Current limiting reactors

Current limiting reactor manufacturer

FDUEG has been designing and manufacturing current limiting reactors for over 20 years, building up experience and skills in order to advise its customers on the right device for their power system.

When a short circuit phenomenon occurs on the line or bus tie of a plant, the sudden drop in impedance causes the generation of high currents that directly impact on the area around the fault. Although the protections intervention is  rather quick (no longer than a few seconds for circuit breakers whose rating is relevant from an industrial facility’s point of view), before they act some damage may appear because of local overheating and electromechanical forces between the cables where fault currents are flowing.

A technically established solution consists in placing a reactance connected in series on the distribution line (feeder reactor), whose effect is to mitigate the fault currents while waiting for the protection devices to operate. This addition results, on the other hand, in a permanent voltage drop on the line. However, this is entirely inductive, so it does not cause large and concentrated heat generation. The added impedance has, moreover, a desirable effect of current disturbance mitigation. This noise may be due to power electronics switching, variations in load of the power line et cetera, something that is rather usual in power system and should be accounted for and kept under control.

Short circuit current limiting reactors based upon a custom design manufacturer

A device working to limit the short circuit current is necessarily built as air core reactor. This choice comes, from a technical point of view, from the need for linearity in impedance as response to current levels that are way different from one another, and eliminates the saturation issue that would arise in case an iron core reactor is being used.

The mechanical strength is a crucial aspect when this type of reactor is considered. In case of fault, the electromechanical forces on the windings rise with the square of the flowing current’s modulus, and have to be restrained in order to keep the device intact and usable. A scarce inductance rating design, aimed at limiting the permanent voltage drop, may result in the side effect of not limiting the current enough under fault conditions, thus destroying the coil when it is asked to perform its function within the power system.

Since current limiting reactors are permanently inserted in series with the power line, it is necessary that they do not cause relevant power loss while functioning normally, thus hampering too much the overall efficiency in handling the power flow. The aspect involving the magnetic field path definition is studied in order to avoid that the conductor is interested by flux crossing its section, translating in AC losses and overheating.

The constant voltage drop induced by a short circuit current limiting reactor is never too large (less than 10 % of the total phase voltage is a reliable estimate). However, for what concerns the whole inductance structure, it has to be insulated with respect to mass adequately. It is also mandatory to study the winding’s terminals, so that the electric field remains under control and neither spike nor corona effects take place.

The experts working at the Technical Department consider all these elements while designing a short circuit current limiting reactor, making it possible to supply a device that performs perfectly under all aspects and keeps into account IEC norms and customer’s specifications.

Custom short circuit current limiting reactors

FDUEG produces air core reactors impregnated in polyester resin, ideal to be installed within a closed and controlled environment as an industrial facility may be. The VPI (Vacuum Pressure Impregnation) technology allows to build particularly resilient coils, while not weighing too much on the structure and granting a correct electrical insulation on the object. This way, the accidental contact with small particles that could impact on the coils has no effect on its dielectric strength, while, at the same time, protecting the windings.

The short circuit current limiting reactors by FDUEG are available, for their three-phase configuration, as three coils piled up or, in modular variant, as single-phase bobbins to be placed side by side.

The first solution is proposed when it is important to limit the footprint used to install the device.

The single-phase variant, on the other hand, is granted all the benefits of modularity, thus shortening maintenance periods and costs. Another advantage not to be underestimated involves simplicity of installation: smaller and lighter coils are easily movable and put in place where their operation is necessary.

In both cases, the structure can be lifted through suitable hooks. The insulation towards mass in granted by post insulators, bearing the needed dielectric strength, and fiberglass blocks.

The shape of the electrical terminals and their position on the sides of the reactor can be freely decided, based upon the needs a customer has for its electrical connections both in terms of fixing and ampere rating. These are in particular studied considering all mechanical stresses that may be present while the reactor is working.

FDUEG is specialized in manufacturing short circuit current limiting reactors based upon a custom design. Its technical department is able to handle all special requests, managing to accommodate all the heaviest service conditions, environment or footprint needs.