Alternatorexcitation

TYPES OF EXCITATION

IN ALTERNATOR

A SEMINAR ON

Submitted by:Ranjan naikB.Tech EERoll no:8EE78

Submitted to:Mr.Pankaj TripathiMrs. Deepika chauhan

The functions of an excitation system are to provide direct current to the synchronous generator field

winding to perform control and protective functions essential to the

satisfactory operation of the power system Should be reliable and faster

Functions of Excitation Systems

Elements of an Excitation System

Types of Excitation Systems

Classified into following categories :• DC excitation systems• AC excitation systems• Static excitation systems• Brushless excitation

DC Excitation Systems:

• utilize dc generators as source of power; driven by a motor or the shaft of main generator; self or separately excited

• represent early systems (1920s to 1960s); lost favor in the mid-1960s because of large size; superseded by ac exciters

• slow response. • Normally for 10 MVA synchronous generator, the exciter

power rating should be 20 to 35 KW for which we require huge the DC generator

AC Excitation Systems:

• use ac machines (alternators) as source of power• usually, the exciter is on the same shaft as the turbine-

generator• the ac output of exciter is rectified by either controlled or

non-controlled rectifiers• rectifiers may be stationary or rotating• early systems used a combination of magnetic and rotating

amplifiers as regulators; most new systems use electronic amplifier regulators

FIG. AC EXCITATION SYSTEM

STATIC EXCITATION

• portion of the AC from each phase of synchronous generator output is fed back to the field windings, as DC excitations, through a system of transformers, rectifiers, and reactors.

• external source of DC is necessary for initial excitation of the field windings.

BATTERIESFIELD WDG OF ALT.

RECTIFIER DC VOLTAGE

BRUSHLESS AC EXCITATION SYSTEMS

Old type AC excitation system has been replaced by brushless AC excitation system

Contains no brushes, no slip rings but required rotating armature type alternators with PMG

inverted alternator (with field at the stator provided by PMG and armature at the rotor) is used as exciter.

Rectifiers mounted on same shaft Dc o/p is given to alternator field wdg

(PMG)PILOT EXCITER

MAIN EXCITER

RECTIFIER

ROTATINGFIELD

ARMATURE ROT.FIELD STAT.FIELD (PM)ROT

ARMATURE STAT.

ALTERNATORFIELD

FIG. BRUSHLESS AC EXCITATION SYSTEM

It is to be noted that error voltage e = |V|ref - |V|causes increased values of vR, ie, vf and if raising the magnitude of the generator emf and hence the terminal voltage

Mathematical modeling of the exciter:

EXCITER MODELING

If Re and Le represent respectively the resistance and inductance of the exciter field, then

Modeling of the exciter field.

Block diagram representation of comparator, amplifier and exciter

The time constants TA will be in the range of 0.02 – 0.1 sec. while Te will be in the range of 0.5 – 1.0 sec.

CONLUSION

Iwould like to conclude that a seminar presentation has allowed as an

opportunity to get and acquire the knowledge of practical implements of theoretical fundamentals.

It also helps to understand how the generators works .

Such seminar are very useful and may be continued in future to update technological knowledge.

ANY QUERIES ?