Dr. Tawfiq Hussein Elmenfy

University of Benghazi

Libya

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Outlines

1. Introduction.

2. Turbine & Generator Control.

3. Elements of Excitation System.

4. The main functions of an Automatic Voltage Regulator

(AVR).

5. Static Excitation System.

6. The main functions of a Power System Stabilizer (PSS).

7. Type of PSS in (UNITROL D, M & THYRIPOL).

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Outlines

8. Type of PSS in (UNITROL P & F).

9. Basic PSS Theory.

10. UNITROL Products Life Cycle.

11. Solutions

12. Synchronous Machine Transient Simulation-REAL TIME.

13. Synchronous Machine Designed By MATLAB.

14. Simulation Results.

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1. Introduction

Power system are strongly nonlinear and often have low frequency oscillations.

To overcome this problem, a power system stabilizer is introduced as supplementary controller to the excitation system.

Benghazi north power plants (BNPPs) are the biggest power plants working in General Electricity Company of Libya (GECOL).

The parameter of the power system stabilizers (PSS3B) was tuned in 1995 based on the power system structure in that time. Power system are steadily growing with ever large capacity. Furthermore an oscillations in speed and active power are noted in Benghazi North Power Plant number three following large disturbance occurred at transmission line.

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1. Introduction (Cont.)

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2. Turbine & Generator Control

GeneratorTurbine

AVR

Excitation

Governor

Load Frequency Control (PI) AVR (PID)

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3. Elements of Excitation System

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4.The main functions of an (AVR)

The major function of the (AVR) is to continually adjust the

terminal voltage to maintained at preset value.

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Challenges:

The normal feedback control actions of (AVR) & Speed

Governor introducing negative damping which can cause

undamped modes of oscillations (Critically stable).

Solutions

Switching (AVR) from Auto/Man.

However, removing AVR from service is not realistic solution to

the problem.

Supplementary feedback signal introduced to AVR as PSS.

4.The main functions of an (AVR) (Cont.)

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4.The main functions of an (AVR) (Cont.)

Power System Stabilizer (PSS) added as supplementary feedback

controller in closed loop AVR.

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4.The main functions of an (AVR) (Cont.)

Voltage regulator with adjustable PID controller (AUTO operating mode).

Field current regulator with adjustable PI controller (MANUAL operating mode)

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5. Static Excitation System (ST5B)

Use with UNITROL (D, P, F & 5000) & the corresponding

stabilizers (PSS2B, PSS3B &PSS4B)

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5. Static Excitation System (ST5B) (Cont.)

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6. The main function of PSS

The objectives of PSS is to add damping to rotor oscillations.

This is achieved by modulating the voltage regulator set point to

produce torque variations in phase with speed.

The PSS will produce variations in electrical torque in phase with

speed and acts to damped out oscillations.

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7. Type of PSS in (Unitrol D , M & THYRIPOL)

I. PSS (PSS3B)

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7. Type of PSS in (Unitrol D & M)

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8. Type of PSS (Unitrol P &F )

II. PSS(PSS2B)

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8. Type of PSS (Unitrol P &F ) (Cont.)

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9. Basic PSS Theory

GeneratorTurbine

ω

Tm

Te

Turbine driving torque Tm

Generator braking torque Te

Mechanical rotational speed ω

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9. Basic PSS Theory (Cont.)

A synchronous generator working on the network is principally

an oscillating structure.

In order to produce a torque the rotating magnetic fields of

the rotor and the stator must form a certain angle (the so

called load angle δ).

The electrical torque (Te) increases, as the angle (δ) increases,

just similar to a torsion spring. Because during steady-state

operation the electrical torque (Te) of the generator and the

mechanical driving torque (Tm) from the turbine are in

equilibrium, the load angle δ remains in a given position.

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9. Basic PSS Theory (Cont.)

The dynamic of the mechanical power (Tm) , electrical power

(Te) , and rotor angular speed (ω) of the synchronous machine

is an origin for theoretical consideration and justifications of

the PSS processing signal. The relationship between the above

physical magnitudes is shown in the motion equation of the

synchronous machine (1 and 2).

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9. Basic PSS Theory (Cont.)

In order to provide a better understanding of equation (2) the

following record shall show the dynamical behavior of the

electrical torque Te and rotor angular speed ω after a sudden

change in the grid configuration. In this simulation the driving

torque has been kept constant.

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9. Basic PSS Theory (Cont.)

Fig. :Electrial torque and rotor angle speed

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10. UNITROL Products Life Cycle

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12. Synchronous Machine Transient Simulation - RT

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12.Synchronous Machine Transient Simulation - RT

SMS-RT 6000 is a powerful, modern tool for real time

simulations.

SMTS-RT 6000 simulates the following plant devices:

• Synchronous machine defined either as generator or as motor

• Excitation system either static or rotating

• Power System Stabilizer (PSS) ABB type APSS or PSS2A/B,

MBPSS (Type 4B) according to IEEE 421.5 1992

• Field suppression circuit including field breaker and linear or

nonlinear discharge resistor.

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12. Synchronous Machine Transient Simulation -RT

• General-purpose turbine with governor (driving power ramp)

• Nonlinear speed dependent shaft load for motor applications

• Step-up transformer

• Network composed of the line series inductance and resistance

connected to an infinite voltage source

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12. Synchronous Machine Designed by MATLAB

Synchronous Machine

1

Continuous

1.0

-K-

Volts > pu

Vf (pu)

Va (pu)

v+-

Va

A

B

C

a

b

c

Three-phase

Transformer

210 MVA 13.8 kV / 230 kV

Pm

Vf _

m

A

B

C

Synchronous Machine

200 MVA 13.8 kV

0.7516

wref

Pref

we

Pe0

dw

Pm

gate

HTG

v ref

v d

v q

v stab

Vf

Excitation

System

?

Double click here for more info

A B C

5 MW

A B CA B C

3-Phase Fault

A

B

C

10,000 MVA, 230 kV

source

A B C

10 MW

Speed (pu)

Iabc (pu)

<Stator current>

<Stator v oltage v q (pu)>

<Stator v oltage v d (pu)>

<Rotor speed wm (pu)>

<Rotor speed dev iation dw (pu)>

<Output activ e power Peo (pu)>

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13.Generator Parameters

The generator parameters in per unit on rated 210 MVA and 15.75 KV base are follow:

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13.Generator Parameters

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14. Simulation Results

Speed Deviation

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15. Simulation Results (Cont.)

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0 2 4 6 8 100

100

200

300

400

500

600

t(sec)

Powe

r Tra

nsfe

r (M

W)

no PSS

MB-PSS

Proposed PSS

Power Transfer

Load Frequency Control

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Maintaining power system stability depends on speedof fault clearing, excitation system speed of response andforcing capacity. Increasing forcing capability anddecreasing response time increases the margin of stability>

Governor Droop - the decrease in frequency to which a governor responds by causing a generator to go from no load to full load.

Load, Speed, Temp. VIGV Controller

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Turbine Control

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Power-angle Curve

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11. Solutions to Improving Power System

1. Modeling of the Generator & Turbine

2. Analysis of PSSs and its effects on power

system stability.

3. Retuning the PSS parameters via intelligent

techniques to Improved its effect on local and

inter-area modes oscillations.

4. Retuning( PI ) & Governor Droop.

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THANK YOU FOR YOUR ATTENTION

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