KPM, LLC is experienced in manufacture of dry neutral grounding reactors.
Intended Purpose
As a rule, neutral grounding reactors are intended for high-voltage networks, which in the Russian Federation are operated in the regime of effectively or dead earthed neutral and are recommended to be used with single-phase autoreclosing (SPARC).
Single phase-to-earth faults — are the most frequent type of overhead power transmission line damage. Most of such faults are unstable. In most cases, disconnection and further connection of the line is enough for power supply recovery. So, SPARC are widely used in high-voltage networks.
However, long power transmission lines are characterized by significant charge capacitance between the line wires and the ground. This might be quite a problem when it is required to disconnect the line in case of single phase-to-earth fault and autoreclose (SPARC) it. Because of the charge stored by the stray capacitor, when the line is disconnected a voltage enough for repeated breakdown at the fault point might appear. In such a case, SPARC is inefficient.
Presence of a reactor in the ground circuit allows to prevent high voltages in the lien (to control transient recovery voltage). It is because energy of the charge capacitance is absorbed by the reactor. This prevents repeated breakdown at the fault point.
As a rule, a single-phase grounding reactor is connected to the neutral point of the shunt reactor. Its size shall be determined based on the network regimes computations. In some instances, the reactor may be connected to the transformer or generator neutrals. The installation site shall be determined based on the design studies.
Design
Design of the grounding reactors is similar to that of the current-limiting reactors manufactured by KPM, LLC, but allows for the operational features of the former — it implies reinforced insulation with due account for potential overvoltages during fault clearances. For the case of significant overvoltages, the measures for insulation coordination in the form of OVS shall be arranged for.
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.