Line reactors

[ptonsparky]

We see enough posts about voltage, or available fault current, too high.

What are the limitations of using line reactors for this correction? Small ones are relatively inexpensive.

 

[synchro]

There will be more voltage drop across a line reactor with inductive loads (e.g., during motor starting) than with resistive loads, given the same amount of load current. That's because the voltage drop from a reactor is the motor's lagging current times the inductive reactance, which will be a voltage that's nearly 180° from the applied voltage. With a resistive load, the voltage developed across an inductive reactance will be at 90° from the applied voltage, and therefore a reactor will have less impact on the total voltage drop. Of course, a practical reactor has some resistance as well that will make some contribution to the voltage drop.

 

[ron]

I have attempted to use a line reactor to reduce fault current, but the AHJ was confused by the equipment / application and wanted it to have a listing to reduce fault current, which there is no such listing.

UL 1561 is for transformers, so I used an isolation type 480 in / 480V out and the internal impedance took care of it.

 

[jim dungar]

I have attempted to use a line reactor to reduce fault current, but the AHJ was confused by the equipment / application and wanted it to have a listing to reduce fault current, which there is no such listing.

UL 1561 is for transformers, so I used an isolation type 480 in / 480V out and the internal impedance took care of it.

I don't think I ever worked on a non-MV system that used a reactor solely for reducing fault current.

 

[augie47]

I don't think I ever worked on a non-MV system that used a reactor solely for reducing fault current.

I hope it's not a case of my old mind playing tricks but I recall a job decades ago with a new service on an old school with 5k breakers and the engineers used reactors on a 240v system.

 

[jim dungar]

I hope it's not a case of my old mind playing tricks but I recall a job decades ago with a new service on an old school with 5k breakers and the engineers used reactors on a 240v system.

That would be a reason, but I usually accomplished it by adding conductor length or by adding transformers.

 

[David Castor]

Current-limiting reactors used to be fairly common. If the available fault current only needs a small reduction, then they are feasible. But they generate heat, reduce efficiency, add voltage drop, and take up space. With modern circuit breakers having much higher short circuit ratings than older versions, using reactors is seldom the best option these days. If you want to reduce 65 kA down too 22 kA, reactors will not be feasible.

Sometimes used at medium-voltage in series with the switchgear tie breaker to allow paralleling of two sources. When tie breaker was normally open, the CLR was out of the circuit.

 

[TwoBlocked]

Saw a situation where the fault current was more than the main 480V breaker could handle on a 4160/480 load center. This was due to the contribution of many, many, inductive motors during a fault scenario. It was cheaper to replace the transformer with one with higher impedance than to replace the breaker, so that's what was done. (It also gave us a spare transformer, the size of which were throughout the plant.

 

[topgone]

We see enough posts about voltage, or available fault current, too high.

What are the limitations of using line reactors for this correction? Small ones are relatively inexpensive.

They're impedances inserted in between the source and the load. The good thing they do is limit the amount of short circuit current to the load. Take note that they are basically impedances, they introduce a little voltage drop when the current passes and will certainly have I2R losses!

 

[ptonsparky]

They're impedances inserted in between the source and the load. The good thing they do is limit the amount of short circuit current to the load. Take note that they are basically impedances, they introduce a little voltage drop when the current passes and will certainly have I2R losses!

A 3% VD would be all some of these installs need for the technicals that say "251" is to high.

 

[synchro]

We see enough posts about voltage, or available fault current, too high.

What are the limitations of using line reactors for this correction? Small ones are relatively inexpensive.

I doubt that line reactors would be suitable for the current limiting function. I suspect that their magnetic core would start to saturate at a fraction of the system voltage that they are rated for. That's OK because the voltage developed across them will be relatively small in a line reactor application, and so saturation will not normally occur. As a result, only a shorter air gap within the magnetic path of the core would be needed to maintain linear operation without saturation, allowing more reactance to be achieved in a smaller physical size.

If a reactor starts to saturate its impedance will drop drastically if additional voltage is applied, as it will during a bolted fault. And therefore a current limiting reactor needs to have a sufficiently long air gap in its core to prevent saturation and maintain its reactance during a fault. But this will decrease its nominal amount of reactance, and therefore for the current limiting function a physically larger reactor will be needed to obtain a given reactance, which obviously adds to its cost.

Another issue is that a current limiting reactor needs to withstand the mechanical forces from large magnetic fields during a fault. I've seen this referred to as the mechanical current rating of a current limiting reactor.

This is one company that makes current limiting reactors:

https://lcmagnetics.com/inductors/current-limiting-reactor/

 

[topgone]

I doubt that line reactors would be suitable for the current limiting function. I suspect that their magnetic core would start to saturate at a fraction of the system voltage that they are rated for. That's OK because the voltage developed across them will be relatively small in a line reactor application, and so saturation will not normally occur. As a result, only a shorter air gap within the magnetic path of the core would be needed to maintain linear operation without saturation, allowing more reactance to be achieved in a smaller physical size.

If a reactor starts to saturate its impedance will drop drastically if additional voltage is applied, as it will during a bolted fault. And therefore a current limiting reactor needs to have a sufficiently long air gap in its core to prevent saturation and maintain its reactance during a fault. But this will decrease its nominal amount of reactance, and therefore for the current limiting function a physically larger reactor will be needed to obtain a given reactance, which obviously adds to its cost.

Another issue is that a current limiting reactor needs to withstand the mechanical forces from large magnetic fields during a fault. I've seen this referred to as the mechanical current rating of a current limiting reactor.

This is one company that makes current limiting reactors:

https://lcmagnetics.com/inductors/current-limiting-reactor/

Nope. Air core reactors do not saturate. Maybe your idea of a reactor is focused on iron-cored reactors. Years of experience have proven line reactors work. If not, the power plant in my green days should have been damaged with many incidences of line faults.