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F a c t o r s P h e n o m e n
a
Voltage Instability
Long Lines Cables
Flicker
Bottlenecks
Asynch. Connection
Power Oscillators

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2
Asynchronous connection The interconnected AC
networks that tie the power generation plants to
the consumers are in most cases large. The map
below shows the European situation. There is one
grid in Western Europe, one in Eastern Europe,
one in the Nordic countries. Islands like Great
Britain, Ireland, Iceland, Sardinia, Corsica,
Crete, Gotland, etc. also have their own grid
with no AC connection to the continent. The other
continents on the globe have a similar
situation. Even if the networks in Europe have
the same nominal frequency, 50 cycles per second
or Hertz (Hz), there is always some variation,
normally less than 0.1 Hz, and in certain cases
it may prove difficult or impossible to connect
them with AC because of stability concerns. An AC
tie between two asynchronous systems needs to be
very strong to not get overloaded. If a stable AC
tie would be too large for the economical power
exchange needs or if the networks wish to retain
their independence, than a HVDC link is the
solution. And in other parts of the world (South
America and Japan) 50 and 60 Hz networks are
bordering each other and it would be impossible
to exchange power between them with an AC line or
cable. HVDC is then the only solution.

European interconnected power grids.
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3
Bottlenecks Constrained transmission paths or
interfaces in an interconnected electrical
system The term Bottlenecks is often
interchangeable to congested transmission paths
or interfaces. A transmission path or interface
refers to a specific set of transmission elements
between two neighboring control areas or utility
systems in an interconnected electrical system. A
transmission path or interface becomes congested
when the allowed power transfer capability is
reached under normal operating conditions or as a
result of equipment failures and system
disturbance conditions. The key impacts of
Bottlenecks are reduction of system reliability,
inefficient utilization of transmission capacity
and generation resources, and restriction of
healthy market competition.The ability of the
transmission systems to deliver the energy is
dependent on several main factors that are
constraining the system, including thermal
constraints, voltage constraints, and stability
constraints. These transmission limitations are
usually determined by performing detailed power
flow and stability studies for a range of
anticipated system operating conditions. Thermal
limitations are the most common constraints, as
warming and consequently sagging of the lines is
caused by the current flowing in the wires of the
lines and other equipment. In some situations,
the effective transfer capability of transmission
path or interface may have to be reduced from the
calculated thermal limit to a level imposed by
voltage constraints or stability constraints.
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4
Flicker A fluctuation in system voltage that can
lead to noticeable changes in light
output. Voltage Flicker can either be a periodic
or aperiodic fluctuation in voltage magnitude
i.e. the fluctuation may occur continuously at
regular intervals or only on occasions. Voltage
Flicker is normally a problem with human
perception of lamp strobing effect but can also
affect power-processing equipment such as UPS
systems and power electronic devices. Slowly
fluctuating periodic flickers, in the 0.5
30.0Hz range, are considered to be noticeable by
humans. A voltage magnitude variation of as
little as 1.0 may also be noticeable. The main
sources of flicker are industrial loads
exhibiting continuous and rapid variations in the
load current magnitude. This type of loads
includes electric arc furnaces in the steel
industry, welding machines, large induction
motors, and wind power generators. High impedance
in a power delivery system will contribute
further to the voltage drop created by the line
current variation.
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5
Harmonics Harmonics are associated with
steady-state waveform distortion of currents and
voltages Harmonics are components that make up a
waveform where each component has a frequency
that is an integral multiple of the fundamental
frequency. The term Harmonic is normally applied
to waveform components that have frequencies
other than the fundamental frequency. For a 50 Hz
or 60Hz system the fundamental frequency is 50HZ
or 60Hz. A waveform that contains any components
other than the fundamental frequency is
non-sinusoidal and considered to be distorted.
  Nonlinear loads draw currents that are
non-sinusoidal and thus create voltage drops in
distribution conductors that are non-sinusoidal.
Typical nonlinear loads include rectifiers,
variable speed drives, and any other loads based
on solid-state conversion. Transformers and
reactors may also become nonlinear elements in a
power system during overvoltage conditions.
Harmonics create many concerns for utilities and
customers alike. Typical phenomena include
neutral circuit overloading in three phase
circuits, motor and transformer overheating,
metering inaccuracies and control system
malfunctions.
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6
Interruptions Occur when the supply voltage
drops below 10 of the nominal value An
Interruption occurs whenever a supplys voltage
drops below 10 of the rated voltage for a period
of time no longer than one minute. It is
differentiated from a voltage sag in that the
late is not a severe power quality problem. The
term sag covers voltage drops down to 10 of
nominal voltage whereas an interruption occurs at
lower than 10. A Sustained Interruption occurs
when this voltage decrease remains for more than
one minute. An interruption is usually caused
by downstream faults that are cleared by breakers
or fuses. A sustained interruption is caused by
upstream breaker or fuse operation. Upstream
breakers may operate due to short-circuits,
overloads, and loss of stability on the bulk
power system. Loss of stability is usually
characterized by out-of-tolerance voltage
magnitude conditions and frequency variations
which exceed electrical machine and transformer
tolerances. This phenomenon is often associated
with faults and deficiencies in a transmission
system but can also be the result of lack of
generation resources. The concerns created by
interruptions are evident and include
inconvenience, loss of production time, loss of
product, and loss of service to critical
facilities such as hospitals.
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7
Long lines Long lines need special consideration
in the planning of a power system. This
transmission carries more than 12,000 MW over 800
km. There is an HVDC system with two 600 kV
bipoles of 3150 MW each is direct route to São
Paulo while the three 800 kV shunt and series
compensated AC lines has two intermediate
substations that allow connection to the local
grids. For long AC lines one must consider i.e.
the reactive power compensation, the transient
stability and switching overvoltages and how many
intermediate substations one needs. If the line
length is longer than approx. 600 km one should
also consider if an HVDC alternative brings lower
investment costs and/or lower losses or if the
inherent controllability of an HVDC system brings
with some other benefits. Another factor to
consider is the land use The figure at the right
compares two 3,000 MW HVDC lines for the 1,000 km
Three Gorges - Shanghai transmission, China, to
five 500 kV AC lines that would have been used if
AC transmission had been selected. Go to Long
Cables
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8
Long cables Cables have large capacitances and
therefore, if fed with AC, large reactive
currents. Cables for DC are also less expensive
than for AC. One must distinguish between
submarine cables and land (underground)
cables. Submarine cables Since no shunt reactor
can be installed at intermediate points (in the
sea) and DC cables are less expensive, the
majority of cables gt 50 km are for
DC. Underground cables Long underground cables (gt
50 km) have been generally avoided since the cost
for an overhead line was deemed to be only 10
20 of the cost for the cable. In many parts of
the world it is now almost impossible to get
permission to build a new overhead line. HVDC
Light has changed the cost relation and the
cable solution is less expensive than before.
Laying of the 200 km Fenno-Skan HVDC cable (500
MW).
Laying of the 180 km Murraylink HVDC Light cable
(220 MW).
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9
Loop Flow Unscheduled power flow on a given
transmission path in an interconnected electrical
system The terms Loop Flow and Parallel Path Flow
are sometimes used interchangeable to refer to
the unscheduled power flows, that is, the
difference between the scheduled and actual power
flows, on a given transmission path in an
interconnected electrical system. Unscheduled
power flows on transmission lines or facilities
may result in a violation of reliability criteria
and decrease available transfer capability
between neighboring control areas or utility
systems.   The reliability of an interconnected
electrical system can be characterized by its
capability to move electric power from one area
to another through all transmission circuits or
paths between those areas under specified system
conditions. The transfer capability may be
affected by the contract path designated to
wholesale power transactions, which assumes that
the transacted power would be confined to flow
along an artificially specified path through the
involved transmission systems. In reality, the
actual path taken by a transaction may be quite
different from the designated routes, determined
by physical laws not by commercial agreements,
thus involving the use of transmission facilities
outside the contracted systems. These unexpected
flow patterns may cause so-called Loop Flow and
Parallel Path Flow problems, which may limit the
amount of power these other systems can transfer
for their own purposes.
Transmission Loop Flows for 1000 KW scheduled
Transfer from Area A to Area C in an
Interconnected System
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10
Power Oscillations Periodic variations in
generator angle or line angle due to transmission
system disturbances Oscillations of generator
angle or line angle are generally associated with
transmission system disturbances and can occur
due to step changes in load, sudden change of
generator output, transmission line switching,
and short circuits. Depending on the
characteristics of the power system, the
oscillations may last for 3 -20 seconds after a
severe fault. Drawn out oscillations that last
for a few seconds or more are usually the result
of very light damping in the system and are
pronounced at power transfers that approach the
lines stability limit. During such angular
oscillation period significant cycle variations
in voltages, currents, transmission line flows
will take place. It is important to damp these
oscillations as quickly as possible because they
cause mechanical wear in power plants and many
power quality problems. The system is also more
vulnerable if further disturbances occur. The
active power oscillations on a transmission line
tend to limit the amount of power that may be
transferred, thus may result in stability
concerns or utilization restrictions on the
corridors between control areas or utility
systems. This is due to the fact that higher
power transfers can lead to less damping and thus
more severe and possibly unstable oscillations.

