Ferroresonance

[dbrown20]

This stuff is from some information I have on ferroresonance. The complicated stuff I will leave out as I don't understand it either.

Ferroresonance is an electrical phenomena which produces destructive voltages and currents in electrical systems. Feroresonance occurs in circuits which have single phase switching or fusing.

A simple example.

Suppose 2 people are playing tennis. One is named inductor and the other capacitor. Inductor uses magnetic energy to hit the ball and capacitor uses electric field energy to hit the ball. Each time inductor hits the ball he sends all his magnetic energy with the ball. When capacitor receives the ball he changes all the magnetic energy that is with it into electric field energy; he then has energy to hit the ball back to inductor. When inductor receives the ball it has all of capacitors electric field energy with it, and inductor changes it to magnetic field energy and starts the cycle over again.

When Inductance and Capacitance are equal and opposite you have a circuit that is said to be ferroresonant.

This stuff is from the mid 80's and came from Pacific Power and Light.

The following lists ferroresonant conditions for Wye/Wye, Wye/Delta and Delta/Delta banks.

Switching Location: At Transformer:2.4/4.16 KV & 7.2/12.5 KV. NO. Through 200' of open wire. No. Through 200' of cable. YES.

12/20.8 KV. Same sequence. YES. YES. YES.
19.9/34.5 KV. Same sequence. YES. YES. YES. At the bottom of the chart it says that for the 20.8 the probability is occassionally. For the 34.5 it is definitely possible. It is definite for transformers smaller than 3-50 KVA's and possible for larger than 50 KVA. For a grounded Wye/Wye bank this claims conditions are ideal only through 200' feet of cable.

Now all of this does not claim that ferroresonance will occur, but that the conditions do exist for it to happen under certain setups. I have only seen what I realized later was ferresonance about 3 times. I notice that the local power company here does not build Wye/Delta banks on 34.5 KV. Only Wye/Wye and Open Wye/ Open Delta banks. dbrown20

[bobcat12]

Well we have it alot here in southern california. I work for Edison and when we make our circuit maps we try to indicate what circuit has it. Manily we try to identify the apparatus equipment that is none switch able and label it. If it is a nonswitchable padmount being fed from a urd to the line then you have ferro, depending on the distance from the source. If so you will have to by-pass the line and install a cut-out and load bust it open. If you do not and you remove it off line then you will have a fire down your ass so big that you will wish you have never took the job. How I know is because we had some contractors to do it and it relayed the circuit. They did not know wht caused it until my partner and i responded to it over the radio and we told them what happened. I will get more information and put it on here for you if you guys need. it. Believe me it is some tricky and dangerous shit to mess with.

[dbrown20]

I will add to my original post from the info. I have and we'll see if it agrees with Edison's ideas. dbrown20

[LINETRASH]

I have experienced it in a 3 phase loop scheme where the 3 phase tx had no load, it was on generation.

I opened the elbow on the high side of the loop, which happened to be 1 cable run from the tx in question.

As soon as the elbow cleared the bushing, I saw fire dancing all over the elbow and cable. (This was the dead phase, I was restoring after an unscheduled outage)

I almost dropped the stick and ran, but instead plugged her into the parking bushing, at which time the fireworks stopped. After refusing the barrel, I pulled the same elbow from the parking bushing and witnessed the fireworks again. I pulgged it into the hot line side bushing and the loop came back up, no problem.

An engineer later tried to explain the whole thing, but my eyes glazed over halfway through. I do remember about the 3 phase tx with no load and the fact he said just a little load, lightbulb, whaterver, on this tx would have cured it.

[Koga]

and I might be the one thats not sure , but what was the primary voltage on these 3 phase pad mounts you were switching and what was the weather conditions during the switching ?

Koga

[LINETRASH]

It was a 23 area, 13,2 phase to ground.

The weather was typicla for SoFla, hon 'n humid!

[Koga]

and had problems pluggin and unplugin elbows on some of ours 19 kv in high humidity. Im not sure how much ferro has to do with it vs the humidity, as the way you described what was happening.

Koga

[44kv]

The same as when gas builds inside of the tx and the primary arcs across the gas to the grounded tank wall?

[upntheair]

I have experienced it in a 3 phase loop scheme where the 3 phase tx had no load, it was on generation.

I opened the elbow on the high side of the loop, which happened to be 1 cable run from the tx in question.

As soon as the elbow cleared the bushing, I saw fire dancing all over the elbow and cable. (This was the dead phase, I was restoring after an unscheduled outage)

I almost dropped the stick and ran, but instead plugged her into the parking bushing, at which time the fireworks stopped. After refusing the barrel, I pulled the same elbow from the parking bushing and witnessed the fireworks again. I pulgged it into the hot line side bushing and the loop came back up, no problem.


An engineer later tried to explain the whole thing, but my eyes glazed over halfway through. I do remember about the 3 phase tx with no load and the fact he said just a little load, lightbulb, whaterver, on this tx would have cured it.

You got the nail right on the head! In these situations we put an old heater on the secondary side and this stops any probs. Don't know if a lightbulb would be enough but I guess it would depend on the circuit characteristics.