ABSTRACT
In most cases per unit values are used and a common base in practice is 100 megavolt-ampere at the particular system kilovolt. For three-phase electric power systems there are three distinct sets of symmetrical components: positive, negative, and zero sequence for both currents and voltages. The sequence quantities are always line to neutral or line to ground, as appropriate. This is an exception to the general power system practice of using line-to-line voltages. It is very important to remember that throughout the sequence networks, all voltages are line to neutral. Generators and synchronous motors that can continue to contribute power to the unbalance must be included in the positive -sequence networks. The voltage drops in the three-sequence networks are always line-to-neutral or line-to-ground voltage drops. The negative- and zero-sequence networks can be reduced in a manner similar to a single impedance or reactance value to a fault point and with appropriate distribution factors.
