This document discusses power quality issues and solutions. It begins with an introduction to concepts like reactive power, power factor, harmonics, and crest factor. It then discusses common power quality disturbances such as voltage sags, swells, harmonics, and unbalance. Standards like IEEE 519 are mentioned. The document concludes with an overview of power quality mitigation techniques including active and passive filters, DVRs, and UPQC devices. Case studies are provided on how these solutions can compensate for reactive power, harmonics, voltage issues, and control power flow.

1. Presented by
KRISHNAKUMAR.R
ASSISTANT ENGINEER,
SWITCHYARD SUB DIVISION ,
MOOLAMATTOM.
Power Quality Issues

2. Organisation of the Talk
Introduction
Understanding
 Reactive Power
 Harmonic Power
 Power Factor and Crest Factor
Power Quality ( PQ )
 Common PQ Disturbances
 Causes for PQ Disturbances
 Need for PQ
 PQ Standards
Power Quality Mitigation Techniques
Conclusion

3. Basic Requirements for Critical
Loads
 Continuous, No Break in Power
 Voltage Regulation
 Sine wave Supply
 Isolation
 Constant Frequency
Load
Vs
Is

4. Understanding
Reactive Power and Power Factor
Vs
Is
R
Is
Vs XL
Reactive
Power(Q)
in
VAR
Imp. Phase
Angle
True Power(P)
in Watts
XL
Vs
Is
R

5. 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 ”

6. Understanding Crest Factor
Non
Linear
Load
Vs
Is
Current drawn by single Phase diode rectifier
Crest Factor = --------------------------
Peak Amplitude
RMS Value

7. 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.

8. 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
=
=


9. 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 
=
have fundamental component only
be balanced
have declared magnitude under all conditions

10. PQ affected by Polluting Load
Polluting
Load
A
B
PCC
Distorted
voltage
Pure Sinusoidal
Line Impedance ZL

11. Common PQ Disturbances
 Reactive Power Demand
 Harmonic Distortion
 Voltage sags and swells
 Undervoltages and overvoltages
 Voltage Unbalance
 Voltage Flicker
 Voltage Interruption
 Transient Disturbances
 Frequency variations

12. Harmonics-Polluting Loads
 Rectifiers
 Arc furnaces
 Adjustable Speed drives
 Power Electronic converters

13. 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

14. 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
Overheating and loss of life & equipments
Major Increase in cost

15. 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

16. 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

17. 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

18. 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

19. 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

20. 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

21. 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

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 THD
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

29. References
 IEEE 519 “Recommended Practices and
Requirements for Harmonic Control in
Electric Power Systems”
 www.ieeexplore.ieee.org

30. Thank You

32. Power Quality Solutions
Conventional Method
• Tuned Filters
Upcoming Solutions –Custom Power devices
• Shunt Active Filters
• Dynamic Voltage Restorer (DVR)
• Unified Power Quality Controller (UPQC)

33. Shunt Active Filter
Vdc
VPCC
IF
Vinv
Ls
An ideal shunt compensator can be considered as a voltage
source, controlled in magnitude and phase angle, with the
same frequency of the system to which it is connected.
Compensates
 Reactive Current
 Harmonic Current

34. Dynamic Voltage Restorer
Vdc
Vload
Vdvr
Vgrid
Corrects
 Voltage sag and Swell
 Voltage unbalance
 Voltage flicker

35. Unified Power Quality Controller
GRID LOAD
Vdc
Series Active
Filter
Shunt Active
Filter
Ls

36. Power Flow Control of UPQC
Under Low Voltage Condition
CONTACTOR TRANSFORMER LOAD
SHUNT
AF
SERIES
AF
3 Phase
grid
Supply
VOLTAGE
CURRENT
POWER
90%
110%
100%
10%
100%
110%
110%
100%
100%
100%
10%
10%

37. Power Flow Control of UPQC
Under High Voltage Condition
CONTACTOR TRANSFORMER LOAD
SHUNT
AF
SERIES
AF
3 Phase
grid
Supply
VOLTAGE
CURRENT
POWER
110%
90%
100%
100%
90%
90%
10%
100%
100%
100%
10%
10%

38. • THE END.