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TxModelSlides

# TxModelSlides - Simple Models of the Transmission System...

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1 Simple Models of the Transmission System Judy Cardell February 19, 2002 ESD.126 2 Overview • Load Flow Equations – ‘dc’ load flow • Kirchoff’s Laws • Power Transfer Distribution Factors • Uses of Transmission Models

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3 Objective of Discussion • Understand origin of load flow programs • Understand use of load flow programs • Become comfortable with these basic equations, since they are also important for the economics of operating power systems – Economic dispatch, security constrained dispatch – Unit commitment 4 Impedance and Ohm’s Law V IR VI ZI R j X Y Z Gj B I V Z ZV Y V = == + + = () 1 1 • Terms: Impedance, Admittance
5 ac Voltage and Current VV t V II t I iV V iI I = + =∠ =+ = || c o s ( ) c o s ( ) ϖ δ ϖδ 6 Load flow equations • Complex power flow, S i , at node I – Where ‘*’ indicates complex conjugate SV I V y V Pj Q ii i i i k k k == *( ) *

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7 Real and Reactive Power Flow • Power injected at node i ( ) ( ) [] ( ) ( ) PV V g b QV V g b ii k i k i k i k i k k k i k i k i k i k k =− + cos sin sin cos δδ 8 The Load Flow Problem • Objective: To solve for complex S and V – S = P + jQ –V = |V | • There are two equations and four unknowns at each node, so we must make assumptions – Assume the load is known, P and Q – Assume generators can control P, |V| and that these are known
9 Using a Load Flow Program • The user specifies – The line parameters (impedance), g and b – P and Q at all loads – P and |V| at all generators –|V | and at the swing bus • The load flow program solves for the remaining variables 10 Running a Load Flow Program • Enter initial values for a ‘flat start’ – All |V| = 1 – Swing bus = 0 – P and Q, normalized, based on knowledge of the system – Line parameters, usually given as part of problem definition (data from company, filed with government, or standard test case)

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TxModelSlides - Simple Models of the Transmission System...

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