Damping of ferro-resonance 2

[mikeangel]

A magnetic voltage transformer will be protected from ferro-resonance oscillation by connecting a resistor across the open delta point in the three-phase secondary winding.

I need to know the formulas to dimensioning this damping reistor

VT data:
30000: ?3 - 100: ?3 - 100: 3 V
Pe=120VA
Us=100/3 V

I will be very happy if someone could help me in this subject.

Thanks
Miguel

 

[slavag]

Hey Miguel.
Again your customer with formulas and calculation .
Please see attached
P=(3 x Us)^2/R (Us= 100/3 or 110/3).
But power P ( of resistor) must not exceed rated power of VT. for 27Ohm is 450W ( on 110/3). or 22Ohm is 450W for VT
100/3.
Regards.
Slava

 

[wareagle]

http://books.google.com/books?id=SS...tsHRewk&sig=7m-E8Ti65AarbOWci3qRBGu6O9M&hl=en

 

[slavag]

Yes, its also correct. A typical size of this resistor is 50 to 60 ohms. But, if the oscillation happens at a half rated frequency, a lower resistance is usually needed.
Regards,
Slava

 

[mikeangel]

Thank you both of you you're very helpful.

Hey Slavag.

My customer makes me crazy

He wants that i justify theoretical and mathematical all the project decisions.

Thanks again Slavag.

 

[scottf]

Mikeangel-

Just to be clear, the resistor needs to be placed across a broken delta and not an open delta connection.

If you want to seriously prove the ferroresonance dampening, then you're in for quite a project. To really calculate the dampening needed, you need to know a lot of parameters of the VT design that aren't going to be readily available to you (air-core inductance for example) and...to do it correctly...you'll need to know a lot of system parameters.

The easiest, and most common, method is to size the resistor to the thermal burden of the VT. The thermal burden of the VT you describe is probably 1000-2000 VA or so.

If we assume 1000 VA for the thermal burden and a 100/3 V secondary, that would be about a 3 ohm resistor rated for 1kW.

Using a resistor across the broken delta will work for the most common modes of ferroresonance.

The only way to have something that will work for every conceivable situation is to use an active ferroresonance suppression device, which normally doesn't make a lot of sense for a 30 kV application, IMO.

 

[slavag]

Miguel.
We have agreement with our US folks.
Used term broken delta instead our term open delta, becouse open delta is other term in ANSI land.
US term Open delta is V connection of IEC land.
Regards.
Slava

 

[mikeangel]

You've been very helpful to me. I working in this subject by now.

Thank you both slavag and scotff.

 

[prc]

Please see excellent Basler Application Note No.PC-59N01on the subject.

http://www.basler.com/downloads/pc-59n01.pdf

 

[mikeangel]

Thank you for the help salavg, scottf, prc and wareagle.

Dear Slavag, you wrote about a device that can be use for damping instead resistor. Could you tell about it?

Thanks
Miguel

PS: great paper the Basler Application Note No.PC-59N01on

 

[slavag]

H Miguel.
I didnt test it on the site, but we would like bay one and try.
Please see attached.
Good Luck.
Slava

 

[slavag]

And Miguel.
my recommendation is used 22Ohm 450W for 100V VT, of course its up to you, Im not responsible for your desition. Theory and calculation is good, site practic from time to time is better.