1. Power Quality Issues
Power Electronics Group

2. Basic Requirements for Critical LoadsVs Is
Continuous, No Break in Power
Voltage Regulation
Sine wave Supply
Isolation
Constant Frequency
Power Electronics Group

3. Understanding Reactive Power and Power FactorVs Is R Is Vs XL
Apparent
Power(S) in VA
Imp. Phase
Angle XL Vs Is R
Reactive Power(Q)
in VAR
True Power(P)
in Watts
Power Electronics Group

4. Displacement and True Power Factor
Displacement Power Factor:
“Ratio of the active power of the fundamental, in watts, to the apparent Power of the fundamental wave, in volt-amperes”
True Power Factor:
“Ratio of the total power, in watts, to the total volt-amperes. This includes fundamental and all harmonic components ”
Power Electronics Group

5. Understanding Crest Factor
Non Linear Load Vs Is
Current drawn by single Phase diode rectifier
Crest Factor =
Peak Amplitude
RMS Value
Power Electronics Group

6. Understanding Harmonics
Non Linear Load Vs Is
Deviation from a perfect sine wave can be represented by Harmonics.
Sinusoidal Component having a frequency that is an integral multiple of the Fundamental frequency.
Power Electronics Group

7. Total Harmonic Distortion
Defines the total harmonic content of current or voltage
Ratio of the RMS of the harmonic content to the RMS of the
Fundamental, as % of Fundamental
THD =
sum of squ
ares of am
plitudes o
f all harm
onics
square of
amplitude
of fundame
ntal
x 100
Mathematic
ally,
THD of a
voltage wa
ve form ca
n be defin
ed as,
THD = V
100 x h 2 1   
Power Electronics Group

8. Power Quality Supply Voltage at load must
The Voltage at any point in the distribution system is uniquely described by
Where
v,f are constants (declared Value) for all t
have fundamental component only
be balanced
have declared magnitude under all conditions
Power Electronics Group

9. PQ affected by Polluting Load
PCC
Distorted voltage
Pure Sinusoidal
Line Impedance ZL
Power Electronics Group

10. Common PQ Disturbances
Reactive Power Demand
Harmonic Distortion
Voltage sags and swells
Undervoltages and overvoltages
Voltage Unbalance
Voltage Flicker
Voltage Notching
Voltage Interruption
Transient Disturbances
Frequency variations
Power Electronics Group

11. Harmonics-Polluting Loads
Rectifiers
Arc furnaces
Adjustable Speed drives
Power Electronic converters
Power Electronics Group

12. Harmonics-FFT Analysis
Current drawn by PC
6 Pulse Converter/Battery Charger
Harmonic Spectrum of PC Current Waveform
Harmonic Spectrum of 6 Pulse Converter/Battery Charger
Power Electronics Group

13. Implication of Reactive and Harmonics currents
Oversize of all installation equipments to transmit Reactive and Harmonic currents namely
Transformer
Cables
Circuit breakers & distribution switch boards
Neutral overloads
Increase in Transmission & Distribution loss
Reduction in voltage stability margin
Overheating and loss of life & equipments
Major Increase in cost
Power Electronics Group

14. Voltage sags and swells
Reduction in the ac voltage, at the power frequency, for durations from a half-cycle to a few seconds.
Voltage Sag is Characterized by two parameters – Magnitude and Duration
Power Electronics Loads are Sensitive to Voltage Sags
Power Electronics Group

15. Causes of Voltage sags and swells
Voltage sag due to Motor Starting 1 2 3 4 5 6 7 8 9 10 11
190
195
200
205
210
215
220
RMS voltage in V
Time in Cycles
Causes for Sag
Motor Starting
Transformer Energization
Transmission Faults
Voltage sag due to Transformer Energization
Causes for Swell
Single line to ground fault
Removing a large load / adding a large capacitor bank 5 10 15 20 25
10.1
10.2
10.3
10.4
10.5
10.6
10.7
10.8
10.9 11
Time in Cycles
RMS voltage in kV
Power Electronics Group

