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 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.

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 On Tuesday Quinn called it a “smart greed” plan Law authorizes a ten year, $3 billion project to “modernization” the electric grid in Illinois All ComEd customers and most of Ameren will get “smart” meters Effort will be paid for through rate increases over the period; ComEd estimated the average increase of $36 per year would be offset by electricity savings

Network Fault Analysis Simplifications To simplify analysis of fault currents in networks we'll make several simplifications: 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

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

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

Network Fault Example, cont'd

Fault Analysis Solution Techniques 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: 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

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