Sumários
Xfs, phase-phase and phase-phase-ground
28 novembro 2017, 09:30 • Luis Marcelino Ferreira
Review of transformers YD and their connections
Zd as Zsc, Zi as Zd or Zd and phase rotation
Zh as infinite, Zmagnet or Zsc
Examples from the YY connections
YD transformer
The role of neutral impedance in Y
The role of delta
Why homopolar currents flow freely in delta
Delta is a short circuit for homopolar system
Delta blocks homopolar currents
Delta helps balance disequilibrium or unbalances of secondary Ys
The grounding transformer or zigzag transformer
Description, how it works, symbol
How zigzag is a very high impedance for direct and inverse systems
How zigzag is a very low impedance for homopolar systems
Zigzag not as a power transformer
Phase-phase fault: Ia=0
Why this choice
Id+Ii+Ih=0, Vd=Vi, Ih=0, Vh undefined (later to be verified to be null, as Vb=Vc=-1/2Va)
Overall circuit (two in parallel, one out)
Phase-phase-ground fault: Ia=0
Id+Ii+Ih=0, Vd=Vi=Vh
Overall circuit (three in parallel, duality from single phase to ground fault)
Formulas and how to apply the results obtainedModels and parameters for network components
23 novembro 2017, 11:00 • Luis Marcelino Ferreira
Review of concepts of symmetrical components
Generator models and parameters: Z, Zd, Zi, Zh, E’, E”
Transmission line models (Carson’s formulas for Zd and Zh)
Transformer models: Zd and Zcc
Zi and YD winding systems
Zh and the importance of neutral connection in Y windings
YY and YD