EE587_ Ch4_sp10

EE587_ Ch4_sp10 - EE 587 Electric Power...

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Unformatted text preview: EE 587 Electric Power Distribution/Utilization Dr. M. Safiuddin, Research Professor Department of Electrical Engineering University at Buffalo [State University of New York] EE 587_Sp 10 1 EE 587 Electric Power Distribution/Utilization TEXT BOOK: ANSI/IEEE -Std. 141-1993 [ The Red Book]; Published by Institute of Electrical & Electronics Engineers, New York. Lecture Topics: 1. 2. 3. System Protection I Sources of fault currents, Fundamentals of fault current calculations, Restraints of simplified calculations, Example case studies. [Ch. 4] EE 587_Sp 10 Introduction, System Planning & Design Course orientation, Overview, Definitions, Planning guide for the supply and distribution system [Ch 2] Voltage Considerations Voltage control, Voltage selection, Effects of voltage variations on low and medium voltage equipment, voltage quality considerations.[Ch. 3] 2 1 System Protection I [Ch. 4] ! " &' # ! $ $ $ % $ EE 587_Sp 10 3 ( % ) $ * $ + 4.5 Detailed procedure Step 1: Step 2: Step 3: Step 4: Prepare system diagrams Collect & convert impedance data Combine impedances Calculate short-circuit currents First-cycle network; Interrupting network Time-delayed relaying devices EE 587_Sp 10 4 2 % /0 10 , - . 2 4 456 34 7 8 - EE 587_Sp 10 5 Background- Circuit Analysis ) + :5 :5 5 ; ::5 :::5 < < EE 587_Sp 10 6 9 ∝∝+ ∝+ , , . . 3 Equivalent circuit > >=" 0 >= = EE 587_Sp 10 7 Electric Machine Fundamentals MAGNETIC FLUX (O) FLUX DENSITY (B) N l S I APPLIED CURRENT N S RESULTANT FORCE EE 587_Sp 10 8 4 Electric Machine Fundamentals FLUX DENSITY (B) A MAGNETIC FLUX (O) TORQUE RESULTANT FORCE N S N S I RESULTANT FORCE EE 587_Sp 10 9 Electric Machine Fundamentals ? 8# : $ ? # @ $ ? ! ? ! EE 587_Sp 10 10 # @ @ 5 Sources of Fault Currents 0 A : ) ! & * & ! $ ! $ * EE 587_Sp 10 11 Sources of Fault Currents A A &' ! # B EE 587_Sp 10 12 6 Synchronous Machines: ?A ?# ?% + - % , ? ? ? ! : $ % ! &' ( !* ) " # " # : EE 587_Sp 10 # 13 EE 587_Sp 10 14 7 P. C. Sen, Principles of electric machines and power electronics. EE 587_Sp 10 15 EE 587_Sp 10 16 8 Source: P. C. Sen, Principles of electric machines and power electronics. isc = 2 Ef Xd + Ef ′ Xd − Ef Xd e −t ′ Td 0 + Ef ′ X d′ − Ef ′ Xd e − t ′′ Td 0 sin ωt + I dc 0e −t Ta EE 587_Sp 10 17 Induction Machines ?& ! ?! C ? ! DE ?! ! EE 587_Sp 10 18 9 Electric utility systems F & ! $ ! ! * ! $ EE 587_Sp 10 19 Adjustable speed motor drive systems , $ ! . ! C ! &! - EE 587_Sp 10 20 10 ; * G ( , H 0I> . ! $ $ 0 > % J 8 ! $ EE 587_Sp 10 21 Ch. 4.3- Fundamentals of calculations Maximum values are used for selecting interrupting devices of adequate short-circuit ratings. Minimum values are used to establish sensitivity of protective relays. Minimum values are sometimes estimated as fractions of maximum values Types of short-circuits Three-phase short circuit is frequently the only one considered since it generally results in maximum value and simplifies calculations. Line-to-line short-circuit currents are approximately 87% of three-phase short-circuit currents. EE 587_Sp 10 22 11 Types of short-circuits…cntd. $ ! $ $ ! $ $ "L K EE 587_Sp 10 23 Types of short-circuits & $ ! 