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11
Reactive Power Factor Effects of reactive power
on the efficiency of transmission and
distribution Reactive power is defined as the
product of the rms voltage, current, and the sine
of the difference in phase angle between the two.
It is used to describe the effects of a
generator, a load, or other network equipment,
which on the average neither supplies nor
consumes power. Synchronous generators, overhead
lines, underground cables, transformers, loads
and compensating devices are the main sources and
sinks of reactive power, which either produce or
absorb reactive power in the systems. To maintain
efficient transmission and distribution, it is
necessary to improve the reactive power balance
in a system by controlling the production,
absorption, and flow of reactive power at all
levels in the system. By contrast, inefficient
reactive power management can result in high
network losses, equipment overloading,
unacceptable voltage levels, even voltage
instability and outages resulting from voltage
collapse. Local reactive power devices for
voltage regulation and power factor correction
are also important especially for balancing the
reactive power demand of large and fluctuating
industrial loads.
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12
Sags and Swells Short duration decrease/increase
(sag/swell) in supply voltage A Voltage Sag or
Voltage Dig is a decrease in supply voltage of
10 to 90 that lasts in duration from half a
cycle to one minute. A Voltage Swell is an
increase in supply voltage of 10 to 80 for the
same duration. Voltage sags are one of the most
commonly occurring power quality problems. They
are usually generated inside a facility but may
also be a result of a momentary voltage drop in
the distribution supply. Sags can be created by
sudden but brief changes in load such as
transformer and motor inrush and short
circuit-type faults. A sag may also be created
by a step change in load followed by a slow
response of a voltage regulator. A voltage swell
may occur by the reverse of the above
events. Electronic equipment is usually the main
victim of sags, as they do not contain sufficient
internal energy to ride through the
disturbance. Electric motors tend to suffer less
from voltage sags, as motor and load inertias
will ride through the sag if it is short enough
in duration.
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13
Unbalanced Load A load which does not draw
balanced current from a balanced three-phases
supply An unbalanced load is a load which does
not draw balanced current from a balanced
three-phase supply. Typical unbalanced loads are
loads which are connected phase-to-neutral and
also loads which are connected phase-to-phase.
Such loads are not capable of drawing balanced
three-phase currents. They are usually termed
single-phase loads.  A single-phase load, since
it does not draw a balanced three-phase current,
will create unequal voltage drops across the
series impedances of the delivery system. This
unequal voltage drop leads to unbalanced voltages
at delivery points in the system. Blown fuses on
balanced loads such as three-phase motors or
capacitor banks will also create unbalanced
voltage in the same fashion as the single-phase
and phase-phase connected loads. Unbalanced
voltage may also arise from impedance imbalances
in the circuits that deliver electricity such as
untransposed overhead transmission lines. Such
imbalances give the appearance of an unbalanced
load to generation units.  An unbalanced supply
may have a disturbing or even damaging effect on
motors, generators, poly-phase converters, and
other equipment. The foremost concern with
unbalanced voltage is overheating in three-phase
induction motors. The percent current imbalance
drawn by a motor may be 6 to 10 times the voltage
imbalance, creating an increase in losses and in
turn an increase in motor temperature. This
condition may lead to motor failure.
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14
Voltage Instability Post-disturbance excursions
of voltages at some buses in the power system out
of the steady operation region Voltage
instability is basically caused by an
unavailability of reactive power support in an
area of the network, where the voltage drops
uncontrollably. Lack of reactive power may
essentially have two origins firstly, a gradual
increase of power demand without the reactive
part being met in some buses or secondly, a
sudden change in the network topology redirecting
the power flows in such a way that the required
reactive power cannot be delivered to some buses.
The relation between the active power consumed
in the considered area and the corresponding
voltages is expressed in a static way by the P-V
curves (also called nose curves). The increased
values of loading are accompanied by a decrease
in voltage (except in case of a capacitive load).
When the loading is further increased, the
maximum loadability point is reached, beyond
which no additional power can be transmitted to
the load under those conditions. In case of
constant power loads the voltage in the node
becomes uncontrollable and decreases rapidly.
This may lead to the partial or complete collapse
of a power system.
Back to Overview
15

