Starting Reactors

Photo of the starting reactor 15 kV

KPM, LLC manufactures starting reactors for electrical machines of various rating power.

Intended Purpose

Starting of electrical machines (synchronous and asynchronous motors) is characterized by starter currents that may be equal to 5 to 6 or even 10 times the rated current of the motor.

Such high currents may be unwanted due to a number of reasons. The simplest way to reduce the starter currents is reactor start.

In case of reactor start, at the initial instant of time, the electric motor is connected to the electrical network via the reactor, rather than in direct manner. As a result, starter currents of the machine are reduced by half or even more. A circuit breaker is installed in parallel to the reactor. After the electric motor reaches the rated (or close to that) revolution speed, the reactor is bypassed and the electrical machine is connected directly to the network.

Although such an operating regime of the reactor is similar to that of current-limiting reactors, it has some significant differences:

  • Duration of starting may be much longer than short-circuit (SC) duration. According to PUE, with due account for actuation of backup protection and CBFP, SC must be cleared in 3 seconds or less. Starting of a motor may last for several tens of seconds.
  • Electrical machines are sources of free current components. That is, aperiodic and low-frequency components (due to electromechanical transients in the machines).
  • A current-limiting reactor shall be capable of withstanding the maximum of 100 events of design SC current. While frequency of starting for an electrical machine within its service life is unlimited.

All that produces specific heat and mechanical loads applied to the reactor’s structures. In case of high-power machines, the above factors cannot be neglected and design of the reactor shall be tailored to such conditions.


Design of starting reactors is similar to that of current-limiting reactors manufactured by KPM, LLC, but is tailored to multiple and long-lasting loads of starter currents.

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.