Reactive Power Management and Voltage Control in Transmission Lines By using STATCOM Presented by

Eng. Hussein Ali Hussein Eng. Khaldoon Mohammed

Aeal AEAL

University of Turkish Aeronautical AssociationFaculty of Engineering

EEE department

SupervisionProf. Dr. Ibrahim

Mahariq

TURKEY - ANKARA 2016

CONTENTS

• Introduction • Definition of reactive power.• Need for reactive power compensation.

• Definition of FACTS devices. • Definition of STATCOM. • Basic principle of operation of STATCOM.

• STATCOM , reactive power management and voltage control in transmission lines.

• Conclusion .

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Introduction

AC transmission lines are used to transfer electrical power from power generating stations to the distribution system, which then supplies electrical power to consumers. Since the power generating stations in an AC power network can be quite far from the centers of energy consumption, AC transmission lines often have to transfer electrical power over great distances.

Generation, transmission and distribution of electrical energy

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Introduction

This complication in the grid, coupled with the fact that AC transmission lines are primarily inductive, has many effects on the operation of AC transmission lines. One of the main effects of this complication is a significant voltage drop occurring at the receiver end of AC transmission lines .

Simplified equivalent circuit of an AC transmission line transferring power from a generating station (sender

end) to a distribution station (receiver end).

- The line inductive reactance is represented by the inductance and the distribution station is represented by the load.

- The voltage across the inductance: = where - The voltage (receiver voltage): =- -Therefore, the higher the line current and the line inductive reactance , the higher the voltage drop across the line and the lower the voltage across the load.

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The voltage drop occurring across the ac transmission line must be continually compensated in order to maintain the receiver voltage equal to the sender voltage.

Introduction-This is commonly achieved using capacitors connected in parallel to the line at the receiver end. However, using shunt-capacitor substations for reactive power and voltage compensation of long AC transmission lines has some drawbacks. The primary drawback is potential difficulty in coordinating operation at all substations along the line to achieve proper voltage compensation.- A number of different systems have been

developed to diminish or eliminate the drawbacks of using shunt capacitor substations for voltage compensation of AC transmission lines. These systems are part of flexible ac transmission systems (commonly abbreviated as FACTS) device family, one of the most common FACTS devices, the static synchronous compensator (commonly abbreviated as STATCOM).

Bank of shunt capacitors used to compensate the voltage at substations installedalong an AC transmission line.

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Definition of the reactive power Reactive power is the power that supplies the stored energy in

reactive elements. Power, as we know, consists of two components, active and reactive power. The total sum of active and reactive power is called as apparent power.

Current vector diagram

Power vector diagram

- In current vector diagram, the current vector can be split into two components :

- For most electrical loads like motors, the current I is lagging behind the voltage V by an angle ϕ.

is called the "active" component of the current. is called the "reactive" component of the current.

-The previous diagram was drawn up for currents also applies to powers, by multiplying each current by the common voltage V.

Apparent power: S = V x I (kVA)Active power: P = V x Ia (kW)Reactive power: Q = V x Ir (kvar)

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- Analogy to explain the reactive power.- Take a boat on a canal, pulled by a horse .

- The fact that the horse is not walking straight in front of the boat.

Consequences:• The fact that the rope is pulling at the flank of the horse and not straight behind it, and limit the horse’s capacity to deliver work.•The turned rudder leads to extra losses.

- The vector representation of the force to pull the boat is similar to the vector representation of power in an electric system.

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Definition of the reactive power

Need for reactive power compensation

Voltage control and reactive power management are two aspects of a single activity that both supports reliability and facilitates commercial transactions across transmission networks. On an alternating-current (AC) power system, voltage is controlled by managing production and absorption of reactive power.

If reactive power decreases

Apparent power

decreases

Losses in transmission

line decrease

Voltage drop

decreases composition of the total power of a transmission grid

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Reactive power compensation by using capacitors

principle of reactive power compensation using low voltage power capacitor

-Reactive power compensation is commonly achieved using capacitors connected in parallel to the line at the receiver end. However, using shunt-capacitor substations for voltage compensation of long ac transmission lines has some drawbacks.

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Reactive power

compensation

Improvement in voltage

Improves

system power factor

Reduction in

system losses

Saves cost

Reduction of KVA

demand

Higher load

capability

Benefits of reactive power compensation :

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Definition of FACTS devices FACTS ( Flexible Alternating Current Transmission System) :AC transmission systems

incorporating the power electronic-based to enhance controllability and increase power transfer capability.FACTS Controllers :A power electronic based system and other static equipment that provide control of one or more AC transmission parameters (series impedance, shunt impedance, current, voltage and phase angle ).