• Factors / Phenomena Harmonics
• Technology / System Harmonic Filters
• Example of application Reducing harmonics in
  heavy industry
• Harmonic Filters may be used to mitigate, and in
  some cases, eliminate problems created by power
  system harmonics. Non-linear loads such as
  rectifiers, converters, home electronic
  appliances, and electric arc furnaces cause
  harmonics giving rise to extra losses in power
  equipment such as transformers, motors and
  capacitors. They can also cause other, probably
  more serious problems, when interfering with
  control systems and electronic devices.
  Installing filters near the harmonic sources can
  effectively reduce harmonics. For large, easily
  identifiable sources of harmonics, conventional
  filters designed to meet the demands of the
  actual application are the most cost efficient
  means of eliminating harmonics. These filters
  consist of capacitor banks with suitable tuning
  reactors and damping resistors. For small and
  medium size loads, active filters, based on power
  electronic converters with high switching
  frequency, may be a more attractive solution.
• Benefits
• Eliminates harmonics
• Improved Power Factor
• Reduced Transmission Losses
• Increased Transmission Capability
• Improved Voltage Control
• Improved Power Quality
• Other applications
• Shunt Capacitors

more about Harmonic Filters and Harmonics
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16
Factors / Phenomena Reactive Power
Factor Technology / System Harmonic
Filters Example of application Regulation of the
power factor to increase the transmission
capability and reduce transmission losses as well
as reducing harmonics. Harmonic Filters produced
reactive power as well as mitigate, and in some
cases, eliminate problems created by power system
harmonics. Where the main need is power factor
compensation the best solution can still be a
harmonic filter due to the amount of harmonics.
Non-linear loads such as rectifiers, converters,
home electronic appliances, and electric arc
furnaces cause harmonics giving rise to extra
losses in power equipment such as transformers,
motors and capacitors. They can also cause other,
probably more serious problems, when interfering
with control systems and electronic devices.
Installing filters near the harmonic sources can
effectively reduce harmonics. For large, easily
identifiable sources of harmonics, conventional
filters designed to meet the demands of the
actual application are the most cost efficient
means of eliminating harmonics as well as
producing reactive power. These filters consist
of capacitor banks with suitable tuning reactors
and damping resistors. For small and medium size
loads, active filters, based on power electronic
converters with high switching frequency, may be
a more attractive solution. Benefits Improved
power factor, Reduced transmission losses,
Increased transmission capability Improved
voltage control, Improved power quality,
Eliminates harmonics Other applications Shunt
capacitors
more about Harmonic Filters and Reactive Power
Factor
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17

• Factors / Phenomena Asynchronous connection
• Technology / System HVDC and HVDC Light
• Example of application Interconnection of power
  systems
• It is sometimes difficult or impossible to
  connect two AC networks due to stability reasons.
  In such cases HVDC is the only way to make an
  exchange of power between the two networks
  possible.
• Several HVDC links interconnect AC system that
  are not running in synchronism with each other.
  For example the Nordel power system in
  Scandinavia is not synchronous with the UCTE grid
  in western continental Europe even though the
  nominal frequencies are the same. And the power
  system of eastern USA is not synchronous with
  that of western USA. There are also HVDC links
  between networks with different nominal
  frequencies (50 and 60 Hz) in Japan and South
  America.
• Direct current transmissions in the form of
  classical HVDC or HVDC Light are the only
  efficient means of controlling power flow in a
  network. HVDC can therefore never become
  overloaded. An AC network connected with
  neighboring grids through HVDC links may as the
  worst case loose the power transmitted over the
  link, if the neighboring grid goes down - the
  HVDC transmission will act as a firewall against
  cascading disturbances.
• Benefits
• The networks can retain their independence
• An HVDC link can never be overloaded
• HVDC transmission will act as a firewall against
  cascading disturbances.

The Scandinavia - Northern Europe HVDC
interconnections

• Links
• HVDC transmission for controllability of power
  flow
• HVDC transmission for asynchronous connection
• Applications in Power Systems Interconnection
• ABB HVDC Portal

more about HVDC Asynchronous Connection
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18

• Factors / Phenomena Bottlenecks
• Technology / System HVDC and HVDC Light
• Example of application Interconnection of power
  systems
• Bottlenecks may be relieved by the use of an HVDC
  or HVDC Light link in parallel with the limiting
  section of the grid. By using the inherent
  controllability of the HVDC system the power
  system operator can decide how much power that is
  transmitted in the AC-link and how much by the
  HVDC system.
• Longer AC lines tend to have stability
  constrained capacity limitations as opposed to
  the higher thermal constraints of shorter lines.
  By using the inherent controllability of an HVDC
  system in parallel with the long AC lines, the
  power system can be stabilized and the
  transmission limitations on the AC line can be
  increased.
• Benefits
• Increased Power Transfer Capability
• Additional flexibility in Grid Operation
• Improved Power and Grid Voltage Control
• An HVDC link can never be overloaded!
• .

