DC Electric Circuit Electric Power

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1/30/2014
DC Electric Circuit
 DC Electric Circuits Examples (source: http://hyperphysics.phyastr.gsu.edu/hbase/electric/dcex.html)
 Multisim Circuit Simulation
 DC Circuit Construction, PhET Interactive Simulations,
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http://phet.colorado.edu/en/simulation/circuit-construction-kit-dc
Electric Power
 DC Electric Power = Voltage * Current
 P = V * I = (joules/coulomb)*(coulomb/sec)
= joules/sec = watts
 Ohm’s Law: V = I * R
 P = V * I = (I*R)*I = I2*R
 P = V * I = V * (V/R) = V2/R
 Other References
 Electric Power – HyperPhysics, http://hyperphysics.phyastr.gsu.edu/hbase/electric/elepow.html
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1/30/2014
A DC Relay Circuit with R, L and C .
• DC Circuit
• DC Power Supply V (volts), Resistor R (Ohms, mΩ, kΩ,
MΩ, etc), Inductor L (Henry, mH, μH), Capacitor C
(Farad, μF, nF, pF)
• Circuit Configuration
L
• Relay coil: L and R --- in series
158.9mH
E
12 V
• 12V DC coil:
R
• Calculated current 64.9 mA
• Measured current 64.x … 59.x mA
C
330µF
25V
185Ω
• Contact
• 120V, 1/6 HP
• 240V, 1/3 HP
Relay
• Normally Open (NO) contact
• Normally Closed (NC) contact
• C in parallel with the relay coil
DC 12V, AC 120V 1/6 HP, 240V 1/3 HP
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FIGURE 2-2 Waveforms for the voltage and current represented by equation 2.3.
% sinewave2.m
Vm = 170;
Vrms = Vm/sqrt(2);
f = 60;
T = 1/f;
dt = T/100;
t = 0: dt: 2*T;
w = 2*pi*f;
vt = Vm*sin(w*t);
Im = 30;
Irms = Im/sqrt(2);
theta = pi/6;
it = Im * sin(w*t - theta);
plot(t, vt, t, it), grid on
xlabel('Time sec'), ylabel('Volt/Ampere');
200
150
100
50
0
-50
-100
-150
-200
0
0.005
0.01
0.015E. 0.02
Timothy
L.
Skvarenina
and William
Time sec
DeWitt
Electrical Power and Controls, 2e
0.025
0.03
0.035
4
Copyright ©2005 by Pearson Education, Inc.
Upper Saddle River, New Jersey 07458
All rights reserved.
2
1/30/2014
Example 2-1 Phasor Doagram
FIGURE 2-3
reference.
Phasor diagrams for the voltage and current of Example 2-1; (a) voltage as reference, (b) current as reference, (c) cos(t) as
170 sin
30 sin
Timothy L. Skvarenina and William E.
DeWitt
Electrical Power and Controls, 2e
120 2 sin(
21.21 2 sin(
5
Copyright ©2005 by Pearson Education, Inc.
Upper Saddle River, New Jersey 07458
All rights reserved.
3
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