What Is Pilot Exciter

What are the uses of an exciter model?

It has only one use: modeling excitement. Serially, what kind of excitement are you talking about?

What is the purpose of exciter in generator?

Alternators need DC excitation at the rotor to create rotating magnetic field. DC power→ electromagnets→ Rotation → Rotating Magnetic field.Working exciter is known as the primary source of DC power for rotor excitation.In this answer, i have discussed various excitation schemes. Here i have refered main exciter is refered to as working exciter.There are 3 ways to excite the rotor of an AlternatorBy using DC Generator2. Staic Excitation3.Brushless Excitation1st and the 3rd have a dedicated main exciter machine.The 2nd one has a power electronic based system to power the rotor. In order for the excitation system to work, both the pilot exciter and the main exciter have to work. There is no choice.In the 1st scheme of excitation, we have a pilot exciter and a main exciter coupled to the Alternator . Pilot exciter is a DC Shunt generator which feeds the field winding of the main generator.The main exciter is a DC Separately excited generator which is used to excite the rotor winding.The second scheme has the output of Alternator tapped to a Thyristorised converter through a transformer to achieve DC excitation. For initial excitation a battery bank is used and when sufficient output voltage is achieved, the Thyristor converter is used to provide excitation to the alternator.In the third scheme, we again have a pilot exciter and a main exciter and coupled to the alternator. The pilot exciter is a permanant magnet alternator which gives out single phase AC. This is rectified using a controller.This DC output is given to the field of the main exciter whose armature is on its rotor. Output is AC on its rotor and is converted to DC using a diode wheel which is mounted on the alternator shaft and this DC power is provided to the rotor of the Alternator.With this Answer, i hope your concept of Working exciter is clear.

How does self excited generator starts?

Generators have to have prime movers: i.e. an engine, wind turbine, water wheel etc to rotate them. You don’t get something for nothing. A generator is an energy CONVERTER, it converts mechanical energy to electrical energy. So, when you ask how does a self excited generator start, I assume you mean produce electricity after its already being rotated with a prime mover. That being the case, one way is that a self excited generator has enough residual magnetism in its field windings which is of sufficient magnitude to build more magnetism and bring the output voltage to its rated value. Another way is if a generator has permanent magnet field windings which, by definition provide enough magnetism to excite the generator. Still another way (usually in larger generators) is to have incorporated on the field windings shaft a SEPARATE additional winding which generates AC voltage, WITH an incorporatedbridge rectifier which rectifies the AC output of the excitation winding to DC. (This arrangement is similar to a car alternator except the output of an alternator goes through a bridge rectifier and DC output terminals to the battery of the car. )The voltage regulator then regulates the exciter windings output to the rotating field windings for sufficient strength to have the output of the generator produce the desired voltage. Note: The entire exciter winding is on the same shaft as the main field winding, thus eliminating the need for slip rings and brushes. Thus becoming a brush less generator.