• Links
• HVDC transmission for controllability of power
  flow
• Applications in Power Systems Interconnection
• ABB HVDC Portal

more about HVDC Bottlenecks
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19

• Phenomena / Factor Long lines
• Technology / System HVDC
• Example of application Expressway for power
• A HVDC transmission line costs less than an AC
  line for the same transmission capacity. However,
  the terminal stations are more expensive in the
  HVDC case due to the fact that they must perform
  the conversion from AC to DC and vice versa. But
  above a certain distance, the so-called
  "break-even distance", the HVDC alternative will
  always give the lowest cost. Therefore many long
  overhead lines (gt 700 km) particularly from
  remote generating stations are built as DC lines.
  
• Benefits
• Lower investment cost
• Lower losses
• Lower right-of-way requirement for DC lines than
  for AC lines
• HVDC does not contribute to the short circuit
  current
• gt Go to Long Submarine Cables
• .

• Links
• HVDC transmission for lower investment cost
• HVDC transmission has lower losses
• Applications in Power Systems Connection of
  generation
• ABB HVDC Portal

more about HVDC Long Lines
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20

• Phenomena / Factor Long submarine cables
• Technology / System HVDC
• Example of application long distance water
  crossing
• In a long AC cable transmission, the reactive
  power flow due to the large cable capacitance
  will limit the maximum possible transmission
  distance. With HVDC there is no such limitation,
  why, for long cable links, HVDC is the only
  viable technical alternative. There are HVDC and
  HVDC Light cables from 40 km up to 580 km in
  operation or under construction with power
  ratings from 40 to 700 MW.
• Benefits
• Lower investment cost
• Lower losses
• .

• Links
• HVDC submarine cables
• ABB HVDC Portal

more about HVDC Long Submarine Cables
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21

• Factors / Phenomena Loop Flow
• Technology / System HVDC and HVDC Light
• Example of application Interconnected power
  systems
• Loop Flows, or Parallel Path Flows, may be
  alleviated by the use of HVDC or HVDC Light. In
  interconnected power systems, the actual path
  taken by a transaction from one area to another
  may be quite different from the designated routes
  as the result of parallel path admittance, thus
  diverting or wheeling power over parallel
  connections.
• The figure shows how parallel path flow can be
  avoided by replacing an AC line with a HVDC/HVDC
  Light link between area A and area C
• Benefits
• HVDC can be controlled to transmit contracted
  amounts of power and alleviate unwanted loop
  flows.
• An HVDC link can alternatively be controlled to
  minimize total network losses
• An HVDC link can never be overloaded!
• .

Links HVDC transmission for controllability of
power flow      Applications in Power Systems
Interconnection ABB HVDC Portal
more about HVDC Loop Flow
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22

• Factors / Phenomena Power Oscillations
• Technology / System HVDC and HVDC Light
• Example of application Steady State and
  Transient Stability Improvement
• Long AC lines tend to have stability constrained
  capacity limitations as opposed to the higher
  thermal constraints of shorter lines. By using
  the inherent controllability of an HVDC system in
  parallel with the long AC lines, the power system
  can be stabilized and the transmission
  limitations on the AC line can be increased.
• The HVDC damping controller is a standard feature
  in many HVDC projects in operation. It normally
  takes its input from the phase angle difference
  in the two converter stations.
• Benefits
• Increased Power Transfer Capability
• Improved Power and Grid Voltage Control
• An HVDC link can never be overloaded!
• .

Links HVDC transmission for controllability of
power flow Applications in Power Systems
Interconnection HVDC Light System Interaction
Tutorial. ABB HVDC Portal
more about HVDC Power Oscillations
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23

• Factors / Phenomena Flicker
• Technology / System MiniCap
• Example of application Installation of a MiniCap
  to reduce flicker during large motor starting
• Voltage flicker can become a significant problem
  for power distributors when large motor loads are
  introduced in remote locations. Installation of a
  series capacitor in the feeder strengthens the
  network and allows such load to be connected to
  existing lines, avoiding more significant
  investment in new substations or new distribution
  lines.
• The use of the MiniCap on long distribution
  feeders provides self-regulated reactive power
  compensation that efficiently reduces voltage
  variations during large motor starting.
• Benefits
• Reduced voltage fluctuations (flicker)
• Improved voltage profile along the line
• Easier starting of large motors
• Self-regulation

more about MiniCap and Flicker
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24

• Factors / Phenomena Long lines cables
• Technology / System MiniCap
• Example of application Improved voltage profile
  of long distribution lines by adding a MiniCap
• The voltage profile on a radial circuit depends
  on the circuit parameters and the load
  characteristics. The voltage profile can be
  significantly improved by installing a MiniCap
  along the line. A typical voltage profile for a
  radial circuit with and without a series
  capacitor is shown below. Note that the voltage
  profile curve has a jump at the location of the
  series capacitor which represents a large voltage
  rise downstream of the series capacitor.
• The use of the MiniCap on long distribution
  feeders provides improved voltage profile for all
  loads downstream of the installation.
• Benefits
• Increased power transmission capability through
  decreased total line reactance
• Improved voltage profile along the line
• Reduced line losses

more about MiniCap and Long lines cables
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25

