Damping reactors

Purpose

Damping reactors are intended for series connection between power network and bank of capacitors and ensure the following:

  • Current surge limiting during switching of banks of capacitors;
  • Control of overcurrents that might occur during transient-state conditions in the bank of capacitors’ circuit.

The necessity in balancing the reactive power and voltage across the consumer power substation busbars lead to wide use of capacitors. At their simplest, such banks of capacitors are made non-adjustable or with mechanical switching. Mechanical switching means connection or disconnection of part of a bank of capacitors by means of a mechanical switch (unlike semiconductor switches — thyristors or transistors).

Since a bank of capacitors is an electric charge integrator, current surges with sharp fronts and peak overvoltages might occur when it is switched. Because of its operating principle, the reactor resists abrupt changes in current and damps potential current surges and overvoltages.

Resistance of banks of capacitors is in reverse proportion of the voltage frequency . Because of that, banks of capacitors have some adverse effects.

During any transient processes in an electrical network, transient components appear. These components are the power system response to changes. Unlike the forced components, the transient ones may have any oscillation frequency or may be aperiodic. Forced oscillations are oscillations with the mains frequency — in Russia it is 50 Hz.

During a transient process, the frequency content in circuits with capacitors changes — energy is re-distributed towards the high-frequency oscillations range, where resistance of capacitors is less than that for commercial-frequency oscillations. In case of a resonance, equivalent resistance of the system and bank of capacitors might approach zero. This poses a threat to the electrical network, since supercurrents may occur. Such supercurrents might lead to overheating and failure of capacitors and other circuit elements.

The damping reactor limits magnitude of currents and allows to reduce the probability of resonance in the bank of capacitors’ circuit.

Design

Design of damping reactors is similar to that of current-limiting reactors manufactured by KPM, LLC. Performance of the reactors is adapted to specific conditions of their use — to current surges and HF 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 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.