Generator Operation

J

Thread Starter

jack

Can we adjust the flow rate to turbine such that generator can produce any amount of power (0 to its rated value). I read in some books that if the generator is in operation (connected to the grid or any local network), there should be a minimum amount of load on the generator why?

What actually mean by prohibited zone of operation of turbine generator set? Will each T-G set (in general) has the prohibited operating zones or it applicable to certain types of designs?

Whats mean by ramp rates and valve point effect and how they affects the generator real power output?
 
jack,

You're on the right track. Generators are devices for converting torque into amperes (and electric motors are devices for converting amperes back into torque!). Vary the torque produced by the prime mover driving the generator (a turbine or a reciprocating engine) and the amperes flowing out of the generator will vary.

Some prime movers have operating "restrictions." Some steam turbines, for example, can't run in certain regions because steam will condense in the turbine before it reaches the condenser--which can cause serious damage to the turbine blades and nozzles and packing. Some gas turbines have low-emissions combustion systems which will emit high pollutant levels if operated in certain regions.

It's not usually the generator that dictates operating restrictions--but the prime mover, or the flow-control valves or components of the prime mover that force operating restrictions on the generator-set. Generators are relatively "benign" and not very smart--they will produce amperes based on how much torque is provided to them--generators will produce amperes as long as there is torque being applied, whether it's 0% of torque, or 3% or 37% or even 112.367% or any value of torque. Generators just convert torque into amperes. So if there's something about the way the prime mover driving the generator (providing the torque to the generator) that precludes operating in certain regions (torque outputs) then the generator-<b>set</b> output will also be restricted.

Does this help?
 
P
Yes, adjusting the flow rate is done through controlled opening or closing of main steam valves and that is generally done by governor
Minimum loading is required because

1) below a certain amount of steam intake,the cooling effect provided by steam in Lp and Ip turbine exhaust stages are reduced. So hotspots may be created if operation is continued above some duration.

2) There is problem of flame stability in furnace below a certain load.

i think the prohibited zone of TG sets is set by frequency and prime mover considerations. Below and above certain frequency (speed), the turbine blade may incur damage and above a certain prime mover output. the heating losses will be quite high in prime mover.

Ramp rate means the maximum rate at which a generator can load or increase its output after synchronizing. Every generator has some generation rate limit due to differential stress developed in turbine and boiler metal parts as a result of rapid increase in steam temperature and pressure with increased loading rate.

i dunno about valve point effect. may be somebody else can enlighten us regarding the issue. i myself am new to this site and was searching for a topic of this nature to initiate conversation.
 
Thanks CSA..

It really helped to get some intuition about these terms. As an electrical engineer, I come across these terms when I was studying power engineering course in my bachelor as well as in masters. I asked many teachers but every body has the same way of mathematical explanation, which does not give any true feeling or intuition about the concepts, I think. I read many publications but the same story repeats everywhere, most of this research is publication oriented research instead of requirement oriented research.

It would be very great if you explain these terms and their ranges in specific to any T-G set (of a particular company with particular rating). I love the feeling of matching our technical intuition with practicality and finally with mathematical proof, and most of your posts especially related to electrical part were on this track. Eager to see you many more answers from you.
 
jack,

Unfortunately a couple of the more specific questions you asked I'm not that familiar with as most of my experience is with GE-design heavy duty gas turbines and generators. While a lot of the basic principles of electric power generation are all the same--supply sufficient torque to a generator and the generator will convert that torque to amperes--the specifics of many prime movers (steam turbines; reciprocating engines; gas turbines; etc.) are all different. To make matters worse, many manufacturers and packagers of generator sets (prime movers and generators) use different terminology to describe the same function or principle (ain't the English language wonderful?!?!?!) and so sometimes two people can be talking about the same thing--arguing, in fact--without even knowing it.

It's really hard to be so specific for so many types of prime movers. I have worked at thermal power plants with 600 MW steam turbines that could not be operated below 200 MW because the flow of steam through the turbine was insufficient to cool (yes--cool!) the turbine. When being started and loaded, it was very important to get the unit loaded as quickly as possible (while observing the standard precautions for long rotor and differential expansion) and get above 200 MW. And when shutting down, the generator breaker was actually opened when load got below 200 MW (and the steam inlet stop valves were shut).

Some gas turbines with newer low emissions combustion systems can't be operated at or below some load because of the inability to maintain emissions below legal permitted values (which just frustrates the HECK out of some owners and plant managers when they learn of these restrictions--which many older gas turbines didn't have). In some cases, it's not that the unit can't be operated at some loads--it's that the emissions or some other parameter can't be maintained at some load (load range). So, it's not an equipment restriction, per se, it's an "output" (emissions) restriction.

Without having specifics it's very difficult to respond generally.

If you have specific questions about specific equipments--we can try to answer them here. Just be aware that while we have a lot of people reading and responding to these posts, the power generation community here at control.com isn't very large and has mostly been focused on GE-design heavy duty gas turbines and generators. And, this is control.com, though we sometimes answer a lot of some people (okay; many) consider to be too many technical questions, a lot of control systems include mechanical components (a fact too many people fail to recognize or understand in many industries).

Have you used the control.com 'Search' feature? It's very useful. Also, clicking on a poster's name will show you their posts (or replies, as the case may be). The 'Search' feature, while not intuitive, is helpful (HINT: use the Search Help before using Search).

Welcome!
 
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