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*Introduction

*Modeling of Synchronous Generators

*Modeling of Transformer, Transmission line

*Load Modeling

*ALFC & AVR Modeling, Simulation & Analysis

*Load Flow Simulation & Analysis

*Short Circuit Simulation & Analysis

*Stability Studies

*Power System Security Analysis

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*Current scenario of power system: large dimensionality of interconnections, complexity and problems pertaining to stability

*Need for contemporary approach to study and assess power system performance

*Accurate modeling of power system components

*Use of simulation packages (like ETAP, NEPLAN, MiPOWER, PSCAD, Dig-Silent, SKM)

* Deployment of FACT devices at EHV levels

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*What is modeling and simulation?

*To express physical device/ equipment /system in terms of mathematical expressions containing various parameters/variables (e.g. V, I, P, Q, S, f etc.) so as to make computer understand its typical behavior / characteristics.

*Simulation is the process of solving these modeled equations on digital computer with proper programming methods for predicting behavior of system under some typical given situations.

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*The most crucial component of power system

*Turbo-alternators and Hydro-generators

*Mathematical modeling requires Park’s transformations (dq0) to be used

*For load flow analysis classical model is used i.e. Constant voltage source in series with synchronous impedance/reactance

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*IEEE classification synchronous machine models for computer simulation*Model (0.0): Classical model of synchronous machine

neglecting flux decay and damper winding *Model (1.0): Field Circuit model with no damper windings

and only field winding on d-axis is considered.*Model (1.1): field circuit with only one equivalent damper

on q-axis.*Model (2.1): field circuit with one equivalent damper on d-

axis and one damper on q-axis.*Model (2.2): field circuit with one equivalent damper on d-

axis and two dampers on q-axis.*Model (3.2): field circuit with two dampers on d-axis and

two dampers on q-axis*Model (3.3): field circuit with two dampers on d-axis and

three dampers on q-axis.

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d-axis equivalent circuit of Model (2.1)

q-axis equivalent circuit Model (2.1)

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*Transformer is modelled as an impedance in percentage (pu x 100) value

*Load Tap Changer settings to be specified

i.e. taps need to be given in terms of min. and max. tap in % of rated kV alongwith total no. of taps available

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*There are two ways to model it for large system study i.e. T and

*In all software packages is preferred.

Why?

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*Three static loads: Constant power, constant impedance, constant current

*Dynamic load model: induction motor, synchronous motors

*Composite load modeling

V

P Constant current

Constant impedance

Constant power

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*Need for generator controllers

*P-f control loop: ALFC

*Q-V control loop: AVR

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Speed governing

system

Speed reg./Droop

Power system

Non-reheat turbine

Power signal from PI controller

Load/Demand variation

Frequen. error output

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Time domain response of frequency error for unit step load

23/02/2012Viren B. Pandya 18Drooping Characteristics of Speed Governing System or primary ALCF

loop characteristics

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Load frequency control loop with PI controller

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Time domain response of frequency error for unit step load with PI controller

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TWO AREA control

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Time domain response of frequency error for TWO AREA control

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*To brace control on terminal voltage of synchronous generator

*Reactive power control

*Q-V loop controller

*Various excitation systems like DC, controlled and uncontrolled rectifier type Brushless excitation systems with automatic voltage regulators

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DC Excitation System

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Brushless Rotating Rectifier Excitation System

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Modeling steps for brushless excitation

system without

compensation

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*To mitigate small signal oscillations in generator rotor by controlling its excitation using an auxiliary signal

*Produces component of electrical torque in such a phase so as to decrease rotor oscillation

*Frequency range is 0.1 to 2.0 Hz

*For small signal stability simulation

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*Steady state analysis of power system with solution of non-linear algebraic equation (static load flow equations) keeping total generation and load constant.

*Methods: GS, Accelerated GS, NR, FDLF

*Classical Model approach

*Data required for different models

*Swing, voltage controlled and MVAr controlled buses

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*Symmetrical and Unsymmetrical faults, simulation as per IEC and IEEE

*Use of Zbus

*To determine fault level in terms of MVAshortcircuit

bshortcircuit

pu

MVAMVA

Z

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*It is the ability of the dynamic power

system to remain in synchronism under

normal operating condition & to regain an

acceptable equilibrium state after being

subjected to perturbation.

*Broad classification according to IEEE has

been taken here.

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* Power system security is the ability of the system to provide electricity/power with appropriate quality under normal and disturbance conditions

* Power system security is broken into three major functions being done at control centre: System monitoring i.e. SCADA and State

Estimation

Contingency analysis

Security constrained optimal power flow

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* Data received via SCADA system are having errors not only in form of in accuracy of measurement but many times also unavailability.

* Unavailability of data is referred as BAD data* STATE ESTIMATION is a programme that

minimizes errors of such measurements and detects bad data and then it gives the real state of power system in form of bus voltage magnitude and bus voltage angles

* Weighted least squares method is used for state estimation in power system

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* Contingency refers to known OUTAGE of any

component of power system

* Basically contingency analysis assess the

security of power system when there is sudden

switching (ON or OFF) of large power dealing

component like generator, power transformer or

tie-line

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Here contingency analysis is combined with

OPF which searches to make changes

optimal dispatches of generation so that

when security analysis is run, no

contingency results in violations.

500 MWUnit 1

700 MWUnit 2

1200 MW

250 MW

250 MW

Optimal DispatchOptimal Dispatch

Line max loadability is 400 MWLine max loadability is 400 MW

500 MWUnit 1

700 MWUnit 2

1200 MW

500 MW

Post contingency Post contingency

Secure dispatchSecure dispatch

400 MWUnit 1

800 MWUnit 2

1200 MW

200 MW

200 MW

Secure post contingency stateSecure post contingency state

400 MWUnit 1

800 MWUnit 2

1200 MW

400 MW

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*“Power System Stability” by Edward Wilson Kimbark

*“Power System Stability and Control” by P. S. Kundur

*“Power System Dynamics” by K. R. Padiyar

*“Power System Operation and Control” by Halder and Chakrabarti

*EEE Committee Report, “Computer Representation of Excitation

System”, IEEE Trans. on PAS, Vol. PAS-87, No. 6, June 1968.

*IEEE Committee Report, “Dynamic Models for Steam and Hydro

Turbines in Power System Studies”, IEEE Trans. on PAS, Vol. PAS-

92, No. 6, Nov./Dec. 1973.

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