Ferroresonance

[vtpower]

I have begun my career as an Electrical Engineer in the utility feed and have been thrown right into it. There has been a large push to correct power factor at our tie points to near unity. My question is, is there info or literature that puts ferroresonance in understandable terms? I have read papers on it, but still am uncertain on how exactly it is caused and what occurs. I want to be sure this is not an issue as I begin installing distribution capacitor banks. Thank You.

 

[davidbeach]

I would think that the 12,000V system is actually a delta system. In central California, Pacific Gas and Electric had (it's be 15 years since I worked there, who knows what has happened in the mean time) a lot of 12kV delta systems where single phase transformers were connected phase to phase. As substations and circuits began to need more capacity PG&E would convert the 12kV circuits to 20780Y/12000V and then the same transformer, with different insulators, would be reconnected line to neutral.

 

[wrong100]

vtpower cuky2000 jgrist davidbeach mc5w jghrist electricpete

I think I got everyone.

My background is in power supply design.
If I do not know what is coming in, I have no chance of
control over the output. Been there done that.

Electricpete (first answer)is correct.
Did not give a background only a ref (LC).
expected you to do homework.
I tried to give a pratical use background, and show that it was a reso. effect.
If you extend what I wrote, any transformer can become
resonate (ferroresonace). The effect for you is
(the currents and voltages can get out of hand), voltages
and currents can become 1 times, to 100 times expected "Q".
Result magnetics saturate and stop transfering energy,
caps explode (short) or just die (open).

My design examples
20 v in 3000 v out at 10 mil a.
Use a voltage multiper (1 to 3) (standerd
concept).
Out voltage from transformer = 1000 v.
this means a tight wound transformer with
its winding cap in an ungapped core will
will resonate at a fc that is lower
than the opreating fc.
Result.
Energy transfer is restricted, (to output)
input current too high (just heating parts).
Resonance must be above operating fc and
controled. Higher reso fc the better.

O K so you are 100 million times large in power.
I do not remember anything that implies that when you go from .1 watts to 1 million watts that the concepts change.

Voltage , current, power, is only relative to itself.

vtpower question answered?

think.

 

[cuky2000]

Dear worng100,

I would prefer to turn this discussion into a cooperation effort to mutually benefit of each other knowledge.

The ferroresonance principles, as you pointed out, does not change with the application since this is the result of the interaction of the resistance, inductive and capacitive of any RLC circuit. It is also truth your statement that “. Voltage , current, power, is only relative to itself”

On the other hand, I am afraid not to be 100% agree with your statement [red] “O K so you are 100 million times large in power. I do not remember anything that implies that when you go from .1 watts to 1 million watts that the concepts change” .[/red] This is because the likelihood of ferroresonance in power distribution systems is significant different at different voltage level, transformer size, type of lines, system connection and other factors because that change the inherent values of the RLC parameters: For example:

a) Voltage Levels:
Up to 7,200/12,470V: Unlikely
>14,400/24,900 V potential problem

b) Transformer Size: Smaller transformers are more susceptible to ferroresonance problems than larger transformers. For instance < 30 kVA units there is potential problem in system > 7.2/12.5kV.

c) Type of Line: “The capacitance to ground of cable may be 50 or more times that of overhead line, and this fact greatly increases the probability that the capacitances will be above the lower bound of the range at which ferroresonance can occur with the connections in Table 2” bellow.

d) System Connections: Transformer banks with certain connections are more likely than others to experience ferroresonance when the bank is energized or de-energized with single-pole switches at a location remote from the transformer, or when a conductor or fuse at a remote location opens. There are three phase configurations more prone to other to produce ferroresonance. See the enclose figures for sample from the C57 Standard .

 

[wrong100]

vtpower cuky2000 and all others.

I think we are saying the same thing.
Your application is different from mine, but the results
are the same.
Having limited background in AC power distrubition
systems. I gave an example of what I know.
I think what you are saying is different transformer configurations and voltage levels control the capacitance
to gnd and line to line, and also the inductance, and
therefor the ability to become ferroresonance.
I agree.
The question asked was, what is it I do not understand.
I wanted to give vtpower an basic understanding of the conceps, I could not in his? contex. You did this very
well.
I think we have all learned, I know I have.