HYDEL/Thermal Generator

Sir,

1) which components in Hydel generator makes costlier than thermal generator?

2) How the Speed rise & pressure rise is controlled in Hydel/Thermal Generators when the full Load on the Generator is thrown off? ( during Tripping due to faults)

1) is open ended, you are making the assumption that one is more costly than the other without stating what you are comparing; i.e., are you referring to the electrical generator itself, including the turbine, the BOP (Balance Of Plant), the fuel source, the power transmission equipment, and/or any combination?

2.) Are you questioning if the inertia of the rotating mass somehow causes it to overspeed during a full load rejection? If so then you are under a common misconception since it does not. Think about it, inertia is the physical property that keeps a body in motion, in motion, until it is acted upon by an outside force.

Where does that force come from, certainly not from the rotating mass since it is inert and has no internal source of power. It comes from the inertia of the residual fluid driving the turbine; i.e., what ever water is still in motion in the penstock after the sluice gates slam closed, or whatever steam is still entering the turbine from the steam chest after the emergency stop valves slam shut. All of this presumes that everything is operating properly prior to, during, and after the emergency trip is initiated.

Most people who have never had the chance to analyze, model, witness, or test the multiple systems that go into the overspeed trip mechanisms will immediately respond with "No, can't be, what happens to all that energy stored in the rotor, it HAS to go somewhere and it HAS to go into making it turn faster post-trip..." I know first hand, because that was my exact reaction when I started writing programs (in BASIC!!) for modeling the second and third order dynamic effects.

Here's a mind experiment that may help. Consider a machine that's at synchronous speed just prior to closing the breaker, just enough steam/water is being admitted to overcome friction and windage. What would happen if the valves were closed? Think of the forces acting on the rotating mass, a very small amount of low pressure steam/water just overcoming the rotational losses, take away that pressure and the only force left is friction, and it can only SLOW things down, it's a decelerating force! There is no accelerating force to make it go faster. If you're still troubled by this then take the time to calculate the stored energy in an unloaded vs. fully loaded machine.

So why do machines overspeed? Because somebody, something, or both, screwed up and didn't stop the flow of steam/water. The operator admitted too much steam when the safeties were blocked, the governor wasn't set properly, the emergency stop valves jammed, the clearances weren't checked/set properly, a jumper wasn't removed (happened to me), a relay got stuck, a subsystem was tagged out, the operator had a "heavy" hand, a technician dropped a screwdriver, the backup systems were on the same DC supply as the main systems which happened to fail, etc., etc.

I hope this helped, class dismissed.

1. Start by turning off Caps Lock.
2. A Google search on "inertia GD2" produced 13,000 results in 0.42 seconds, including a methodology for doing it. So, that's probably the next step.