16. Voltage Unbalance Definition
In a balanced sinusoidal supply system the three line-neutral voltages are equal in magnitude and are phase displaced from each other by 120 degrees Va Vb Vc
1200 Va Vb Vc
1200
1210
1190
Balanced System
Unbalanced System
Causes for Unbalance
Unequal system impedances
Unequal distribution of
single-phase loads
Phase to Phase loads
Unbalanced Three phase loads
Power Electronics Group

17. Effect of Voltage Unbalance
Induction Motor drive
Overheating and loss of Insulation life
Reduced Motor Efficiency
Noisy in their operation due Torque and speed pulsation
Motor derating factor
NEMA Induction motor derating curve
Power Electronics Group

18. Effect of Voltage Unbalance
AC Variable Speed drive M
3Ø Diode Rectifier
Line Current of 3Ø diode Rectifier for Balanced Input
Line Current of 3Ø diode Rectifier for 5%unbalanced Input
Line Current of 3Ø diode Rectifier for 15%unbalanced Input
Draws uncharacteristic triplen harmonics
Triplen harmonic current can lead to undesirable harmonic problems
Excessive thermal stress on diodes
Power Electronics Group

19. Voltage Flicker Definition
Repetitive or random variations of the voltage envelope modulated at frequencies less than 25 Hz, which the human eye can detect as a variation in the lamp intensity of a standard bulb due to sudden changes in the real and reactive Power drawn by a load
Voltage waveform showing flicker created by an arc furnace
Power Electronics Group

20. Voltage Flicker Causes Induction Motor drive Effect lamp flicker
Human eye is most sensitive to voltage waveform
modulation around a frequency of 6-8Hz.
Causes
Induction Motor drive
Arc furnaces
Arc welders
Frequent motor starts
Power Electronics Group

21. Voltage Notching Causes Adjustable Speed Drives Solid State rectifiers
Power Electronics Group

22. Voltage Interruption Complete loss of electrical supply Cause
Transmission Fault clearing time
Opening / Recloser of circuit breaker
Power Electronics Group

23. Transient Disturbances
Transient disturbances are caused by the injection of energy by switching or by lightning
Causes
Lightning
Capacitor Switching
Load switching
Oscillatory transient waveform caused by capacitor energizing
Power Electronics Group

24. Need for Power Quality Business Problems:
Momentary disturbance can cause scrambled data, interrupted
communications, system crashes and equipment failure
Lost productivity and idle people and equipment
Overtime required to make up for lost work time
Revenue and accounting problems such as invoices not
prepared, payments held up etc
According to Electric Light and Power Magazine, 30 to 40 percent of all business downtime is related to Power Quality Problems
Power Electronics Group

25. IEEE 519 Harmonic Standard
IEEE 519 “Recommended Practices and Requirements for Harmonic Control in Electric Power Systems”
Specifies load current harmonic limits at PCC
Specifies supply voltage harmonic limits at PCC
HARMONIC CURRENT DISTORTION LIMITS IN % OF IL V 
69 kV h 11
< 17 23 35
TDD
4.0
2.0
1.5
0.6
0.3
5.0
7.0
3.5
2.5
1.0
0.5
8.0
10.0
4.5
0.7
12.0
5.5
15.0 I SC
/ I L 20
20-50
50-100 
1000
6.0
1.4
20.0
Power Electronics Group

26. Reactive and Harmonic Demand
PQ Mitigation
Reactive and Harmonic Demand
Active Filter
Passive Filter
Voltage sag and Swell
Dynamic Voltage Restorer
Tap changing transformer
Power Electronics Group

27. PQ Mitigation Voltage Unbalance Voltage Flicker Static Power balancer
Redistribution of single-phase loads equally
to all phases (Utility level).
Load Balancing (Plant level)
Voltage Flicker
Distribution static VAR compensator
Power Electronics Group

28. Transient Disturbances
PQ Mitigation
Transient Disturbances
Surge Arrester
Isolation transformer
Active/Passive Filter
Power Electronics Group