flexible AC transmission systems

FLEXIBLE AC TRANSMISSION SYSTEMS BY:SUSMITA PANDA

CONTENTS     

INTRODUCTION WHAT IS THE NEED? LIMITATIONS OF LARGE AC SYSTEMS. ADVANTAGES of FACTS. SERIES COMPENSATION • • •



PARALLEL COMPENSATION • • •

  

Static Synchronous Series Compensator. (SSSC) Thyristor controlled series compensator. (TCSC) COMPARISON STATCOM SVC COMPARISON

COMBINED SHUNT AND SERIES CONNECTED CONTROLLER. SCCL with FACTS. HVDC and FACTS.

INTRODUCTION

INTRODUCTION 

The FACTS technology is a collection of controllers, which can be applied individually or in coordination with others to control one or more of the interrelated system parameters, such as series impedance, shunt impedance, current, voltage, and damping of oscillations.



GENERATIONS:• • •

1st Generation of FACTS (SVC & TCSC). 2nd Generation of FACTS (STATCOM & SSSC). 3rd Generation of FACTS (UPFC & IPFC).

What is the Need? 

Thermal For overhead line, thermal capability is a function of ambient temperature, wind conditions, conditions of conductor, and ground clearance. The FACTS technology can help in making an effective used of newfound line capability.



Dielectric Being designed very conservatively, most lines can increase operation voltage by 10% or even higher. FACTS technology could be used to ensure acceptable overvoltage and power flow conditions.



Stability The stability issues that limit the transmission capability include: transient stability, dynamic stability, steady-state stability, frequency collapse. Voltage collapse, and sub-synchronous resonance. The FACTS technology can certainly be used to overcome any of the stability limits.

LIMITATIONS OF LARGE AC SYSTEMS 

(LONG DISTANCE TRANSMISSION SYSTEMS) • • • •

Voltage stability Reactive power problems Steady state stability Transient Stability



(INTERCONNECTED SYSTEMS) •

• • • •

Load Flow Problems (needs management of Congestion) Voltage Stability Frequency Control Oscillation Stability Inter-Area Oscillations

ADVANTAGES of FACTS 

  



Increase of Power Transfer without adding new transmission lines. Transmission Cost minimization. Steady state and dynamic voltage control. Improvement of System Stability and Voltage quality. Active damping of Oscillations.

BASIC TYPE OF FACTS CONTROLLERS 

Series controllers:

The series controller could be a variable impedance or a variable source both are power electronics based. In principle, all series controllers inject voltage in series with the line. 

Shunt controllers:

The shunt controllers may be variable impedance connected to the line voltage causes a variable current flow hence represents injection of current into the line. 

Combined series-series controllers:

The combination could be separate series controllers or unified seriesseries controller--- Interline Power Flow Controller. 

Combined series-shunt controllers:

The combination could be separated series and shunt controllers or a unified power flow controller.

BASIC TYPE OF FACTS CONTROLLERS FACTS

SERIES

SSSC

TCSC

SHUNT

SVC

STATCOM

SERIESSERIES

SERIESSHUNT

UPFC

IPFC

SERIES COMPENSATION – STATIC SYNCHRONOUS SERIES COMPENSATOR (SSSC) 

Allows rapid and continuous changes in the transmission line impedance so that the active power flow along the compensated transmission line can be controlled within a specified range .



Its output voltage is in series with the line, thus, it controls voltage across the line.



Used for • •

Damping Oscillations. Voltage Stability Improvement.

STATIC SYNCHRONOUS SERIES COMPENSATOR (SSSC)

STATIC SYNCHRONOUS SERIES COMPENSATOR (SSSC)

THYRISTOR CONTROLLED SERIES COMPENSATION(TCSC) 

Series Capacitor banks installations protected by thyristors.



BENEFITS • • • •



Increased Power Transfer Capability. Improved Transient Stability. Lower Transmission Losses. Improved Grid voltage control.

OTHER APPLICATIONS • • •

Power Oscillation Damping. Sub-synchronous Resonance Mitigation. Transient Stability Mitigation.

THYRISTOR CONTROLLED SERIES COMPENSATION(TCSC)

THYRISTOR CONTROLLED SERIES COMPENSATION(TCSC)

COMPARISON

PARALLEL COMPENATION STATIC VAR COMPENSATOR(SVC) 

Consists of fixed capacitor banks in parallel with reactor bank.



BENEFITS • • •



Increased Power Transfer Capability. Improved Grid Voltage Control. Improved Power Factor.

OTHER APPLICTIONS • •

Power Oscillation Damping. Power Quality (Flicker Mitigation, Voltage Balancing).

STATIC VAR COMPENSATOR(SVC)

STATIC VAR COMPENSATOR(SVC)

STATCOM-STATIC COMPENSATOR 

 

 

Same as SVC but its capacitive or inductive o/p current can be controlled independent of system voltage. It can be based on Voltage sourced or Current sourced Converter. When inverter fundamental o/p voltage is higher than the system line voltage, then STATCON acts as a capacitor and reactive VARS are generated. Otherwise, It acts as inductor and absorbs reactive VARS from the system. Can be designed to be an Active Filter to absorb System harmonics.

STATCOM-STATIC COMPENSATOR

STATCOM-STATIC COMPENSATOR

STATCOM-STATIC COMPENSATOR 

BENEFITS • • • • •



Increased Power Transfer Capability. Improved Grid Voltage Stability. Improved Power Factor. Eliminated Flicker. Harmonic Filtering.

OTHER APPLICATIONS •

Power Quality ( Flicker Mitigation & Voltage Balancing).

COMPARISON

UNIFIED POWER FLOW CONTROLLER (UPFC)

UNIFIED POWER FLOW CONTROLLER  



It is a Combined Series-Shunt Controller. STATCOM and SSSC used for shunt and series compensation respectively. BENEFITS • Increases Transmission line capacity (by installing a series capacitor which reduces the net series impedance) . • Power System Oscillation Damping. • Control of active and reactive power flow at both sending- and receiving-end.

UNIFIED POWER FLOW CONTROLLER-OPERATION

UNIFIED POWER FLOW CONTROLLER-OPERATION 







Reactive power is generated or absorbed by the shunt inverter to control bus voltage. Reactive power is generated or absorbed by the series inverter to control the real and/or reactive power flow on the transmission line. A portion of the real power flow on the transmission line is drawn from the bus by the shunt inverter to charge the DC capacitor. Real power is inserted into the line through the series inverter.

SCCL (Short Circuit Current Limitation) WITH FACTS. 

REASONS OF SHORT CIRCUIT CURRENT • •

Increasing Generation in high load density networks. Interconnection between systems.



If the short-circuit current rating of the equipment in the system is exceeded, the equipment must be either upgraded or replaced, both are either very cost- or time-intensive.



Previously,Current Limitation by using reactor was done but it reduces system stability.

SCCL (Short Circuit Current Limitation) WITH FACTS. 

This new device operates with zero impedance in steady-state conditions and in case of a short circuit, it is switched to the limiting-reactor impedance within a few milliseconds.



Uses a reactor along with TPSC (Thyristor Protected Series Compensator).

HVDC and FACTS 

HVDC •

•

•

Economically transmit electrical energy long distances via overhead lines or cable.



FACTS •

Offers low-cost power delivery with the same advantages as HVDC.

•

Increases Capacity of existing electrical Transmission System.

•

Rapidly Implemented Installations.

Connects asynchronous grids or grids with different frequencies. Costly equipments used and takes time-not so widespread.

THANK YOU ANY QUESTIONS?