# Lagging or leading synchronous generator

• tim9000
In summary, the armature excitation results in the generator being lagging or leading. The direction of the current through the stator/armature inductance determines the VARs.
tim9000
Hi,
It has been a long time since I studied synchronous machines and I am trying to understand the mechanism of how the armature excitation can result in the generator being lagging or leading. So please correct me if I say something like it's axiomatic but its really erroneous.

Now, according to wiki:

"the stator of the machine is connected to a three-phase supply of voltage Vs (assumed to be constant)...the rotor is excited with a DC current (Ie)...The rotating electromagnet induces a three-phase voltage (Vg) in the stator windings...If the machine is considered to be ideal, with no mechanical, magnetic, or electrical losses, its equivalent circuit will be an AC generator in series with the winding inductance (L) of the stator. The magnitude of Vg depends on the excitation current (Ie)...If Ie is critically adjusted to a value Ie0, Vg will be equal and opposite to Vs, and the current in the stator (Is) will be zero...If, Ie is increased above Ie0, Vg will exceed Vs, and the difference is accounted for by a voltage (Vl) appearing across the stator inductance L: Vl = Is x Xl where Xl is the stator reactance. Now the stator current (Is) is no longer zero. Since the machine is ideal, Vg, Vl and Vs will all be in phase, and Is will be entirely reactive (i.e. in phase quadrature). Viewed from the supply side of the machine's terminals, a negative reactive current will flow out of the terminals, and the machine will therefore appear as a capacitor, the magnitude of whose reactance will fall as Ir increases above Is0. If Ie is adjusted to be less than Ie0, Vs will exceed Vg, and a positive reactive current will flow into the machine. The machine will then appear as an inductor whose reactance falls as Ie is reduced further."

So the mechanism underlying this operation is that all current to and from the stator coils passes through (ideally) just an inductor:

So is it just the direction of this current (through the stator/armature inductance) which determines if the VARs is + or - ?

I don't understand how you can have an armature voltage less than the source voltage (as is the case for an under excited generator) and still be pushing current back out onto the bus. Or how if you have an over-excited motor if the armature voltage is induced to be greater than the source voltage, how is any current coming into the stator to keep the rotor spinning?

http://machineryequipmentonline.com...roubleshooting-and-maintenance-0171_thumb.jpg

Thanks

Last edited:

## 1. What is a synchronous generator?

A synchronous generator is a type of electrical machine that converts mechanical energy into electrical energy. It is commonly used in power plants to generate electricity.

## 2. What is the difference between a lagging and leading synchronous generator?

A lagging synchronous generator produces electrical energy that lags behind the mechanical input, while a leading synchronous generator produces electrical energy that leads the mechanical input. This difference is caused by the power factor, which is the ratio of real power to apparent power.

## 3. How does a lagging or leading synchronous generator work?

A synchronous generator works by using a magnetic field and conductors to convert mechanical energy into electrical energy. The magnetic field is created by a rotor, which rotates inside a stator. As the rotor spins, it induces an electrical current in the stator windings, which is then transmitted to a power grid.

## 4. What are the applications of lagging or leading synchronous generators?

Lagging and leading synchronous generators are commonly used in power plants to generate electricity for commercial and residential use. They can also be used in industrial applications, such as powering large machinery and equipment.

## 5. How do you control the power factor of a synchronous generator?

The power factor of a synchronous generator can be controlled by adjusting the excitation of the rotor. This is typically done by using an automatic voltage regulator (AVR) that monitors the voltage and adjusts the excitation as needed to maintain a desired power factor.

• Electrical Engineering
Replies
2
Views
659
• Electrical Engineering
Replies
1
Views
1K
• Electrical Engineering
Replies
37
Views
3K
• Electrical Engineering
Replies
14
Views
3K
• Electrical Engineering
Replies
6
Views
1K
• Electrical Engineering
Replies
5
Views
1K
• Electrical Engineering
Replies
5
Views
2K
• Electrical Engineering
Replies
8
Views
3K
• Electrical Engineering
Replies
5
Views
7K
• Electrical Engineering
Replies
7
Views
942