This document provides an introduction to power quality and describes various power quality phenomena including under-voltage, over-voltage, dips, swells, transients, unbalance, flicker, harmonics, and total harmonic distortion (THD). It defines each phenomenon, explains typical causes, and discusses potential impacts on equipment. Key power quality issues covered include voltage variations, transients from lightning or capacitor switching, phase imbalances, light flicker from voltage fluctuations, and current harmonics from non-linear loads.

1. 1
An Introduction to Power Quality

2. 2
Moderator
n Ron Spataro
AVO Training Institute Marketing Manager

3. 3
Q&A
n Send us your
questions and
comments during
the presentation

4. 4
Today’s Presenter
n Andy Sagl
Megger® Product Manager

5. 5
Power Quality
n What is Power Quality?
n The concept of powering and grounding sensitive
equipment in a manner that is suitable to the operation of
that equipment.

6. 6
Types of Power Quality Phenomenon
n Under-Voltage
n Over-Voltage
n Dips (Sags) and Swells
n Transients
n Unbalance
n Flicker
n Harmonics (THD/TDD)
n RVC

7. 7
Under-voltage
n An under-voltage is a decrease in rms voltage
less than 0.9 pu for a duration longer than 1
min.
• Typical values are between 0.8 pu and 0.9 pu.
n Under-voltages can be caused by faults or
overloaded lines.
n Under voltage conditions can cause motors to
overheat.
n Motors require constant power. When the
voltage drops the current needs to rise.
n The rise in current causes a rise in heating.
𝑃= ​ 𝐼↑2 × 𝑅

8. 8
Over-voltage
n An over-voltage is an rms increase in ac voltage greater than 1.1 pu
for a duration longer than 1 min.
• Typical values are 1.1 pu to 1.2 pu.
n Over-voltages can be the result of the following:
• Variations in the reactive compensation (switching of cap
banks).
• Solar Panels
• Poor system voltage regulation capabilities or controls.
n Over-voltage conditions can cause motors to go into saturation,
breakers to trip, excessive energy use, reduced life in lighting
systems to name a few.

9. 9
Voltage Dips (Sags) and Swells
n A voltage dip or sag is a decrease in rms voltage less than 0.9 pu for a
duration less than 1 min.
n An voltage swell is an rms increase in ac voltage greater than 1.1 pu
for a duration less than 1 min.
n The most common power quality events.
n Cannot be prevented on the power system. As impedances
change during the day the voltage will fluctuate.
n Sags can cause process shutdowns requiring hours to re-
start.
n Swells are a common cause of tripping breakers.

10. 10
Voltage Dips (Sags) and Swells
n Sag and Swells:
n Voltage sags are caused by abrupt
increases in loads such as short
circuits or faults, motors starting, or
electric heaters turning on, or they
are caused by abrupt increases in
source impedance, typically caused
by a loose connection.
n Voltage swells are almost always
caused by an abrupt reduction in
load on a circuit with a poor or
damaged voltage regulator,
although they can also be caused
by a damaged or loose neutral
connection.

11. 11
Voltage Dips (Sags) and Swells
n Class A – Dip (Sag) Detection
(Single Phase)
n On single-phase systems a voltage dip begins
when the Urms(1/2) voltage falls below the dip /
sag threshold.
n The event ends when the Urms(1/2) voltage is
equal to or above the dip threshold plus the
hysteresis voltage.
Note This value is used only for voltage dip
(sags), swells, interruption, and RVC detection
and evaluation.

12. 12
Voltage Dips (Sags) and Swells
n Class A – Dip (Sag) Detection
(Poly-phase)
n The dip / sag begins when the Urms(1/2)
voltage of one or more channels is below the
dip threshold.
n The dip / sag ends when the Urms(1/2) voltage
on all measured channels is equal to or above
the dip threshold plus the hysteresis voltage.

13. 13
Voltage Dips (Sags) and Swells
n Class A – Swell Detection
n On single-phase systems a swell begins when the Urms(1/2) voltage rises
above the swell threshold,
n The swell ends when the Urms(1/2) voltage is equal to or below the swell
threshold minus the hysteresis voltage.
n On poly-phase systems a swell begins when the Urms(1/2) voltage of one or
more channel rises above the swell threshold.
n The swell ends when the Urms(1/2) voltage on all measured channels is
n equal to or below the swell threshold minus the hysteresis voltage.

