2.2 Voltage And Reactive Power

2.2 Voltage and reactive power

Voltage and reactive power

2.2.1 Heavy load situation:

Equality constraints for active and reactive power:

PG = PL + Ploss QG = QL + Qloss

PG=10300 MW

Ploss= 300 MW

QG= 3500 MVAR

Qloss=1500 MVAR QL= 2000 MVAR

PL=10000 MW

Low load situation:

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PG= 5100 MW

Ploss=

QG= -500 MVAR

Qloss= -1500 MVAR QL=1000 MVAR

100 MW

PL= 5000 MW

2.2 Voltage and reactive power

2.2.2

The synchronous generator jX aI

I Xa

Xσ

R

Ef Ef

Er

Vg

jXσ I

Er

RI

if

Vg

Xa

armature reactance

Ef

excitation emf

Xσ

leakage reactance

Er

air gap emf

armature resistance

Vg

terminal voltage

if

excitation current

R

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I

2.2 Voltage and reactive power

2.2.3

The synchronous generator Active and reactive power supplied by the generator:

X d = X a + Xσ

R << X a + X σ

jX d I

I Xd

Ef

Ef

Vg Vg

if

δ ϕ

Pg =

Ef ⋅ Vg Xd

⋅ sin δ

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Qg =

Ef ⋅ Vg Xd

⋅ cos δ

−

Vg2 Xd

I

2.2 Voltage and reactive power

2.2.4

The synchronous generator Over excitation

jX d I

Under excitation

jX d I jX d I

Ef

Ef

Vg

Vg

Vg

jX d I Vg

Ef Ef

ϕ

ϕ

I

I

Pg = 0 Qg > 0 Pg > 0 Qg > 0 Phase shifter Generator Lagging power factor Lagging power factor (Synchronous capacitor)

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I Pg > 0 Qg < 0 Generator Leading power factor

ϕ

I Pg = 0 Qg < 0 Phase shifter Leading power factor (Synchronous reactor)

2.2 Voltage and reactive power

2.2.5

Automatic Voltage Regulator (AVR) Synchronous generator

Excitation

Step-up Transformer 1: t

if

Network

V

Amplifier

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Vg −

∑

+

Vref

2.2 Voltage and reactive power

Increase of reactive power supply (MVAR) - Change of reference voltage Vref 1 0 Vref > Vref

V >0;

2.2.6 Decrease of reactive power supply (MVAR) - Change of reference voltage Vref 1 0 Vref < Vref

V <0;

i 1f > i f0 ;

Q1g > Qg0

i 1f < i f0 ;

Q1g < Qg0

- Change of tap setting t

t1 > t 0 :

- Change of tap setting t

t1 < t 0 :

Vg1 < Vg0 ; Q1g > Qg0

V >0;

i 1f > i f0

Vg1 > Vg0 ; Q1g < Qg0

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V <0;

i 1f < i f0

2.2 Voltage and reactive power

2.2.7

Voltage and reactive power control mechanisms AVR

Secondary Voltage Control

Communication

400 kV

AVR 220 kV

AVR 110 kV

AVC 20, 10 kV

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2.2 Voltage and reactive power

Voltage and reactive power Voltages at boundary nodes 220 kV

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2.2.7 /7

2.2 Voltage and reactive power

Voltage and reactive power Voltages at boundary nodes 380 kV

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2.2.7 /8

2.2 Voltage and reactive power

Voltage and reactive power Voltages drops on 220 kV boundary lines

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2.2.7 /9

2.2 Voltage and reactive power

Voltage and reactive power Voltages drops on 380 kV boundary lines

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2.2.7 /10