Current-Limiting Reactors

KPM, LLC has manufactured current-limiting reactors for a long time. Thousands of reactor coils have been made, and huge experience in their manufacture and operation has been gained.

Intended Purpose

State-of-the-art electrical networks are characterized by complex layout with great number of generation and consumption assemblies. Production sectors, transport and society as a whole require more and more electric power. Capacities of power stations grow, new power generating units and stations are commissioned.

Reliability requirements to power supply, possibility of significant power flows (transit) cause the necessity in multiple parallel electrical connections within a network. Connectiveness of networks grows, share of radial systems drops, number of division points also drops. Modern electrical networks are mostly meshed system with regard to their layouts.

All of it leads to increase in short-circuit (SC) currents within networks of all voltage classes and to increase in power flows in electrical networks.

Increase in short-circuit currents is a problem of great concern. High SC currents require costly switching gear with high breaking capacity. Large SC currents occurring in case of a fault cause drastic consequences — major damage to the equipment, high risk of fire after SC, risk of cascade fault.

The simplest and the cheapest way of SC currents limiting is to use dry current-limiting reactors. This solution (in the form of concrete reactors) has long ago proven itself in 6 kV and 10 kV networks. Based on the state-of-the-art technologies, KPM, LLC manufactures sophisticated dry reactors designed for all voltage classes, from 6 kV to 330 kV.

Ohmic resistance of a current-limiting reactor is minimal, and inductive reactance may be up to several tens of Ohm. In normal operation mode, losses in the reactor are insignificant. However, in case of a short-circuit equivalent resistance of an electrical system containing the reactor becomes much greater than without it. Which, according to the Ohm’s law, leads to SC current reduction to safe values.

Other use of current-limiting reactors is to equalize the power flows in parallel electric connections of a complex-layout electrical network. The most typical case is availability of connections (power transmission lines) rated as belonging to different voltage classes and connecting two network assemblies with power flow between them. Currents are distributed among parallel connections proportionally to their electrical impedance, not proportionally to their transfer capability.

Not infrequent are the situations when power transmission lines with less electrical impedance becomes overloaded and the one with higher impedance — underloaded. If we connect a reactor into the overloaded power transmission line, the line’s electrical impedance goes up, which allows us to re-distribute the flows in proportion to the transfer capability of the power transmission lines. This, in its turn, increases the total transfer capability of the network and prevents power transmission line overload in various operation modes.

Design

The distinguishing feature of KPM reactors is use of single-wire aluminum conductors with composite insulation consisting of polyimide-fluoroplastic film and two layers of glass fabric impregnated with heat-resistant silicone varnish. This allows not only to ensure the required electric strength, but also to create a one-piece mechanical connection between the conductors in the reactor windings. The windings becomes self-supported — it doesn’t need a framework or other structural elements to ensure its mechanical strength.

Composite insulation of the KPM, LLC reactors is resistant to temperature fluctuations, chemical and radiation exposure. The insulation is hydrophobic (it doesn’t imbibe water and doesn’t let it through) and low-combustible (it is virtually impossible to set the insulation afire when it is exposed to an electric arc).

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 has 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.