14. 14
Transients
n Generally there are two different
types of transient over voltages:
low frequency transients with
frequency components in the few-
hundred-hertz region typically
caused by capacitor switching,
(Oscillatory transients) and high-
frequency transients with
frequency components in the few-
hundred-kilohertz region typically
caused by lighting and inductive
loads. (Impulsive Transients)
-1000
-500
0
500
1000

15. 15
Transients
n Transient voltages can result in degradation or immediate
dielectric failure in all classes of equipment.
n High magnitude and fast rise time contribute to insulation
breakdown in electrical equipment like switchgear,
transformers and motors.
n Repeated lower magnitude application of transients to
equipment can cause slow degradation and eventual
insulation failure, decreasing equipment mean time between
failures.

16. 16
Transients
n Transients can damage insulation
because insulation, like that in
wires has capacitive properties.
n Both capacitors and wires have
two conductors separated by an
insulator.
n The capacitance provides a path
for a transient pulse.
n If the transient pulse has enough
energy it will damage that section
of insulation.

17. 17
Transients
n This can be understood by
examining the basic formula
for Capacitive Reactance.
n It can now be seen that as
the value of the frequency
increases, the lower the
reactive capacitance and
therefore the lower the
impedance path.

18. 18
Transients
n Lightning is a major cause of
transients.
• A bolt of lightning can be over 5
miles long, reach temperatures in
excess of 20,000 degrees Celsius.
n Lightning strikes or high
electromagnetic fields produced
by lighting can induce voltage &
current transients in power lines
& signal carrying lines.
n These are typically seen as
unidirectional transients.

19. 19
Transients
n When capacitor banks are switched
on there is an initial inrush of
current.
n This will lead to a low-frequency
transient that will have a
characteristic ringing.
n These types of transients are
referred to as oscillatory transients.
n Oscillatory transients can cause
equipment to trip out and cause
UPS systems to turn on and off
erroneously.
08/12/2007 14:22:30.600 SUBCYCLE on X3-1
Time (ms)
35.48 45.12 54.76 64.40 74.04
-905.00
-354.50
196.00
746.50
1297.00
X2-3(Volts)

20. 20
Transients
n (Extremely fast transients, or EFT's, have rise and fall
times in the nanosecond region. They are caused by
arcing faults, such as bad brushes in motors, and are
rapidly damped out by even a few meters of distribution
wiring. Standard line filters, included on almost all
electronic equipment, remove EFT's.)
n These typically will cause issues in areas with short cable
runs, such as off shore platforms

21. 21
Unbalance
n Unbalance is a condition in a poly-phase system in which the RMS
values of the line voltages (fundamental component), or the phase
angles between consecutive line voltages, are not all equal per IEEE
1159 and IEC 61000-4-27.
-200
-100
0
100
200
RMS Voltage
Phase A Voltage Phase B Voltage Phase C Voltage

22. 22
Unbalance
n Voltage unbalance more
commonly emerges in
individual customer loads due
to phase load imbalances,
especially where large, single
phase power loads are used,
such as single phase arc
furnaces.
• A small unbalance in the phase
voltages can cause a large
unbalance in the phase currents.

23. 23
Unbalance
n Unbalanced voltages can
effect equipment on the
power system, such as
induction motors and
adjustable speed drives. In
addition unbalance voltages
can cause heating effects in
transformers and neutral
lines.

24. 24
Unbalance
n Voltage unbalanced can be
described as a set of
symmetrical components.
• In a balanced three phase system
the three line-neutral voltages are
equal in magnitude and phase and
are displaced from each other by
120 degrees.
n Any change in voltage
magnitudes and/or a shift in the
phase will cause an unbalanced

25. 25
Flicker
n Flicker is a very specific
problem related to human
perception and incandescent
light bulbs. It is not a general
term for voltage variations.

