Reactive Capability Curve
Reactive Capability Curve
(OP)
Does anyone know how to draw a generator reactive capability curve as a function of the cooling air (for an air cooled machine)? The centers of the circles are fixed but the radii of the circles will vary as a function of temperature (assuming constant voltage and frequency). Both stator and rotor have Class 155 insulation.





RE: Reactive Capability Curve
Let’s use the following as example to describe an approximate procedure:
Ex. 250 MVA air-cooled generator, 15oC inlet air and 85% PF lagging. Determine the reactive capability curve for 40oC at rated power factor.
1- From the Generator MW vs. Gas Temperature curve, determine the normalized MW increment factor, K.
Ex. K= 1- MW40oC/Rate MW15oC = 0.80.
NOTE: In absence of any data for K, use the following approximation:
MW(T) = 180-1.44. T. T = Ambient Temp (oC)
2- Maintain fix the under excited point witch is the point (MW=0, -MVAR). This point does not set by thermal limits because is determined by the minimum excitation and stability limits requirements.
MVAR40oC @ 0 MW = MVAR15oC @ 0 MW.
3- Determine a set of points Adjust set of points
For MW: MW40oC = K . MW15oC.
For MVAR: MVAR40oC = [K+(1+K).(1-MW15oC/Tarted max MW15oC)].MVAR15oC.
4- Draw the new reactive capability curve for 40 oC with the new values determined in 2 & 3 above.
References:
1- IEEE 67-1990, “IEEE Guide for Operation & Maintenance of Turbine Generator”
2- Siemens/Westinghouse: Technical Appendix, “Adjustment of Generator Capability Curves-General Guideline”.
RE: Reactive Capability Curve
RE: Reactive Capability Curve
1. A synchronous generator capability curve has approximate equations for circles:
1a. For the armature heating limit (circle)
Apparent power = (P**2 x Q**2)**(.5)=Vta x Ia
where
Vta x Ia is the circle radius from the power coordinates center will vary as temperature and Ia change
Assume the operation under conditions of constant terminal voltage and armature current (at the maximum value permitted by heating limitations.)
1b. For field heating limit (circle)
P**2 + (Q + (Vta**2)/Xs)**2 = (Vta x Eaf / Xs)**2
The circle is centered on Qc=-(Vta**2/Xs)
Assume Terminal Voltage constant
Eaf is limited to a maximum value as determined by heat limitations. Eaf (and Iaf) will vary as temperature changes.
RE: Reactive Capability Curve
RE: Reactive Capability Curve
1. Correction (I beg your pardon):
Apparent power = (P**2 + Q**2)**(.5)=Vta x Ia
2. Check with
http://www.beckwithelectric.com/infoctr/upgrading.pdf
since they upgrade generator protection for the coming digital technology.
RE: Reactive Capability Curve
http://www.siemenstd.com/PA/10GenAppPage.html
relays that track the actual generator capability curve.
RE: Reactive Capability Curve
http://www.siemenswestinghouse.com/en/steamservice/steamonsite/geservice/index.cfm
RE: Reactive Capability Curve
Any thoughts? Any alternative way of achieving the same results? The machine is 30 years old.
RE: Reactive Capability Curve
RE: Reactive Capability Curve
If you do not have this program use the mathcad browser to see this work. I believe the browser is free download software.
MATHCAD APPLICATION PROGRAMS: http://www.mathsoft.com/appsindex.html
RE: Reactive Capability Curve
RE: Reactive Capability Curve