Generator Negative and Zero Sequence Resistance
Generator Negative and Zero Sequence Resistance
(OP)
I am interested to know more about the negative and zero sequence RESISTANCE for small (i.e. 1 MVA) low voltage (i.e. 480V) STANDBY GENERATORS.
Is the negative sequence resistance equal or similar to the positive sequence resistance?
Is the negative sequence resistance typically a percentage of the positive sequence resistance which I do know?
How about the zero sequence resistance? Can I estimated it based on the positive sequence resistance?
The reason for this question is that I want to model this generator as accurately as possible in the SKM software. In the generator component editor in the second subview named ANSI Contribution, you enter the positive sequence reactance and then its corresponding X/R ratio. You also need to enter the negative sequence reactance and the corresponding X/R ratio. Finally you need to enter the zero sequence reactance and its corresponding X/R ratio. I know all the information for the positive sequence section. I also know the negative sequence reactance and the zero sequence reactance. To enter the negative and zero sequence X/R I will their corresponding resistance.
Thanks.
Is the negative sequence resistance equal or similar to the positive sequence resistance?
Is the negative sequence resistance typically a percentage of the positive sequence resistance which I do know?
How about the zero sequence resistance? Can I estimated it based on the positive sequence resistance?
The reason for this question is that I want to model this generator as accurately as possible in the SKM software. In the generator component editor in the second subview named ANSI Contribution, you enter the positive sequence reactance and then its corresponding X/R ratio. You also need to enter the negative sequence reactance and the corresponding X/R ratio. Finally you need to enter the zero sequence reactance and its corresponding X/R ratio. I know all the information for the positive sequence section. I also know the negative sequence reactance and the zero sequence reactance. To enter the negative and zero sequence X/R I will their corresponding resistance.
Thanks.






RE: Generator Negative and Zero Sequence Resistance
RE: Generator Negative and Zero Sequence Resistance
Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.
RE: Generator Negative and Zero Sequence Resistance
For rotating machines, the negative sequence resistance will be different than the positive sequence resistance due to the negative sequence circling the rotor at twice the rotating frequency so it will have a different resistance due to the skin depth being different.
I think that a generator connected in delta instead of wye would change things,too.
RE: Generator Negative and Zero Sequence Resistance
It's also fairly common just to set negative sequence quantities equal to positive sequence for generators.
Good luck.
Dave
RE: Generator Negative and Zero Sequence Resistance
You should be asking about impedance.
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Generator Negative and Zero Sequence Resistance
RE: Generator Negative and Zero Sequence Resistance
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Generator Negative and Zero Sequence Resistance
3.4 The frequency of the negative sequence current induced in the rotor will be equal to (supply frequency) x (2-slip) Hz. This is due to the fact that it is revolving in the opposite direction . This frequency will be typically around 99 Hz during normal motor operation . Due to skin effect, high frequency negative sequence currents encounter high rotor resistance. This inturn results in over heating. The increased resistance is typically 5 times the normal positive sequence resistance.
http://www.lntebg.com/mps/neg.html
RE: Generator Negative and Zero Sequence Resistance
OK, I see now. Most of us didn't think so far. Skin effect makes a lot of difference. Thanks for being so persistent.
Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.
RE: Generator Negative and Zero Sequence Resistance
I would try values from 3 times to 7 times and compare the results. This will give you some indication as to whether it is safe to make an assumption in the absence of hard data.
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Generator Negative and Zero Sequence Resistance