The document discusses power quality, emphasizing the importance of powering and grounding sensitive equipment as the modern power grid evolves with increased green energy sources and new technologies like electric vehicles. Common power quality issues include voltage sags, swells, transients, unbalances, flicker, and harmonics, each having specific causes and impacts on equipment. The implementation of smart grid technologies is noted to improve reliability but does not necessarily enhance the quality of power delivered.

1. 1
Power Quality
Basics
Presented by: Jason Huneycutt

2. 2
Power Quality
 What is Power Quality?
 The concept of powering and grounding sensitive equipment
in a manner that is suitable to the operation of that equipment.

3. 3
Introduction
 The modern power grid is changing.
 The addition of green energy sources
• Solar
• Wind energy
 The reduction of coal bulk generation plants
 As loads increase coupled with the intermittent nature of solar
and wind energy the voltage stability will suffer.
 New technologies such as, electric vehicles are adding new
loads to the grid which, can lead to altered peak hours.
 The implementation of the smart grid technology which is
designed to makes the grid more efficient.

4. 4
Smart Grid
 Will smart grid reduce power quality issues, making power
quality investigations rare?
 No!
• The smart grid will increase grid reliability not the quality of the
power being delivered.
 As technology advances there will always be new types of loads
and sources added to the grid. This will always create new power
quality challenges.
 The most common power quality issues faced today include sags
and swells, transients, unbalance as well as harmonics.

5. 5
Types of Power Quality
Phenomenon
 Under-Voltage
 Over-Voltage
 Dips (Sags) and Swells
 Transients
 Unbalance
 Flicker
 Harmonics (THD/TDD)
 RVC

6. 6
Under-voltage
 An under-voltage is a decrease in RMS voltage less than 0.9
pu (percentile unit) for a duration longer than 1 min.
• Typical values are between 0.8 pu and 0.9 pu.
 Under-voltages are caused by loads switching on, or capacitor
banks switching off.
 The under-voltage can continue until voltage regulation
equipment on the system can bring the voltage back within
tolerances.
 Overloaded circuits can also result in under-voltages.

7. 7
Over-voltage
 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.
 Over-voltages can be the result of the following:
• Load switching (switching off a large loads such as motors)
• Variations in the reactive compensation (switching of cap
banks).
• Solar Panels
• Poor system voltage regulation capabilities or controls.
• Incorrect tap settings on transformers

8. 8
Voltage Dips (Sags) and Swells
 Voltage sags and swells are two of the most common power
quality events. Voltage Sags and Swells cannot be prevented
on the power system. As impedances change during the
course of a day the voltage will momentarily change as well.
 Even instantaneous short duration sags can cause process
shutdowns requiring hours to re-start.
 Voltage swells are one of the most common cause of tripping
breakers.
 The malfunction or failure of this equipment can cause large
financial losses to various manufacturers.

9. 9
Voltage Dips (Sags) and Swells
 Common Causes of voltage sags include source voltage
changes, inrush currents as well as inadequate wiring.
 Common Causes of voltage swells can include load switching,
utility faults, and damaged or loose neutral connections.
 Another Common Cause includes the wrong voltage for
equipment in use coming into the building. These wrong
voltages can include 230volt equipment being fed from 208 volts
or vice versa, 460 volt equipment being fed from 480 volts.
 The goal of power quality is to limit the number of sags and
swells as well as the magnitude of these events such that they
do not cause equipment malfunction or failure.

10. 10
Voltage Dips (Sags) and Swells
 On single-phase systems a voltage dip
begins when the Urms(1/2) voltage
falls below the dip / sag threshold.
 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.

11. 11
Voltage Dips (Sags) and Swells
 Class A – Dip (Sag) Detection
(Poly-phase)
 The dip / sag begins when the
Urms(1/2) voltage of one or more
channels is below the dip threshold.
 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.

12. 12
Voltage Dips (Sags) and Swells
 Class A – Swell Detection
 On single-phase systems a swell begins when the Urms(1/2)
voltage rises above the swell threshold,
 The swell ends when the Urms(1/2) voltage is equal to or below
the swell threshold minus the hysteresis voltage.
 On poly-phase systems a swell begins when the Urms(1/2)
voltage of one or more channel rises above the swell threshold.
 The swell ends when the Urms(1/2) voltage on all measured
channels is equal to or below the swell threshold minus the
hysteresis voltage

13. 13
Transients
 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)

14. 14
Transients
 Transient voltages can result in degradation or immediate
dielectric failure in all classes of equipment.
 High magnitude and fast rise time contribute to insulation
breakdown in electrical equipment like switchgear,
transformers and motors.
 Repeated lower magnitude application of transients to
equipment can cause slow degradation and eventual insulation
failure, decreasing equipment mean time between failures.

