Post on 25-Dec-2015
description
transcript
By
ABDUL HAKIM HJ ABU BAKAR
Topic 5:
FUNDAMENTAL OF FUNDAMENTAL OF
ELECTRICAL & ELECTRONICSELECTRICAL & ELECTRONICS
CLB 10402CLB 10402
Objective
After this lesson, student should be able to :
Understand the concept of peak, rms,
and average value
Understand the concept of shape factor
and peak factor
Objective
• Average heating effect over half – cycle :
2
2/ 2 ( ) 1
( )( ) 2
P
P
I R watt radianI R watt
rad
• If I is the value of dc voltage through the same resistance to produce the same heating effect :
therefore
2 21
2rms PI R I R
0.70712
Prms P
II I
Sinusoidal current
2 ( )
( )
Pave
I amp radI
rad
Average value of current
over a half-cycle :
0.637ave PI I amp
The total area under the half-cycle curve divided by the distance in radian of the curve along the horizontal axis
The voltage across the resistor is directly proportional to the current It follows that the relationship derived for current
also apply to voltage So, in general, average value of sinusoidal current or voltage is
0.637ave PI I
0.637 x maximum value
What is power factor?
• Is the ratio of true power to
apparent power in an AC circuit.
• PF = PT/ PA
Conclusion
Purely resistive Purely reactive Equal
PF = 1 PF = 0 PF = 0.7071
100% consumed No power consumed 70% consumed
Objectives
• Understand the use of resistance,
inductance and capacitance in circuit
• Understand the concept of R-L-C circuit
in series and parallel
• Determine the total impedance, Z and
current, I in a circuit
What we want to know?What we want to know? What we want to know?What we want to know?
• To know the value of each components
• To calculate Xc and XL
• To find current of each components
• To calculate total current
• To calculate the impedance
PropertiesProperties PropertiesProperties
• Voltage is constant
• Different current flow in each branch
Step by stepStep by step Step by stepStep by step
1. Value of each components
Resistance Ohm
Inductance Henry, H
Capacitance Farad, F
2. To find Xc and XL
fcX c
2
1
fLX L 2
If Xc = XL, it will be a resonance,
IC and IL will have a same amplitude but,
differs 180 in phase.
POWER
Electrical power is the rate at which
electrical energy is converted to another
form, such as motion, heat, or an
electromagnetic field
Power, P (Watt)
APPARENT POWER
A measure of alternating current power that
is computed by multiplying the root-mean-
square current by the root-mean-square
voltage.
EIP
Measured in Volt-amps(VA)
TRUE POWER
In a resistive circuit, power consumed
by the resistor is dissipated into heat
and not returned to the source.
cosEIP
Measured in Watts,W
APPLICATION
Electric Utility Company
- supply both true and apparent power
- apparent power is larger than true power thus
current supplied will be larger
- cost will arise
- Utility company will raise its raise for customers
operating at low power factors
Summary
If a circuit is purely resistive, the current is in phase with the voltage. If it is purely inductive, the current lags the voltage by 90°. If the circuit is purely capacitive, the current leads the voltage by 90°.
If a circuit contains both resistance and inductance, the current lags the voltage by an angle less than 90o but the angle is greater than 0°.
If a circuit contains resistance and capacitance, the currents leads the voltage by an angle less than 90°, but the angle is greater than 0°