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 H27 load disconnectors complies with the requirements of IEC 694, IEC 129 and IEC 265 standards.
The H27 load disconnectors are supplied with the following phase pitch design: 275 mm, 225 mm and 170 mm.
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 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.

• 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
• no necessity to use burn-up contacts or contacts with delayed operation

¹⁾ Starting actuating force of the rod is 80 N.

All models with the exception of H 27 SuT and H 27 F-SuT are available with or without integrated earthing switch with short-circuit making capability (UESV). In the case of load disconnector H 27 SuT is the earthing switch with short-circuit making capability (UESV) mounted on the special consol (this can be fitted subsequently).
The H27 F-SuT load disconnectors can be provided with a special earthing load having the short-circuit withstand capability (UESV) and with a built-in drive disc used for the loading via operating lever.

Supplementary material to the disconnectors

The customer has to state in his order the respective load disconnector design, with regard especially to the installation position (horizontal or for ceiling assembly).

Energy storage mechanism

One of the robust, low-maintenance energy storage mechanism of type EK or EA is mounted on the base frame, on which the three switch poles are installed. Many hundred thousands of these devices have already been used successfully in the H 22 load disconnectors.
The EK energy storage mechanism operates with only a single torsion spring gor quick-make and quick-break operation without trip-free release. The torsion spring is tensioned for switching ON or OFF. After tensioning, the spring energy is released for the particular switching operation (ON or OFF).
The EA energy storage mechanism operates with two torsion springs for trip-free quick-make and quick-break operation.
Both torsion springs are tensioned when the switch is closed.
The ON switch spring is tripped after tensioning and releases its energy for switching ON, while the OFF witch spring remains tensioned until it is released by the tripping device, HV HBC fuses with striker release, or manually for switching OFF.
With non-manual release the operating shaft remains in the ON position and must be moved to the neutral position OFF manually for reclosing.
Wall-mounting devices can be actuated via a linkage system operated by a detachable lever or by any of the actuators according to requirements and situation.
Laterally mounted switches can be operated directly by fixing a sleeve for D-drives with internal twelve-sided polygon 24 on the operating shaft and using the detachable lever with hexagonal attachment.
Front-panel mounted devices can be operated by means of a detachable lever with a driving pulley integrated in the switch.

Arc extinction

When a breaking process occurs to the load disconnector the loading knife (5) with arcing tip (6) moves from its position in the front-side contact (2). The electric arc is then interrupted in the arcing chamber (4). The chamber is of closed design, consisting of four parts, encompassing the pressure and expansion room. The pressure room there are two extinguishing elements (3) that are moved into the path of arc by using the side pressure of spring. 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 load disconnector.
The arcing chambers as such are completely maintenance free.

	<-ON	OFF->
	1 upper connecting contact 2 contact jaw 3 extinguishing plates 4 arcing chamber 5 switch blade 6 arcing tip 7 roller guide contact 8 guide lug 9 lower connecting contact

Maintenance-free load disconnector operations as a function of the breaking current at cos j ³ 0.7.

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