This gives you brief description to electrical power quality problems such as Ttransients, short and long duration voltage variation, voltage unbalance, waveform distortion,voltage fluctuations and power frequency variations.

1. INTRODUCTION TO POWER QUALITY
Dr. S. Rajalingam
Senior Lecturer/EEE
Sunyani Technical University
rajalingamstu@gmail.com
For explanation:
https://youtu.be/VX69IzldHJw

2. What is Power Quality?
• Power Quality expresses the quality of voltage or the
quality of current (quality of sine waves).
• Electric power quality involves voltage, current
frequency, and its waveform.
Dr.S.Rajalingam/EEE/STU

3. Power Quality-Definition
• As per IEEE, power quality is defined as “The
concept of powering and grounding sensitive
equipment in a manner that is suitable to the
operation of that equipment”
– IEEE (Institute of Electrical and Electronic
Engineers) www.ieee.org
Dr.S.Rajalingam/EEE/STU

4. Power quality problem
• “Any power problem manifested in voltage,
current or frequency deviations that result in
failure or mal-operation of customer
equipment” is called power quality problem.
• The most common source of power quality
problems are Power electronic devices,
Arching devices, Load switching and other
natural/ environmental accidents(trees).
Dr.S.Rajalingam/EEE/STU

5. Types of Power quality problem
1. Transients
2. Short duration variations
3. Long duration variations
4. Voltage unbalance
5. Waveform distortion
6. Voltage fluctuations
7. Power frequency variations
Dr.S.Rajalingam/EEE/STU

6. Transients in Power Quality
For explanation:
https://youtu.be/VX69IzldHJw

7. Transient/Surge
• Transients are defined as the power quality
disturbances that involve destructive high
magnitudes of current and voltage or even both
which is undesirable and momentary in nature.
• It may reach thousands of volts and amps even
in low voltage systems. However, such
phenomena only exist in a very short duration
from less than 50 nanoseconds to as long as 50
milliseconds.

8. Power Quality Transient- Sources
• Lightning Strikes
• Switching activities
– Capacitor bank switching
– Opening and closing of disconnects on energized lines
– Tap changing on transformers
• Loose connections in the distribution system that
results to arcing
• Accidents, human error, animals and bad weather
conditions

9. Power Quality Transients- Effects
• Electronic Equipment
– Equipment will malfunction and produces corrupted results
– Efficiency of electronic devices will be reduced
• Motors
– Transients will make motors run at higher temperatures
– Degrades the insulation of the motor winding resulting to
equipment failure.
– Increases the motor’s losses (hysteresis) and its operating
temperature
• Lights
– Fluorescent bulb and ballast failure
– Appearance of black rings at the fluorescent tube ends (indicator
of transients)
– Premature filament damage leading to failure of the incandescent
light.

10. Transients - Classification
• They are classified as
– Impulsive transient
– Oscillatory transient
• An impulsive transient (IEEE 1159) is defined as a sudden
change in the steady-state condition of voltage, current, or
both that is unidirectional in polarity (primarily either
positive or negative).
• It is normally a single, very high impulse like lightning.
Impulsive transients are generally described by their rise
and decay times.
• An oscillatory transient is a sudden change in the steady-
state condition of voltage, current, or both, that includes
both positive and negative polarity values.

11. Impulsive and Oscillatory Transients

12. Transients - Classification
• The impulsive transient can be further classified into
– Nanosecond impulsive transient
– Microsecond impulsive transient
– Millisecond impulsive transient
• The Oscillatory transient can be further classified into
– Low frequency oscillatory transient
– Medium frequency oscillatory transient
– High frequency oscillatory transient

13. • Long duration voltage variations
• Short duration voltage variations
For more explanation:
https://youtu.be/fD5UD87epZ4

14. Long duration voltage variation
• When the voltage deviations are exceeded for
greater than 1 minute, then it is said to be Long
duration voltage variation.
• The Long duration voltage variation can be
classified into three types
– Overvoltage
– Undervoltage
– Sustained interruption
Consider the Supply frequency = 50Hz
i.e., 50 cycles per second
1 minute = 60 seconds
Hence Number of cycles per minute
= 50 × 60
= 3000 cycles per minute

15. Long duration voltage variation
• Overvoltage: An increase in the RMS AC voltage
greater than 110% at power frequency for duration
more than 1 minute
Causes: Switching off a large load or energizing a large
capacitor bank.
• Undervoltage: A decrease in RMS AC voltage to less
than 90% at power frequency for duration more than 1
minute
Causes: Switching on a large load or Switching off a large
capacitor bank.
• Sustained interruption: When voltage is 0 for
duration more than 1 minute.

16. Long duration voltage variation-Effects
• The overvoltage and undervoltage is not the
result of system faults but they are caused by
the load variations on the system.
• Incorrect tap setting on transformers can also
cause undervoltage and over voltage
• Effects: Since they are greater than one
minute, they stress computers, controllers and
motors and shorten the life of power system
equipment's and motors.

