2. 1. WHAT IS POWER QUALITY
IT DETERMINES THE FITNESS OF A POWER SUPPLY SYSTEM
IT CAN BE A MEASURE OF RELIABILITY OF A SUPPY; or
IT CAN BE THOSE CHARACTERISTICS OF A SUPPLY THAT WILL ENABLE
A DEVICE TO WORK PROPERLY.
A POWER SUPPLY WHICH IS FREE FROM DISTURBANCES CAN BE
CONSIDERED AS A GOOD QUALITY POWER.
3. 2.POWER QUALITY ISSUES
THOSE DISTURBANCES WHICH AFFECT THE POWER SUPPLY SYSTEM
“Any power problem manifested in voltage, current, or frequency
deviations that results in failure or misoperation of customer
equipment”.
5. 3. CLASSIFICATION OF POWER
QUALITY ISSUES
1. Conducted low-frequency phenomena
a. Harmonics, interharmonics
b. Signalling voltages
c. Voltage fluctuations
d. Voltage dips and interruptions
e. Voltage unbalance
f. Power frequency variations
g. Induced low-frequency voltages
h. DC in AC networks
6. 3. CLASSIFICATION OF POWER
QUALITY ISSUES
2. Radiated low-frequency phenomena
a. Magnetic fields
b. Electric field
3. Conducted high-frequency phenomena
A. Directly coupled or induced voltages or currents
B. Unidirectional transients
C. Oscillatory transients
7. 3. CLASSIFICATION OF POWER
QUALITY ISSUES
4. Radiated high-frequency phenomena
a) Magnetic fields
b) Electric fields
c) Electromagnetic fields
5. Electrostatic discharge phenomena (ESD)
Sudden discharge between two electrically charged bodies
6. Nuclear electromagnetic pulse (NEMP)
The sudden burst of electro-magnetic radiation (EM Pulse) during nuclear
explosion will change the electric and magnetic field
8. 4. TRANSIENTS
“AN EVENT THAT IS UNDESIRABLE AND MOMENTARY IN NATURE”
2 TYPES : IMPULSIVE AND OSCILLATORY
An impulsive transient is a sudden, non–power frequency change in the
steady-state condition of voltage, current, or both that is unidirectional
in polarity (ositive or negative)
An oscillatory transient is a sudden, non–power frequency change in the
steady-state condition of voltage, current, or both, that includes both
positive and negative polarity values
10. 4. TRANSIENTS
OSCILLATORY – 3 TYPES
High frequency transients (Frequency greater than 500 kHz).
Medium frequency transients (Frequency between 5-500 kHz).
Low frequency transients (Frequency less than 5 kHz)
CAUSE
Lightning
13. 5.1 OVER VOLTAGE
“Increase in the RMS ac voltage greater than 110 percent at the
power frequency for a duration longer than 1min”
CAUSE
Switching off a large load
Energizing a capacitor bank
14. 5.2 UNDER VOLTAGE
“Decrease in the RMS ac voltage less than 90 percent at the
power frequency for a duration longer than 1 min”
CAUSE
Switching ON a large load
De-energizing a capacitor bank
15. 6. SUSTAINED INTERUPTIONS
Situation when the supply voltage is ZERO for more
than 1 min.
Requires human intervention to repair and restore the
system.
> 1 min
16. 7. SHORT DURATION VOLTAGE
VARIATIONS
Def :
• Short and temporary disturbances occurring in power system.
Cause:
• Switching on large loads
• Loose connections
• faults
Types:
• Voltage sag
• Voltage swell
• Interruptions
18. 7.1 INTERRUPTIONS
“An interruption occurs when the supply voltage or load current decreases
to less than 0.1 pu for a period of time not exceeding 1 min”
CAUSE
Power system faults
Equipment failure
Control malfunctions
< 1 min
19. 7.2 VOLTAGE SAG (DIP)
“A sag is a decrease in voltage to a value between 0.1 and 0.9
pu in RMS voltage or current at the power frequency for
durations from 0.5 cycle to 1 min”
CAUSE
Single line to ground fault
Switching ON heavy loads
Starting of large inductions motors
20. 7.3 VOLTAGE SWELLS
“A swell is defined as an increase to between 1.1 and 1.8 pu in
RMS voltage or current at the power frequency for durations
from 0.5 cycle to 1 min”
CAUSE
Switching OFF heavy loads
Energizing capacitor banks
21. 8. VOLTAGE FLUCTUATIONS
“Voltage fluctuations are systematic variations of the voltage to
a value between 0.9 to 1.1 pu”
CAUSE
Loads with continuous variation in current
SOLUTION
• Power
Conditioners.
EFFECTS
• Hardware failures.
• Crashes in PLC &
22. 8. VOLTAGE FLUCTUATIONS
•Max Permissible Voltage Variation - 1.5%.
NOMINAL SYSTEM VOLTAGE (KV
RMS)
MAXIMUM
(KV RMS)
MINIMUM
(KV RMS)
765 800 728
400 420 380
220 245 198
132 145 122
110 121 99
66 72 60
33 36 30
23. 9. POWER FREQUENCY
VARIATIONS
MAX PERMISSIBLE RANGE
49.2 to 50.3 Hz
“Deviation of the power system fundamental frequency from it
specified nominal value (e.g., 50 or 60 Hz)”
CAUSE
Poor speed regulation of alternator
EFFECTS
System crash
Speed variation in motors
SOLUTION
• Power
Conditioners.
• VDF, UPS
24. 10. WAVEFORM DISTORTION
“Waveform distortion is defined as a steady-state deviation
from an ideal sine wave of power frequency principally
characterized by the spectral content of the deviation”
26. 10.1 HARMONICS
“Harmonics are sinusoidal voltages or currents having
frequencies that are integer multiples of the fundamental
frequency (usually 50 or 60 Hz)”
27. 10.2 INTER HARMONICS
“Voltages or currents having frequency components that are not
integer multiples of the fundaments frequency are called inter
harmonics ”
28. 10.2 INTER HARMONICS &
HARMONICS
CAUSE
• Non-linear loads.
• SMPS used by personal
computers.
• VFD.
• Electronics devices.
SOLUTION
• Power
Conditioners.
• Harmonic filters.
EFFECTS
• Overheating
conductors and
transformers.
• Decreased efficiency.
• Increases losses
29. 10.3 DC OFFSET
“The presence of a dc voltage or current in an ac power system
is termed dc offset”
30. 10.3 DC OFFSET
CAUSE
• Fault in power
electronic devices.
SOLUTION
• DC Filters
EFFECTS
• Overheating of
transformers.
• Saturation of transformer
core
• Reduction in transformer
life.
32. 10.4 NOTCHING
CAUSE
• 3-phase power
electronic converter.
SOLUTION
• Isolation of
sensitive devices.
EFFECTS
• Injects harmonics to the
supply.
• Causes over heating
33. 10.5 NOISE
“Unwanted electrical signals with broadband spectral content
lower than 200 kHz superimposed upon the power system
voltage or current in phase conductors, or found on neutral
conductors or signal lines ”
34. 10.5 NOISE
CAUSE
• Power electronic
devices.
• Control circuits
• Arcing equipments
• SMPS.
SOLUTION
• Isolation of
sensitive devices.
• Filters.
• Power
conditioners
EFFECTS
• Injects harmonics to the
supply.
• Disturbance in micro
controller, computers and
PLC.
