Effects and Impact of Cyclic operation on 700MW Generators
Effects and Impact of Cyclic operation on 700MW Generators
(OP)
Hi all,
Our power plant was initially designed for base load operation but due to some reason we were then required to change operating regime to two shifting (cyclic operation). This meant increased barring hours, increased number of stop starts which had bad impact to our rotors and all rotor were rewound after reaching certain allowable starts and during inspection i have seen lots of defects on rotor windings, associated insulation, overhangs, cracking of connectors and D-leads the list is endless. However i am now doing a reaserch on the effect of cyclic operation on the stators. I have searched for related report from other contries to see if there was a stator failure due to excessive cyclic operation.
Any other information or comments will help as i must compile a risk assesment to address impact of extending generator outages. Our generators are water cooled(copper windings)and hydrogen cooled( rotor and core).
Thanks,
Our power plant was initially designed for base load operation but due to some reason we were then required to change operating regime to two shifting (cyclic operation). This meant increased barring hours, increased number of stop starts which had bad impact to our rotors and all rotor were rewound after reaching certain allowable starts and during inspection i have seen lots of defects on rotor windings, associated insulation, overhangs, cracking of connectors and D-leads the list is endless. However i am now doing a reaserch on the effect of cyclic operation on the stators. I have searched for related report from other contries to see if there was a stator failure due to excessive cyclic operation.
Any other information or comments will help as i must compile a risk assesment to address impact of extending generator outages. Our generators are water cooled(copper windings)and hydrogen cooled( rotor and core).
Thanks,






RE: Effects and Impact of Cyclic operation on 700MW Generators
Water cooled stator windings are running at about 35 to 40 degrees centigrade at the inlet portion of the cooling circuits (stator bars). The outlet temperatures at the end of the cooling circuits (stator bars) reach only 60 to 70 degrees centigrade (at full load). Thermal expansion matters are therefore of less importance, compared with the rotor windings. Because of the low temperature level, thermal degradion of stator bar insulation is negligible.
Regards
Wolf
WWW.HYDROPOWER-CONSULT.COM
RE: Effects and Impact of Cyclic operation on 700MW Generators
for the stator, the inspection of blocking and wrapping of end turns and lead extensions should be increased do phasing in stresses. again operations guide lines for angle and potential mismatch during phasing should be stricter.
RE: Effects and Impact of Cyclic operation on 700MW Generators
The best solution may not be just an engineering solution but a compromise of engineering, economic and political considerations.
Bill
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"Why not the best?"
Jimmy Carter
RE: Effects and Impact of Cyclic operation on 700MW Generators
10% output is likely at or below the minimum stable loading - on a steam set you get into all sorts of prime mover problems at low loads, the most onerous being if water starts to condense in the final LP turbine stages. It gets expensive real quick.
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If we learn from our mistakes I'm getting a great education!
RE: Effects and Impact of Cyclic operation on 700MW Generators
Thanks.
Bill
Bill
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"Why not the best?"
Jimmy Carter
RE: Effects and Impact of Cyclic operation on 700MW Generators
as for turbine damages, not only will there be the effects of pumping condensing vapor in the last stages, there will be the pulsing of the first stage if it is 4 nozzle block design
RE: Effects and Impact of Cyclic operation on 700MW Generators
I don't see much problem with stator also with cyclic loading unless the full load was picked up in a very short time resulting in differential expansion between copper and iron.
RE: Effects and Impact of Cyclic operation on 700MW Generators
Just because they can do it doesn't mean that the equipment doesn't suffer. The same units have had all the HP and IP FWH's changed because they weren't designed for cyclic duty. The replacements are, however. I don't know if any detrimental effects on the turbine/generator (G3's). The furnaces catch heck, but they just attribute that to the ravages of coal firing.
rmw
RE: Effects and Impact of Cyclic operation on 700MW Generators
Keith Cress
kcress - http://www.flaminsystems.com
RE: Effects and Impact of Cyclic operation on 700MW Generators
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Effects and Impact of Cyclic operation on 700MW Generators
Every turbine has not only a high back pressure limit, (normally a hot summer day issue) but a low back pressure limit as well, definitely a cold cooling water source issue. So whatever you are doing with respect to modifying condenser operation, you are working within a rather narrow range, say 1.5" hga. to 5.5" hga (specific numbers that I remember from the 780 MW unit whose heat balance is depicted in the book Steam by B&W - that is a real unit at a real plant and I have spent a real lot of time working on and in and under it.)
So if the operating parameters permit, reducing the condenser vacuum (increasing the back pressure) is a beneficial option. It is kind of a pain in the butt, however, as the circ water pumps are large pieces of equipment, as is the valving in the circuit so this isn't something that you do on a whim. The size range of the circ water piping for a unit this size is in the upper double digit to low triple digit range on an inch scale.
rmw
RE: Effects and Impact of Cyclic operation on 700MW Generators
Bill
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Effects and Impact of Cyclic operation on 700MW Generators
Bekza was asking what effects cyclic operation might have on his water-cooled generator stator windings.
As edison123 hinted, the temperature difference between stator winding and stator core (slot portion) is of importance. Temperatures of a water-cooled stator winding reach their maximum value within minutes after application of full load. The stator core temperatures reach higher values but will approach their maximum at a later stage. Measurement of stator winding cooling water temperatures, slot RTD temperatures and stator core temperatures will be important to determine the effects of thermal expansion.
Duration and number of load changes per day will also be important factors. Stator cores keep their temperatures for quite a time compared with water-cooled stator bars.
Regards
Wolf
WWW.HYDROPOWER-CONSULT.COM