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Home > Forums > Engineering Forums by Industry > Transportation > Engine & turbine engineering Forum

cosphi problem

thread666-299363
Read More Threads Like This One
scorpion2620 (Mechanical)
23 May 11 10:29
While turbine is running, cosphi is decreasing from 0,95 to 0.35-0.40. Current is increasing from 30 A to 60 A. Voltage is decreasing from 10.800 to 10.000 V. Alternator is 50 Hz.Also, alternator NDE and DE side vibrations are quiet high that is about 6 mm/s on both sides and turbine gives alarm. Vibrations are measured with external device and it shows 6 mm/s too. What might be problem? this happenned suddenly.
ScottyUK (Electrical)
23 May 11 16:17
Sounds like an AVR problem, or more likely a correctly-functioning AVR which has been placed in the wrong operating mode. Does the PF go leading (VAr importing) or lagging (VAr exporting) when the voltage drops?
 
 
  

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If we learn from our mistakes I'm getting a great education!
 
scorpion2620 (Mechanical)
24 May 11 4:21
actually we couldnt see it. We have no experience on these. WE asked to some companies about problem. They say alternator rotor might have problem such as short circuit. Is it possible?
rmw (Mechanical)
24 May 11 21:09
A rotor short is the first thing I thought of.  Do you have any type of rotor ground fault detection equipment?

rmw
scorpion2620 (Mechanical)
25 May 11 6:07
no we dont have. We must have service for this.  
rmw (Mechanical)
25 May 11 21:34
Where are you in the world and what make (brand) of generator is it?

rmw
scorpion2620 (Mechanical)
26 May 11 1:35
in Turkey. It is AEG kanis 1,6 MW alternator.  
scorpion2620 (Mechanical)
2 Jun 11 2:23
a service company measured poles, checked bearings and coils. There isnt any problem. However, high vibration on alternator bearings still existing.We suspect AVR systems.Might it be?  
ScottyUK (Electrical)
2 Jun 11 14:52
It's still possible that you have a rotor fault which only becomes active when the rotor is spinning at rated speed, which can be tricky to pinpoint.

Does the AVR have different modes, such as voltage control, power factor control, constant reactive power, etc? What mode is selected? Do you understand how each mode will interact with a larger system?
  

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If we learn from our mistakes I'm getting a great education!
 
abeltio (Mechanical)
5 Jun 11 12:21
Measure vibrations with an external, hand held device, to confirm the vibrations given by the control system.

Electrical faults can be read by vibration systems as high vibrations (induced noise)

If the vibrations measured by the hand held equipment (like IRD or Bently Nevada):

1. matches the control system: there might be a problem in the generator field (rotor).

2. are different (and very low): there might be an electrical problem in the exciter.


Hope this helps, tell us how you fared.  

saludos.
a.

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