Filter

1
Filter Transfer Function
To determine filter type, look how HV as a
function of frequency
Z1 and Z2 could include multiple components
2
RLC at Resonance

• At resonance
• current is max.
• Zeq R
• current and voltage are in phase.
• the higher Q, the narrower the resonant peak.

3
Exam II Review AC Power
Average power
rms value

• The average ac power (Pav) is the power
  dissipated on the load resistor.
• 0?cosq?1, dependent on the complex load.
• ideal power factor cosq 1, ZR, pure
  resistive load

4
AC Power instantaneous and average power
5
Complex Power

• real power Pav(unit watts) power absorbed by
  the load resistance.
• reactive power Q (unit volt-amperes-reactive,
  VAR) exchange of energy between the source and
  the reactive part of the load. No net power is
  gained or lost during the process. QQL-QC, if
  Qlt0, the load is capacitive, Qgt0, the load is
  inductive
• Apparent power SVrmsIrms (unit
  volt-amperes, VA) computed by measuring the rms
  load voltage and currents without regard for the
  phase angle.

6
Example 7.8, P345 power factor correction
7
Transformer
Transformation of Voltage
Transformation of Resistance
8
Residential Wiring
GFCI
9
Example Midterm 1998

• An electrical engineering major has designed and
  constructed a motor for your sophomore design
  project. It has been wound with an inductance of
  16 mH and a resistance of 3.0 ohm. You had
  specified that it be optimized for the best
  possible power factor at 60 Hz consequently, a
  354 microFarad capacitor was added in parallel
  with the motor, as shown below.
• a. Operated at 120 V, what is the current through
  the motor when operated at 60 Hz?
• b. What power is delivered by the voltage source?
  
• c. What power is dissipated by the motor?
• Your complete project was so innovative that your
  engineering professor entered it in an
  international competition. You arrive in Germany
  for the competition before remembering that the
  line frequency there is 50 Hz.
• d. What is the power factor of this circuit at
  50 Hz?
• e. What capacitance do you need to replace 354 mF
  capacitor in order to correct the power factor
  back to unity?

10
Example Cont.
a. Operated at 120 V, what is the current through
the motor when operated at 60 Hz?
b. What power is delivered by the voltage source?
d. What is the power factor of this circuit at
50 Hz?
e. What capacitance do you need to correct the
power factor back to unity?
Note you calculate S only on the motor part!
Negative just means Capacitor
11
Example 3 1st Fall 199

• An electrical engineering firm has designed a
  motor for your sophomore design project. You
  specified that it should be wound with an
  inductance of 16 mH and a resistance of 3.0  ohm.
  You had specified that it be optimized for the
  best possible power factor at 60 Hz
  consequently, a 354 mF capacitor was added in
  parallel with the motor. Unfortunately the motor
  was actually wound with an inductance of 61 mH
  and a resistance of 30 ohm because of
  typographical errors in the FAX to the motor
  manufacturer.
•                                                 
                                                    
                                       
• What power is delivered by the voltage source?
• What power is dissipated by the motor?
• What capacitance do you need to replace 354 mF
  capacitor in order to correct the power factor
  back to unity?

12
Example Cont.
a. What power is delivered by the voltage source?
b. What power is dissipated by the motor?
d. What capacitance do you need to correct the
power factor back to unity?