ELE B7 Power Systems Engineering - University of Waterloo

ELE B7 Power Systems Engineering

Power Flow- Introduction

Introduction to Load Flow Analysis Dr. A.M. Gaouda UAE University

Dr. A.M. Gaouda

ELEC572, 04/05

UAE University

ELEC572, 04/05

The power flow is the backbone of the power system

operation, analysis and design. It is necessary for

planning, operation,Dr.eA.cM.oGanoudoa mic scheduling and exchange Dr. A.M. Gaouda

power

between

utilities. UAE University ELEC572, 04/05

UAE University ELEC572, 04/05

Dr. A.M. Gaouda UAE University ELEC572, 04/05

G G

G

The power flow is also required for many other applications such as short-circuit calculations, transient

G

stability and contingency analysis.

Dr. A.M. Gaouda

Dr. A.M. Gaouda

Dr. A.M. Gaouda

UAE University

UAE University

UAE University

For the network ELEC572, 04/05shown, there are some buses ELEC572, 04/05 connected with thEeLECg572e, 0n4/0e5 rators and

other buses are connected to the loads.

The Real and Reactive power is known at each Load bus. The Generator Voltages

are Also Specified atDrt. Ah.Me. Gagoudea nerator buses.

UAE University ELEC572, 04/05

Dr. A.M. Gaouda UAE University ELEC572, 04/05

The Transmission Lines interconnecting the buses have resistance and

inductance. Therefore, the Electric Current flowing through the lines results in

Electrical Losses.

The Generators in the System Must supply Dr. A.M. Gaouda the Total Electrical Loads pulse the

Dr. A.M. Gaouda

Electrical UAE University Losses. ELEC572, 04/05

UAE University ELEC572, 04/05

Dr. A.M. Gaouda

2 UAE University

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There are Dr. A.M. Gaouda UAE University

some

constrains

should

beDrc. Ao.Mn. Gasouidda ered

while

running

the

system:Dr. A.M. Gaouda UAE University

ELEC572, 04/05

UAE University

ELEC572, 04/05

ELEC572, 04/05

1. The Generators Must Operate within their Generation Capabilities.

2. The Generators Must Deliver the required power at the Desired Voltage at

the Loads.

Dr. A.M. Gaouda UAE University ELEC572, 04/05

Dr. A.M. Gaouda UAE University ELEC572, 04/05

3. There should be no bus voltage either above or below the specified Voltage

operating limits.

4. There Should be no Over-Loading of equipment, including Transmission

Lines and Transformers Dr. A.M. Gaouda UAE University ELEC572, 04/05

Dr. A.M. Gaouda UAE University ELEC572, 04/05

Dr. A.M. Gaouda UAE University ELEC572, 04/05

In Case of

An Equipment Over-Loaded Or Voltage-Limit Violation.

The Generation Schedule have to be adjusted and Power Flow in the

Dr. A.M. Gaouda

Dr. A.M. Gaouda

transmission

lines

have to UAE University ELEC572, 04/05

be

Re-routed

or

Capacitor Banks UAE University ELEC572, 04/05

have

to

be

switched

in order to bring the system into its Normal Operating Conditions.

To Satisfy all the previous requirement for a Reliable Power System Operation,

Power Flow Study is a MUST. The Power Dr. A.M. Gaouda flow study is an essential part in

power system Operation, Planning and Design. Dr. A.M. Gaouda UAE University

UAE University ELEC572, 04/05

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Dr. A.M. Gaouda

3 UAE University

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Power Flow Concept Dr. A.M. Gaouda UAE University ELEC572, 04/05

Dr. A.M. Gaouda UAE University

ELEC572, 04/05

Consider the three-bus power system. Generators (G1and G2) are

connected to the first two buses and an electric load is connected

Dr. A.M. Gaouda

UAE University

G1

ELEC572, 04/05 G2

Bus 1

Bus 2

to the third bus.

Dr. A.M. Gaouda

Dr. A.M. Gaouda

UAE University

UAE University

The real and reactiveELpECo57w2, 04e/0r5 demands are known for the load ELEC572, 04/05 bus (3).

The generator voltages are also specified at bus 1 and bus 2.

Bus 3

The three transmission lines interconnecting the buses contain both resistance and reactance, thus currents flow through these lines results in electrical-losses.

Dr. A.M. Gaouda

Dr. A.M. Gaouda

Dr. A.M. Gaouda

The

two

generators UAE University ELEC572, 04/05

(G1

and

G2 )

must jointly UAE University ELEC572, 04/05

supply

the

total

load requirements UAE University

ELEC572, 04/05

and the power losses in the transmission lines.

The generators are constrained to operate within their power generation capabilities.

The generators are Dar.lAs.Mo. Gaocudoa nstrained to deliver the required Dr. A.M. Gaouda power at the desired

UAE University

UAE University

voltage at the customEeLErC57l2,o04a/05ds.

ELEC572, 04/05

In addition, there should be no over-loading of the power system equipments including transmission lines and transformers.

FvaDEuUrLA.lEArEuC.MU5t7ne.h2iGv,sea0reo4su/i0todry5amf tohreeb, utshevroeltasgheouoplderbateinngolimbDEUurLA.iEAEtCs.MsU57n..2iGv,vea0ro4sou/i0tdy5altage

either

above

or

below

specified Dr. A.M. Gaouda

4 UAE University

ELECS5l7i2d, e04#/05

Power Flow Analysis

Consider the above circuit, if all the components and loads are expressed in terms of constant power loads (i.e., in power systems, powers are known rather than currents), then the equation to be solved are given by

YV I

I

S* V*

It is clear that the set of equations are nonlinear and the solution (bus voltages) can only obtained by iterative techniques

Slide # 5

Power Flow Analysis Dr. A.M. Gaouda UAE University

Dr. A.M. Gaouda

ELEC572, 04/05

UAE University

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It is the solution for the static operating condition of a power system.

Dr. A.M. Gaouda UAE University ELEC572, 04/05

The node voltage method is commonly used for the power system analysis. The

formulation of the network Dr. A.M. Gaouda equations results in compDlre. Ax.M. Glaionudaear equations in terms

UAE University

UAE University

of node currents. ELEC572, 04/05

ELEC572, 04/05

In power systems, powers are known rather than currents. Thus, resulting equations in terms of power become non-linear and must be solved by iterative techniques.

Dr. A.M. Gaouda

Dr. A.M. Gaouda

Dr. A.M. Gaouda

These non-linear equations are known as power flow equations or load flow UAE University ELEC572, 04/05

UAE University ELEC572, 04/05

UAE University ELEC572, 04/05

equations.

The power flow programs compute the voltage magnitude and phase angle at

each bus bar in the system under steady-state operation condition.

Dr. A.M. Gaouda

Dr. A.M. Gaouda

UAE University

UAE University

ELEC572, 04/05

ELEC572, 04/05

These programs use the bus-voltage data to compute the power flow in the

network and the power losses for all equipment and transmission lines.

Dr. A.M. Gaouda UAE University

Dr. A.M. Gaouda UAE University ELEC572, 04/05

Dr. AS.Mli. dGeao#uda6

UAE University

What are the power flow equations? What do you expect to get by solving the power flow equations? How do we benefit from the solution of the power flow equations?

Slide # 7

Bus Admittance Matrix or Ybus

? First step in solving the power flow is to formulate the bus admittance matrix, often call the Ybus.

? The Ybus gives the relationships between all the bus current injections, I, and all the bus voltages, V, I = Ybus V

? The Ybus is developed by applying KCL at each bus in the system to relate the bus current injections, the bus voltages, and the branch impedances and admittances

Slide # 8

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