17. Short duration voltage variation
• “The variation of RMS voltage for a time greater than
0.5 cycle to one minute/60 seconds” is called short
duration variation.
Causes: fault conditions, intermittent loose connections in wiring.
• Short Duration Voltage Variations are defined as the
variations in the supply voltage for durations not
exceeding one minute.
• The Short duration voltage variation can be classified
into three types
– Sag (dip)
– Swell
– Interruption

18. Short duration voltage variation
• Sag/Dip: A sag is a decrease to between 0.1 and
0.9 p.u in RMS voltage or current at the power
frequency for durations from 0.5 cycle to 1 min.
Causes: voltage drop due to fault current or starting of
large motors.
• Swell: An increase in RMS voltage in the range
of 1.1 to 1.8 p.u. for duration from 0.5 cycles to 1
minute.
• Interruption: a reduction in the supply voltage,
or load current, to a level less than 0.1 p.u for a
time not exceeding 1 minute.

19. Short duration voltage variation
• They are further classified into Instantaneous,
momentary and Temporary

20. Long/short duration voltage variation

21. Voltage unbalance,
Waveform distortion,
Voltage fluctuation, and
power frequency variation
For more explanation:
https://youtu.be/2iI5Cy6SYx8

22. Voltage unbalance
• It is defined as the variation in the amplitudes of three
phase voltages relative to one another.
(or)
• It is defined as the deviation of each phase from the
average voltage of all three phases.

23. Voltage unbalance
• Causes: unequal distribution of loads in the
distribution system, Large single phase loads
(induction furnace, traction loads)
• Effects: It can produce network problems such as
mal-operation of protection relays and voltage
regulation equipment, and also overheat of motor
and transformer. It affects three phase loads
(three phase induction machine)
• The effect can be mitigated by voltage regulators.

24. Voltage unbalance
• Voltage unbalance can be estimated as the maximum deviation
from the average of the three-phase voltages divided by the
average of the three-phase voltages, expressed in percent.
Voltage unbalance =
Max deviation from Average Voltage
Average Voltage
Example:
• Assume the following phase-to-phase voltage readings of 226,
232, and 235.
• Average Voltage = (226 + 232 + 235) / 3 = 231
• Maximum Deviation from Average Voltage = 231 - 226 = 5 V
• Voltage Unbalance = 5 / 231
• Voltage Unbalance = 0.0216 or 2.16%

25. Waveform distortion
• Waveform distortion is defined as a steady-
state deviation from an ideal sine wave of
power frequency.
• There are 5 types of waveform distortion
– DC offset
– Harmonics
– Inter-Harmonics
– Notching
– Noise

26. DC Offset
• DC offset: It is the defined as the presence of DC
voltage/current in the AC power system.
Causes: Asymmetry of power converters
Effects: heating and reduce the life span

27. Harmonics & Inter-harmonics
• Harmonics: It is the sinusoidal voltages or
currents having frequencies that are integer
multiples of the fundamental frequency.
Sources: Non linear devices like computers, VFD,
UPS
• Inter-Harmonics: It is the sinusoidal voltages
or currents having frequencies that are not the
integer multiples of the fundamental
frequency.
Sources: Static frequency converters, cyclo-
converters, power line carrier signals.

28. Harmonics

29. Harmonic indices
• The THD and TDD are the commonly used
harmonic indices.
• The amount of harmonic distortion is
measured by a factor called Total harmonic
distortion(THD%).
• The THD is defined as the ratio between the
RMS value of the harmonics to the RMS value
of the fundamental.

30. THD
• The formulas to calculate the voltage THD,
Current THD are as follows

31. TDD
• The Total Demand Distortion (TDD) is defined
as the square root of the sum of the squares of
the RMS value of the currents from 2nd
harmonic current to the highest harmonic
divided by the peak demand load current and
is expressed as a percent.
• The TDD index most often describe the
current harmonic distortion level

32. Notching
• Notching: It is a periodic voltage disturbance caused
by normal operation of power electronic devices
when current is commutated from one phase to
another (two phases of supply are effectively short-
circuited for a short time).

33. Noise
• Noise: It is defined as 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.
• Electrical noise adds “hash” or mess onto the fundamental sine
wave
Causes:
– Power electronic devices
– Arcing equipment
Effects:
– Affects Microcomputer
– Affects Programmable controllers

34. Voltage fluctuation/flicker
• Rapid changes in voltage within the allowable limits
of the nominal voltage, e.g. 0.9 to 1.1 p.u.
Causes: loads that exhibit continuous rapid
variations in current magnitude.
• If the impact of the voltage fluctuation on lamps
perceived by the human eye then it is called flicker.
• Flicker : undesirable result of fluctuation
• These two terms are linked together in standards and
hence the common term voltage flicker is used.

35. Power frequency variation
• It is defined as the “Deviation of power system
fundamental frequency from its specified nominal
value” (50Hz to 60Hz).
• Frequency variations that go outside of accepted
limits for normal steady-state operation of the
power system can be caused by faults on the bulk
power transmission system, a large block of load
being disconnected, or a large source of
generation going off-line.
• On modern interconnected power systems,
significant frequency variations are rare.

