Reactive Power and Voltage Control Problems_Rev_B_Julio_Chinchilla

7/27/2019 Reactive Power and Voltage Control Problems_Rev_B_Julio_Chinchilla

1/16

Reactive Power and Voltage

Control ProblemsJulio Csar Chinchilla Guarn

223141

Analysis of Power Systems

Universidad Nacional de Colombia


2/16

Agenda

Introduction.

Equivalent Circuit. Thvenin Equivalent Circuit.

Equivalent Circuit of a Tapped Transformer.

Some Configurations of Automatic Tap-Changers in PowerSystems. Voltage Control of a Radial Load (Case I).

Tie-Transformer Between Systems of Various Strengths (Case II). Two Very Strong Systems.

Two Very Weak Systems. One Very Strong and One Very Weak System.

Conclusions.

References.


3/16

Introduction

Voltage and

ReactivePowerProblems

Equivalent circuitsof power systems

and powertransformer

Strategies forthe optimum

control of Qand V.

Manytechniques

for analysis ofpower flows.


4/16

ThveninEquivalent

Circuit

EquivalentCircuit of a

TappedTransformer

EquivalentCircuit

Y1=n(n-1)Y

Y2=(1-n)Y

n Y1/Y Y2/Y1,25 0,31 -0,25

1,20 0,24 -0,20

1,15 0,17 -0,15

1,10 0,11 -0,10

1,05 0,05 -0,05

1,00 0 0

0,95 -0,05 0,05

0,90 -0,09 0,10

0,85 -0,13 0,15

0,80 -0,16 0,20

0,75 -0,19 0,25

Table 1. Effect of n

on Y1 and Y2.

=

sin

=

cos

=

sin

=

cos

2

=

sin

=

2 cos


5/16

SOME CONFIGURATIONS OFAUTOMATIC TAP-CHANGERS IN POWER

SYSTEMS


6/16

Case I Voltage control of a radial load

Load

Lagging power factor.

Leading or unity power factor.

Objective

To keep the bus 2 voltage at its rated value.

Regardless of the magnitude and the p.f. of the load.

Tap-changer

If V2 drops, tap-changer changes to restore.

In terms of model, its shunt capacitor cancels reactive part of theload.

For its shunt inductor, there is a transfer of reactive power from bus2 to bus 1.


7/16


Y1=n(n-1)Y

Y2=(1-n)Y


8/16


Minimumcurrent

detector

Control of

the tap-changer

Out ofvoltagedetector


9/16

CASE II TIE-TRANSFORMERBETWEENSYSTEMSOFVARIOUSSTRENGTHS


10/16

Differences between systems of

various strengths

Two very strong systems

Two very weak systems

One very weak system

and one very strong

system


11/16

Differences between systems of

various strenghts

System Impedance Reactive power flow Voltage Tap-changer

Two very

strong

X1=j0

X2=j0

- Flows in between generator

and Y1 (source/sink) or Y2

(source/sink).- Q through nY=0.

Cannot vary. - Transfer Q.

- Not to

regulatevoltage.

Two very

weak

X1=j

X2=j

Flows between Y1 and Y2. It isnt

necessary.

One verystrong and

one very

weak

X1=j0X2=j

From stronger to weakersystem.


12/16

Conclusions

Equivalent circuits allow to analyze someproblems about voltage and reactive powercontrol associated with power system operation.These models give insight into some phenomena

about reactive power and voltage control. To add a suplementary minimum current

detector to out of voltage range detector canallow to optimize or minimize branch nY

loading for any given load connected totransformer. This optimum condition is near unitypower factor.


13/16

Conclusions

Tap-changers can be used for strategies as

transfer reactive power between two strong

systems, this strategy can be considered as

voltage control.

We cannot use tap-changers as voltage

regulator because it could have undesirable

consequence like as generator falls out ofsynchronism.


14/16

References

Smolinski, W. J., 1981, Equivalent Circuit

Analysis Of Power System - Reactive Power

And Voltage Control Problems, University of

New Brunswick, Canada.


15/16

Are there any questions?


16/16

Thanks for your attention!

Reactive Power and Voltage Control Problems_Rev_B_Julio_Chinchilla

Documents