15. 15
Transients
 Transients can damage insulation
because insulation, like that in
wires has capacitive properties.
 Both capacitors and wires have
two conductors separated by an
insulator.
 The capacitance provides a path
for a transient pulse.
 If the transient pulse has enough
energy it will damage that section
of insulation.

16. 16
Transients
 This can be understood by
examining the basic formula
for Capacitive Reactance.
 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.

17. 17
Transients
 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.
 Lightning strikes or high
electromagnetic fields
produced by lighting can
induce voltage & current
transients in power lines &
signal carrying lines.
 These are typically seen as
unidirectional transients.

18. 18
Transients
 When capacitor banks are
switched on there is an initial
inrush of current.
 This will lead to a low-
frequency transient that will
have a characteristic ringing.
 These types of transients are
referred to as oscillatory
transients.
 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)

19. 19
Transients
 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.
 These typically will cause issues in areas with short cable
runs, such as off shore platforms

20. 20
Unbalance
 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.

21. 21
Unbalance
 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.

22. 22
Unbalance
 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.

23. 23
Unbalance
 Voltage unbalance 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.
 Any change in voltage
magnitudes and/or a shift in
the phase will cause an
unbalanced

24. 24
Flicker
 Flicker is a very specific
problem related to human
perception and
incandescent light bulbs. It
is not a general term for
voltage variations.

25. 25
Flicker
 Humans can be very
sensitive to light flicker that
is caused by voltage
fluctuations.
 Human perception of light
flicker is almost always the
limiting criteria for
controlling small voltage
fluctuations.

26. 26
Flicker
 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.

27. 27
Flicker
 In general today, flicker is measured using the IEC method.
• (IEC61000-4-15)
 In this method we take the instantaneous voltage and compare it to a
rolling average voltage.
 The deviation between these two is multiplied by a value in a
weighted curve.
 This curve is based on the sensitivity of the human eye at 120V 60Hz
or 230V 50Hz.
 The end value is called a percentile unit. The percentile units go
through a statistical analysis in order to calculate 2 values.

28. 28
Flicker
 Short Term flicker or Pst; is
calculated based on the
Flicker percentile unit.
 Pst is based on a 10 minute
interval.
 Long Term flicker or Plt; is
calculated based on the
Pst.
 Plt is based on a 2 hour
interval.

29. 29
Flicker
 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.
 This applies to incandescent
lighting ONLY. Other types of
lighting cannot be tested using
this curve.
 Since it uses a weighting curve it
applies only to 120V 60Hz and
230V 50Hz.

30. 30
Harmonics
 Harmonics are a sinusoidal
component of periodic
waves that have
frequencies that are
multiples of the
fundamental frequency
 Harmonics can cause many
problems, such as:
• Neutral wires to over heat
• Motors to overheat
• Transformers to overheat
• Electronic Failures

31. 31
Harmonics
 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.
 IEC 61000-4-30 Defines a harmonic frequency as a frequency
which is an integer multiple of the fundamental frequency
 IEC 61000-4-30 Defines a harmonic component as any of the
components having a harmonic frequency

32. 32
Harmonics
 Linear Loads such as
incandescent light and
motors draw current equally
throughout the waveform.
 Non-Linear loads such as
switching power supplies
draw current only at the
peaks of the wave.
 It is these non linear loads
that cause harmonics.

33. 33
Harmonics
 Typically current harmonics
will not propagate through a
system.
 Voltage harmonics will
propagate through a
system, as they will pass
through transformers.
 When non-linear loads get
high enough they can
cause harmonics in the
voltage.

34. 34
Harmonics
 Harmonics can be characterized based on
their order.
 Odd Harmonics are harmonics with odd order
numbers.
 Even Harmonics are harmonics with even
order numbers.
• Non-symmetrical due to faulty rectifiers.
 Triplens are odd harmonics that are multiples
of 3.
• These will not cancel out and will add and cause high
neutral currents.

