20030802

Electrical Module 1

Basic Electrical Circuit I Current

V Source of EMF

R Resistance

Basic Terms • Current • Voltage • Resistance

Ohm’s Law

I

V R

Capacitors

A C =ε d

Magnetic Field

Coil

Inductors, Capacitors & ac • Ac circuits have continuously changing values of voltage and current • Inductors and capacitors continuously oppose these changes • Opposition to current is called reactance • Measured in ohms

X L = 2ΠfL

1 XC = 2ΠfC

Reactance Voltages & Currents

VX L = I X L × X L VX C = I X C × X C

Terminology

AC Current (I)

R

Resistance

XL

XC Reactance

Impedance

Resistors Current (I)

Current (I) R

R R

+ Potential Source (V) -

Potential Source (V)

Series Circuit R R

+

R

With all 6 Resistances the same value (R) Current would be 6 times less that of 1 resistance (R)

R

R

R

R

Parallel Circuit With all 6 Resistances the same value (R) Current would be 6 times more that of 1 resistance (R)

R

R

Capacitor in a DC circuit Current (I) = 0

+ Potential Source (V)

C -

Capacitors will not pass DC Current

Capacitive Transients VC VC or IC

Capacitor Charging IC Time

Capacitor Dis-Charging VC

Inductor in a DC circuit Current (I) = unlimited

+ Potential Source (V) -

L

Inductors are a Short circuit to DC Current

Inductor Transients

IL VL or IL VL

Time

Sine curves and phasors V1

V

1

Phasor Diagram V2 V2 θ

V1

V1

V2 Leads V1 by θ

Resistive Circuit V I I

V

Series & Parallel Inductors Current (I)

V

L

Current (I)

L

V

L AC Potential Gen Source (V)

Series Circuit L L

AC Potential Gen Source (V)

L

L

L

Parallel Circuit

L

With all 6 Inductances the same value (L) Current would be 6 times less that of 1 Inductance (L)

L

With all 6 Inductances the same value (L) Current would be 6 times more that of 1 Inductance (L)

In both circuits the Current will lag the Voltage by 1/4 cycle

L

L

Inductive Phasors V I 90º I

V

Series & Parallel Capacitors Current (I) C

Current (I)

C

V

V AC Potential Gen Source (V)

C

Series Circuit

C C

C

AC Potential Gen Source (V)

C

C

C

C

Parallel Circuit

With all 6 Capacitances (C) the same value With all 6 Capacitances (C) the same value Current would be 6 times more Current would be 6 times less that of 1 Capacitance that of 1 Capacitance In both circuits the Current will lead the Voltage by 1/4 cycle

C

C

Capacitive Phasors V I

I 90º

V

Phasors for a typical circuit

V

≈25° I

Resistor and Inductor in Series

Impedance Triangle Z θ

XL=10Ω

R=20Ω

What is the impedance of the circuit? What is the phase angle?

Acrostic V comes before (leads) I in an Inductor

CI V

I L

I comes before (leads) V in a Capacitor

Power Power Supplied P=V x I I

Voltage reaquired to force current through resistor V=I x R

V

~

R Power transformed to heat P= I 2 x R

Power wave in a resistive circuit

Power in a capacitive circuit

Power in an inductive circuit

Power in a real circuit

Power Triangle Watts Apparent Power

XL

θ Active Power Volts-Amperes

Reactive Power Vars

Direction of magnetic field

Motor Action

Electromagnetic Induction

Transformer

Motor

Motor

Series Motor

Basic Generator

Generation of Sinusoidal Voltage

Spinning Magnet

Three phase Generation

Field and Stator Windings CLo f Stato r & Ro to r Dire ction of Rota tion of Roto r

Vo ltag e E be ing in du ced in s tato r con du ctors

F

Roto r Con du ctors Roto r

Flux

3 Phase Connections

Grounded Star

Magnetic Circuit Losses • Hysteresis • Eddy currents

Saturation Curve

For you to do