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Power Quality Issues
Basic Requirements for Critical Loads
Continuous, No Break in Power
Voltage Regulation
Sine wave Supply
Isolation
Constant Frequency
Load
Vs
Is
Understanding
Reactive Power and Power Factor
Vs
Is
R
Is
Vs
XL
Reactive
Power(Q)
in
VAR
Apparent
Power(S) in
VA
Imp. Phase
Angle
True Power(P)
in Watts
XL
Vs
Is
R
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 ”
Understanding Crest Factor
Non
Linear
Load
Vs
Is
Current drawn by single Phase diode rectifier
Crest Factor = --------------------------
Peak Amplitude
RMS Value
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.
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 squares of amplitudes of all harmonics
square of amplitude of fundamental
x 100
Mathematically,
THD of a voltage wave form can be defined as,
THD =
V
V
100
x
h
h
h
2
1
2
2
=
=∞
∑
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
)
2
(
2
V(t) ft
VSin π
=
have fundamental component only
be balanced
have declared magnitude under all conditions
PQ affected by Polluting Load
Polluting
Load
A
B
PCC
Distorted
voltage
Pure Sinusoidal
Line Impedance ZL
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
Harmonics-Polluting Loads
Rectifiers
Arc furnaces
Adjustable Speed drives
Power Electronic converters
Harmonics-FFT Analysis
Current drawn by PC
Harmonic Spectrum of PC
Current Waveform
6 Pulse Converter/Battery Charger
Harmonic Spectrum of 6 Pulse
Converter/Battery Charger
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
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
Causes of Voltage sags and swells
Causes for Sag
Motor Starting
Transformer Energization
Transmission Faults
Causes for Swell
Single line to ground fault
Removing a large load /
adding a large
capacitor bank
0 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
0 5 10 15 20 25
10
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
Voltage sag due to Motor Starting
Voltage sag due to Transformer
Energization
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
Causes for Unbalance
Unequal system impedances
Unequal distribution of
single-phase loads
Phase to Phase loads
Unbalanced Three phase loads
Va
Vb
Vc
1200
1200
1200
Va
Vb
Vc
1200
1210
1190
Balanced System Unbalanced System
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
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
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
Voltage Flicker
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
Voltage Notching
Causes
Adjustable Speed Drives
Solid State rectifiers
Voltage Interruption
Complete loss of electrical supply
Cause
Transmission Fault clearing time
• Opening / Recloser of circuit breaker
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
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
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
< 11<h<17 17<h<23 23<h<35 35<h 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 4.0 1.5 0.7 12.0
12.0 5.5 5.0 2.0 1.0 15.0
ISC/ IL
< 20
20-50
50-100
100-1000
> 1000 15.0 7.0 6.0 2.5 1.4 20.0
PQ Mitigation
Reactive and Harmonic Demand
 Active Filter
 Passive Filter
Voltage sag and Swell
 Dynamic Voltage Restorer
 Tap changing transformer
PQ Mitigation
Voltage Unbalance
 Static Power balancer
 Redistribution of single-phase loads equally
to all phases (Utility level).
 Load Balancing (Plant level)
Voltage Flicker
 Distribution static VAR compensator
PQ Mitigation
Transient Disturbances
 Surge Arrester
 Isolation transformer
 Active/Passive Filter

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powerqualityissues-150802081939-lva1-app6892.pdf

  • 2. Basic Requirements for Critical Loads Continuous, No Break in Power Voltage Regulation Sine wave Supply Isolation Constant Frequency Load Vs Is
  • 3. Understanding Reactive Power and Power Factor Vs Is R Is Vs XL Reactive Power(Q) in VAR Apparent Power(S) in VA Imp. Phase Angle True Power(P) in Watts XL Vs Is R
  • 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 ”
  • 5. Understanding Crest Factor Non Linear Load Vs Is Current drawn by single Phase diode rectifier Crest Factor = -------------------------- Peak Amplitude RMS Value
  • 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.
  • 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 squares of amplitudes of all harmonics square of amplitude of fundamental x 100 Mathematically, THD of a voltage wave form can be defined as, THD = V V 100 x h h h 2 1 2 2 = =∞ ∑
  • 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 ) 2 ( 2 V(t) ft VSin π = have fundamental component only be balanced have declared magnitude under all conditions
  • 9. PQ affected by Polluting Load Polluting Load A B PCC Distorted voltage Pure Sinusoidal Line Impedance ZL
  • 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
  • 11. Harmonics-Polluting Loads Rectifiers Arc furnaces Adjustable Speed drives Power Electronic converters
  • 12. Harmonics-FFT Analysis Current drawn by PC Harmonic Spectrum of PC Current Waveform 6 Pulse Converter/Battery Charger Harmonic Spectrum of 6 Pulse Converter/Battery Charger
  • 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
  • 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
  • 15. Causes of Voltage sags and swells Causes for Sag Motor Starting Transformer Energization Transmission Faults Causes for Swell Single line to ground fault Removing a large load / adding a large capacitor bank 0 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 0 5 10 15 20 25 10 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 Voltage sag due to Motor Starting Voltage sag due to Transformer Energization
  • 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 Causes for Unbalance Unequal system impedances Unequal distribution of single-phase loads Phase to Phase loads Unbalanced Three phase loads Va Vb Vc 1200 1200 1200 Va Vb Vc 1200 1210 1190 Balanced System Unbalanced System
  • 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
  • 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
  • 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
  • 20. Voltage Flicker 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
  • 21. Voltage Notching Causes Adjustable Speed Drives Solid State rectifiers
  • 22. Voltage Interruption Complete loss of electrical supply Cause Transmission Fault clearing time • Opening / Recloser of circuit breaker
  • 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
  • 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
  • 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 < 11<h<17 17<h<23 23<h<35 35<h 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 4.0 1.5 0.7 12.0 12.0 5.5 5.0 2.0 1.0 15.0 ISC/ IL < 20 20-50 50-100 100-1000 > 1000 15.0 7.0 6.0 2.5 1.4 20.0
  • 26. PQ Mitigation Reactive and Harmonic Demand  Active Filter  Passive Filter Voltage sag and Swell  Dynamic Voltage Restorer  Tap changing transformer
  • 27. PQ Mitigation Voltage Unbalance  Static Power balancer  Redistribution of single-phase loads equally to all phases (Utility level).  Load Balancing (Plant level) Voltage Flicker  Distribution static VAR compensator
  • 28. PQ Mitigation Transient Disturbances  Surge Arrester  Isolation transformer  Active/Passive Filter