Smoothing Reactors

Photo of the smoothing reactor
Photo of the smoothing reactor

Smoothing reactors are intended to be used in rectified (direct) current circuits of various voltage classes. Such as power circuits of melters, municipal transport overhead contact systems, powerful industrial drives and DC current installations, inserts and lines, etc.

Current and voltage ripples during rectification of direct current are inevitable. If a load is connected to a DC circuit via a controlled inverter, additional ripples may occur due to switching of semiconductor elements in the inverter.

With respect to its operation principle, the reactor is an inductance coil. When current flowing through the coil changes, back emf proportional to the current change rate (first-order derivative) is produced: . Thus, the reactor resists quick changes ("spikes") of current in the circuit it has been connected to.

Smoothing reactors ensure smoothing of current ripples and spikes caused by operation of power electronics. The reactors are connected to a circuit in series, after rectifiers and before inverters.

To ensure high inductance of a small-sized reactor, smoothing reactors are equipped with ferromagnetic cores. A core is a single-bar magnetic conductor made of electrical steel.


Design of smoothing reactors is similar to (except for the ferromagnetic core) that of current-limiting reactors manufactured by KPM, LLC.

The most important design features of a KPM, LLC reactor are:

  • The reactor is a solid construction, its base and main load-bearing element are represented by the reactor winding itself. The winding needs no support framework or other elements to ensure extra strength.
  • All metal parts of the reactor are under the same voltage as its winding. Absence of significant potential drops inside the reactor minimizes the probability of its internal damage. E. g., breakdowns between the layers, breakdowns between the cross-piece and winding, etc.
  • Secondary elements of the reactor (rods, bindings) are made of fully nonmagnetic materials that have no electrical conductivity. This fully prevents their interaction with the magnetic field of the reactor. Since such elements are secondary, their strength is many times greater than the loads applied to them in the process of operation.
  • The reactor windings have absolutely no dismountable mechanical connections (such as screw-and-nut connections, etc.). This ensures highest strength, durability and reliability of the whole structure; prevents the necessity in maintenance of mechanical connections in the process of operations.
  • All electrical connections are made by soldering (welding), which prevents their heating, deterioration of contact joints, minimizes the losses.
  • The reactor does not contain any liquids and highly flammable materials, it cannot be a source of fire and is explosion-proof. The reactor is designed for long-term maintenance-free service.
  • Presence of vertical and horizontal through channels between the windings ensures reliable natural cooling of the reactor.