On ferroresonance damping resistor

[Naali]

Hi all!

I am quite a fresh engineer working on a project where cvt:s are added to 110 kV system for metering and residual voltage protection. Used VT's have two secondary windings: star, and broken delta secondary winding for Uo detection and apparently this winding should also be used for ferroresonance dampening via a resistor. the winding is rated 100/3 V for 50VA, so the resistor should be a 120 ohm resistor, right? Should the resistor be installed parallel or in series with the protection relay, and why?

thanks in advance

 

[waross]

Should the resistor be installed parallel or in series with the protection relay, and why?

Well, resistances in series tend to sum, so if you connect the resistor in series with the relay, you may no longer have 120 Ohms in the open delta.

 

[scottf]

If I'm reading your original post correctly, you should not have to provide external ferroresonance damping for CVTs.

With VTs, one has to be concerned with system ferroresonance, therefore, an external damping strategy.

With CVTs, there is a concern with internal ferroresonance, therefore, CVTs have internal ferroresonance suppression circuits.