ECE 476 POWER SYSTEM ANALYSIS Lecture 19 Balance

ECE 476 POWER SYSTEM ANALYSIS Lecture 19 Balance Fault Analysis, Symmetrical Components Muhammad Abdul Retha lefte Al-Badri Department of Electrical and Computer Engineering

Announcements l l l Be reading Chapter 8 HW 8 is 7. 6, 7. 13, 7. 19, 7. 28; due Nov 3 in class. Start working on Design Project. Tentatively due Nov 17 in class. 1

In the News • Earlier this week the Illinois House and Senate overrode the Governor’s veto of the Smart Grid Bill; it is now law • • Law authorizes a ten year, $3 billion project to “modernization” the electric grid in Illinois • • On Tuesday Quinn called it a “smart greed” plan All Com. Ed customers and most of Ameren will get “smart” meters Effort will be paid for through rate increases over the period; Com. Ed estimated the average increase of $36 per year would be offset by electricity savings 2

Network Fault Analysis Simplifications l To simplify analysis of fault currents in networks we'll make several simplifications: 1. 2. 3. 4. 5. Transmission lines are represented by their series reactance Transformers are represented by their leakage reactances Synchronous machines are modeled as a constant voltage behind direct-axis subtransient reactance Induction motors are ignored or treated as synchronous machines Other (nonspinning) loads are ignored 3

Network Fault Example For the following network assume a fault on the terminal of the generator; all data is per unit except for the transmission line reactance generator has 1. 05 terminal voltage & supplies 100 MVA with 0. 95 lag pf 4

Network Fault Example, cont'd Faulted network per unit diagram 5

Network Fault Example, cont'd 6

Fault Analysis Solution Techniques l l Circuit models used during the fault allow the network to be represented as a linear circuit There are two main methods for solving for fault currents: 1. 2. Direct method: Use prefault conditions to solve for the internal machine voltages; then apply fault and solve directly Superposition: Fault is represented by two opposing voltage sources; solve system by superposition – first voltage just represents the prefault operating point – second system only has a single voltage source 7

Superposition Approach Faulted Condition Exact Equivalent to Faulted Condition Fault is represented by two equal and opposite voltage sources, each with a magnitude equal to the pre-fault voltage 8