Sähköverkoista

Liittyy generaattoreihin ja tasapainottomiin kolmivaihesähköverkkoihin. Impedanssi on vaihtovirtavastus. Verkko mallinnetaan kolmena erilaisena verkkona riippuen siitä, mitä seikkaa tarkastellaan: Positiivista sekvenssiä, negatiivista sekvenssiä vaiko nollasekvenssiä. Näihin liittyy verkon positiivinen impedanssi, negatiivinen impedanssi ja nollaimpedanssi. Todellisuudessa on vain yksi verkko. Kyseessä on laskennan apuväline.

(Lainaus alku)

Simply said, the three phase unbalanced network must be split into three separate networks, positive sequence network, negative sequence network, and zero sequence network. Furthermore, each network has to be reduced to a Thevenin equivalent circuit, as seen from the location of the fault.

1. Positive sequence impedance is the normal impedance of three phase circuits to the flow of balanced three phase current that is given in the equipment specifications.

2. Negative sequence impedance is the impedance of three phase circuits to the flow of currents whose phasors rotate in the opposite direction. For most equipment the negative sequence impedance is the same as the positive sequence impedance. The exception may be some rotating machines. If the negative sequence impedance differs from the positive sequence impedance, it must be given in the equipment specifications.

3. Zero sequence impedance is different from positive and negative sequence impedances because the zero sequence currents must return to the source through the ground and/or the neutral wire. The exact path of zero sequence current depends on the connection of the equipment and on the current path through the ground.

(Lainaus loppu)