Under Frequency Protection
Under Frequency Protection
(OP)
Hi,
I am actually on a site where a 2,5 MW 400 V 50 Hz steam turbine used to operate on underfrequency(below 45 Hz) very often without tripping.Actually the turbine operates in islanding mode and provide power to a plant.The turbine is rated 25 Bar and when steam pressure dropped below 20 Bar,the turbine lost speed but continue to supply the load as there is practically no under frequency protection on the alternator.Nobody seems to be aware or rather does not want to consider this problem.An under frequency protection is of no interest to them as it will be tripping the generator and cause downtime to them.
I know that operating a steam turbine below rated speed,at least below a threshold frequency,could have resonance effects on the turbine blades and obviously detrimental effects on the life of the turbine.How far is this argument true?
Guardiano
I am actually on a site where a 2,5 MW 400 V 50 Hz steam turbine used to operate on underfrequency(below 45 Hz) very often without tripping.Actually the turbine operates in islanding mode and provide power to a plant.The turbine is rated 25 Bar and when steam pressure dropped below 20 Bar,the turbine lost speed but continue to supply the load as there is practically no under frequency protection on the alternator.Nobody seems to be aware or rather does not want to consider this problem.An under frequency protection is of no interest to them as it will be tripping the generator and cause downtime to them.
I know that operating a steam turbine below rated speed,at least below a threshold frequency,could have resonance effects on the turbine blades and obviously detrimental effects on the life of the turbine.How far is this argument true?
Guardiano






RE: Under Frequency Protection
How do they manage to keep the auxiliaries working at 45 Hz anyway?
Any overexcited equipments enjoying the 45 Hz frequency?
Any vibrations?
May you grow up to be righteous, may you grow up to be true...
RE: Under Frequency Protection
I have seen stations with relay logic that started timers to document the time operated off frequency
RE: Under Frequency Protection
Does it trip the main breaker only?
This maybe what the system was designed for, to allow enough auxiluty power to bring the plant down.
RE: Under Frequency Protection
Guardiano
RE: Under Frequency Protection
therefore 48Hz would be 120sec, 47hz 30sec 46hz 3 sec 45hz instanstanous
But I also was thinking the frequency deviation between bucket resonances are usually like +/1 2 to 3 hz. I'm not a rotating element expert but I think that is called the Campbell curve
RE: Under Frequency Protection
from my expirience, 47Hz 10sec is a lower setting of U/f protection of steam turbines.
Good Luck.
Slava
RE: Under Frequency Protection
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(2B)+(2B)' ?