Seminar OnPower System Contingencies

Power System Power System voltage control has a hierarchy structure with three Power System voltage control has a hierarchy structure with three

levels: the primary, secondary, and the tertiary voltage control. levels: the primary, secondary, and the tertiary voltage control. Over the past 20 yrs, one of the most successful measures Over the past 20 yrs, one of the most successful measures proposed to improve Power System voltage regulation has been proposed to improve Power System voltage regulation has been the application of secondary voltage control, initiated by the the application of secondary voltage control, initiated by the French Electricity Company.French Electricity Company.

Important Of Features Power System

FlickersFlickers HarmonicsHarmonics InterruptionInterruption Long LinesLong Lines Long Cables Long Cables Loop Flow Loop Flow Reactive Power Reactive Power Sags & SwellsSags & Swells Unbalanced LoadUnbalanced Load Voltage InstabilityVoltage Instability

Flickers

A fluctuation in system voltage that can A fluctuation in system voltage that can lead to noticeable changes in light output.lead to noticeable changes in light output.

Voltage Flicker can either be a periodic or Voltage Flicker can either be a periodic or non-periodic fluctuation in voltage non-periodic fluctuation in voltage magnitude i.e. the fluctuation may occur magnitude i.e. the fluctuation may occur continuously at regular intervals or only continuously at regular intervals or only on occasions. on occasions.

How To Reduce FlickersHow To Reduce Flickers

Installation of a MiniCap to reduce flicker during large motor Installation of a MiniCap to reduce flicker during large motor starting . starting .

Minicap is nothing but the Installation of a series capacitor in Minicap is nothing but the Installation of a series capacitor in the feeder strengthens the network .the feeder strengthens the network .

BenefitsBenefits

•Reduced voltage fluctuations (flicker)

•Improved voltage profile along the line

•Easier starting of large motors

•Self-regulation

Harmonics Harmonics are associated with steady-state Harmonics are associated with steady-state

waveform distortion of currents and voltages.waveform distortion of currents and voltages.

Harmonics are components that make up a Harmonics are components that make up a waveform where each component has a frequency waveform where each component has a frequency that is an integral multiple of the fundamental that is an integral multiple of the fundamental frequency. The term Harmonic is normally applied frequency. The term Harmonic is normally applied to waveform components that have frequencies to waveform components that have frequencies other than the fundamental frequency. For a 50 Hz other than the fundamental frequency. For a 50 Hz or 60Hz system the fundamental frequency is 50HZ or 60Hz system the fundamental frequency is 50HZ or 60Hz. A waveform that contains any or 60Hz. A waveform that contains any components other than the fundamental frequency components other than the fundamental frequency is non-sinusoidal and considered to be distorted.is non-sinusoidal and considered to be distorted.

How To Reduce HarmonicsHow To Reduce Harmonics

Installing filters near the harmonic Installing filters near the harmonic sources can effectively reduce sources can effectively reduce harmonics.harmonics.

BenefitsBenefits

Eliminates harmonics.Eliminates harmonics. Improved Power Factor.Improved Power Factor. Reduced Transmission Losses.Reduced Transmission Losses. Increased Transmission Capability.Increased Transmission Capability. Improved Voltage Control.Improved Voltage Control. Improved Power Quality.Improved Power Quality.

Interruptions• Occur when the supply voltage drops below 10% of the nominal Occur when the supply voltage drops below 10% of the nominal

value.value. An interruption is usually caused by downstream faults that are An interruption is usually caused by downstream faults that are

cleared by breakers or fuses. A sustained interruption is caused cleared by breakers or fuses. A sustained interruption is caused by upstream breaker or fuse operation. Upstream breakers may by upstream breaker or fuse operation. Upstream breakers may operate due to short-circuits, overloads, and loss of stability on operate due to short-circuits, overloads, and loss of stability on the bulk power system.the bulk power system.

Long Lines Long lines need special consideration in the Long lines need special consideration in the

planning of a power system.planning of a power system.

For long AC lines one must consider i.e. the For long AC lines one must consider i.e. the reactive power compensation, the transient reactive power compensation, the transient stability and switching over voltages and how stability and switching over voltages and how many intermediate substations one needs.many intermediate substations one needs.

Area of application:-Expressway Area of application:-Expressway for powerfor power

A HVDC transmission line costs less than A HVDC transmission line costs less than an AC line for the same transmission an AC line for the same transmission capacity.capacity.

BenefitsBenefits

Lower investment costLower investment cost

Lower losses Lower losses

Lower right-of-way requirement for DC lines than for AC linesLower right-of-way requirement for DC lines than for AC lines

HVDC does not contribute to the short circuit current HVDC does not contribute to the short circuit current

Long cables Basically Long cables are of two typesBasically Long cables are of two types

Submarine CablesSubmarine Cables

Under Ground CablesUnder Ground Cables

Submarine CablesApplicationApplication

Submarine Cables are used for long distance water crossing.Submarine Cables are used for long distance water crossing.

