balanced fault analysis 1
DESCRIPTION
Fault calculationsTRANSCRIPT
EE 434 POWER SYSTEM PROTECTIONLECTURE 3: BALANCE FAULT ANALYSIS (1)
Ernesto Vazquez‐Martinez, ECERF
Power system faults
Short circuits:
Single‐line‐ground (unbalance).
Double‐line‐ground (unbalance).
Line‐line (unbalance).
Three‐phase (balance).
Network fault analysis simplifications (1) Transformers are represented by their leakage reactances.
Network fault analysis simplifications (2) Transmission lines are represented by their series reactance.
Network fault analysis simplifications (3) Synchronous machines are modeled as a constant voltage behind direct‐axis subtransient reactance.
Network fault analysis simplifications (4) Other (nonspinning) loads are ignored.
Network fault analysis simplifications (5) Induction motors are ignored or treated as synchronous machines (small motors rated less than 50 hp).
Network fault example: three‐phase short circuit at bus 1
Network fault example: three‐phase short circuit at bus 1
Network fault example: three‐phase short circuit at bus 1
Network fault example: three‐phase short circuit at bus 1
Network fault example: three‐phase short circuit at bus 1
Review the example 7.3 from text book.
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.
Complex power system
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.
Nodal analysis (example)
Nodal analysis
Nodal analysis
Nodal analysis
Nodal analysis
Nodal analysis
Nodal analysis
For inspection:
EE 434 POWER SYSTEM PROTECTIONLECTURE 3: BALANCE FAULT ANALYSIS (1)
Ernesto Vazquez‐Martinez, ECERF