26. 26
Flicker
n Humans can be very sensitive
to light flicker that is caused by
voltage fluctuations.
n Human perception of light flicker
is almost always the limiting
criteria for controlling small
voltage fluctuations.

27. 27
Flicker
n The figure illustrates the level of
perception of light flicker from a
60 watt incandescent bulb for
rectangular variations. The
sensitivity is a function of the
frequency of the fluctuations
and it is also dependent on the
voltage level of the lighting.

28. 28
Flicker
n In general today, flicker is measured using the IEC method.
• (IEC61000-4-15)
n In this method we take the instantaneous voltage and compare it to a
rolling average voltage.
n The deviation between these two is multiplied by a value in a weighted
curve.
n This curve is based on the sensitivity of the human eye at 120V 60Hz or
230V 50Hz.
n The end value is called a percentile unit. The percentile units go through
a statistical analysis in order to calculate 2 values.

29. 29
Flicker
n Short Term flicker or Pst; is
calculated based on the
Flicker percentile unit.
n Pst is based on a 10 minute
interval.
n Long Term flicker or Plt; is
calculated based on the Pst.
n Plt is based on a 2 hour
interval.

30. 30
Flicker
n The basic criteria is simple. If the Pst
is less than 1.0 then flicker levels are
good. If Pst is greater than 1.0 then
the flicker levels could be causing
irritation.
n This applies to incandescent lighting
ONLY. Other types of lighting cannot
be tested using this curve.
n Since it uses a weighting curve it
applies only to 120V 60Hz and 230V
50Hz.

31. 31
Harmonics
n Harmonics are a sinusoidal
component of periodic waves that
have frequencies that are
multiples of the fundamental
frequency
n Harmonics can cause many
problems, such as:
• Neutral wires to over heat
• Motors to overheat
• Transformers to overheat
• Electronic Failures

32. 32
Harmonics
n IEEE 519 Defines a harmonic:
• A component of order greater than one of the Fourier series of a
periodic quantity.
– For example, in a 60 Hz system, the harmonic order 3, also
known as the “third harmonic,” is 180 Hz.
n IEC 61000-4-30 Defines a harmonic frequency as a frequency
which is an integer multiple of the fundamental frequency
n IEC 61000-4-30 Defines a harmonic component as any of the
components having a harmonic frequency

33. 33
Harmonics
n Linear Loads such as
incandescent light and
motors draw current equally
throughout the waveform.
n Non-Linear loads such as
switching power supplies
draw current only at the
peaks of the wave.
n It is these non linear loads
that cause harmonics.

34. 34
Harmonics
n Typically current harmonics
will not propagate through a
system.
n Voltage harmonics will
propagate through a system,
as they will pass through
transformers.
n When non-linear loads get
high enough they can cause
harmonics in the voltage.

35. 35
Harmonics
n Harmonics can be characterized based on their order.
n Odd Harmonics are harmonics with odd order numbers.
n Even Harmonics are harmonics with even order numbers.
• Non-symmetrical due to faulty rectifiers.
n Triplens are odd harmonics that are multiples of 3.
• These will not cancel out and will add and cause high neutral currents.

36. 36
Harmonics
n Harmonics can characterized in different sequences, based on the
rotation of their magnetic field. Positive sequence harmonics creates
a magnetic field in the direction of rotation. The fundamental
frequency is considered to be a positive sequence harmonic.
n Negative sequence harmonics develop magnetic fields in the
opposite direction of rotation. This reduces torque and increases the
current required for motor loads.
n Zero sequence harmonics create a single-phase signal that does not
produce a rotating magnetic field of any kind. These harmonics can
increase overall current demand and generate heat.

37. 37
Harmonics
n In three-phase systems, the fundamental currents will cancel each
other out, add up to zero amps in the neutral line.
n Zero sequence harmonic (such as the third harmonic) will be in phase
with the other currents of the three-phase system.
n Since they are in phase they will sum together and can lead to high
neutral currents.

38. 38
Harmonics
n The positive, negative, and
zero sequence harmonics
run in sequential order
(positive, negative, and then
zero).Since the fundamental
frequency is positive, this
means that the second
order harmonic is a
negative sequence
harmonic. The third
harmonic is a zero
sequence harmonic.

