Hello everybody!

I have read many posts here about how to increase the power of a synchronous generator without affecting either frequency or voltage. Most people write that it takes place by changing the torque and thus the amps. But how can one increase the amps while keeping the voltage constant? According to ohm's law, shouldn't the voltage increase in proportion to the amperes when the resistance is constant? Is there anyone who can explain to me what I am misunderstanding? I need to use it for a project about synchronous generators.

Best regards

 

There are counter-emf's and back-emf's and armature reactions and all sorts of things that go on inside a synchronous generator. There are all manner of textbooks and references and YouTube videos all about this very thing; some are videos of university lectures, even.

A synchronous generator has an excitation system--an exciter. Some refer to it as an Automatic Voltage Regulator, or AVR. It is the duty of the exciter/AVR to control the excitation to maintain the generator terminal voltage, though generator terminal voltage can also be used to control VArs (Volt-Amperes, Reactive) and Power Factor.

But, to increase the amperes produced by a synchronous generator it is necessary to increase the torque being applied to the generator rotor from the prime mover. There's no other way. Those amperes (at some voltage, usually a very constant voltage) are then transmitted via wires to loads some distance away from the location of the generator and its prime mover. And, if the loads are motors, the motors then convert those amperes into torque to do useful work. (Televisions and computers and computers monitors and lights and tea kettles are also forms of "work", though that can often be a subject for discussion, eh?) Electricity is all about producing power in one area, and then transmitting that power over long distances to areas where it's needed using wires, where it is converted back into "useful" work. The same could be done with long shafts and pulleys, but wires are much easier to run and to maintain (until they start wildfires because the utility didn't trim the brush/trees beneath them).

 

Hello everybody!

I have read many posts here about how to increase the power of a synchronous generator without affecting either frequency or voltage. [...]

Best regards

Hi, ChristianFM97!

You can increase the amps if the additional heat can be properly removed from the generator. The extra amps means additional braking torque from the part of the generator, so a decrease in frequency if the active/motor torque of the turbine will remain the same. In order to maintain the right frequency (after all it is a synchronous generator), we need to balance the two above mention torques: braking and motor. This balance is obtained by increasing the active power of the turbine, usually a hydraulic turbine, by feeding it with a larger flow of water or by raising the head of the turbine.

Actually you need a new unit (generator and turbine)...

 

Hello everybody!

I have read many posts here about how to increase the power of a synchronous generator without affecting either frequency or voltage. Most people write that it takes place by changing the torque and thus the amps. But how can one increase the amps while keeping the voltage constant? According to ohm's law, shouldn't the voltage increase in proportion to the amperes when the resistance is constant? Is there anyone who can explain to me what I am misunderstanding? I need to use it for a project about synchronous generators.

Best regards

For a generator connected to grid (much more power than generator), frequency is defined by grid.
Simplified, there is an internal induced voltage (Es) that is coupled to terminal voltage (Vt) by stator reactance.
Value of Es is determined by rotor field and rotor speed.
Value of Vt is imposed by grid (marginaly 5-7%, may be changed by generator when is under / over excitied - when used to import/export reactive power only - in this regim generator is named synchronous compensator - used for reactive power only).
To supply active power to grid, need that mechanical energy to be converted in electrical energy and "pushed" in grid.
To do this, need that Es to lead Vt by some angle - this is power angle (delta).
If delta is zero - no active power is pushed to grid... and sure, no torque is requested from prime mover (just torque to spin and keep rotor at requested speed).
So, when increase speed of prime mover (turbine/etc), Es will lead Vt and a current Is will flow in circuit.
Es leading Vt mean that instantaneous value of Es is greater that Vt - so current Is will be injected in grid and active power sqrt(3)*Vt*Is*cos(fi) too.
More increase in delta angle mean more torque needed (more energy from prime mover) and Es will increase with respect to Vs (that is constant), so a higher Is will be in circuit - so more power injected in grid.
Theoretical limit for delta is 90 degree, after that generator may loss synchronism with grid.