STATIC SYNCHRONUS SERIES COMPENSATOR

PRESENTED BY:BHUPENDRA KUMAR

CONTENTSIntroduction-Fact technologyApplicationsFact key device-SSSCTheory of SSSCDigital simulation modelOperation of SSSCRating of SSSCAdvantagesReferences

INTRODUCTION

FACTS-TechnologyFlexible AC Transmission System (Facts) is a new

integrated concept based on power electronic

switching converters and dynamic controllers to

enhance the system utilization and power transfer

capacity as well as the stability, security, reliability

and power quality of AC system interconnections

APPLICATIONSPower Flow ControlSeries CompensationVoltage Regulation of Long Transmission SystemEconomic OperationVoltage Stability EnhancementHarmonic SSR Torsional Mode Damping by

Detuning Resonance Conditions

FACTS KEY DEVICE Static Synchronous Series Compensator (SSSC)

The SSSC has been applied to different power system studies to improve the system performance.

A static synchronous Series Compensator operated

without an external energy source as Reactive Power with

output voltage.

SSSC controls the electric power flow by increasing or

decreasing the overall reactive voltage drop across the

transmission line.

The SSSC FACTS device can provide either capacitive or

inductive injected voltage compensation.

If SSSC-AC injected voltage, (Vs), lags the line current

IL by 90º, a capacitive series voltage compensation is

obtained in the transmission line .

if leads IL by 90º, an inductive series compensation is

achieved.

Theory of the SSSC

Figure 1 shows a single line diagram of a

simple Transmission line with an inductive

transmission reactance, XL, connecting a sending-

end (S.E.) voltage source, , and a receiving end

(R.E.) voltage source, respectively.

(i)

(iii)

(ii)

(iv)

expression of power flow given in eq.1 and eq. 2 become :

Where Xeff is the effective total transmission line reactance between its sending and Receiving power system ends, including the equivalent “variable reactance” inserted by the equivalent injected voltage (Vs) (Buck or Boost) by the SSSC-FACTS Compensator.

Digital Simulation Model

Figure 2 shows a simple power system 230-kV network grid equipped with SSSC rated at ±70 Mvar and its novel controllers which connected in series with the transmission system. The 48 pulse (VSC) SSSC connected in series with transmission line at bus B1 by coupling transformer T1.

Figure 2: The single line diagram representing the SSSC interface at S.E. of a Radial Distribution System

The feeding AC network is represented by an equivalent Thevenin is at (bus B1) where the voltage source is a 230 kV with 10000 MVA short circuit level (resistor 0.1 pu and an equivalent reactance of 0.3 pu) followed by the 230 kV radial transmission line connected to bus B2. The full system parameters are given in Table 1.

Table 1The power system parameter

Operation of SSSCA SSSC can work like a controllable serial

condenser and a serial reactance.The main difference is that the voltage infected

through a SSSC is not related to the line intensity and can be controlled independently.

SSSC can be used with excellent results with low loads as well as with high loads.

The main function of the SSSC device is to regulate the feeder power flow.

This can be accomplished by either direct control of the AC line current or indirect control by compensating the impedance, Xs via a (Buck/Boost) compensating injected voltage, Vs.

SSSC is made to operate capacitor by inducing a voltage 90 deg lagging to that of the line current

It is also operated as an inductor by making the induced voltage lead the line current by 90 deg.

The simulation results of both inductive and capacitive regions are obtained.

SSSC as capacitor

0 0.2 0.4 0.6 0.8 1 1.20.1 0.5 0.90

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9Active & Reactive Power of the Trans. Line (pu)

Time (sec)

PL

& Q

L o

f th

e T

ran

s.L

ine

(pu

)

SSSCConnected

Load 2Injected

Load 2Rejected

QL

PL

0.4 0.41 0.42 0.43 0.44 0.45 0.46 0.47 0.48 0.49 0.5-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

Time (sec)

Vs

& I

L (

pu

)

Seies Injected Voltage & Line Current vs t

Vs

IL

SSSC as inductor

0 0.2 0.4 0.6 0.8 1 1.20.1 0.5 0.9-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

1

1.2Active & Reactive Power in Trans. Line vs t

Time (sec)

PL

& Q

L o

f th

e T

ran

s. L

ine

(pu

)

Load 2Injected

Load 2Rejected

PL

QL

0.6 0.65 0.7-1

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

1Series Injected Voltage & Line Current (pu) vs t

Time (sec)

Vs

& I

L (

pu

) Vs

IL

RATING OF THE SSSCThe SSSC can provide capacitive or inductive

compensating voltage independent of the line current.

The VA rating of the SSSC (solid-state inverter and coupling transformer) is simply the product of the maximum line current (at which compensation is still desired) and the maximum series compensating voltage: VA = Imax *Vmax.

An SSSC of 1 p.u. VA rating covers a control range corresponding to 2 p.u. compensating VARs, that is the control range is continuous from -1 p.u. (inductive) VARs to +1 p.u. (capacitive) VARs.

ADVANTAGESThese devices (SSSC, DVR, UVC) correct the

voltage when there is a fault in the network but also have a lot of advantages in normal use, when there are no disturbances, like:

Due to the continuous voltage injection and in combination with a properly structured controller, it is possible to control the power factor of connected loads.

In the interconnected distribution network topologies, the additional voltage with its controllable magnitude and phase, can be used to work on the power flows.

It can also help to cover the capacitive reactive power demand if cable networks, which is higher than in aerial lines, mainly during low load periods that cause inadmissible load elevations.

It balances loads in interconnected distribution networks, providing a balanced system.

It reduces the harmonics caused because of the use of distributed electrical generation pants at a distribution network level, by active filtering by injecting voltage with the converter at the load side.

COMPARISON OF FACTS CONTROLLERS

CONCLUSION1- The SSSC device is a controlled/injected voltage

source that injects a near sinusoidal AC voltage in series with the transmission line.

2- The dynamic power flow in the Transmission line always decreases when the injected voltage by the SSSC in an inductive reactance mode and the power flow increases when the injected voltage by the SSSC in a capacitive reactance mode.

SSSC with its superior characteristics like immunity to sub synchronous resonance, power oscillation damping, quick response time, wider control range, and lower maintenance cost can be used effectively for series compensation of the Transmission line.

Thus due to above superior characteristics SSSC is going to replace all the conventional series compensators.

REFERENCESA.M. Sharaf & M. S. El-Moursi, Department of

Electrical/Computer Engineering, University of New Brunswick.

N.G. Hingorani, L. Gyugyi, Understanding FACTS, Concepts and Technology of Flexible AC Transmission Systems, IEEE press 2000.

Chintan R Patel, Sanjay N Patel and Dr. Axay J Mehta, B.V.M. Engineering College, V.V.Nagar,Gujarat,India.

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