M. Ettehadi , H. Ghasemi , S. Vaez-Zadeh

Electr. & Comput. Eng., Univ. of Tehran, IEEE Power & Energy society 2013

Student ; Reza Shahbazi

2014 December

Voltage Stability-Based DG Placementin Distribution Networks

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Power system stability

Rotor angle stability

Transient stability

Small Disturbance

Frequency stability

Short term Long term

Voltage stability

Small Disturbance

Large Disturbance

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View on Stability :

I. Introduction DG

II. Voltage-stability Problem In Distribution Networks Problem Identification

Modal Analysis

CPF : Continuous Power-Flow Methodology

III. DG Placement Algorithm DG Placement Process

DG Placement Evaluation Indices

IV. Short-term Reactive Power Ranking Qualified Load Index (QLI)

Ranking Process

V. Case Study

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Introduction :

DG

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DG (Distributed Generation)

Distributed generation (DG) is any electricity generating technology installed by a customer.

Generating power on-site (close to the load), rather than centrally, eliminates the cost, complexity, interdependencies, and inefficiencies associated with transmission and distribution.

Since reactive power cannot travel over long distances, system operators/dispatchers should provide it locally.

DG units are good local reactive power sources.

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Voltage-stability Problem In Distribution Networks

Problem Identification

Modal Analysis

CPF : Continuous Power-Flow Methodology

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Problem Identification

:فروپاشی ولتاژ

دد بدون هیچ پاسخ بنابراین ناپایداری ولتاژ در طبیعت خود یک پدیده ناحیه ای است، که میتواند بصورت فروپاشی ولتاژ کلی بدل گر .سریعی

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ه غیرقابل کنترل شدن ولتاژ در ناحی(افزایش تقاضای بار)بارافزایش ناپایداری ولتاژمشخصی از سیستم قدرت

Voltage stability (IEEE ):

refers to the ability of a power system to maintain steady voltages at all buses in the system after being subjected to a disturbance from a given initial operating condition

Voltage collapse :

usually occurs in heavily loaded systems that do not have sufficient local reactive power sources.

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This reactive power shortage may lead to wide-area Blackouts

Tools for voltage stability analysis

Different methods exist in the literature for carrying out a steady state voltage stability analysis:

P-V curve method.

V-Q curve method and reactive power reserve.

Methods based on singularity of power flow Jacobian matrix at the point of voltage collapse.

Continuation power flow method.

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Modal analysis :

.ناپایداری ولتاژ/یکی از روشهای ریاضی برای بررسی و پیش بینی در مورد پایداری A modal analysis can discover the instability characteristics and can be

used to find the best sites for reactive power compensation

For a (n*n) square matrix A, left and right eigenvectors are defined as follows:

A.x = λx y.A = λy

λ = eigenvalue of the matrix Ax (n*1) = right eigenvectory (1*n) = left eigenvector

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The characteristic equation of both equations

det (A-λ*I) = 0

The solution of this equation: [ λ1 , λ2,…. , λn] are the eigenvalues of A

if λi > 0 The system is voltage stable

if λi < 0 The system is voltage unstable

if λi > 0, then the variation of Vi and Qi are in the same direction.

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Continuous Power-Flow ( CPF ( Methodology

VSM : Voltage Security Margin

The higher the VSM ,the more secure the system

Near the voltage collapse point It is difficult to obtain a power flow solution

Continuation power flow is a technique by which the power flow solutions can be obtained near or at the voltage collapse point

According to the proposed algorithm, a CPF is executed on the system under study

In this step we use CPF to identify the most sensitive bus to voltage collapse.

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DG Placement Algorithm

DG Placement Process

DG Placement Evaluation Indices

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DG Placement Process

The DG placement problem can be formulated by many objectiveFunctions including

Loss Minimization Voltage Profile Improvement Economical Revenue Environmental Impact Reduction Improvement On Reliability Aspects

Voltage security margin enhancement and loss reduction

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the modal analysis is used concurrently to determine the critical modes and their associated buses.

The CPF can be used for the determination of

the VSM and the bus voltages at collapse points.

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bus with a minimum voltage at the collapse point is defined as the most sensitive bus to voltage collapse.

This bus is selected as a candidate for DG placement.

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Receive the network data

Execute the CPF and determine the most sensitive bus to voltage collapse as a candidate

Execute the modal analysis and determinate the worst modes

Determine the most participating bus in each mode as a candidate

Add a DG to the candidate bus

Execute CPF and calculate the maximum loading

Is it the last candidate?

Next candidate

Select the candidate bus with the highest loading

Do we want to place another DG ?

Print the result

Locate a DG at the

bus which has the

maximum loading

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DG Placement Evaluation Indices

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The higher the VSM, the more secure the system.

ALR and RLR show active and reactive loss

reduction after installing DG/DGs.

Higher values of and indicate better performance

of ALR and RLR DGs in loss reduction.

The lower the VI, the better the performance of

DG units.

• Application of the Placement Algorithm

CASE STUDY

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Application of the placement method and the corresponding

indices are examined on the well-known 33-bus radial distribution

Network.

Single-line diagram of the 33-bus radial distribution network

The system total apparent loadis 4.3694 MVA and DGpenetration is considered to be40% (i.e., 1.7477 MVA).

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I. Voltage Stability-Based DG Placement in Distribution Networks

M. Ettehadi , H. Ghasemi , S. Vaez-Zadeh : Electr. & Comput. Eng., Univ. of Tehran, IEEE Power & Energy

society 2013

II. Voltage Stability Evaluation of The Khuzestan Power System in Iran Using CPF Method and Modal Analysis(2010)

Farbod Larki-Ahvaz, Iran ; Mahmood Joorabian-Ahvaz, Iran ; Homayoun Meshgin Kelk, Mojtaba Pishvaei-

Tafresh, Iran

III. Notes on Power System Voltage Stability By S. Chakrabarti, Dept. of EE, IIT, Kanpur

Refrences

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I Really Appreciate Your Concern.

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