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

2. 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.

3. 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

4. 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

5. 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

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

7. Network Fault Example, cont'd

8. 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

9. 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