9 ! $ 47 M ! 41 75 4 75 4 4 " "7 45 44 " 7 " 45 44 "5 4 4( " 1 7 15 EE 587_Sp 10 24 12 Basic equivalent circuit ! G * ! ! , =C H 5==I√ (. 5 EE 587_Sp 10 25 Basic equivalent circuit % ' ! $!$ ! ! $ ! ! J $ , 45 . "7 EE 587_Sp 10 26 $ $ !* ! 13 Basic equivalent circuit F , . M 4 ! ! $ ! $ EE 587_Sp 10 27 The differential equation: A - = 2 I 6 + 2 H0 N 6 9 ω 2 6 2 H &2 α 6 6 α I = = α H N, = , & 6 .N & 6 2I 2α α α &6 2I &6 2I $ & 6 +& 6 α . H 0 2N 2 ω ω α N2 N+ & 6 α H0 = 62 2α N +&2 α H 4 = 66 EE 587_Sp 10 28 14 $ &2 α H 4 6 $ = 2I=6 + =α N + H 4 , & 6 . H0 2I 2I=6 + + α H 2I=6 ω ω ω & 6 H2 2I 0I=6 $ &2 H 2 6 0I=6 2I=6 + 8 9 D Hω = EE 587_Sp 10 29 ! E A (t ) = ωL e $ ( R )t L ( R ωL sin ω t − cos ω t ) 2 R ωL + A1 +1 E i (t ) = ωL 1 R 2 ( +1 R ωL sin ωt − cos ωt ) R 2 + A1 e − ( R / L )t ωL ωL +1 EE 587_Sp 10 30 15 Sin φ = 1 R ωL 2 +1 R L Cos φ = ( R / ωL ) R ωL 2 +1 ø L Sin (A –B) = Sin A Cos B - Sin B Cos A EE 587_Sp 10 31 ! iss = E ωL 1 R ωL 2 Sin (ω t − Tan −1ϕ ) +1 + + * . EE 587_Sp 10 32 16 4.4 Restraints of simplified calculations 4.4.1 Impedance elements– Z = R + j (XL-XC) 4.4.2 Switching transients -- I = 4.4.3 Decrement factor 4.4.4 Multiple switching transients 4.4.5 Practical impedance network synthesis 4.4.6 Other analytical tools 4.4.7 Respecting the imposed restraints 4.4.8 Conclusions EE 587_Sp 10 33 E Sin (ω t ) + I dc e( − Rt ) / L jωL 4.4 Restraints of simplified calculations , "& ( ! & ! * 4( K 44 K EE 587_Sp 10 34 .! , ! . 6! $ ! 4 4( 7 / $ < ! 2 ! * 17 4.4 Restraints of simplified calculations /; O $ ! ! EE 587_Sp 10 35 ! 4.4 Restraints of simplified calculations 7. Analysis based on simplified per-phase line-to-neutral balanced system concepts require that: a) The power system components shall be of symmetrical design pattern b) The electric loading imposed on the system shall be balanced and symmetrical. EE 587_Sp 10 36 18 4.4.8 Conclusions ! $ !0 ! ! < < ! + ! & ! ' EE 587_Sp 10 37 EE 587_Sp 10 38 19 4.5 – Detailed Procedure C <, $ & 5& 5&! I# 9% "9 (- ! 9 9B . $ $ EE 587_Sp 10 39 4.5 – Detailed Procedure "9 B actual quantity base quantity per − unit quantity (voltage , current , etc .) = base current (amperes) = base kVA(1000) 3 (base V ) base MVA(106 ) 3 (base V ) base V 3 (base A) = = base kVA 3 (base kV ) base MVA (1000) 3 (base kV ) = = base impedance (ohms) = (base V ) 2 base kVA(1000) = (base kV ) 2 (base kV ) 2 = base kVA base MVA EE 587_Sp 10 40 20 4.5 – Detailed Procedure Step 2: Collect & convert impedance data per − unit impedance Zpu = actual impedance in ohms (base MVA) (base kV) 2 = actual impedance in ohms (base kVA) (base kV) 2 (1000) per − unit reactance (base kVA) kVA rating X pu = EE 587_Sp 10 41 4.6 – Example Case Study & & & ! EE 587_Sp 10 42 21 ...
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This note was uploaded on 02/16/2011 for the course EE 587 taught by Professor Dr.mohammedsafiuddin during the Spring '11 term at SUNY Buffalo.

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