Sistema de Exc. vs Estabilidad

7/27/2019 Sistema de Exc. vs Estabilidad

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Impact of excitation system on power system stability

ABBABB Industrie AG

1.INTRODUCTION


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ABBABB Industrie AG

- 2 -


HV SYSTEM

THE POWER STATIONSTEP UP

CONTROL ROOM

TRANSFORMER LV SWITCHGEAR

HV- BREAKERAC & DC

AUXILIARYSYSTEMS

GOVERNOR

1GENERATOR

BREAKER

AUX.TRANSF

.

PROTECTION

1

CONTROLSYSTEMS

SYNCHRONIZING

PTs&CTs

TURBINESYNCHRONOUS

GENERATOR

EXCITATIONSYSTEM

STARPOINT

CUBICLEEXCITATION

TRANSFORMER


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ABBABB Industrie AG

If Synchronous Ug

Machine

ExcitationSystem

Grid

Controller

The automatic voltage control system


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ABBABB Industrie AG

~=

SM E ~SM =

1 a 200 A

Rotating exciter100 a 10000

A

Static excitation


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ABBABB Industrie AG

Basic Requirements Excitation Current up to 10000 amps

Input frequency range from 16 Hz to 400 Hz

Adaptable to different redundancy requirements for controls andconverters

State of the art man machine interface

Compatibility with most applied power plant control systems

Remote diagnostics

Comfortable commissioning tools


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ABBABB Industrie AG

Operational Application


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Main Components of an UNITROL 5000 System

AVR

ABB Industrie AG

ABB


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Measuring

System overview

AVR 2

AVR 1

Protection

Monitoring

AVR + FCR

Logic Control

CONVERTER N

CONVERTER 2

CONVERTER 1

Converter

Control

Field flashing

Field suppressionFieldbreaker

AVR = Autom. Voltage Reg.

FCR = Field Current Reg. ABB


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ABBABB Industrie AG

MeasuringandA/D

conversion

Min.

/max.value

priorityQ

Main Functions of the AVR

with Field Current Controller

UG, I

G

UG

UG, I

G, I

f

UG, I

G, I

f

UG, IG

If

AVR Setpoint-V/Hz limiter

- Soft start _- I Compensation

- IP

Compensation

+

Underexcit. limiter-Q=F(P,U,UG)

-Stator current lead

-Min. field current

Overexcit. limiter-Max field current

-Stator current lag

Power System

Stabilizer PSS

Man setpoint _

+

PID

PI

To pulse

generation


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2. IMPACT ON POWER SYSTEM STABILITY

Voltage Control Dynamics ( controller, power stage and power source)

Limiters

Power System Stabilizer


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ABBABB Industrie AG

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2.1 Voltage Control Dynamics ( controller, power stage and power source)


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Parameter Description Unit Range

TR Measuring filter time constant s 0.020

Ts Gate control unit and converter time constant s 0.004

KIR Reactive power compensation factor p.u. -0.20...+0.20

KIA active power compensation factor p.u. -0.20...+0.20

KR Steady state gain p.u. 10...1000

Kc Voltage drop to commutations andimpedances p.u. Acc. Transf.

TB1 Controller first lag time constant s TB1 TB2TB2 Controller second lag time constant s 0


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ABB Industrie AG

IR UR

IDR

UT

ITIDT

If Uf

IDS

IS

US

Synchronous machinethree-phase representation ABB


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IQ2

IQ1

D axisra

Idd Ud

Stator

dD

rdD

IdD

rf f

Uf If Q1

Q2

q Q axis

rQ1 rQ2ra

IqRotor

Uq

d


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decompositionABB


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Torque TM =

TE =

PM

speed

US Ep sin

Xq +

TM

XT +XE

Motion equation:

0o 45o 180o

TM TE = 2Hd

dt

The characteristic Dynamic Equation

ABB


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IEEE 421.1

UF ceiling

NR

c

b

UF nominald

AVR - Voltage control dynamic

System type (Static excitation, Brush-less, DC Exciter)

Settings of control algorithm

Response time

Ceiling capabilitiesExcitation system nominal

response

=c e -ao

(ao)(oe)

a

oe=0.5s

ABB


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ABBABB Industrie AG

Comparison of Excitation System Types

Mechanical

-Conversion of

mech. to electr.