• Factors / Phenomena Reactive Power Factor
• Technology / System MiniCap
• Example of application Improved power factor at
  the utility source with a MiniCap
• The reactive power produced by the series
  capacitor is proportional to the capacitor
  impedance and the line current. With the series
  capacitor supplying a significant portion of the
  reactive power requirements of the distribution
  line and of inductive motor loads, much less
  reactive power is drawn from the utility source,
  resulting in a greatly improved power factor at
  the sending end of the line.
• The use of the MiniCap on a distribution feeder
  provides self-regulated reactive power for
  improved power factor at the utility source.
• Benefits
• Increased power factor at the utility source
• Easier starting of large motors
• Improved voltage regulation and reactive power
  balance
• Self-regulation

more about MiniCap and Reactive Power Factor
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26

• Factors / Phenomena Bottlenecks
• Technology / System PSGuard Wide Area Monitoring
  System
• Example of application Phase angle monitoring
• The phase angle monitoring application
  facilitates the monitoring of network stresses
  caused by heavily loaded lines. It provides
  operators with real-time information about
  voltage phase angle deviations a crucial issue
  e.g. for the successful reclosing of transmission
  lines.
• Its main function is to supply sufficient
  information to the power system operator to
  evaluate the present angle difference between two
  locations. Upon detection of an extraordinary
  status, PSGuard alerts the operator by giving an
  early warning or, in critical cases, an emergency
  alarm.
• The present version provides monitoring
  functionality, and its outputs are intended as
  mature decision support for operators in taking
  stabilizing measures. Actions that the operator
  may take to improve grid stability range from
  generation rescheduling or actions on the
  reactive power compensation, blocking of tap
  changers in the load area and load shedding in
  extreme cases.
• Benefits
• Improved system stability, security and
  reliability
• Safe operation of power carrying components
  closer to their limits
• Optimized utilization of transmission capacities
• Enhanced operational and planning safety
• Other applications
• Line Thermal Monitoring (LTM)
• Voltage Stability Monitoring (VSM)
• Power Oscillation Monitoring (POM)

PSGuard display Phase angle monitoring with
early warning and emergency alarm
more about PSGuard Wide Area Monitoring System
and Bottlenecks
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27

• Factors / Phenomena Long lines and cables
• Technology / System PSGuard Wide Area Monitoring
  System
• Example of application Line thermal monitoring
• Loading of power lines or HV cables is in many
  cases constrained by thermal limits rather than
  by voltage instability concerns. A thermal limit
  of a line is usually set according to
  conservative and stabile criteria, i.e. high
  ambient temperature and calm air. This yields
  assumptions of very limited cooling possibilities
  and thus low loadability. However, the ambient
  conditions are often much better in terms of
  possible cooling and would allow higher loading
  of a line with a minimal risk. This can be
  achieved if an on-line tool for line temperature
  assessment is available. One of the algorithms of
  PSGuard serves this purpose. However, its
  functionality and applicability on the real power
  systems should be tested in the practice.
• The algorithm works as follows
• The voltage and current phasors measured at both
  ends of a line are collected (the phasors have to
  be measured at the same instant, which is
  possible through the GPS-synchronization of the
  phasor measurement units, PMUs)
• Actual impedance and shunt admittance of a line
  are computed.
• Resistance of the line/cable is extracted
• Based on the known properties of the conductor
  material (reference temperature and dependency
  coefficient are usually supplied by the
  manufacturer), the actual average temperature of
  the line is determined.
• The obtained temperature is an average, not the
  spot one. The relation between them shall be
  verified, i.e. through consideration of the
  impact of the various weather conditions along
  the line at a given time.
• Benefits
• Improved power flow control
• Safe operation of power carrying components
  closer to their limits
• Other applications
• Power Oscillation Monitoring (POM)

PSGuard display Line thermal monitoring with
early warning and emergency alarm
PSGuard display Line temperature pattern
computed by PSGuard
more about PSGuard Wide Area Monitoring System
and Long Lines Cables
Back to Overview
28

• Factors / Phenomena Oscillations
• Technology / System PSGuard Wide Area Monitoring
  System
• Example of application Power oscillation
  monitoring
• Power oscillation monitoring is the algorithm
  used for the detection of power swings in a high
  voltage power system. The algorithm processes the
  selected voltage and current phasor inputs and
  detects the various power swing (power
  oscillation) modes. It quickly identifies the
  frequency and the damping of swing modes. The
  algorithm deploys adaptive Kalman filtering
  techniques.
• Displayed results
• Damping of the dominant oscillatory mode (time
  window, i.e. trend display)
• Frequency of the dominant oscillatory mode (time
  window, i.e. trend display)
• Amplitude of the oscillation (time window, i.e.
  trend display)
• Optional
• Damping of other oscillatory modes (all in one
  time window, distinguished by different colors)
• Frequencies of other oscillatory modes (all in
  one time window, distinguished by different
  colours
• Alarms
• When the damping of any oscillation mode
  decreases to below a predefined value (in two
  steps, first is alert, the second emergency
  alarm)
• Read more

Measurements by PSGuard WAMS The loss of a power
plant in Spain (1000 MW) initiated Wide Area
Oscillations Measurement by PSGuard
Back to Overview
29

• Factors / Phenomena Oscillations
• Technology / System PSGuard Wide Area Monitoring
  System
• Example of application Power oscillation
  monitoring
• Benefits
• Increased power transfer
• Enhanced security
• Short-term operation benefits
• Immediate awareness of the power system state in
  terms of the presence of oscillations, thus an
  operator sees the urgency of the situation
• Indication of the frequency of an oscillation
  which may then be associated with the known
  existing mode of the power system, i.e. the
  operator may distinguish if a local or inter-area
  mode is excited
• Long-term benefits
• With the help of the stored data, long-term
  statistics can be collected and, based on their
  evaluation, the system reinforcements can be
  performed (such as retuning of Power System
  Stabilizers (PSS) to damp the frequencies
  appearing most often as dangerous ones).