39. 39
THD
n Total harmonic distortion (THD) is the measure of the sum of the
harmonic components of a distorted waveform.
n THD can be calculated for either current or voltage.
n THD is the RMS (root-mean-square) sum of the harmonics, divided by
one of two values: either the fundamental value, or the RMS value of the
total waveform.
n THD is typically, represented as a percentage of fundamental amplitude
THD = √ ​ 𝑆 𝑢𝑚 𝑜𝑓 𝑡ℎ𝑒 𝑠𝑞𝑢𝑎𝑟𝑒𝑠 𝑜𝑓 𝑡ℎ𝑒 𝑎𝑚𝑝𝑙𝑖𝑡𝑢𝑑𝑒 𝑜𝑓
𝑎𝑙𝑙 𝑡ℎ𝑒 ℎ𝑎𝑟𝑚𝑜𝑛𝑖𝑐 𝑜𝑟𝑑𝑒𝑟𝑠/𝑆𝑞𝑢𝑎𝑟𝑒 𝑜𝑓 𝑡ℎ𝑒 𝑎𝑚𝑝𝑙𝑖𝑡𝑢𝑑𝑒
𝑜𝑓 𝑡ℎ𝑒 𝑓𝑢𝑛𝑑𝑎𝑚𝑒𝑛𝑡𝑎𝑙 𝑣𝑎𝑙𝑢𝑒 x 100%

40. 40
THD
n THD can be misleading when analyzing current harmonics.
n THD can be referenced to the amplitude of the fundamental.
n The voltage fundamental value is always present in non-faulted
conditions.
n Not necessarily true for current.
n The current amplitude will fluctuate with the loads impedance.
• As loads turn off, the fundamental current amplitude decreases.
n If the current being drawn by the load is low (near zero) then the THD
value will appear to be very high.

41. 41
THD
n If the total harmonic current is 0.2A and the fundamental current being
drawn by the load is 200A then the THD will equal 3.16%
n THD = √ ​0.2/200 x 100 = 3.16%
n If the fundamental current being drawn by the load then drops to
200mA then the THD will equal 100%
n THD = √ ​0.2/0.200 x 100 = 100%
n This is deceiving because the current THD level appears to be high,
but this is only because there is little to no current being draw.

42. 42
TDD
n Total demand distortion (TDD) measurements should be used for total
current harmonic measurements.
n The total demand distortion references the total root-sum-square
harmonic current distortion, to the maximum average demand current
recorded during the test interval.
n Therefore, the reference value is the same throughout the test interval
and it is a valid value.
n Total Demand Distortion should be calculated in accordance with the
IEEE 519 document: “Recommended Practices and Requirements for
Harmonic Control in Electrical Power Systems”), published by the
IEEE Standards Association.

43. 43
RVC
n A rapid voltage change is a fast rise or fall of the
RMS voltage.
n RVC events cause mainly changes in lighting
and will normally not bring damage to electrical
equipment.
n Residential households are most commonly
affected, especially in weak networks.
n This is seen as a lighting continuously changing
in intensity.
n If the RMS drops below 3% of the steady state
average then a RVC event is triggered.

44. 44
RVC
n RVC Events can be caused by the
switching on of a specific load or by a
sudden change in source voltage.
n Sudden source voltage changes can occur
in solar grids when the sun is obscured by
clouds.
n Source voltage changes can also occur in
wind farms when then wind speed
decreases.

45. 45
AVO Hands-On Power Quality Training
n Power Quality & Harmonics: 4 Days – 3.2 CEUs
n Protective Device Coordination for Utilities: 3 Days – 2.4 CEUs
n Protective Device Coordination for Industry: 3 Days – 2.4 CEUs
n Power Factor Testing: 3 Days – 2.4 CEUs
n Short Circuit Analysis: 4 Days – 3.2 CEUs

46. 46
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n Transients down to 1µ sec
n Harmonics, Inter-Harmonics, THD, TDD
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47. 47
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Tuesday June 26, 2018 at 1pm – 2pm CDT
Title: "A field technician basics of transformer fundamentals "
Presented by: Mike Carter
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48. 48
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