Ferroresonance damping.

[BigClive]

Let's inject some electrical science into the discussions...

I was just pondering the issue of where a lightly loaded transformer is disconnected on the primary side, and the collapsing field causes a high voltage transient that can cause a spike on the primary just as the circuit is opened, via the arc at the point of disconnection. That transient can cause false triggering of some sensitive lightning arrestors and cause them to avalanche and operate.

In the past this was resolved with a load buster, namely a high resistive load (heating elements and a fan) to dampen the transient in the core of the transformer. But has anything ever been tried with something as simple as a capacitor and resistor snubber network just connected across a single output phase to shunt the sharp and high frequency transients? It could theoretically be made quite small compared to the traditional load buster device.

[bluestreak]

The cheapest which is the way companies do it is to use a load box [resistive load, heat element] next up would be a three phase gang switch on the primary but the cost of installing at all three phase locations is way to costly. While the load box is relatively cheap the only time you tend to have one is when the work is planned ahead of time, they never seem to be around when doing trouble type work and that is 90% of the time you run into a Ferroresonance problem. The big problem is the management around here don't seem to care or understand the issue and it's real easy to sit in an office and tell you open or close fuses when they are not on the end of a hotstick. If the management doesn't know or care they're not going to look into or invest in an alternative, that's where these profits above all companies are failing their employees and customers.

[Orgnizdlbr]

Can you explain what a "load box" is ?

[bluestreak]

Like Clive mentioned in his post it's basically a heating element you clip on the secondary's while switching the trans either on or off, it balances the load between the time it takes opening or closing of the fuses. Balances is probably incorrect electrically speaking but using it stops the pad or bank from dancing around and causing an overvoltage situation the causes the arresters and fuses from blowing, I've seen homemade boxes with stove elements and manufactured units with high tech elements they all seem to work some just easier to install and operate

[Lineman North Florida]

We run into some overhead closed Delta banks that are fed by URD and we hang a fourth cutout with a solid blade in it and temporarily ground down the floating neutral while we are closing in the bank and then open 4th cutout when were done and it solved our issues.

[bobbo]

We run into some overhead closed Delta banks that are fed by URD and we hang a fourth cutout with a solid blade in it and temporarily ground down the floating neutral while we are closing in the bank and then open 4th cutout when were done and it solved our issues.

I understand closed delta straight power you will have a ferro situation. But how can you have a ferro situation on a wye wye,'situation floating neutral bus primary switch to ground, 7200 12470, and 3 cans all 50 KVAs, and 120/ 208. The only circulating current would be with the neutral... Correct?

[stiffneck]

Our 2 newest CCR's use the phenomenon of Ferroresonance to vary the voltage to maintain a "Constant Current" for the Airfield series loop circuits. This would be the "Christmas Lights" you see at any major airport airfield around the world. http://www.adb-air.com (ADB Airfield Solutions) has an excellent product support. These units have a Core type Transformer, capacitance, SCR and electronics that I need the schematic to trouble shoot. The load is the resistance. The older ones are "Thyristor" type which includes a large and small choke. From my limited knowledge, resistance is the conventional method for switching issues.

[bobbo]

Our 2 newest CCR's use the phenomenon of Ferroresonance to vary the voltage to maintain a "Constant Current" for the Airfield series loop circuits. This would be the "Christmas Lights" you see at any major airport airfield around the world. http://www.adb-air.com (ADB Airfield Solutions) has an excellent product support. These units have a Core type Transformer, capacitance, SCR and electronics that I need the schematic to trouble shoot. The load is the resistance. The older ones are "Thyristor" type which includes a large and small choke. From my limited knowledge, resistance is the conventional method for switching issues.

i am sure it's the same type situation where it's hi load from lighting, long length of cable and CCRs they have for airfield lighting. When you have great length of cable. The relationship on the power side is length of cable and KVA of a pad mount. You can't plug it in one at a time with elbows. Pad mounts with ferro situations have a switch where you can turn off the secondary load as you plug in your elbows, or the have a 3 phase vacuum switch set up, seen that. The engineer puts it in if its a ferro situation. And the equation is length of cable to the KVA of the can. And a bad situation is when the older guys plugged in a 3 phase pad mount and blew off the pinning bolts and high potted factories. The,way,it was explained to me the cable builds up like a capacitor and hi pots, when it gets one phase gets plugged in at a time with load, the cable builds up and hi pots. Either gang switch the 3 phase with a vacuum switch or kill the load before energizing. I am not a mathematician but there is,a,formula when you have ferro,situations. And on the prints they will highlight it on the circuit maps.

[bobbo]

We run into some overhead closed Delta banks that are fed by URD and we hang a fourth cutout with a solid blade in it and temporarily ground down the floating neutral while we are closing in the bank and then open 4th cutout when were done and it solved our issues.
Just built a ferro cutout for wye wye. I understand straight power,delta but wye secondary with a nuetral. It did have primary floating nuetral bus. Was that the reason?