Example Estimation of relative frequency and
damping
more about PSGuard Wide Area Monitoring System
and Power Oscillations
Back to Overview
30

• Factors / Phenomena Voltage instability
• Technology / System PSGuard Wide Area Monitoring
  System
• Example of application Voltage stability
  monitoring
• The voltage stability monitoring application
  facilitates the monitoring of the grids dynamic
  behavior and provides stability calculations for
  steady state situations as well as stability
  predictions in contingency cases. It builds on
  and extends the basic functionality of PSG830
  with functions related to the monitoring of
  voltage stability for a transmission line /
  corridor.
• Its main function is to provide the operator of
  the power system with sufficient information to
  evaluate the present power margin with respect to
  voltage stability, that is, the amount of
  additional active power that can be transported
  on a transmission corridor without jeopardizing
  the voltage stability. The present version
  provides monitoring functionality, and its
  outputs are intended as mature decision support
  for operators in taking optimizing resp.
  stabilizing measures. Actions that the operator
  may take to improve voltage stability range from
  generation rescheduling or actions on the
  reactive compensation, blocking of tap changers
  in the load area and to load shedding in extreme
  cases.
• Applied directly, the application is assigned to
  a single line or cable. However, on a
  case-by-case basis, the method can be applied
  also to transmission corridors with more complex
  topologies.
• Benefits
• Improved system stability, security and
  reliability
• Reduced cost and greater functionality of
  Protection Control systems
• Safe operation of power carrying components
  closer to their limits
• Optimized utilization of transmission capacities

PSGuard display Voltage stability monitoring P-V
Curve
more about PSGuard Wide Area Monitoring System
and Voltage Instability
Back to Overview
31

• Factors / Phenomena Bottlenecks
• Technology / System Series Compensation
• Example of application Transient Stability
  Improvement
• Bottlenecks may be relieved by the use of Series
  Compensation. Longer lines tend to have
  stability-constrained capacity limitations as
  opposed to the higher thermal constraints of
  shorter lines. Series Compensation has the net
  effect of reducing transmission line series
  reactance, thus effectively reducing the line
  length. Series Compensation also offers
  additional power transfer capability for some
  thermal-constrained bottlenecks by balancing the
  loads among the parallel lines. Figure shows a
  two-area interconnected system where the power
  transfer from area A to area B is limited to
  1500MW due to stability constraints. Additional
  electricity can be delivered from area A to area
  B if Series Compensation is applied to increase
  the maximum stability limits.
• Benefits
• Increased Power Transfer Capability
• Additional flexibility in Grid Operation
• Improved Grid Voltage Control
• Other applications
• Power Flow Control

more about Series Compensation and Bottlenecks
Back to Overview
32

• Factors / Phenomena Loop Flows
• Technology / System Series Compensation
• Example of application Power Flow Control
• Loop Flows, or Parallel Path Flows, may be
  alleviated by the use of Series Compensation. In
  interconnected power systems, the actual path
  taken by a transaction from one area to another
  may be quite different from the designated routes
  as the result of parallel path admittance, thus
  diverting or wheeling power over parallel
  connections.
• Figure shows parallel path flow alleviation by
  the use of Series Compensation. With a reduction
  in the direct interconnection impedance between
  area A and area C, the Parallel Path Flow which
  is routed through area B is decreased.
• Benefits
• Increased Power Transfer Capability
• Additional flexibility in Grid Operation
• Lower Transmission Losses
• Improved Transient Stability
• Improved Grid Voltage Control
• Other applications
• Transient Stability Improvement

more about Series Compensation and Loop Flows
Back to Overview
33

• Factors / Phenomena Reactive Power Factor
• Technology / System Shunt Capacitor
• Example of application
• Regulation of the power factor to increase the
  transmission capability and reduce transmission
  losses
• Shunt capacitors are primarily used to improve
  the power factor in transmission and distribution
  networks, resulting in improved voltage
  regulation, reduced network losses, and efficient
  capacity utilization. Figure shows a plot of
  terminal voltage versus line loading for a system
  that has a shunt capacitor installed at the load
  bus. Improved transmission voltage regulation can
  be obtained during heave power transfer
  conditions when the system consumes a large
  amount of reactive power that must be replaced by
  compensation. At the line surge impedance loading
  level, the shunt capacitor would decrease the
  line losses by more than 35. In distribution
  and industrial systems, it is common to use shunt
  capacitors to compensate for the highly inductive
  loads, thus achieving reduced delivery system
  losses and network voltage drop.
• Benefits
• Improved power factor
• Reduced transmission losses
• Increased transmission capability
• Improved voltage control
• Improved power quality
• Other applications
• Harmonic Filters

more about Shunt Capacitor and Reactive Power
Factor
Back to Overview
34

• Factors / Phenomena Voltage instability
• Technology / System Shunt Reactor
• Example of application Extra/Ultra High Voltage
  air insulated transmission line and cable line
  voltage stability
• The primary purpose of the shunt reactor is to
  compensate for capacitive charging voltage, a
  phenomenon getting more prominent for increasing
  line voltage. Long high-voltage transmission
  lines and relatively short cable lines (since a
  power cable has high capacitance to earth)
  generate a large amount of reactive power during
  light power transfer conditions which must be
  absorbed by compensation. Otherwise, the
  receiving terminals of the transmission lines
  will exhibit a voltage rise characteristic and
  many types of power equipment cannot withstand
  such overvoltages. Figure shows at top level
  voltage at the receiving end when transmission
  line is loaded with rated power. Then shunt
  reactor is not needed. Next figure shows a
  voltage increase when line is lightly loaded and
  bottom figure shows what happens when a shunt
  reactor is connected. The voltage stability is
  kept due to the inductive compensation from the
  reactor.
• A better fine tuning of the reactive power can be
  made by the use of a tap changer in the shunt
  reactor. It can be possible to vary the reactive
  power between 50 to 100 of the needed power.
• Benefits
• Simple and robust customer solution with low
  installation costs and minimum maintenance
• No losses from an intermediate transformer when
  feeding reactive compensation from a lower
  voltage level.
• No harmonics created which may require filter
  banks.

