T&D Question: Grid - Voltage & Frequency Regulation
T&D Question: Grid - Voltage & Frequency Regulation
(OP)
New to forum; M.E. migrating to T&D role in ESCO. Having difficulty understanding Frequency and Voltage relationships in grid and ultimately for qualifying and registering assets for Reserves and Regulation programs. From M.E. perspective - Voltage = Pressure; Current = Flow; Resistance = Pipe Losses.....so, what is Mechanical Equivalent of Frequency? Why does Grid need frequency stabilization when demand fluctuates -- Isn't all power generated at 60Hz continuously as a function of basic 3-phase relationships and rotor/stator construction? Why won't electric generators with governors regulate frequency of grid correctly and keep frequency stable, then you would only have voltage (pressure) fluctuations when demand inc or decr, no? So, isn't grid stability ultimately one of voltage stabilization and not frequency stabilization? Help me understand the difference and / or relationship. Any good explanations / articles / diagrams would be helpful and appreciated.






RE: T&D Question: Grid - Voltage & Frequency Regulation
Frequency instability can occur when the load suddenly increases or decreases. The prime mover for a generator cannot respond instantly and the frequency will increase if the load suddenly drops and vice versa. Think of pushing in the clutch on your car while climbing a hill with your foot on the gas. The load on the engine disappears and until you can reduce the throttle, the rpms will go up.
RE: T&D Question: Grid - Voltage & Frequency Regulation
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: T&D Question: Grid - Voltage & Frequency Regulation
Now you can think of many mechanical analogies to electrical synchronization. One of them could be what if the two drives driving a common shaft starts rotating at different speed?
Or saw the movie Speed? If the two bus speed and direction are not exactly the same and physically next to each other, it becomes difficult to trasfer people from one another while still in motion.
Rafiq Bulsara
http://www.srengineersct.com
RE: T&D Question: Grid - Voltage & Frequency Regulation
Rafiq Bulsara
http://www.srengineersct.com
RE: T&D Question: Grid - Voltage & Frequency Regulation
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: T&D Question: Grid - Voltage & Frequency Regulation
RE: T&D Question: Grid - Voltage & Frequency Regulation
The grid acts the same. Load swings tend to try to slow down the drivers that furnish the frequency to the grid on load increases (or speed them up on load loss).
You dump a big enough load on a generator (or a grid full of generators) and it will bog it down just like your engine would if you let out the clutch too quickly. Frequency suffers in the process.
It is a hard thing for ME's (like me) to get our minds around because there is no mechanical analogy to apply to it.
rmw
RE: T&D Question: Grid - Voltage & Frequency Regulation
rjmaurer:
Try this, in response to your second half of the question:
The frequency of a generator is directly related to rpm of the prime mover. n=2f/p where n is in rps and p in no. of poles, which is fixed for a given machine. The change in electrical load, directly affect the rpm of a prime mover which directly affect the frequency of the generator. So is the voltage affected by change in loads.
To take the mechanical analogy further, a simplified grid is analogous to a long rotating shaft driven by several prime movers connected via gear and pinion arrangement along its length. Similarly the load are also connected using other gear and pinions along the shaft. Imagine the challenge of keeping the rpm of the shaft precisely at a fixed number while there are constantly varying loads and quite an array of types and sizes of prime movers and even the fuels. Even the quality of a bad fuel batch could affect the speed of a prime mover.
A weak prime mover will start getting driven by the massive shaft, same as a weak generator end up being driven as a motor (reverse powering). If one resists, something will break. This again simultaneously making sure that shaft does not fall over or sag or sway at any location, this is "loosely" akin to maintaining voltage at the same time.
The above analogy is not a make believe thing, that is how initial workshops used to run, with a steam engine driving a shaft and a number of belt and pulleys off the shaft running different machines.
If you can extend your imagination to visualize the a mesh of flexible rotating shafts, prime movers and loads transferring power over a wide area network, that is what a grid of three phase ac power lines is like. In fact the grid is another expression of a mesh.
Rafiq Bulsara
http://www.srengineersct.com
RE: T&D Question: Grid - Voltage & Frequency Regulation
This forum can't be a substitute for a formal education and experience.
Rafiq Bulsara
http://www.srengineersct.com
RE: T&D Question: Grid - Voltage & Frequency Regulation
Have you ever seen a flyball governor? They were used to control the steam feed to early generating plants. A couple of phrases that originated with the old flyballs are still in use although the origin is probably mostly forgotten.
A flyball governor had a construction similar to an umbrella with only two sets of ribs left. There was a ball on the end of each rib. As the shaft was turned centrifugal force caused the balls to arc out and up. Coarse frequency control was done with the flyball governors. Fine control was by a chronograph and an electric clock. If the clock was getting ahead of the chronograph the flyball governor was set a little slower until the clocks were even. If the clock got far behind, the governor was set faster and the balls rose higher. With the generator running at the maximum allowable overspeed the ribs would be flat out and the balls at the greatest radius of rotation. Hence the phrases, "Balls to the Walls" and "Flat Out".
And by the way, I have set the frequency/speed of a couple of generators by comparing an old synchronous type electric clock and a digital wristwatch. Just a couple of my adventures in the Moskito Coast.
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: T&D Question: Grid - Voltage & Frequency Regulation
http://ww
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: T&D Question: Grid - Voltage & Frequency Regulation
No, I haven't. But thanks for rectifying my distorted image of balls to the walls!
Rafiq Bulsara
http://www.srengineersct.com
RE: T&D Question: Grid - Voltage & Frequency Regulation
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: T&D Question: Grid - Voltage & Frequency Regulation
Sure I'll have many more inquiries of this forum as I am involved in a mid-size CHP project at the moment installed on the Distr side that is expected to participate in Transmission-side programs.....interesting spin on my first project. At the point of understanding just what I don't understand.
RE: T&D Question: Grid - Voltage & Frequency Regulation
http: