Ferroresonance.

[BigClive]

In the past i thought that ferroresonance was an effect experienced when a line was of a specific length, capacitance and inductance to cause electrical oscillations. I think I'm wrong. (Although I'm sure there are scenarios where those factors combine to cause problems.)

Am I right in saying that ferroresonance is actually describing the effect of disconnecting a large inductor like a transformer that has no load to damp the resultant "ring" which causes high voltage spikes?

Is that why they sometimes connect a meaty resistive load across the secondary of the transformer to try and dampen the ringing to prevent damage to lightning arrestors in the vicinity?

[Special ED]

Is that why they sometimes connect a meaty resistive load across the secondary of the transformer to try and dampen the ringing to prevent damage to lightning arrestors in the vicinity?

I've heard of doing that in the past and I believe theres an artical from cooper systems describing one such instance and blowing their lighting arresters.

[topgroove]

your right on clive... with no load on the secondary very high circulating voltage develops within the windings. to make matters worse we usually are opening switches one at a time at the end of a switch stick. if you could open all three phases at the same time , like with a gang switch the field would collapse harmlessly without blowing the arrestors all to hell.

[Trbl639]

your right on clive... with no load on the secondary very high circulating voltage develops within the windings. to make matters worse we usually are opening switches one at a time at the end of a switch stick. if you could open all three phases at the same time , like with a gang switch the field would collapse harmlessly without blowing the arrestors all to hell.

Right on Top!!!

[rcdallas]

On underground primary from what I've been taught if the length of the cable exceeds the KVA of the transformer you'll get ferro... like 1000 foot feeding a 500KVA. Just need to open the switch at the transformer or put a small load on it if it doesn't have a switch.

On a 3 pot floating wye-delta, something with how you close one you get so much voltage coming out of H2 feeding into H1, forget the specifics... just install the 4th cutout!!!

I have heard it's more common with higher primary voltages with small KVA transformers, not sure if that's true or not.

[Trbl639]

We always dumped the load on the pot/padmount....opened the pot........then opened the source switches and reversed it going back in..........closed the source switches...closed the pot in and then put load on the pot.........we never cut the 4th switch in, heard of it, but we never did it on Entergy property, that I saw.......

With the exception of long UG runs in the oil field, most of our 3 phase UG runs were fairly short.........

[topgroove]

I've always found ferroresonance absoulutly facinating. I wish I could demonstrate it in a lab. When induction ( coils of wire in a transformer) match capacitance ( a length of underground cable) ferroresonance can occure. Its kinda like when soldiers are marching in step and when they come to a bridge they stop marching in step because the perfect rhythem of their march would amplify the stress on the bridge and possibly bring it down. It has a lot to do with harmonic frequency. If only there was a way to capture that energy.
In the field we see it all the time with large ratio banks and overhead distribution. It can happen inside substations also.

[BigClive]

I've always found ferroresonance absoulutly facinating. I wish I could demonstrate it in a lab. When induction ( coils of wire in a transformer) match capacitance ( a length of underground cable) ferroresonance can occure.

Y'see, that's what I thought ferroresonance was, but at other times it seems to be used to describe the "ringing" of a transformer when it is disconnected. Hmm, i wonder if there's any good literature on this on the 'net.

[Edge]

Y'see, that's what I thought ferroresonance was, but at other times it seems to be used to describe the "ringing" of a transformer when it is disconnected. Hmm, i wonder if there's any good literature on this on the 'net.

sounds to me like your thinkin of harmonic distortion... the ping from start ups... or caused by caps... or shutdowns.... the harmonics travel back and forth from the moters to the pot eventually causing the windsing in the tub to burn up unless there are some harmonic filter reactors insatlled... see them alot around steel mills and heavy metal works....

I remember a thread where we talked about this once don't recall it off hand... and it is a different issue.... hell I may have even said ferro in the thread but it is a different issue to be sure...

just like a git fiddle... 3rd 5th... and 7th are usually the worse... 3ed and 5th on most 'bustion systems...

loose hard ware can cause some harmonic distorion as well... aeolian vibration...sixth step for you git fiddlers...

linetrash like loose bolt ons and shit can add to it... not to mention long spans an a soft steady breeze on some bad poles....

hell some hiline structures have to be built and tied down now adays cuz the hilites don't and enuff weight to counter the vibration.... it you ain't got some to dampen it... you come back monday and the sumbitch will be tore to the fuggin ground...

not sure if this is what our talking about but sounds cloes 'nuff to me...

for what it's worth...

Edge

[rcdallas]

I was waiting to bring harmonics up in another thread, but here goes...

From what I was taught, a poor man's way to check for harmonics would be to check with your voltmeter between the ground and the neutral at an outlet, if there is a difference of 5 volts or more you need to have some concern.

I was over my buddies house not too long ago, he has a ton of dimmers in his house and I checked it was sitting right at 5 volts... good way to start a fire overloading the neutral!!

[Trbl639]

I was waiting to bring harmonics up in another thread, but here goes...

From what I was taught, a poor man's way to check for harmonics would be to check with your voltmeter between the ground and the neutral at an outlet, if there is a difference of 5 volts or more you need to have some concern.

I was over my buddies house not too long ago, he has a ton of dimmers in his house and I checked it was sitting right at 5 volts... good way to start a fire overloading the neutral!!

That's a good one Dallas...reminds me of a low voltage call I got one day......narrowback had just put some dimmers on some flotube fixtures, and they would barely come on..........he didn't have a clue...thought it was our problem!!!!!!!

[wtdoor67]

I can't say I understand Ferro but I have always tried to recognize the conditions that might lead to it.

Here is some verbatim stuff I have. These are not my words but I acquired this stuff from an engineer who seemed to know about it.

A Simple Example of Ferroresonance

Inductor and Capacitor are playing tennis. 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. Energy is passed back and forth between the Inductor and the Capacitor.


Some conditions for Y/Y, Y/D, and D/D banks, For 2400/4160 Switched at transformers, possible NO, through 200' open wire, possible NO, thru 200' of cable, possibility YES.

7200/12470 Same conditions as former example. NO, NO and YES.

12/20.8 YES, YES and YES.

19.9/34.5 YES, YES and YES.

From what I've been told you can expect it pretty much on 12 KV and above with the aforementioned conditions.

However this does not mean it will surely happen, just that with the previous mentioned conditions it can happen.

We had a classic example I can remember where I once worked. This was in a sub. On a report of single phasing the troubleman went to the sub. The primary was 115 KV and the secondary was 12470. The getup consisted of 115 coming into some gang switches and hence to the sub transformer which had 3 horizonal mounted fuses. One of these fuses had dropped open. The troubleman's plan was to dump the secondary with the breaker, then open the gang switch, which wasn't load break, then with the transformer de-energized he could safely replace the fuse and then of course close the gangs and then the breaker putting everything back to normal. When he dumped the breaker though, the transformer went into ferroresonance. After that a policy was sent out that in a similar situation the dispatcher would dump the transmission and then the gang switch could be opened. It was not reckoned to be done often as it was a rare occurrence. It was later on figured out that the design of the horizonal fuse holders was amiss. It was later re-designed I think. S & C it seems like.

The hook up was probably a Delta/Wye but I can't recall.

[Brooks]

ANSI/IEEE Std 100-1984 defines ferroresonance as “A phenomenon usually characterized by overvoltages and very irregular wave shapes and associated with the excitation of one or more saturable inductors through a capacitance in series with the inductor.”


The key elements are saturable inductors in series with capacitance.

I have seen it in Wye-Delta banks, 12.5kv, 25kv and 34.5kv. Also in 3phase pad mounts with 5 legged cores on 34.5kv.




If someone can host the file, I have an excellent .pdf from Cooper Power systems.

[Steve B]

ANSI/IEEE Std 100-1984 defines ferroresonance as “A phenomenon usually characterized by overvoltages and very irregular wave shapes and associated with the excitation of one or more saturable inductors through a capacitance in series with the inductor.”

In a nutshell; when energizing 3phase cable into a 3phase transformer without a load, use a gang operated switch. With the proper loading its ok to energize cable and transformer without a gang switch. The "phenomenon" occurs when with-out a load (inductive reactance), the capacitive reactance ( cable) is canceld, equaling zero impedance (or resistance), which in effect creates an irregular wave shape, overvoltages, etc., and things can get terribly rocky. When in doubt use a gang operated switch to energize cables and transformer at the same time. Or isolate cables from transformer, then close in cables then close in transformer.

For energizing a single phase Y, close into a load.

Single phase delta (phase to phase) follow the rules of 3phase closing.

Formulas for size of URD cable and length of run are available to instruct on how much load is needed for the proper impedance to create a non ferroresenace situation.

[T-Man]

http://www.ece.mtu.edu/faculty/bamork/FR_WG/Panel/DuganPanel.pdf

[Squizzy]

We clip a heater bank ( the old bar heater type) as a resistor bank on the Low Voltage side to disapate any resonate voltages, was told a guy was killed over here about 30 years ago from ferro resonance...

[Boomer gone soft]

http://www.ece.mtu.edu/faculty/bamork/FR_WG/Panel/DuganPanel.pdf

nice article....Thanks, T-Man!

[King]

I had an encounter with ferroresonance one time at a textile mill which had closed up and the serviceman got a order to reconnect the power. Service had been disconnected prior to his arrival at a UG Dip pole about 150' from a vault of OH transformers the primary voltage was 23KV and the secondary I think but not for sure was straight 480 wye delta bank. Everytime he would close in the third fuse one of the others would blow. These faults ended up messing up one of the T-Mods or ug terminations and it had to be replaced. Well this was a head scratcher because I was new and none of the other guys had experienced this ferroresonance before. We ended up getting a call from some guy possibly a engineer who told the senior it sounded like ferroresonance and we should open up a 3 phase switch on the source side close in the 3 fuses at the UG dip pole and then close back in the 3 phase switch. That worked problem solved. After that incident took notice and at a lot of these type banks their is a 4th switch that grounds the floating neutral or a 3 gang switch that closes in all 3 primary phases just before the transformer. I have also been told if you know the phasing you can energize the bank by closing in C phase, A phase and lastly B phase and open the bank by opening in order B, A, and then C phase. Operating the switches in that sequence should prevent the unwanted affects of ferroresence. I have heard that never done that if anyone has done this and would care to elaborate I would greatly appreciate it.

[Lineman North Florida]

I had an encounter with ferroresonance one time at a textile mill which had closed up and the serviceman got a order to reconnect the power. Service had been disconnected prior to his arrival at a UG Dip pole about 150' from a vault of OH transformers the primary voltage was 23KV and the secondary I think but not for sure was straight 480 wye delta bank. Everytime he would close in the third fuse one of the others would blow. These faults ended up messing up one of the T-Mods or ug terminations and it had to be replaced. Well this was a head scratcher because I was new and none of the other guys had experienced this ferroresonance before. We ended up getting a call from some guy possibly a engineer who told the senior it sounded like ferroresonance and we should open up a 3 phase switch on the source side close in the 3 fuses at the UG dip pole and then close back in the 3 phase switch. That worked problem solved. After that incident took notice and at a lot of these type banks their is a 4th switch that grounds the floating neutral or a 3 gang switch that closes in all 3 primary phases just before the transformer. I have also been told if you know the phasing you can energize the bank by closing in C phase, A phase and lastly B phase and open the bank by opening in order B, A, and then C phase. Operating the switches in that sequence should prevent the unwanted affects of ferroresence. I have heard that never done that if anyone has done this and would care to elaborate I would greatly appreciate it.I've hung the fourth cutout and grounded down the floating neutral while closing in delta banks where URD fed overhead and closed in the fuses 1 at a time and it has always worked like a champ but I've never heard of the C A B in that order being an option, but I'd sure like to know if it's true.:D

[T-Man]

Not sure electricity is that smart or cares which phase closes in which order. This problem has to do with length of cable (capasitance) and size of windings (inductance) and associated load. It has to be just the right amount of each to occur.
You will expieriance Ferroresonance on what we called T wound Transformers, and in energizing and de-energizing those puppies you never wanted to make an L (winding) out of a T (winding) so we always opened the phase attached to the T first and closed ot last, which could have been any phase depending how it was constructed.

[King]

Not sure electricity is that smart or cares which phase closes in which order. This problem has to do with length of cable (capasitance) and size of windings (inductance) and associated load. It has to be just the right amount of each to occur.
You will expieriance Ferroresonance on what we called T wound Transformers, and in energizing and de-energizing those puppies you never wanted to make an L (winding) out of a T (winding) so we always opened the phase attached to the T first and closed ot last, which could have been any phase depending how it was constructed.

Thanks T-Man, How do you determine what is the T (winding)?

[T-Man]

When you look at the name plate of the transformer you will see a diagram of the primary windings and the H's labled on the ends. Two primary coils will be tapped end to end and the third winding will tap to the center of the other two. This is the T winding. It will look like an upside down T, or to save room they may draw the T laying on it's side and running parallel to one of the other windings.
Back in the day we used to mark the T winding with a stencil of a T on the outside of the tank but that has gone to the wayside so you need to read the name plate. We had them on the 13.2 system and it was a three phase tank.

I'm not talking about a Wye or Star connection this is a T

[King]

When you look at the name plate of the transformer you will see a diagram of the primary windings and the H's labled on the ends. Two primary coils will be tapped end to end and the third winding will tap to the center of the other two. This is the T winding. It will look like an upside down T, or to save room they may draw the T laying on it's side and running parallel to one of the other windings.
Back in the day we used to mark the T winding with a stencil of a T on the outside of the tank but that has gone to the wayside so you need to read the name plate. We had them on the 13.2 system and it was a three phase tank.

I'm not talking about a Wye or Star connection this is a T


I appreciate you elaborating that makes good sense. I will keep it in mind next time I pick up or drop a 3 phase delta transformer.

[Trojan]

When you look at the name plate of the transformer you will see a diagram of the primary windings and the H's labled on the ends. Two primary coils will be tapped end to end and the third winding will tap to the center of the other two. This is the T winding. It will look like an upside down T, or to save room they may draw the T laying on it's side and running parallel to one of the other windings.
Back in the day we used to mark the T winding with a stencil of a T on the outside of the tank but that has gone to the wayside so you need to read the name plate. We had them on the 13.2 system and it was a three phase tank.

I'm not talking about a Wye or Star connection this is a T

We call those "Teasers". right on about checking the nameplate and closing in sequence.

[Trojan]

When you look at the name plate of the transformer you will see a diagram of the primary windings and the H's labled on the ends. Two primary coils will be tapped end to end and the third winding will tap to the center of the other two. This is the T winding. It will look like an upside down T, or to save room they may draw the T laying on it's side and running parallel to one of the other windings.
Back in the day we used to mark the T winding with a stencil of a T on the outside of the tank but that has gone to the wayside so you need to read the name plate. We had them on the 13.2 system and it was a three phase tank.

I'm not talking about a Wye or Star connection this is a T

I don't think that is true. The cable length and transformer size determine if ferroresonance ( or is it ressoferronance?) will happen.
What type of transformer is involved in that situation with the fourth cut-out on the neutral? Unless it is wye primary, I don't think it would work because the primary has no relationship to the neutral.