leads current Reactance: 0º 90º 180º 270º 360º VOLTAGE CURRENT Reactance: The resistance encountered during the change of flow © 2005 Refrigeration Training Services - E1#2 AC and DC Current v1.1

© 2005 Refrigeration Training Services - E1#2 AC and DC Current v1.1 Capacitive Reactance Capacitors can create an out-of-phase condition between voltage and amperage The voltage lags behind the amperage Capacitors increase motor starting torque © 2005 Refrigeration Training Services - E1#2 AC and DC Current v1.1

Capacitive Reactance Capacitors cause voltage to lag behind current 0º 90º 180º 270º 360º CURRENT VOLTAGE Capacitors cause voltage to lag behind current © 2005 Refrigeration Training Services - E1#2 AC and DC Current v1.1

© 2005 Refrigeration Training Services - E1#2 AC and DC Current v1.1 END OF A/C and D/C Current © 2005 Refrigeration Training Services - E1#2 AC and DC Current v1.1