Why doesn’t the generator’s speed increase when the steam turbine increases the air intake?

Increasing the steam supply to a turbine when it is operating in parallel only increases the load; the grid frequency remains constant. When the turbine operates alone (without being in parallel), increasing the steam supply merely adjusts its speed. I hope my answer can be of some help to you.

Once the generator is connected to the grid, it becomes fully synchronized with the system, and its frequency remains fixed at that of the system. At this point, adjusting the amount of air intake merely changes the load level, without affecting the speed of the generator; similarly, the speed of the turbine also does not change.

Once the engine is connected to the grid, no active power is outputted, whether under normal excitation or over-excitation conditions. Adjusting the excitation current can only adjust reactive power, not active power. Only by adjusting the torque of the prime mover, that is, by adjusting the amount of air supplied to the turbine or the amount of water supplied to the hydro turbine, can the active power of the engine be regulated. When the engine is over-excited and the torque of the prime mover is increased, the rotor of the engine must accelerate temporarily, causing the magnetic field of the poles to shift forward by a certain angle; as a result, the electromotive force E it generates lags behind the terminal voltage U by the same angle. Under the action of △u, the phase difference between current and voltage in the armature winding is an angle less than 90 degrees. Thus, the generator outputs active power. The armature current, in interaction with the magnetic field, generates a braking torque. When the torque of the prime mover balances the opposing torque, the generator resumes operating stably at synchronous speed.

Once the engine is connected to the grid, no active power is outputted, whether under normal excitation or over-excitation conditions. Adjusting the excitation current can only adjust reactive power, not active power. Only by adjusting the torque of the prime mover, that is, by adjusting the amount of air supplied to the turbine or the amount of water supplied to the hydro turbine, can the active power of the engine be regulated. When the engine is over-excited and the torque of the prime mover is increased, the rotor of the engine must accelerate temporarily, causing the magnetic field of the poles to shift forward by a certain angle; as a result, the electromotive force E it generates lags behind the terminal voltage U by the same angle. Under the action of △u, the phase difference between current and voltage in the armature winding is an angle less than 90 degrees. Thus, the generator outputs active power. The armature current, in interaction with the magnetic field, generates a braking torque. When the torque of the prime mover balances the opposing torque, the generator resumes operating stably at synchronous speed.

It’s possible that the power of your generator has increased. When the generator is operating at its maximum power, the prime mover needs to maintain a certain speed, and of course this requires an increase in air volume. Am I right?

On the one hand, the turbine control system itself includes a speed regulation system; on the other hand, the generator mounted on the same shaft as the turbine is connected to the grid, and the frequency of the system remains constant, which in turn limits the rotational speed. f=np/60, where f is the frequency, n is the speed of the generator, and p is the number of pole pairs in the generator.

Once the generator is connected to the grid, its speed is regulated by the frequency of the larger power grid. Since the capacity of the system is much larger than that of the generator, any increase in air intake by the generator results in a very small change in frequency, which can be ignored. Let’s use an analogy, though it may not be exact. A large cargo ship loaded with sand and stones (the power grid) is pulled by hundreds of porters (generators), each using an elastic rope. Suddenly, one of the pullers exerted more force; the speed of the large ship hardly changed. It was simply because the rope used by that puller became straighter and longer, indicating that the puller had applied more strength. The air intake volume of the generator increases; the frequency remains unchanged, but its power angle increases, similar to a rope being pulled taut by a pole-dancer. When the power angle is positive, that is, when the generator’s angle is ahead of the system’s angle, the generator is in a generating mode. If the power angle is negative, the generator operates in motor mode, absorbing power from the system. It’s similar to when some porters slack off and go behind the cargo ship, with the ship pulling them along using a rope.

The speed of the power generation turbine is rated and cannot be changed arbitrarily; the amount of steam supplied is adjusted depending on the level of power generation load. The generator is driven by the turbine.

The speed of the generator, which is also the power generation frequency, is a dynamic value; however, its range of variation is very small. When the amount of air intake increases, the speed rises and the frequency increases as well, but the generator’s automatic frequency control system adjusts the frequency accordingly. This is a PID closed-loop control system. How is it adjusted? By increasing the excitation current – this current generates a magnetic field that opposes the magnetic field produced by the rotor coils, thereby preventing the rotor from rotating.