BenefitsBenefits

Lower investment costLower investment cost Lower losses Lower losses

Loop flow• Unscheduled power flow on a given transmission path in an Unscheduled power flow on a given transmission path in an

interconnected electrical system.interconnected electrical system.

• Unscheduled power flows on transmission lines or facilities may Unscheduled power flows on transmission lines or facilities may result in a violation of reliability criteria and decrease available result in a violation of reliability criteria and decrease available transfer capability between neighbouring control areas or utility transfer capability between neighbouring control areas or utility systems.systems.

Area of application:

Interconnected power systems

BenefitsBenefits

HVDC can be controlled to transmit contracted HVDC can be controlled to transmit contracted amounts of power and alleviate unwanted loop flows.amounts of power and alleviate unwanted loop flows.

An HVDC link can alternatively be controlled to An HVDC link can alternatively be controlled to minimize total network losses minimize total network losses

An HVDC link can never be overloadedAn HVDC link can never be overloaded

Reactive Power Factor

• Reactive power is defined as the product of the r.m.s. voltage, Reactive power is defined as the product of the r.m.s. voltage, current, and the sine of the difference in phase angle between the current, and the sine of the difference in phase angle between the two.two.

• To maintain efficient transmission and distribution, it is necessary To maintain efficient transmission and distribution, it is necessary to improve the reactive power factor.to improve the reactive power factor.

How to Improve power factorHow to Improve power factor

• The use of the MiniCap on a distribution The use of the MiniCap on a distribution feeder provides self-regulated reactive power feeder provides self-regulated reactive power for improved power factor at the utility for improved power factor at the utility sourcesource..

BenefitsBenefits

Increased power factor at the utility sourceIncreased power factor at the utility source..

Easier starting of large motorsEasier starting of large motors . .

Improved voltage regulation and reactive power balance.Improved voltage regulation and reactive power balance.

Self-regulationSelf-regulation Improved power factorImproved power factor, , Reduced Reduced transmission lossestransmission losses, , Increased transmission capability.Increased transmission capability.

Improved voltage controlImproved voltage control, , Improved power quality, Improved power quality, Eliminates harmonicsEliminates harmonics S. S.

Sags & Swells Short duration decrease/increase (sag/swell) in Short duration decrease/increase (sag/swell) in

supply voltage.supply voltage.

Voltage sags are one of the most commonly Voltage sags are one of the most commonly occurring power quality problems. They are occurring power quality problems. They are usually generated inside a facility but may also usually generated inside a facility but may also be a result of a momentary voltage drop in the be a result of a momentary voltage drop in the distribution supply.distribution supply.

Electronic equipment is usually the main victim Electronic equipment is usually the main victim of sags, as they do not contain sufficient internal of sags, as they do not contain sufficient internal energy to ‘ride through’ the disturbance.energy to ‘ride through’ the disturbance.

Voltage Instability

• Post-disturbance excursions of voltages at some buses in the Post-disturbance excursions of voltages at some buses in the power system out of the steady operation region.power system out of the steady operation region.

• Voltage instability is basically caused by an unavailability of Voltage instability is basically caused by an unavailability of reactive power support in an area of the network, where the reactive power support in an area of the network, where the voltage drops uncontrollablyvoltage drops uncontrollably..

Unbalanced Load

• A load which does not draw balanced current from a balanced A load which does not draw balanced current from a balanced three-phases supply.three-phases supply.

A single-phase load, since it does not draw a balanced three-A single-phase load, since it does not draw a balanced three-phase current, will create unequal voltage drops across the phase current, will create unequal voltage drops across the series impedances of the delivery system.series impedances of the delivery system.

Area of application:-Railway Area of application:-Railway Feeder connected to the Public Feeder connected to the Public

GridGrid Modern electric rail system is a major source Modern electric rail system is a major source

of unbalanced loads.of unbalanced loads. STATCOM can elegantly be used to restore STATCOM can elegantly be used to restore

voltage and current balance in the grid, and voltage and current balance in the grid, and to mitigate voltage fluctuations generated by to mitigate voltage fluctuations generated by the traction loads.the traction loads.

Benefits Voltage BalancingVoltage Balancing Harmonic Filtering Harmonic Filtering Power Factor CorrectionPower Factor Correction

Other applications:Other applications: Power Quality Improvement, Flicker MitigationPower Quality Improvement, Flicker Mitigation Grid Voltage SupportGrid Voltage Support

Summary The new electricity supply industry presents increasing The new electricity supply industry presents increasing

challenges for stable and secure operation of power systems.challenges for stable and secure operation of power systems.

State-of-the-art methods and tools have advanced our State-of-the-art methods and tools have advanced our capabilities significantly facing the challenges-capabilities significantly facing the challenges-

comprehensive stability analysis tools

coordinated design of robust stability controls

on-line dynamic security assessment

Industry yet to take full advantage of these developments!Industry yet to take full advantage of these developments!

Need to review and improveNeed to review and improve

The reliability criteria.

Thank You …..!