A Transformation Technique for Decoupling Power Networks

Iraj Rahimi Pordanjani, Yunfei Wang, and Wilsun Xu,

University of Alberta Department of Electrical and Computer Engineering

Overview 2

  Introduction   The proposed Transformation   Decomposition of PV Curves

  Potential Applications   Summary

Introduction 3

The network wide-area phasors (voltages and currents with synchronized phase angles) are available.

  Phasor Measurement Units (PMU): The most accurate and advanced time-synchronized technology available to power engineers

How to use the data for power system analysis and monitoring is still not quite clear.

Introduction 4

Ib

Va

Ia

Vb

Ic Vc

3-phase data

Symmetrical Components Transform

Various monitoring and protection schemes

PMUs data (network wide-area data)

How to make effective use of the data How to use the data

A Support Theory

Power systems analysis and monitoring

Special focus: Voltage stability analysis, and monitoring

Analogy with 3-phase data:

Decompose the data into:

Zero, positive, and negative sequences

The Proposed Transformation 5

A three-phase symmetrical line

  The symmetrical components transform is a method for decoupling the above system and is based on the eigen-decomposition of the [Z] matrix of the system

The Proposed Transformation 6

Multiple “phase” view of a power network

A general electric power network

One generator One multi-phase line One load

Phase coupling

Eigen-decomposition:

The Proposed Transformation 7

 Conduct a modal transform to decouple the n-phase network into a n de-coupled networks called channel networks.

Then:

A complex network has been transformed into a set of decoupled simple circuits.

By analyzing the decoupled networks, one may extract important information about the actual network.

Decomposition of PV Curves 8

PV curves

Difficult to be obtained

especially in online applications Can be easily obtained.

Actual PV curves Channel PV curves

Decomposition of PV Curves 9

Conceptual case studies: Case study 1

responsible for power transfer

Decomposition of PV Curves 10

PV curves of the actual system Channel PV curve (Channel 1)

 The channel PV curve reaches its nose point when the physical PV curves reach their noise points.

Decomposition of PV Curves 11

Case study 2  The same network configuration but unequal impedances

Channel 1 transfers the highest power and the maximum power transfer stops at the nose point of channel 1 PV curve.

Channel 1 is the critical channel.

Decomposition of PV Curves 12

Results for IEEE 30-bus system:

Decomposition of PV Curves 13

Results for IEEE 57-bus system:

Potential Applications 14

  Monitoring the stability level by monitoring the critical channel’s margin.

  Identification of the critical load by determining the contributions of loads to the critical channel’s load.

  Identification of the critical generator by determining the contributions of generators to the critical channel’s voltage source.

  ...

Summary 15

  A transformation has been proposed to convert a complex power system into simple decoupled modal networks.

  By analyzing and monitoring the characteristics of modal networks, one can extract important information about the actual system.

  This paper has presented the progress made on the voltage stability analysis and monitoring using the proposed transform. It has been shown that the PV curves of decoupled modal networks may be used instead of actual PV curves to monitor the voltage stability.

16

Thanks for your attention

Current Research Progress Critical Load Identification

17

 Once the critical channel is known, it can be used to identify the critical bus.

 The critical load bus is the most responsible for the voltage drop of the critical channel.

Low stability margin

 Since the channel voltage drop is caused by the channel current, the contribution of bus currents I to the critical channel current Ji can be used.

Large voltage drop

 The bus whose current has the highest contribution to the critical channel current is the critical bus.

Verifications methods:

 Modal analysis method

 The sensitivity of loadability margin with respect to load shedding at different load buses

Current Research Progress Critical Load Identification

18

Bus ranking results in IEEE 30-bus system:

Proposed index

Modal analysis method Sensitivity-based method

Current Research Progress Critical Load Identification

19

Bus ranking results in IEEE 57-bus system:

Proposed index

Modal analysis method Sensitivity-based method

Current Research Progress Critical Load Identification

20

System Critical channel Critical load bus

Proposed mthod Modal analysis Sensitivity-based

6-bus 1 5 5 5

WSCC 9-bus 1 9 9 9

30-bus 4 8 8 8

IEEE 30-bus 1 30 30 30

IEEE 57-bus 1 31 31 31

AIES 2038-bus 18 630 630 630

Summary of results:

  The proposed method can accurately identify the critical bus.