January 2019IEEE

The Increasing Application of FACTS

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Power System Constraints Steady State Power Transfer Limits

Voltage Stability Limit

Dynamic Voltage Limit

Transient Stability Limit

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Power System Constraints Power Oscillation Damping Limit

Inadvertent Loop Flow

Thermal Limit

Short Circuit Limit

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Conventional Solution Switched Shunt

Transformer LTC

Phase Shifting Transformer

Others- Include re-conductoring, new line etc.

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FACTS What are FACTS?

– Flexible AC Transmission Systems

– Enhances the transmission network by increasing the use of their capacity

– Fast Operating Controllers which enhances the safe operating limits of the transmission system without risking stability

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Power Flow

Changing the above parameters will result in increase in power flow through the existing system

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FACT Devices Different types of FACT Devices:

– Fixed Series Capacitor

– Thyristor Controlled Series Capacitor (TCSC)

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FACT Devices– Static Var Compensator (SVC)

– Static Synchronous Compensator (STATCOM)

– Static Synchronous Series Compensator (SSSC)

– Unified Power Flow Controller (UPFC)

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Advantages of FACTS Increase/Control of power transmission capacity in line

Improvement of transient stability limits

Enhancement of System Damping

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Advantages of FACTS Limiting Short Circuit Currents

Alleviation of Voltage Stability

Power Factor Improvement

Renewable Power Integration into the Grid

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Series Capacitors Connected in series with line

Used to reduce the effective impedance of the line

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Series Capacitors

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Series Capacitors

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Series Capacitors

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Series Capacitors

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Application of FSC Enhanced base power flow and loadability of the series-

compensated line

Reduces the effective impedance of the transmission line and improves load sharing

Economical Solution and widely used

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Application of FSC Smaller kvar and kV ratings required for providing same

compensation as shunt devices

Reactive power regulation

Angular stability

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Limitation Sub-synchronous Interaction

Fixed impedance- No controllability of the impedance/ power flow

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TCSC A fixed series compensation module as described in the

previous section

A module consisting of the series capacitor in parallel with a thyristor controlled air core reactor

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TCSC When Thyristor is blocked, it is an FSC

When Thyristor is in full conduction, Cap bank is effectively bypassed

Between blocked and full conduction, it is possible to smoothly vary the TCSC impedance.

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TCSC

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Application of TCSC Rapid Continuous control of the transmission line series

compensation level

Dynamic Control of power flow in selected transmission lines which enables optimal power- flow conditions and prevent the loop flow of power

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Application of TCSC Damping of power swings from local and inter- area oscillations

Suppression of sub synchronous oscillation.

Decreasing dc-offset voltage resulting from insertion of series capacitor

Quick insertion and bypass of series capacitors

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Application of TCSC Voltage Support and alleviation of voltage instability

Reduction of short-circuit current

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SVC Introduction SVC is Static Var Compensator

SVCs are meant to provide dynamic Voltage support (fast response)

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SVC Introduction SVC can have following configurations:

– MSC-TCR

– TCR- FC

– TCR-FC-MSC

– TCR-FC-TSC

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TCR

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Harmonics Generated by TCR

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Harmonics Generated by TCR

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SVC Applications Power Factor Improvement

Voltage Control or low voltage issue

Reactive Power Compensation

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SVC Applications Flicker Improvement

Harmonic Improvement

Power Oscillation Damping

Increase Power Transfer Capability

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SVC Applications

Improve steady-state and dynamic stability of the grid with fast response time

No short circuit contribution

Negative sequence control (system unbalance)

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SVC Applications Reactive Margin Improvement

– PV and QV Margin Improvement

Induction Motor load area where voltage recovery will be an issue

Arc Furnace/Welding- Industrial Load

Widely used and several installations across globe

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Limitations Harmonic Source

Response time in several 10s of milliseconds

Performance in the under-voltage conditions

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Limitations Layout or footprint

Limited Flicker improvement compared to STATCOM

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STATCOM STATCOM – Static Synchronous Compensator

– Shunt Connected reactive power compensation device

– Voltage Source Converter, from a given DC voltage, produces a set of 3-phase ac-output voltages, each in phase and coupled to corresponding AC system through an interface inductance or interface transformer.

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STATCOM– DC Voltage is provided by an energy-storage capacitor

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STATCOM

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STATCOM

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SVC vs STATCOM

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Advantage of STATCOM over SVC STATCOM can be used for the same applications as SVC

STATCOM has the following advantage over SVC

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Advantage of STATCOM over SVC Smaller Foot print

Generate no or minimal harmonics

Better Flicker mitigation than SVC

Faster response time

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Advantage of STATCOM over SVC Can limit transient/switching overvoltage

Compensation for DC transmission LCC especially when short circuit capacity is too low

Relocatable

Superior performance during undervoltage condition

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Advantage of STATCOM over SVC Can be interfaced with battery and used as dynamic energy

storage device– Black Start

– Wind Farm Storage

– Delay in building new distribution lines

– Rapid power schedule changes

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Summary TableIssue Device

Steady State Voltage Control

SVC

STATCOM

Dynamic and post- contingency voltage control

SVC

STATCOM

Improvement of steady state load sharing FSC

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Issue Device

Transient Stability Improvement

FSCSVC

STATCOM

Power Oscillation DampingSVCTCSC

Power Quality ImprovementSVC

STATCOMSub-synchronous reasonance

mitigationTCSCLoop flow mitigation

Summary Table

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Other FACT Devices SSSC- Static Synchronous Series Compensator

– VSC connected in series

– Controls Power flow

– Provides series compensation

– Avoids SSR

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Other FACT Devices Unified Power Flow Controller (UPFC)

– VSCs connected in series and parallel

– Encompasses all capabilities of voltage regulation, series compensation and phase shifting

– Provides independent control of both real and reactive flow (extremely fast)

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Thank You!For inquiries, contact:

Kalyan ChilukuriPower Networks ManagerPSCKalyan.Chilukuri@pscconsulting.com