35. 35
Harmonics
 Harmonics can characterized in different sequences, based on the
rotation of their magnetic field.
 Positive sequence harmonics create a magnetic field in the
direction of rotation. The fundamental frequency is considered to be
a positive sequence harmonic.
 Negative sequence harmonics develop magnetic fields in the
opposite direction of rotation. This reduces torque and increases the
current required for motor loads.
 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.

36. 36
Harmonics
 In three-phase systems, the fundamental currents will cancel
each other out, add up to zero amps in the neutral line.
 Zero sequence harmonic (such as the third harmonic) will be in
phase with the other currents of the three-phase system.
 Since they are in phase they will sum together and can lead to
high neutral currents.

37. 37
Harmonics
 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.

38. 38
THD
 Total harmonic distortion (THD) is the measure of the sum of the
harmonic components of a distorted waveform.
 THD can be calculated for either current or voltage.
 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.
 THD is typically, represented as a percentage of fundamental
amplitude
THD =
𝑆𝑢𝑚 𝑜𝑓 𝑡ℎ𝑒 𝑠𝑞𝑢𝑎𝑟𝑒𝑠 𝑜𝑓 𝑡ℎ𝑒 𝑎𝑚𝑝𝑙𝑖𝑡𝑢𝑑𝑒 𝑜𝑓 𝑎𝑙𝑙 𝑡ℎ𝑒 ℎ𝑎𝑟𝑚𝑜𝑛𝑖𝑐 𝑜𝑟𝑑𝑒𝑟𝑠
𝑆𝑞𝑢𝑎𝑟𝑒 𝑜𝑓 𝑡ℎ𝑒 𝑎𝑚𝑝𝑙𝑖𝑡𝑢𝑑𝑒 𝑜𝑓 𝑡ℎ𝑒 𝑓𝑢𝑛𝑑𝑎𝑚𝑒𝑛𝑡𝑎𝑙 𝑣𝑎𝑙𝑢𝑒
x 100%

39. 39
THD
 THD can be misleading when analyzing current harmonics.
 THD can be referenced to the amplitude of the fundamental.
 The voltage fundamental value is always present in non-faulted
conditions.
 Not necessarily true for current.
 The current amplitude will fluctuate with the loads impedance.
• As loads turn off, the fundamental current amplitude decreases.
 If the current being drawn by the load is low (near zero) then the THD
value will appear to be very high.

40. 40
THD
 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%
 THD =
0.2
200
x 100 = 3.16%
 If the fundamental current being drawn by the load then drops to
200mA then the THD will equal 100%
 THD =
0.2
0.200
x 100 = 100%
 This is deceiving because the current THD level appears to be
high, but this is only because there is little to no current being
drawn.

41. 41
TDD
 Total demand distortion (TDD) measurements should be used for
total current harmonic measurements.
 The total demand distortion references the total root-sum-square
harmonic current distortion, to the maximum average demand
current recorded during the test interval.
 Therefore, the reference value is the same throughout the test
interval and it is a valid value.
 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.

42. 42
THD & TDD
 The power quality industry has developed certain index values to
assess the distortion caused by the presence of harmonics.
 The two values most frequently indexed are total harmonic
distortion and total demand distortion.
 Individual harmonic values are also indexed in different
specifications, such as the North American IEEE 519 document
and the European Standard EN50160 on power quality; issue by
the European Committee for Electrotechnical Standardization
(CENELEC).

43. 43
RVC
 A rapid voltage change (RVC) is a fast rise
or fall of the RMS voltage.
 RVC events cause mainly changes in
lighting and will normally not bring damage
to electrical equipment.
• A reduction in the voltage by 10% can
result in a 34% reduction in the light
intensity from a 60 W incandescent lamp.
 Residential households are most
commonly affected, especially in weak
networks.
 This is seen as a lighting continuously
changing in intensity.

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

45. 45
RVC
 An RVC event starts with a steep down-
going step followed by an up-going ramp
ending at a voltage value less than that
existing before the switching.
• The fall time can be as short as 10 ms,
while the recovery ramp can last several
cycles.
 NOTE: for an event to be classified as a
rapid voltage change the voltage must
not fall below the lower voltage limit.
• If the voltage did fall below the lower
tolerance limit then the event would be
classified as a voltage dip (sag).

46. Questions or Comments?
Email Nicole VanWert-Quinzi
nicole.vanwert@Transcat.com
Transcat: 800-800-5001
www.Transcat.com
For related product information, go to:
www.Transcat.com/Megger

47. 47
Questions?
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