LHSUniSec Air

Each unit is made of pre-galvanized sheet steel and divided into dedicated cable, busbar and apparatus compartments.

LV compartment. Houses auxiliary circuits and instrumentation.

Main busbars. The busbar compartment contains the copper busbar system rated up to 630A, connected to the upper fixed contacts of the switching device.

Interlocks. Standard and optional interlocks ensure the correct operating sequence.

Cable compartment. Front and side access to cables. Up to 2 single-core cables per phase can be connected, depending on voltage, unit width and cross-section.

LV compartment for auxiliary circuits. Each unit has an LV compartment for low-voltage components.

Finish. Pre-galvanised sheet-steel structure. The standard MV compartment door is painted RAL 7035 grey.

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Compliant with Regulation (EU) 2024/573. Meets IEC 62271-102, IEC 62271-103 and IEC 62271-105.

Electrical characteristics

(1) For the T2 operating mechanism; for T2F, the maximum value depends on the installed fuse.

Mechanical and electrical performance

Operating mechanisms

T1 – operating mechanism without stored energy. Once the dead centre is passed, energy is released and the device closes or opens.

T2 – stored-energy operating mechanism. The springs are charged by lever or motor and held by a retaining system. Closing and opening are then performed locally by pushbutton or remotely by coils.

Accessories

1. Key locks

(1) Mandatory for the IB version.

2. Padlock kit (standard). Locks the device in the open, line or earth position; up to three padlocks per device, with a maximum diameter of 6 mm. Padlocks not supplied.

3. Auxiliary contacts. 4 changeover contacts for the line position and 4 for the earth position, usable as NO or NC contacts.

4. Motor operation. Allows remote operation of the line contact; manual lever operation remains possible at all times. With the T2 mechanism, moving the selector from the intermediate position to local or remote automatically charges the springs.

5. MBO4 opening release (GSec Air/T2). Opens the line contact when the coil is energised. Total opening time 300 ms.

6. MBC4 closing release (GSec Air/T2). Closes the line contact when the coil is energised.

7. RLE5 electromagnetic lock on the line operating-lever socket (GSec Air/T1). Prevents insertion of the lever when the coil is de-energised. Available with the T1 mechanism only.

8. RLE3 electromagnetic lock on the earth operating-lever socket. Prevents insertion of the earthing lever when the coil is de-energised. Alternative to the earth key lock.

9. Fuse-operation indication. When a fuse operates, a linkage activates an indicator visible from the front. On request, a microswitch with an NO or NC contact provides electrical indication.

10. Pressure monitoring (mandatory). A pressure switch with a volt-free contact is supplied as standard, providing local or remote low-pressure indication when pressure falls below 1,9 bar absolute. Alternatively, an analogue pressure gauge with front indication and remote signalling via dedicated wiring and a terminal block is available on request.

Vacuum circuit-breaker to IEC 62271-100, with a spring operating mechanism (O-0.3 s-CO-15 s-CO).

Standard equipment: closing and opening pushbuttons, operation counter, spring-status indicator and manual charging lever. Kit 1: five NO/NC auxiliary contacts (Un = 24…250 V AC-DC). Kit 2: opening release for remote operation. Kit 3: key lock in the open position, with different or identical keys.

Accessories: spring-charging motor (MAS), closing release (MBC), additional opening release (MBO2), undervoltage release (MBU).

For your project. Table names and values are reproduced from the catalogue. Breaking/making ratings expressed together with a duration, and incomplete footnote references, require confirmation in the project technical documentation.

In units requiring a separate cable-side earthing switch, different models are used depending on the application.

In the SFC unit, the switch-disconnector is connected in series with three current-limiting fuses, one per phase. The fuse protects the MV side of the transformer, while overload protection is normally provided on the LV side. Selection must balance two opposing requirements:

withstand the no-load inrush current without deterioration; this can exceed 10 times the rated current, with the maximum value occurring when closing at the voltage zero crossing;

operate quickly for faults in the LV winding and in the section up to the secondary-side circuit-breaker: oversized fuses should therefore be avoided. Good practice is to check the operating time on the fuse time-current curve at the short-circuit current at the secondary terminals.

The table gives the fuse rated current as a function of transformer voltage and power, for current transfer compliant with IEC 60282-1.

CEF fuse selection for transformer protection (SFC unit) – fuse rated current [A]

Headers: transformer rated voltage [kV], transformer load, transformer power [kVA], fuse rated voltage [kV]. (*) Value marked with a note in the fuse manufacturer’s documentation: check each case individually.

CEF-VT fuse selection for VT measurement and protection (SFV unit)

I1 = maximum breaking current; I3 = minimum breaking current; Pn = rated power losses; R0 = cold resistance.

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DIN current transformers. Resin-insulated, with one or more cores and burdens and accuracy classes suited to the installation. Compliant with IEC 61869-2, with dimensions according to DIN 42600 narrow type. They can include a capacitive tap for voltage-presence indicators. Reference range: TPU.

DIN voltage transformers. Epoxy-resin-insulated, single- or double-pole, for fixed installation or mounting on a withdrawable plate in withdrawable circuit-breaker units, optionally with a protective MV fuse. Compliant with IEC 61869-3, with DIN 42600 narrow-type dimensions. Reference range: TJC, TDC, TJP (with fuse).

Toroidal current transformers. Resin-insulated for low voltage, closed-core or split-core, for up to two cables per phase; for phase-current measurement or earth-fault detection. Compliant with IEC 61869-2. Much lighter than DIN CTs, they fit around the insulated cable and can be installed close together, providing substantial space and weight savings.

The LV compartments of LHS UniSec Air units accommodate a wide range of protection relays. Depending on the technical requirements, the following can be used:

Self-powered relay

Protects secondary distribution feeders and transformers against overcurrent, earth faults and overloads, and is ideal as the main protection for distribution transformers. It requires no external power supply: it takes its energy directly from the current transformers. It can also receive trip signals from the transformer, for example in the event of overheating.

Feeder protection

Protects overhead lines and cables against short circuits, overcurrent and earth faults in both primary and secondary distribution, and is also suitable for transformer protection. Several versions are available, progressively adding thermal protection, automatic reclosing for overhead lines, circuit-breaker supervision and fault recording. For more complex protection and control applications, specific devices can be used according to the required functions.