FACTS technology provides

Increase loading capacity

Of transmission

lines

Prevent blackouts

Improve generation

productivity

Reduce circulating

reactive power

Improves system stability

limit

Reduce voltage

flicker

Reduce system

damping and

oscillations

Control power flow

FACTS technology provides the opportunity to:

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Classification of FACTS devices

The classification of the FACTS Controllers done on the basis of their types of arrangement in the Power system:

FACTS

SERIES

SSSC Static

Synchronous series

Compensator

TSSC

Thyristor

Controlled

Series Compen

sator

TCSCThyristor Controlled Series

Capacitor

SHUNT

SVC Static

Var Compen

sator

STATCOM

Static synchron

ous Compens

ator

SERIES-

SERIES

IPFC Interline

Power flow

controller

SERIES-

SHUNT

UPFC unified power flow

controller

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Some FACTS controllers

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Working principle of FACTS

Single line diagram between a generation station and load

Consider a transmission line connecting generating station to a load . Assuming the line to be lossless and ignoring the line charging, the power flow (P= real power) and (Q=reactive power) given by :

𝑷=𝑽𝟏𝑽 𝟐

𝑿 ¿ ( - COS Ѳ),Where Ѳ = - and X= the series line reactance.

- FACTS can control the real power and reactive power flow by controlling one or more of the components ( , , X , Ѳ ) .

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A static compensator (STATCOM), also known as static synchronous compensator, is a member of the flexible alternating current transmission system (FACTS) devices. It is a power-electronics-based regulating device which is composed of a voltage source converter (VSC).

STATCOM is a shunt connected reactive compensation equipment which is capable of generating and/or absorbing reactive power whose output can be varied so as to maintain control of specific parameters of the electric power system.

Definition of STATCOM

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(STATCOM )

Structure of STATCOM The main components of STATCOM are :

1- A three-phase step-down transformer.

2- A three-phase PWM rectifier/inverter. - A three-phase bridge - A three-phase filter. - Line inductors. - A controller.

3-A large capacitor () is used as a dc power source for the three-phase PWM rectifier/inverter.

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Basic principle of operation of STATCOM

For two AC sources which have the same frequency and are connected through a series inductance, the active power flows from the leading source to the lagging source and the reactive power flows from the higher voltage magnitude source to the lower voltage magnitude source.

Thus, the STATCOM can be used to regulate the reactive power flow by changing the magnitude of the VSC voltage with respect to source bus voltage. ( - COS Ѳ)Where is the reactive power which can be generated and/or absorbed by STATCOM .

AND Ѳ = The phase angle which can be controlled by inverter. PAG.16

Basic principle of operation of STATCOM

- Operation mode of STATCOM at different levels of voltage :

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The size of STATCOM

- STATCOM has a small size.

The small size of STATCOM makes it possible to transport the STATCOM in a trailer truck.

(Copyright 2012 Guc kalitesi) PAG.18

STATCOM substation

STATCOM , reactive power management and voltage control

in transmission lines Since 1980 when the first STATCOM (rated at 20 Mvar) using force-commutated thyristor inverters was put into operation in Japan, many examples have been installed and the ratings have been increased considerably in reactive power management and voltage control in transmission lines .

Partial list of utility scale of STATCOM

Place PurposeVolta

geLevel

(KV)

Capacity

MVARCountry Year

InstalledS.N

Inumaya substation

Power System and voltageStabilization 154

±80MVA Japan 1991 1

Shin ShinanoSubstation

NagoyaReactive

compensation 500 50MVA Japan 1992 2

VELCO Essexsubstation

Dynamic reactive

compensation duringcritical

contingencies

115 -41 to+133 USA 2001 3

The Doha South substation

(Qatar) and Al-Jasra

Substation (Bahrain)

Reactivecompensation and voltageStabilization 400 500

Mvar

between

Qatar and

Bahrain

2012 4PAG.19

STATCOM , reactive power management and voltage control

in transmission lines

A 500-Mvar STATCOM is implemented in between Qatar and Bahrain network which is part of Gulf cooperative council ,Qatar, Oman, Bahrain, KSA, UAE and Kuwait (GCC) where the total symmetrical range of the reactive output from the STATCOM, from full inductive to full capacitive, could be utilized without applying fixed capacitors to :

1- Regulate voltage on a three-bus 400kV in order to meet long transmission system operational requirements.

2- Reactive power compensation.

STATCOM between Qatar and Bahrain as an example of reactive power management and voltage control in transmission lines.

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STATCOM between Qatar and Bahrain

Simulation process of STATCOM

During a simulation process (MATLAB) it was observed that the reactive current was oscillating from 0.1 to 0.3 second to maintain reference reactive current to the main certain level of the voltage level.

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A simulation process (MATLAB)

Simulation process of STATCOM

Indicates STATCOM waveforms (a) reactive power (b) measured and reference voltage (c) DC voltage

- The reactive current was oscillating form 0.1 to 0.3 second to maintain reference reactive current to main certain level of voltage level.

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Simulation process of STATCOM Receiving end voltages at both sides of Bahrain and Qatar without STATCOM and

ends improved voltages at both sides with STATCOM.

(a )receiving end improved voltage (b) sending end improved voltage

(a ) ) ( receiving end voltage b sending end voltage without STATCOM PAG.2

3

Conclusion- The benefits of using STATCOM to compensate

Reactive power and voltage control.1- By using a STATCOM control device both capacitive and inductive modes of operations are demonstrated.2- STATCOM has a number of advantages, quick response time, less space requirement and optimum voltage platform.3- Tighter control of the voltage at the end of the line.4- Increased line stability during transients (i.e., during sudden changes in the load at the receiver end of the AC transmission line), due to the superior quickness of the STATCOM response.5- Increased power transfer capability in the power grid.6- Improved power grid operational reliability. 7- STATCOM installation is small in size but is significantly more expensive.

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