more about Shunt Capacitor and Voltage
Instability
Back to Overview
35

• Factors / Phenomena Bottlenecks
• Technology / System Static Var Compensator (SVC)
• Example of application Grid Voltage Support
• Static Var Compensators are used in transmission
  and distribution networks mainly providing
  dynamic voltage support in response to system
  disturbances and balancing the reactive power
  demand of large and fluctuating industrial loads.
  A Static Var Compensator is capable of both
  generating and absorbing variable reactive power
  continuously as opposed to discrete values of
  fixed and switched shunt capacitors or reactors.
  Further improved system steady state performance
  can be obtained from SVC applications. With
  continuously variable reactive power supply, the
  voltage at the SVC bus may be maintained smoothly
  over a wide range of active power transfers or
  system loading conditions. This entails the
  reduction of network losses and provision of
  adequate power quality to the electric energy
  end-users.
• Benefits
• Increased Power Transfer Capability
• Additional flexibility in Grid Operation
• Improved Grid Voltage Stability
• Improved Grid Voltage Control
• Improved Power Factor
• Other applications
• Power Oscillation Damping
• Power Quality (Flicker Mitigation, Voltage
  Balancing)

more about Static Var Compensator and
Bottlenecks
Back to Overview
36

• Factors / Phenomena Power Oscillations
• Technology / System Static Var Compensator (SVC)
• Example of application Power Oscillation Damping
• Static Var Compensators are mainly used to
  perform voltage and reactive power regulation.
  However, when properly placed and controlled,
  SVCs can also effectively counteract system
  oscillations. A SVC, in effect, has the ability
  to increase the damping factor (typically by 1-2
  MW per Mvar installed) on a bulk power system
  which is experiencing power oscillations. It does
  so by effectively modulating its reactive power
  output such that the regulated SVC bus voltage
  would increase the system damping capability.
  Figure shows power oscillation prompted by a
  disturbance on a transmission system. The
  uncompensated system undergoes substantial
  oscillations following the disturbance while the
  same system with SVC experiences much improved
  response.
• Benefits
• Increased Power Transfer Capability
• Additional flexibility in Grid Operation
• Improved Dynamic Stability
• Other applications
• Power Quality (Flicker Mitigation, Voltage
  Balancing)
• Grid Voltage Support

more about Static Var Compensator and Power
Oscillations
Back to Overview
37

• Factors / Phenomena Voltage instability
• Technology / System Static Var Compensator (SVC)
• Example of application Grid Voltage Support
• Static Var Compensators are used in transmission
  and distribution networks mainly providing
  dynamic voltage support in response to system
  disturbances and balancing the reactive power
  demand of large and fluctuating industrial loads.
  A Static Var Compensator is capable of both
  generating and absorbing variable reactive power
  continuously as opposed to discrete values of
  fixed and switched shunt capacitors or reactors.
  Further improved system steady state performance
  can be obtained from SVC applications. With
  continuously variable reactive power supply, the
  voltage at the SVC bus may be maintained smoothly
  over a wide range of active power transfers or
  system loading conditions. This entails the
  reduction of network losses and provision of
  adequate power quality to the electric energy
  end-users.
• Benefits
• Increased Power Transfer Capability
• Additional flexibility in Grid Operation
• Improved Grid Voltage Stability
• Improved Grid Voltage Control
• Improved Power Factor
• Other applications
• Power Oscillation Damping
• Power Quality (Flicker Mitigation, Voltage
  Balancing)

more about Static Var Compensator and Voltage
Instability
Back to Overview
38

• Factors / Phenomena Flicker
• Technology / System SVC (Industry)
• Example of application Power Quality
  Improvement, Flicker Mitigation
• SVC is used most frequently for compensation of
  disturbances generated by the Electrical Arc
  Furnaces (EAF). With a well-designed SVC,
  disturbances such as flicker from the EAF are
  mitigated. Figure shows the flicker mitigation
  effect of a SVC installed at a steel making
  plant.
• Flicker, the random variation in light intensity
  from incandescent lamps caused by the operating
  of nearby fluctuating loads on the common
  electric supply grid, is highly irritating for
  those affected. The random voltage variations can
  also be disturbing to other process equipment fed
  from the same grid. The proper mitigation of
  flicker is therefore a matter of power quality
  improvement as well as an improvement to human
  environment.
• Benefits
• Reduced Flicker
• Harmonic Filtering
• Voltage Balancing
• Power Factor Correction
• Furnace/mill Process Productivity Improvement
• Other applications
• General Reactive Power Compensation at Steelworks
  
• Grid Voltage Support

more about SVC (Industry) and Flicker
Back to Overview
39

• Factors / Phenomena Reactive Power Factor
• Technology / System SVC (Industry)
• Example of application Reactive Power
  Compensation at Steelworks
• Static Var Compensators provide dynamic voltage
  support to balance the reactive power demand of
  large and fluctuating industrial loads. A Static
  Var Compensator is capable of both generating and
  absorbing variable reactive power continuously as
  opposed to discrete values of fixed and switched
  shunt capacitors or reactors. With continuously
  variable reactive power supply, the voltage at
  the SVC bus may be maintained smoothly over a
  wide range of operating conditions. This entails
  the improved power factor and sufficient power
  quality, leading to better process and production
  economy.
• Benefits
• Power Factor Correction
• Furnace/mill Process Productivity Improvement
• Harmonic Filtering
• Other applications
• Power Quality Improvement, Flicker mitigation
• Power Quality Improvement, Voltage Balancing

more about SVC (Industry) and Reactive Power
Factor
Back to Overview
40

• Factors / Phenomena Unbalanced Load
• Technology / System SVC (Industry)
• Example of application Railway Feeder connected
  to the Public Grid
• The traction system is a major source of
  unbalanced loads. Electrification of railways, as
  an economically attractive and environmentally
  friendly investment in infrastructure, has
  introduced an unbalanced and heavy distorted load
  on the three-phase transmission grid. Without
  compensation, this would result in significant
  unbalanced voltage affecting most neighboring
  utility customers. The SVC can elegantly be used
  to counteract the unbalances and mitigate the
  harmonics such that the power quality within the
  transmission grid is not impaired. Figure shows
  a typical traction substation arrangement with a
  load balancer (an asymmetrically controlled SVC).
  The load balancer transfers active power between
  the phases such that the balanced voltage can be
  created (seen from the grid).
• Benefits
• Voltage Balancing
• Harmonic Filtering
• Power Factor Correction
• Other applications
• Power Quality Improvement, Flicker Mitigation
• Grid Voltage Support