Energy

- Size of exciter

- Sliprings

Electrical

- Rectifier

- Directmeasuring

of field current

- Fast field

suppression

DC-Exciter

yes

power and speed

yes

not required

possible

possible

AC-Exciter

stat. diodes

yes

power and speed

yes

static external

possible

possible

AC-Exciter

rot. diodes

yes

power and speed

no

static rotary

not possible

not possible

Stat. Exciter

stat. thyristors

main machine

power

yes

static

possible

possible


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ABBABB Industrie AG

Comparison of Exciter Characteristics

Dynamic

Performance

- Major time

constant of control circuit

- Ceiling factor

- Negative fieldcurrent

Reliability (MTBF)

- Machine, Transformer

- Converter

Maintenance

- Machine, Transf.

- Converter

DC-Exciter

TdL+TE

limited

possible

good

good

at standstill

at standstill

AC-Exciterstat. diodes

TdL+TE

not limited

not possible

good

better

at standstill

duringoperation

AC-Exciterrot. diodes

TdL+TE

limited

not possible

good

better

at standstill

at standstill

Stat. Exciterstat. thyristors

TdL

not limited

possible

better

better

at standstill

duringoperation


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ABBABB Industrie AG

Ceiling limit


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ABBABB Industrie AG

2.2 LIMITERS


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ABBABB Industrie AG

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Setpoint building

Automatic

channel

-Setpoint

Follow up

Automatic

Ug

ACTransducer

and filter

-Soft start

-V/Hz limiter

-Q influence

-P influence

Ug actual

effective setpoint

+

-

Powersystem

stabilizer

(PSS)

HVGate

Gain

+ DC

Gain

Ucmax

HF gain

+

UcAVRUnderexcitation

limiters (UEL)

Overexcitation

limiters (OEL)

LV +

Gate

+

UcP gain

1/TA 1/TB

Ucmin Ucmax

IFTransducer

-

and filter

+

Gain

DC

Gain

P gain

Uc FCR

Manual set point

Follow up

Automatic

Follow up Manual

Follow upcontrol

UcAVR

Uc FCR

Ucmin

1/TA 1/TB AVR

FCR


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ABBABB Industrie AG

Theorectical stability

limit

Practical

stability

limit

P [p.u.]

Declared rated

operation point

ofgenerating

unit

Turbine

ouputpowerlimit

Thermal limit

of stator

LEADING

(underexcited

)

n

LAGGING(overexcited

)

Thermal

limit of

rotor

-1.0 p.u. U2

Xq

U2

Xd

Minimum

Field current

limitSafe operationrange

1.0 Q [p.u.]


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ABBABB Industrie AG

The Power Chart of a solid polesynchronous machine


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Synchronous machine operation Limits

Max.Max. fieldfield currentcurrent limiterlimiter

Min.Min. fieldfield currentcurrent limiterlimiter

StatorStatorcurrentcurrent limiterlimiter

UnderUnderexcitationexcitation P,QP,Q limiterlimiterP

Theoreticalstability limit

-Q 1/Xd +Q


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ABBABB Industrie AG

Main duty of the limiters:

Keep the synchronous machine operating withinthe safe and stable operation limits, avoidingthe action of protection devices that may tripthe unit.


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ABB Industrie AG

VOLTAGE REGULATOR WITH LIMITERS

ABB


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ABBABB Industrie AG

LOWERVAL.GATE

Voltagesetpoint

Supply

~ - +

=-

Ifth setpoint

Ifact-

+

IfmaxI2dt max

= / ~

=

+ I2

dt

COMP

/ #

SM =

~

THE OPERATING PHILOSOPHY OF Ifmax LIMITER


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Fieldcurrent

xIFN

Ceiling limit

thermal limit

setpoint

switch time

Time [s]


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ABB Industrie AG

Machine

frequencyfT [p.u]

Machineterminalvoltage

UT [p.u]

Machine field

1

1+ sTR

V / Hz Limiter

x yy=KVHZ.x+U_fn-KVHZ

-KVHZ

U_fn +

x>0

T_V_Hz

Delay

UTMAX

UTMAX

0

U_V/HZ

Volt/Hz

influence

signal

toAVR

[p.u.]current

IF [p.u.]1

1+ sTR

Max. field current limiter-

KIFmax+

x2

-KCF

+

EmaxFy

Setpoint 2 forIF max limiter

(option)

Stator

IFth1

IFth2

KHF

x>0 0IFmax1

IFmax2

1s

xx>y

LV

Gate

Current

IT [p.u.]1

1+ sTR

Stator current limiter

+

-KCS

EmaxSy

- KITind

+

To OEL limiter

gate ofAVRKHS

x>0

1s

0

xx>y

ITth

ITmaxTo UEL limiter

gate ofAVR

-+

KITcap

Min. field current limiter+

KIFmin

-

HV

Gate

Generatorreactivepower

1 P/Q limiter

IFmin

QT[p.u.]

