Three-phase,abbreviated 3φ, refers to three voltages or currents that that differ by a third of a cycle, or 120 electrical degrees , from each other. They go through their maxima in a regular order, called the phase sequence. The three phases could be supplied over six wires, with two wires reserved for the exclusive use of each phase. However, they are generally supplied over only three wires, and the phase or line voltages are the voltages between the three possible pairs of wires. The phase or line currents are the currents in each wire. Voltages and currents are usually expressed as rms or effective values, as in single-phase analysis. When you connect a load to the three wires, it should be done in such a way that it does not destroy the symmetry. This means that you need three equal loads connected across the three pairs of wires. This looks like an equilateral triangle, or delta, and is called a delta load. Another symmetrical connection would result if you connected one side of each load together, and then the three other ends to the three wires. This looks like a Y, and is called a wye load. These are the only possibilities for a symmetrical load. The center of the Y connection is, in a way, equidistant from each of the three line voltages, and will remain at a constant potential. It is called the neutral, and may be furnished along with the three phase voltages. The benefits of three-phase are realized best for such a symmetrical connection, which is called balanced. If the load is not balanced, the problem is a complicated one one whose solution gives little insight, just numbers. Such problems are best left to computer circuit analysis. Three-phase systems that are roughly balanced (the practical case) can be analyzed profitably by a method called symmetrical components. Here, let us consider only balanced three-phase circuits, which are the most important anyway. The key to understanding three-phase is to understand the phasor diagram for the voltages or currents. In the diagram at the right, a, b and c represent the three lines, and o represents the neutral. The red phasors are the line or delta voltages, the voltages between the wires. The blue phasors are the wye voltages, the voltages to neutral. They correspond to the two different ways a symmetrical load can be connected. The vectors can be imagined rotating anticlockwise with time with angular velocity ω = 2πf, their projections on the horizontal axis representing the voltages as functions of time. Note how the subscripts on the V's give the points between which the voltage is measured, and the sign of the voltage. Vab is the voltage at point a relative to point b, for example. The same phasor diagram holds for the currents. In this case, the line currents are the blue vectors, and the red vectors are the currents through a delta load. The blue and red vectors differ in phase by 30°, and in magnitude by a factor of √3, as is marked in the diagram. where Vph is the phase voltage. In Y(Star) connected system VLine = √3 VPhase , ILine = IPhase . In Delta connected system VLine = VPhase , ILine = √3 IPhase . The above figure sows the one voltage cycle of a three - phase system .The three colours represent 3 phase voltages displaced by 120 electrical degrees.In the figure Phase 'a' in black , phase 'b' in red ,phase 'c' in blue colour are represented.
Fife comes to South Bay Brokers as a residential home sales
specialist. A third generation native of California, Jenny received
her B.A. from USC. She earned her M.A. in Education from Pepperdine
University where she graduated summa cum laude. She has worked for
major Los Angeles based real estate corporations including Watt
Industries, and Kaufman and Broad Home Corporation.
Jenny offers a superior
level of client service. Jenny's educational background has given
her tremendous support. She believes in educating her clients, which
in turn establishes a level of trust they can count on throughout
their transaction. Her expertise in the development of promotional
and marketing materials has been part of her success for both buyers
and sellers. Jenny's work ethic is unsurpassed. She is focused and
dedicated to getting the job done.
Fife, a third generation California native, received his BA
from USC and his MBA from Pepperdine University where he graduated
magna cum laude. He has worked extensively in real estate development
since receiving his MBA. His expertise is in property/land acquisition,
contract negotiations, development and construction supervision
along with financing of multi-million dollar projects. He has acted
as managing partner in the evaluation and acquisition of investment
properties. His diversity of experience ranges from single family
home to duplexes to four hundred unit complexes. Dave's most recent
position was as Chief Financial Officer for a large Los Angeles
based development firm.
Dave's disposition remains
unpretentious and genuine. His integrity is unparalleled. He is willing
to do whatever it takes to get the job done properly.