delta is the neutral current in a 3 phase system.
what is the neutral current in a 3 phase system?
delta
in electrical engineering, three-phase electric power systems have at least three conductors carrying alternating current voltages that are offset in time by one-third of the period. a three-phase system may be arranged in delta (∆) or star (y) (also denoted as wye in some areas). a wye system allows the use of two different voltages from all three phases, such as a 230/400 v system which provides 230 v between the neutral (centre hub) and any one of the phases, and 400 v across any two phases. a delta system arrangement only provides one voltage magnitude, but it has a greater redundancy as it may continue to operate normally with one of the three supply windings offline, albeit at 57.7% of total capacity. harmonic current in the neutral may become very large if nonlinear loads are connected.
three-phase
three-phase electrical generation is very common. the simplest way is to use three separate coils in the generator stator, physically offset by an angle of 120° (one-third of a complete 360° phase) to each other. three current waveforms are produced that are equal in magnitude and 120° out of phase to each other. if coils are added opposite to these (60° spacing), they generate the same phases with reverse polarity and so can be simply wired together. in practice, higher "pole orders" are commonly used. for example, a 12-pole machine would have 36 coils (10° spacing). the advantage is that lower rotational speeds can be used to generate the same frequency. for example, a 2-pole machine running at 3600 rpm and a 12-pole machine running at 600 rpm produce the same frequency; the lower speed is preferable for larger machines. if the load on a three-phase system is balanced equally among the phases, no current flows through the neutral point. even in the worst-case unbalanced (linear) load, the neutral current will not exceed the highest of the phase currents. non-linear loads (e.g. the switch-mode power supplies widely used) may require an oversized neutral bus and neutral conductor in the upstream distribution panel to handle harmonics. harmonics can cause neutral conductor current levels to exceed that of one or all phase conductors.
alternating current