KVAR and RPM of wind generator

R

Thread Starter

Rajen Mehta

Hello,

Would like to know if anyone can provide information on KVAR required at different RPM speeds of a wind generator, say for example 250KW generator running at 50RPM will require what amount of KVAR to reach a unity PF? As per manufacturer data available at 750RPM, 250KW will require 150KVAR to reach unity. So is any correlation available between RPM and KVAR?

(Excuse my limited knowledge on the subject especially the jargon.)

Really appreciate your inputs, thanks.

Rajen
(rajenmehta @ powermatrix. in)
 
P

Phil Corso, PE

Responding to Rajen’s 22-Sep (hh:mm) question… are you asking about an induction machine operating as: (a) an isolated generator at 50-rpm; or (b) as a generator connected to an established grid, say 50-frequency?

If (a) then, the answer is yes! A capacitor is required to provide self-excitation, and its value is dependent on rpm.

If (b) the machine will draw reactive volt-amperes (kVAr) from the grid to satisfy its magnetizing current and core-loss requirement. However, an internal emf is not possible at 50-rpm, so the machine must be driven hyper-synchronously, i.e., above grid frequency!

Regards,
Phil Corso ([email protected])
 
T

Tomy Zacharia

Wind generators try to maintain constant rotation speed by varying blade pitch and through a gearbox in the nacelle. Thus something is missing in your question. Something specific to the particular machine in question?

Tomy Zacharia
 
R
Hello,

Firstly, thanks for the quick response. To be more specific the details of the induction generator are:
Make - Siemens
Frame size - 355
Class on insulation - F
Duty - S1
Protection - IP - 55
Eff. - 95.5%
Voltage - 415 V, 50 Hz, 3 ph,
Kw - 90/250
F.L.A. - 414/1102 Amps
R.P.M. - 1010 / 1501

GENERATOR GEAR RATIO
p - 250 Kw, N1- 42 RPM, N2- 1501 RPM

Now the primary aim is to size the amount of capacitor required to ensure a unity or near unity PF considering worst case scenario, i.e. max. amt of KVAR required at whichever RPM. The generator is coupled to the grid at 50 Hz and depending on the wind speed the RPM may vary.

Thanks,
Rajen
 
P

Phil Corso, PE

Whoa, big fella! Assuming your 27-Sep (00:09) comments were addressed to me, then additional data is required:

1) Before the value of a pf-correction capacitor can be determined one must know the minimum size capacitor for the motor to generate rated no-load voltage!

2) Once the above is known, then the self- excitation capacitance must be determined for the full-load case (which should be somewhat less than 250-kW)

3) Once the above is known, then the pf-correction capacitance can be determined.

4) The fly-in-the ointment, so to speak, is that the motor's design parameters must be known. Specifically, capacitor current must just equal the motor's magnetizing current!

5) The above requires that the impedance (or admittance) components associated with the motor's magnetizing circuit be known!

6) Your data shows a negative slip of 0.0667 percent. Output is 261-kVA at unity pf! Are these values correct? Are they shown on the nameplate as the full-load output parameters?.

In conclusion, the task you pose can't be done with the snap of one's fingers. However, it's do-able, but you will have to provide more detail!

Regards, Phil Corso ([email protected])

P.S. Why haven't you approached Siemens?
 
Top