The decrease in terminal voltage of a separately excited generator can be attributed to several factors, including increased load demand, which causes a drop in output voltage due to the internal resistance of the generator. Additionally, losses such as copper losses (I²R losses) in the armature and excitation system, as well as core losses, can contribute to a reduction in voltage. Another factor could be a decrease in the excitation current, which reduces the magnetic field strength and subsequently lowers the generated voltage. Lastly, any faults or issues in the electrical connections or components can also lead to decreased terminal voltage.
You have a seperately excited generator and then you have a shunt generator which has the field winding in parallel with the armature terminals. In DC machines a separately excited generator could be run as a shunt generator provided the field winding is designed to work on the generated voltage. A separately excited alternator needs a DC supply for the field winding. In car alternators that is taken from the main winding via a rectifier and a voltage regulator.
Some generators are self excited; this means their terminal voltage is fed back to the excitation system to supply power to the rotor of the generator (which makes it into an electromagnet); the more power that is fed back, the stronger the electromagnet becomes, which makes it harder to turn the generator, which causes the generator to push out more power (simplified, really quick version). If there is a fault electrically near the terminal of a self excited generator, the terminal voltage will sage to near zero; this means the voltage supplied to the excitation system will drop by the same percentage (say the terminal voltage is 30% of what it should be, then the maximum supplied voltage to the excitation system drops to 30% of what it normally is, since P = V*I). Since the input power is less, the output of the generator will decrease (current will decrease). The terminal voltage is determined by the impedance between the generator and the fault such that V = I*Z; As I decreases, V will also continue to fall, causing the terminal voltage to sag even more. A non-self excited generator gets its' excitation power from the grid, specifically from a location that is electrically separated from its' terminal voltage. If the terminal voltage sagged to 30% (same fault location as above example), the excitation system voltage may be impacted slightly (say 2%) so the excitation system power is near maximum (98% for this example). Since the excitation system is much farther removed from the terminal voltage, it is not dependent upon it, thus the terminal voltage will not continue to sag as with a self excited system.
there are 2 different types f excitation 1 seperately excited 2 self excited
The armature resistance of a shunt excited DC generator is calculated using the formula ( R_a = \frac{V - E}{I_a} ), where ( R_a ) is the armature resistance, ( V ) is the terminal voltage, ( E ) is the generated EMF (electromotive force), and ( I_a ) is the armature current. The difference between the terminal voltage and the generated EMF accounts for the voltage drop across the armature resistance due to the current flowing through it.
Voltage regulation of a separately excited generator is generally better than that of a shunt excited generator because it allows for independent control of the excitation level. In a separately excited generator, the excitation current can be adjusted without being influenced by the load current, leading to more stable output voltage under varying load conditions. In contrast, a shunt excited generator's field winding is connected in parallel with the load, making voltage regulation more susceptible to changes in load, which can lead to voltage fluctuations. Thus, the separate excitation enhances performance in terms of maintaining a constant voltage.
Excitation is the phenomenon by which you control the excitation of field winding of a generator. In DC generator field winding is placed on stator and this field winding can be self excited or seperately excited depending upon the type on generator used. AC generators can also be self excited or seperately excited type but field winding is placed on rotor nad armature winding on stator.
When reverse the direction of a seperately excited DC generator,only polarities has been reversed,i.e., (+) becomes (-) and (-) become (+).
The difference between a separately excited DC generator and a Shunt DC generator is that for a separately excited Dc generator , the excitation field winding is supplied by an external source different from that supplying the armature while for shunt generator, the excitation field windind is connected in series with the armature and supplied by a single source.
You have a seperately excited generator and then you have a shunt generator which has the field winding in parallel with the armature terminals. In DC machines a separately excited generator could be run as a shunt generator provided the field winding is designed to work on the generated voltage. A separately excited alternator needs a DC supply for the field winding. In car alternators that is taken from the main winding via a rectifier and a voltage regulator.
Some generators are self excited; this means their terminal voltage is fed back to the excitation system to supply power to the rotor of the generator (which makes it into an electromagnet); the more power that is fed back, the stronger the electromagnet becomes, which makes it harder to turn the generator, which causes the generator to push out more power (simplified, really quick version). If there is a fault electrically near the terminal of a self excited generator, the terminal voltage will sage to near zero; this means the voltage supplied to the excitation system will drop by the same percentage (say the terminal voltage is 30% of what it should be, then the maximum supplied voltage to the excitation system drops to 30% of what it normally is, since P = V*I). Since the input power is less, the output of the generator will decrease (current will decrease). The terminal voltage is determined by the impedance between the generator and the fault such that V = I*Z; As I decreases, V will also continue to fall, causing the terminal voltage to sag even more. A non-self excited generator gets its' excitation power from the grid, specifically from a location that is electrically separated from its' terminal voltage. If the terminal voltage sagged to 30% (same fault location as above example), the excitation system voltage may be impacted slightly (say 2%) so the excitation system power is near maximum (98% for this example). Since the excitation system is much farther removed from the terminal voltage, it is not dependent upon it, thus the terminal voltage will not continue to sag as with a self excited system.
when the current is passing through the winding then it is called "Excitation". Types of excitation (1)seperately excited generator. (2)self excited generator. self generator is classified into 3 types. 1.shunt generator. 2.series generator. 3.compound generator. compoud generator is again classified into 2 types. 1.short shunt generator. 2.long shunt generator.
when the current is passing through the winding then it is called "Excitation". Types of excitation (1)seperately excited generator. (2)self excited generator. self generator is classified into 3 types. 1.shunt generator. 2.series generator. 3.compound generator. compoud generator is again classified into 2 types. 1.short shunt generator. 2.long shunt generator.
There are 2 major forms of generators. one is a synchronous generator that converts mechanical power to ac power. the other is a dc generator. there are 5 basic categories of a dc generator: 1)seperately excited generator 2)shunt generator 3)series generator 4)cumulatively compounded generator 5)differentially compounded generator
There are 2 major forms of generators. one is a synchronous generator that converts mechanical power to ac power. the other is a dc generator. there are 5 basic categories of a dc generator: 1)seperately excited generator 2)shunt generator 3)series generator 4)cumulatively compounded generator 5)differentially compounded generator
the rotating will chang.but if you chang terminal connection nothing wont happen.
There are two types me dc generator 1 separately excited dc generator 2 self excited dc generator
in a separately excited generator the field coils are excited from a separate source like a dc battery may be or any other small generator. They are self starting generators.