36. CBEMA and ITEC Curves
For more explanation:
https://youtu.be/hSU0y7njh3U

37. CBEMA Curves
• CBEMA Curve is one of the most frequently
employed power acceptability curves.
• This curve was originally developed by Computer &
Business Equipment Manufacturers Association
(CBEMA) in the year 1970 to describe the tolerance of
mainframe computer equipment to the magnitude and
duration of voltage variations on the power system.
• The association designed the curve, to point out ways in
which system reliability could be provided for
electronic equipment.
• The CBEMA curve was derived from experimental and
historical data taken from mainframe computers.

38. CBEMA Curves
• Many modern computers have greater tolerance
than this, the curve has become a standard design
target for sensitive equipment to be applied on the
power system and a common format for reporting
power quality variation data.
• The CBEMA curve was adapted from IEEE
Standard 446 which is typically used in the
analysis of power quality monitoring results.
• The horizontal axis represent the duration of the
event.
• The vertical axis represent the percentage of
voltage applied to the power circuit.

39. CBEMA Curves

40. CBEMA Curves

41. CBEMA Curves
• Voltage values above the envelope are supposed to
cause malfunctions such as insulation failure,
overexcitation and overvoltage trip.
• Voltages below the envelope are assumed to cause the
load to drop out due to lack of energy.
• The concept is that if the supply voltage stays within
the acceptable power area then the sensitive equipment
will operate well.
• In short, computers, programmable logic controllers
(PLCs), power distribution units (PDUs),
instrumentation, telecom and other solid-state systems
will operate reliably when applied properly.

42. CBEMA and ITIC Curves
• However, in 1994, the Information Technology
Industry Council was formed by a working group
of the CBEMA. They developed the curve called
ITIC curve. ITIC Curve is a modified version of
the CBEMA power acceptability curve
• The intent was to derive a curve that can better
reflect the performance of typical single-phase,
120 V, 60 Hz computers and their peripherals, and
other information technology items like fax
machines, copiers and point-of-sales terminals.
• Both curves are used to define the withstand
capability of various loads and devices for
protection from power quality variations.

43. ITIC Curves
• It is used as a reference to define the withstand
capability of various loads and devices for
protection from power quality problems.
• This is because the curve is generally
applicable to other equipment containing solid-
state devices aside from being specifically
applicable to computer-type equipment.

44. ITIC Curves

45. ITIC Curves
• Compared to the old CBEMA curve, the ITIC
curve has an expanded acceptable power area or
operating region for the portions of ΔV − t plane.
• The ITIC Curve illustrate an AC input voltage
envelope, which typically can be tolerated by
most Information Technology Equipment (ITE).
• The ITIC Curve describes both steady-state and
transitory conditions.
• The ITIC Curve is applicable to 120 V nominal
voltages obtained from 120 V, 208Y/120 V and
120/240 V 60 Hz systems.

46. ITIC Curves
• Steady-State Tolerances: The steady-state range
is ±10% from the nominal voltage. Any voltages
in this range may be present for an indefinite
period and are a function of the normal loadings
and losses in the distribution system.
• Voltage Swell: This region describes a voltage
swell having an RMS amplitude of up to 120% of
the RMS nominal voltage, with a duration of up
to 0.5 seconds. This transient may occur when
large loads are removed from the system or when
voltage is supplied from sources other than the
electric utility.

47. Low-Frequency Decaying Ring wave
• This region describes a decaying ring wave transient
which typically results from the connection of power
factor correction capacitors to an AC distribution
system. The frequency of this transient may range from
200 Hz to 5 kHz, depending upon the resonant
frequency of the AC distribution system.
• The magnitude of the transient is expressed as a
percentage of the peak 60 Hz nominal voltage (not the
RMS value).
• The amplitude of the transient varies from 140% for
200 Hz ring waves to 200% for 5 KHz ringwaves, with
a linear increase in amplitude and increasing frequency.

48. Low-Frequency Decaying Ring wave

49. High-Frequency Impulse and Ring wave
• This region describes the transients that
typically occur as a result of lightning strikes.
• Wave shapes applicable to this transient and
general test conditions are described in
ANSI/IEEE C62.41-1991.
• This region of the curve deals with both
amplitude and duration (energy), rather than
RMS amplitude. The intent is to provide an 80
Joule minimum transient immunity.

50. Voltage Sags
• Two different RMS voltage sags are described
in the curve.
• Generally, these transients result from
application of heavy loads, as well as fault
conditions, at various points in the AC
distribution system.
• Sags to 80% of nominal are assumed to have a
typical duration of up to 10 seconds, and sags
to 70% of nominal are assumed to have a
duration of up to 0.5 seconds.

51. No Damage Region
• Events in this region include sags and dropouts
which are more severe than others and
continuously applied voltages which are less
than the lower limit of the steady-state
tolerance range.
• The normal functional state of the ITE is not
typically expected during these conditions, but
no damage to the ITE should result.

52. Prohibited Region
• This region includes any surge or swells,
which exceeds the upper limit of the envelope.
If ITE is subjected to such conditions, damage
may result.

53. CBEMA & ITIC Curves

54. THANK YOU
Dr.S.Rajalingam/EEE/STU