The load disconnectors are used as loading devices in medium voltage, indoor operating environment, in normal operating conditions (class "minus 15", indoor design).
The design of H22 load disconnectors complies with the requirements of IEC 694, IEC 129 and IEC 265 standards.
All parts and frames made of steel are galvanized and chromate coated.
The drive shafts are seated in bronze bearings and this is why the material as such can not be subjected to corrosion.
All parts of the current carrying path are made of drawn electrolytical copper.
The current carrying paths for the transfer of rated current of 400 A are nickel coated. Paths to carry currents of 630 A and higher are silver coated, as well as all the elements of the current carrying path, with a layer of 10 mm.
An appropriate contact pressure is ensured by pressure springs made of stainless steel.
All parts of the current carrying path are made of drawn electrolytical copper.

The control of load disconnectors occurs through the following:

• SHA hand operated drives (for load disconnectors mounted on the front wall), with the possibility of both right-side and left-side mounting to the load disconnector
• adaptor for "D" type drive, with an extension part (in case of necessity, for load disconnectors mounted to the side wall)
• UM50 motor operated drives (mounted directly to the operating shaft of load disconnector, usually installed on the left side)
• UM10, UM20 or UM30 motor operated drives (control and manipulation from the front side of cubicle)

In case when the load disconnector is equipped with earthing switch there is to be additional drive mechanism to provide for the control of the earthing switch.
Under normal operating conditions it is not necessary for the load disconnectors to undergo a preventive maintenance during the period of ten years.

Main advantages

• a reliable and safe arc extinguishing
• increased safety of the operating personnel due to the use of earthing loades with an increased short-circuit withstand capability
• load disconnectors of a compact design, necessitating only a very limited area in the respective loadgear frame or cubicle
• current disconnecting path which can visually be inspected
• easy operation
• high number of loading cycles
• very limited maintenance requirements

Supplementary material to the disconnectors

Function of load disconnectors

When breaking the current this is the main contacts that are disconnected first, in which case there is a short-time current passing through the breaking contacts connected in parallel. During the process of disconnection of the main contacts energy is accumulated in the spring to be used for the control of breaking contact. When an appropriate distance of the main contact has been reached the breaking contacts are pulled apart. At the same time electric arc starts to burn in the gap between the hold-up contact and the arcing tip of the breaking contact, which however, immediately is interrupted in the arcing chamber. The arcing chamber is of closed design, and partitioned on the pressure and expansion rooms. In the ranges of small currents the arc extinguishing process is based on the deionization effect of the arc which is cooled down on the walls of arc extinguishing plates. High current arc is extinguished by gas flow which is generated by the arc in the chamber pressure room and which flows into the expansion room.

As you can see, in all the cases there is a combination of a series of arc extinguishing principles that provide for a safe current breaking over the whole current range of the switch disconnector. Due to the fact that there is no a liquid to be used for arc extinguishing, nor a pressurized air, the arcing chambers as such are completely maintenance free.