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Brushless Marine Alternator

The working principle of an alternator is very simple. it's just like a basic principle of DC generator. It also depends upon Faraday's laws of electromagnetic induction which says the current is induced in the conductor inside a magnetic field when there is a relative motion between that conductor and the magnetic field in other words when the conductor cuts magnetic field the emf will be induced.

In a loop of conductor, is rotated in a magnetic field of opposite polarity, the EMF can be measured by a slip rings. Here we need a slip ring and a carbon brush assembly to pick up the power of the rotating parts and hence it needs contact maintenance and the voltage cannot be controlled. we can avoid slip ring by keeping the conductor stationary and rotating the magnet and get the same effect with slip ring assembly.

The brushless self-excited alternator is an advanced version of alternator, where the voltage can be controlled by adjusting the field current in the excited state and also pick up the main power output from the main alternator stator will stop this means the brushless self-excited 3 phase alternator have to generator mounted in the same staff and the main alternative field coil is internally power and control externally by exciter. 

Principle of operation:
Diagram of a simple alternative with a rotating magnetic core (rotor) and a stationary wire (stator) also showing the current induced in the status by the rotating magnetic field of the router. A conductor moving relative to wear magnetic field develops an electromotive force EMF in its Faraday's law this email reverses its polarity when it moves under magnetic poles of opposite polarity typically rotating magnet called the rotor turns within a stationary set of conductor wants in a coil on an iron core called the status the field cuts across the conductors generating an induced EMF electromotive force as the mechanical input causes the router to turn. The rotating magnetic field induces and an AC voltage in the stator windings since the current in the stator winding varies in steps with the position of the rotor an alternator is a synchronous generator.

The Rotor magnetic field may be produced by permanent magnets or by a field coil electromagnetic. Automatic alternators use a rotor winding which allows control of The alternators generated voltage by wearing the current in the rotor field winding is of permanent magnet machines avoid the Lost due to magnetized current in the router but a restricted in size due to the cost of the magnetic materials. Since the magnetic field is constant The Terminal voltage varies directly with the speed of the generator. The brushless AC generator is usually larger than those used in automatic applications.

An automatic voltage-current device controls the field Gun to keep output voltage constant. If the output voltage from the stationary armature calls drops due to an increase in demand, more current is fed into the rotating field call through the voltage regulator or an automatic voltage regulator AVR. This increases the magnetic field around the field called which induces and grid voltage in an armature coil does the output voltage is brought back up to its original value. Often there are three sets of stator windings physically offset so that the rotating magnetic field produces three-phase current displaced by one-third of the period with respect to each other.  

The three-phase brushless alternator construction as shown above for better understanding the right-hand side part in the main alternator and the left-hand side part is exciter attached in the same shaft. The exciter output connects internally to the main alternator field coil through the drive shaft after passing through the rotating diodes. 

The main alternative field is adjusted by the field current from the exciter output to maintain the constant voltage for wearing loads stop the exciter output current/voltage is maintained by the exciter field coil in its stator winding by the AVR automatic voltage regulator we do not measure the exciter output voltage or correct since our interest is to maintain the main alternator output voltage constant for varying load / current the standard form of sine wave seen in excellent scope for a 3 phase alternating supply black red and blue a three-phase respectively at a phase angle of 120 degrees apart. For simple understanding taking only one page to explain the synchronization process with synchroscope meter or lamp methods.

There are other conditions to satisfy are:

  1. Equal voltage: The Terminal voltage of incoming alternator must be equal to the bus power voltage. 
  2. Similar frequency: the frequency of generator voltage must be equal to the frequency of bus bar voltage.
  3.  Phase sequence: the phase sequence of the three phases of alternator must be similar to that of the grade of the busbar.
  4.  Phase angle: the phase angle between the generated voltage and the voltage of the grid must be zero.

In the above lamp method of synchronization know that the lamp connection carefully between the busbar and the incoming generator 

  1. L1 is connected in the same face of red line 
  2. L2 is connected across Yellow and Blue Number
  3. L3 is connected across blue and yellow
With the above connection, the bus bar and incoming alternator are said to be in Phase the lamp L1 must be dark because of the lamp connect in the same face 

At the same time lamp, L2 & L3 are connected across blue and yellow will have maximum potential different and should glow brightly.  

The Lambs are arranged in such a way the direction of rotation indicates clockwise rotation for incoming alternator frequency is higher for the engine to indicate slightly higher frequency of incoming alternator frequency assist in taking small load soon we close the breaker during synchronization and prevent incoming alternator going on reverse power.


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