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Three-phase alternator principle


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Three-phase alternating current is generated by a three-phase Alternator. Figure 3.1 (a) is a schematic diagram of the principle of a three-phase alternator. It is mainly composed of two parts, the rotating part inside is called the rotor, and the direct current is passed through the coil of the rotor, so that a magnetic field distributed in a sinusoidal manner is generated in the space; Three-phase alternator schematic Figure 3.1 Principle of three-phase alternator (a) Schematic diagram of three-phase alternator; (b) The part of the three-phase electromotive force that is fixed to the outside in the positive direction is called the stator, and three structures are completely embedded in the core slot of the stator. The same coils U1—U2, V1—V2, W1—W2, which are 120° apart from each other in space, are called three-phase stator windings. U1, V1, and W1 are called the beginnings of three windings, U2, V2, and W2. Called the end. When the engine drags the rotor to rotate at an angular velocity ω, the three-phase stator winding cuts the magnetic lines of force to induce an electromotive force. Since the magnetic field is distributed according to the sinusoidal law, the induced electromotive force is a sinusoidal electromotive force, and the three-phase windings have the same structure, the cutting magnetic lines have the same speed, and the positions are mutually different by 120°, so the electromotive force induced by the three-phase windings has the same amplitude and the same frequency. The phases are 120° out of phase. Such a three-phase electromotive force is called a symmetrical three-phase electromotive force, and the direction of each phase electromotive force is directed from the end to the beginning, as shown in Fig. 3.1(b). And with eU as the reference quantity, the instantaneous value expressions of the three electromotive forces are: Three-phase alternator schematic The waveform and phasor diagrams are shown in Figure 3-2. At any instant, the sum of the symmetrical three-phase electromotive forces is zero, ie Three-phase alternator schematic The order in which the three electromotive forces in the three-phase power supply reach the maximum value (or zero value) in sequence is called the phase sequence of the three-phase power source, and the phase sequence of the three-phase power source represented by the equation (3.1) is U-V-W-U, that is, V The phase lags behind the U phase, and the W phase lags behind the V phase, which is called the positive sequence. If the phase sequence is W-V-U-W, it is called reverse order. The general purpose of engineering is positive sequence. The U phase can be arbitrarily assumed, but once the U phase is determined, the V phase is 120° behind the U phase, and the W phase is 120° ahead of the U phase, which is not confusing. In the industry, the three-phase busbars of the alternator lead-out line and the power distribution device are usually coated with yellow, green and red colors to represent the U, V and W three phases.

STC Three Phase Alternator Suppliers
This series generators are to be used in town, countryside, worksites, mountain and pasture as electric power source for lighting purpose, it can also he used as reserved power source for emergent case using. 

The generators are of dripproof with rotary field type and adopt harmonic excitation system, easy operation and maintenance. 
The generators are three-phase, four-wire type, adopting star connection with neutral point. The rated line voltage is 400V, phase voltage 230V, frequency 50Hz. power factor 0.8(lag). We can provide 60Hz and the other voltage's generator according to the customer's request. 
They can be coupled with a prime mover directly or through v-belt making right or reverse continuous rotation at the rated speed. When the rotation speed of prime mover changs 3% or so and load varies in the range of 0~100% cos j 0.8~1.0, the generators offer constant voltage, when sudden change (increase or decrease) of load, the generator will soon return to their normal working state, at the same time, without any starting device the generator can directly start an unloaded squirrel cage induction motor.

Operating Condiyions: 
Under the following environment, The generator could be continuous and rated running: 
1.Above sea level: Not exceed 1000m 
2.Cooling air temperature: 258~313K(-15 oC ~ 40 oC) 

3.Relative air damping: not exceed 90%  

Brush Alternator

Alternator Generator

STC Series Three Phase Alternator, Three Phase Alternator, 3 Phase AC Generator, 3 Phase Generator Alternator