balanced fault analysis 1
DESCRIPTION
Fault calculationsTRANSCRIPT
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EE 434 POWER SYSTEM PROTECTIONLECTURE 3: BALANCE FAULT ANALYSIS (1)
Ernesto Vazquez‐Martinez, ECERF
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Power system faults
Short circuits:
Single‐line‐ground (unbalance).
Double‐line‐ground (unbalance).
Line‐line (unbalance).
Three‐phase (balance).
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Network fault analysis simplifications (1) Transformers are represented by their leakage reactances.
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Network fault analysis simplifications (2) Transmission lines are represented by their series reactance.
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Network fault analysis simplifications (3) Synchronous machines are modeled as a constant voltage behind direct‐axis subtransient reactance.
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Network fault analysis simplifications (4) Other (nonspinning) loads are ignored.
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Network fault analysis simplifications (5) Induction motors are ignored or treated as synchronous machines (small motors rated less than 50 hp).
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Network fault example: three‐phase short circuit at bus 1
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Network fault example: three‐phase short circuit at bus 1
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Network fault example: three‐phase short circuit at bus 1
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Network fault example: three‐phase short circuit at bus 1
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Network fault example: three‐phase short circuit at bus 1
Review the example 7.3 from text book.
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Fault analysis solutiontechniques 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.
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Complex power system
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Fault current calculations
Create a per‐phase per‐unit equivalent circuit of the power system using either subtransientreactances (if subtransient currents are needed) or transient reactances (if transient currents are needed).
Add a short circuit between one node of the equivalent circuit and the neutral and calculate the current flow through that short by standard analysis: This approach always works but can get complex while
dealing with complex systems. Therefore, a nodal analysis technique will be used.
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Nodal analysis (example)
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Nodal analysis
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Nodal analysis
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Nodal analysis
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Nodal analysis
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Nodal analysis
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Nodal analysis
For inspection:
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EE 434 POWER SYSTEM PROTECTIONLECTURE 3: BALANCE FAULT ANALYSIS (1)
Ernesto Vazquez‐Martinez, ECERF