more about SVC (Industry) and Unbalanced Load
Back to Overview
41

• Factors / Phenomena Bottlenecks
• Technology / System STATCOM
• Example of application Grid Voltage Support
• STATCOM, when connected to the grid, can provide
  dynamic voltage support in response to system
  disturbances and balance the reactive power
  demand of large and fluctuating industrial loads.
  A STATCOM is capable of both generating and
  absorbing variable reactive power continuously as
  opposed to discrete values of fixed and switched
  shunt capacitors or reactors. With continuously
  variable reactive power supply, the voltage at
  the STATCOM bus may be maintained smoothly over a
  wide range of system operation conditions. This
  entails the reduction of network losses and
  provision of sufficient power quality to the
  electric energy end-users.
• Benefits
• Increased Power Transfer Capability
• Additional flexibility in Grid Operation
• Improved Grid Voltage Stability
• Improved Grid Voltage Control
• Improved Power Factor
• Other applications
• Power Quality (Flicker Mitigation, Voltage
  Balancing)

more about STATCOM and Bottlenecks
Back to Overview
42

• Factors / Phenomena Flicker
• Technology / System STATCOM
• Example of application Power Quality
  Improvement, flicker mitigation
• STATCOM is an effective method used to attack
  the problem of flicker. The unbalanced, erratic
  nature of an electric arc furnace (EAF) causes
  significant fluctuating reactive power demand,
  which ultimately results in irritating electric
  lamp flicker to neighboring utility customers. In
  order to stabilize voltage and reduce disturbing
  flicker successfully, it is necessary to
  continuously measure and compensate rapid changes
  by means of extremely fast reactive power
  compensation. STATCOM uses voltage source
  converters to improve furnace productivity
  similar to a traditional SVC while offering
  superior voltage flicker mitigation due to fast
  response time. Figure shows the flicker
  mitigation effect of an STATCOM installed at a
  steel making plant.
• Benefits
• Eliminated Flicker
• Harmonic Filtering
• Voltage Balancing
• Power Factor Correction
• Furnace/mill Process Productivity Improvement
• Other applications
• Grid Voltage Support
• Power Quality Improvement

more about STATCOM and Flicker
Back to Overview
43

• Factors / Phenomena Unbalanced Load
• Technology / System STATCOM
• Example of application Railway Feeder connected
  to the Public Grid
• Modern electric rail system is a major source of
  unbalanced loads. Electrification of railways, as
  an economically attractive and environmentally
  friendly investment in infrastructure, has
  introduced an unbalanced and heavy distorted load
  on the three-phase transmission grid. Without
  compensation, this would result in significant
  unbalanced voltage affecting most neighboring
  utility customers. Similar to SVC, the STATCOM
  can elegantly be used to restore voltage and
  current balance in the grid, and to mitigate
  voltage fluctuations generated by the traction
  loads. Figure shows a conceptual diagram of
  STATCOM application for dynamic load balancing
  for traction.
• Benefits
• Voltage Balancing
• Harmonic Filtering
• Power Factor Correction
• Other applications
• Power Quality Improvement, Flicker Mitigation
• Grid Voltage Support

more about STATCOM and Unbalanced Load
Back to Overview
44

• Factors / Phenomena Voltage instability
• Technology / System STATCOM
• Example of application Grid Voltage Support
• STATCOM, when connected to the grid, can provide
  dynamic voltage support in response to system
  disturbances and balance the reactive power
  demand of large and fluctuating industrial loads.
  A STATCOM is capable of both generating and
  absorbing variable reactive power continuously as
  opposed to discrete values of fixed and switched
  shunt capacitors or reactors. With continuously
  variable reactive power supply, the voltage at
  the STATCOM bus may be maintained smoothly over a
  wide range of system operation conditions. This
  entails the reduction of network losses and
  provision of sufficient power quality to the
  electric energy end-users.
• Benefits
• Increased Power Transfer Capability
• Additional flexibility in Grid Operation
• Improved Grid Voltage Stability
• Improved Grid Voltage Control
• Improved Power Factor
• Other applications
• Power Quality (Flicker Mitigation, Voltage
  Balancing)

more about STATCOM and Voltage Instability
Back to Overview
45

• Factors / Phenomena Bottlenecks
• Technology / System TCSC
• Example of application Transient Stability
  Improvement
• Bottlenecks may be effectively relieved by the
  use of entirely or partially thyristor controlled
  series compensation. As with conventional SC
  technology, TCSC can improve stability of power
  transmission, reactive power balance, and load
  sharing between parallel lines, thus mitigating
  the impact of transmission bottlenecks. Figure
  shows a two-area interconnected system where the
  power transfer from area A to area B is limited
  to 1500MW due to stability constraints.
  Additional electricity can be delivered from area
  A to area B if series compensation is applied to
  increase the maximum stability limits. High
  degree of series compensation level is permitted
  with the controlled series compensation achieving
  further improved transmission capacity
  utilization.
• Benefits
• Increased Power Transfer Capability
• Additional flexibility in Grid Operation
• Improve Dynamic Stability
• Improved Grid Voltage Control
• Immunity against Subsynchronous Resonance
• Other applications
• Power Oscillation Damping
• Subsynchronous Resonance Mitigation

more about TCSC and Bottlenecks
Back to Overview
46

• Factors / Phenomena Loop Flows
• Technology / System TCSC
• Example of application Power Flow Control
• Loop Flows, or Parallel Path Flows, may be
  effectively a