1+ sTRGeneratorterminal

voltageUT [p.u.]

x2

1

le

- KPQ

+

ABB


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ABB Industrie AG

Generator

active powerPT [p.u.]

1+ sTR Look-upTab

yn

= f(xn)


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2.3 Power system Stabilizer

ABB


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IXq(s) XT XE

Ep UG

Ep

XT+XE

US

InfiniteBus

Ep-S = I. Xq

Ep

H

UG

=I.Xq

X q ( s ) = X q 1 + s Tq '

1 + s Tq ' '

= I. (XE+XT)

US

1 + sT q o ' 1 + s T q o ' '

Stationary and transient air gap voltages ABB


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Pe E

p U G US

90o

phasorrotation

Transient behavior ofand PEPE

ABB


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2

A) HXT+XE

Infinite Bus

B)H1 H2 Equivalent Inertia Heq =

XT+XE

H1 H2

H1+H2

TM TE = 2 H d TM TE Hd

taking dt = 2

dt2

For small oscillations keeping the drivingtorque constant the dynamic equationlinearized can be written as: 2 H

n

d2

dt2

+ D d

n dt +K1=0

Inertia. Ang. Acc. Dampingtorque

SynchronizingTorque


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Dynamic equation of synchronousmachine+grid for small oscillations ABB


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Oscillation frequency

phasorrotation K1

n

2 H

rad/s

Negative Damping(Unstable Region)

UG

D/ws*

Torque

Positive Damping(Stable Region)

Damping axis

K1=synchronizing coefficient

operating point

K1 =slope =T

=E p ' . Us

coso'Te=K1.

ResultingTorque

Xq'+XE +XT

Synchronizing Axis 0o o 90o


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Phasor diagram of machine+gridfor small oscillations ( without AVR) ABB


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2H n

d2

dt2

+D

d

n dt+K1

+K2 Ep'=0

Inertia.Ang. Acc. Dampingtorque

Synchron.Torque

Add .Torquefrom exc. system

Negative Damping(Unstable Region)

K2.Ep

UGD/ws*

-UG

phasorrotation

Positive Damping(Stable Region)

Resulting torque componentwithou t excitation system

Te=K1.Resulting torque componentwit h excitation system

ABB Industrie AG

Synchronizing Axis

Phasor diagram of machine+grid+excitation systemfor small oscillations ABB


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ABBABB Industrie AG

AVR

FINAL

CTRLELEMENT

~

ALTERNATIVE

PSS

UG

M

P,Q

Fig3: PSS in the excitation system


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Main Target of PSS:

It provides an additional torque component in order to get:

1) A positive resulting torque component on damping axis, even for thehighest possible rotor oscillation frequency.

2) A positive torque component on synchronizing axis for partialcompensation of generator terminal voltage variations even forthe highest possible oscillation frequency


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ABBABB Industrie AG

PSS2A acc. IEEE 421.5 1992PM

1 + s.2.H

+ N+

PA

1 + s.2.H VSTmax VSTmax

s.TW1 s.TW2 (1 + s

T 8)

1+s.T1 1+s.T3 VST

1 + s.TW1 1 + s.TW2 (1+

s

T9)M

+ Ks1

-

1+s.T2 1+s.T4

Ks3

VSTmin VSTmin

PE s.TW3

1 + s.TW3

s.TW4

1 + s.TW4

Ks2

1 + s.T7

PE

1 + s.2.H


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ABBABB Industrie AG

Adaptive PSS (APSS) Alternative to PSS2A

Driving Power Pa

UG , IGUref +

+ -

AVR+

Uf

+

Synchronous

Generator

UG

Measurement

P

GRID

APSS3rd Order System Model

Filter

P

Estimator

White

noise+ Regulator

+


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ABBABB Industrie AG

+

Multi Band PSS (MBPSS)

FB1(s)

+ K b-

FI1(s)

+

K i

-FI2(s)

Limit To

AVR

+

FH1(s)

+

K h-

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Sistema de Exc. vs Estabilidad