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In a three-phase system, at least two transducers are required to measure power when there is no neutral, or three transducers when there is a neutral. [5] Blondel's theorem states that the number of measurement elements required is one less than the number of current-carrying conductors.
Set of three unbalanced phasors, and the necessary symmetrical components that sum up to the resulting plot at the bottom. In 1918 Charles Legeyt Fortescue presented a paper [4] which demonstrated that any set of N unbalanced phasors (that is, any such polyphase signal) could be expressed as the sum of N symmetrical sets of balanced phasors, for values of N that are prime.
An important class of three-phase load is the electric motor. A three-phase induction motor has a simple design, inherently high starting torque and high efficiency. Such motors are applied in industry for many applications. A three-phase motor is more compact and less costly than a single-phase motor of the same voltage class and rating, and ...
Two-phase motors draw constant power, just as three-phase motors do, so a balanced two-phase load is converted to a balanced three-phase load. However if a two-phase load is not balanced (more power drawn from one phase than the other), no arrangement of transformers (including the Scott-T transformers) can restore balance: Unbalanced current ...
For example, in order to match an inductive load into a real impedance, a capacitor needs to be used. If the load impedance becomes capacitive, the matching element must be replaced by an inductor. In many cases, there is a need to use the same circuit to match a broad range of load impedance and thus simplify the circuit design.
The development of CPC-based power theory by Leszek S. Czarnecki was initiated in 1983 when he challenged the correctness of existing power theories as applied to single-phase linear, time-invariant (LTI) loads with nonsinusoidal voltage, and next, he revealed the existence of a scattered current, and invented a method of reactance compensation.
Similarly, an unbalanced load may occur if one line is consistently closest to the ground and operates at a lower impedance. Because of this phenomenon, conductors must be periodically transposed along the line so that each phase sees equal time in each relative position to balance out the mutual inductance seen by all three phases.
A semi-flexible tower is designed so that it can use overhead grounding wires to transfer mechanical load to adjacent structures, if a phase conductor breaks and the structure is subject to unbalanced loads. This type is useful at extra-high voltages, where phase conductors are bundled (two or more wires per phase).